Volume 29,Issue 3,2022 Table of Contents
2022, 29(3):1-10.
DOI: 10.13673/j.cnki.cn37-1359/te.202103021
Abstract:
Fault types and activities were analyzed to reveal the control of fault characteristics on differences of oil and gas enrichment in the Neogene in the eastern Chengdao area，Jiyang Depression. On this basis，3D seismic data，as well as logging and drilling data，were utilized to study the fault activities during hydrocarbon accumulation and their relationships with the Neogene oil and gas enrichment in terms of the fault activity rate. Studies have shown that three types of faults are in the eastern Chengdao area，i.e.oil source typeⅠ，oil source typeⅡ，and adjustment faults. There are obvious differences in the activities of the three types of faults during the main accumulation period（Minghuazhen period）：the activity rates of most oil source typeⅠfaults，oil source typeⅡfaults and most adjustment faults are more than 15 m/Ma，10-15 m/Ma and less than 10 m/Ma respectively. The oil source faults in the study area control the differences in enrichment and spatial distribution of oil and gas in the Neogene. Zhuanghai fault zone has developed many oil source typeⅠand typeⅡ faults at an activity rate greater than 10 m/Ma，and the fault-caprock assemblage is favorable. A typical fault transport-vertical migration mode can be found，and the degree of oil and gas enrichment is high in the Neogene. In addition，oil source faults are few in the east slope of Chengdao area，with weak fault activities（10-12 m/Ma），following a fault-sand body transportstepped migration mode. The degree of Neogene oil and gas enrichment is low，and they are mostly distributed in the underlying reservoirs.
Fault types and activities were analyzed to reveal the control of fault characteristics on differences of oil and gas enrichment in the Neogene in the eastern Chengdao area，Jiyang Depression. On this basis，3D seismic data，as well as logging and drilling data，were utilized to study the fault activities during hydrocarbon accumulation and their relationships with the Neogene oil and gas enrichment in terms of the fault activity rate. Studies have shown that three types of faults are in the eastern Chengdao area，i.e.oil source typeⅠ，oil source typeⅡ，and adjustment faults. There are obvious differences in the activities of the three types of faults during the main accumulation period（Minghuazhen period）：the activity rates of most oil source typeⅠfaults，oil source typeⅡfaults and most adjustment faults are more than 15 m/Ma，10-15 m/Ma and less than 10 m/Ma respectively. The oil source faults in the study area control the differences in enrichment and spatial distribution of oil and gas in the Neogene. Zhuanghai fault zone has developed many oil source typeⅠand typeⅡ faults at an activity rate greater than 10 m/Ma，and the fault-caprock assemblage is favorable. A typical fault transport-vertical migration mode can be found，and the degree of oil and gas enrichment is high in the Neogene. In addition，oil source faults are few in the east slope of Chengdao area，with weak fault activities（10-12 m/Ma），following a fault-sand body transportstepped migration mode. The degree of Neogene oil and gas enrichment is low，and they are mostly distributed in the underlying reservoirs.
2022, 29(3):11-19.
DOI: 10.13673/j.cnki.cn37-1359/te.202103027
Abstract:
The lacustrine lamina represents a sedimentary response to the sedimentary process and environmental change.The inner texture and genesis of carbonate laminae of Paleogene lacustrine shale in Dongying Sag were studied by thin-section analysis of core samples，scanning electron microscopy（SEM），and micro-fluorescence analysis. The results show that the Paleogene lacustrine shale carbonate laminae in Dongying Sag can be divided into micritic carbonate laminae and spar carbonate laminae，which are characterized by diverse mineral compositions and fabrics.Carbonate lens and lamina have a genetic relationship of inheritance，and the formation of carbonate laminae is closely related to microbial activities. The development and sedimentation of those laminae are controlled by both environmental conditions and their growth. A variety of mineral components confirm that lamina development has undergone a complex biological-chemical-physical process，and the inner texture and combination form of the laminae reflect the multi-cycle erosion–deposition activities. The development of lacustrine shale follows a sedimentary sequence from lens to laminae and from a single lamina to laminae couples，which records abundant geological information，such as changes of lake water environment，ecological evolution，and fluctuation in sedimentary base levels.
The lacustrine lamina represents a sedimentary response to the sedimentary process and environmental change.The inner texture and genesis of carbonate laminae of Paleogene lacustrine shale in Dongying Sag were studied by thin-section analysis of core samples，scanning electron microscopy（SEM），and micro-fluorescence analysis. The results show that the Paleogene lacustrine shale carbonate laminae in Dongying Sag can be divided into micritic carbonate laminae and spar carbonate laminae，which are characterized by diverse mineral compositions and fabrics.Carbonate lens and lamina have a genetic relationship of inheritance，and the formation of carbonate laminae is closely related to microbial activities. The development and sedimentation of those laminae are controlled by both environmental conditions and their growth. A variety of mineral components confirm that lamina development has undergone a complex biological-chemical-physical process，and the inner texture and combination form of the laminae reflect the multi-cycle erosion–deposition activities. The development of lacustrine shale follows a sedimentary sequence from lens to laminae and from a single lamina to laminae couples，which records abundant geological information，such as changes of lake water environment，ecological evolution，and fluctuation in sedimentary base levels.
2022, 29(3):20-28.
DOI: 10.13673/j.cnki.cn37-1359/te.202107040
Abstract:
The distribution of remaining oil is a common concern in the later period of oilfield development，and the complexity of underground conditions makes the detection of remaining oil more difficult. The cased hole saturation logging is the most direct and effective method to detect remaining oil，which can provide strong support for the adjustment of oilfield development plans. However，one saturation logging method can hardly be applied to all geological conditions. Hence，we compared the current saturation logging methods applied in Shengli Oilfield and analyzed the characteristics of reservoirs that these methods can be applied to. According to the geological characteristics of the region，an appropriate saturation logging method was selected to evaluate the remaining oil saturation（ROS）. It can more accurately determine the channeling outside the casing，indicate the location of water leakage，and recognize the gas reservoir，the oil reservoir with low resistivity，and the oil reservoir that is injected with fresh water and produced water alternately. Additionally，this method can distinguish and analyze the fluid properties in pores near the well，determine the distribution of remaining oil，and excavate the potential oil reservoirs. As a result，the multiplicity of solutions and the influence of factors such as lithology，porosity，wellbore environment，and the salinity of formation water are reduced；the coincidence rate of interpretation results has been effectively improved. Given the result of logging interpretations，the potential reservoirs are provided for acidizing，fracturing，and perforation adding. Upon the implementation of the measures，the water cut decreases，and the oil production increases.
