四川盆地合川-潼南地区栖霞组白云岩天然气地质特征及有利勘探区带

Geological characteristics and favorable exploration plays of gas in Qixia Formation dolomite in Hechuan-Tongnan area of Sichuan Basin

近年来,四川盆地中部的下二叠统栖霞组白云岩储层勘探接连获得重大突破,但储层发育较薄,研究程度和勘探程度较低,白云岩储层的分布特征认识不清。以四川盆地合川-潼南地区下二叠统栖霞组为研究对象,综合利用HS4井、HS2井等新钻探井资料,结合露头剖面和地震资料,系统分析了栖霞组的沉积格局、生储盖空间配置关系及储层分布特征,揭示了有利勘探区带的分布特征。结果表明:栖霞组的沉积格局受川中古隆起控制,具有洼隆相间的特征,表现为沿川中古隆起发育台内滩和滩间相带,其中白云岩储层主要受控于局限的微古地貌高部位,叠加云化和岩溶改造作用可形成优质白云岩储集层;寒武系—二叠系发育多套烃源岩,为栖霞组天然气富集提供了优越的生烃条件,同时具备较好的盖层和保存条件,发育“下生上储”“旁生侧储”和“自生自储”3种源储匹配关系,其中“下生上储”和“自生自储”具有较好的源储匹配关系;合川-潼南地区栖霞组古地貌围斜—高部位和滩体发育区的叠合部位是栖霞组白云岩储层发育的优势地带;根据这一认识并结合源储匹配关系;将合川-潼南地区栖霞组白云岩储层划分为2个有利勘探区带。研究成果为合川-潼南地区的层序评价及区带优选提供了理论指导。

In recent years,exploration of dolomite reservoirs of Lower-Permian Qixia Formation in central Sichuan Basin have got a series of great achievement,but existing challenge of relatively thin reservoirs developed,low research and exploration degree less understanding on dolomite reservoirs distribution. Taking Lower-Permian Qixia Formation in Hechuan-Tongnan area of Sichuan Basin as research object,by comprehensively using data from new drilled well HS4 and HS2 and combined with outcrop section and seismic data,the sedimentary framework,sourcereservoir-seal spatial configuration relationship and reservoir distribution of Qixia Formation are systematically analyzed and the distribution characteristics of favorable exploration plays are revealed. The study shows that sedimentary framework of Qixia Formation is controlled by central Sichuan paleo-uplift,characterized by alternating sags and uplifts appearing as intraplatform beaches and interbeaches along central Sichuan paleo-uplift. In this framework,dolomite reservoirs are mainly controlled by limited high position of micro-palaeogeomorphology,and superimposed dolomization and karst transformation can form high-quality dolomite reservoirs. Several sets of hydrocarbon source rocks developed in Cambrian-Permian strata providing excellent hydrocarbon generation conditions for gas enrichment in Qixia Formation,and also presented better seal and preservation conditions,developing 3 sourcereservoir assemblages including“lower generation and upper accumulation”,“lateral generation and accumulation”and“generation and accumulation in same formation”,among which the former and latter possess better source-reservoir matching relations. The superimposition part of paleogeomorphology pericline-high and beaches in Qixia Formation of Hechuan-Tongnan area are favorable zones of dolomite reservoir development. Based on these understandings and source-reservoir assemblage relationships,dolomite reservoirs of Qixia Formation in HechuanTongnan area are divided into 2 favorable exploration plays. The research provides theoretical guidance for sequence evaluation and plays optimization in Hechuan-Tongnan area.