川北地区下侏罗统大安寨段陆相页岩油勘探方向再认识

Reassessment of exploration directions of continental shale oil in Lower Jurassic Da’anzhai Member in northern Sichuan Basin

川北地区下侏罗统大安寨段是四川盆地产油主力层系之一。近年来,随着非常规勘探理论的发展,开始转变思路针对大安寨段页岩储层开展勘探,川北地区陆相页岩油勘探方向的认识得到提高。基于LY1及YY2等页岩油探井的岩心、实验、钻井、压裂等资料,对其油气形成条件、资源潜力、工程地质条件等3个方面进行了再认识。研究表明:(1)阆中大安寨段二亚段页岩具备良好的资源基础和形成条件,勘探潜力巨大。大二亚段主要发育页岩、介壳灰岩、页岩夹介壳灰岩3种岩性,页岩烃源品质较好,整体处于中成熟—高成熟阶段,生烃强度为(20~90)×10^(4)t/km^(2),滞留烃量占总生烃量的66%~78%,页岩油资源量为3.26×10^(8)t;(2)研究区大二亚段页岩样品的裂缝网络不发育,具有渗流条件差、可钻性和可压性条件差的特征,基质型页岩油具有原油黏度大、含蜡量高的特征,页岩样品渗流条件和页岩油流动性之间的耦合配置关系是目的层高产的关键;(3)在目前基质型页岩勘探成效不佳的情况下,建议采用常规—非常规结合的勘探思路,对研究区页岩—灰岩互层型储层成藏体系进行研究,将优质页岩与裂缝—孔隙型灰岩的层段作为有利的勘探目标,通过地质—工程一体化研究方法,对可钻性、可压性及排采等方面的技术难题进行攻关,提升工程工艺水平。

The Da’anzhai Member of the Lower Jurassic in northern Sichuan Basin is one of the major oil⁃bearing formations in the basin.In recent years,with the development of unconventional exploration theories,exploration efforts have shifted towards the shale reservoirs in the Da’anzhai Member,enhancing the understanding of the exploration directions for continental shale oil in northern Sichuan.Based on the data from shale oil exploration wells LY1 and YY2,including core samples,experiments,drilling,and fracturing data,a reassessment of the oil and gas formation conditions,resource potential,and engineering geological conditions was conducted.The results indicate that:(1)The second submember of the Da’anzhai Member in Langzhong has a good resource base and formation conditions,indicating great exploration potential.The second submember mainly develops three lithologies:shale,shell limestone,and shale interbedded with shell limestone.The shale exhibits good hydrocarbon source quality and is generally in a middle to high⁃mature stage.Its hydrocarbon production intensity is(20-90)×10^(4)t/km^(2),and the retained hydrocarbon accounts for 66%to 78%of the total hydrocarbon produc⁃tion,with a shale oil resource amounting to 3.26×10^(8)t.(2)The shale samples from the second submember in the study area have poorly developed fracture networks,characterized by poor permeability conditions,difficult drilling and compressibility conditions.The matrix⁃type shale oil has high crude oil viscosity and high wax content.The coupling configuration relationship between the permeability of the shale samples and the fluidity of the shale oil is key to achieving high production in target layers.(3)Given the current poor production results in matrix⁃type shale exploration,it is recommended to adopt a combined conventional and unconventional exploration method to study the formation system of the shale and limestone interlayer reservoirs in the research area,considering high⁃quality shale and fracture-porosity type limestone as favorable exploration targets.Through the integration of geological and engineering research methods,efforts should be made to tackle technical challenges related to drillability,compressibility,and production,thereby improving engineering and technological levels.