The Baiyun （白云） sag in the southern Pearl River Mouth basin is the largest and deepest sag in deepwater northern South China Sea. Researches and exploration in this sag have revealed many distinct features of the ...The Baiyun （白云） sag in the southern Pearl River Mouth basin is the largest and deepest sag in deepwater northern South China Sea. Researches and exploration in this sag have revealed many distinct features of the sag. This article reports its Idling history through backstripping of depth data of interpreted sequence boundaries. Maps of sediment rates of 10 sequences from 49 Ma to the present were constructed, showing the spatio-temporal variation of the sediment rate. Three stages of sediment infilling, 49-17.5 Ma, 17.5-10.5 Ma, and 10.5-0 Ma, were divided by abrupt changes of sedimentary patterns. If the breakup of the South China Sea took place at -30 Ma, significant post-breakup acceleration of sedimentation was observed at 17.5-15.5 Ma and 13.8-12.5 Ma, indicating acceleration of subsidence at these times. We propose that the onset of strong post-breakup subsidence at ～17.5 Ma was an important tectonic event that changed the pattern of sedimentation from discrete and medium-rate deposition centers in both main and south subsags to restricted but high-rate deposition in the main subsag. The cause and implications of this newly recognized event need to be investigated.展开更多
A significant geologic event occurred on the Oligocene/Miocene boundary at 23.8 Ma in the northern South China Sea, which is named the Baiyun （白云） movement in this article. This event strongly affected not only th...A significant geologic event occurred on the Oligocene/Miocene boundary at 23.8 Ma in the northern South China Sea, which is named the Baiyun （白云） movement in this article. This event strongly affected not only the South China Sea, but also East Asia. After the Baiyun event, the ridge of seafloor spreading of the South China Sea jumped southward and rotated counterclockwise, and a strong subsidence occurred in the Baiyun sag of the Pearl River Mouth basin. The shelf break shifted suddenly from the south to the north of the Baiyun sag, and the deposition environment in this sag changed from continental shelf with neritic deposition to continental slope with deep-water deposition. Sediment geochemistry study indicated that the Baiyun event played a key role in the rapid change of sediment provenance for the Pearl River Mouth basin. Between 32 and 23.8 Ma, the source of sediments was mainly from the granites in South China, while after 23.8 Ma some sediments might have come from the eastern Himalaya, as the Pearl River drainage extended westward after the uplift of Tibet since that time. The Baiyun event led to a great change in the drainage framework of the paleo- Pearl River, sediment types and the depositional environments in the Pearl River Mouth basin, and relative sea level of the northern South China Sea, as well as sedimentation and hydrocarbon accumulation in the area.展开更多
To investigate the thinning of the whole crust, and the contribution of the upper versus lower crust to the stretching since Cenozoic, we calculated the stretching factor of the northern margin of South China Sea with...To investigate the thinning of the whole crust, and the contribution of the upper versus lower crust to the stretching since Cenozoic, we calculated the stretching factor of the northern margin of South China Sea with data such as whole crustal thickness, depth of Cenozoic sedimentary basement and the horizontal displacement of faults. An isometric line drawing on whole crustal stretching factor is then obtained. Along the seismic Line 1530 in Baiyun sag, we also calculated the stretching factors of the upper and lower crust. The results suggest that the whole crustal thickness decreases seaward while the whole crustal stretching factor increases from shelf to slope. The Moho upwells highest beneath where the crust is thinned most. The value of the whole crustal stretching factor ranges from 1.5 to 6. Two areas were thinned intensely: the center of Yinggehai Basin, and the Baiyun sag in the Pearl River Mouth Basin. The calculation of the upper and lower crustal stretching factors from DSP1530 in Baiyun sag shows that the original crust of Baiyun sag should be thinned before deformation. Its pre-Cenozoic evolution as well as tectonic position during Cenozoic might be responsible for that.展开更多
The Baiyun sag is a deep one developing on the slope of the Pearl River Mouth Basin. It occurs as a composite graben horizontally, and is composed of two sub-sags versus one low uplift. Vertically, the sedimentary arc...The Baiyun sag is a deep one developing on the slope of the Pearl River Mouth Basin. It occurs as a composite graben horizontally, and is composed of two sub-sags versus one low uplift. Vertically, the sedimentary architecture could be divided into three layers, i.e. the faulted layer on the bottom, the faulted-ductile stretching layer in the middle and the draping layer on the top. The main rifting stage of the sag is supposed to be characterized by ductile extension and thinning of the crust. The special deformation pattern is probably attributed to the fact that the Baiyun sag is located in the transfer zone of the pre-existing weak zone, which made the sag a strongly deformed area, characterized by the greatly thinned lithosphere and active magmatism. The highly rising mantle under the Baiyun sag should be an important mechanism responsible for the ductile deformation, which caused partial melting of the upper mantle. Upweiling to the upper crust and the sedimentary layers, the partial melting materials accommodated extensional strain and caused non-faulted vertical subsidence. Magma was collected under the transfer zone after the first stage of rifting, and transferred laterally in a direction perpendicular to the extension to the ENE and WSW parts of the sag and upwelled along the NW-trending basal faults, where WNW-trending shear faults developed in swarms. The faulting activity and sedimentation history of the Baiyun sag may have been affected by the ocean ridge jump around 24 Ma and the cessation of sea floor spreading around 16 Ma.展开更多
The Baiyun Sag is the deepest sag in the Pearl River Mouth Basin in northern continental margin of South China Sea,with the maximum sediment thickness over 12.5 km above the basement including >6.5 km sediments abo...The Baiyun Sag is the deepest sag in the Pearl River Mouth Basin in northern continental margin of South China Sea,with the maximum sediment thickness over 12.5 km above the basement including >6.5 km sediments above the 30 Ma breakup unconformity.According to the theoretical models for the rifted basins,the post-rift subsidence is driven solely by the thermal contraction and can be calculated as the function of the lithospheric stretching factor.A method combining the forward modeling and reverse backstripping was designed to estimate lithospheric stretching factor.Using the 2D forward modeling based on the flexural cantilever model,we simulated the multi-rifting process of the Baiyun Sag with constrain of the backstripped profiles.By doing this the lithospheric stretching factor was obtained,and then the theoretical post-rift subsidence was calculated.The calculated theoretical subsidence was much smaller than the observed subsidence given by backstripping.Along the 1530 line in the Baiyun Sag,the anomalous post-rift subsidence is over 2 km in the sag center,and varies slightly to the north and south edges of the sag.This suggests that the anomalous post-rift subsidence continues beyond the sag both in the continental shelf to the north and in the continental slope to the south.The sensitivity tests in the forward modeling process indicate that only the use of low-angle faults (≤13°) can we simulate the shape of the backstripped profile.展开更多
The newly acquired long-cable multi-channel seismic （MCS） lines were used to study the crustal structure and extension in an NW-SE elongated 150 km by 260 km strip from the slope to the deepsea basin in the northern...The newly acquired long-cable multi-channel seismic （MCS） lines were used to study the crustal structure and extension in an NW-SE elongated 150 km by 260 km strip from the slope to the deepsea basin in the northern South China Sea （SCS）. These profiles are of good penetration that Moho is recognizable in -70% length of the lines. Seismostratigraphic interpretation and time-depth conversion were conducted. A power function D = ath ＋ c was used in the time-depth conversion, which avoided the under- or over-estimation of the depths of deep-seated interfaces by cubic or quadratic polynomial functions. Contour maps of basement depth, Moho depth, crustal thickness, and crustal stretching factor were obtained for the study area. In the dip direction, the Mobo depth decreases stepwisely from 28 km in the outer shelf southwards to 19, 15, and 12 km in the deepsea basin, with ramps at the shelf break, lower slope, and the continent ocean boundary （COB）, respectively. Accordingly, the crustal thickness decreased southwards from 25 to 15, 13, and 7 km, respectively. Under the center of the Baiyun （白云） sag, the crust thins significantly to 〈 7 km. The crustal stretching factor βc was calculated by assuming the original crust thickness of 30 km. In the centers of the Baiyun sag, βc exceeds 5. Tertiary and Quaternary volcanic activities show a general trend of intensifying towards the COB. An important finding of this study is the along-strike variation of the crustal structure. A Moho rise extends from the COB NW-ward until the shelf break, about 170 km long and 50-100 km wide, with Moho depth 〈 20 km. This is called the Baiyun Moho Nose, which is bounded to the east, west, and north by belts of high Moho gradients indicative of crustal or even lithospheric faults. The doming of Moho in the nose area might be the cause of the W-E segmentation of the crustal and geological structures along the slope of the northern South China Sea, and the cause of the strong crustal stretching in the Baiyun and Liw展开更多
