Based on the drilling data of the Upper Ordovician Wufeng Shale and the Lower Silurian Longmaxi Shale in southern Sichuan Basin,the construction of matrix pores and the development condition of fractures in a marine o...Based on the drilling data of the Upper Ordovician Wufeng Shale and the Lower Silurian Longmaxi Shale in southern Sichuan Basin,the construction of matrix pores and the development condition of fractures in a marine organic-rich shale are quantitatively evaluated through the establishment of the reservoir petrophysical models and porosity mathematical models.Our studies show that there are four major characteristics of the Longmaxi Shale confirmed by the quantitative characterization:(1)the pore volume of per unit mass is the highest in organic matter,followed in clay minerals,finally in brittle minerals;(2)the porosity of the effective shale reservoir is moderate and equal to that of the Barnett Shale,and the main parts of the shale reservoir spaces are interlayer pores of clay minerals and organic pores;(3)the porosity of the organic-rich shale is closely related to TOC and brittle mineral/clay mineral ratio,and mainly increases with TOC and clay mineral content;(4)fractures are developed in this black shale,and are mainly micro ones and medium-large ones.In the Longmaxi Shale,the fracture density increases from top to bottom,reflecting the characteristics with high brittle mineral content,high Young’s modulus,low Poisson's ratio and high brittleness at its bottom.展开更多
Measuring gas content is an essential step in estimating the commerciality of gas reserves. In this study,eight shale core samples from the Mouye-1 well were measured using a homemade patented gas desorption apparatus...Measuring gas content is an essential step in estimating the commerciality of gas reserves. In this study,eight shale core samples from the Mouye-1 well were measured using a homemade patented gas desorption apparatus to determine their gas contents. Due to the air contamination that is introduced into the desorption canister, a mathematical method was devised to correct the gas quantity and quality.Compared to the chemical compositions of desorbed gas, the chemical compositions of residual gas are somewhat different. In residual gas, carbon dioxide and nitrogen record a slight increase, and propane is first observed. This phenomenon may be related to the exposure time during the transportation of shale samples from the drilling site to the laboratory, as well as the differences in the mass, size and adsorptivity of different gas molecules. In addition to a series of conventional methods, including the USBM direct method and the Amoco Curve Fit(ACF) method, which were used here for lost gas content estimation, a Modified Curve Fit(MCF) method, based on the 'bidisperse' diffusion model, was established to estimate lost gas content. By fitting the ACF and MCF models to gas desorption data, we determined that the MCF method could reasonably describe the gas desorption data over the entire time period, whereas the ACF method failed. The failure of the ACF method to describe the gas desorption process may be related to its restrictive assumption of a single pore size within shale samples. In comparison to the indirect method, this study demonstrates that none of the three methods studied in this investigation(USBM, ACF and MCF) could individually estimate the lost gas contents of all shale samples and that the proportion of free gas relative to total gas has a significant effect on the estimation accuracy of the selected method. When the ratio of free gas to total gas is lower than 45%, the USBM method is the best for estimating the lost gas content, whereas when the ratio ranges from 45% to 75% or is more than 75%, t展开更多
Shale gas is one of the most promising unconventional resources both in China and abroad. It is known as a form of self-contained source-reservoir system with large and continuous dimensions. Through years of consider...Shale gas is one of the most promising unconventional resources both in China and abroad. It is known as a form of self-contained source-reservoir system with large and continuous dimensions. Through years of considerable exploration efforts, China has identified three large shale gas fields in the ruling, Changning and Weiyuan areas of the Sichuan Basin, and has announced more than 540 billion m3 of proven shale gas reserves in marine shale systems. The geological theories for shale gas development have progressed rapidly in China as well. For example, the new depositional patterns have been introduced for deciphering the paleogeography and sedimentary systems of the Wufeng shale and Longmaxi shale in the Sichuan Basin. The shale gas storage mechanism has been widely accepted as differing from conventional natural gas in that it is adsorbed on organic matter or a mineral surface or occurs as free gas trapped in pores and fractures of the shale. Significant advances in the techniques of microstructural characterization have provided new insights on how gas molecules are stored in micro- and nano-scale porous shales. Furthermore, newly-developed concepts and practices in the petroleum industry, such as hydraulic fracturing, microseismic monitoring and multiwell horizontal drilling, have made the production of this unevenly distributed but promising unconventional natural gas a reality. China has 10-36 trillion m3 of promising shale gas among the world＇s whole predicted technically recoverable reserves of 206.6 trillion m3. China is on the way to achieving its goal of an annual yield of 30-50 billion m3 by launching more trials within shale gas projects.展开更多
The Ordos Basin is the largest petroliferous basin in China, where the Chang 7 Member shale serves as the major source rock in the basin, with an area of more than 100,000 km^2 So far, sedimentary and geochemical char...The Ordos Basin is the largest petroliferous basin in China, where the Chang 7 Member shale serves as the major source rock in the basin, with an area of more than 100,000 km^2 So far, sedimentary and geochemical characterizations have rarely been conducted on the shale in shallow(< 1000 m) areas in the southeastern part of the basin, but such characterizations can help identify the genesis of organic-rich shale and promote the prediction and recovery of shale oil. In this paper,several outcrop sections of the Chang 7 Member in the Tongchuan area were observed and sampled, and sedimentary and geochemical characterizations were conducted for the well-outcropped YSC section. The study results show that the Chang7 Member shale is widely distributed laterally with variable thickness. The organic-rich shale is 7-25 m thick in total and exhibits obvious horizontal variation in mineral composition. In the eastern sections, the shale contains organic matter of TypeⅡ_2-Ⅲ and is low in thermal maturity, with high clay mineral content, low K-feldspar content, and no pyrite. In the western sections, the shale contains Type Ⅱ_1 organic matter and is low in thermal maturity, with high clay mineral, K-feldspar, and pyrite contents. The YSC section reveals three obvious intervals in vertical mineral composition and organic abundance.The Chang 7 Member organic-rich shale(TOC > 10%) contains mainly sapropelite and liptinite, with Type Ⅱ kerogen. It is generally characterized by a hydrocarbon potential of more than 70 mg/g, low maturity, and shallow-semideep lacustrine facies. In the western sections, the shale, still in a low maturity stage, has a higher hydrocarbon potential and is optional for shale oil recovery. However, the Chang 7 Member shale in the study area is highly heterogeneous and its shale oil recovery is practical only in the organic-rich intervals.展开更多
