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Structural Characteristics, Formation Evolution And Its Relation With Hydrocarbon Accumulation In Jiangling Depression

Posted on:2006-05-15Degree:DoctorType:Dissertation
Country:ChinaCandidate:C Q YangFull Text:PDF
GTID:1100360155958554Subject:Paleontology and stratigraphy
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The sub-project of Relations between Structural Features, Evolution And Accumulation of Oil & Gas is carried out basing on project of Studies on Conditions for Oil & Gas Formation of Jiangling Depression And Its Exploration Direction (P01027) , which is an important scientific research project of SINOPEC.Under the guidance of method of Analysis on Basin Structure and theory of Petroleum System, the article synthesizes a number of practical data such as geological, geophysical and drilling data etc. and analyzes the relations between structural geometric features, kinematical features, dynamic features and accumulations of oil & gas and then perform synthetic studies on structure controlling petroleum and hydrocarbon-bearing system and then opens out the features of structures, its evolution and the functions to control petroleum and at the same time analyzes the favorable areas for oil & gas exploration in Jianghan basin.By using the method of structural geometry, structural kinematics as well as balance profile, the article considers that the original one of Jiangling Depression is an tensile faulted basin, which is controlled by Gongan-Songzi Fault and Yajiao-Xirigouzui Fault, developing three sub-structural units as Jiangkou Faulted Depression, Wancheng-Caixue Faulted Heave and Jiangling Faulted Depression and eleven forth level structural units.There develop four groups fault systems with three episodes: the first one is the time when K2y-Ex are formed, which is dominated by extension and the strike is dominated by NE or NEE, supplemented with nearly EW, controlling the structural framework of depression; the second one is the time when Ej-Ejh are formed. The whole is represented as tensile movement and the strike is dominated by NE on plane; the third one is the end of Ejh and the time when Ejh is formed. The whole is compression-shearing structure and some parts are early tensile reversed faults, the strike is dominated by nearly SN or NW on plane.There develop 106 traps in Jiangling Depression, which are controlled by faults. The main type of faults are compression anticline (including salt swell), faulted anticline, faulted nose, faulted block etc. and their formation are related with the differential upthrown and downthrown movement of faults, horizontal compression and salt swelling.According to the structural kinematics studies on Jiangling Depression, the article considers that the evolution of Jiangling Depression has undertaken the stage of formation of lateJurassic;-early Cretaceous basins, the first faulting-depressing stage of Xingouzui Formation of upper Cretaceous-Eocene, the second strong faulting-depressing stage of Jingsha Formation-Jinhezhen Formation and the uplifting-eroding stage at the end of early Palaeogene and late Neogence. The faulting-depressing events during late Cretaceous-early Palaeogene are characterized by multiple times and episodes.The formation of salt structures is characterized by serial structural events such as doming-extension of faulted depression-volcanism-thermal subsidence.Analytic Structure is used to analyze the structural formation of depression and its mechanism of controlling on petroleum. (1) According to analysis on deformational evolution of Jiangling Depression, the article considers Jiangling Depression has three main deformational stages: late Yanshanian Movement, early Himalayan Orogeny and mid-late Himalayan Orogeny, corresponding to three main unconformities. (2) According to the analyses on ingredients of volcanic rocks and times of volcanic activities, the development of volcanic rocks can be divided into four stages: stage to deposit Shashi Formation, Xingouzui Formation, Jingsha Formation and Qianjiang Formation. The lithology is dominated by basic basalts, which can be considered as the reservoirs of oil & gas. The traps formed synchronously, which are related with volcanic movement, becoming the favorable sites for oil & gas accumulation.(3) Salt structures in Jiangling Depression are formed during the course of Jingsha Formation-Jinghezhen Formation deposited and be finalized lastly at the end of age of Guanghuasi Formation. The salt structures mainly develop at the two sides of Jingzhou Anticline Belts and southern faulted depression, which are favorable for migration of oil & gas, controlling the accumulations of oil & gas of Jiangling Depression at the same time.The article studies conditions to form New-Generation-Old-Storage oil & gas accumulations and puts forward the pattern of formation of New-Generation-Old-Storage oil & gas accumulations as well as the exploration direction in the future. The author considers that activities of large deep faults (with large separation) make young hydrocarbon