Determining the width of an induced hydraulic fracture is the first step for applying wellbore strengthening and hydraulic fracturing techniques. However, current 2-D analytical solutions obtained from the plane strai...Determining the width of an induced hydraulic fracture is the first step for applying wellbore strengthening and hydraulic fracturing techniques. However, current 2-D analytical solutions obtained from the plane strain assumption may have large uncertainties when the fracture height is small. To solve this problem, a 3-D finite element method(FEM) is used to model wellbore strengthening and calculate the fracture width. Comparisons show that the 2-D plane strain solution is the asymptote of the 3-D FEM solution. Therefore, the 2-D solution may overestimate the fracture width. This indicates that the2-D solution may not be applicable in 3-D conditions. Based on the FEM modeling, a new 3-D semi-analytical solution for determining the fracture width is proposed, which accounts for the e ects of 3-D fracture dimensions, stress anisotropy and borehole inclination. Compared to the 2-D solution, this new 3-D semi-analytical solution predicts a smaller fracture width.This implies that the 2-D-based old design for wellbore strengthening may overestimate the fracture width, which can be reduced using the proposed 3-D solution. It also allows an easy way to calculate the fracture width in complex geometrical and geological conditions. This solution has been verified against 3-D finite element calculations for field applications.展开更多
Fractures in oil and gas reservoirs have been the topic of many studies and have attracted reservoir research all over the world. Because of the complexities of the fractures, it is difficult to use fractured reservoi...Fractures in oil and gas reservoirs have been the topic of many studies and have attracted reservoir research all over the world. Because of the complexities of the fractures, it is difficult to use fractured reservoir core samples to investigate true underground conditions. Due to the diversity of the fracture parameters, the simulation and evaluation of fractured rock in the laboratory setting is also difficult. Previous researchers have typically used a single material, such as resin, to simulate fractures. There has been a great deal of simplifying of the materials and conditions, which has led to disappointing results in application. In the present study, sandstone core samples were selected and sectioned to simulate fractures, and the changes of the compressional and shear waves were measured with the gradual increasing of the fracture width. The effects of the simulated fracture width on the acoustic wave velocity and amplitude were analyzed. Two variables were defined： H represents the amplitude attenuation ratio of the compressional and shear wave, and x represents the transit time difference value of the shear wave and compressional wave divided by the transit time of the compressional wave. The effect of fracture width on these two physical quantities was then analyzed. Finally, the methods of quantitative evaluation for fracture width with H and x were obtained. The experimental results showed that the rock fractures linearly reduced the velocity of the shear and compressional waves. The effect of twin fractures on thecompressional velocity was almost equal to that of a single fracture which had the same fracture width as the sum of the twin fractures. At the same time, the existence of fractures led to acoustic wave amplitude attenuations, and the compressional wave attenuation was two times greater than that of the shear wave. In this paper, a method was proposed to calculate the fracture width with x and H, then this was applied to the array acoustic imaging logging data.The application examples 展开更多
To quantitatively determine the effect of different factors such as fracture width,dip angle,extension and filling material on Stoneley wave amplitude decreasing,the shock tube experiment method was changed from fixin...To quantitatively determine the effect of different factors such as fracture width,dip angle,extension and filling material on Stoneley wave amplitude decreasing,the shock tube experiment method was changed from fixing the sample and vertically moving the sensor in the borehole to fixing the sensors along the shock tube wall and vertically moving the sample without drilling the borehole in it.The measurement accuracy and the signal-to-noise ratio of the first Stoneley wave were improved by the time corrections and amplitude corrections of Stoneley wave signals.At the same time,21 sets of core models with different fracture parameters were processed for this measurement method by using full-diameter carbonate core,and relative amplitudes were defined to characterize Stoneley wave amplitude decreasing.The experimental results show that the relative amplitude of Stoneley wave exponentially decreases with increasing fracture width.The relative amplitude of Stoneley wave linearly decreases with increasing fracture dip angle.The relative amplitude of Stoneley wave exponentially decreases with increasing fracture extension.The relative amplitude of Stoneley wave decreases with increasing the permeability of filling material in the fracture.Under the above four conditions,the fracture width has the greatest effect on the decreasing of Stoneley wave amplitude,followed by the fracture extension and the permeability of filling material,and finally the fracture dip angle.展开更多