The distribution of remaining oil is a common concern in the later period of oilfield development，and the complexity of underground conditions makes the detection of remaining oil more difficult. The cased hole saturation logging is the most direct and effective method to detect remaining oil，which can provide strong support for the adjustment of oilfield development plans. However，one saturation logging method can hardly be applied to all geological conditions. Hence，we compared the current saturation logging methods applied in Shengli Oilfield and analyzed the characteristics of reservoirs that these methods can be applied to. According to the geological characteristics of the region，an appropriate saturation logging method was selected to evaluate the remaining oil saturation（ROS）. It can more accurately determine the channeling outside the casing，indicate the location of water leakage，and recognize the gas reservoir，the oil reservoir with low resistivity，and the oil reservoir that is injected with fresh water and produced water alternately. Additionally，this method can distinguish and analyze the fluid properties in pores near the well，determine the distribution of remaining oil，and excavate the potential oil reservoirs. As a result，the multiplicity of solutions and the influence of factors such as lithology，porosity，wellbore environment，and the salinity of formation water are reduced；the coincidence rate of interpretation results has been effectively improved. Given the result of logging interpretations，the potential reservoirs are provided for acidizing，fracturing，and perforation adding. Upon the implementation of the measures，the water cut decreases，and the oil production increases.
2022, 29(3):29-35.
DOI: 10.13673/j.cnki.cn37-1359/te.202104011
Abstract:
From the perspective of reservoir identification and production，the lower limits of reservoir physical properties are divided into four types：“reservoir”，“oil-bearing reservoir”，“produced reservoir”，and“effective reservoir”. Based on the reservoir percolation theory，comprehensively considering the percolation response characteristics of different-scale pores and the difference in minimum flow pore diameters under the driving pressure，theoretical discussion and case analysis were performed on the connotation and determination method of four lower limits of reservoir physical properties. The research results show that：①the lower limits of physical properties of“reservoirs”，“oil-bearing reservoirs”，“produced res? ervoirs”，and“effective reservoirs”are respectively the boundaries between reservoirs and non-reservoirs，between oilbearing and non-oil-bearing reservoirs，between produced and non-produced reservoirs，and between effective and ineffective reservoirs. The porosity and permeability increase in the sequence of“reservoirs”，“produced reservoirs”，“oil-bearing reservoirs”，and“effective reservoirs”. ②The lower limits of physical properties of“reservoirs”，“oil-bearing reservoirs”，and“produced reservoirs”respectively correspond to the minimum flow pore diameters of theoretical percolation，charging percolation，and production percolation and can be determined by the minimum flow pore diameter method. ③The lower limits of physical properties of“effective reservoirs”have a low correlation with the minimum flow pore diameter under the test percolation and are mainly limited by the industrial oil flow standard. They need to be determined with the physical property analysis of cores，tests，and production test data. The simple study on the lower limits of physical properties of“effective reservoirs”has gradually shifted to a comprehensive study on the lower limits of physical properties of“reservoirs”，“oil-bearing reservoirs”，“produced reservoirs”，and“effective reservoirs”，which is an important direction for in-depth research on the lower limits of reservoir physical properties.
From the perspective of reservoir identification and production，the lower limits of reservoir physical properties are divided into four types：“reservoir”，“oil-bearing reservoir”，“produced reservoir”，and“effective reservoir”. Based on the reservoir percolation theory，comprehensively considering the percolation response characteristics of different-scale pores and the difference in minimum flow pore diameters under the driving pressure，theoretical discussion and case analysis were performed on the connotation and determination method of four lower limits of reservoir physical properties. The research results show that：①the lower limits of physical properties of“reservoirs”，“oil-bearing reservoirs”，“produced res? ervoirs”，and“effective reservoirs”are respectively the boundaries between reservoirs and non-reservoirs，between oilbearing and non-oil-bearing reservoirs，between produced and non-produced reservoirs，and between effective and ineffective reservoirs. The porosity and permeability increase in the sequence of“reservoirs”，“produced reservoirs”，“oil-bearing reservoirs”，and“effective reservoirs”. ②The lower limits of physical properties of“reservoirs”，“oil-bearing reservoirs”，and“produced reservoirs”respectively correspond to the minimum flow pore diameters of theoretical percolation，charging percolation，and production percolation and can be determined by the minimum flow pore diameter method. ③The lower limits of physical properties of“effective reservoirs”have a low correlation with the minimum flow pore diameter under the test percolation and are mainly limited by the industrial oil flow standard. They need to be determined with the physical property analysis of cores，tests，and production test data. The simple study on the lower limits of physical properties of“effective reservoirs”has gradually shifted to a comprehensive study on the lower limits of physical properties of“reservoirs”，“oil-bearing reservoirs”，“produced reservoirs”，and“effective reservoirs”，which is an important direction for in-depth research on the lower limits of reservoir physical properties.
2022, 29(3):36-44.
DOI: 10.13673/j.cnki.cn37-1359/te.202110029
Abstract:
Under the fan-delta sedimentary environment of Mahu Sag in Junggar Basin，the tight glutenite reservoirs feature complex internal structure，variable physical properties，and complicated spatial distribution. Therefore，the quantitative description for the variation rules of the spatial distribution，physical properties and oil content of the reservoirs is required.However，former studies have proved that it is difficult to solve the problem efficiently by routine seismic attribute analysis and post-stack or pre-stack seismic inversion methods. Thus，the extended elastic impedance（EEI）inversion technology is adopted for the quantitative prediction of tight glutenite reservoirs. By using petrophysical analysis based on logging data，we analyzed the correlation of geological parameters and EEI of multi-well target intervals with variation of Chi projection angle.In this way，the optimal Chi projection angle was determined，and the data of drilled wells were applied to make cross-plots. We performed high-resolution acoustic impedance（AI）and gradient impedance（GI）inversion by the joint method of amplitude versus offset（AVO）attribute analysis，pre-stack simultaneous inversion and stochastic inversion.Then，given the optimal Chi projection angle，the EEI attributes corresponding to reservoir parameters to be predicted were estimated.Finally，we made cross-plots with the reservoir parameters and estimated EEI attributes，fitted relationship expressions according to classes from the neural network clustering of lithofacies，calculated reservoir parameters，and corrected errors. The practical applications indicate that the key geological parameters of reservoirs such as physical properties and oil/gas content can be quantitatively and effectively described by the EEI inversion. The technology is conducive to raising the success rate of the prospecting and development of tight oil and gas reservoirs，which is worthy of trials and wide application.
