基于数字岩心的低渗储层孔隙结构及水驱剩余油分布特征

Pore Structure of Low-permeability Reservoir and Distribution Characteristics of Remaining Oil after Water Flooding Based on Digital Core

针对低渗砂岩储层水驱开发后期剩余油形成机理和赋存状态不清等问题,以涠洲11-1和涠洲12-1油田低渗砂岩为研究对象,基于Micro-CT扫描技术构建了储层三维数字岩心模型,提取连通孔隙结构并定量表征岩样微观孔隙结构特征,建立了非结构化四面体网格模型。基于N-S方程和水平集算法建立了油水两相微观渗流数学模型,采用有限元方法求解模型,开展了微观水驱油流动模拟。研究结果表明:孔喉大小及连通性是决定储层渗透能力的主要因素;微观水驱油模拟中可以观察到明显的黏性指进现象,水驱剩余油主要以网状剩余油、盲端孔隙剩余油、小孔喉滞留剩余油、并联孔道剩余油及油膜形式存在;提高注水强度可有效动用网状剩余油及小孔喉滞留剩余油,改善油水黏度比可获得更大波及体积,改善润湿性则可有效动用盲端孔隙及亲油孔道内剩余油。研究成果对低渗油藏水驱剩余油挖潜具有指导意义。

To address the unclear understanding of formation mechanism and occurrence of remaining oil in the late stage of water flooding of low-permeability sandstone reservoirs,a three-dimensional digital core model of the reservoir was established based on Micro-CT scanning technology to extract the inter-connected pore structure and quantitatively characterize the microscopic pore structure of rock samples,and an unstructured tetrahedral grid model was established,taking the low-permeability sandstone of Weizhou 11-1 and Weizhou 12-1 oil fields as the study object.On the basis of N-S equation and level set algorithm,a mathematical micro seepage model of oil-water flow was established,and the finite element method was used to solve the model,the micro water-oil displacement flow was simulated.The results of the study show that the pore throat size and connectivity are the key factors to determine the permeability of the reservoir.Viscous fingering can be found in the micro water-oil displacement simulation.The remaining oil after water flooding are mainly in the form of reticulated remaining oil,remaining oil in pores with dead ends,remaining oil in small pore throats,remaining oil in parallel pore channel,and oil film.With the improved water injection intensity,the reticulated remaining oil and retaining oil in small pore throats can be recovered effectively.After the oil-water viscosity ratio is improved,the sweep volume can be increased.With enhanced wettability,the remaining oil in pores with dead ends and in oil-philic pores can be recovered effectively.The results of the study are of guiding significance for further developing the remaining oil after water flooding in low permeability reservoirs.