基金partially supported by National Key R&D Program of China (2017YFC0804108) during the 13th Five-Year Plan PeriodNational Science Foundation of China (51774136)+1 种基金Natural Science Foundation of Hebei Province of China (D2017508099)the Program for Innovative Research Team in the University sponsored by Ministry of Education of China (IRT-17R37)
文摘Determining the width of an induced hydraulic fracture is the first step for applying wellbore strengthening and hydraulic fracturing techniques. However, current 2-D analytical solutions obtained from the plane strain assumption may have large uncertainties when the fracture height is small. To solve this problem, a 3-D finite element method(FEM) is used to model wellbore strengthening and calculate the fracture width. Comparisons show that the 2-D plane strain solution is the asymptote of the 3-D FEM solution. Therefore, the 2-D solution may overestimate the fracture width. This indicates that the2-D solution may not be applicable in 3-D conditions. Based on the FEM modeling, a new 3-D semi-analytical solution for determining the fracture width is proposed, which accounts for the e ects of 3-D fracture dimensions, stress anisotropy and borehole inclination. Compared to the 2-D solution, this new 3-D semi-analytical solution predicts a smaller fracture width.This implies that the 2-D-based old design for wellbore strengthening may overestimate the fracture width, which can be reduced using the proposed 3-D solution. It also allows an easy way to calculate the fracture width in complex geometrical and geological conditions. This solution has been verified against 3-D finite element calculations for field applications.
基金supported in part by the National Natural Science Foundation of China (Grant No. 41174096)the Graduate Innovation Fund of Jilin University (Project No. 2016103)
文摘Fractures in oil and gas reservoirs have been the topic of many studies and have attracted reservoir research all over the world. Because of the complexities of the fractures, it is difficult to use fractured reservoir core samples to investigate true underground conditions. Due to the diversity of the fracture parameters, the simulation and evaluation of fractured rock in the laboratory setting is also difficult. Previous researchers have typically used a single material, such as resin, to simulate fractures. There has been a great deal of simplifying of the materials and conditions, which has led to disappointing results in application. In the present study, sandstone core samples were selected and sectioned to simulate fractures, and the changes of the compressional and shear waves were measured with the gradual increasing of the fracture width. The effects of the simulated fracture width on the acoustic wave velocity and amplitude were analyzed. Two variables were defined： H represents the amplitude attenuation ratio of the compressional and shear wave, and x represents the transit time difference value of the shear wave and compressional wave divided by the transit time of the compressional wave. The effect of fracture width on these two physical quantities was then analyzed. Finally, the methods of quantitative evaluation for fracture width with H and x were obtained. The experimental results showed that the rock fractures linearly reduced the velocity of the shear and compressional waves. The effect of twin fractures on thecompressional velocity was almost equal to that of a single fracture which had the same fracture width as the sum of the twin fractures. At the same time, the existence of fractures led to acoustic wave amplitude attenuations, and the compressional wave attenuation was two times greater than that of the shear wave. In this paper, a method was proposed to calculate the fracture width with x and H, then this was applied to the array acoustic imaging logging data.The application examples
基金Supported by the PetroChina’s Fundamental Research Project(2019A-3609)。
文摘To quantitatively determine the effect of different factors such as fracture width,dip angle,extension and filling material on Stoneley wave amplitude decreasing,the shock tube experiment method was changed from fixing the sample and vertically moving the sensor in the borehole to fixing the sensors along the shock tube wall and vertically moving the sample without drilling the borehole in it.The measurement accuracy and the signal-to-noise ratio of the first Stoneley wave were improved by the time corrections and amplitude corrections of Stoneley wave signals.At the same time,21 sets of core models with different fracture parameters were processed for this measurement method by using full-diameter carbonate core,and relative amplitudes were defined to characterize Stoneley wave amplitude decreasing.The experimental results show that the relative amplitude of Stoneley wave exponentially decreases with increasing fracture width.The relative amplitude of Stoneley wave linearly decreases with increasing fracture dip angle.The relative amplitude of Stoneley wave exponentially decreases with increasing fracture extension.The relative amplitude of Stoneley wave decreases with increasing the permeability of filling material in the fracture.Under the above four conditions,the fracture width has the greatest effect on the decreasing of Stoneley wave amplitude,followed by the fracture extension and the permeability of filling material,and finally the fracture dip angle.