Eleven lithofacies and five lithofacies associations were indentified in the Miocene Zhujiang Formation on the basis of detailed core analysis. It could he determined that three depositional types developed, namely su...Eleven lithofacies and five lithofacies associations were indentified in the Miocene Zhujiang Formation on the basis of detailed core analysis. It could he determined that three depositional types developed, namely submarine fan, basin and deep-water traction current. Six microfacies were further recognized within the fan, including main channels in the inner fan, distributary channels in the middle fan, inter-channels, levees and the outer fan. The lower Zhujiang Formation, mainly sandstone associations, was inner fan and inner-middle fan deposits of the basin fan and the slope fan. The middle part, mainly mudstone associations, was outer fan deposits. With the transgression, the submarine fan was finally replaced by the basinal pelagic deposits which were dominated by mudstone associations, siltstone associations, and deep-water limestone associations. During the weak gravity flow activity, the lower channels, the middle-upper outer fans and basin deposits were strongly modified by the deep-water traction current. The identification of the deep-water traction deposition in Miocene Zhujiang Formation would be of great importance. It could be inferred that the deep- water traction current had been existing after the shelf-break formation since the Late Oligocene （23.8 Ma） in the Baiyun sag, influencing and controlling the sediment composition, the distribution, and depositional processes. It would provide great enlightenment to the paleo-oceanic current circulation in the northern South China Sea.展开更多
The Oligocene Zhuhai sandstones are significant reservoirs for hydrocarbons in the Baiyun Sag, South China Sea.For effective appraisal, exploration and exploitation of such a deep-water hydrocarbon sandstone, samples ...The Oligocene Zhuhai sandstones are significant reservoirs for hydrocarbons in the Baiyun Sag, South China Sea.For effective appraisal, exploration and exploitation of such a deep-water hydrocarbon sandstone, samples of five wells from depths of 850 m to 3 000 m were studied. A series of comprehensive petrographic and geochemical analyses were performed to unravel the diagenetic features and their impact on the reservoir quality.Petrographically, the sandstones are dominated by feldspathic litharenites and lithic arenites with fine to medium grain sizes and moderate to good sorting. The reservoir quality varies greatly with a range of porosity from 0.2% to 36.1% and permeability from 0.016 ×10~(–3) μm~2 to 4 301 ×10~(–3) μm~2, which is attributed to complex diagenetic evolution related to sedimentary facies;these include compaction, cementation of calcite, dolomite, siderite and framboidal pyrite in eogenetic stage;further compaction, feldspar dissolution, precipitation of ferrocalcite and ankerite, quartz cements, formation of kaolinite and its illitization, precipitation of albite and nodular pyrite, as well as hydrocarbon charge in mesogenetic stage. The dissolution of feldspar and illitization of kaolinite provide internal sources for the precipitation of quartz cement, while carbonate cements are derived from external sources related to interbedded mudstones and deep fluid. Compaction is the predominant factor in reducing the total porosity, followed by carbonate cementation that leads to strong heterogeneity. Feldspar dissolution and concomitant quartz and clay cementation barely changes the porosity but significantly reduces the permeability.The high-quality reservoirs can be concluded as medium-grained sandstones lying in the central parts of thick underwater distributary channel sandbodies(>2 m) with a high content of detrital quartz but low cement.展开更多
The coupling relationship between shelf-edge deltas and deep-water fan sand bodies is a hot and cutting-edge field of international sedimentology and deep-water oil and gas exploration.Based on the newly acquired high...The coupling relationship between shelf-edge deltas and deep-water fan sand bodies is a hot and cutting-edge field of international sedimentology and deep-water oil and gas exploration.Based on the newly acquired high-resolution 3D seismic,logging and core data of Pearl River Mouth Basin(PRMB),this paper dissected the shelf-edge delta to deep-water fan(SEDDF)depositional system in the Oligocene Zhuhai Formation of Paleogene in south subsag of Baiyun Sag,and revealed the complex coupling relationship from the continental shelf edge to deep-water fan sedimentation and its genetic mechanisms.The results show that during the deposition of the fourth to first members of the Zhuhai Formation,the scale of the SEDDF depositional system in the study area showed a pattern of first increasing and then decreasing,with deep-water fan developed in the third to first members and the largest plane distribution scale developed in the late stage of the second member.Based on the development of SEDDF depositional system along the source direction,three types of coupling relationships are divided,namely,deltas that are linked downdip to fans,deltas that lack downdip fans and fans that lack updip coeval deltas,with different depositional characteristics and genetic mechanisms.(1)Deltas that are linked downdip to fans:with the development of shelf-edge deltas in the shelf area and deep-water fans in the downdip slope area,and the strong source supply and relative sea level decline are the two key factors which control the development of this type of source-to-sink(S2S).The development of channels on the continental shelf edge is conducive to the formation of this type of S2S system even with weak source supply and high sea level.(2)Deltas that lack downdip fans:with the development of shelf edge deltas in shelf area,while deep water fans are not developed in the downdip slope area.The lack of“sources”and“channels”,and fluid transformation are the three main reasons for the formation of this type of S2S system.(3)Fans that lack展开更多
Geochemical and detrital zircon U-Pb dating data for drilled sediments from the Baiyun deepwater area of the northern South China Sea demonstrate a change of sedimentary sources from the Oligocene to the Miocene.Zirco...Geochemical and detrital zircon U-Pb dating data for drilled sediments from the Baiyun deepwater area of the northern South China Sea demonstrate a change of sedimentary sources from the Oligocene to the Miocene.Zircon ages of the pre-rift Eocene sequences are dominated by Yanshanian ages with various peak values（110–115 Ma for U1435 and L21; 150 Ma for H1）, indicating local sediment supply from the pre-existing Mesozoic magmatic belt. For the Oligocene sediments in the northern part of the basin, the rare earth elements show different distribution characteristics, indicating sediment supply from the paleo-Zhujiang River（Pearl River）, as also confirmed by the multimodal zircon age spectra of the Lower Oligocene strata in Well X28. By contrast, a positive Eu anomaly characterizes sediments from the western and southern parts of the basin, indicating potential provenances from intermediate to basic volcanic rock materials. The Baiyun Movement at the end of the Oligocene contributed to a large-scale subsidence in the deepwater area and also a northward retreat of continental shelf break, leading to deepening depositional environment in the basin. As a result, all the detrital zircon ages of the Upper Oligocene strata from Wells X28, L13, and L21 share a similar distribution, implying the possible control of a common source like the Zhujiang River. During the Miocene, whereas sediments in the northern area were mainly sourced from the Zhujiang River Delta, and those in the southern deepwater area continued to be affected by basic volcanic activities, the Dongsha Uplift could have contributed as the main source to the eastern area.展开更多
The Baiyun Sag, located in the deep-water area of the northern South China Sea, is the largest and deepest subbasin in the Pearl River Mouth Basin and one of the most important hydrocarbon-accumulation depression area...The Baiyun Sag, located in the deep-water area of the northern South China Sea, is the largest and deepest subbasin in the Pearl River Mouth Basin and one of the most important hydrocarbon-accumulation depression areas in China. Thermal history is widely thought to be of great importance in oil and gas potential assessment of a basin as it controls the timing of hydrocarbon generation and expulsion from the source rock. In order to unravel the paleo-heat flow of the Baiyun Sag, we first analyzed tectonic subsidence of 55 pseudo-wells constructed based on newly interpreted seismic profiles, along with three drilled wells. We then carried out thermal modeling using the multi-stage finite stretching method and calibrated the results using collected present-day vitrinite reflectance data and temperature data. Results indicate that the first and second heating of the Baiyun Sag after 49 Ma ceased at 33.9 Ma and 23 Ma. Reconstructed average basal paleo- heat flow values at the end of the rifting periods are -57.7- 86.2 mW/m2 and -66.7-97.3 mW/m2, respectively. Following the last heating period at 23 Ma, the study area has undergone a persistent thermal attenuation phase, and basal heat flow has cooled down to ～64.0-79.2 mW/m2 at present.展开更多
