特低-超低渗透砂岩储层微观水驱油特征及影响因素:以鄂尔多斯盆地马岭油田长8_1储层为例

Microscopic Waterflooding Characteristics of Extra-Ultra Low Permeability Sandstone Reservoir and Its Influence Factors: A Case from the Chang 8_1 Reservoir in Maling Oilfield in Ordos Basin

为了更加深入地探究特低-超低渗透储层油水的微观流动特征及其表现出差异性的因素,以马岭油田长8_1储层为代表,对典型样品进行了微观渗流实验,并结合物性、铸体薄片、扫描电镜、恒速压汞及核磁共振等多种实验测试结果对储层流体的微观驱替机理及导致驱油效率高低不同的因素进行了研究。结果表明:研究区块长8_1油藏按微观渗流通道类型可分为溶孔-粒间孔型、溶孔型、微孔型3类,其驱油效率逐类降低,不同微观渗流通道类型样品的渗流特征表现出较大的差异性,其中溶孔-粒间孔型样品平均驱油体积为0.010 cm^3,最终平均驱油效率高达45.60%,驱替效果最为理想。储层微观条件中,喉道半径大小及分布状况对驱油效率的大小起决定性的作用,物性和可动流体饱和度两者对驱油效率的大小均具有较低程度的控制作用;外部实验条件中,对驱油效率产生较大控制作用的为注入水体积倍数和驱替压力。因此,在油藏实际水驱采油过程中应当采用较为合理的注水压力和注入水体积倍数。

In order to further explore the microscopic flow characteristics of oil and water in extra-ultra low permeability reservoirs and the factors that show differences, this paper takes the Chang 81 reservoir of Maling Oilfield as the representative, and carries out microscopic seepage experiments on typical samples, and combines physical properties, cast thin sections, scanning electron microscopy, constant-velocity mercury intrusion and nuclear magnetic resonance to test fluids. This paper explores in detail the microscopic displacement mechanism and the factors that lead to different oil displacement efficiencies. The results show that the Chang 81 reservoir in the study block can be divided into three types: dissolved pore-intergranular pore type, dissolved pore type and microporous type. The oil displacement efficiency is reduced by class, and different microscopic seepage channel type samples are obtained. The percolation characteristics show a large difference. The average oil displacement volume of the dissolved pore-intergranular pore sample is 0.010 cm^3, and the final average oil displacement percentage is as high as 45.60%. The displacement effect is the most ideal. In the microscopic characteristics of reservoirs, the size and distribution of throat radius play a decisive role in the efficiency of oil displacement. Both physical properties and dynamic fluid saturation have a lower degree of control over the efficiency of oil displacement. Among the external experimental conditions the injection water volume and the displacement pressure are greatly responsible for the oil displacement efficiency. Therefore, a reasonable water injection pressure and volume of injection water should be used in the actual waterflooding process of the reservoir.