准噶尔盆地南缘高探1井超压成因与盖层封闭能力

准噶尔盆地南缘是典型的高压—超压含油气区,明确超压成因机制以及强超压条件下油气保存机制,对于认识油气富集规律、预测有利勘探区十分重要。从高探1井超压油藏特征及其勘探成果出发,在分析高探1井超压成因机制的基础上,对超压系统中盖层水力破裂动态封闭的烃柱高度进行了预测。研究认为：高探1井白垩系清水河组超压为多种成因,其中构造挤压增压占51.03%,超压传递占14.94%,欠压实增压占34.03%,喜马拉雅运动期的构造冲断—侧向挤压应力是深层异常高压的主要诱因。高探1井白垩系清水河组泥岩盖层厚度大,排替压力大,封闭能力强,超压系统盖层水力破裂和先存断层重新滑动动态控制了盖层能承受的最大超压和能封闭的最大烃柱高度。高探1井白垩系清水河组和侏罗系头屯河组为2套独立的压力系统,清水河组压力系数为2.32,接近先存断层滑动的临界压力条件,推测盖层破裂前能够动态封闭的最大烃柱高度为200 m。高泉背斜中—上侏罗统为下一步重点勘探层系,河道—三角州前缘砂体可为优质储集层,构造-岩性油气藏可能是下一步勘探重点。

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

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.