Dissolution mechanism and favorable reservoir distribution prediction are the key problems restricting oil and gas exploration in deep-buried layers.In this paper,the Enping Formation and Zhuhai Formation in Baiyun Sa...Dissolution mechanism and favorable reservoir distribution prediction are the key problems restricting oil and gas exploration in deep-buried layers.In this paper,the Enping Formation and Zhuhai Formation in Baiyun Sag of South China Sea was taken as a target.Based on the thin section,scanning electron microscopy,X-ray diffraction,porosity/permeability measurement,and mercury injection,influencing factors of dissolution were examined,and a dissolution model was established.Further,high-quality reservoirs were predicted temporally and spatially.The results show that dissolved pores constituted the main space of the Paleogene sandstone reservoir.Dissolution primarily occurred in the coarse-and medium-grained sandstones in the subaerial and subaqueous distributary channels,while dissolution was limited in fine-grained sandstones and inequigranular sandstones.The main dissolved minerals were feldspar,tuffaceous matrix,and diagenetic cement.Kaolinization of feldspar and illitization of kaolinite are the main dissolution pathways,but they occur at various depths and temperatures with different geothermal gradients.Dissolution is controlled by four factors,in terms of depositional facies,source rock evolution,overpressure,and fault activities,which co-acted at the period of 23.8–13.8 Ma,and resulted into strong dissolution.Additionally,based on these factors,high-quality reservoirs of the Enping and Zhuhai formations are predicted in the northern slope,southwestern step zone,and Liuhua uplift in the Baiyun Sag.展开更多
The Baiyun deposit is a large gold deposit at the western end of the Liaoji rift zone in Liaoning Province, which has produced both auriferous quartz-vein type and altered-rock type mineralization. The ore bodies are ...The Baiyun deposit is a large gold deposit at the western end of the Liaoji rift zone in Liaoning Province, which has produced both auriferous quartz-vein type and altered-rock type mineralization. The ore bodies are mainly hosted in schist from the Gaixian Formation of the Liaohe Group. A detailed field geological survey showed that the quartz-vein type gold ore bodies are distributed in the near EW-trending and occur in the extensional tectonic space of schist in the Gaixian Formation, and the altered-rock type gold ore bodies are distributed in the near EW-trending structural belt and occur near in the Gaixian Formation of biotite schist, biotite granulite, marble and the upper footwall of dike. To further elucidate the source of ore-forming fluid and material in the Baiyun gold deposit, the H-O isotopes for quartz, S and Pb isotopes, in-situ trace elements for sulfides from quartz-vein and altered-rock type mineralization were studied. The H-O isotopic δD_(V-SMOW) and δ^(18)O_(H2O) values of the auriferous quartz range were from-88.8‰ to-82.2‰ and-1.95‰ to 4.85‰, respectively, suggests that the ore-forming fluids were mainly magmatic water with minor meteoric water. The distribution ranges of in-situ S isotopic compositions of Au-bearing pyrite in the quartz-vein type and altered-rock type ores were-8.38‰–-10.47‰(with average values of-7.89‰) and 11.38‰– 17.52‰(with average values of 11.55‰), respectively, indicating that the S isotopic compositions of the two ore types were clearly different. The in-situ Pb isotopic ratios changed almost uniformly, which showed that they had the same lead isotopic source. Based on the analysis of S and Pb isotopic compositions, the metallogenic materials in the Baiyun gold deposit were primarily from deep magma, and some wall rock materials may have been mixed in the metallogenic process. Co/Ni diagram shows that most Au-bearing pyrites have magmatic-hydrothermal or sedimentary alteration properties, and Au/As ratios were between 0.001 and 0.828(the展开更多
Ichnofossils are well developed in clastic rock reservoirs in marine and transitional facies, which can considerably change the physical properties of the reservoir. However, this influence is not well understood, rai...Ichnofossils are well developed in clastic rock reservoirs in marine and transitional facies, which can considerably change the physical properties of the reservoir. However, this influence is not well understood, raising an important problem in the effective development of petroleum reservoirs. This paper analyzes continental shelf margin delta reservoirs through core observation, cast thin section observation and reservoir physical property test. Some important scientific insights are obtained:(1) The presence of Cruziana ichnofacies, including Asterosoma, Ophiomorpha, Planolites, Skolithos, Thalassinoides, and other ichnofossils can be used to identify in subaqueous distributary channels, subaqueous levee, frontal sheet sand, abandoned river channels, crevasse channels, main channels and channel mouth bars. Considerable differences in the types of ichnofossils and the degree of bioturbation can be observed in the different petrofacies.(2) Ichnofossils and bioturbation play a complex role in controlling reservoir properties. The reservoir physical properties have the characteristics of a decrease–increase–decrease curve with increasing bioturbation degree. This complex change is controlled by the sediment mixing and packing of bioturbation and the diagenetic environment controlled by the ichnofossils.(3) Sea-level cycle changes affect the modification of the reservoir through sediment packing. Bioturbation weakens the reservoir's physical property when sea level slowly rises and improves the reservoir's physical property when base level slowly falls.展开更多
The eastern main sub-sag(E-MSS)of the Baiyun Sag was the main zone for gas exploration in the deep-water area of the Zhujiang River(Pearl River)Mouth Basin at its early exploration stage,but the main goal of searching...The eastern main sub-sag(E-MSS)of the Baiyun Sag was the main zone for gas exploration in the deep-water area of the Zhujiang River(Pearl River)Mouth Basin at its early exploration stage,but the main goal of searching gas in this area was broken through by the successful exploration of the W3-2 and H34B volatile oil reservoirs,which provides a new insight for exploration of the Paleogene oil reservoirs in the E-MSS.Nevertheless,it is not clear on the distribution of“gas accumulated in the upper layer,oil accumulated in the lower layer”(Gas_(upper)-Oil_(lower))under the high heat flow,different source-rock beds,multi-stages of oil and gas charge,and multi-fluid phases,and not yet a definite understanding of the genetic relationship and formation mechanism among volatile oil,light oil and condensate gas reservoirs,and the migration and sequential charge model of oil and gas.These puzzles directly lead to the lack of a clear direction for oil exploration and drilling zone in this area.In this work,the PVT fluid phase,the origin of crude oil and condensate,the secondary alteration of oil and gas reservoirs,the evolution sequence of oil and gas formation,the phase state of oil and gas migration,and the configuration of fault activity were analyzed,which established the migration and accumulation model of Gas_(upper)-Oil_(lower)cocontrolled by source and heat,and fractionation controlled by facies in the E-MSS.Meanwhile,the fractionation evolution model among common black reservoirs,volatile reservoirs,condensate reservoirs and gas reservoirs is discussed,which proposed that the distribution pattern of Gas_(upper)-Oil_(lower)in the E-MSS is controlled by the generation attribute of oil and gas from source rocks,the difference of thermal evolution,and the fractionation controlled by phases after mixing the oil and gas.Overall,we suggest that residual oil reservoirs should be found in the lower strata of the discovered gas reservoirs in the oil-source fault and diapir-developed areas,while volatile oil reservoirs sho展开更多
