苏里格南部地区盒8段致密砂岩储层成岩作用及成岩相划分

苏里格南部地区是苏里格气田新的资源接替区，目的层段为下二叠统石盒子组盒8段致密砂岩低渗透储层。为预测该区有利孔渗性成岩相，利用铸体薄片、扫描电镜等资料对盒8段储层的成岩作用及其演化规律进行了综合研究。结果发现：盒8段经过强烈的压实作用，原生孔隙基本消失殆尽，硅质胶结、黏土胶结、碳酸盐胶结现象在储层中都有发育，压实作用和胶结作用是造成储层致密和低孔低渗的主要因素，但是溶蚀作用又使得储层发育次生孔隙，从而为气藏形成提供了基础。通过判别自生矿物类型、镜下颗粒接触形态、孔隙类型、胶结物类型，以及对泥岩镜质体反射率的测定，认为该区盒8段已处于中成岩的B期和晚成岩期的过渡阶段。结合勘探现状及沉积相展布特征的研究成果，将该区储集层划分为4种成岩相，其中相对高渗粗粒弱压实-溶蚀相为最有利的储集相带；低孔渗中-粗粒溶蚀-胶结相次之；低孔渗中-细粒胶结相、特低孔渗细粒-泥质致密压实相为非有利储集相带，储集条件较差。

Diagenesis and diagenetic facies of tight sandstone reservoirs in the 8th member of the Shihezi Formation,southern Sulige Gas Field

The low permeability tight sand reservoirs in the 8th member of the Lower Permian Shihezi Formation are the targeted pay zones in the southern Sulige as the successive resource district of the Sulige Gas Field.In order to identify the diagenetic facies with favorable poroperm characteristics in this area,we studied the diagenesis and its evolutional patterns of reservoirs in the 8th member of the Shihezi Formation by using the data of cast thinsection,SEM,etc.The following conclusions were obtained.The 8th member of the Shihezi Formation must have experienced strong compaction,leading to the complete lost of most primary pores;siliceous,clay and carbonate cementations are common in the reservoirs.So both compaction and cementation are the major factors causing the tightness and low permeability and porosity of the reservoirs.However,dissolution resulted in the well-developed secondary pores,providing a basis for the development of gas reservoirs.The identification of authigenic mineral types,grain contact states,pore types,and cement types as well as the measurement of Ro reveal that the 8th member of the Shihezi Formation is in the transitional stage from the moderate diagenetic stage B to the late diagenetic stage.Based on exploration achievements and distribution of sedimentary facies,4 diagenetic facies are recognized in the studied interval,of which coarse-grained & poorly-compacted dissolution facies with relatively high permeability is most favorable for gas exploration,followed by the moderate-to coarse-grained dissolution-cementation facies with low porosity and permeability.In contrast,the moderate-to fine-grained cementation facies with low porosity and permeability and the fine-grained & argillaceous tight compaction facies with ultra-low permeability and porosity are unfavorable for gas exploration.