Under the fan-delta sedimentary environment of Mahu Sag in Junggar Basin，the tight glutenite reservoirs feature complex internal structure，variable physical properties，and complicated spatial distribution. Therefore，the quantitative description for the variation rules of the spatial distribution，physical properties and oil content of the reservoirs is required.However，former studies have proved that it is difficult to solve the problem efficiently by routine seismic attribute analysis and post-stack or pre-stack seismic inversion methods. Thus，the extended elastic impedance（EEI）inversion technology is adopted for the quantitative prediction of tight glutenite reservoirs. By using petrophysical analysis based on logging data，we analyzed the correlation of geological parameters and EEI of multi-well target intervals with variation of Chi projection angle.In this way，the optimal Chi projection angle was determined，and the data of drilled wells were applied to make cross-plots. We performed high-resolution acoustic impedance（AI）and gradient impedance（GI）inversion by the joint method of amplitude versus offset（AVO）attribute analysis，pre-stack simultaneous inversion and stochastic inversion.Then，given the optimal Chi projection angle，the EEI attributes corresponding to reservoir parameters to be predicted were estimated.Finally，we made cross-plots with the reservoir parameters and estimated EEI attributes，fitted relationship expressions according to classes from the neural network clustering of lithofacies，calculated reservoir parameters，and corrected errors. The practical applications indicate that the key geological parameters of reservoirs such as physical properties and oil/gas content can be quantitatively and effectively described by the EEI inversion. The technology is conducive to raising the success rate of the prospecting and development of tight oil and gas reservoirs，which is worthy of trials and wide application.
2022, 29(3):45-52.
DOI: 10.13673/j.cnki.cn37-1359/te.202103026
Abstract:
The variation of carbon and oxygen isotopes composition of carbonate rock is highly indicative of the sedimentary environment，water salinity，and climate change of lake basins. The lake shale of Lower Es3（the Lower Submember of the 3rd Member of Eocene Shahejie Formation）and Upper Es4（the Upper Submember of the 4th Member of Eocene Shahejie Formation）in Bonan Sag was studied，according to the on-line analysis method of the carbon and oxygen isotopes of trace carbonate rock. The results show that δ13CPDB and δ18OPDB in Upper Es4 are both negative，and are positively correlated. It indicated a closed brackish lacustrine environment with a high temperature during the development of fault depression. The negative deviation of δ13CPDB was not only influenced by freshwater supply but also related to the high sulfate content in the lake during the sedimentary period. The light δ18OPDB resulted mainly from the cementation in the middle-late period of diagenesis.The δ13CPDB and δ18OPDB in Lower Es3 were relatively heavy and well correlated，which implied that the lacustrine environment during the peak period of fault depression was hydrologically closed and stable. The variation of carbon and oxygen isotopes of carbonate rocks in the longitudinal direction indicated a shift from a relatively dry climate to a warm and humid climate during the early to late sedimentation.Meanwhile，the water salinity gradually decreased.
The variation of carbon and oxygen isotopes composition of carbonate rock is highly indicative of the sedimentary environment，water salinity，and climate change of lake basins. The lake shale of Lower Es3（the Lower Submember of the 3rd Member of Eocene Shahejie Formation）and Upper Es4（the Upper Submember of the 4th Member of Eocene Shahejie Formation）in Bonan Sag was studied，according to the on-line analysis method of the carbon and oxygen isotopes of trace carbonate rock. The results show that δ13CPDB and δ18OPDB in Upper Es4 are both negative，and are positively correlated. It indicated a closed brackish lacustrine environment with a high temperature during the development of fault depression. The negative deviation of δ13CPDB was not only influenced by freshwater supply but also related to the high sulfate content in the lake during the sedimentary period. The light δ18OPDB resulted mainly from the cementation in the middle-late period of diagenesis.The δ13CPDB and δ18OPDB in Lower Es3 were relatively heavy and well correlated，which implied that the lacustrine environment during the peak period of fault depression was hydrologically closed and stable. The variation of carbon and oxygen isotopes of carbonate rocks in the longitudinal direction indicated a shift from a relatively dry climate to a warm and humid climate during the early to late sedimentation.Meanwhile，the water salinity gradually decreased.
2022, 29(3):53-61.
DOI: 10.13673/j.cnki.cn37-1359/te.202104014
Abstract:
Low resistivity wells were drilled successively in Longmaxi Formation of Changning area，and the gas-bearing properties of these wells were damaged to varying degrees. Based on the characteristics of low-resistivity shale reservoirs，seismic survey，structural and fault stages，logging，and core experiments，the research was performed on the causes and main influencing factors of low-resistivity shale gas reservoirs in Changning area. The results reveal that the daily gas production of low-resistivity shale reservoirs in Changning area show resistivity >5 Ω·m，total hydrocarbon display >2%，porosity >4.2%，gas content >2.0 m3/t，and gas saturation >60%. The low resistivity wells in Longmaxi Formation shale reservoirs of Changning area are mainly affected by faults. The compression by faults destroys the gas-bearing properties of reservoirs，which is characterized by relatively low resistivity，and the footwall exerts a greater influence on resistivity than the hanging wall；the shale reservoirs in the footwall are prone to low resistivity，while those in the hanging wall tend to be normal.In addition，the low resistivity wells in the study area are mainly related to the faulting stages. All the low resistivity wells in Jianwu syncline are controlled by the faults during the Caledonian. The natural gas in the footwall wells partially migrates to the hanging wall，and formation water enters the fractures induced by faults. Water accumulates in the structural low in a short distance，resulting in the low resistivity wells with a lower output. However，the natural gas in the hanging wall is enriched，leading to many high-yield wells. The low resistivity wells in Tiangongtang anticline and Shuanglong-Luo·chang syncline as well as to the west of Jianwu syncline are controlled by NE-trending faults in the middle and late Himalayan.Moreover，some low resistivity wells in Changning area are due to the decrease in resistivity caused by the higher water saturation of shale reservoirs near the fault.
Low resistivity wells were drilled successively in Longmaxi Formation of Changning area，and the gas-bearing properties of these wells were damaged to varying degrees. Based on the characteristics of low-resistivity shale reservoirs，seismic survey，structural and fault stages，logging，and core experiments，the research was performed on the causes and main influencing factors of low-resistivity shale gas reservoirs in Changning area. The results reveal that the daily gas production of low-resistivity shale reservoirs in Changning area show resistivity >5 Ω·m，total hydrocarbon display >2%，porosity >4.2%，gas content >2.0 m3/t，and gas saturation >60%. The low resistivity wells in Longmaxi Formation shale reservoirs of Changning area are mainly affected by faults. The compression by faults destroys the gas-bearing properties of reservoirs，which is characterized by relatively low resistivity，and the footwall exerts a greater influence on resistivity than the hanging wall；the shale reservoirs in the footwall are prone to low resistivity，while those in the hanging wall tend to be normal.In addition，the low resistivity wells in the study area are mainly related to the faulting stages. All the low resistivity wells in Jianwu syncline are controlled by the faults during the Caledonian. The natural gas in the footwall wells partially migrates to the hanging wall，and formation water enters the fractures induced by faults. Water accumulates in the structural low in a short distance，resulting in the low resistivity wells with a lower output. However，the natural gas in the hanging wall is enriched，leading to many high-yield wells. The low resistivity wells in Tiangongtang anticline and Shuanglong-Luo·chang syncline as well as to the west of Jianwu syncline are controlled by NE-trending faults in the middle and late Himalayan.Moreover，some low resistivity wells in Changning area are due to the decrease in resistivity caused by the higher water saturation of shale reservoirs near the fault.