The depositional environment of organic-rich shale and the related tectonic evolution in China are rather different from those in North America. In China, organic-rich shale is not only deposited in marine environment...The depositional environment of organic-rich shale and the related tectonic evolution in China are rather different from those in North America. In China, organic-rich shale is not only deposited in marine environment, but also in non-marine environment： marine-continental transitional environment and lacustrine environment. Through analyzing large amount of outcrops and well cores, the geologic features of organic-rich shale, including mineral composition, organic matter richness and type, and li- thology stratigraphy, were analyzed, indicating very special characteristics. Meanwhile, the more complex and active tectonic movements in China lead to strong deformation and erosion of organic-rich shale, well-development of fractures and faults, and higher thermal maturity and serious heterogeneity. Co-existence of shale gas, tight sand gas, and coal bed methane （CBM） proposes a new topic： whether it is possible to co-produce these gases to reduce cost. Based on the geologic features, the primary pro- duction issues of shale gas in China were discussed with suggestions.展开更多
The organic-rich shale of the Chang 7 member is the most important source rock in the Ordos basin.The sedimentary environment and the controlling factors of organic matter enrichment,however,are still in contention.In...The organic-rich shale of the Chang 7 member is the most important source rock in the Ordos basin.The sedimentary environment and the controlling factors of organic matter enrichment,however,are still in contention.In this investigation,the Yishicun outcrop,located on the south margin of the Ordos basin,has been considered for the study.X-ray diffraction,polarizing microscopy,field emission scanning electron microscopy and cathodoluminescence(CL)were used to investigate the petrological features of the organic-rich shale.The content of volcanic ash and the diameter of pyrite framboid pseudocrystals were measured to illustrate the relationship between oxygen level,ash content and the enrichment of organic matter.It has been found that the diameter of pyrite framboid pseudocrystals has a strong correlation with the total organic carbon,demonstrating that the redox status degree of the water column has a positive impact on the enrichment of organic matter.Additionally,with an increase in the ash content,the content of organic matter increased at first and then decreased,and reached a maximum when the ash content was about 6%,illustrating that the ash input has a double effect on the enrichment of organic matter.展开更多
Sedimentary organic matter(OM) is a major reservoir of organic carbon in the global carbon cycle. Despite many studies, there still exist many debates on the mechanism of OM accumulation and preservation in marine sed...Sedimentary organic matter(OM) is a major reservoir of organic carbon in the global carbon cycle. Despite many studies, there still exist many debates on the mechanism of OM accumulation and preservation in marine sediments. We present a new field study of a Lower Cambrian shallow marine shelf sequence in the northern edge of the Yangtze Plate, China. Our results show that palynological OM and biogenic silica(Bio-Si) could be used alongside more conventional redox and paleo-productivity proxies to study the distribution of OM in marine sediments. The qualitative and quantitative study of palynological OM provides more detailed information on the nature of sedimentary organic carbon, which can be helpful in the assessment of primary productivity and OM preservation. In addition, the presence of Bio-Si stimulates the physical preservation of OM. Further analysis indicates that an increase in Bio-Si can promote OM preservation. This case-study provides insight into the intertwined factors controlling OM accumulation in the Early Cambrian.展开更多
The deformation structure of soft sediments has always been a research hotspot,which is of great significance for analyzing the tectonic and sedimentary evolution background of a basin,as well as the physical properti...The deformation structure of soft sediments has always been a research hotspot,which is of great significance for analyzing the tectonic and sedimentary evolution background of a basin,as well as the physical properties of reservoirs.Previous studies have reported that a large number of soft sediment deformation structures are developed in the western part of Liaohe depression.In this study,through core observation and thin section identification,various types of deformation structures are identified in the core samples which are collected from the upper Es4 in the Leijia region,western sag of Liaohe depression,such as liquefied dikes,liquefied breccia,convoluted laminae,annular bedding,synsedimentary faults,vein structures,etc.Based on the characteristics of core structure,single well profile and continuous well profile,combined with the regional background,this study clarifies that the deformation structure of soft sediments in the study area is mainly caused by seismic action.It is found that the permeability and porosity of deformation layers in the study area are higher than those of the undeformation layers,which proves that the deformation structure of soft sediments has a good effect on improving the physical properties of reservoirs.展开更多
Globally,most organic-rich shales are deposited with volcanic ash layers.Volcanic ash,a source for many sedimentary basins,can affect the sedimentary water environment,alter the primary productivity,and preserve the o...Globally,most organic-rich shales are deposited with volcanic ash layers.Volcanic ash,a source for many sedimentary basins,can affect the sedimentary water environment,alter the primary productivity,and preserve the organic matter(OM)through physical,chemical,and biological reactions.With an increasing number of breakthroughs in shale oil exploration in the Bohai Bay Basin in recent years,less attention has been paid to the crucial role of volcanic impact especially its influence on the OM enrichment and hydrocarbon formation.Here,we studied the petrology,mineralogy,and geochemical characteristics of the organic-rich shale in the upper submember of the fourth member(Es_(4)^(1))and the lower submember of the third member(Es_(3)^(3))of the Shahejie Formation,aiming to better understand the volcanic impact on organic-rich shale formation.Our results show that total organic carbon is higher in the upper shale intervals rich in volcanic ash with enriched light rare earth elements and moderate Eu anomalies.This indicates that volcanism promoted OM formation before or after the eruption.The positive correlation between Eu/Eu*and Post-Archean Australian Shale indicates hydrothermal activity before the volcanic eruption.The plane graph of the hydrocarbon-generating intensity(S1+S2)suggests that the heat released by volcanism promoted hydrocarbon generation.Meanwhile,the nutrients carried by volcanic ash promoted biological blooms during Es_(4)^(1 )and Es_(3)^(3) deposition,yielding a high primary productivity.Biological blooms consume large amounts of oxygen and form anoxic environments conducive to the burial and preservation of OM.Therefore,this study helps to further understand the organic-inorganic interactions caused by typical geological events and provides a guide for the next step of shale oil exploration and development in other lacustrine basins in China.展开更多
