Dongyuemiao Member shale in the Sichuan Basin,China,is characterized by organic-rich shale intervals with different types of interbeds and accumulation modes.The aim of this study is to elucidate the impact of paleoen...Dongyuemiao Member shale in the Sichuan Basin,China,is characterized by organic-rich shale intervals with different types of interbeds and accumulation modes.The aim of this study is to elucidate the impact of paleoenvironmental indicators on interbed development.With this aim in mind,we established an interbed classification scheme and quantified the development of different types of interbeds and their frequencies.We categorized the shale interbeds into three types based on interbed type:silt interbeds(SIs),shell fragment interbeds(SFIs),and shell skeleton interbeds(SSIs).The SIs,SFIs,and SSIs are respectively the products of extrabasinal low-density turbidity currents,intrabasinal debris flow,and intrabasinal low-density turbidity currents.We propose that variations in paleoenvironmental conditions primarily influenced the types of interbeds that developed but had minimal impact on the frequency of their development.Models depicting the interbed development within the 1st Submember of Dongyuemiao Member indicate that during the early Dongyuemiao depositional period,under conditions of relatively aridity,weak weathering,high terrigenous input,and strong hydrodynamic activity,SSIs were well developed.In the middle depositional period,as the climate gradually transitioned to more humid conditions,and the weathering intensity and amount of terrestrial input increased,the development of SIs and SFIs significantly increased.During the late depositional period,with a continuous decrease in terrestrial inputs and sedimentation rates,the development of SIs decreased while that of SSIs increased.展开更多
Whether hydraulic fractures could connect multiple gas zones in the vertical plane is the key to fracturing treatment to jointly exploit coalbed methane and tight sandstone gas through integrative hydraulic fracturing...Whether hydraulic fractures could connect multiple gas zones in the vertical plane is the key to fracturing treatment to jointly exploit coalbed methane and tight sandstone gas through integrative hydraulic fracturing in tight sandstone–coal interbedded formations. Laboratory true triaxial hydraulic fracturing experiments were conducted on layered specimens with di erent combination types of natural sandstone and coal to simulate the propagation behavior of hydraulic fractures. The effects of the fracture initiation position, fracturing fluid viscosity and injection rate were discussed. The results showed that di erent fracture morphologies could be found. When initiating from coal seams, three patterns of fracture initiation and propagation were obtained:(1) The main hydraulic fracture initiated and propagated along the natural fractures and then diverged due to the effects of in situ stress and formed secondary fractures.(2) The hydraulic fracture initiated and propagated in the direction of the maximum horizontal stress.(3) Multiple fractures initiated and propagated at the same time. With the same fracturing fluid viscosity and injection rate, the hydraulic fractures initiating in sandstones had greater chances than those in coal seams to penetrate interfaces and enter neighboring layers. Excessively small or large fracturing fluid viscosity and injection rate would do harm to the vertical extension height of the induced fracture and improvement of the stimulated reservoir volume. Compared with operation parameters(fracturing fluid viscosity and injection rate), the natural weak planes in coals were considered to be the key factor that a ected the fracture propagation path. The experimental results would make some contributions to the development of tight sandstone–coal interbedded reservoirs.展开更多
The occurrence of interbeds in thick oil formations is one of the main reasons that cause the difference of remaining oil distribution. A quantitative method for predicting interbeds was proposed and the sedimentary o...The occurrence of interbeds in thick oil formations is one of the main reasons that cause the difference of remaining oil distribution. A quantitative method for predicting interbeds was proposed and the sedimentary origin and division criterion were demonstrated. The distribution of interbeds in different types of sedimentary sand bodies were predicted and analyzed by combining the theory of sedimentology and reservoir bed architectural-element analysis. The interbeds in a single well were recognized from high resolution well logs, and inter-well interbeds were predicted by using the methods of cyclothem correlation, physical properties trtmcation, and conditional simulation. Finally a 3-D model of interbed was built. Application to the Gudao Oilfield was successful.展开更多
This paper discusses the effect of influencing factors on the distribution of incremental oil displaced by a polymer flood （extra-displaced oil） using numerical reservoir simulation. These factors include the locati...This paper discusses the effect of influencing factors on the distribution of incremental oil displaced by a polymer flood （extra-displaced oil） using numerical reservoir simulation. These factors include the location, area and permeability of a thin low-permeability interbed, and the perforation location relative to the interbed. Simulation results show the locations from where the incremental oil was displaced by the polymer solution. The interbed position from the oil formation top affects the location of extra-displaced oil. The interbed area has a slight influence on the whole shape of extra-displaced oil. Larger interbed area leads to higher partition extent of extra-displaced oil. Higher vertical permeability of interbeds contributes to worse partition extent of extra-displaced oil and the partition effect disappears if the ratio of vertical to horizontal permeability is more than 0.05. The perforation location relative to the interbed affects polymer displacement efficiency, and also has a significant effect on the distribution of extra-displaced oil in polymer flooding.展开更多
