Mississippi Valley-type(MVT) Zn-Pb deposits predominantly form within both orogenic forelands and fold-andthrust belts, yet the mineralization process within the latter tectonic setting remains inadequately understood...Mississippi Valley-type(MVT) Zn-Pb deposits predominantly form within both orogenic forelands and fold-andthrust belts, yet the mineralization process within the latter tectonic setting remains inadequately understood. This study, through a comprehensive review of MVT deposits across global fold-and-thrust belts, introduces a novel model elucidating the mineralization process in the context of tectonic belt evolution. It is demonstrated that during the stage Ⅰ, regional compression is introduced by early stages of plate convergence, causing the folding and thrusting and creating structural or lithological traps such as evaporite diapirs and unconformity-related carbonate dissolution-collapse structures. Thereafter, in stage Ⅱ, hydrocarbons begin to migrate and accumulate within these traps, where reduced sulfur is generated through thermochemical or bacterial sulfate reduction concurrent with or preceding Zn-Pb mineralization. In the subsequent stage Ⅲ, as plate convergence persists, the regional stress transitions from compression to transpression or extension. Under these conditions, steeply-dipping extensional faults are generated, facilitating the ascent of metalliferous brines into early-formed structural or lithological traps. Precipitation of Zn and Pb sulfides occurs through the mixing of Zn-Pb-transporting fluids with pre-existing reduced sulfur or by interaction with hydrocarbons.展开更多
Deep basin gas (DBG) reservoirs, in view of the characteristics of their main parts containing gas, are a type of subtle stratigraphic lithologic traps. But they have different reservoir-forming principles, especially...Deep basin gas (DBG) reservoirs, in view of the characteristics of their main parts containing gas, are a type of subtle stratigraphic lithologic traps. But they have different reservoir-forming principles, especially in the distribution of oil, gas and water. DBG is characterized by gas-water invertion, namely the water located above the gas; however, normal non-anticline subtle reservoirs have normal distribution of gas and water, namely the water located under the gas. The theory of DBG broke the conventional exploration idea that gas is usually found in the high part of reservoir and water is under the gas. So, it provided a wide field and a new idea for the exploration of natural gas. Recently Ben E. Law (2002), in his article entitled "Basin-centered Gas Systems", discussed global DBG systemically. He listed 72 basins or areas containing known or suspected DBG, covering North America, South America, Europe, Asia-Pacific, South Asia, Middle East and Africa. Ordos basin, the Sichuan basin and the Jungar basin in China are presented and assumed to be of very high possibility. In China more attention has been paid to the research and exploration of DBG in the past years. The symposiums on DBG were held twice, in Guangzhou in 1998 and in Xi'an in 2000 respectively. In 2002 in particular, the publication of the book named Deep Basin Gas in China by Professor Wangtao indicated that China has entered a new stage in the research on DBG Meanwhile, it is more cheering that the exploration of DBG in the Ordos Basin has achieved remarkable success. Therefore, analyzing the exploration experiences and problems regarding the Ordos basin will promote the exploration and research of DBG in China.展开更多
Based on the seismic, logging, drilling and other data, the distribution, structural types and mound-shoal hydrocarbon accumulation characteristics of platform margins of the Sinian Dengying Formation in the Deyang-An...Based on the seismic, logging, drilling and other data, the distribution, structural types and mound-shoal hydrocarbon accumulation characteristics of platform margins of the Sinian Dengying Formation in the Deyang-Anyue Rift and its periphery were analyzed. Four types of platform margins are developed in the Dengying Formation, i.e., single-stage fault-controlled platform margin, multi-stage fault-controlled platform margin, gentle slope platform margin, and overlapping platform margin. In the Gaoshiti West-Weiyuan East area, single-stage fault controlled platform margins are developed in the Deng 2 Member, which trend in nearly NEE direction and are shielded by faults and mudstones, forming fault-controlled–lithologic traps. In the Lezhi-Penglai area, independent and multi-stage fault