2022, 29(3):62-67.
DOI: 10.13673/j.cnki.cn37-1359/te.202104002
Abstract:
Based on the laboratory test and development data of Yanchuannan Block in the southeastern margin of the Or? dos Basin，this paper studied the role of burial depth in the reservoir petrophysical properties，development performance，as well as the enrichment and production of coalbed methane reservoirs. The quantitative evaluation index and calculation formula were put forward for the enrichment and high-production zone of deep coalbed methane reservoirs.The results show that the deeper burial depth can lead to the more enriched coalbed methane and the greater maximum vitrinite reflectance.It indicates that the paleo-geotemperature continues to increase with the greater burial depth，resulting in the constant growth in hydrocarbon generation capacity. Coupled with the high-temperature hydrothermal baking，the paleo-geotemperature is rather higher than the normal value，leading to massive coalbed methane；thus the CH4 content tends to be higher with the greater burial depth in the study area. Burial depth has a dual influence on the production of coalbed methane wells. On one hand，an exponential decrease is observed in the reservoir permeability with the greater burial depth，down to about 0.1 mD at 1 500 m around. On the other hand，however，the adsorption time declines with the greater burial depth，namely that the desorption efficiency grows，which is favorable for the development of deep coalbed methane reservoirs.Based on the gas content，permeability and adsorption time，the calculation formula for the gas production index is devised，and this index has a good correlation with the single well production. The enrichment and high-production zone of coalbed methane in the study area can be correctly predicted. The gas production index of the study area rises first and then drops with the greater burial depth. It reaches the highest at the burial depth around 1 100 m，revealing the most favorable development zone in the study area.
Based on the laboratory test and development data of Yanchuannan Block in the southeastern margin of the Or? dos Basin，this paper studied the role of burial depth in the reservoir petrophysical properties，development performance，as well as the enrichment and production of coalbed methane reservoirs. The quantitative evaluation index and calculation formula were put forward for the enrichment and high-production zone of deep coalbed methane reservoirs.The results show that the deeper burial depth can lead to the more enriched coalbed methane and the greater maximum vitrinite reflectance.It indicates that the paleo-geotemperature continues to increase with the greater burial depth，resulting in the constant growth in hydrocarbon generation capacity. Coupled with the high-temperature hydrothermal baking，the paleo-geotemperature is rather higher than the normal value，leading to massive coalbed methane；thus the CH4 content tends to be higher with the greater burial depth in the study area. Burial depth has a dual influence on the production of coalbed methane wells. On one hand，an exponential decrease is observed in the reservoir permeability with the greater burial depth，down to about 0.1 mD at 1 500 m around. On the other hand，however，the adsorption time declines with the greater burial depth，namely that the desorption efficiency grows，which is favorable for the development of deep coalbed methane reservoirs.Based on the gas content，permeability and adsorption time，the calculation formula for the gas production index is devised，and this index has a good correlation with the single well production. The enrichment and high-production zone of coalbed methane in the study area can be correctly predicted. The gas production index of the study area rises first and then drops with the greater burial depth. It reaches the highest at the burial depth around 1 100 m，revealing the most favorable development zone in the study area.
2022, 29(3):68-79.
DOI: 10.13673/j.cnki.cn37-1359/te.202203035
Abstract:
For oilfield enterprises，constructing intelligent oilfields is an inevitable development direction to meet the needs of high-quality development and severe external challenges. This paper summarizes the advanced practice of oilfield enterprises in China and abroad in intelligent construction and concludes that intelligent oilfields should have four abilities：comprehensive perception，integration and coordination，early warning and prediction，and analysis and optimization. On the basis of comprehensively promoting the construction of the Internet of things，China’s oil and gas industry has conducted a series of explorations and practice by leveraging the massive data resources accumulated gradually and resorting to intelligent technologies to improve the quality and efficiency of the exploration and development and production operation of oilfields and gasfields. Favorable application results have been achieved in business scenarios of reservoir prediction，reservoir description，and working condition diagnosis. For the comprehensive implementation of digital transformation and intelligent development of oilfield enterprises，key research problems need to be further tackled for the technology of dynamic automatic monitoring and intelligent control on the production site，new-generation intelligent oilfield technology based on industrial big data，intelligent optimization technology for oil reservoir development，and digital twin and intelligent operation command technology for oilfields. The objective is to develop a leading series of basic key technologies of intelligent acquisition，comprehensive perception，intelligent control，and early warning and prediction for intelligent oilfields and thereby support the high-quality development of oilfields and ensure national energy security.
For oilfield enterprises，constructing intelligent oilfields is an inevitable development direction to meet the needs of high-quality development and severe external challenges. This paper summarizes the advanced practice of oilfield enterprises in China and abroad in intelligent construction and concludes that intelligent oilfields should have four abilities：comprehensive perception，integration and coordination，early warning and prediction，and analysis and optimization. On the basis of comprehensively promoting the construction of the Internet of things，China’s oil and gas industry has conducted a series of explorations and practice by leveraging the massive data resources accumulated gradually and resorting to intelligent technologies to improve the quality and efficiency of the exploration and development and production operation of oilfields and gasfields. Favorable application results have been achieved in business scenarios of reservoir prediction，reservoir description，and working condition diagnosis. For the comprehensive implementation of digital transformation and intelligent development of oilfield enterprises，key research problems need to be further tackled for the technology of dynamic automatic monitoring and intelligent control on the production site，new-generation intelligent oilfield technology based on industrial big data，intelligent optimization technology for oil reservoir development，and digital twin and intelligent operation command technology for oilfields. The objective is to develop a leading series of basic key technologies of intelligent acquisition，comprehensive perception，intelligent control，and early warning and prediction for intelligent oilfields and thereby support the high-quality development of oilfields and ensure national energy security.
2022, 29(3):80-84.
DOI: 10.13673/j.cnki.cn37-1359/te.202108032
Abstract:
In 1945，ARPS proposed the theoretically significant decline rate and its differential form based on the statistics and analysis of the production decline curve. The exponential decline model，hyperbolic decline model，and harmonic decline model were first built，of which the hyperbolic decline model was the core of the Arps decline model. The exponential decline model has been widely used due to its simplicity and ease of operation. The application research shows that the empirical hyperbolic decline model is rarely used in practice because of its obvious uncertainty. The harmonic decline model simplified from the hyperbolic decline model has hardly been applied. At the same time，the Arps hyperbolic decline model with n=0.5 is the best choice through the comparison with the generic exponential decline model by Chen Yuanqian，which can be effectively used to predict the production rate and recoverable reserves of shale gas wells.
