鄂尔多斯盆地三叠系延长组长7致密油成藏组合与模式

Accumulation conditions and regulations of tight oil in Chang 7 Member of Triassic Yanchang Formation,Ordos Basin

鄂尔多斯盆地致密油勘探、开发已经取得了较大突破。盆地内沉积构造背景、源储条件及其组合造成了成藏动力及过程的复杂性。该文综合利用理论计算、压汞测试、成藏物理模拟及盆地模拟等方面资料分析当前致密油成藏动力条件;利用地球化学资料、成藏物理模拟结果以及成岩-成藏耦合过程来研究致密油的成藏规律,对源储组合进行分类并分析石油在其中的充注规律,总结致密油成藏模式。研究表明,长7优质烃源岩生烃增压是致密油充注成藏的主要动力,生烃物理模拟及盆地模拟过剩压力分别高达38MPa、25 MPa,远大于致密储层成藏阻力,具备大规模成藏的动力条件;微观上看致密油在充注过程中优先充注到相互连通的大孔隙中,其次才充注到小孔隙中,孔喉极小的储层石油难以充注;宏观上看,优先充注在紧邻优质烃源岩的连续式主砂带或透镜砂体中,然后逐步通过连通砂体、微裂缝等通道运移至与优质烃源岩不直接接触的连续式主砂带中,其运移规模及距离受成藏动力、储层物性条件控制。

The tight oil’s exploration and development of Ordos basin has made a great breakthrough. The complexity about the pressure and process of reservoir accumulation were resulted by the sedimento-tectonic setting,source-reservoir condition and their combinations. In this paper,theory calculation,mercury injection test,physical simulation of reservoir and basin simulation were used to analysis pressure condition. The reservoir-forming regularity of tight oil was researched by geochemical proxies,physical simulation of reservoir-forming and coupling process between reservoir diagenesis and oil accumulation. Furthermore classification and analysis of the source-reservoir combinations were used to study the assemblage rules and to summarize accumulation models of tight oil. Pressurization from hydrocarbon generation in the high-quality source rocks of the Chang 7 Member is the main accumulation dynamics of tight oil,which the excess pressure is up to 25-38 MPa,much larger than the accumulation resistance,and is the main dynamics of large-scaled accumulation. In the micro scale,the tight oil was firstly charged to the larger pore communicated with each other,then filled into the small pores. In the macro scale,the tight oil was priority charged to the continuous sand belt or lens sand close to the good hydrocarbon source rock,and then gradually migrated into the continuous sand belt,not directly contacting with the high quality hydrocarbon source rock,through the connected sand bodies and fractures. The migration scale and distance are controlled by the accumulation pressure and reservoir.