Subsidence And Uplift Characteristics And Their Relationship With Faults And Fractures And Petroleum Reservoiring Characteristics,in Tertiary Western Of Qaidam Basin

Through the analysis of deposition and subsidence features in the Tertiary western Qaidam, E1+2, E31, E32, N1, N21, N22and map compilation, erosion thickness restoration of N23,the difference of deposition and subsidence features of major hydrocarbon source rocks, such as E31, subside and uplift in E32, N1, N21, N22sedimentary period and map compilation, erosion thickness restoration of N23and the Quaternary. Through the analysis of seismic reflector in Tertiary, core and slice observation of fracture, the experiments of rock mechanics, and porosity and permeability of rock, the relationship between the major hydrocarbon source rocks and the faults&cracks, Based on the above research, the characteristics of reservoir forming in the Tertiary western Qaidam is discussed. The main conclusion as follows:(1)The deposition,subsidence and erosion in Tertiary western Qaidam and the difference of deposition and subsidence features of major hydrocarbon source rocks①At western of Qaidam Basin, the subsidence and uplift of Tertiary, in E31, E32, N1, N21, N22sedimentary period are unbalanced. In N23and the Quaternary, sedimentary period occur unbalanced subsidence,uplift and erosion.From E1+2to N22sedimentary period the depocenter is different but subsidence center is steady. The depocenter of E1+2sedimentary period is near Shizigou. The depocenter of E31sedimentary period is near Huatugou and Mangya. The depocenter of E32sedimentary period is near Huatugou-Nanyishan-Mangya. The depocenter of N1sedimentary period is near Huatugou-Jiandingshan-Mangya. The depocenter of N21sedimentary period is near Nanyishan-Eboshan. The depocenter of N22sedimentary period is near Nanyishan-Mangya-Yiliping. The subsidence center of Tertiary western Qaidam is steadily located near Yilipng area.N23and the Quaternary. sedimentary period is the main erosion period. The consuming eroded area(erosion thickness more than500m) is Gansen, Mangya, Yingxiongling-Ganchaigou, Dongchaishan, Nanyishan, Jiandingshan, Heiweiliang, Honggouzi. The medium eroded area (erosion thickness between200m and500m) is Luoyanshan, Dafengshan, Nanyishan and northwest of Qigequan area. The other area is subsidence area(erosion thickness less than200m).②In Tertiary western Qaidam,the largest degree of subsidence of the major hydrocarbon source rocks, the depocenter of E31, in E32, N1, N21, N22, N23and the Quaternary sedimentary period is near Manya-Yiliping area. In E32sedimentary period the thickness of stratum is more than2000m, in N22sedimentary period the thickness of stratum is more than10000m, in Quaternary sedimentary period the thickness of stratum is more than12000m. The thickness decreases from Yiligou and Yiliping to Qigequan-Huatugou area, with thickness of2000m.(2)The differences of subsidence, uplift and the relationship with faults and cracks in Tertiary western Qaidam.①Differences of subsidence and uplift is closely related to tectonic framework and faults in Tertiary western Qaidam. At western of Qaidam Basin, the deepest area of regional structure is Yiligou-Yiliping.This formation is formed since E1+2sedimentary period and developed in Tertiary. Based on the relationship between the regional structure and faults, Study area is divided into two areas. One area is at nose construction in the northeast, with faults spreading in northwest, pointing the maximum thickness area of overlying strata. The other area is at southwest slope area, with network faults.②Differences of subsidence and uplift have a major impact on formation and evolution of cracks in Tertiary western Qaidam.The burial process of stratum could divided into three phase:compaction phase, elastic-plastic compression phase, fracturing phase. At western of Qaidam Basin, there is parallel crack, vertical crack and oblique crack in rocks, there are slip plane in the parallel crack. Parallel crack usually develop along level and lithology boundaries. Vertical crack usually develop in homogeneous rock. Vertical crack don’t cross the parallel crack. The main kind of fracture is "gong" assemblage type. When the strata is horizontal, the boundary of a large number of development of cracks is2000m. When there is transverse shrinkage in the strata, the boundary is less than2000m. Denudation could also lead the same result.(3)Differences of subsidence,uplift and the combination of faults and cracks have a major impact on coupling relationship of driving force and passage system, and the formation and distribution of oil and gas reservoirs, in Tertiary western Qaidam.①The greatest source region of Tertiary at western Qaidam is areas of deepest burial. The area is near Yiligou-Yiliping since E32sedimentary period.. The greatest driving force distribute in down-dip direction of the monoclinic structure and flank of anticline structures.②Pores of the sandstone and mudstone, cracks and faults have different properties of transporting When there is no fracture, parallel permeability is greater than the vertical (Parallel permeability is1.18-60.3times of vertical permeability in mudstone, parallel permeability of sandstone is1.81-11.01times of vertical permeability). When there is fracture, Fractured permeability is greater than the others(Fractured mudstone permeability is393942times of no crack mudstone. Fractured sandstone permeability is4.15times of no crack sandstone.).③Pores of the sandstone and mudstone, cracks are main transporting medium in the monoclinic structure. The main transporting direction of monoclinic structure along the direction of bedding plane to up dip direction. The main transporting direction of anticline along the direction of bedding plane in the anticline wing and along the crack to the shallow formation in the axes. Faults formed by the cracks, the transporting properties depends on the development and stability of cracks. In elastic-plastic compression phase and fracturing phase, cracks formed by fault movement is not easy to close. The transporting properties depends on the cracks of the sandstone and mudstone, in the compaction phase, cracks formed by fault movement is easy to close. The transporting properties depends on the pores of the sandstone and mudstone. In the strata on both sides of fault, the main transporting properties depends on the pores of the sandstone and mudstone.④In different structural belt,different coupling relationship of driving force and passage system, related to the different formation and distribution of oil and gas reservoirs. In the monoclinic structure, the hydrocarbon mainly move along the parallel direction to the traps and accumulated after filled the pores and cracking of source rock. In the anticline structure, the hydrocarbon mainly move along the parallel direction in the wing and the crack in the axes. Hydrocarbon first filled the deep strata, then the shallow formation in the axes. In fault structure, the buoyancy-driven hydrocarbon easily float up to the top of the fault, and move along the top of the fault, gathered in the adjacent traps and reservoir.⑤In the exploration in the western Qaidam, attention should be paid to the top of the high parts of the fault traps. The sand body and lithologic traps in updip direction of monoclinal structure should be exploration at first, then the downdip direction. In the anticline, oil and gas exploration should start from the main source rocks for the bottom line, from deep to shallow. Boundary of sandstone and mudstone, boundary of argillaceous rock,marl, carbonate rock is unconventional reservoir, which beneficial to oil and gas accumulation.