低渗透油藏菱形反九点井网不等缝长优化研究
Optimization Study of Unequal Fracturing Length for Rhombus Inverse Ninespot Well Pattern in Low Permeability Reservoir

摘要： 在低渗透油藏开发中广泛使用菱形反九点井网，但针对不同位置生产井及注水井的裂缝缝长配比关系还缺少广泛深入的研究。基于长庆油田某低渗透油藏参数，建立了数值模拟模型，在菱形反九点井网中分别设置不同的边井、角井和注水井裂缝穿透比，研究不同裂缝配置模式对水驱开发效果的影响。流线模拟及数值模拟计算结果表明，在注水开发中，注水井缝长是影响油田产液量及水驱效果的关键因素；边井裂缝较角井裂缝更易见水，对油田综合含水影响较大，在菱形反九点井网中需要进行不等缝长优化设计；边井裂缝缝长对水驱效果的影响分为早、中、晚期(Ⅰ、Ⅱ、Ⅲ)曲线段，随着注水井裂缝穿透比增加，早期(Ⅰ)曲线段增长，中期(Ⅱ)曲线段缩短，而晚期(Ⅲ)曲线段变化较小；随着角井裂缝穿透比增加，采出程度逐渐增大，当角井裂缝穿透比较大时，存在“反转”现象；随着注水井裂缝穿透比增加，角井裂缝优化穿透比减小，而边井裂缝优化穿透比增加。该研究成果对于指导低渗透油藏菱形反九点井网裂缝优化设计，提高波及系数和开发效果具有重要的指导意义。
Abstract: The inverse rhombus ninespot well pattern is widely used in the development of low permeability reservoirs, but there are few extensive and intensive studies for the fracture length ratio of production wells and waterinjection wells at different locations. Based on the parameters in a low permeability reservoir of Changqing Oilfield, a numerical simulation model was established. In this paper, to study the different configuration modes effect of fracture waterflooding, different fracture lengths were disposed in the side parts of the production wells, the corners of the production wells and injection wells at the inverse rhombus ninespot well pattern. Streamline simulation and numerical simulation results show that the fracture length of injection wells is key to reservoir fluid production and water flooding effect. The fracture of side portion of the production wells is easier to flow into the water compared with the fracture at the corner section of the production wells, and has a great influence on the watercut of the reservoir. In the inverse rhombus ninespot well pattern, it is required to optimally design unequal lengths of fractures in low permeability reservoir. Fractures effects of the length of the side parts of the production wells on waterflooding development can be divided into three distinct phases. With the length of the injection wells fracture increasing, the early (Ⅰstage) curve becomes long, the medium term (Ⅱstage) curve is shortened, and the later period (Ⅲstage) curve almost has no change at all. With the increase of the fracture length at corner section of a production well, oil recovery of the reservoir increases, and there exists a “reversal” phenomenon when the fracture length is too long at corner section of a production well. With the fracture length of injection wells increasing, the optimum fracture length at the corner section of the production well is reduced, while the fracture length of the side parts of the production well increases. The research results have important guiding significance for optimizing the crack design, improving the sweep coefficient