致密油二次运移动力和阻力实验研究——以四川盆地中部侏罗系为例

Simulation experiments of tight oil secondary migration driving force and resistance:a case study of Jurassic oilfield in middle Sichuan basin

为阐明非常规致密油二次运移动力特征,以四川盆地中部侏罗系为例,基于实际地质参数解剖,采集研究区岩心样品开展了两类动力学模拟实验.通过实验数据和地质参数揭示了致密油二次运移的动力和阻力特征.认为在致密油的二次运移中,传统动力浮力无法克服运移阻力,烃源岩生烃产生的异常高压则能克服阻力成为主要动力.研究结果表明:致密油二次运移阻力在模拟实验中数值处于10 MPa数量级,对应地区浮力上限仅0.090 65 MPa.同时,现场致密油层中含水率极低,两个油田80%的产井含水率低于5%,表明浮力缺乏形成的物质基础.生烃增压实验则表明,研究区源岩生烃增压峰值可达38 MPa,足以克服阻力促使石油运移.生产数据表明,与烃源岩层紧密接触的致密油层异常高压越大,石油越富集,单井产量越高,揭示致密油的聚集受生烃增压的明显控制.运聚动力的不同,导致致密油与常规石油在运移距离和分布上的差异性,这种差异性成藏规律,对于油田勘探开发过程中针对不同类型油藏开展差异化勘探部署具有重要意义.

To analyze the characteristics of tight oil secondary migration driving force, Jurassic oilfield of central Sichuan basin was selected as the research object in this paper. Based on the physical analog experiments of core samples and the geological data of the oilfield, both the driving force and resistance of tight oil secondary migration were studied. It is discovered that during secondary migration of tight oil, traditional buoyancy cannot overcome the migration resistance of the tight reservoir, while abnormal overpressure caused by hydrocarbon generation is large enough to break through the resistance and become the major driving force. According to the physical analog experiments of secondary migration resistance, the magnitude of resistance is about 10 MPa, while the maximum value of buoyancy in the corresponding area is only 0. 090 65 MPa. Meanwhile, the production data of the oilfield also suggests that the water content of tight oil layers is extremely low, less than 5% among 80% of producing wells in the two oilfieds, which indicates the lack of material foundations for the formation of buoyancy. On the other hand, physical analog experiment of hydrocarbon generation pressurization proved that the maximum overpressure caused by hydrocarbon generation can reach 38 MPa, which is large enough to break through the resistance and speed up the secondary migration of tight oil. What＇s more, the production data suggests that the higher the abnormal overpressure in tight oil layers contacted with the source rock, the richer the oil accumulation and the larger the production of wells, which reveals that the tight oil accumulation is controlled by the overpressure caused by hydrocarbon generation. Different migration driving forces also result in different migration distances between tight oil and conventional oil. Acquiring these different oil distribution patterns is of great significance to the exploration of different kinds of petroleum resources.