The relationships between crustal stretching and thinning,basin structure and petroleum geology in Baiyun deep-water area were analyzed using large area 3D seismic,gravity,magnetic,ocean bottom seismic(OBS),deep-water...The relationships between crustal stretching and thinning,basin structure and petroleum geology in Baiyun deep-water area were analyzed using large area 3D seismic,gravity,magnetic,ocean bottom seismic(OBS),deep-water exploration wells and integrated ocean drilling program(IODP).During the early syn-rifting period,deep-water area was a half-graben controlled by high angle faults influenced by the brittle extension of upper crust.In the mid syn-rifting period,this area was a broad-deep fault depression controlled by detachment faults undergone brittle-ductile deformation and differentiated extension in the crust.In the late syn-rifting period,this area experienced fault-sag transition due to saucer-shaped rheology change dominated by crustal ductile deformation.A broad-deep fault depression controlled by the large detachment faults penetrating through the crust is an important feature of deep-water basin.The study suggests that the broad-deep Baiyun sag provides great accommodation space for the development of massive deltaic-lacustrine deposition system and hydrocarbon source rocks.The differentiated lithospheric thinning also resulted in the different thermal subsidence during post-rifting period,and then controlled the development of continental shelf break and deep-water reservoir sedimentary environment.The high heat flow background caused by the strong thinning of lithosphere and the rise of mantle source resulted in particularities in the reservoir diagenesis,hydrocarbon generation process and accumulation of deep-water area in northern South China Sea.展开更多
The Qingchengzi ore field is an important gold-polymetallic center of the North China Cra-ton.It has been recognized that the gold deposits in Qingchengzi were controlled by structures like litho-logical interfaces an...The Qingchengzi ore field is an important gold-polymetallic center of the North China Cra-ton.It has been recognized that the gold deposits in Qingchengzi were controlled by structures like litho-logical interfaces and fractures along mechanically weak bedding and foliation planes,but it still remains poorly understood how the structures affected the localization of the gold deposits.Finite element based numerical modeling was used to reproduce the deformation process of the Baiyun gold deposit during the mineralization period.Paleoproterozoic schist and marble are widely exposed in Qingchengzi,and a large part of the Baiyun gold ores occurs along the interfaces between the schist and the marble.The modeling results suggest that the mechanical contrast between the schist and the marble may be a major reason why the stress was localized along their lithological interfaces under a compressional stress regime.Two parts of their lithological interfaces were identified to be easily stress-localized and first fractured:the interface between the schist and its underlying marble at shallower levels and the one between the schist and its overlying marble at deeper levels.Stress concentration in these two parts is independent on the dipping angle and direction of the interfaces.Therefore,mineralizing fluids may have been concentrated into these two parts.The first one is consistent with the present ore bodies of the Baiyun gold deposit,and the second one could be considered for deep prospecting.These findings also provide implications for the structural controls of lithological interfaces on the mineralization in other gold deposits of this region.展开更多
Exploration of deep mineralization,particularly where the mineralization of interest is covered by a conductive overburden,is still a challenge for the conventional transient electromagnetic(TEM)method,which measures ...Exploration of deep mineralization,particularly where the mineralization of interest is covered by a conductive overburden,is still a challenge for the conventional transient electromagnetic(TEM)method,which measures TEM response using induction coils as the sensor.However,sensors such as fluxgate and superconductive quantum interfere device(SQUID)magnetometers can measure the B-field directly,which can provide more reliable deep information for mineralization exploration.In this paper,we report on the research and development of our newly developed high-temperature su-perconductor(HTS)SQUID magnetometer,which is cooled by liquid nitrogen at 77 K,and its applica-tion in TEM measurement for deep exploration in a gold deposit in China.This improved SQUID magnetometer version has a good performance with noise(60 fT/√Hz),slew rate(0.8 mT/S),dynamic range(100 dB),sensitivity(6.25 mV/nT),and bandwidth(DC-20 kHz).To find deep and peripheral ore in the Baiyun gold deposit located in Liaoning Province,NE China,both the SQUID magnetometer and induction coil were used for TEM data acquisition.Results show that TEM can detect the distribution of local strata and the faults contained within them.Results also indicate that the SQUID magnetome-ter has superior response performance for response over geological targets with slower decay time when compared to the induction coil signals.The SQUID magnetometer is more sensitive at observing the induced-polarization effect which is closely related to the ore-controlling faults.展开更多
Corals are comparatively abundant in the upper member of the Baiyun'an Formation (upper Aeronian to lowerest Telychian, Llandovery, Silurian) of Huaying, eastern Sichuan Province, Southwest China. Three coral asso...Corals are comparatively abundant in the upper member of the Baiyun'an Formation (upper Aeronian to lowerest Telychian, Llandovery, Silurian) of Huaying, eastern Sichuan Province, Southwest China. Three coral associations have been recognized, i.e., in ascending order, the Mesofavosites Association, the Dentilasma Association, and the Paraceriaster Association. The Mesofavosites Association occurs at horizons indicating a shallow and high-energy environment. It is dominated by large favositids accompanied by a few broken pieces of halysitids and small solitary rugose corals. The Dentilasma Association has a pretty high coral diversity, dominated by the solitary rugose coral Dentilasma meitanense, together with some subordinative heliolitids and favositids. The sedimentary evidence shows that this association might live in a quiet and nutritive shallow water environment. The Paraceriaster Association yields in the grayish green calcareous mudstone indicating a comparatively deep water environment. Systematically it contains abundant fasciculate Paraceriaster micropora and a few favositids. The distinction among these three coral associations shows that corals could adopt different adaptive strategies under different environments, which provide some new data for the investigation on the ecology of Silurian corals and further study on the "Lower Red Beds".展开更多
This paper investigates the origin and migration characteristics of petroleum in the northeastern part of the Baiyun Depression,Pearl River Mouth Basin(PRMB).The discovered petroleum in the study area is mainly locate...This paper investigates the origin and migration characteristics of petroleum in the northeastern part of the Baiyun Depression,Pearl River Mouth Basin(PRMB).The discovered petroleum in the study area is mainly located in the Lower Zhujiang Member(N_(1)z^(2))and mainly originated from the Enping Formation source rocks in the eastern sag.Active faults(vertical migration)and N_(1)z^(2)sandstones(lateral migration)acted as the petroleum migration systems.The fault activities in the Dongsha event controlled the episodic petroleum migration.Fractures in the fault zones provided effective conduits,and overpressure was the driving force.The vertical migration could not cross the fault zones laterally.The petroleum injection areas in the carrier beds were the contact zones of petroleum-migration faults and carrier beds.The lateral migration was steady-state migration,and buoyancy was the driving force.The migration pathways in the carrier beds were controlled by the structural morphology.Secondary petroleum migration in the study area could be divided into two parts:vertical migration along the fractures in the fault zones and lateral migration through preferential petroleum migration pathways(PPMPs)in the carrier beds.The petroleum migration behaviors,including migrating direction,driving force,and migration pattern,in the faults and sandstone carrier beds were quite different.This study provides a typical example for comprehending secondary migration processes and has great importance for determining future exploration targets in the deep-water area of the PRMB.展开更多
基金supported by the National Natural Science Foundation of China (Nos. 40576027, 40238060)the High-Tech R&D Program of China (No. 2008AA09Z306)
文摘The Baiyun （白云） sag in the southern Pearl River Mouth basin is the largest and deepest sag in deepwater northern South China Sea. Researches and exploration in this sag have revealed many distinct features of the sag. This article reports its Idling history through backstripping of depth data of interpreted sequence boundaries. Maps of sediment rates of 10 sequences from 49 Ma to the present were constructed, showing the spatio-temporal variation of the sediment rate. Three stages of sediment infilling, 49-17.5 Ma, 17.5-10.5 Ma, and 10.5-0 Ma, were divided by abrupt changes of sedimentary patterns. If the breakup of the South China Sea took place at -30 Ma, significant post-breakup acceleration of sedimentation was observed at 17.5-15.5 Ma and 13.8-12.5 Ma, indicating acceleration of subsidence at these times. We propose that the onset of strong post-breakup subsidence at ～17.5 Ma was an important tectonic event that changed the pattern of sedimentation from discrete and medium-rate deposition centers in both main and south subsags to restricted but high-rate deposition in the main subsag. The cause and implications of this newly recognized event need to be investigated.