source rocks juxtapose with old reservoirs and form the space matches of source rocks and reservoirs of pattern of New-Generation-Old-Storage oil & gas accumulations, being the key factor for forming New-Generation-Old-Storage oil & gas accumulations. The article probes profoundly the conditions to form New-Generation-Old-Storage oil & gas accumulations of Cretaceous of Wancheng Faulted Convex Belt and point out that the intensive activities of Wancheng Fault happened during the term of deposition of Jingsha Formation-forth member of QianjiangFormation make fault separate more than one thousand meters, which makes hydrocarbon source strata of Es1*11"—Ex10*" of Meihui Sag of downthrown side juxtapose with reservoir of Cretaceous of upthrown side, thus fairly favorable space match of hydrocarbon source rocks and reservoirs come into being and communications between main hydrocarbon source area in Jiangling Depression and qualified developed reservoirs and developed area are realized and finally New-Generation-Old-Storage oil & gas accumulations come into being. Wancheng Faulted Convex Belt is an important area for exploring New-Generation-Old-Storage oil & gas accumulations and also one of the second large area collecting oil & gas. New-Generation-Old-Storage oil & gas accumulation is the important exploration field and direction for next exploration step in Jiangling Depression.The article summarizes main factors controlling reservoir formation in Jiangling Depression: 1) The distributions of effective hydrocarbon source rocks control the ranges of oil & gas accumulation. Such features that reservoirs are controlled strictly by hydrocarbon sources implies that Jiangling Depression has features of close hydrocarbon sources and short distance;(2)Early framework of basin controls the distributions of hydrocarbons and reservoirs. Jiangling Depression was a dish-like basin which was controlled by two faults in the south and north when Shashi Formation and Xingouzui Formation were deposited. It was affected by faults in NE direction (such as Wangcheng Fault, Huduhe Fault etc.) and dustpan-like faulted depressions were formed regionally, having the embryo of blocks divided in east-western direction. Subsiding center of the depression leaned to the south and further more it was affected by northern sedimentary system, thus the appearance of southern-source-northern-reservoirs came into being. Xingouzui Formation is the interval where the main hydrocarbon source rocks and reservoirs develop. Due to the influences by paleao-terrain(The north is high and south low), Mashan Sedimentary System and Hougang Sedimentary System advance from the north to the south and no materials sources develop in other directions, therefore structural features of strata that are dominated by sandy clastic sediments in the north part of Jiangling Depression and by muddy clastic sediments in the south part. Hydrocarbon source rocks develop mainly in southern sag belt and reservoirs in the gentle slope in the north. The distributions of hydrocarbon source rocks and reservoirs take the appearances of planar facies changes and the structural features of strata of interlays of source rocks and reservoirs are absent. Such kind of space matching feature of source rocks-reservoirs plays an important role in controlling the distribution of oil & gas. At the transition belt of hydrocarbon source rocks and reservoirs, there exits the phenomena of finger-like intersection of source-reservoirs in present Jingzhou Anticline Structural Belt, being the important areas forming oil & gas accumulation; (3) Mid-late structural framework of basin controls theenrichments of oil & gas. Wangcheng fault was active when Jingsha Formation—the forth member of Qiangjiang Formation deposited, leading to the formation of Wangcheng Faulted Uplift Belt in south-north direction, therefore it made the structural framework of blocks divided in east-west direction of Jiangling Basin come into being; When Jingsha Formation deposited, a series of salt structures came into being, leading to the embryo of Jingzhou Anticline Structural Belt, finally the structural framework of belt divided in south-north direction of Jiangling Depression was formed regionally and preliminarily. II episode of Himalaya Movement at the end of sedimentary term of Jinghezhen Formation deformed the strata of Jiangling Depression strongly, leading to the formation of present Jingzhou Anticline Structural Belt, Wangcheng-Caixue Faulted Uplifted Belt. The structural framework of Jingling Depression with the characteristics of blocks divided in east-west direction and belts in south-north direction was formed at the end of Jingsha Formation, which is earlier than the times of generation, migration, accumulation of oil & gas. Its shape was fixed at the end of the stage when Jinghezhen Formation deposited and the shape-fixed stage is at the same time when reservoirs were formed. Late structural framework controls the distribution of oil & gas;(4) Communication of faults play an important role in controlling the formation of oil & gas accumulation