Lacustrine shale is an important target for the exploration of unconventional oil and gas in China beyond marine shale gas.However,the formation environment of lacustrine shale differs from that of marine shale,result...Lacustrine shale is an important target for the exploration of unconventional oil and gas in China beyond marine shale gas.However,the formation environment of lacustrine shale differs from that of marine shale,resulting in a different reservoir composition,organic matter,oil and gas content,and hydrocarbon mobility.In this study,the Chang 7 shale of the Yanchang Formation in the Ordos Basin was used to analyze the effect of volcanic activity on the paleoproductivity and preservation conditions during the formation of lacustrine shale.The results show that algae and bacteria were developed before the eruption.After the eruption,the number of bacteria declined,but the increased prosperity of algae reflects that the volcanic activity enhanced ancient productivity.The sulfate generated by volcanic activity promotes bacterial sulfate reduction,and the produced H_(2)S leads to a strong reducing environment in the waterbody,which is conducive to the preservation of organic matter.Organic geochemical analysis shows that the black shale in the shale strata has a high total organic carbon(TOC)content and strong hydrocarbon generation potential,whereas the tuff has a low TOC content and can scarcely generate hydrocarbons,indicating that the tuff deposited by volcanic activity cannot be considered as effective source rock.In terms of storage space,shale is mainly laminar and dispersed,and it includes organic and inorganic pores.The development of organic pores is affected by thermal maturity,whereas inorganic pores mainly occur between detrital particles and crystals.Tuff is mainly supported by heterogeneous matrix and associated with alteration.Its pores include inter-and intragranular mineral pores.The development of tight sandstone pores is affected by compaction,cementation,and dissolution,which mainly consist of intra-and intergranular pores.The Chang 7 lacustrine shale generally contains oil,but different lithologies have different oil drainage efficiencies.Sandstone and shale exhibit the best and worst oil drainage e展开更多
In-situ conversion processing (ICP) of shale oil underground at the depth ranging from 300 m to 3 000 m is a physical and chemical process caused by using horizontal drilling and electric heating technology, which con...In-situ conversion processing (ICP) of shale oil underground at the depth ranging from 300 m to 3 000 m is a physical and chemical process caused by using horizontal drilling and electric heating technology, which converts heavy oil, bitumen and various organic matter into light oil and gas in a large scale, which can be called"underground refinery". ICP has several advantages as in CO2capture, recoverable resource potential and the quality of hydrocarbon output. Based on the geothermal evolution mechanism of organic materials established by Tissot et al., this study reveals that in the nonmarine organic-rich shale sequence, the amount of liquid hydrocarbon maintaining in the shale is as high as 25%in the liquid hydrocarbon window stage (R o less than 1.0%), and the unconverted organic materials (low mature-immature organic materials) in the shale interval can reach 40%to 100%. The conditions of organic-rich shale suitable for underground in-situ conversion of shale oil should be satisfied in the following aspects, TOC higher than 6%, R o ranging between 0.5%and 1%, concentrated thickness of organic-rich shale greater than 15 meters, burial depth less than 3 000 m, covering area bigger than 50 km2, good sealing condition in both up-and down-contacting sequences and water content smaller than 5%, etc. The shale oil resource in China’s onshore region is huge. It is estimated with this paper that the technical recoverable resource reaches 70-90 billion tons of oil and 60-65 trillion cubic meters of gas. The ICP of shale oil underground is believed to be a fairway to find big oil in the source kitchen in the near future. And it is also believed to be a milestone to keep China long-term stability of oil and gas sufficient supply by putting ICP of shale oil underground into real practice in the future.展开更多
Kerogen content and kerogen porosity play a significant role in elastic properties of organic-rich shales. We construct a rock physics model for organic-rich shales to quantify the effect of kerogen content and keroge...Kerogen content and kerogen porosity play a significant role in elastic properties of organic-rich shales. We construct a rock physics model for organic-rich shales to quantify the effect of kerogen content and kerogen porosity using the Kuster and Toks6z theory and the selfconsistent approximation method. Rock physics modeling results show that with the increase of kerogen content and kerogen-related porosity, the velocity and density of shales decrease, and the effect of kerogen porosity becomes more obvious only for higher kerogen content. We also find that the Poisson＇s ratio of the shale is not sensitive to kerogen porosity for the case of gas saturation. Finally, for the seismic reflection responses of an organic-rich shale layer, forward modeling results indicate the fifth type AVO re- sponses which correspond to a negative intercept and a positive gradient. The absolute values of intercept and gradient increase with kerogen content and kerogen porosity, and present predictable variations associated with velocities and density.展开更多
