The Hydrocarbon Accumulation Of Shaximiao Formation Of Middle Jurassic Of Luodai Gas Field In Western Sichuan Basin

This paper investigates the Shaximiao Formation in Middle Jurassic system in Sichuan Basin,using theories as sedimengtology,petroleum geology,goephysics,et al.Based on abundant outcrop sections,well drilling and the manifold testing sample of drill core,this paper unites microcosmic and macroscopic instrument, systematicly analysises sedimentary facies, the distribution of formation water and the conditions of hydrocarbon accumulation of Shaximiao Formation of Middle Jurassic of Luodai Gas Field in Western Sichuan Basin.This paper in depth studys the formation mechanism of secondary gas field of Shaximiao Formation,and established the formation of gas filed mode,and generalized the accumulation regularity of hydrocarbon of Shaximiao Formation in Middle Jurassic system in Sichuan Basin.The sedimentary facies is fluvial and lacustrine facies of Shaximiao Formation of Middle Jurassic of Luodai Gas Field. The sedimentary facies from northeast to southwest is fluvial facies, delta facies, lacustrine facies.The sand body along NE-SW longitudinaly zonalities.The petrological classification of the reservoir of Shaximiao Formations are lithic arkose, arcose, arkose lithic and a little lithic quartz sandstone.The destructiveness diagenesis consists of compaction, cementation, metasomasis and the formation of authigenic mineral.The constructiveness diagenesis consists of the chlorite rim cementation and denudation. Based on the X ray Diffraction of clay mineral and the scanning electron microscopic,the diagenetic stages here are classified as Earlier Diagenetic A, Earlier Diagenetic B, Middle Diagenetic A and Middle Diagenetic B. The mechanism of induced porosity is the decarboxylation formation fluid from Triassic corrosing the dissoluble component.It is low-porosity and low permeable sublayer reservoir of Shaximiao formation. Some of the reservoir is ultra low porosity and permeable sublayer reservoir.It is pool of the correlation of porosity permeability.The aeolotropism of the reservoir is intense.Based on well logging, well logging, the chemical feature of formation water and the effective permeability,we analysed the origin of formation water,the microcosmic and macroscopic pattern of the formation water. The formation water of Shaximiao Formation resulted of the commixture of formation water from Triassic and aboriginally formation water of Shaximiao Formation.The style of the formation water of Shaximiao Formation is hloride calcium type.It is zonality of the distribution of the formation water of Shaximiao Formation.The hydrocarbon generative capacity simulation is superior of Shaximiao formation in Middle Jurassic system of Sichuan basin:first,the thick generating rock of Triassic offers substance base; second, the overriding sandbody buildups beneficial accumulate; third,the migration of the gas from gas source fault and network of fracture become easyer; quaternary,there are diversified traps; last, the capping formation is very thick.The fluid leaps over the stratas. The fluid from Upper Triassic improved the physical property of Shaximiao Formation in Middle Jurassic. The hydrocarbon accumulation of Shaximiao Formation presents chimney effect.The formation pressure of the palaeo-gas field is high pressure.The hydrocarbon Shaximiao Formation accumulated at early phase and formed late period. The hydrocarbon accumulated in the Triassic and formated primary gas pool at early phase.Under the high pressure background the hydrocarbon transits the fault and the network of fracture quickly and accumulats in the Shaximiao Formation.