川中古隆起北斜坡蓬莱气区上震旦统-下寒武统海相碳酸盐岩天然气多层系立体成藏

Multi-layers three-dimensional natural gas accumulation of the Upper Sinian-Lower Cambrian marine carbonate rocks in Penglai gas area,north slope of central Sichuan paleo-uplift

2022年9月,西南油气田部署于川中古隆起北斜坡(蓬莱气区)的东坝1井在下寒武统龙王庙组取得重大勘探突破,标志着川中古隆起北斜坡上震旦统—下寒武统超深层古老海相碳酸盐岩多层系立体成藏的确立。针对蓬莱气区上震旦统—下寒武统的多个含气目的层的沉积相、岩相、储层特征进行分析,进而从烃源岩及源-储配置、沉积相及成岩作用、多层系含气特征及圈闭等3个方面着手,对斜坡区多层系含气的有利条件进行解剖,建立了立体成藏模式。结果表明:分布广泛的厚层、优质烃源岩(灯三段泥页岩和筇竹寺组黑色页岩)为多层系天然气成藏提供了良好的物质保障,上生下储、旁生侧储的源-储配置关系保证了天然气的高效充注;震旦系灯影组受多期桐湾运动海平面升降旋回影响发育厚层叠置丘滩体,寒武系沧浪铺组和龙王庙组受古地貌控制发育白云石化的高能颗粒滩相,丘滩体和高能颗粒滩构成储层形成的物质基础,而后期广泛发育的岩溶作用进一步改善了储层的物性条件,直接控制了优质储层的形成和分布;局部发育的小型构造圈闭和斜坡背景下的岩性圈闭、构造-岩性复合圈闭共同控制上震旦统—下寒武统多层系含气。

In September 2022,the Well Dongba-1,deployed by PetroChina Southwest Oil&Gas Field Company on the north slope of the central Sichuan paleo-uplift(Penglai gas area),achieved a significant exploration breakthrough in the Longwangmiao Formation of Lower Cambrian.The breakthrough conform the multi-layers three-dimensional natural gas accumulation in ultra deep and ancient marine carbonate rocks of Upper Sinian-Lower Cambrian in the north slope of central Sichuan paleo-uplift.First,this article analyzes the sedimentary facies,lithofacies,and reservoirs of multiple gasbearing layers of Upper Sinian-Lower Cambrian in Penglai gas area.Then,starting from three aspects:source rock and source reservoir configuration,sedimentary facies and diagenesis,multi-layers gas bearing characteristics and traps,the favorable conditions for multi-layers gas bearing in the slope area are dissected,and a three-dimensional reservoir formation model is established.The results indicate the widely distributed thick and high-quality source rock such as the mud shale of the Dengying Member 3 and the black shale of Qiongzhusi Formation,provides a good material guarantee for multi-layers natural gas accumulation.The source-reservoir assemblages of upper generation-lower storage and side generation-side storage ensures the efficient filling of natural gas into the reservoir.The Sinian Dengying Formation is influenced by multiple cycles of Tongwan movement and sea level’s rising and falling,and thick stacked mound-shoals are developed.The Cambrian Canglangpu Formation and Longwangmiao Formation are controlled by paleogeomorphology to develop high-energy granular shoals of dolomitization.The mound-shoals and high-energy granular shoals form the material basis for reservoir formation,and the widely developed karst process in the later stage further improves the physical conditions of the reservoir,directly controlling the formation and distribution of high-quality reservoirs.Locally developed small-scale structural traps,together with lithological traps and structural-lithological composite traps in the slope background,control the multi-layers gas bearing.Exploration practice has shown that the Sichuan Basin is rich in ultra-deep oil and gas resources.Continuously deepening the understanding of ultra-deep reservoir formation and geological theory,emphasizing the simultaneous advancement and mutual promotion of geological theory and engineering technology,and continuing to advance towards the 10000 meter’s ultra-deep layer will inevitably open up new fields of high-quality scale reserve and production.