In 1945，ARPS proposed the theoretically significant decline rate and its differential form based on the statistics and analysis of the production decline curve. The exponential decline model，hyperbolic decline model，and harmonic decline model were first built，of which the hyperbolic decline model was the core of the Arps decline model. The exponential decline model has been widely used due to its simplicity and ease of operation. The application research shows that the empirical hyperbolic decline model is rarely used in practice because of its obvious uncertainty. The harmonic decline model simplified from the hyperbolic decline model has hardly been applied. At the same time，the Arps hyperbolic decline model with n=0.5 is the best choice through the comparison with the generic exponential decline model by Chen Yuanqian，which can be effectively used to predict the production rate and recoverable reserves of shale gas wells.
CUI Chuanzhi
,
HAN Xingyuan
,
BING Shaoxian
,
HUANG Yingsong
,
LI Weizhong
,
LIU Lijie
,
WU Zhongwei
2022, 29(3):85-91.
DOI: 10.13673/j.cnki.cn37-1359/te.202107010
Abstract:
Waterflooding oil reservoirs are prone to develop different degrees of water-consumption zones，which thereby reduces the effect of reservoir development. Therefore，it is of great significance to study the characterization，quantitative grading，and distribution characteristics of water-consumption zones for further potential exploration of waterflooding oil reservoirs. This paper first established the quantitative characterization indexes of water-consumption zones considering reservoir permeability，crude oil viscosity and water saturation. Then，a grading method was developed for water-consumption zones from the perspectives of technology（seepage capacity）and economy，and it was applied to actual blocks in an oilfield. It is found that as the viscosity of crude oil decreases，the high water-consumption zones and extreme water-consumption zones develops rapidly and the corresponding pseudo-water-consumption rate drops when they are formed；as the permeability declines，the economic high water-consumption zones disappear，and non-economic low water-consumption zones appear. The current extreme water-consumption zones in Unit Ng3-4，Area A of Shengli Oilfield are mainly distributed near water wells，with a small development area；non-economic high water-consumption zones surround the extreme water-consumption zones，with a medium development area；economic high water-consumption zones surround non-economic high water-consumption zones，with a large development area；economic low-water consumption zones are distributed in areas with low displacement efficiency and have a large development area.
Waterflooding oil reservoirs are prone to develop different degrees of water-consumption zones，which thereby reduces the effect of reservoir development. Therefore，it is of great significance to study the characterization，quantitative grading，and distribution characteristics of water-consumption zones for further potential exploration of waterflooding oil reservoirs. This paper first established the quantitative characterization indexes of water-consumption zones considering reservoir permeability，crude oil viscosity and water saturation. Then，a grading method was developed for water-consumption zones from the perspectives of technology（seepage capacity）and economy，and it was applied to actual blocks in an oilfield. It is found that as the viscosity of crude oil decreases，the high water-consumption zones and extreme water-consumption zones develops rapidly and the corresponding pseudo-water-consumption rate drops when they are formed；as the permeability declines，the economic high water-consumption zones disappear，and non-economic low water-consumption zones appear. The current extreme water-consumption zones in Unit Ng3-4，Area A of Shengli Oilfield are mainly distributed near water wells，with a small development area；non-economic high water-consumption zones surround the extreme water-consumption zones，with a medium development area；economic high water-consumption zones surround non-economic high water-consumption zones，with a large development area；economic low-water consumption zones are distributed in areas with low displacement efficiency and have a large development area.
12 An evaluation model of water-flooding reservoir development system based on flow field adaptability
2022, 29(3):92-101.
DOI: 10.13673/j.cnki.cn37-1359/te.202106011
Abstract:
At present，the commonly used evaluation indexes for water-flooding development effect are mostly related to the evaluation of the entire reservoir development history，which are difficult to timely reflect the matching degree of the current well pattern and the injection-production pressure system with the reservoir state. Therefore，in view of the nature of the underground flow field evolution in water-flooding reservoirs，the oil saturation and flow velocity are screened out as seepage field evaluation parameters by the logic analysis method. In light of the statistical theory，an evaluation model of flow field adaptability is established with four indexes，including relative adaptation coefficient，flow-saturation difference（FSD），absolute adaptation coefficient，and equilibrium coefficient. With typical injection-production units and actual blocks as examples，the flow field adaptability is evaluated. The analysis results show that the equilibrium coefficient and the actual daily oil production are correlated positively. The developed evaluation model of flow field adaptability can effectively warn the imbalance between the development system and the reservoir state and intuitively reflect unreasonable positions in the area，thus able to guide the adjustment of injection and production，quantitatively evaluate the effectiveness of various adjustment measures，and provide technical support for the following development and adjustment of water-flooding reservoirs.
At present，the commonly used evaluation indexes for water-flooding development effect are mostly related to the evaluation of the entire reservoir development history，which are difficult to timely reflect the matching degree of the current well pattern and the injection-production pressure system with the reservoir state. Therefore，in view of the nature of the underground flow field evolution in water-flooding reservoirs，the oil saturation and flow velocity are screened out as seepage field evaluation parameters by the logic analysis method. In light of the statistical theory，an evaluation model of flow field adaptability is established with four indexes，including relative adaptation coefficient，flow-saturation difference（FSD），absolute adaptation coefficient，and equilibrium coefficient. With typical injection-production units and actual blocks as examples，the flow field adaptability is evaluated. The analysis results show that the equilibrium coefficient and the actual daily oil production are correlated positively. The developed evaluation model of flow field adaptability can effectively warn the imbalance between the development system and the reservoir state and intuitively reflect unreasonable positions in the area，thus able to guide the adjustment of injection and production，quantitatively evaluate the effectiveness of various adjustment measures，and provide technical support for the following development and adjustment of water-flooding reservoirs.
2022, 29(3):102-112.
DOI: 10.13673/j.cnki.cn37-1359/te.202202012
Abstract:
The pore throat microstructure is an internal factor that determines the physical properties of tight sandstone reservoir. Therefore，describing the characteristics of pore throat microstructure in a quantitative manner can provide a basis for studying on the quality characterization of tight sandstone reservoir. However，the micro-nano pore throats in tight sandstone reservoir are developed with strong micro heterogeneity，so it is difficult to accurately determine the characteristic parameters of pore throats by conventional experimental methods. In this paper，on the basis of high-precision digital core image（taking the SEM-Maps scanning image with resolution 10 nm as an example），a porous media model of tight sandstone is constructed. Furthermore，the paper has developed methods，including adaptive recognition and extraction of pore throats，the segmentation of pore throats based on image morphological algorithm，and the calculation of characteristic parameters of pore throat structure. In this way，the quantitative characterization of pore throat microstructure of tight sandstone based on the scanning image is realized. This paper selects three typical rock samples of tight sandstone from Chang8 reservoir in Honghe Oilfield in an attempt to calculate the characteristic parameters of pore throats quantitatively and to analyze the structural differences of pore throats. The results show that the physical properties of rock samples are closely related to the characteristics of pore throat microstructure and the more pore throat，the larger pore throat radius，the higher coordination number and the better connectivity of pore throat all make the permeability and other physical properties of rock samples better.