controlled platform margins are developed in the Deng 2 Member, which trend in NE direction and are controlled by synsedimentary faults;the mound-shoal complexes are aggraded and built on the hanging walls of the faults, and they are shielded by tight intertidal belts and the Lower Cambrian source rocks in multiple directions, forming fault-controlled–lithologic and other composite traps. In the Weiyuan-Ziyang area, gentle slope platform margins are developed in the Deng 2 Member, which trend in NW direction;the mound-shoal complexes are mostly thin interbeds as continuous bands and shielded by tight intertidal belts in the updip direction, forming lithologic traps. In the Gaoshiti-Moxi-Yanting area, overlapping platform margins are developed in the Deng 2 and Deng 4 members;the mound-shoal complexes are aggraded and overlaid to create platform margin buildup with a huge thickness and sealed by tight intertidal belts and the Lower Cambrian mudstones in the updip direction, forming large-scale lithologic traps on the north slope of the Central Sichuan Paleouplift. To summarize, the mound-shoal complexes on the platform margins in the Dengying Formation in the Penglai-Zhongjiang area, Moxi North-Yanting area and Weiyuan-Ziyang area are large in scale, with estimated resources of 1.58×1012 m3, and they will be the key targets for the future exploration of the Dengying Formation in the Sichuan Basin.展开更多
There developed thick gypsum-salt strata in the Lower Paleozoic Ordovician in the Ordos Basin,particularly gypsum-salt in the 6th segment of the 5th member of Majiagou Fm(O_(1)m_(5)^(6))in a wide distribution,serving ...There developed thick gypsum-salt strata in the Lower Paleozoic Ordovician in the Ordos Basin,particularly gypsum-salt in the 6th segment of the 5th member of Majiagou Fm(O_(1)m_(5)^(6))in a wide distribution,serving as a good regional cap.Recent drilling and relevant studies have proven that the hydrocarbon-generating capacity of the marine-facies hydrocarbon source rocks under the Ordovician salt layers in the eastern Basin is poor on the whole,making it difficult to form“self-generating and self-preserving type”commercial gas reservoirs under the salt layer in Mizhi salt subsag.However,further research on reservoir-forming conditions under the gypsolyte on the west side of the salt subsag indicates that the O_(1)m_(5)^(7)-O_(1)m_(5)^(10)strata near the east side of the palaeo-uplift contact directly with the Upper Paleozoic coal measure source rocks,forming a“hydrocarbon supply window”;the Yanshan Movement caused the tectonic inversion of the basin main body,resulting in the tectonic framework“high in the east and low in the west”,which is conductive to the further migration of natural gas generated by the Upper Paleozoic coal measures to the updip high position of the east side along the O_(1)m_(5)^(7)-O_(1)m_(5)^(10)carrier beds after entering the dolomite reservoir under the gypsolyte through the“hydrocarbon-supply window”.In addition,the facies changes in the dolomite rocks under the gypsum-salt provide favorable barrier condition for the regional gathering of natural gas.Therefore,it is concluded through comprehensive analysis that reservoirs may form beneath the Ordovician gypsolith in the central region of the basin on the west side of the salt subsag with hydrocarbon supplied from the Upper Paleozoic source rocks of coal measures,which is expected to open up a new situation of natural gas exploration under the Ordovician gypsum-salt layer in the Ordos Basin.展开更多
At the initial stage of subtle reservoir exploration in the shallow to medium formations of the Taibei Sag, Tuha Basin, so far, three kinds of subtle reservoirs (stratigraphic, lithologic and structural-lithologic res...At the initial stage of subtle reservoir exploration in the shallow to medium formations of the Taibei Sag, Tuha Basin, so far, three kinds of subtle reservoirs (stratigraphic, lithologic and structural-lithologic reservoirs) have been found. Since both the amount and reserve of the discovered subtle reservoirs are small, a great exploration potential remains in the Taibei Sag. The shallow to medium formations in the west of the Taibei Sag were divided into three second-order sequences and ten third-order sequences, of which the rising cyclothems of SQ(J2q) and SQ8 (J2s2) datum level are major exploration targets for the subtle reservoirs (lithologic). The depositional systems of Qiquanhu and Subashi braided river delta were developed there, where the sedimentary sand body is dominated by the regional slopes and slope break belts. There are four main modes the formation of lithologic traps: deltaic front onlap on the slope belt, deltaic front toplap on the slope break belt, lately tilted frontal sand body and sublacustrine fan—slope fan on the slope break belt, of which the first three modes are the major styles of the formation of subtle reservoirs. Major targets for subtle reservoir exploration in the near future include Putaogou Member on the north slope of Huoyanshan, the east slope of Pubei, the nose-like palaeohigh regions of Huobei, Subashi and Lianmuqin, around the Shengbei secondary sag.展开更多
