辫状河三角洲前缘致密砂岩储层特征及优质储层控制因素——以苏里格气田西南部石盒子组8段为例

Characteristics of tight sand reservoir and controlling factors of high-quality reservoir at braided delta front:a case study from Member 8 of Shihezi Formation in southwestern Sulige gas field

辫状河三角洲前缘是油气勘探开发的重点目标区。为研究三角洲前缘的储层特征和优质储层分布,以苏里格气田西南部为例,结合岩心分析、测井资料和薄片鉴定等,分析了不同类型砂体的储层特征,探讨了影响储集性能的因素。研究表明:①辫状河三角洲前缘的储层砂体可细分为河道砂体、坝砂体和席状砂体3类,三者在岩石矿物成分、孔喉类型和储集性能等方面存在较大差异。②3类砂体相互拼贴叠置,呈现出5种砂体构型。其中,河道砂体和多相复合砂体在横向上反复迁移、垂向上多期叠置,砂体面积较大,发育大量粒间孔和晶间孔,其储层以缩颈型喉道为主,孔渗性能较好,为优质储层。③储层的储集性能受沉积作用和成岩作用影响,沉积作用在宏观上决定了砂体的形态和规模,影响优质储层的分布,成岩作用控制了微观孔隙的发育特征。④砂岩的各成岩阶段对孔隙演化的影响不同,同生成岩—早成岩B期的压实作用和胶结作用是储层致密化的主因,中成岩A期占据主导的溶蚀作用可有力地改善孔隙,中成岩B期晚期方解石的胶结作用可阻塞孔隙,形成现今储层低孔、低渗的局面。⑤优质储层多集中于削截式河道砂体和多相复合砂体物性较好的上部,是油气重点富集区,可作为甜点区重点开发。

The braided delta front is the key target area for oil and gas exploration.This study aims at the reservoir characteristics and highquality reservoir distribution of delta front.Taking the southwestern Sulige gas field as an example,based on core analysis,logging data and thin section identification,the reservoir characteristics of different sand body types are analyzed and the influences on the reservoir are discussed.The results show as follows.(1)Sand bodies at the braided delta front can be subdivided into channel sand,beach-bar sand and sheet sand,which largely varied in mineral composition,pore throat and reserving performance.(2)Different sand bodies cohere to and superpose each other,thus showing five types of architecture.Channel sand body and multiphase composite sand body move repeatedly in the horizontal direction and multi-phased overlapping occurs in vertical direction,thus forming a wide distribution.A large number of intergranular pores and intercrystal pores are developed.The high-quality reservoir dominated by necking throats has good porosity and permeability.(3)The reserving performance is affected by sedimentation and diagenesis.Sedimentation controls the sand body shape and scale at the macro level,and further affects the distribution of high-quality reservoirs.Digenesis affects the development characteristics of micro-pores.(4)Each digenesis phase of sandstone has different influences on pore evolution.Compaction and cementation during syngenesis to eodiagenesis B is the main cause of reservoir densification.Erosion dominant in mesodiagenesis A can improve pores greatly.Late calcite cementation in mesodiagenesis B further blocks pores to form the present low porosity and low permeability.(5)High-quality reservoirs are mostly developed in the upper truncated river channel sand body and multiphase composite sand body with good porosities,which is a key area for oil and gas accumulation as the sweet spot for development.