中低渗透储集层压驱提高采收率机理

The mechanism of hydraulic fracturing assisted oil displacement to enhance oil recovery in low and medium permeability reservoirs

针对压裂、渗流、驱油相结合的压驱技术研究需求,研发了压驱储能及反向压驱回注实验系统,模拟了压驱过程中压驱剂的渗流-储能-洗油-返排作用机理。研究表明:压驱技术将压驱剂直接输送至中低渗透储集层深部,可有效避免压驱剂在近井地带的黏度损失与黏附滞留,具有扩大波及体积、提高洗油效率、补充地层能量并将零散分布的剩余油汇集采出的效果。渗透率较高的储集层,压驱见效快,为降低成本,可直接采用高压注水压驱。渗透率较低的储集层吸水困难,采用表面活性剂压驱可有效降低储集层渗流阻力,提高储集层吸水能力与开发效果。地层能量亏空程度是影响压驱剂有效波及范围的主要因素,地层能量亏空越大,化学剂渗流距离越远,有效波及体积越大,采收率提高幅度越大;地层增能作用对提高采收率的贡献最大,是压驱技术提高采收率的关键。

Aiming at the technology of hydraulic fracturing assisted oil displacement which combines hydraulic fracturing,seepage and oil displacement,an experimental system of energy storage and flowback in fracturing assisted oil displacement process has been developed and used to simulate the mechanism of percolation,energy storage,oil displacement and flowback of chemical agents in the whole process.The research shows that in hydraulic fracturing assisted oil displacement,the chemical agent could be directly pushed to the deeper area of the low and medium permeability reservoirs,avoiding the viscosity loss and adhesion retention of chemical agents near the pay zone;in addition,this technology could effectively enlarge the swept volume,improve the oil displacement efficiency,replenish formation energy,gather and exploit the scattered residual oil.For the reservoir with higher permeability,this measure takes effect fast,so to lower cost,and the high pressure hydraulic fracturing assisted oil displacement could be adopted directly.For the reservoir with lower permeability which is difficult to absorb water,hydraulic fracturing assisted oil displacement with surfactant should be adopted to reduce flow resistance of the reservoir and improve the water absorption capacity and development effect of the reservoir.The degree of formation energy deficit was the main factor affecting the effective swept range of chemical agents.Moreover,the larger the formation energy deficit was,the further the seepage distance of chemical agents was,accordingly,the larger the effective swept volume was,and the greater the increase of oil recovery was.Formation energy enhancement was the most important contribution to enhanced oil recovery(EOR),which was the key to EOR by the technology of hydraulic fracturing assisted oil displacement.