The third member of Weixinnanliu in the west of the South China Sea develops thin interbeds, and the vertical extension of fracturing fractures is excessive. Once the fractures extend vertically to the upper and lower...The third member of Weixinnanliu in the west of the South China Sea develops thin interbeds, and the vertical extension of fracturing fractures is excessive. Once the fractures extend vertically to the upper and lower aquifers, it is easy to cause water flooding of oil wells, and the effect after fracturing is not obvious. The present work aims to explore the longitudinal extension law of fractures in Low Permeability Thin Interbed Reservoir based on the finite element calculation platform. A three-dimensional expansion model of hydraulic fractures in the target reservoir was established, and the displacement, fracturing fluid viscosity, minimum horizontal principal stress difference, vertical stress, interlayer thickness, perforation point separation were studied. The interlayer distance and other factors affect the crack propagation law. The research results show that the thin interbed fractures have three forms: T-shaped fractures, through-layer fractures, and I-shaped fractures;for the target layer, the overlying stress is relatively large, and the minimum principal stress is along the horizontal direction. Vertical cracks;the farther the perforation point is or the greater the stress difference, the smaller the thickness of the interlayer required to control the fracture height;the stress difference is 3 MPa, and the distance between the perforation points exceeds 10 m, the thickness of the interlayer is required to be ≥4 m;In order to ensure that the width of the fracture in the middle spacer does not affect the placement of the proppant, it is recommended that the displacement be controlled within 3 m<sup>3</sup>/min and the viscosity of the fracturing fluid is 150 mPa·s;in addition, the thickness of the spacer required to control the fracture height is different due to different geological parameters. Different, different wells need targeted analysis.展开更多
Based on core and casting slice observation, well drilling and logging data, the source of carbonate materials, lithology together with electric properties, types, genesis mechanism and distribution of calcareous inte...Based on core and casting slice observation, well drilling and logging data, the source of carbonate materials, lithology together with electric properties, types, genesis mechanism and distribution of calcareous interbeds in Songtao uplift and its periphery of Qiongdongnan Basin have been thoroughly analyzed. Results show that typical features have been appeared from well logging curves, containing low gamma-ray, low acoustic travel time, low neutron value, high density, as well as bright white calcium nodules or bands in electrical imaging well-logging curves. Drilling results reveal that calcareous interbeds developed mostly in high position of paleostructures and their distribution was controlled by the combined effects of macroscopic and microscopic factors. Macroscopically, calcareous interbeds relate to paleogeomorphology together with the combination of sandstone and mudstone. They are also controlled microscopically by the source of carbonate cements and pore space. Under normal circumstances, with regard to the same sand, the closer to the mudstone and the thicker of mudstone, the more conducive to the formation of calcareous interlayer. Low compaction strength, high content of rigid particles, coarse grain size, well-sorted sandstone and large pore space during carbonate cementation are favorable for the development of calcareous interbeds.展开更多
基金sponsored by the National Natural Science Foundation of China,China(No.42272171)National Science and Technology Major Project of China,China(No.2017ZX05036).
文摘Dongyuemiao Member shale in the Sichuan Basin,China,is characterized by organic-rich shale intervals with different types of interbeds and accumulation modes.The aim of this study is to elucidate the impact of paleoenvironmental indicators on interbed development.With this aim in mind,we established an interbed classification scheme and quantified the development of different types of interbeds and their frequencies.We categorized the shale interbeds into three types based on interbed type:silt interbeds(SIs),shell fragment interbeds(SFIs),and shell skeleton interbeds(SSIs).The SIs,SFIs,and SSIs are respectively the products of extrabasinal low-density turbidity currents,intrabasinal debris flow,and intrabasinal low-density turbidity currents.We propose that variations in paleoenvironmental conditions primarily influenced the types of interbeds that developed but had minimal impact on the frequency of their development.Models depicting the interbed development within the 1st Submember of Dongyuemiao Member indicate that during the early Dongyuemiao depositional period,under conditions of relatively aridity,weak weathering,high terrigenous input,and strong hydrodynamic activity,SSIs were well developed.In the middle depositional period,as the climate gradually transitioned to more humid conditions,and the weathering intensity and amount of terrestrial input increased,the development of SIs and SFIs significantly increased.During the late depositional period,with a continuous decrease in terrestrial inputs and sedimentation rates,the development of SIs decreased while that of SSIs increased.
