Migration law of fracture filling fluid in ultra-deep clastic reservoirs: a case study of the Cretaceous Bashijiqike Formation in Keshen well block, Kuqa depression

The Cretaceous reservoirs in Keshen well block of the Kuqa depression are ultra-deep clastic reservoirs with a burial depth of more than 6 km, which have the typical characteristics of pore-fracture type reservoir. The development and distribution of fractures is an important factor for improving reservoir property. The fluid activity in the fracture system in deep reservoirs is active, mainly shown as the multi-scale, multi-component and multi-stage cemented filling effect; however, there is still not a clear understanding of the characteristics of fluid activity. Aiming at fracture filling in the study area, an analysis is performed on the stage of fracture fillings. On this basis, comprehensively using core observation, thin section identification and cathodoluminescence, in combination with the experimental analysis of carbon and oxygen isotope and the experiment of homogenization temperature of fluid inclusions, this study clarifies the filling degree in different well areas and the characteristics of fillings in the Keshen area. The results show that the fractures have the characteristics of two stages of calcite filling, and there were two stages of large-scale fluid migration activities, both of which occurred during the middle period of the Himalayan Movement since Neogene. The first stage occurred from 12.2 Ma to 7.4 Ma, corresponding to the rapid descent and later slow uplift of the formation; the second stage occurred from 5.5 Ma to 3.8 Ma, when the formation experienced rapid subsidence and the fluid entered the fracture to produce a cemented filling effect. © 2020, Editorial Office of ACTA PETROLEI SINICA. All right reserved.