Recent studies have indicated that the injection of carbon dioxide(CO_(2))can lead to increased oil recovery in fractured shale reservoirs following natural depletion.Despite advancements in understanding mass exchang...Recent studies have indicated that the injection of carbon dioxide(CO_(2))can lead to increased oil recovery in fractured shale reservoirs following natural depletion.Despite advancements in understanding mass exchange processes in subsurface formations,there remains a knowledge gap concerning the disparities in these processes between the matrix and fractures at the pore scale in formations with varying permeability.This study aims to experimentally investigate the CO_(2) diffusion behaviors and in situ oil recovery through a CO_(2) huff‘n’puff process in the Jimsar shale oil reservoir.To achieve this,we designed three matrix-fracture models with different permeabilities(0.074 mD,0.170 mD,and 0.466 mD)and experimented at 30 MPa and 91℃.The oil concentration in both the matrix and fracture was monitored using a low-field nuclear magnetic resonance(LF-NMR)technique to quantify in situ oil recovery and elucidate mass-exchange behaviors.The results showed that after three cycles of CO_(2) huff‘n’puff,the total recovery degree increased from 30.28%to 34.95%as the matrix permeability of the core samples increased from 0.074 to 0.466 mD,indicating a positive correlation between CO_(2) extraction efficiency and matrix permeability.Under similar fracture conditions,the increase in matrix permeability further promoted CO_(2) extraction efficiency during CO_(2) huff‘n’puff.Specifically,the increase in matrix permeability of the core had the greatest effect on the extraction of the first-cycle injection in large pores,which increased from 16.42%to 36.64%.The findings from our research provide valuable insights into the CO_(2) huff‘n’puff effects in different pore sizes following fracturing under varying permeability conditions,shedding light on the mechanisms of CO_(2)-enhanced oil recovery in fractured shale oil reservoirs.展开更多
The parameters such as pore size distribution,specific surface area and pore volume of shale rock samples are analyzed by low-temperature nitrogen adsorption experiment,and then the conversion coefficient between rela...The parameters such as pore size distribution,specific surface area and pore volume of shale rock samples are analyzed by low-temperature nitrogen adsorption experiment,and then the conversion coefficient between relaxation time(T_(2))and pore size is calibrated.Nuclear magnetic resonance experiments of CO_(2)huff and puff in shale samples are carried out to study the effects of gas injection pressure,soaking time and fractures on the oil production characteristics of shale pores from the micro scale.The recovery degrees of small pores(less than or equal to 50 nm)and large pores(greater than 50 nm)are quantitatively evaluated.The experimental results show that the recovery degree of crude oil in large pores increases rapidly with the increase of injection pressure under immiscible conditions,and the effect of injection pressure rise on recovery degree of large pores decreases under miscible conditions;whether miscible or not,the recovery degree of crude oil in small pores basically maintains a linear increase with the increase of injection pressure,and the lower size limit of pores in which oil can be recovered by CO_(2)decreases with the increase of gas injection pressure;with the increase of soaking time,the recovery degree of crude oil in large pores increases slowly gradually,while the recovery degree of crude oil in small pores increases faster and then decelerates,and the best soaking time in the experiments is about 10 h;the existence of fractures can enhance the recovery degrees of crude oil in small pores and large pores noticeably.展开更多
CO_(2)huff and puff experiments of different injection parameters,production parameters and soaking time were carried out on large-scale cubic and long columnar outcrop samples to analyze dynamic characteristics and i...CO_(2)huff and puff experiments of different injection parameters,production parameters and soaking time were carried out on large-scale cubic and long columnar outcrop samples to analyze dynamic characteristics and influencing factors of CO_(2)huff and puff and the contribution of sweeping mode to recovery.The experimental results show that the development process of CO_(2)huff and puff can be divided into four stages,namely,CO_(2)backflow,production of gas with some oil,high-speed oil production,and oil production rate decline stages.The production of gas with some oil stage is dominated by free gas displacement,and the high-speed oil production stage is dominated by dissolved gas displacement.CO_(2)injection volume and development speed are the major factors affecting the oil recovery.The larger the injected CO_(2)volume and the lower the development speed,the higher the oil recovery will be.The reasonable CO_(2)injection volume and development speed should be worked out according to oilfield demand and economic evaluation.There is a reasonable soaking time in CO_(2)huff and puff.Longer soaking time than the optimum time makes little contribution to oil recovery.In field applications,the stability of bottom hole pressure is important to judge whether the soaking time is sufficient during the huff period.The oil recovery of CO_(2)huff and puff mainly comes from the contribution of flow sweep and diffusion sweep,and diffusion sweep contributes more to the oil recovery when the soaking time is sufficient.展开更多
基金National Natural Science Foundation of China via grant number 52174035,52304048China Postdoctoral Science Foundation(2022M722637)Research and Innovation Fund for Graduate Students of Southwest Petroleum University(2022KYCX026).