The geological conditions and processes of fine-grained gravity flow sedimentation in continental lacustrine basins in China are analyzed to construct the model of fine-grained gravity flow sedimentation in lacustrine...The geological conditions and processes of fine-grained gravity flow sedimentation in continental lacustrine basins in China are analyzed to construct the model of fine-grained gravity flow sedimentation in lacustrine basin,reveal the development laws of fine-grained deposits and source-reservoir,and identify the sweet sections of shale oil.The results show that fine-grained gravity flow is one of the important sedimentary processes in deep lake environment,and it can transport fine-grained clasts and organic matter in shallow water to deep lake,forming sweet sections and high-quality source rocks of shale oil.Fine-grained gravity flow deposits in deep waters of lacustrine basins in China are mainly fine-grained high-density flow,fine-grained turbidity flow(including surge-like turbidity flow and fine-grained hyperpycnal flow),fine-grained viscous flow(including fine-grained debris flow and mud flow),and fine-grained transitional flow deposits.The distribution of fine-grained gravity flow deposits in the warm and humid unbalanced lacustrine basins are controlled by lake-level fluctuation,flooding events,and lakebed paleogeomorphology.During the lake-level rise,fine-grained hyperpycnal flow caused by flooding formed fine-grained channel–levee–lobe system in the flat area of the deep lake.During the lake-level fall,the sublacustrine fan system represented by unconfined channel was developed in the flexural slope breaks and sedimentary slopes of depressed lacustrine basins,and in the steep slopes of faulted lacustrine basins;the sublacustrine fan system with confined or unconfined channel was developed on the gentle slopes and in axial direction of faulted lacustrine basins,with fine-grained gravity flow deposits possibly existing in the lower fan.Within the fourth-order sequences,transgression might lead to organic-rich shale and fine-grained hyperpycnal flow deposits,while regression might cause fine-grained high-density flow,surge-like turbidity flow,fine-grained debris flow,mud flow,and fine-grained transiti展开更多
Kerogen plays an important role in shale gas adsorption,desorption and diffusion.Therefore,it is necessary to characterize the molecular structure of kerogen.In this study,four kerogen samples were isolated from the o...Kerogen plays an important role in shale gas adsorption,desorption and diffusion.Therefore,it is necessary to characterize the molecular structure of kerogen.In this study,four kerogen samples were isolated from the organic-rich shale of the Longmaxi Formation.Raman spectroscopy was used to determine the maturity of these kerogen samples.Highresolution transmission electron microscopy(HRTEM),13 C nuclear magnetic resonance(13 C NMR),X-ray diffraction(XRD)and Fourier transform infrared(FT-IR)spectroscopy were conducted to characterize the molecular structure of the shale samples.The results demonstrate that VReqv of these kerogen samples vary from 2.3%to 2.8%,suggesting that all the kerogen samples are in the dry gas window.The macromolecular carbon skeleton of the Longmaxi Formation kerogen is mainly aromatic(fa’=0.56).In addition,the aromatic structural units are mainly composed of naphthalene(23%),anthracene(23%)and phenanthrene(29%).However,the aliphatic structure of the kerogen macromolecules is relatively low(fal*+falH=0.08),which is presumed to be distributed in the form of methyl and short aliphatic chains at the edge of the aromatic units.The oxygen-containing functional groups in the macromolecules are mainly present in the form of carbonyl groups(fac=0.23)and hydroxyl groups or ether groups(falO=0.13).The crystallite structural parameters of kerogen,including the stacking height(Lc=22.84?),average lateral size(La=29.29?)and interlayer spacing(d002=3.43?),are close to the aromatic structural parameters of anthracite or overmature kerogen.High-resolution transmission electron microscopy reveals that the aromatic structure is well oriented,and more than 65%of the diffractive aromatic layers are concentrated in the main direction.Due to the continuous deep burial,the longer aliphatic chains and oxygen-containing functional groups in the kerogen are substantially depleted.However,the ductility and stacking degree of the aromatic structure increases during thermal evolution.This study provides quantitative 展开更多
The Chang 73 sub-member of Triassic Yanchang Formation in the Ordos Basin was taken as an example and the lamina types and combinations,reservoir space features and shale oil enrichment patterns in organic-rich shale ...The Chang 73 sub-member of Triassic Yanchang Formation in the Ordos Basin was taken as an example and the lamina types and combinations,reservoir space features and shale oil enrichment patterns in organic-rich shale strata were investigated using core observation,thin section analysis,XRF element measurement,XRD analysis,SEM,high solution laser Raman spectroscopy analysis,and micro-FTIR spectroscopy analysis,etc.According to the mineral composition and thickness of the laminae,the Chang 73 organic-rich shales have four major types of laminae,tuff-rich lamina,organic-rich lamina,silt-grade feldspar-quartz lamina and clay lamina.They have two kinds of shale oil-bearing layers,"organic-rich lamina+silt-grade feldspar-quartz lamina"and"organic-rich lamina+tuff-rich lamina"layers.In the"organic-rich+silt-grade feldspar-quartz"laminae combination shale strata,oil was characterized by relative high maturation,and always filled in K-feldspar dissolution pores in the silt-grade feldspar-quartz laminae,forming oil generation,migration and accumulation process between laminae inside the organic shales.In the"organic-rich+tuff-rich lamina"binary laminae combination shale strata,however,the reservoir properties were poor in organic-rich shales,the oil maturation was relatively lower,and mainly accumulated in the intergranular pores of interbedded thin-layered sandstones.The oil generation,migration and accumulation mainly occurred between organic-rich shales and interbedded thin-layered sandstones.展开更多
基金supported by the National Basic Research Program of China(Grant No.2013CB228001)Special Issue of Major National Science and Technology(Grant No.2011ZX05018-001)+1 种基金National Oil and Gas Resources Survey and Evaluation Program(Grant No.2009GYXQ15-01)PetroChina Technology Research Project of Unconventional Oil and Gas Exploration and Development(Grant No.2011A-4801)
文摘Based on the drilling data of the Upper Ordovician Wufeng Shale and the Lower Silurian Longmaxi Shale in southern Sichuan Basin,the construction of matrix pores and the development condition of fractures in a marine organic-rich shale are quantitatively evaluated through the establishment of the reservoir petrophysical models and porosity mathematical models.Our studies show that there are four major characteristics of the Longmaxi Shale confirmed by the quantitative characterization:(1)the pore volume of per unit mass is the highest in organic matter,followed in clay minerals,finally in brittle minerals;(2)the porosity of the effective shale reservoir is moderate and equal to that of the Barnett Shale,and the main parts of the shale reservoir spaces are interlayer pores of clay minerals and organic pores;(3)the porosity of the organic-rich shale is closely related to TOC and brittle mineral/clay mineral ratio,and mainly increases with TOC and clay mineral content;(4)fractures are developed in this black shale,and are mainly micro ones and medium-large ones.In the Longmaxi Shale,the fracture density increases from top to bottom,reflecting the characteristics with high brittle mineral content,high Young’s modulus,low Poisson's ratio and high brittleness at its bottom.
