空间变导流能力压裂井CO2驱试井分析

目前利用压裂井进行CO2驱已成为低渗透油藏开发的主要技术之一,水力裂缝导流能力是决定开发效果的关键因素,而试井研究多采用与实际不符的恒定缝宽假设对水力裂缝进行描述。基于三区复合理论,建立考虑空间变导流能力压裂直井的CO2驱试井模型,通过Laplace变换进行求解,进行数值反演,绘制典型试井曲线。典型曲线可分为井筒储集段、井筒储集后过渡段、双线性流段、地层线性流段、第一径向流段、第一过渡流段、第二径向流段、第二过渡流段、第三径向流段共9个阶段。对模型影响因素进行分析,裂缝导流能力越大,双线性流段阶段压差越小,CO2越容易注入;考虑裂缝导流能力变化后,早期压差增大,压力及压力导数曲线都呈现一定的上升,表现出类似表皮系数增大的现象;CO2及过渡区半径主要对径向流的持续时间及过渡流出现时间产生影响,半径越大,对应过渡流出现的时间越晚;一区与二区流度比越大,过渡区及最外区流动阶段所消耗的压差越大;二区与三区流度比,最外区流动阶段所消耗的压差越大。

Pressure transient analysis of hydraulic fractured vertical wells with variable conductivity for CO2 flooding

At present,CO₂ flooding with hydraulic fractured vertical wells has become one of the main technologies for the development of low permeability reservoirs. Hydraulic fracture conductivity is a key factor influencing the production performance of fractured wells,and now most well test models were based on the assumption of a constant fracture width,failing to simulate the space variable width of hydraulic fractures. Based on three-zone composite theory,a CO₂ flooding well test model of hydraulic fractured vertical wells considering with variable conductivity was established, and the Laplace transformation was adopted to solve this model, and then the numerical inversion was carried out to draw typical well test curve. According to the pressure response characteristics, the pressure transient type curve was divided into nine stages including wellbore storage stage,skin effect stage, bilinear flow stage,linear flow stage,the first radial flow stage,the first transition stage,the second radial flow stage,the second transition stage and the late radial flow. Sensitivity analysis was carried out to investigate the influence of several factors on pressure transient. The results show that the larger the fracture conductivity was,the smaller the pressure of the bilinear flow stage was,and the easier CO₂ can be injected. When the space variable conductivity was considered,the pressure of early flow stages increased,and the pressure and pressure derivative curve of early flow stages rised which was similar to the effect of a larger skin factor. The radius of region-1 and region-2 mainly had an influence on the starting time of transition stage and the duration of radial flow. When the radius of region-1 and region-2 was larger,the start time of the transfer stage was prolonged. When M₁₂ was enhanced,the pressure of the flow in both region-2 and region-3 was larger. When M₂₃ was enhanced,the pressure of the flow in region-3 elevated.