A high-yield gasflow is produced from the dolomite reservoirs of the Ordovician Penglaiba Fm in Well Luosi 2 in the Southwest Depression of the Tarim Basin,recording as the most important major oil and gas discovery i...A high-yield gasflow is produced from the dolomite reservoirs of the Ordovician Penglaiba Fm in Well Luosi 2 in the Southwest Depression of the Tarim Basin,recording as the most important major oil and gas discovery in the Maigaiti slope in recent 20 years.In this paper,the success and failure of wells drilled into the Ordovician during the exploration in the Maigaiti slope and its periphery were analyzed to clarify the future exploration targets in this area.Then,the distribution characteristics of Ordovician limestone weathered crust and internal dolomite reservoirs were investigated,the relationship between structural traps(e.g.formation and evolution)and hydrocarbon accumulation was analyzed,and the main factors controlling the Ordovician hydrocarbon accumulation in this area were defined.Finally,the relationship between hydrocarbon distribution and Neoproterozoic rift system was discussed.Accordingly,somefindings were obtained.First,the Ordovician dolomite reservoirs are more developed than limestone reservoirs.Limestone weathered crust reservoirs of Middle Ordovician Yingshan Fm(upper member)are mainly distributed in fault zones,and their reservoir space is mainly composed of high-angle unfilled fractures.Internal dolomite reservoirs of Lower Ordovician Yingshan Fm(lower member)and Penglaiba Fm are laterally and stably distributed and their reservoir space is mainly composed of small dissolved pores which present“strings of beads”reflection characteristics on seismic profiles.Second,the Ordovician hydrocarbon is mainly discovered in the fault zones and the lithologic traps consisting of Ordovician karst dolomite reservoirs at periclines are the main exploration targets in subsequent operations.Third,the distribution of Cambrian source rocks is the key factor restricting the success rate of Ordovician oil and gas exploration.Under the control of Neoproterozoic rift system in the SW Tarim depression,the middle section of this depression is favorable for oil and gas exploration,and it includes multiple hydrocarbon source-reservoir-caprock assemblages,such as Ordovician-Upper Cambrian dolomites and Carboniferous mudstones,and Lower Cambrian dolomite and Middle Cambrian gypsum salt rocks.展开更多
基金funded by National Natural Science Foundation of China (Grant Nos. 42125204, 92155305, 42103068, 42372114, 42372115)。
文摘Mississippi Valley-type(MVT) Zn-Pb deposits predominantly form within both orogenic forelands and fold-andthrust belts, yet the mineralization process within the latter tectonic setting remains inadequately understood. This study, through a comprehensive review of MVT deposits across global fold-and-thrust belts, introduces a novel model elucidating the mineralization process in the context of tectonic belt evolution. It is demonstrated that during the stage Ⅰ, regional compression is introduced by early stages of plate convergence, causing the folding and thrusting and creating structural or lithological traps such as evaporite diapirs and unconformity-related carbonate dissolution-collapse structures. Thereafter, in stage Ⅱ, hydrocarbons begin to migrate and accumulate within these traps, where reduced sulfur is generated through thermochemical or bacterial sulfate reduction concurrent with or preceding Zn-Pb mineralization. In the subsequent stage Ⅲ, as plate convergence persists, the regional stress transitions from compression to transpression or extension. Under these conditions, steeply-dipping extensional faults are generated, facilitating the ascent of metalliferous brines into early-formed structural or lithological traps. Precipitation of Zn and Pb sulfides occurs through the mixing of Zn-Pb-transporting fluids with pre-existing reduced sulfur or by interaction with hydrocarbons.