基金supported by the National Natural Science Foundation of China (No. 40238060)
文摘A significant geologic event occurred on the Oligocene/Miocene boundary at 23.8 Ma in the northern South China Sea, which is named the Baiyun （白云） movement in this article. This event strongly affected not only the South China Sea, but also East Asia. After the Baiyun event, the ridge of seafloor spreading of the South China Sea jumped southward and rotated counterclockwise, and a strong subsidence occurred in the Baiyun sag of the Pearl River Mouth basin. The shelf break shifted suddenly from the south to the north of the Baiyun sag, and the deposition environment in this sag changed from continental shelf with neritic deposition to continental slope with deep-water deposition. Sediment geochemistry study indicated that the Baiyun event played a key role in the rapid change of sediment provenance for the Pearl River Mouth basin. Between 32 and 23.8 Ma, the source of sediments was mainly from the granites in South China, while after 23.8 Ma some sediments might have come from the eastern Himalaya, as the Pearl River drainage extended westward after the uplift of Tibet since that time. The Baiyun event led to a great change in the drainage framework of the paleo- Pearl River, sediment types and the depositional environments in the Pearl River Mouth basin, and relative sea level of the northern South China Sea, as well as sedimentation and hydrocarbon accumulation in the area.
基金the Key Innovative Program of Chinese Academy of Sciences (Grant No. KZCX3-SW-234-3)the Basic Research Program of China (Grant No. 2007CB411704)the National Natural Science Foundation of China (Grant Nos. 40406012 and 40576027)
文摘To investigate the thinning of the whole crust, and the contribution of the upper versus lower crust to the stretching since Cenozoic, we calculated the stretching factor of the northern margin of South China Sea with data such as whole crustal thickness, depth of Cenozoic sedimentary basement and the horizontal displacement of faults. An isometric line drawing on whole crustal stretching factor is then obtained. Along the seismic Line 1530 in Baiyun sag, we also calculated the stretching factors of the upper and lower crust. The results suggest that the whole crustal thickness decreases seaward while the whole crustal stretching factor increases from shelf to slope. The Moho upwells highest beneath where the crust is thinned most. The value of the whole crustal stretching factor ranges from 1.5 to 6. Two areas were thinned intensely: the center of Yinggehai Basin, and the Baiyun sag in the Pearl River Mouth Basin. The calculation of the upper and lower crustal stretching factors from DSP1530 in Baiyun sag shows that the original crust of Baiyun sag should be thinned before deformation. Its pre-Cenozoic evolution as well as tectonic position during Cenozoic might be responsible for that.
文摘The Baiyun sag is a deep one developing on the slope of the Pearl River Mouth Basin. It occurs as a composite graben horizontally, and is composed of two sub-sags versus one low uplift. Vertically, the sedimentary architecture could be divided into three layers, i.e. the faulted layer on the bottom, the faulted-ductile stretching layer in the middle and the draping layer on the top. The main rifting stage of the sag is supposed to be characterized by ductile extension and thinning of the crust. The special deformation pattern is probably attributed to the fact that the Baiyun sag is located in the transfer zone of the pre-existing weak zone, which made the sag a strongly deformed area, characterized by the greatly thinned lithosphere and active magmatism. The highly rising mantle under the Baiyun sag should be an important mechanism responsible for the ductile deformation, which caused partial melting of the upper mantle. Upweiling to the upper crust and the sedimentary layers, the partial melting materials accommodated extensional strain and caused non-faulted vertical subsidence. Magma was collected under the transfer zone after the first stage of rifting, and transferred laterally in a direction perpendicular to the extension to the ENE and WSW parts of the sag and upwelled along the NW-trending basal faults, where WNW-trending shear faults developed in swarms. The faulting activity and sedimentation history of the Baiyun sag may have been affected by the ocean ridge jump around 24 Ma and the cessation of sea floor spreading around 16 Ma.
文摘The Baiyun Sag is the deepest sag in the Pearl River Mouth Basin in northern continental margin of South China Sea,with the maximum sediment thickness over 12.5 km above the basement including >6.5 km sediments above the 30 Ma breakup unconformity.According to the theoretical models for the rifted basins,the post-rift subsidence is driven solely by the thermal contraction and can be calculated as the function of the lithospheric stretching factor.A method combining the forward modeling and reverse backstripping was designed to estimate lithospheric stretching factor.Using the 2D forward modeling based on the flexural cantilever model,we simulated the multi-rifting process of the Baiyun Sag with constrain of the backstripped profiles.By doing this the lithospheric stretching factor was obtained,and then the theoretical post-rift subsidence was calculated.The calculated theoretical subsidence was much smaller than the observed subsidence given by backstripping.Along the 1530 line in the Baiyun Sag,the anomalous post-rift subsidence is over 2 km in the sag center,and varies slightly to the north and south edges of the sag.This suggests that the anomalous post-rift subsidence continues beyond the sag both in the continental shelf to the north and in the continental slope to the south.The sensitivity tests in the forward modeling process indicate that only the use of low-angle faults (≤13°) can we simulate the shape of the backstripped profile.
