CO_(2) huff-n-puff shows great potential to promote shale oil recovery after primary depletion.However,the extracting process of shale oil residing in different types of pores induced by the injected CO_(2) remains un...CO_(2) huff-n-puff shows great potential to promote shale oil recovery after primary depletion.However,the extracting process of shale oil residing in different types of pores induced by the injected CO_(2) remains unclear.Moreover,how to saturate shale core samples with oil is still an experimental challenge,and needs a recommended procedure.These issues significantly impede probing CO_(2) huff-n-puff in extracting shale oil as a means of enhanced oil recovery(EOR)processes.In this paper,the oil saturation process of shale core samples and their CO_(2) extraction response with respect to pore types were investigated using online T1-T2nuclear magnetic resonance(NMR)spectroscopy.The results indicated that the oil saturation of shale core samples rapidly increased in the first 16 days under the conditions of 60℃and 30 MPa and then tended to plateau.The maximum oil saturation could reach 46.2%after a vacuum and pressurization duration of 20 days.After saturation,three distinct regions were identified on the T1-T2NMR spectra of the shale core samples,corresponding to kerogen,organic pores(OPs),and inorganic pores(IPs),respectively.The oil trapped in IPs was the primary target for CO_(2) huff-n-puff in shale with a maximum cumulative oil recovery(COR)of 70%original oil in place(OOIP)after three cycles,while the oil trapped in OPs and kerogen presented challenges for extraction(COR<24.2%OOIP in OPs and almost none for kerogen).CO_(2) preferentially extracted the accessible oil trapped in large IPs,while due to the tiny pores and strong affinity of oil-wet walls,the oil saturated in OPs mainly existed in an adsorbed state,leading to an insignificant COR.Furthermore,COR demonstrated a linear increasing tendency with soaking pressure,even when the pressure noticeably exceeded the minimum miscible pressure,implying that the formation of a miscible phase between CO_(2) and oil was not the primary drive for CO_(2) huff-n-puff in shale.展开更多
The behavior of oil and water in tight rocks can change the distribution of oil or water in pores,which affects the production of crude oil.Nuclear Magnetic Resonance(NMR)method is an effective and nondestructive tool...The behavior of oil and water in tight rocks can change the distribution of oil or water in pores,which affects the production of crude oil.Nuclear Magnetic Resonance(NMR)method is an effective and nondestructive tool for evaluating rocks with comparison and analysis both quantitatively and qualitatively.In our study,20 MHz NMR Relaxometry is used as a key technique to study the changes of water and oil behaviors in Chinese lacustrine Qingshankou shales under different saturated states(imbibition and evaporation without pressure).The results show that variation in different proton populations(water,oil and organic)can be distinguished using 2D T_(1)-T_(2)maps.The comparison among T_(1)-T_(2)maps with different saturated states shows that different signal regions changed during oil and water migrations,which the 1D NMR Relaxometry may be not easy to approach.Combined with the pyrolysis analysis,T2 shift and differences of signal regions in T_(1)-T_(2)maps can reflect properties such as wettability and composition(organic matter,clay and magnetic minerals)to some extent.This study provides better insight into oil and water behaviors in lacustrine oil shales with further understanding of 20 MHz NMR 2D T_(1)-T_(2)maps both in qualitative and quantitative analysis.展开更多
基金the financial support of National Key Research and Development Program of China(2023YFE0120700)National Natural Science Foundation of China(52274041)Distinguished Young Sichuan Science Scholars(2023NSFSC1954)。
文摘CO_(2) huff-n-puff shows great potential to promote shale oil recovery after primary depletion.However,the extracting process of shale oil residing in different types of pores induced by the injected CO_(2) remains unclear.Moreover,how to saturate shale core samples with oil is still an experimental challenge,and needs a recommended procedure.These issues significantly impede probing CO_(2) huff-n-puff in extracting shale oil as a means of enhanced oil recovery(EOR)processes.In this paper,the oil saturation process of shale core samples and their CO_(2) extraction response with respect to pore types were investigated using online T1-T2nuclear magnetic resonance(NMR)spectroscopy.The results indicated that the oil saturation of shale core samples rapidly increased in the first 16 days under the conditions of 60℃and 30 MPa and then tended to plateau.The maximum oil saturation could reach 46.2%after a vacuum and pressurization duration of 20 days.After saturation,three distinct regions were identified on the T1-T2NMR spectra of the shale core samples,corresponding to kerogen,organic pores(OPs),and inorganic pores(IPs),respectively.The oil trapped in IPs was the primary target for CO_(2) huff-n-puff in shale with a maximum cumulative oil recovery(COR)of 70%original oil in place(OOIP)after three cycles,while the oil trapped in OPs and kerogen presented challenges for extraction(COR<24.2%OOIP in OPs and almost none for kerogen).CO_(2) preferentially extracted the accessible oil trapped in large IPs,while due to the tiny pores and strong affinity of oil-wet walls,the oil saturated in OPs mainly existed in an adsorbed state,leading to an insignificant COR.Furthermore,COR demonstrated a linear increasing tendency with soaking pressure,even when the pressure noticeably exceeded the minimum miscible pressure,implying that the formation of a miscible phase between CO_(2) and oil was not the primary drive for CO_(2) huff-n-puff in shale.
基金supported by the Opening Fund of Key Laboratory of Continental Shale Accumulation and Development(Northeast Petroleum University,China)the National Natural Science Foundation of China(Grant No.51605089,Grant No.41972156)
文摘The behavior of oil and water in tight rocks can change the distribution of oil or water in pores,which affects the production of crude oil.Nuclear Magnetic Resonance(NMR)method is an effective and nondestructive tool for evaluating rocks with comparison and analysis both quantitatively and qualitatively.In our study,20 MHz NMR Relaxometry is used as a key technique to study the changes of water and oil behaviors in Chinese lacustrine Qingshankou shales under different saturated states(imbibition and evaporation without pressure).The results show that variation in different proton populations(water,oil and organic)can be distinguished using 2D T_(1)-T_(2)maps.The comparison among T_(1)-T_(2)maps with different saturated states shows that different signal regions changed during oil and water migrations,which the 1D NMR Relaxometry may be not easy to approach.Combined with the pyrolysis analysis,T2 shift and differences of signal regions in T_(1)-T_(2)maps can reflect properties such as wettability and composition(organic matter,clay and magnetic minerals)to some extent.This study provides better insight into oil and water behaviors in lacustrine oil shales with further understanding of 20 MHz NMR 2D T_(1)-T_(2)maps both in qualitative and quantitative analysis.
