克拉2气田储层特征及优质储层形成机理

RESERVOIRS CHARACTERISTICS AND FORMATION MECHANISM OF HIGH QUALITY RESERVOIRS IN KELA-2 GAS FIELD

塔里木盆地库车坳陷北部的克拉2气田的天然气主要储集于白垩系巴什基奇克组辫状河三角洲沉积的岩屑砂岩、长石岩屑砂岩中，储层孔隙发育，连通性好，以受溶蚀作用改造扩大的粒间孔隙为主。储层孔隙度为15％～20％，渗透率为200×10^-3～800×10^-3μm^2，属于中孔中渗储层。通过显微镜下观察发现，岩石在埋藏过程中以机械压实作用为主，颗粒主要为点、点-线接触，压实作用弱-中等；发育碳酸盐和黏土矿物胶结，石英次生加大胶结较少，总体上胶结作用不强烈；溶蚀作用主要发育干长石和岩屑颗粒内部与边缘，以及粒间碳酸盐胶结物；目前岩石处于中期成岩阶段。优质储层的形成主要与砂岩储层早期长时间浅埋、晚期短时间快速深埋，异常高压对压实作用的抑制以及晚期溶蚀作用对孔隙一定程度的改造扩大有关。

In Kela-2 gas field located in the northern Kuqa depression in the Tarim Basin, the natural gas reserves are mainly accumulated in the litharenite and feldspathic litharenite of braided river delta facies in the Cretaceous Bashijiqi Formation. The reservoirs are well developed in porosity and connectivity and are dominated by intergranular pores enlarged by dissolution. They belong to medium porosity and medium permeability reservoirs, with porosity ranging from 15% to 20% and permeability ranging from 200×10-3 to 800×10-3μm2. Microscopic observation shows that the diagenesis is dominated by mechanical compaction in the process of burial, the grains are in point-point and point-line contact, and the compaction is low to medium. Cementation is not intense as a whole, with relatively good carbonate and clay mineral cementation but poor secondary outgrowth cementation of quartz. Dissolution mainly occurs in the interior and edge of feldspar and lithic grains as well as in the intergranular carbonate cements. The reservoirs are in anadiagenetic stage now. The formation of the high quality reservoirs are mainly resulted from the early long-term shallow burial and late short-term deep burial of the sandstone reservoirs, the negative effects of abnormal high pressure on compaction, and the improvement of late dissolution to porosity.