| As one of the most important natural gas producing areas,the Kuqa Depression of Tarim Basin in western China contributes a significant proportion of the resource in West-east natural gas transmission project.Keshen Structural Belts locates on the Kelasu Structure and has great exploration potential.Several big gas reservoirs whose reserves are on the order of hundred billion meters cubed have been discovered under the salt rock bed.Typical gas reservoirs characterized by faulted anticline trap in Keshen Structural Belts belong to deep-ultra deep buried,overpressure and fractured tight sand reservoir.In this paper,based on analysis of homogenization temperature of fluid inclusions,reconstruction of burial history and simulation of thermal history,the key gas accumulation is considered to have occurred 2Ma ago.According to physical simulation in rock sample,the gas saturation varies along with the changings of filling pressure.It is proved that filling pressure has important effect on gas accumulation.Based on physical experiment,excess pressure in source and reservoir has been simulated during gas accumulation in tight sand reservoir in Keshen Structural Belts,and parameter DCA has been defined to evaluate the contributions of filling pressure to gas accumulation.Quantify evaluation based on DCA indicates that accumulation dynamics in Keshen Structural Belts have greatest effect on Keshen 8 Reservoir and least effect on Keshen 2 Reservoir.Seismic interpretation illustrates that fault transportation system contains 7 main large-scale imbricate reverse thrust connecting to source rocks.Several fault parameters(fault displacement,width of fault zone,horizontal expansion distance of fault,vertical expansion distance of fault,fault dip)combined with gas flow viscosity and fault activing time are selected to build a formula to evaluate transpiration ability of gas source faults quantitatively.The quantitative evaluation indicates that transpiration ability of gas source faults is the greatest in the Kela 2 Trap,less in the Keshen 6 Trap and the least in the Keshen 12 Trap.Meanwhile,analysis of configurations between faults and caprocks indicates that fault belts have destructive effect on relatively thinner caprocks which results in gas dissipation in traps.The transportation system is an ensemble of sand and fracture in the reservoir of the research areas.Based on depositional model,well interpretation data,constrained by sand thickness distribution,fine sand transportation model is built by the method of multiple-point geostatistics.Subsequently,constrained by sand model,permeabilitymodel and gas saturation model are built.The research indicates that muddy intercalations has heterogeneous distribution.Take Keshen 9 Reservoir for example,as flow barriers,muddy intercalations obstruct gas migration which results in gas-water inversion.Physical simulation demonstrates positive correlation between matrix permeability and gas saturation when the filling dynamic exceeds 15 MPa.In actual geological situation,measurement of matrix permeability and gas saturation in thin section also obtains that positive correlation.We can conclude that high permeability sand can serve as dominant transporting layer.Fracture transportation system can be divided into extension section,transition section and compresso-shear section vertically.Analysis of fracture pattern and physical property of each section indicates that extension section can serve as dominant transporting layer.The scale of extension section varies at the different position of the structure.It becomes thinner from the peak to the west and east wings of the structure,it varies vaguely along the axis of the structure,it also becomes thinner where the structure gets lower. |
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