玛湖致密砾岩油藏注烃类气混相驱油藏数值模拟

Numerical Simulation Research on Hydrocarbon Gas Miscible Flooding Reservoir in Mahu Conglomerate Reservoir

玛湖凹陷地区衰竭式开发直井初产高、递减快,常规注水开发不适应,通过注烃类气转换开发方式,可以大幅提高采收率。利用细管法测定注气试验区最小混相压力为41.71 MPa,玛湖地区目前地层压力条件下普遍可以实现混相驱;根据玛湖地区储层特征及地质力学参数,同时将天然裂缝及人工描述参与模拟,优化裂缝展布形态,建立了三维压裂缝网模型;基于压后缝网模型开展布井方式、注气速度及气驱油藏动用规律研究。结果表明,水力压裂平均缝网长轴173.90 m,最长846.90 m,短轴6.44 m;采油井部署井轨迹距顶2/3厚位置,气体波及范围更大;以维持混相为目标优化注气量,设计前10 a水平井单井日注气5.5×10^(4) m^(3),后10 a日注气4.0×10^(4) m^(3),试验区采收率可达22.5%;注入烃类会优先沿着采油井压后长压裂缝驱替,优先动用该区域原油,造成注气波及范围不均匀;随着烃类气体的注入,沿驱替前沿原油黏度大幅降低,同时,由于注入烃类气体与原油发生混相,通过蒸发气驱作用,注气5 a后采油井SRV范围内剩余原油黏度明显增大。此研究可以有效指导玛湖注烃类气体提高采收率试验现场开发技术政策制定。

The depleted development vertical wells in the Mahu sag area have high initial production and rapid decline.Conventional water injection is not suitable.Through the conversion of hydrocarbon gas injection can greatly improve the recovery rate.The minimum miscibility pressure in the gas injection test area determined by the slim tube method is 41.71 MPa.Miscible flooding can generally be achieved under the current formation pressure in the Mahu area.According to the reservoir characteristics and geomechanical parameters of the Mahu area,natural fractures and artificial descriptions are also included in the simulation,and optimization of the fracture distribution shape;and a three-dimensional fracture network model is established.Based on the post-fracturing fracture network model,researches on well layout mode,gas injection rate and gas drive reservoir production law are carried out.The results show that the average fracture network of hydraulic fracturing has a major axis of 173.90 m,a longest axis of 846.90 m,and a minor axis of 6.44 m;the deployment well trajectory of oil production wells is 2/3 thicker from the top,and the gas spread is larger;the gas injection rate is optimized with the goal of maintaining miscibility In the first 10 years of the design,55000 cubic meters of gas per day were injected into horizontal wells,and 40000 cubic meters per day in the next 10 years.The recovery rate of the test area can reach 22.5%;hydrocarbon gas will be preferentially displaced along the long pressure fractures of the production well after pressure,give priority to the use of crude oil in this area,resulting in uneven gas injection spread;with the injection of hydrocarbon gas,the viscosity of crude oil along the displacement front is greatly reduced.At the same time,because the injected hydrocarbon gas and crude oil are miscible,the gas is injected 5 years later.The viscosity of the remaining crude oil within the SRV range of the oil well increases significantly.Based on this research,it can effectively guide the formulation of technical policies for field development of the Mahu hydrocarbon gas injection enhanced oil recovery test.