文摘Measuring gas content is an essential step in estimating the commerciality of gas reserves. In this study,eight shale core samples from the Mouye-1 well were measured using a homemade patented gas desorption apparatus to determine their gas contents. Due to the air contamination that is introduced into the desorption canister, a mathematical method was devised to correct the gas quantity and quality.Compared to the chemical compositions of desorbed gas, the chemical compositions of residual gas are somewhat different. In residual gas, carbon dioxide and nitrogen record a slight increase, and propane is first observed. This phenomenon may be related to the exposure time during the transportation of shale samples from the drilling site to the laboratory, as well as the differences in the mass, size and adsorptivity of different gas molecules. In addition to a series of conventional methods, including the USBM direct method and the Amoco Curve Fit(ACF) method, which were used here for lost gas content estimation, a Modified Curve Fit(MCF) method, based on the 'bidisperse' diffusion model, was established to estimate lost gas content. By fitting the ACF and MCF models to gas desorption data, we determined that the MCF method could reasonably describe the gas desorption data over the entire time period, whereas the ACF method failed. The failure of the ACF method to describe the gas desorption process may be related to its restrictive assumption of a single pore size within shale samples. In comparison to the indirect method, this study demonstrates that none of the three methods studied in this investigation(USBM, ACF and MCF) could individually estimate the lost gas contents of all shale samples and that the proportion of free gas relative to total gas has a significant effect on the estimation accuracy of the selected method. When the ratio of free gas to total gas is lower than 45%, the USBM method is the best for estimating the lost gas content, whereas when the ratio ranges from 45% to 75% or is more than 75%, t
基金financially supported by the National Basic Research Program of China(grant No.2014CB239000)the Chinese National Scientific and Technological Program(grant No.2011ZX05018–001)
文摘Shale gas is one of the most promising unconventional resources both in China and abroad. It is known as a form of self-contained source-reservoir system with large and continuous dimensions. Through years of considerable exploration efforts, China has identified three large shale gas fields in the ruling, Changning and Weiyuan areas of the Sichuan Basin, and has announced more than 540 billion m3 of proven shale gas reserves in marine shale systems. The geological theories for shale gas development have progressed rapidly in China as well. For example, the new depositional patterns have been introduced for deciphering the paleogeography and sedimentary systems of the Wufeng shale and Longmaxi shale in the Sichuan Basin. The shale gas storage mechanism has been widely accepted as differing from conventional natural gas in that it is adsorbed on organic matter or a mineral surface or occurs as free gas trapped in pores and fractures of the shale. Significant advances in the techniques of microstructural characterization have provided new insights on how gas molecules are stored in micro- and nano-scale porous shales. Furthermore, newly-developed concepts and practices in the petroleum industry, such as hydraulic fracturing, microseismic monitoring and multiwell horizontal drilling, have made the production of this unevenly distributed but promising unconventional natural gas a reality. China has 10-36 trillion m3 of promising shale gas among the world＇s whole predicted technically recoverable reserves of 206.6 trillion m3. China is on the way to achieving its goal of an annual yield of 30-50 billion m3 by launching more trials within shale gas projects.
基金supported by the National Basic Research Program of China (973 Program, No. 2014CB239001)
文摘The Ordos Basin is the largest petroliferous basin in China, where the Chang 7 Member shale serves as the major source rock in the basin, with an area of more than 100,000 km^2 So far, sedimentary and geochemical characterizations have rarely been conducted on the shale in shallow(< 1000 m) areas in the southeastern part of the basin, but such characterizations can help identify the genesis of organic-rich shale and promote the prediction and recovery of shale oil. In this paper,several outcrop sections of the Chang 7 Member in the Tongchuan area were observed and sampled, and sedimentary and geochemical characterizations were conducted for the well-outcropped YSC section. The study results show that the Chang7 Member shale is widely distributed laterally with variable thickness. The organic-rich shale is 7-25 m thick in total and exhibits obvious horizontal variation in mineral composition. In the eastern sections, the shale contains organic matter of TypeⅡ_2-Ⅲ and is low in thermal maturity, with high clay mineral content, low K-feldspar content, and no pyrite. In the western sections, the shale contains Type Ⅱ_1 organic matter and is low in thermal maturity, with high clay mineral, K-feldspar, and pyrite contents. The YSC section reveals three obvious intervals in vertical mineral composition and organic abundance.The Chang 7 Member organic-rich shale(TOC > 10%) contains mainly sapropelite and liptinite, with Type Ⅱ kerogen. It is generally characterized by a hydrocarbon potential of more than 70 mg/g, low maturity, and shallow-semideep lacustrine facies. In the western sections, the shale, still in a low maturity stage, has a higher hydrocarbon potential and is optional for shale oil recovery. However, the Chang 7 Member shale in the study area is highly heterogeneous and its shale oil recovery is practical only in the organic-rich intervals.
