Genesis of Overpressure and Sealing Ability of Caprocks in Well Gaotan 1 in the Southern Margin of Junggar Basin

doi:10.7657/XJPG20210603

Abstract

Abstract:

The southern margin of the Junggar basin is a typical petroliferous area with high or ultra-high pressure. To understand the oil and gas accumulation law and predict favorable exploration zones, it is important to clarify how the overpressure develops and how the oil and gas are preserved at strong overpressure. According to the overpressure characteristics and the exploration results from Well Gaotan 1, this study analyzed the overpressure causes in Well Gaotan 1, and then predicted the height of the hydrocarbon column that is dynamically closed by the hydraulic fractures in the caprock in the overpressure system. It’s found that there are multiple factors causing the overpressure in the Cretaceous Qingshuihe formation in Well Gaotan 1: tectonic compression accounts for 51.03%, pressure transmission accounts for 14.94% and undercompaction accounts for 34.03%; and the tectonic thrust and lateral compression stress during the Himalayan movement are major inducements of the abnormally high pressure in the deep formation. In the Cretaceous Qingshuihe formation in Well Gaotan 1, the mudstone caprock is thick, the displacement pressure is high and the sealing ability is strong. Therefore, hydraulic fractures in the caprock and the re-slipping of the pre-existing faults in the overpressure system dynamically control the maximum overpressure that the caprock can withstand and the maximum height of the hydrocarbon column that can be closed. The Cretaceous Qingshuihe formation and the Jurassic Toutunhe formation in Well Gaotan 1 are two independent pressure systems. The pressure coefficient of the Qingshuihe formation is 2.32, close to the critical pressure for the sliding of the pre-existing fault, so it is estimated that the maximum height of hydrocarbon column that can be dynamically closed before the burst of the caprocks is 200 m. The Middle and Upper Jurassic strata in the Gaoquan anticline are the next exploration target, the channel-delta front sandbodies may have high-quality reservoirs, and future exploration may focus on structural and lithological reservoirs.

Key words: southern margin of Junggar basin, Well Gaotan 1, overpressure genesis, caprock, sealing ability, hydrocarbon column height, hydraulic fracturing, fault slip

CLC Number:

TE112

LU Xuesong, ZHANG Fengqi, ZHAO Mengjun, ZHUO Qingong, GUI Lili, YU Zhichao, LIU Qiang. Genesis of Overpressure and Sealing Ability of Caprocks in Well Gaotan 1 in the Southern Margin of Junggar Basin[J]. Xinjiang Petroleum Geology, 2021, 42(6): 666-675.

Figures/Tables 9

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