松辽盆地徐家围子断陷火山岩天然气成藏主控因素及模式

徐家围子断陷火山岩天然气藏分布具有4个特征：纵向分布层位多，深度范围大；平面上分布在生气凹陷内或附近，且沿断裂带分布；自储自盖；气-水关系复杂.其成藏与分布主要受3个因素控制，即：源岩区控制着火山岩天然气藏的分布区域，断裂带和古隆起控制着火山岩天然气藏分布的具体部位，火山岩相控制着天然气的储集.源岩排气史、断裂活动史、火山岩罔闭形成史和天然气运聚史的综合研究认为：火山岩气藏形成的主要时期为泉头组沉积晚期-青山口组沉积时期、嫩汀组沉积末期和明水组沉积时期.成藏模式为断陷深部沙河子组源岩生成的天然气在主成藏期沿断裂向上运移至断裂带处的火山岩圈闭中或古隆起上的火山岩圈闭中聚集成火山岩气藏.

Main controlling factors and accumulation model for volcanic gas reservoirs in the Xujiaweizi Fault-Depression, Songliao Basin

By the study of space distribution characteristics of gas in volcanic rocks of the Xujiaweizi Fault-Depression,four laws could be concluded, namely, 1)they being muptiple horzions for gas reservoir vertically,2)distribution of gas reservoirs being coutrolled by the gas-generating sag or fault zones planarly,3)gas being reserved and sealed by volcanic rock,4)having a complicated relation between gas and water.Based on study of relation between space distribution of gas reservoirs and gas accumulation conditions,there might be three main factors controlling gas accumulation and distribution in volcanic rocks, 1)the areas of source rocks controlling distribution of gas reservoirs,2)fault zones and ancient uplifts controlling specific localities of gas reservoirs,3)volcanic lithofacies controlling reservoiring of gas.A comprehensive study focused on expulsion hydrocarbon history of source rocks, motion history of faults, formation history of traps and gas migration and accumulation.The main accumulation periods of gas in volcanic reservoir might be from later sedimentary period of Quantou Formation(K₁q)to sedimentary period of Qingshankou Formation(K₂qn),the end of sedimentary period of Nengjiang Formation(K₂n) and sedimentary period of Mingshui Formation (K₁m).Gas accumulation model for volcanic reservoir in the Xujiaweizi Fauli-Depression was as follows:gas generating from deep source rocks(Shahezi Formation), migrating through fault to traps in volcanic rocks or in ancient uplifts during main accumulation periods, and forming gas reservoirs.