基金supported by the National Natural Science Foundation of China (Nos. 40576027, 40876026)National Basic Research Program of China (Nos. 2007CB41170405, 2009CB219401)the Knowledge Innovation Program of South China Sea Institute of Oceanology, Chinese Academy of Sciences (No. LYQY200704)
文摘The newly acquired long-cable multi-channel seismic （MCS） lines were used to study the crustal structure and extension in an NW-SE elongated 150 km by 260 km strip from the slope to the deepsea basin in the northern South China Sea （SCS）. These profiles are of good penetration that Moho is recognizable in -70% length of the lines. Seismostratigraphic interpretation and time-depth conversion were conducted. A power function D = ath ＋ c was used in the time-depth conversion, which avoided the under- or over-estimation of the depths of deep-seated interfaces by cubic or quadratic polynomial functions. Contour maps of basement depth, Moho depth, crustal thickness, and crustal stretching factor were obtained for the study area. In the dip direction, the Mobo depth decreases stepwisely from 28 km in the outer shelf southwards to 19, 15, and 12 km in the deepsea basin, with ramps at the shelf break, lower slope, and the continent ocean boundary （COB）, respectively. Accordingly, the crustal thickness decreased southwards from 25 to 15, 13, and 7 km, respectively. Under the center of the Baiyun （白云） sag, the crust thins significantly to 〈 7 km. The crustal stretching factor βc was calculated by assuming the original crust thickness of 30 km. In the centers of the Baiyun sag, βc exceeds 5. Tertiary and Quaternary volcanic activities show a general trend of intensifying towards the COB. An important finding of this study is the along-strike variation of the crustal structure. A Moho rise extends from the COB NW-ward until the shelf break, about 170 km long and 50-100 km wide, with Moho depth 〈 20 km. This is called the Baiyun Moho Nose, which is bounded to the east, west, and north by belts of high Moho gradients indicative of crustal or even lithospheric faults. The doming of Moho in the nose area might be the cause of the W-E segmentation of the crustal and geological structures along the slope of the northern South China Sea, and the cause of the strong crustal stretching in the Baiyun and Liw
基金granted by the National Science and Technology Major Project of the Ministry of Science and Technology of China(Grant No.2008ZX05056-02-02)
文摘Eleven lithofacies and five lithofacies associations were indentified in the Miocene Zhujiang Formation on the basis of detailed core analysis. It could he determined that three depositional types developed, namely submarine fan, basin and deep-water traction current. Six microfacies were further recognized within the fan, including main channels in the inner fan, distributary channels in the middle fan, inter-channels, levees and the outer fan. The lower Zhujiang Formation, mainly sandstone associations, was inner fan and inner-middle fan deposits of the basin fan and the slope fan. The middle part, mainly mudstone associations, was outer fan deposits. With the transgression, the submarine fan was finally replaced by the basinal pelagic deposits which were dominated by mudstone associations, siltstone associations, and deep-water limestone associations. During the weak gravity flow activity, the lower channels, the middle-upper outer fans and basin deposits were strongly modified by the deep-water traction current. The identification of the deep-water traction deposition in Miocene Zhujiang Formation would be of great importance. It could be inferred that the deep- water traction current had been existing after the shelf-break formation since the Late Oligocene （23.8 Ma） in the Baiyun sag, influencing and controlling the sediment composition, the distribution, and depositional processes. It would provide great enlightenment to the paleo-oceanic current circulation in the northern South China Sea.
基金The National Natural Science Foundation of China under contract No. 42262020the Research Program of Science and Technology at Universities of Inner Mongolia Autonomous Region under contract No. NJZY22445。
文摘The Oligocene Zhuhai sandstones are significant reservoirs for hydrocarbons in the Baiyun Sag, South China Sea.For effective appraisal, exploration and exploitation of such a deep-water hydrocarbon sandstone, samples of five wells from depths of 850 m to 3 000 m were studied. A series of comprehensive petrographic and geochemical analyses were performed to unravel the diagenetic features and their impact on the reservoir quality.Petrographically, the sandstones are dominated by feldspathic litharenites and lithic arenites with fine to medium grain sizes and moderate to good sorting. The reservoir quality varies greatly with a range of porosity from 0.2% to 36.1% and permeability from 0.016 ×10~(–3) μm~2 to 4 301 ×10~(–3) μm~2, which is attributed to complex diagenetic evolution related to sedimentary facies;these include compaction, cementation of calcite, dolomite, siderite and framboidal pyrite in eogenetic stage;further compaction, feldspar dissolution, precipitation of ferrocalcite and ankerite, quartz cements, formation of kaolinite and its illitization, precipitation of albite and nodular pyrite, as well as hydrocarbon charge in mesogenetic stage. The dissolution of feldspar and illitization of kaolinite provide internal sources for the precipitation of quartz cement, while carbonate cements are derived from external sources related to interbedded mudstones and deep fluid. Compaction is the predominant factor in reducing the total porosity, followed by carbonate cementation that leads to strong heterogeneity. Feldspar dissolution and concomitant quartz and clay cementation barely changes the porosity but significantly reduces the permeability.The high-quality reservoirs can be concluded as medium-grained sandstones lying in the central parts of thick underwater distributary channel sandbodies(>2 m) with a high content of detrital quartz but low cement.
基金Supported by the National Natural Science Foundation of China(91528303)CNOOC Technology Project(2021-KT-YXKY-05).
文摘The coupling relationship between shelf-edge deltas and deep-water fan sand bodies is a hot and cutting-edge field of international sedimentology and deep-water oil and gas exploration.Based on the newly acquired high-resolution 3D seismic,logging and core data of Pearl River Mouth Basin(PRMB),this paper dissected the shelf-edge delta to deep-water fan(SEDDF)depositional system in the Oligocene Zhuhai Formation of Paleogene in south subsag of Baiyun Sag,and revealed the complex coupling relationship from the continental shelf edge to deep-water fan sedimentation and its genetic mechanisms.The results show that during the deposition of the fourth to first members of the Zhuhai Formation,the scale of the SEDDF depositional system in the study area showed a pattern of first increasing and then decreasing,with deep-water fan developed in the third to first members and the largest plane distribution scale developed in the late stage of the second member.Based on the development of SEDDF depositional system along the source direction,three types of coupling relationships are divided,namely,deltas that are linked downdip to fans,deltas that lack downdip fans and fans that lack updip coeval deltas,with different depositional characteristics and genetic mechanisms.(1)Deltas that are linked downdip to fans:with the development of shelf-edge deltas in the shelf area and deep-water fans in the downdip slope area,and the strong source supply and relative sea level decline are the two key factors which control the development of this type of source-to-sink(S2S).The development of channels on the continental shelf edge is conducive to the formation of this type of S2S system even with weak source supply and high sea level.(2)Deltas that lack downdip fans:with the development of shelf edge deltas in shelf area,while deep water fans are not developed in the downdip slope area.The lack of“sources”and“channels”,and fluid transformation are the three main reasons for the formation of this type of S2S system.(3)Fans that lack
基金The National Natural Science Foundation of China under contract Nos 41576059,91128207 and 91528302the National Major Science and Technology Projects under contract No.2011ZX05025-006-02
文摘Geochemical and detrital zircon U-Pb dating data for drilled sediments from the Baiyun deepwater area of the northern South China Sea demonstrate a change of sedimentary sources from the Oligocene to the Miocene.Zircon ages of the pre-rift Eocene sequences are dominated by Yanshanian ages with various peak values（110–115 Ma for U1435 and L21; 150 Ma for H1）, indicating local sediment supply from the pre-existing Mesozoic magmatic belt. For the Oligocene sediments in the northern part of the basin, the rare earth elements show different distribution characteristics, indicating sediment supply from the paleo-Zhujiang River（Pearl River）, as also confirmed by the multimodal zircon age spectra of the Lower Oligocene strata in Well X28. By contrast, a positive Eu anomaly characterizes sediments from the western and southern parts of the basin, indicating potential provenances from intermediate to basic volcanic rock materials. The Baiyun Movement at the end of the Oligocene contributed to a large-scale subsidence in the deepwater area and also a northward retreat of continental shelf break, leading to deepening depositional environment in the basin. As a result, all the detrital zircon ages of the Upper Oligocene strata from Wells X28, L13, and L21 share a similar distribution, implying the possible control of a common source like the Zhujiang River. During the Miocene, whereas sediments in the northern area were mainly sourced from the Zhujiang River Delta, and those in the southern deepwater area continued to be affected by basic volcanic activities, the Dongsha Uplift could have contributed as the main source to the eastern area.
基金Research in this paper was supported by the National Natural Science Foundation of China （Grant No. 41602251）, the Chinese Postdoc Fund, No.58 General Fund, 2015 （No. 2015M582636） and the Research Fund for New Teachers of Xi＇an Jiaotong University. We are grateful to CNOOC Research Institute for providing the seismic profiles. We also thank anonymous reviewers for their careful and insightful suggestions on the paper.
