临兴地区致密气“多层系准连续”成藏模式与大气田勘探实践

"Multi-series and quasi-continuous"tight gas accumulation pattern and giant gas field exploration practice in Linxing area

2013年底,在位于鄂尔多斯盆地东部晋西挠褶带的临兴地区石炭—二叠系探获了一口高产气井,此后又陆续发现了一批高产气井。为了给该区上古生界天然气资源评价提供支撑,基于地质背景调查、构造演化解剖、钻井地质分析以及大量的岩心取样及实验分析等手段,对该区致密砂岩气的成藏条件、富集规律、成藏模式等开展了研究和勘探开发实践,并于2020年底探明了临兴千亿立方米大气田。研究结果表明:①该区上古生界烃源岩主要为海陆过渡环境沉积的含煤层系,具有有机质丰度高、厚度及分布面积较大的特点;②储集体以多期摆动、往返迁移的水上或水下分流河道沉积为主,砂体纵向叠置、平面复合连片,次生溶孔发育,泥质岩盖层纵横向广泛分布;③上古生界储层在中侏罗世时期发生普遍的致密化,上石炭统本溪组及下二叠统太原组大量的煤系烃源岩在晚侏罗世开始规模排烃,在源内储层聚集富集以后,在逐次扩散到近源的中二叠统下石盒子组致密砂岩中,其顶部受石盒子组中部区域性大盖层遮挡,进而形成源内及近源成藏体系;④紫金山于早白垩世侵入上古生界地层中,形成大量贯通的断裂体系,石盒子组中部区域性盖层遭受明显破坏,源内与近源天然气沿断裂向中二叠统上石盒子组、上二叠统石千峰组运移,形成远源成藏体系;⑤生储盖组合有效搭配,共同为临兴大气田的形成奠定了基础。结论认为,临兴气田具有充足的气源条件,优质砂岩与泥岩互层的“三明治”岩性组合,良好的断层、裂缝输导体系,三者共同作用形成了“多层系准连续”的致密气成藏模式;该成果为中海油实现陆上油气储量与产量突破提供了现实的途径。

Linxing area is located in Jinxi flexure zone of the eastern Ordos Basin,where the first high-yield gas well was explored in the Carboniferous-Permian at the end of 2013 and since then several high-yield gas wells have been discovered.For the purpose of providing support for the evaluation of the Upper Paleozoic natural gas resources in Linxing area,studies and exploration and development practices were conducted on the hydrocarbon accumulation conditions,enrichment laws and hydrocarbon accumulation patterns of tight sandstone gas in this area by means of geological setting investigation,structural evolution dissection,drilling geological analysis and abundant core sampling and experiments.And at the end of 2020,Linxing giant gas field with hundreds of billions of reserves was discovered.The following research results were obtained.First,the Upper Paleozoic source rocks in Linxing area are mainly coal-bearing series deposited in a transitional environment,and they are characterized by high organic abundance,great thickness and a large distribution area.Second,the reservoir is dominated by water or underwater distributary channel deposits that swing frequently and migrate back and forth.Sand bodies are superimposed vertically and connected areally.Secondary dissolution pores are developed.Argillaceous cap rocks are distributed widely in vertical and horizontal directions.Third,the Upper Paleozoic reservoirs were generally densificated in the period of Middle Jurassic.A large number of coal-measure source rocks of Upper Carboniferous Benxi Formation and Lower Permian Taiyuan Formation began to expel hydrocarbon in the Late Jurassic.After hydrocarbon was accumulated and enriched in the reservoirs inside the source rocks,it migrated gradually to the tight sandstone of Middle Permian Lower Shihezi Formation near the source rocks.The top was under the barrier of the regional major cap rocks in the middle of Shihezi Formation.In this way,an intra-source and near-source hydrocarbon accumulation system was formed.Fourth,the Zijinshan Mountain invaded into the Upper Paleozoic in the Early Cretaceous to form a large number of through fault systems.As a result,the regional cap rock in the middle of Shihezi Formation was destroyed,and intra-source and near-source natural gas migrated to Middle Permian Upper Shihezi Formation and Upper Permian Shiqianfeng Formation along faults to form a far-source hydrocarbon accumulation system.Fifth,the effective configuration of source rock-reservoir-cap rock assemblage lays the foundation for the formation of Linxing giant gas field.In conclusion,Linxing gas field has sufficient gas source conditions,"sandwich"lithology combination of quality sandstone-mudstone interbed and good fault and fracture system,which jointly form the"multi-series and quasi-continuous"tight gas accumulation pattern.These research results provide a practical way for CNOOC to realize a breakthrough in onshore oil and gas reserves and production.