Analysis Of Factors For Accumulation And Enrichment Of Jurassic Coalbed Methane In Yuqia Coalfield Of The North Margin Of The Qaidam Basin

In order to explore the regularity of accumulation and enrichment of Jurassic Coalbed Methane Reservoirs in Yuqia coalfield of the North Margin of the Qaidam Basin,the paper researched from geological action and the Source-reservoir-cap respectively.In terms of geological action,the deposition controlling role of gas and tectonic controlling role of gas were discussed from sedimentation and tectonic respectively.In terms of sedimentary controlling gas,according to the research on the Yuqia Jurassic sedimentary system, sedimentary facies and sedimentary microfacies,this paper discussed the control of different sedimentary systems and sedimentary microfacies on coal roof and floor closure performance and the effects of different depositional systemthe on the spatial distribution of coal reservoirs.In terms of tectonic controlling gas,the influence on the enrichment and accumulation of CBM reservoir was analyzed from coal-bearing basin basement tectonic subsidence, tectonic activities in CBM reservoir accumulation period as well as adjustment and reform after the accumulation period.In terms of the Source-reservoir-cap,the paper evaluated the performance of hydrocarbon source rock, reservoir and capping layer in the studied area,and summarized its influence on enrichment and accumulation of CBM reservoir.Through the analysis of hydrocarbon generation type and maturity of coal petrography in the study area to evaluate coal petrography hydrocarbon generation ability;Through the analysis of coal reservoir porosity and permeability in the study area to evaluate reservoir storage capacity;Through the quantitative evaluation of the Cap Capability of coalbed methane reservoirs capping layer to analyze the influence on enrichment and accumulation of CBM reservoir.The results showed that:(1)Tectonic evolution controlled the enrichment,accumulation and distribution of CBM reservoir.(2)Sedimentation influenced the spatial distribution of the coal seam and the Cap Capability of the capping layer, thereby controlled the enrichment and accumulation of CBM reservoir.(3)The coal petrography had great hydrocarbon generation potentiality,but low maturity constrained CBM reservoir accumulation and high productivity.(4)Coal reservoir layer had good reservoir properties, which would help the accumulation and high productivity of CBM reservoir.(5)CBM reservoir capping layer capping performance impacted preservation and enrichment of coalbed methane reservoirs, the size of capping capacity of capping layer and the gas content was positively correlated.