基金financially supported by the National Natural Science Foundation of China (Grant Nos. 41372213, 41030422)Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDA05030100)
文摘The depositional environment of organic-rich shale and the related tectonic evolution in China are rather different from those in North America. In China, organic-rich shale is not only deposited in marine environment, but also in non-marine environment： marine-continental transitional environment and lacustrine environment. Through analyzing large amount of outcrops and well cores, the geologic features of organic-rich shale, including mineral composition, organic matter richness and type, and li- thology stratigraphy, were analyzed, indicating very special characteristics. Meanwhile, the more complex and active tectonic movements in China lead to strong deformation and erosion of organic-rich shale, well-development of fractures and faults, and higher thermal maturity and serious heterogeneity. Co-existence of shale gas, tight sand gas, and coal bed methane （CBM） proposes a new topic： whether it is possible to co-produce these gases to reduce cost. Based on the geologic features, the primary pro- duction issues of shale gas in China were discussed with suggestions.
文摘The organic-rich shale of the Chang 7 member is the most important source rock in the Ordos basin.The sedimentary environment and the controlling factors of organic matter enrichment,however,are still in contention.In this investigation,the Yishicun outcrop,located on the south margin of the Ordos basin,has been considered for the study.X-ray diffraction,polarizing microscopy,field emission scanning electron microscopy and cathodoluminescence(CL)were used to investigate the petrological features of the organic-rich shale.The content of volcanic ash and the diameter of pyrite framboid pseudocrystals were measured to illustrate the relationship between oxygen level,ash content and the enrichment of organic matter.It has been found that the diameter of pyrite framboid pseudocrystals has a strong correlation with the total organic carbon,demonstrating that the redox status degree of the water column has a positive impact on the enrichment of organic matter.Additionally,with an increase in the ash content,the content of organic matter increased at first and then decreased,and reached a maximum when the ash content was about 6%,illustrating that the ash input has a double effect on the enrichment of organic matter.
基金supported by the National Natural Science Foundation of China(No.41430101)the State Special Fund from Ministry of Science and Technology(No.2017ZX05036002)
文摘Sedimentary organic matter(OM) is a major reservoir of organic carbon in the global carbon cycle. Despite many studies, there still exist many debates on the mechanism of OM accumulation and preservation in marine sediments. We present a new field study of a Lower Cambrian shallow marine shelf sequence in the northern edge of the Yangtze Plate, China. Our results show that palynological OM and biogenic silica(Bio-Si) could be used alongside more conventional redox and paleo-productivity proxies to study the distribution of OM in marine sediments. The qualitative and quantitative study of palynological OM provides more detailed information on the nature of sedimentary organic carbon, which can be helpful in the assessment of primary productivity and OM preservation. In addition, the presence of Bio-Si stimulates the physical preservation of OM. Further analysis indicates that an increase in Bio-Si can promote OM preservation. This case-study provides insight into the intertwined factors controlling OM accumulation in the Early Cambrian.
基金funded by the National Natural Science Foundation“Event Sedimentation in Lacustrine Organic-Rich Mudrock:Taking the Chang 7-8 Member of the Ordos Basin as an Example”(Grant No.41802130).
文摘The deformation structure of soft sediments has always been a research hotspot,which is of great significance for analyzing the tectonic and sedimentary evolution background of a basin,as well as the physical properties of reservoirs.Previous studies have reported that a large number of soft sediment deformation structures are developed in the western part of Liaohe depression.In this study,through core observation and thin section identification,various types of deformation structures are identified in the core samples which are collected from the upper Es4 in the Leijia region,western sag of Liaohe depression,such as liquefied dikes,liquefied breccia,convoluted laminae,annular bedding,synsedimentary faults,vein structures,etc.Based on the characteristics of core structure,single well profile and continuous well profile,combined with the regional background,this study clarifies that the deformation structure of soft sediments in the study area is mainly caused by seismic action.It is found that the permeability and porosity of deformation layers in the study area are higher than those of the undeformation layers,which proves that the deformation structure of soft sediments has a good effect on improving the physical properties of reservoirs.
