四川盆地东南部五峰组-龙马溪组深层页岩气藏类型、特征及勘探方向

Types,characteristics,and exploration targets of deep shale gas reservoirs in the Wufeng-Longmaxi formations,southeastern Sichuan Basin

四川盆地东南部是中国石化五峰组-龙马溪组深层页岩气勘探的主战场,钻井受工程技术约束目前深度主要集中在小于4500 m的深层,大于4500 m的超深层尚未取得实质性勘探突破。构造类型是该地区页岩气藏局部深度差异的主控因素,同时也是保存条件和工程技术条件的重要控制因素,开展页岩气藏构造类型划分和特征研究,查明该地区页岩气藏深度分布的整体特征对后续勘探评价与部署具有重要参考意义。通过将研究区深层页岩气藏划分为盆缘背斜型、盆缘斜坡型、盆内高陡型和盆内向斜型4种主要类型,明确了不同类型深层页岩气藏的特征和主要勘探目标。盆缘背斜型的阳春沟、新场西部、丁山、林滩场、桂花,以及盆缘斜坡型的新场东部、东溪东部、良村北、永乐-古蔺等目标最为有利。构造类型对储层含气性及产量也具有一定的控制作用,研究表明控制作用具有盆缘背斜型>盆缘斜坡型>盆内高陡型的特征。同时构造类型还控制着深层页岩气的深度分布特征以及工程改造的效果和资源分布特征,其中改造效果较好的3500~4500 m深层主要分布在盆缘背斜型和盆缘斜坡型,但其资源量占比相对较小,深度大于4500 m的超深层在4种构造类型中都有分布,其资源量占主体地位。综合考虑构造类型、深度分段、资源规模和工程技术条件,认为研究区深层页岩气的勘探应分3个层次逐步开展:①效益攻关盆缘背斜型和盆缘斜坡型3500~4500 m深度段;②突破攻关盆缘背斜型、盆缘斜坡型和盆内高陡型4500~5000 m深度段;③跟踪评价盆内向斜型大于5000 m深度段。

The southeastern Sichuan Basin serves as a major region for the exploration of deep shale gas reservoirs in the Wufeng-Longmaxi formations to the Sinopec.Due to the constraints of engineering technology,the current drilling depth has focused on the layers at depth less than 4500 m,while no substantial exploration breakthroughs have been made in the ultra-deep layers with depth exceeding 4500 m.The structural type acts as a dominant factor governing the local depth differences of shales in this region.Furthermore,it significantly influences shale gas preservation conditions and the applicability of available engineering technologies.Therefore,determining the structural types of deep shale gas reservoirs therein,as well as the characteristics and the overall depth distribution of various types,can provide critical references for subsequent exploration elevation and exploration well emplacement.In this study,the deep shale gas reservoirs in the study area are classified into four major types in terms of structure:the basin-marginanticline type,the basin-margin-slope type,the highly-steep-structure type,and the basin-interior-syncline type.We determine the characteristics and target areas of these various types of deep shale gas reservoirs.The most favorable exploration targets concluded include the Yangchungou,western Xinchang,Dingshan,Lintanchang,and Guihua structure of the basin-margin-anticline type,as well as the eastern Xinchang,eastern Dongxi,northern Liangcun,and Yongle-Gulin structure of the basin-margin-slope type.The structural type has a certain control effect on the gasbearing capacity and production of reservoirs.Structure of the basin-margin-anticline type is the best in terms of both gas-bearing capacity and production,followed by the basin-margin-slope type and the highly-steep-structure type.Moreover,the structural type governs the depth distribution of deep shale,thus indirectly controlling the fracturing performance and resource potential.Deep shale gas layers at depth interval 3500~4500 m with a great fracturing performance primarily include those of the basin-margin-anticline and basin-margin-slope types,the resources of which accounts for a relatively small proportion.The ultra-deep reservoirs at depth exceeding 4500 m are seen in these four types of structures,accounting for a large portion in resources.By combining the structural types,depth segmentation,estimated in-place gas,and engineering technology conditions,it is recommended that the deep shale gas reservoirs in the study area should be explored progressively in three stages:(1)targeting shale gas reservoirs of the basin-marginanticline and basin-margin-slope types at depth interval 3500~4500 m for exploration benefit;(2)targeting shale gas reservoirs of the basin-margin-anticline,basin-margin-slope,and highly-steep-structure types at depth interval 4500~5000 m for exploration breakthrough;and(3)targeting shale gas reservoirs of the basin-interior-syncline type at depth interval over 5000 m for exploration appraisal.