松辽盆地北部中央古隆起带基岩风化壳气藏富集规律

Gas Enrichment in Basement Weathering Crust in the Central Paleouplift Belt in Northern Songliao Basin

为明确松辽盆地北部中央古隆起带基岩风化壳气藏分布规律及主控因素,利用岩心、测井及地震等油气勘探资料,探讨了研究区天然气成藏的烃源岩、储层及盖层条件及气藏形成的地质背景。结果表明:主力烃源岩以徐家围子断陷沙河子组为主,储层以花岗岩类风化壳为主,区域盖层为登娄库组泥岩;早期区域隆升、晚期差异沉降形成近SN向的中央古隆起带。基岩风化壳具有新生古储、侧向运移的成藏模式,富集规律分析结果表明:基岩与泥岩对接、供烃窗口大的地区是天然气藏富集的平面有利区;纵向上,风化淋滤作用控制着天然气藏在基岩风化壳内富集;花岗岩类为优势岩性,是天然气富集高产的重要因素之一。

In order to investigate the distribution principles and main controlling factors of the basement weathering crust gas accumulations in the central paleouplift belt in the northern Songliao basin,the conditions of hydrocarbon source rock,reservoir and cap rock,and the geological background of gas reservoir formation in the study area are discussed based on core,logging,seismic,and other oil and gas exploration data.The results show that the main source rock is Shahezi Formation in Xujiaweizi fault depression,the reservoir is mainly granite weathering crust,and the regional caprock is the mudstone of Denglouku Formation.The early regional uplift and late differential subsidence formed a central paleouplift belt in nearly SN direction.The weathering crust of bedrock has a hydrocarbon accumulation model of lateral migration of hydrocarbon from young sources to old reservoirs.The analysis of gas enrichment show the following principles.The favorable area for gas accumulation in basement weathering crust is benefitted from the direct contact of the bedrock to the mudstone and a large hydrocarbon supply window laterally,and weathering and leaching vertically.The granite as dominant lithology is one of the essential factors for gas enrichment and high yield.