基金the financial support from the National Natural Science Foundation of China(42172151,42090025,41811530094,and 41625009)the China Postdoctoral Science Foundation(2021M690204)the National Key Research and Development Program(2019YFA0708504&2023YFF0806200)。
文摘Globally,most organic-rich shales are deposited with volcanic ash layers.Volcanic ash,a source for many sedimentary basins,can affect the sedimentary water environment,alter the primary productivity,and preserve the organic matter(OM)through physical,chemical,and biological reactions.With an increasing number of breakthroughs in shale oil exploration in the Bohai Bay Basin in recent years,less attention has been paid to the crucial role of volcanic impact especially its influence on the OM enrichment and hydrocarbon formation.Here,we studied the petrology,mineralogy,and geochemical characteristics of the organic-rich shale in the upper submember of the fourth member(Es_(4)^(1))and the lower submember of the third member(Es_(3)^(3))of the Shahejie Formation,aiming to better understand the volcanic impact on organic-rich shale formation.Our results show that total organic carbon is higher in the upper shale intervals rich in volcanic ash with enriched light rare earth elements and moderate Eu anomalies.This indicates that volcanism promoted OM formation before or after the eruption.The positive correlation between Eu/Eu*and Post-Archean Australian Shale indicates hydrothermal activity before the volcanic eruption.The plane graph of the hydrocarbon-generating intensity(S1+S2)suggests that the heat released by volcanism promoted hydrocarbon generation.Meanwhile,the nutrients carried by volcanic ash promoted biological blooms during Es_(4)^(1 )and Es_(3)^(3) deposition,yielding a high primary productivity.Biological blooms consume large amounts of oxygen and form anoxic environments conducive to the burial and preservation of OM.Therefore,this study helps to further understand the organic-inorganic interactions caused by typical geological events and provides a guide for the next step of shale oil exploration and development in other lacustrine basins in China.
基金supported by the National Natural Science Foundation of China(Grant Nos.41625009,U20B6001,42002139,42090025)the Strategic Priority Research Program of the Chinese Academy of Sciences,China(Grant No.XDA14010404)Tencent Xplorer Prize。
文摘Lacustrine shale is an important target for the exploration of unconventional oil and gas in China beyond marine shale gas.However,the formation environment of lacustrine shale differs from that of marine shale,resulting in a different reservoir composition,organic matter,oil and gas content,and hydrocarbon mobility.In this study,the Chang 7 shale of the Yanchang Formation in the Ordos Basin was used to analyze the effect of volcanic activity on the paleoproductivity and preservation conditions during the formation of lacustrine shale.The results show that algae and bacteria were developed before the eruption.After the eruption,the number of bacteria declined,but the increased prosperity of algae reflects that the volcanic activity enhanced ancient productivity.The sulfate generated by volcanic activity promotes bacterial sulfate reduction,and the produced H_(2)S leads to a strong reducing environment in the waterbody,which is conducive to the preservation of organic matter.Organic geochemical analysis shows that the black shale in the shale strata has a high total organic carbon(TOC)content and strong hydrocarbon generation potential,whereas the tuff has a low TOC content and can scarcely generate hydrocarbons,indicating that the tuff deposited by volcanic activity cannot be considered as effective source rock.In terms of storage space,shale is mainly laminar and dispersed,and it includes organic and inorganic pores.The development of organic pores is affected by thermal maturity,whereas inorganic pores mainly occur between detrital particles and crystals.Tuff is mainly supported by heterogeneous matrix and associated with alteration.Its pores include inter-and intragranular mineral pores.The development of tight sandstone pores is affected by compaction,cementation,and dissolution,which mainly consist of intra-and intergranular pores.The Chang 7 lacustrine shale generally contains oil,but different lithologies have different oil drainage efficiencies.Sandstone and shale exhibit the best and worst oil drainage e
基金Supported by the International Cooperation Project of China National Petroleum Corporation(2015D-4810-02)China National Science and Technology Major Project(2016ZX05046)
文摘In-situ conversion processing (ICP) of shale oil underground at the depth ranging from 300 m to 3 000 m is a physical and chemical process caused by using horizontal drilling and electric heating technology, which converts heavy oil, bitumen and various organic matter into light oil and gas in a large scale, which can be called"underground refinery". ICP has several advantages as in CO2capture, recoverable resource potential and the quality of hydrocarbon output. Based on the geothermal evolution mechanism of organic materials established by Tissot et al., this study reveals that in the nonmarine organic-rich shale sequence, the amount of liquid hydrocarbon maintaining in the shale is as high as 25%in the liquid hydrocarbon window stage (R o less than 1.0%), and the unconverted organic materials (low mature-immature organic materials) in the shale interval can reach 40%to 100%. The conditions of organic-rich shale suitable for underground in-situ conversion of shale oil should be satisfied in the following aspects, TOC higher than 6%, R o ranging between 0.5%and 1%, concentrated thickness of organic-rich shale greater than 15 meters, burial depth less than 3 000 m, covering area bigger than 50 km2, good sealing condition in both up-and down-contacting sequences and water content smaller than 5%, etc. The shale oil resource in China’s onshore region is huge. It is estimated with this paper that the technical recoverable resource reaches 70-90 billion tons of oil and 60-65 trillion cubic meters of gas. The ICP of shale oil underground is believed to be a fairway to find big oil in the source kitchen in the near future. And it is also believed to be a milestone to keep China long-term stability of oil and gas sufficient supply by putting ICP of shale oil underground into real practice in the future.
基金supported by the National Natural Science Foundation of China under Grants U1262208the National Natural Science Foundation of China under Grants 41404090
文摘Kerogen content and kerogen porosity play a significant role in elastic properties of organic-rich shales. We construct a rock physics model for organic-rich shales to quantify the effect of kerogen content and kerogen porosity using the Kuster and Toks6z theory and the selfconsistent approximation method. Rock physics modeling results show that with the increase of kerogen content and kerogen-related porosity, the velocity and density of shales decrease, and the effect of kerogen porosity becomes more obvious only for higher kerogen content. We also find that the Poisson＇s ratio of the shale is not sensitive to kerogen porosity for the case of gas saturation. Finally, for the seismic reflection responses of an organic-rich shale layer, forward modeling results indicate the fifth type AVO re- sponses which correspond to a negative intercept and a positive gradient. The absolute values of intercept and gradient increase with kerogen content and kerogen porosity, and present predictable variations associated with velocities and density.