基金the support from the National Science and Technology Major Projects of China(Grant No.2016ZX05066)Major Program of National Natural Science Foundation of China(Grant No.51490650)PetroChina Innovation Foundation(No.2018D-5007-0307)
文摘Whether hydraulic fractures could connect multiple gas zones in the vertical plane is the key to fracturing treatment to jointly exploit coalbed methane and tight sandstone gas through integrative hydraulic fracturing in tight sandstone–coal interbedded formations. Laboratory true triaxial hydraulic fracturing experiments were conducted on layered specimens with di erent combination types of natural sandstone and coal to simulate the propagation behavior of hydraulic fractures. The effects of the fracture initiation position, fracturing fluid viscosity and injection rate were discussed. The results showed that di erent fracture morphologies could be found. When initiating from coal seams, three patterns of fracture initiation and propagation were obtained:(1) The main hydraulic fracture initiated and propagated along the natural fractures and then diverged due to the effects of in situ stress and formed secondary fractures.(2) The hydraulic fracture initiated and propagated in the direction of the maximum horizontal stress.(3) Multiple fractures initiated and propagated at the same time. With the same fracturing fluid viscosity and injection rate, the hydraulic fractures initiating in sandstones had greater chances than those in coal seams to penetrate interfaces and enter neighboring layers. Excessively small or large fracturing fluid viscosity and injection rate would do harm to the vertical extension height of the induced fracture and improvement of the stimulated reservoir volume. Compared with operation parameters(fracturing fluid viscosity and injection rate), the natural weak planes in coals were considered to be the key factor that a ected the fracture propagation path. The experimental results would make some contributions to the development of tight sandstone–coal interbedded reservoirs.
文摘The occurrence of interbeds in thick oil formations is one of the main reasons that cause the difference of remaining oil distribution. A quantitative method for predicting interbeds was proposed and the sedimentary origin and division criterion were demonstrated. The distribution of interbeds in different types of sedimentary sand bodies were predicted and analyzed by combining the theory of sedimentology and reservoir bed architectural-element analysis. The interbeds in a single well were recognized from high resolution well logs, and inter-well interbeds were predicted by using the methods of cyclothem correlation, physical properties trtmcation, and conditional simulation. Finally a 3-D model of interbed was built. Application to the Gudao Oilfield was successful.
基金support from the National Natural Science Foundation of China (NO.10772200,10972237)the Important National Science & Technology Specific Projects of China(No.2011ZX05011)
文摘This paper discusses the effect of influencing factors on the distribution of incremental oil displaced by a polymer flood （extra-displaced oil） using numerical reservoir simulation. These factors include the location, area and permeability of a thin low-permeability interbed, and the perforation location relative to the interbed. Simulation results show the locations from where the incremental oil was displaced by the polymer solution. The interbed position from the oil formation top affects the location of extra-displaced oil. The interbed area has a slight influence on the whole shape of extra-displaced oil. Larger interbed area leads to higher partition extent of extra-displaced oil. Higher vertical permeability of interbeds contributes to worse partition extent of extra-displaced oil and the partition effect disappears if the ratio of vertical to horizontal permeability is more than 0.05. The perforation location relative to the interbed affects polymer displacement efficiency, and also has a significant effect on the distribution of extra-displaced oil in polymer flooding.
文摘The third member of Weixinnanliu in the west of the South China Sea develops thin interbeds, and the vertical extension of fracturing fractures is excessive. Once the fractures extend vertically to the upper and lower aquifers, it is easy to cause water flooding of oil wells, and the effect after fracturing is not obvious. The present work aims to explore the longitudinal extension law of fractures in Low Permeability Thin Interbed Reservoir based on the finite element calculation platform. A three-dimensional expansion model of hydraulic fractures in the target reservoir was established, and the displacement, fracturing fluid viscosity, minimum horizontal principal stress difference, vertical stress, interlayer thickness, perforation point separation were studied. The interlayer distance and other factors affect the crack propagation law. The research results show that the thin interbed fractures have three forms: T-shaped fractures, through-layer fractures, and I-shaped fractures;for the target layer, the overlying stress is relatively large, and the minimum principal stress is along the horizontal direction. Vertical cracks;the farther the perforation point is or the greater the stress difference, the smaller the thickness of the interlayer required to control the fracture height;the stress difference is 3 MPa, and the distance between the perforation points exceeds 10 m, the thickness of the interlayer is required to be ≥4 m;In order to ensure that the width of the fracture in the middle spacer does not affect the placement of the proppant, it is recommended that the displacement be controlled within 3 m<sup>3</sup>/min and the viscosity of the fracturing fluid is 150 mPa·s;in addition, the thickness of the spacer required to control the fracture height is different due to different geological parameters. Different, different wells need targeted analysis.
文摘Based on core and casting slice observation, well drilling and logging data, the source of carbonate materials, lithology together with electric properties, types, genesis mechanism and distribution of calcareous interbeds in Songtao uplift and its periphery of Qiongdongnan Basin have been thoroughly analyzed. Results show that typical features have been appeared from well logging curves, containing low gamma-ray, low acoustic travel time, low neutron value, high density, as well as bright white calcium nodules or bands in electrical imaging well-logging curves. Drilling results reveal that calcareous interbeds developed mostly in high position of paleostructures and their distribution was controlled by the combined effects of macroscopic and microscopic factors. Macroscopically, calcareous interbeds relate to paleogeomorphology together with the combination of sandstone and mudstone. They are also controlled microscopically by the source of carbonate cements and pore space. Under normal circumstances, with regard to the same sand, the closer to the mudstone and the thicker of mudstone, the more conducive to the formation of calcareous interlayer. Low compaction strength, high content of rigid particles, coarse grain size, well-sorted sandstone and large pore space during carbonate cementation are favorable for the development of calcareous interbeds.