文摘Deep basin gas (DBG) reservoirs, in view of the characteristics of their main parts containing gas, are a type of subtle stratigraphic lithologic traps. But they have different reservoir-forming principles, especially in the distribution of oil, gas and water. DBG is characterized by gas-water invertion, namely the water located above the gas; however, normal non-anticline subtle reservoirs have normal distribution of gas and water, namely the water located under the gas. The theory of DBG broke the conventional exploration idea that gas is usually found in the high part of reservoir and water is under the gas. So, it provided a wide field and a new idea for the exploration of natural gas. Recently Ben E. Law (2002), in his article entitled "Basin-centered Gas Systems", discussed global DBG systemically. He listed 72 basins or areas containing known or suspected DBG, covering North America, South America, Europe, Asia-Pacific, South Asia, Middle East and Africa. Ordos basin, the Sichuan basin and the Jungar basin in China are presented and assumed to be of very high possibility. In China more attention has been paid to the research and exploration of DBG in the past years. The symposiums on DBG were held twice, in Guangzhou in 1998 and in Xi'an in 2000 respectively. In 2002 in particular, the publication of the book named Deep Basin Gas in China by Professor Wangtao indicated that China has entered a new stage in the research on DBG Meanwhile, it is more cheering that the exploration of DBG in the Ordos Basin has achieved remarkable success. Therefore, analyzing the exploration experiences and problems regarding the Ordos basin will promote the exploration and research of DBG in China.
基金Supported by the Science and Technology Project of PetroChina (2021DJ0605)。
文摘Based on the seismic, logging, drilling and other data, the distribution, structural types and mound-shoal hydrocarbon accumulation characteristics of platform margins of the Sinian Dengying Formation in the Deyang-Anyue Rift and its periphery were analyzed. Four types of platform margins are developed in the Dengying Formation, i.e., single-stage fault-controlled platform margin, multi-stage fault-controlled platform margin, gentle slope platform margin, and overlapping platform margin. In the Gaoshiti West-Weiyuan East area, single-stage fault controlled platform margins are developed in the Deng 2 Member, which trend in nearly NEE direction and are shielded by faults and mudstones, forming fault-controlled–lithologic traps. In the Lezhi-Penglai area, independent and multi-stage fault controlled platform margins are developed in the Deng 2 Member, which trend in NE direction and are controlled by synsedimentary faults;the mound-shoal complexes are aggraded and built on the hanging walls of the faults, and they are shielded by tight intertidal belts and the Lower Cambrian source rocks in multiple directions, forming fault-controlled–lithologic and other composite traps. In the Weiyuan-Ziyang area, gentle slope platform margins are developed in the Deng 2 Member, which trend in NW direction;the mound-shoal complexes are mostly thin interbeds as continuous bands and shielded by tight intertidal belts in the updip direction, forming lithologic traps. In the Gaoshiti-Moxi-Yanting area, overlapping platform margins are developed in the Deng 2 and Deng 4 members;the mound-shoal complexes are aggraded and overlaid to create platform margin buildup with a huge thickness and sealed by tight intertidal belts and the Lower Cambrian mudstones in the updip direction, forming large-scale lithologic traps on the north slope of the Central Sichuan Paleouplift. To summarize, the mound-shoal complexes on the platform margins in the Dengying Formation in the Penglai-Zhongjiang area, Moxi North-Yanting area and Weiyuan-Ziyang area are large in scale, with estimated resources of 1.58×1012 m3, and they will be the key targets for the future exploration of the Dengying Formation in the Sichuan Basin.
基金Special and Significant Project of National Science and Technology of the“12th Five-Year-Plan”:“Development of Large Oil/gas Fields and Coalbed Methane”(No.2011ZX05004-006).