基金Supported by the Petrochina Science and Technology Project(2021DJ18).
文摘The geological conditions and processes of fine-grained gravity flow sedimentation in continental lacustrine basins in China are analyzed to construct the model of fine-grained gravity flow sedimentation in lacustrine basin,reveal the development laws of fine-grained deposits and source-reservoir,and identify the sweet sections of shale oil.The results show that fine-grained gravity flow is one of the important sedimentary processes in deep lake environment,and it can transport fine-grained clasts and organic matter in shallow water to deep lake,forming sweet sections and high-quality source rocks of shale oil.Fine-grained gravity flow deposits in deep waters of lacustrine basins in China are mainly fine-grained high-density flow,fine-grained turbidity flow(including surge-like turbidity flow and fine-grained hyperpycnal flow),fine-grained viscous flow(including fine-grained debris flow and mud flow),and fine-grained transitional flow deposits.The distribution of fine-grained gravity flow deposits in the warm and humid unbalanced lacustrine basins are controlled by lake-level fluctuation,flooding events,and lakebed paleogeomorphology.During the lake-level rise,fine-grained hyperpycnal flow caused by flooding formed fine-grained channel–levee–lobe system in the flat area of the deep lake.During the lake-level fall,the sublacustrine fan system represented by unconfined channel was developed in the flexural slope breaks and sedimentary slopes of depressed lacustrine basins,and in the steep slopes of faulted lacustrine basins;the sublacustrine fan system with confined or unconfined channel was developed on the gentle slopes and in axial direction of faulted lacustrine basins,with fine-grained gravity flow deposits possibly existing in the lower fan.Within the fourth-order sequences,transgression might lead to organic-rich shale and fine-grained hyperpycnal flow deposits,while regression might cause fine-grained high-density flow,surge-like turbidity flow,fine-grained debris flow,mud flow,and fine-grained transiti
基金supported by the National Science and Technology Major Project(2017ZX05035004–002)the National Natural Science Foundation of China(no.41702167)+1 种基金the Fundamental Research Funds for the Central Universities(No.2017CXNL03)the Scientific Research Foundation of the Key Laboratory of Coalbed Methane Resources and Reservoir Formation Process,Ministry of Education(China University of Mining and Technology)(No.2017–007)
文摘Kerogen plays an important role in shale gas adsorption,desorption and diffusion.Therefore,it is necessary to characterize the molecular structure of kerogen.In this study,four kerogen samples were isolated from the organic-rich shale of the Longmaxi Formation.Raman spectroscopy was used to determine the maturity of these kerogen samples.Highresolution transmission electron microscopy(HRTEM),13 C nuclear magnetic resonance(13 C NMR),X-ray diffraction(XRD)and Fourier transform infrared(FT-IR)spectroscopy were conducted to characterize the molecular structure of the shale samples.The results demonstrate that VReqv of these kerogen samples vary from 2.3%to 2.8%,suggesting that all the kerogen samples are in the dry gas window.The macromolecular carbon skeleton of the Longmaxi Formation kerogen is mainly aromatic(fa’=0.56).In addition,the aromatic structural units are mainly composed of naphthalene(23%),anthracene(23%)and phenanthrene(29%).However,the aliphatic structure of the kerogen macromolecules is relatively low(fal*+falH=0.08),which is presumed to be distributed in the form of methyl and short aliphatic chains at the edge of the aromatic units.The oxygen-containing functional groups in the macromolecules are mainly present in the form of carbonyl groups(fac=0.23)and hydroxyl groups or ether groups(falO=0.13).The crystallite structural parameters of kerogen,including the stacking height(Lc=22.84?),average lateral size(La=29.29?)and interlayer spacing(d002=3.43?),are close to the aromatic structural parameters of anthracite or overmature kerogen.High-resolution transmission electron microscopy reveals that the aromatic structure is well oriented,and more than 65%of the diffractive aromatic layers are concentrated in the main direction.Due to the continuous deep burial,the longer aliphatic chains and oxygen-containing functional groups in the kerogen are substantially depleted.However,the ductility and stacking degree of the aromatic structure increases during thermal evolution.This study provides quantitative
基金Supported by the National Natural Fund Petrochemical Joint Fund Key Project(U1762217)Fundamental Scientific Research Operations Project of China Central Universities(19CX02009A)
文摘The Chang 73 sub-member of Triassic Yanchang Formation in the Ordos Basin was taken as an example and the lamina types and combinations,reservoir space features and shale oil enrichment patterns in organic-rich shale strata were investigated using core observation,thin section analysis,XRF element measurement,XRD analysis,SEM,high solution laser Raman spectroscopy analysis,and micro-FTIR spectroscopy analysis,etc.According to the mineral composition and thickness of the laminae,the Chang 73 organic-rich shales have four major types of laminae,tuff-rich lamina,organic-rich lamina,silt-grade feldspar-quartz lamina and clay lamina.They have two kinds of shale oil-bearing layers,"organic-rich lamina+silt-grade feldspar-quartz lamina"and"organic-rich lamina+tuff-rich lamina"layers.In the"organic-rich+silt-grade feldspar-quartz"laminae combination shale strata,oil was characterized by relative high maturation,and always filled in K-feldspar dissolution pores in the silt-grade feldspar-quartz laminae,forming oil generation,migration and accumulation process between laminae inside the organic shales.In the"organic-rich+tuff-rich lamina"binary laminae combination shale strata,however,the reservoir properties were poor in organic-rich shales,the oil maturation was relatively lower,and mainly accumulated in the intergranular pores of interbedded thin-layered sandstones.The oil generation,migration and accumulation mainly occurred between organic-rich shales and interbedded thin-layered sandstones.
