Diagenetic Response of Clastic Buried Hill Buried-Uplifted-Reburied: A Case Study from Upper Shihezi Formation in Permian of Gubei Buried Hill of Jiyang Depression

In this paper it aims to gain new insights into clastic buried hill reservoirs. For this purpose, the Permian sandstone reservoirs in Upper Shihezi Formation, Gubei low buried hill, Jiyang depression, was taken as the object. Referring to the diagenesis in the process of burial-lifting-reburning of the reservoirs, with the aid of techniques like core observation, casting sheet observation, scanning electron microscopy (SEM), cathode luminescence, carbon-oxygen isotope analysis and fluid inclusion. The results show that: It is found that the diagenetic evolution of the sandstone reservoir of Upper Shihezi Formation of Permian in Gubei buried hill of Jiyang Depression has gone through three stages from early to late. Stage I: Late Triassic and Early-Middle Jurassic, Gubei buried hill was uplifted and the Permian strata were denuded by the Indosinian movement, and the main diagenetic environment was shallow burial and uplift exposure denudation. The main diagenetic responses are feldspar dissolution, kaolinite cementation, stage ①quartz cementation and limonite invasion. Stage II: Jurassic and Cretaceous, the sinistral strike-slip movement occurred in the Tancheng-Lujiang fault zone, the strong tectonic activity accompanied by active volcanic activity, and the hydrothermal activity associated with volcanic activity greatly affected the reservoir. The diagenetic response is the development of stage ① carbonate cementation, stage ② quartz cementation, pyrite, sericite, chlorite and long columnar apatite. Stage Ⅲ: Cenozoic, under the action of regional transtensional stress, the burial depth of Gubei buried hill increased, the maturity of organic matter increased, and the diagenetic environment was dominated by organic acid. The diagenetic response was mainly from carbonate cementation and quartz dissolution in stage ② to carbonate dissolution and feldspar dissolution in late stage. The results of quantitative restoration of pore evolution show that the compaction and cementation in stages Ⅰ and Ⅱ have a great influence on the porosity, which decreases from 40% to 19%, and the diagenesis in early alkaline environment in stage Ⅲ has a destructive effect on the porosity of the reservoir, which decreases from 19% to 6.7%. After that, the porosity of the reservoir increased from 6.7% to 9.1% due to the dissolution reconstruction in acidic environment, and the secondary dissolution pores were developed and well preserved.