库车坳陷白垩系超深层储集层特征与勘探潜力

Characteristics and Exploration Potential of Ultra-Deep Cretaceous Reservoir in Kuqa Depression,Tarim Basin

塔里木盆地库车坳陷白垩系储集层为一套超深、超高压、高温、孔隙型低孔砂岩地层,为查明其储集层特征、成因机制及勘探潜力,依据激光共聚焦扫描、工业CT、高压压汞、扫描电镜、碳氧同位素、全直径岩心物性分析、电子探针能谱和成像测井等资料,运用构造演化恢复及系统表征的方法,对白垩系砂岩储集层进行了综合研究。研究表明,克拉苏深层区带白垩系巴什基奇克组辫状河（扇）三角洲前缘砂体叠置连片分布,厚度150-250m;超深层残余原生孔隙及溶蚀孔隙较发育,网状、高角度未充填—半充填构造裂缝发育,储集层性质总体为低孔中低渗;早中期浅埋藏、晚期构造推覆膏盐岩顶棚构造、表生成岩期—早成岩期溶蚀作用与晚期构造挤压相互耦合、叠加改造是储集层的主要成因机制;有效储集层厚80-200m,相对优质储集层厚30-90m,主要分布在水下分流河道、构造背斜东西轴部、距不整合面220m以内的“三者”叠合区,成带连片分布,埋深8000m仍然存在有效储集层,具有巨大的天然气资源潜力。

The Cretaceous reservoir in Kuqa depression of Tarim basin is a set of ultra-deep, ultra-high pressure, high temperature and low-porosity fractured sandstones. To identify characteristics, genesis and exploration potential of the reservoir, an integrated research is performed using structural evolution reconstruction and systematical characterization and based on the data of confocal laser scanning, industrial CT, high-pressure mercury injection, SEM, carbon and oxygen isotopes analysis, physical properties of full-diameter cores, electron microprobe spectroscopy and so on. The study shows that the braided delta-front sand bodies are superimposed and distributed continuously in Cretaceous Bashijiqike formation of Crassus deep zones with the thickness of 150-250 m; in ultra-deep layers, residual primary porosity and dissolved pores are relatively developed, netlike, high-angle, filled to semi-filled fractures are developed, too. The reservoir generally belongs to low-porosity, medium-low permeability in nature; the genesis mechanism is dominated by 3 mechanisms such as shallow burial during the early and middle stages, celling structure of nappe-type, gypsum-salt rocks during the late stage and intercoupling and superimposition between dissolution during epidiagenetic stage to early diagenesis stage and tectonic compression at the late stage; the effective reservoir thickness ranges from 80 m to 200 m and the relatively high quality reservoir thickness reaches to 30-90 m, which are mainly continuously distributed in the areas superimposed by underwater distributary channel, E-W axis of structural anticline and zone within 220 m to unconformity surface. The effective reservoirs could still exist in the burial depth of 8 000 m. All the areas may have natural gas reserves potentials of trillions of cubic meters by estimation.