渤海湾盆地歧口凹陷古近系沙一下亚段中等成熟页岩油富集主控因素与勘探突破

Main factors controlling the medium-mature shale oil enrichment and exploration breakthrough in the Paleogene lower E3s1Lin Qikou Sag,Bohai Bay Basin

陆相湖盆中等成熟页岩油资源丰富,而该类型资源具有岩相变化快、成岩演化程度低、储层敏感性强及原油粘滞性高等特点,工程开发对策仍处于探索阶段。以渤海湾盆地歧口凹陷西南缘古近系沙河街组一段下亚段(沙一下亚段)典型湖相中等偏低成熟烃源岩为研究对象,分析该类型页岩油富集主控因素及工程应对策略,探索中等成熟页岩油开发动用方案。研究表明:云灰质页岩夹薄层碳酸盐岩段粘土含量矿物小于30%,海水基滑溜水防膨压裂液体系能够抑制该类储层敏感性,并解决因粘土矿物吸水膨胀而导致的地层坍塌问题;储层脆性、生烃条件、含油性和储层水敏性是中等成熟页岩油甜点分布的主控因素,甜点厚度一般在10~12 m左右,应用叠前偏移数据体开展储层预测、读准靶点深度、旋转导向精准定向、打准甜点段及提高甜点钻遇率是获得高产-稳产的前提条件;采用海水基压裂液防膨、趾端蓄能体积压裂和前置CO增能降粘可实现压裂提产。利用新认识优化QY1H井部署和实施方案,该井437 d累产油7303.28 t(平均日产16.75 t),实现中等成熟度页岩油高产-稳产勘探突破。

Continental lacustrine basins are rich in shale oil resources of medium maturity,which features rapid lithofacies change,low diagenetic evolution,strong reservoir sensitivity,and high crude oil viscosity.Engineering development strategies in this regard are thereby still in the exploratory stage.The typical lacustrine source rocks of medium maturity in the lower sub-member of the first member of the Paleogene Shahejie Formation(Es)at the southwestern margin of Qikou Sag,Bohai Bay Basin are analyzed to discover the major control factors of medium-mature shale oil enrichment and engineering countermeasures to them,and explore the development and production plan of medium-maturity shale oil.The research shows that the clay mineral content in the dolomitic limy shale intercalated by thin-bedded carbonate rocks is less than 30%,and the anti-swelling fracturing fluid system of seawater-based slickwater can inhibit the sensitivity of such reservoirs and solve the problem of formation collapse caused by the water swelling of clay minerals;Factors including reservoir brittleness,hydrocarbon generation condition,oil content and reservoir water sensitivity are the key in controlling the distribution of medium-maturity shale oil sweet spots,and the thickness of these sweet spots generally ranges between 10 m and 12 m.Application of pre-stack migration data volumes to carry out reservoir prediction,accurately reading the depth of the landing point,accurately steering rotary drilling,accurately keeping lateral within the sweet spot interval,and improving the drilling encounter rate of sweet spots,all are the prerequisites for gaining high and stable production;and swelling resistance with seawater-based fracturing fluid,volume fracturing with energy accumulated at the toe end,and energy enhancement and viscosity reduction with COas pad fluid,can help realize production enhancement by fracturing.These new understandings have been applied to optimize the completion of Well QY1H,resulting in a total production of 7303.28 tonnes of oil in 437 days(a daily output of 16.75 tonnes on average),which marks a breakthrough made in the exploration of the medium-maturity shale oil.