开江-梁平地区上二叠统长兴组储层岩石学特征

以露头剖面测量、单井岩芯观察和室内薄片鉴定为依据,结合不同结构和成因类型白云岩(或白云石)的n(Mg)/n(Ca)比值,有序度和C、O、Sr同位素特征,对开江-梁平地区长兴组碳酸盐岩储层成岩作用与孔隙发育和演化规律进行了综合研究,确定研究区对储层破坏最大的成岩作用是胶结、压实-压溶、新生变形和次生矿物的充填等作用,而对储层贡献最大的建设性成岩作用主要为埋藏白云岩化、重结晶、溶蚀和破裂等作用,有效地改善了储层的孔渗性,形成以粒间溶孔、粒内溶孔、铸模孔、晶间溶孔、超大溶孔、溶洞和溶裂缝等多种次生孔隙类型组合的礁、滩相储层基本特征。在再造成岩序列和恢复孔隙演化历史的基础上,对储层发育与孔隙演化的关系可得出如下几点结论:①有利的礁、滩相带决定了储层发育的位置和空间展布规律;②礁、滩复合体的多期次埋藏白云岩化是形成储层的基础;③破裂作用和溶蚀作用是改造储层和提高储层质量的关键。

Reservoir sedimentological characteristics of the Upper Permian Changxing Formation in Kaijiang-Liangping area

Based on field section measurement, well core observation and thin section identification in combination with n(Mg)/n(Ca) ratio, the degree of order and C, O, Sr isotope characteristics of dolomites with different textures and genetic types, the authors made a synthetic study of the diagenesis, porosity development and evolution regularity of carbonate reservoirs of Changxing Formation in Kaijiang-Liangping area. The destructive diagenetic processes in the reservoirs of the study area are mainly cementation, compaction-pressure solution, neomorphism and secondary mineral filling, whereas the constructive diagenetic processes are mainly burial dolomitization, recrystallization, dissolution and fracturing, which effectively improve the reservoir porosity and permeability and constitute the basic characteristics of the reef and beach reservoir that has the combination of a variety of secondary porosity types such as intergranular pores, intragranular pores, moldic pores, intercrystal pores, superlarge dissolved pores, dissolved caverns and fractures. Dolomitization, as the most important and common diagenetic action, went through penecontemporaneous dolomitization in early diagenetic stage, burial dolomitization in early diagenetic stage, burial dolomitization in middle diagenetic stage, burial dolomitization and the formation of tectonoclastic dolostone in late diagenetic stage. Further studies suggest that carbonate reservoirs of Chang-xing Formation experienced a very complex diagenetic and evolutionary history, which can be divided into five phases: penecontemporaneous diagenesis, early diagenesis, middle diagenesis, late diagenesis and tectonic period. On the basis of the reconstruction of diagenetic sequence and the restoration of porosity evolution history, the authors have reached some conclusions: ① favorable reef and beach facies determine the locations and spatial distribution of the reservoirs;② the multistage burial dolomitization of reef and beach complexes constitutes the basis of reservoir formation; ③ fracturing and dissolution constitute the key to the formation of high quality reservoirs.