The Hydrocarbon Accumulation Study Of Volcanic Rock Gas Field In The Xujiaweizi Faulting Zone

Combining theoretical problems with regional geologic setting and structural evolution characteristics, this paper starts research on basic geologic conditions of hydrocarbon source rock in Shahezi Formation and volcanic rock in Yingcheng Formation and analyzes typical volcanic gas reservoirs to determine main controlling factors of gas accumulation, summarize distribution rules of volcanic gas reservoirs, classify 4 reservoir types controlled by several factors, and predict next-step exploration prospects of deep gas in Xujiaweizi Rift.Using structural form analysis method combining with regional geologic setting, several structural styles including extensional, compressive and strike-slip styles are identified. Through integrated analysis on stratigraphic extension in rifting period and development rules of Shahezi Formation, a structural framework of "two depression-one uplift-one slope" is proposed. It is further divided into Xuxi Sag, Zhaozhou Sag, Xuxi Faulted Zone, Anda Sag, Xudong Sag, Songzhan High, Shengping High, Fengle High and Wolitun Sag and Chaoyanggou Uplift, extending as " four highs and five sags " .Deep volcanic edifice in Xujiaweizi Rift has combined development area of 4 types of facies belt including volcanic cone, proximal, distal and volcanic sediments. Core, cuttings and microstructure observation combined with petrology, reservoir space features and development rules study shows 3 types of pore space in volcanic rock in Xujiaweizi Rift, including primary pores, secondary pores and fractures. Reservoir property is controlled by lithology and lithofacies. Volcanic cone facies belt combination is favorable area of volcanic reservoirs. Later structural movement(faults development area) has reformation impact on proximal facies belt combination and volcanic reservoir of proximal facies belt combination, being favorable reservoir development area.Analysis on typical volcanic reservoir shows that 4 types of typical gas reservoirs form by combined control of several factors, including high-porosity and high-permeability structural reservoir, medium-porosity and medium-permeability lithologic-structural reservoir, complex lithofacies structural-lithology reservoir and tight lithology reservoir. Generally, gas distribution appears vertically as crossing and overlapping, multi-layered development and multi-sets of gas-water relation, and areally as zoning in EW trend and multi-zoned division.Volcanic gas reservoir distribution in Xujiaweizi Rift is controlled by spatial matching relation between volcanic rock facies belt extension and Shahezi source rock development rules. Superimposition area of Shahezi Formation and volcanic rock controlled by uplift in large depression is main gas reservoir distribution area. Eastern Anda Rift, Xuxi Slope, Xudong Sag, Zhaozhou Sag and Chaoyanggou Uplift are next-step exploration prospects.