The pore throat microstructure is an internal factor that determines the physical properties of tight sandstone reservoir. Therefore，describing the characteristics of pore throat microstructure in a quantitative manner can provide a basis for studying on the quality characterization of tight sandstone reservoir. However，the micro-nano pore throats in tight sandstone reservoir are developed with strong micro heterogeneity，so it is difficult to accurately determine the characteristic parameters of pore throats by conventional experimental methods. In this paper，on the basis of high-precision digital core image（taking the SEM-Maps scanning image with resolution 10 nm as an example），a porous media model of tight sandstone is constructed. Furthermore，the paper has developed methods，including adaptive recognition and extraction of pore throats，the segmentation of pore throats based on image morphological algorithm，and the calculation of characteristic parameters of pore throat structure. In this way，the quantitative characterization of pore throat microstructure of tight sandstone based on the scanning image is realized. This paper selects three typical rock samples of tight sandstone from Chang8 reservoir in Honghe Oilfield in an attempt to calculate the characteristic parameters of pore throats quantitatively and to analyze the structural differences of pore throats. The results show that the physical properties of rock samples are closely related to the characteristics of pore throat microstructure and the more pore throat，the larger pore throat radius，the higher coordination number and the better connectivity of pore throat all make the permeability and other physical properties of rock samples better.
2022, 29(3):113-120.
DOI: 10.13673/j.cnki.cn37-1359/te.202108037
Abstract:
Since 2020，3D development with deploying adjustment wells between wells in the upper，middle and lower layers has achieved good results in some well group tests of Fuling Shale Gas Field，which is expected to improve the overall recovery of the whole play. Adopting the numerical simulation method to evaluate the development effect of different technical schemes for shale gas 3D development is the basis for further optimizing the scheme and improving the overall recovery.Accordingly，this paper proposes a numerical simulation method based on an embedded discrete fracture model. Taking the Fuling Jiangdong Block as an example，the paper comprehensively analyzes the influence of factors such as results of different fracturing technologies and inter-well interference on well group productivity. It also evaluates the effects of 3D development and proposes corresponding countermeasures for stabilizing and increasing production. The results indicate that the embedded discrete fracture model can depict the distribution of fracture networks in multi-layers with 3D development of horizontal wells and simulate the interference of fractures. There are not effectively producing and basically unproducing shale gas reserves in the lower and the upper layers respectively，which are the potentials of infill adjustment. 3D development can effectively improve the production of shale gas reserves.
Since 2020，3D development with deploying adjustment wells between wells in the upper，middle and lower layers has achieved good results in some well group tests of Fuling Shale Gas Field，which is expected to improve the overall recovery of the whole play. Adopting the numerical simulation method to evaluate the development effect of different technical schemes for shale gas 3D development is the basis for further optimizing the scheme and improving the overall recovery.Accordingly，this paper proposes a numerical simulation method based on an embedded discrete fracture model. Taking the Fuling Jiangdong Block as an example，the paper comprehensively analyzes the influence of factors such as results of different fracturing technologies and inter-well interference on well group productivity. It also evaluates the effects of 3D development and proposes corresponding countermeasures for stabilizing and increasing production. The results indicate that the embedded discrete fracture model can depict the distribution of fracture networks in multi-layers with 3D development of horizontal wells and simulate the interference of fractures. There are not effectively producing and basically unproducing shale gas reserves in the lower and the upper layers respectively，which are the potentials of infill adjustment. 3D development can effectively improve the production of shale gas reserves.
2022, 29(3):121-127.
DOI: 10.13673/j.cnki.cn37-1359/te.202102022
Abstract:
The oil displacement characteristics of CO2 in low permeability heterogeneous multi-layer reservoirs are different from those in single-layer reservoirs. To clarify the CO2 flooding characteristics in heterogeneous multi-layer reservoirs，we simulated the CO2 flooding process in low permeability heterogeneous multi-layer reservoirs through the displacement experiments with three pipes of long core in parallel connection. The oil displacement efficiency of high，medium and low permeability layers after continuous CO2 flooding and water-alternating-gas（WAG）flooding were evaluated under immiscible and miscible pressures. The damage characteristics of asphaltene precipitation to heterogeneous multi-layer reservoirs were clarified. The results reveal that continuous injection of CO2 under immiscible or miscible pressures will lead to the rapid breakthrough of the high permeability layer，and the breakthrough of CO2 under miscible pressure is earlier than that under immiscible pressure. After the breakthrough，the contribution rate of the high permeability layer to the total recovery factor is more than 91.7%，while those of the medium permeability layer under immiscible and miscible pressure are 5.6% and 2.1%，and that of the low permeability layer is 0. After CO2 flooding is converted to WAG flooding，the swept volume of CO2 increases significantly，and the recovery factors of medium and low permeability layers are improved considerably. However，the medium and low permeability layers still represent the main direction for tapping the reservoir potential in the later stage. Under miscible pressure，the damage of asphaltene precipitation to heterogeneous multi-layer reservoirs mainly concentrates in the rear of the high permeability layer，near the outlet；while under immiscible pressure，it is mainly in the front and middle of the high permeability layer，near the inlet，but the degree of damage is lower than that under miscible pressure. The influence of asphaltene precipitation on the medium and low permeability layers can be ignored.
The oil displacement characteristics of CO2 in low permeability heterogeneous multi-layer reservoirs are different from those in single-layer reservoirs. To clarify the CO2 flooding characteristics in heterogeneous multi-layer reservoirs，we simulated the CO2 flooding process in low permeability heterogeneous multi-layer reservoirs through the displacement experiments with three pipes of long core in parallel connection. The oil displacement efficiency of high，medium and low permeability layers after continuous CO2 flooding and water-alternating-gas（WAG）flooding were evaluated under immiscible and miscible pressures. The damage characteristics of asphaltene precipitation to heterogeneous multi-layer reservoirs were clarified. The results reveal that continuous injection of CO2 under immiscible or miscible pressures will lead to the rapid breakthrough of the high permeability layer，and the breakthrough of CO2 under miscible pressure is earlier than that under immiscible pressure. After the breakthrough，the contribution rate of the high permeability layer to the total recovery factor is more than 91.7%，while those of the medium permeability layer under immiscible and miscible pressure are 5.6% and 2.1%，and that of the low permeability layer is 0. After CO2 flooding is converted to WAG flooding，the swept volume of CO2 increases significantly，and the recovery factors of medium and low permeability layers are improved considerably. However，the medium and low permeability layers still represent the main direction for tapping the reservoir potential in the later stage. Under miscible pressure，the damage of asphaltene precipitation to heterogeneous multi-layer reservoirs mainly concentrates in the rear of the high permeability layer，near the outlet；while under immiscible pressure，it is mainly in the front and middle of the high permeability layer，near the inlet，but the degree of damage is lower than that under miscible pressure. The influence of asphaltene precipitation on the medium and low permeability layers can be ignored.