文摘Recent studies have indicated that the injection of carbon dioxide(CO_(2))can lead to increased oil recovery in fractured shale reservoirs following natural depletion.Despite advancements in understanding mass exchange processes in subsurface formations,there remains a knowledge gap concerning the disparities in these processes between the matrix and fractures at the pore scale in formations with varying permeability.This study aims to experimentally investigate the CO_(2) diffusion behaviors and in situ oil recovery through a CO_(2) huff‘n’puff process in the Jimsar shale oil reservoir.To achieve this,we designed three matrix-fracture models with different permeabilities(0.074 mD,0.170 mD,and 0.466 mD)and experimented at 30 MPa and 91℃.The oil concentration in both the matrix and fracture was monitored using a low-field nuclear magnetic resonance(LF-NMR)technique to quantify in situ oil recovery and elucidate mass-exchange behaviors.The results showed that after three cycles of CO_(2) huff‘n’puff,the total recovery degree increased from 30.28%to 34.95%as the matrix permeability of the core samples increased from 0.074 to 0.466 mD,indicating a positive correlation between CO_(2) extraction efficiency and matrix permeability.Under similar fracture conditions,the increase in matrix permeability further promoted CO_(2) extraction efficiency during CO_(2) huff‘n’puff.Specifically,the increase in matrix permeability of the core had the greatest effect on the extraction of the first-cycle injection in large pores,which increased from 16.42%to 36.64%.The findings from our research provide valuable insights into the CO_(2) huff‘n’puff effects in different pore sizes following fracturing under varying permeability conditions,shedding light on the mechanisms of CO_(2)-enhanced oil recovery in fractured shale oil reservoirs.
基金Supported by the National Natural Science Foundation of China Youth Project(52004221)National Natural Science Foundation of China Project(5207042143)Shaanxi Provincial Department of Education Scientific Research Project(21JY034)。
文摘The parameters such as pore size distribution,specific surface area and pore volume of shale rock samples are analyzed by low-temperature nitrogen adsorption experiment,and then the conversion coefficient between relaxation time(T_(2))and pore size is calibrated.Nuclear magnetic resonance experiments of CO_(2)huff and puff in shale samples are carried out to study the effects of gas injection pressure,soaking time and fractures on the oil production characteristics of shale pores from the micro scale.The recovery degrees of small pores(less than or equal to 50 nm)and large pores(greater than 50 nm)are quantitatively evaluated.The experimental results show that the recovery degree of crude oil in large pores increases rapidly with the increase of injection pressure under immiscible conditions,and the effect of injection pressure rise on recovery degree of large pores decreases under miscible conditions;whether miscible or not,the recovery degree of crude oil in small pores basically maintains a linear increase with the increase of injection pressure,and the lower size limit of pores in which oil can be recovered by CO_(2)decreases with the increase of gas injection pressure;with the increase of soaking time,the recovery degree of crude oil in large pores increases slowly gradually,while the recovery degree of crude oil in small pores increases faster and then decelerates,and the best soaking time in the experiments is about 10 h;the existence of fractures can enhance the recovery degrees of crude oil in small pores and large pores noticeably.
文摘CO_(2)huff and puff experiments of different injection parameters,production parameters and soaking time were carried out on large-scale cubic and long columnar outcrop samples to analyze dynamic characteristics and influencing factors of CO_(2)huff and puff and the contribution of sweeping mode to recovery.The experimental results show that the development process of CO_(2)huff and puff can be divided into four stages,namely,CO_(2)backflow,production of gas with some oil,high-speed oil production,and oil production rate decline stages.The production of gas with some oil stage is dominated by free gas displacement,and the high-speed oil production stage is dominated by dissolved gas displacement.CO_(2)injection volume and development speed are the major factors affecting the oil recovery.The larger the injected CO_(2)volume and the lower the development speed,the higher the oil recovery will be.The reasonable CO_(2)injection volume and development speed should be worked out according to oilfield demand and economic evaluation.There is a reasonable soaking time in CO_(2)huff and puff.Longer soaking time than the optimum time makes little contribution to oil recovery.In field applications,the stability of bottom hole pressure is important to judge whether the soaking time is sufficient during the huff period.The oil recovery of CO_(2)huff and puff mainly comes from the contribution of flow sweep and diffusion sweep,and diffusion sweep contributes more to the oil recovery when the soaking time is sufficient.
