库车坳陷不同构造带沉降差异性及其对储层孔隙度的影响

Difference of subsidence history and its influence on reservoir porosity in Kuqa Depression

利用回剥原理,采用盆地模拟技术,选择东、西两条剖面对库车坳陷不同构造带典型井的沉降史进行了对比研究。结果表明,克拉苏构造带早期相对深埋、晚期持续深埋;秋里塔格构造带早期浅埋、晚期快速深埋;前缘隆起带早期缓慢浅埋、晚期相对浅埋。库车坳陷不同构造带的构造活动和沉降差异性导致其储层孔隙度差异明显。这种沉降差异性反映出由北向南从克拉苏构造带到前缘隆起带储层经历的深埋时间和最大埋深由大变小,储层在埋藏过程中所受的成岩压实作用由强变弱、孔隙度由小变大。时间深度指数定量地反映了这种沉降差异性及其对孔隙度的影响。

We analyze and contrast the subsidence history of typical wells in the eastern section and the western section of Kuqa Depression with the principle of backstripping and basin modeling technology. In Kelasu structural belt, the subsidence curve reveals that the stratum is buried deep at the early stage and continues to be buried deep at the late stage. In Qiulitage structural belt, the buried stratum is shallower early compared with the stratum of Kelasu structural belt while it becomes deeper late. In Forebulge structural belt,the subsidence curve shows that the buried stratum is shallow early and remains shallow late. The distinct strength of tectonic movement and the visible difference of subsidence history lead to the different porosity between different structural belts in Kuqa Depression. The difference of subsidence history suggests that burial time and burial depth decrease from Kelasu structtiral belt to Forebulge structural belt, which leads to the decline in the pressure of reservoirs during burial history. Owing to those, the compaction intension of reservoirs decreases from Kelasu structural belt to Forebulge structural belt, leading to the porosity increasing from north to south. Time-depth index can quantitatively reflect the difference of subsidence history and its influence on the porosity.