2022, 29(3):128-136.
DOI: 10.13673/j.cnki.cn37-1359/te.202104030
Abstract:
Generally，elastoplastic reservoirs have threshold pressure gradients and pressure-sensitive effects that can change the permeability during development. Therefore，their flow characteristics and the effective production laws of reserves are dramatically different from those of conventional reservoirs，and the design methods for conventional well patterns and spacing cannot meet the actual development requirements. Based on the traditional mechanics of fluid flow in porous media，a flow model considering the influence of the pressure-sensitive effects and threshold pressure gradients was built with the typical injection-production well pattern，and the distribution law of injection-production flow fields was obtained using the steady successive substitution method. According to the characteristics of elastoplastic reservoirs，an evaluation method for the effective production effect of reserves was proposed，and the effective production limit of reserves under different conditions was obtained. The results show that the production range and effective production intensity of reserves in injection-production units have obvious changes under the influence of pressure sensitivity and threshold pressure gradients. In given reservoir development conditions，the limit of effective reserve production is determined，and the change chart of inject-production well spacing that can achieve the target of effective reserve production is obtained through calculation，providing a theoretical basis for the optimization design of well patterns in oilfields.
Generally，elastoplastic reservoirs have threshold pressure gradients and pressure-sensitive effects that can change the permeability during development. Therefore，their flow characteristics and the effective production laws of reserves are dramatically different from those of conventional reservoirs，and the design methods for conventional well patterns and spacing cannot meet the actual development requirements. Based on the traditional mechanics of fluid flow in porous media，a flow model considering the influence of the pressure-sensitive effects and threshold pressure gradients was built with the typical injection-production well pattern，and the distribution law of injection-production flow fields was obtained using the steady successive substitution method. According to the characteristics of elastoplastic reservoirs，an evaluation method for the effective production effect of reserves was proposed，and the effective production limit of reserves under different conditions was obtained. The results show that the production range and effective production intensity of reserves in injection-production units have obvious changes under the influence of pressure sensitivity and threshold pressure gradients. In given reservoir development conditions，the limit of effective reserve production is determined，and the change chart of inject-production well spacing that can achieve the target of effective reserve production is obtained through calculation，providing a theoretical basis for the optimization design of well patterns in oilfields.
2022, 29(3):137-145.
DOI: 10.13673/j.cnki.cn37-1359/te.202106023
Abstract:
Class III reservoirs in Daqing Oilfield account for nearly half of the total reserves in La-Sa-Xing Oilfield of Daqing Placanticline，which have geological characteristics including thin thickness，low permeability，poor connectivity，and serious heterogeneity. For the synchronous displacement of high-and low-permeability oil reservoirs by chemical flooding and balanced reservoir efficiency，the displacement experiment with a laboratory plane model was carried out and the development effects of enhanced oil recovery（EOR）technology were compared at different production modes in Class III reservoirs. As a result，the staged chemical flooding production mode was selected and applied in oilfields.In the first stage，polymer flooding was performed in thin and poor oil reservoirs with effective thickness less than 0.5 m and effective permeability less than 0.05 D and untabulated oil reservoirs. In the second stage，commingled weak-alkalinity ASP flooding was carried out in other oil reservoirs by supplement perforation. The results show that in laboratory experiments，staged polymer flooding for medium-and low-permeability oil reservoirs registers ultimate recovery of up to 65.8%. The field application of staged chemical flooding in Gaotaizi reservoir of Beierdong Block indicates that the overall ultimate recovery is expected to increase by more than 12% in the test area，and remarkable results have been achieved.
Class III reservoirs in Daqing Oilfield account for nearly half of the total reserves in La-Sa-Xing Oilfield of Daqing Placanticline，which have geological characteristics including thin thickness，low permeability，poor connectivity，and serious heterogeneity. For the synchronous displacement of high-and low-permeability oil reservoirs by chemical flooding and balanced reservoir efficiency，the displacement experiment with a laboratory plane model was carried out and the development effects of enhanced oil recovery（EOR）technology were compared at different production modes in Class III reservoirs. As a result，the staged chemical flooding production mode was selected and applied in oilfields.In the first stage，polymer flooding was performed in thin and poor oil reservoirs with effective thickness less than 0.5 m and effective permeability less than 0.05 D and untabulated oil reservoirs. In the second stage，commingled weak-alkalinity ASP flooding was carried out in other oil reservoirs by supplement perforation. The results show that in laboratory experiments，staged polymer flooding for medium-and low-permeability oil reservoirs registers ultimate recovery of up to 65.8%. The field application of staged chemical flooding in Gaotaizi reservoir of Beierdong Block indicates that the overall ultimate recovery is expected to increase by more than 12% in the test area，and remarkable results have been achieved.
2022, 29(3):146-152.
DOI: 10.13673/j.cnki.cn37-1359/te.202110021
Abstract:
After several cycles of steam huff and puff development，the oil-steam ratio of heavy oil reservoirs decreases significantly and the number of ineffective and low effective wells increases，which causes worse economic benefits. It is urgent to explore the transformation development technology of heavy oil after multiple rounds of huff and puff. As the existing chemical cold production additives cannot meet the requirements of viscosity reduction and oil displacement under a low dynamic in field，a comb-shaped amphiphilic permeable agent PDE-1 for viscosity reduction and oil displacement was synthesized in this paper. Specifically，the effects of polymerization conditions such as the initiator dosage，and monomer ratio on the performance of PDE-1 were investigated by single-factor experiments. In addition，the technical means such as the optical microscope and microfluidics were applied to analyze the performance of PDE-1，including the penetration and depolymerization，wettability，viscosity reduction，and static oil washing. The results revealed that for the synthesis of PDE-1，the optimal monomer ratio should satisfy that acrylamide：sodium acrylate：functional monomer BBAM：monomer containing ether bonds equals 75∶20∶1.5∶3.5，with the initiator dosage of 0.3%，polymerization temperature of 40 ℃，total monomer mass fraction of 25%，and reaction time of 6 h. The synthesized PDE-1 can spontaneously permeate and depolymerize heavy oil under a low dynamic in reservoirs，change the rock wettability in the capillaries，and turn the reservoir capillary resistance into oil displacement power. At the mass concentration of 1 500 mg/L，the viscosity reduction rate of PDE-1 in ordinary heavy oil is 97.5%，and at 500 mg/L，the oil washing rate of oil sand reaches 58.7%，which indicates that PDE-1 has excellent viscosity reduction and oil washing performance.