文摘There developed thick gypsum-salt strata in the Lower Paleozoic Ordovician in the Ordos Basin,particularly gypsum-salt in the 6th segment of the 5th member of Majiagou Fm(O_(1)m_(5)^(6))in a wide distribution,serving as a good regional cap.Recent drilling and relevant studies have proven that the hydrocarbon-generating capacity of the marine-facies hydrocarbon source rocks under the Ordovician salt layers in the eastern Basin is poor on the whole,making it difficult to form“self-generating and self-preserving type”commercial gas reservoirs under the salt layer in Mizhi salt subsag.However,further research on reservoir-forming conditions under the gypsolyte on the west side of the salt subsag indicates that the O_(1)m_(5)^(7)-O_(1)m_(5)^(10)strata near the east side of the palaeo-uplift contact directly with the Upper Paleozoic coal measure source rocks,forming a“hydrocarbon supply window”;the Yanshan Movement caused the tectonic inversion of the basin main body,resulting in the tectonic framework“high in the east and low in the west”,which is conductive to the further migration of natural gas generated by the Upper Paleozoic coal measures to the updip high position of the east side along the O_(1)m_(5)^(7)-O_(1)m_(5)^(10)carrier beds after entering the dolomite reservoir under the gypsolyte through the“hydrocarbon-supply window”.In addition,the facies changes in the dolomite rocks under the gypsum-salt provide favorable barrier condition for the regional gathering of natural gas.Therefore,it is concluded through comprehensive analysis that reservoirs may form beneath the Ordovician gypsolith in the central region of the basin on the west side of the salt subsag with hydrocarbon supplied from the Upper Paleozoic source rocks of coal measures,which is expected to open up a new situation of natural gas exploration under the Ordovician gypsum-salt layer in the Ordos Basin.
文摘At the initial stage of subtle reservoir exploration in the shallow to medium formations of the Taibei Sag, Tuha Basin, so far, three kinds of subtle reservoirs (stratigraphic, lithologic and structural-lithologic reservoirs) have been found. Since both the amount and reserve of the discovered subtle reservoirs are small, a great exploration potential remains in the Taibei Sag. The shallow to medium formations in the west of the Taibei Sag were divided into three second-order sequences and ten third-order sequences, of which the rising cyclothems of SQ(J2q) and SQ8 (J2s2) datum level are major exploration targets for the subtle reservoirs (lithologic). The depositional systems of Qiquanhu and Subashi braided river delta were developed there, where the sedimentary sand body is dominated by the regional slopes and slope break belts. There are four main modes the formation of lithologic traps: deltaic front onlap on the slope belt, deltaic front toplap on the slope break belt, lately tilted frontal sand body and sublacustrine fan—slope fan on the slope break belt, of which the first three modes are the major styles of the formation of subtle reservoirs. Major targets for subtle reservoir exploration in the near future include Putaogou Member on the north slope of Huoyanshan, the east slope of Pubei, the nose-like palaeohigh regions of Huobei, Subashi and Lianmuqin, around the Shengbei secondary sag.
文摘A high-yield gasflow is produced from the dolomite reservoirs of the Ordovician Penglaiba Fm in Well Luosi 2 in the Southwest Depression of the Tarim Basin,recording as the most important major oil and gas discovery in the Maigaiti slope in recent 20 years.In this paper,the success and failure of wells drilled into the Ordovician during the exploration in the Maigaiti slope and its periphery were analyzed to clarify the future exploration targets in this area.Then,the distribution characteristics of Ordovician limestone weathered crust and internal dolomite reservoirs were investigated,the relationship between structural traps(e.g.formation and evolution)and hydrocarbon accumulation was analyzed,and the main factors controlling the Ordovician hydrocarbon accumulation in this area were defined.Finally,the relationship between hydrocarbon distribution and Neoproterozoic rift system was discussed.Accordingly,somefindings were obtained.First,the Ordovician dolomite reservoirs are more developed than limestone reservoirs.Limestone weathered crust reservoirs of Middle Ordovician Yingshan Fm(upper member)are mainly distributed in fault zones,and their reservoir space is mainly composed of high-angle unfilled fractures.Internal dolomite reservoirs of Lower Ordovician Yingshan Fm(lower member)and Penglaiba Fm are laterally and stably distributed and their reservoir space is mainly composed of small dissolved pores which present“strings of beads”reflection characteristics on seismic profiles.Second,the Ordovician hydrocarbon is mainly discovered in the fault zones and the lithologic traps consisting of Ordovician karst dolomite reservoirs at periclines are the main exploration targets in subsequent operations.Third,the distribution of Cambrian source rocks is the key factor restricting the success rate of Ordovician oil and gas exploration.Under the control of Neoproterozoic rift system in the SW Tarim depression,the middle section of this depression is favorable for oil and gas exploration,and it includes multiple hydrocarbon source-reservoir-caprock assemblages,such as Ordovician-Upper Cambrian dolomites and Carboniferous mudstones,and Lower Cambrian dolomite and Middle Cambrian gypsum salt rocks.