and it is the key factor for formation of New-Generation-Old-Storage Reservoirs. The faults in east-north direction control the areas where oil & gas accumulate, which play an important role in communication for formation of oil & gas accumulations. Late faults control the formation of secondary oil & gas accumulations directly; (5)Salt structures play important role in controlling the oil & gas accumulations, a. Salt structures develop mainly in the range of effective hydrocarbon source rocks, being the important sites for forming oil & gas accumulations, b. The stage when salt structures came into being is earlier than the stage when oil & gas were generated and migrated, being favorable traps for oil & gas accumulating, c. Oil & gas accumulation of Salt structure is an important kind of reservoirs in Jiangling Depression. Presently, among five oil fields founded three ones belong to salt structural reservoirs, they are Shashi Oil Field, Jingxi Oil Field, Huayuan Oil Field, additionally Nangang is also an important salt structure, d. Jingzhou Anticline Belt, which developed on the base of a series of salt structures, is the secondary most important areas for accumulating oil & gas. e. The formation of salt structures change the visage of structural traps in important reservoir-forming areas in Jiangling Depression and provide the sites for accumulating oil & gas; (6) The development of reservoirs is the key factor for formation of oil & gas accumulations. At the stage of deposition of the lower member of Xingouzui Formation, as the expansion of basin, Mashan Sedimentary System, Hougang Sedimentary System regressed gradually from the south to north and the location of reservoirs developed raised also graduallyfrom the south to north, taking shape the distributing features of main petroleum strata in Jiangling Depression. From north to south, the oil set distributes as following: oil sets I —>oil sets II —?oil sets m, that is the northern part is dominated by oil sets I, the central part by oil sets II and the southern part by oil sets HI. Division of reservoirs controls the division of strata accumulating oil & gas; (7) Match of stage of trap formation and the stage of oil & gas generation, migration and accumulation is also an important factor for formation of oil & gas accumulations.The article summarizes the rules of oil & gas enrichment in Jiangling Depression: ?The positive structural belt in main hydrocarbon source areas near southern sag belt and the central uplift of the depression are favorable belts for oil & gas enrichment. Jingzhou Anticline Belt not only has the ability of supporting hydrocarbons by itself but also has Meihuiqiao—Zifusi Sag Belt which is close to its southern part and develops hydrocarbon source rocks having strong ability to support hydrocarbons, being the main areas of hydrocarbon source rocks in Jingling Depression. Jingzhou Anticline Belt is the guiding areas to oil & gas migration and also a important belt enriching oil & gas in Jiangling Depresion; (D The two sides of fairly great faults with early growth times and multiple activities are the favorable sites to enrich oil & gas. Wangcheng fault controls the formation of Wangcheng Faulted Convex Belt. Wangcheng Fault is a great deep fault with early growth time, multiple activities, its eastern side is close to Meihuiqiao sag with hydrocarbon generation. Oil & gas migrated via Wangcheng Fault and entered into Cretaceous and accumulated, therefore it has fairly favorable conditions for forming oil & gas accumulation. Wangcheng—Caixue Faulted Convex Belt formed due to Wangcheng faulting activity is an important belt enriching oil & gas in Jingling Depression; ?Interweaved belt of hydrocarbon source rocks and reservoirs in the lower member of Xingouzui Formation is favorable for enrichment of oil & gas and the distribution of hydrocarbon source rocks and reservoirs in the lower member of Xingouzui Formation in Jiangling Depression has the relation of planar facies changes and vertical interlays of source rocks and reservoirs are absent, therefore the space matches of source rocks and reservoirs are not so good. Jingzhou Anticline Structural Belt is a interweaved belt of hydrocarbon source rocks and reservoirs, it not only has the planar finger-like interlays but spaciously has the interlay structure of source rocks and reservoirs, being the favorable belt to enrich oil & gas; ?Salt structures are favorable sites for forming oil & gas accumulations. The salt structures of Jiangling Depression are mainly located in the range of effective hydrocarbons source rocks. The stage at which the salt structures came into being is earlier than the stage when oil & gas were generated and migrated, being the favorable sites to form reservoirs as well as the sites to enrich oil & gas.Jiangling Depression has three petroleum systems, among which petroleum system...
Keywords/Search Tags:Jiangling Depression, Kinematics Features, Geometric Features, Structural Dynamics Features, Petroleum Controlled by Structures, Petroleum System
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