Research On The Natural Gas Accumulation Mechanism Of Volcanic Rock In The Yingcheng Formation Of The Xujiaweizi Fault Depression, The North Songliao Basin

In this paper, using the geological, seismic, logging and testing data of Xujiaweizi faultdepression, combined with regional geological background, to systematic analysisaccumulation condition such as generation, storage, transportation and accumulation ofvolcanic rock natural gas reservoir in the Yingchang Formation of the Xujiaweizi faultdepression; for the first time using the full diameter volcanic core, combined with the actualcharacteristics of volcanic rock gas infill injection, carried out volcanic rock gas fillingmigration physical simulation; for the first time divided volcanic rock weathering crust in theYingcheng Formation of the Xujiaweizi fault depression into four types which combined withthe five-story structure of volcanic rock weathering crust, and discussed the control effect ofvolcanic rock weathering crust on reservoir physical property of volcanic rock, and “faultcrust” control accumulation theory and accumulation model of volcanic rock in the YingchengFormation of the Xujiaweizi fault depression is proposed.The result of gas infilling experiment of volcanic rock of Yingcheng Formation showthat, volcanic rock gas constant volume attenuation filling process can be divided into "initialstart-up",“continuous diversion",“episodic migration","high-speed attenuation episodicmigration" and "diffusion" five stages. Fractured volcanic rock medium mainly play amigration role in the process of natural gas accumulation; high pore type (corrosion and poredevelopment type) volcanic rock medium has the good channel capacity and natural gasreservoir performance is obviously controlled by cap rock and tectonic conditions; mediumporosity and medium permeability type volcanic rock at higher pressures can’t be to cover gascounseling, can be used as gas reservoir.Based on the lithology, core, physical properties and testing data statistical analysisshows that the lithology is not the main factors to control volcanic reservoir properties, themain factors is weathering dissolution which produces secondary porosity. By statisticanalyzing the FIR interpretation data found that74.6%of secondary porosity belongs to thecomplex of fracture and solution pores,89.9%of the cracks belongs to the type abovemedium-high type, this shows that cracks has strong control function in the formation ofsecondary porosity, and the control function mainly reflects in longitudinal range. Volcanicrock weathering crust type can be divided into "complete","lack of clay layer","Hydrolysiszone missing" and "Hydrolysis zone above missing" four types in the Yingcheng Formation ofthe fault depression. The effective reservoir thickness and spatial distribution of volcanic rockis controlled by volcanic rock weathering dissolution extent, volcanic rock weathering crustprediction results shows that volcanic rock weathering crust in the Yingcheng Formation ofthe fault depression has widely development area, the development degree is controlled by thepaleo tectonic and fracture. In weathering crust structure the clay layer and hydrolysis zone (dense volcanic rock) complementary superimposed on the space play the effective cap rockSealing role in volcanic gas in the Yingcheng Formation. High-yield range of volcanic rocknatural gas reserves is mainly controlled by gas source faults configuration ofmicro-amplitude structure high positions of volcanic rock weathering crust. Comprehensiveanalysis shows that the gas source faults, volcanic rock weathering crust and nowadays microstructure is the main control factors of natural gas control reservoir of volcanic rock in theYingcheng Formation of the Xujiaweizi fault depression, and weathering degree of volcanicweathering crust covers and reflects the comprehensive factors such as migration of volcanicgas reservoir conditions, cap rock conditions, reservoir conditions and nowadays microstructure, so the "fault crust" is the main factors to control the gas accumulation of volcanicrock in the Yingcheng Formation of the Xujiaweizi fault depression, and the natural gasaccumulation model in the study area is divided into five types in view of the above.