库车坳陷克拉苏冲断带深部巴什基奇克组致密储层孔隙演化定量研究

Quantitative research on porosity evolution of deep tight reservoir in the Bashijiqike Formation in Kelasu structure zone,Kuqa Depression

综合利用岩心观察、普通薄片、铸体薄片鉴定观察、图像分析、埋藏演化史与有机质热史演化分析,膏盐层脱水及黏土矿物转化分析等技术方法,对库车坳陷克拉苏冲断带克深区块深部巴什基奇克组致密储层进行了孔隙演化定量研究。这套致密储层主要经历了"黏土膜→早期缓慢浅埋压实作用→长石、岩屑溶蚀和石英加大→早期方解石胶结→中期快速深埋强烈压实作用→长石、碳酸盐胶结物溶蚀→碳酸盐致密胶结→晚期挤压推覆形成裂缝→裂缝溶蚀扩大"的埋藏-成岩演化过程。以孔隙结构特征为基础,定量计算各关键成岩作用对储集空间的影响量(初始孔隙度为37.87%,压实损孔量为27.62%,胶结损孔量为7.51%,溶蚀增孔量为1.7%,裂缝增孔量为1.32%),并以埋藏-成岩演化史为主线及约束,恢复校正不同历史时期不同成岩作用对储层物性演化的控制量,从而恢复储层实际孔隙演化史。研究表明,不同成岩作用对储集层孔隙度的影响量不同,孔隙度整体变化趋势为逐渐减小。克深区块晚期气藏充注时期与区域构造挤压造缝时期配置良好,结合较好的储层孔隙度(6.2%),有利于烃类充注成藏,形成有利勘探目标。

Based on core observation, thin section identification, image analysis, analyses of thermal and burial histories of organic matters, analyzes of dehydration of gypsum bed and clay mineral transformation, and other technical methods, quantitative studies on porosity evolution were conducted in the deep tight reservoir in the Bashijiqike Formation in Keshen area, Kelasu structure zone, Kuqa Depression. The results show that the buried diagenetic sequences mainly experienced sequentially from clay coasting to early-stage shallow buried and slowly compaction, followed by dissolution of feldspars and rock fragments, secondary growth of quartz, early calcite cementation, middle-stage rapidly buried and strong compaction, dissolution of carbonate cement, tight carbonate cementation, and finally late-stage fissures created by compression and thrusting to enlarged fissures formed by dissolution. Each key factor in the reservoir porosity evolution was quantitatively characterized on the basis of current reservoir composition and pore structure （the initial porosity was found to be 37.87%~ porosity losses were 27.62% and 7.51% due to compaction and cementation, respectively, porosity increases were 1.7% and 1.32% due to dissolution and fracturing, respectively）. In addition, the quantitive controls on the evolution of reservoir physical properties in different geological periods and diagenesis types were studied to recover the actual porosity evolutionary history constrained by buried diagenetic evolution. It is concluded that the influences from different types of diagenesis on porosity varied greatly, however, the tendency of porosity decreasing was unavoidable. The late-stage hydrocarbon accumulation in the Bashijiqike Formation with relatively high porosity （6.2%） was well matched with fissures formed by regional compression. Therefore, the deep tight reservoir was beneficial for hydrocarbon accumulation, making it a favorable exploration target in Keshen area.