文摘The Baiyun Sag, located in the deep-water area of the northern South China Sea, is the largest and deepest subbasin in the Pearl River Mouth Basin and one of the most important hydrocarbon-accumulation depression areas in China. Thermal history is widely thought to be of great importance in oil and gas potential assessment of a basin as it controls the timing of hydrocarbon generation and expulsion from the source rock. In order to unravel the paleo-heat flow of the Baiyun Sag, we first analyzed tectonic subsidence of 55 pseudo-wells constructed based on newly interpreted seismic profiles, along with three drilled wells. We then carried out thermal modeling using the multi-stage finite stretching method and calibrated the results using collected present-day vitrinite reflectance data and temperature data. Results indicate that the first and second heating of the Baiyun Sag after 49 Ma ceased at 33.9 Ma and 23 Ma. Reconstructed average basal paleo- heat flow values at the end of the rifting periods are -57.7- 86.2 mW/m2 and -66.7-97.3 mW/m2, respectively. Following the last heating period at 23 Ma, the study area has undergone a persistent thermal attenuation phase, and basal heat flow has cooled down to ～64.0-79.2 mW/m2 at present.
基金The National Natural Science Foundation of China under contract No.42202157the China National Offshore Oil Corporation Co.,Ltd.Major Production and Scientific Research Program under contract No.2019KT-SC-22。
文摘Dissolution mechanism and favorable reservoir distribution prediction are the key problems restricting oil and gas exploration in deep-buried layers.In this paper,the Enping Formation and Zhuhai Formation in Baiyun Sag of South China Sea was taken as a target.Based on the thin section,scanning electron microscopy,X-ray diffraction,porosity/permeability measurement,and mercury injection,influencing factors of dissolution were examined,and a dissolution model was established.Further,high-quality reservoirs were predicted temporally and spatially.The results show that dissolved pores constituted the main space of the Paleogene sandstone reservoir.Dissolution primarily occurred in the coarse-and medium-grained sandstones in the subaerial and subaqueous distributary channels,while dissolution was limited in fine-grained sandstones and inequigranular sandstones.The main dissolved minerals were feldspar,tuffaceous matrix,and diagenetic cement.Kaolinization of feldspar and illitization of kaolinite are the main dissolution pathways,but they occur at various depths and temperatures with different geothermal gradients.Dissolution is controlled by four factors,in terms of depositional facies,source rock evolution,overpressure,and fault activities,which co-acted at the period of 23.8–13.8 Ma,and resulted into strong dissolution.Additionally,based on these factors,high-quality reservoirs of the Enping and Zhuhai formations are predicted in the northern slope,southwestern step zone,and Liuhua uplift in the Baiyun Sag.
基金supported by theNational Key Research and Development Program(No.2018YFC0603806)the Geological Surveying Project of China Geological Survey(No.DD20190166).
文摘The Baiyun deposit is a large gold deposit at the western end of the Liaoji rift zone in Liaoning Province, which has produced both auriferous quartz-vein type and altered-rock type mineralization. The ore bodies are mainly hosted in schist from the Gaixian Formation of the Liaohe Group. A detailed field geological survey showed that the quartz-vein type gold ore bodies are distributed in the near EW-trending and occur in the extensional tectonic space of schist in the Gaixian Formation, and the altered-rock type gold ore bodies are distributed in the near EW-trending structural belt and occur near in the Gaixian Formation of biotite schist, biotite granulite, marble and the upper footwall of dike. To further elucidate the source of ore-forming fluid and material in the Baiyun gold deposit, the H-O isotopes for quartz, S and Pb isotopes, in-situ trace elements for sulfides from quartz-vein and altered-rock type mineralization were studied. The H-O isotopic δD_(V-SMOW) and δ^(18)O_(H2O) values of the auriferous quartz range were from-88.8‰ to-82.2‰ and-1.95‰ to 4.85‰, respectively, suggests that the ore-forming fluids were mainly magmatic water with minor meteoric water. The distribution ranges of in-situ S isotopic compositions of Au-bearing pyrite in the quartz-vein type and altered-rock type ores were-8.38‰–-10.47‰(with average values of-7.89‰) and 11.38‰– 17.52‰(with average values of 11.55‰), respectively, indicating that the S isotopic compositions of the two ore types were clearly different. The in-situ Pb isotopic ratios changed almost uniformly, which showed that they had the same lead isotopic source. Based on the analysis of S and Pb isotopic compositions, the metallogenic materials in the Baiyun gold deposit were primarily from deep magma, and some wall rock materials may have been mixed in the metallogenic process. Co/Ni diagram shows that most Au-bearing pyrites have magmatic-hydrothermal or sedimentary alteration properties, and Au/As ratios were between 0.001 and 0.828(the
基金The National Natural Science Foundation of China under contract Nos 41872112 and 42077410the Key Research Project of Higher Education Institutions in Henan University under contract No. 20A170010+1 种基金the Program for Innovative Research Team (in Science and Technology) of Henan Polytechnic University under contract No. T2022-05the Foundation of Shandong Provincial Key Laboratory of Depositional Mineralization and Sedimentary Mineral under contract No. DMSM2018027。
文摘Ichnofossils are well developed in clastic rock reservoirs in marine and transitional facies, which can considerably change the physical properties of the reservoir. However, this influence is not well understood, raising an important problem in the effective development of petroleum reservoirs. This paper analyzes continental shelf margin delta reservoirs through core observation, cast thin section observation and reservoir physical property test. Some important scientific insights are obtained:(1) The presence of Cruziana ichnofacies, including Asterosoma, Ophiomorpha, Planolites, Skolithos, Thalassinoides, and other ichnofossils can be used to identify in subaqueous distributary channels, subaqueous levee, frontal sheet sand, abandoned river channels, crevasse channels, main channels and channel mouth bars. Considerable differences in the types of ichnofossils and the degree of bioturbation can be observed in the different petrofacies.(2) Ichnofossils and bioturbation play a complex role in controlling reservoir properties. The reservoir physical properties have the characteristics of a decrease–increase–decrease curve with increasing bioturbation degree. This complex change is controlled by the sediment mixing and packing of bioturbation and the diagenetic environment controlled by the ichnofossils.(3) Sea-level cycle changes affect the modification of the reservoir through sediment packing. Bioturbation weakens the reservoir's physical property when sea level slowly rises and improves the reservoir's physical property when base level slowly falls.