After several cycles of steam huff and puff development，the oil-steam ratio of heavy oil reservoirs decreases significantly and the number of ineffective and low effective wells increases，which causes worse economic benefits. It is urgent to explore the transformation development technology of heavy oil after multiple rounds of huff and puff. As the existing chemical cold production additives cannot meet the requirements of viscosity reduction and oil displacement under a low dynamic in field，a comb-shaped amphiphilic permeable agent PDE-1 for viscosity reduction and oil displacement was synthesized in this paper. Specifically，the effects of polymerization conditions such as the initiator dosage，and monomer ratio on the performance of PDE-1 were investigated by single-factor experiments. In addition，the technical means such as the optical microscope and microfluidics were applied to analyze the performance of PDE-1，including the penetration and depolymerization，wettability，viscosity reduction，and static oil washing. The results revealed that for the synthesis of PDE-1，the optimal monomer ratio should satisfy that acrylamide：sodium acrylate：functional monomer BBAM：monomer containing ether bonds equals 75∶20∶1.5∶3.5，with the initiator dosage of 0.3%，polymerization temperature of 40 ℃，total monomer mass fraction of 25%，and reaction time of 6 h. The synthesized PDE-1 can spontaneously permeate and depolymerize heavy oil under a low dynamic in reservoirs，change the rock wettability in the capillaries，and turn the reservoir capillary resistance into oil displacement power. At the mass concentration of 1 500 mg/L，the viscosity reduction rate of PDE-1 in ordinary heavy oil is 97.5%，and at 500 mg/L，the oil washing rate of oil sand reaches 58.7%，which indicates that PDE-1 has excellent viscosity reduction and oil washing performance.
2022, 29(3):153-161.
DOI: 10.13673/j.cnki.cn37-1359/te.202101030
Abstract:
After large-scale fracturing of shale reservoirs，the shape of hydraulic fractures，the complex seepage mechanism after fracturing，and the interaction among multiple action mechanisms are the keys to the prediction of post-fracturing productivity and the deployment of shale gas well patterns. Based on the workflow of geology-engineering integration，the hydraulic fracturing network modeling and numerical simulation of shale reservoirs were carried out to optimize development technology policies and maximize economic benefits. The hydraulic fracture propagation model was built to simulate the post-fracturing network. The model considered the stress shadow between hydraulic fractures，natural fractures，in-situ stress，and the heterogeneity of fracturing fluid flow，ensuring that the simulated hydraulic fractures agreed more with the field reality. On this basis，post-fracturing numerical simulation was performed，considering complex gas seepage mechanisms. The research results show that the horizontal stress difference coefficient is small in the well area DP2 of the Nanchuan block，and hydraulic fracturing can produce a complex fracturing network. Hydraulic fractures are effectively supported in the lateral direction，and there is room for further improvement in productivity in the vertical direction. In light of stress sensitivity and economic benefit evaluation，the optimal production system is determined to be 6×104 m3/d，and the reasonable length of the horizontal segment is 2 000 m.
After large-scale fracturing of shale reservoirs，the shape of hydraulic fractures，the complex seepage mechanism after fracturing，and the interaction among multiple action mechanisms are the keys to the prediction of post-fracturing productivity and the deployment of shale gas well patterns. Based on the workflow of geology-engineering integration，the hydraulic fracturing network modeling and numerical simulation of shale reservoirs were carried out to optimize development technology policies and maximize economic benefits. The hydraulic fracture propagation model was built to simulate the post-fracturing network. The model considered the stress shadow between hydraulic fractures，natural fractures，in-situ stress，and the heterogeneity of fracturing fluid flow，ensuring that the simulated hydraulic fractures agreed more with the field reality. On this basis，post-fracturing numerical simulation was performed，considering complex gas seepage mechanisms. The research results show that the horizontal stress difference coefficient is small in the well area DP2 of the Nanchuan block，and hydraulic fracturing can produce a complex fracturing network. Hydraulic fractures are effectively supported in the lateral direction，and there is room for further improvement in productivity in the vertical direction. In light of stress sensitivity and economic benefit evaluation，the optimal production system is determined to be 6×104 m3/d，and the reasonable length of the horizontal segment is 2 000 m.
2022, 29(3):162-170.
DOI: 10.13673/j.cnki.cn37-1359/te.202101049
Abstract:
With the increasing concern of the oil industry about cost reduction and environmental protection，ever more attention has been paid to the research on the working fluid capable of both fracturing and oil displacement. For the further study on the fracturing-oil displacement integrated working fluid，the research on the composition，the oil displacement performance，and the field application of the oil displacement system of fracturing flowback fluid and the oil-displacement fracturing fluid system were reviewed，and future developments were forecasted. The construction of the oil displacement system of fracturing flowback fluid is based on clean fracturing fluid，especially the one with cationic surfactant as the main component；the oil-displacement fracturing fluid system includes the ones based on clean fracturing fluid，polymer，slickwater，etc.，among which the clean oil-displacement fracturing fluid system with enhanced efficiency presents the greatest potential. Reducing cost，enhancing high temperature resistance，and strengthening the study on microstructure and static and dynamic rheological properties are the keys to the future research on the fracturing-oil displacement integrated working fluid. The comparison between the field application and laboratory test results demonstrates that further improving the oil displacement system of fracturing flowback fluid also represents an important direction for the future work.
With the increasing concern of the oil industry about cost reduction and environmental protection，ever more attention has been paid to the research on the working fluid capable of both fracturing and oil displacement. For the further study on the fracturing-oil displacement integrated working fluid，the research on the composition，the oil displacement performance，and the field application of the oil displacement system of fracturing flowback fluid and the oil-displacement fracturing fluid system were reviewed，and future developments were forecasted. The construction of the oil displacement system of fracturing flowback fluid is based on clean fracturing fluid，especially the one with cationic surfactant as the main component；the oil-displacement fracturing fluid system includes the ones based on clean fracturing fluid，polymer，slickwater，etc.，among which the clean oil-displacement fracturing fluid system with enhanced efficiency presents the greatest potential. Reducing cost，enhancing high temperature resistance，and strengthening the study on microstructure and static and dynamic rheological properties are the keys to the future research on the fracturing-oil displacement integrated working fluid. The comparison between the field application and laboratory test results demonstrates that further improving the oil displacement system of fracturing flowback fluid also represents an important direction for the future work.
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