基金The Major Science and Technology Project of China National Offshore Oil Corporation during the“14th Five-Year Plan”under contact No.KJGG2022-0103-03。
文摘The eastern main sub-sag(E-MSS)of the Baiyun Sag was the main zone for gas exploration in the deep-water area of the Zhujiang River(Pearl River)Mouth Basin at its early exploration stage,but the main goal of searching gas in this area was broken through by the successful exploration of the W3-2 and H34B volatile oil reservoirs,which provides a new insight for exploration of the Paleogene oil reservoirs in the E-MSS.Nevertheless,it is not clear on the distribution of“gas accumulated in the upper layer,oil accumulated in the lower layer”(Gas_(upper)-Oil_(lower))under the high heat flow,different source-rock beds,multi-stages of oil and gas charge,and multi-fluid phases,and not yet a definite understanding of the genetic relationship and formation mechanism among volatile oil,light oil and condensate gas reservoirs,and the migration and sequential charge model of oil and gas.These puzzles directly lead to the lack of a clear direction for oil exploration and drilling zone in this area.In this work,the PVT fluid phase,the origin of crude oil and condensate,the secondary alteration of oil and gas reservoirs,the evolution sequence of oil and gas formation,the phase state of oil and gas migration,and the configuration of fault activity were analyzed,which established the migration and accumulation model of Gas_(upper)-Oil_(lower)cocontrolled by source and heat,and fractionation controlled by facies in the E-MSS.Meanwhile,the fractionation evolution model among common black reservoirs,volatile reservoirs,condensate reservoirs and gas reservoirs is discussed,which proposed that the distribution pattern of Gas_(upper)-Oil_(lower)in the E-MSS is controlled by the generation attribute of oil and gas from source rocks,the difference of thermal evolution,and the fractionation controlled by phases after mixing the oil and gas.Overall,we suggest that residual oil reservoirs should be found in the lower strata of the discovered gas reservoirs in the oil-source fault and diapir-developed areas,while volatile oil reservoirs sho
基金Supported by the Science and Technology Project of CNOOC Ltd.(YXKY-2012-SHENHAI-01)China National Science and Technology Major Project(2011ZX05025-003+1 种基金 2016ZX05026-003)the National Natural Science Foundation of China(91128207)
文摘The relationships between crustal stretching and thinning,basin structure and petroleum geology in Baiyun deep-water area were analyzed using large area 3D seismic,gravity,magnetic,ocean bottom seismic(OBS),deep-water exploration wells and integrated ocean drilling program(IODP).During the early syn-rifting period,deep-water area was a half-graben controlled by high angle faults influenced by the brittle extension of upper crust.In the mid syn-rifting period,this area was a broad-deep fault depression controlled by detachment faults undergone brittle-ductile deformation and differentiated extension in the crust.In the late syn-rifting period,this area experienced fault-sag transition due to saucer-shaped rheology change dominated by crustal ductile deformation.A broad-deep fault depression controlled by the large detachment faults penetrating through the crust is an important feature of deep-water basin.The study suggests that the broad-deep Baiyun sag provides great accommodation space for the development of massive deltaic-lacustrine deposition system and hydrocarbon source rocks.The differentiated lithospheric thinning also resulted in the different thermal subsidence during post-rifting period,and then controlled the development of continental shelf break and deep-water reservoir sedimentary environment.The high heat flow background caused by the strong thinning of lithosphere and the rise of mantle source resulted in particularities in the reservoir diagenesis,hydrocarbon generation process and accumulation of deep-water area in northern South China Sea.
基金The work was financially funded by the National Key R&D Program of China(No.2018YFC0603802)the Basic Research Fund for Central Research Institutes(No.JYYWF20180602)the National Natural Science Foundation of China(No.41822206).
文摘The Qingchengzi ore field is an important gold-polymetallic center of the North China Cra-ton.It has been recognized that the gold deposits in Qingchengzi were controlled by structures like litho-logical interfaces and fractures along mechanically weak bedding and foliation planes,but it still remains poorly understood how the structures affected the localization of the gold deposits.Finite element based numerical modeling was used to reproduce the deformation process of the Baiyun gold deposit during the mineralization period.Paleoproterozoic schist and marble are widely exposed in Qingchengzi,and a large part of the Baiyun gold ores occurs along the interfaces between the schist and the marble.The modeling results suggest that the mechanical contrast between the schist and the marble may be a major reason why the stress was localized along their lithological interfaces under a compressional stress regime.Two parts of their lithological interfaces were identified to be easily stress-localized and first fractured:the interface between the schist and its underlying marble at shallower levels and the one between the schist and its overlying marble at deeper levels.Stress concentration in these two parts is independent on the dipping angle and direction of the interfaces.Therefore,mineralizing fluids may have been concentrated into these two parts.The first one is consistent with the present ore bodies of the Baiyun gold deposit,and the second one could be considered for deep prospecting.These findings also provide implications for the structural controls of lithological interfaces on the mineralization in other gold deposits of this region.
基金This study was supported by the National Key Research and Development Project of China(No.2018YFC0603803)Fundamental Research Funds of Chinese Academy of Geological Sciences(Nos.AS2020Y01,AS2020P01).
文摘Exploration of deep mineralization,particularly where the mineralization of interest is covered by a conductive overburden,is still a challenge for the conventional transient electromagnetic(TEM)method,which measures TEM response using induction coils as the sensor.However,sensors such as fluxgate and superconductive quantum interfere device(SQUID)magnetometers can measure the B-field directly,which can provide more reliable deep information for mineralization exploration.In this paper,we report on the research and development of our newly developed high-temperature su-perconductor(HTS)SQUID magnetometer,which is cooled by liquid nitrogen at 77 K,and its applica-tion in TEM measurement for deep exploration in a gold deposit in China.This improved SQUID magnetometer version has a good performance with noise(60 fT/√Hz),slew rate(0.8 mT/S),dynamic range(100 dB),sensitivity(6.25 mV/nT),and bandwidth(DC-20 kHz).To find deep and peripheral ore in the Baiyun gold deposit located in Liaoning Province,NE China,both the SQUID magnetometer and induction coil were used for TEM data acquisition.Results show that TEM can detect the distribution of local strata and the faults contained within them.Results also indicate that the SQUID magnetome-ter has superior response performance for response over geological targets with slower decay time when compared to the induction coil signals.The SQUID magnetometer is more sensitive at observing the induced-polarization effect which is closely related to the ore-controlling faults.
基金supported by National Natural Science Foundation of China (Grant Nos. 40825006,41221001, 41290260)State Key Laboratory of Palaeobiology and Stratigraphy
文摘Corals are comparatively abundant in the upper member of the Baiyun'an Formation (upper Aeronian to lowerest Telychian, Llandovery, Silurian) of Huaying, eastern Sichuan Province, Southwest China. Three coral associations have been recognized, i.e., in ascending order, the Mesofavosites Association, the Dentilasma Association, and the Paraceriaster Association. The Mesofavosites Association occurs at horizons indicating a shallow and high-energy environment. It is dominated by large favositids accompanied by a few broken pieces of halysitids and small solitary rugose corals. The Dentilasma Association has a pretty high coral diversity, dominated by the solitary rugose coral Dentilasma meitanense, together with some subordinative heliolitids and favositids. The sedimentary evidence shows that this association might live in a quiet and nutritive shallow water environment. The Paraceriaster Association yields in the grayish green calcareous mudstone indicating a comparatively deep water environment. Systematically it contains abundant fasciculate Paraceriaster micropora and a few favositids. The distinction among these three coral associations shows that corals could adopt different adaptive strategies under different environments, which provide some new data for the investigation on the ecology of Silurian corals and further study on the "Lower Red Beds".
基金supported by the National Science and Technology Major Projects of China(Grant No:2016ZX05026-007)。
文摘This paper investigates the origin and migration characteristics of petroleum in the northeastern part of the Baiyun Depression,Pearl River Mouth Basin(PRMB).The discovered petroleum in the study area is mainly located in the Lower Zhujiang Member(N_(1)z^(2))and mainly originated from the Enping Formation source rocks in the eastern sag.Active faults(vertical migration)and N_(1)z^(2)sandstones(lateral migration)acted as the petroleum migration systems.The fault activities in the Dongsha event controlled the episodic petroleum migration.Fractures in the fault zones provided effective conduits,and overpressure was the driving force.The vertical migration could not cross the fault zones laterally.The petroleum injection areas in the carrier beds were the contact zones of petroleum-migration faults and carrier beds.The lateral migration was steady-state migration,and buoyancy was the driving force.The migration pathways in the carrier beds were controlled by the structural morphology.Secondary petroleum migration in the study area could be divided into two parts:vertical migration along the fractures in the fault zones and lateral migration through preferential petroleum migration pathways(PPMPs)in the carrier beds.The petroleum migration behaviors,including migrating direction,driving force,and migration pattern,in the faults and sandstone carrier beds were quite different.This study provides a typical example for comprehending secondary migration processes and has great importance for determining future exploration targets in the deep-water area of the PRMB.
