摘要
在井网压裂基础上进行注水，可以有效改善流场，增大泄油面积，是开发低渗透油藏的重要手段。快速准确预测低渗透油藏注水开发产量可以为开发优化设计奠定基础，但低渗透油藏注水开发呈现非稳态、非线性渗流特征，基于达西定律形成的油藏工程方法并不适用。本次研究通过流场分析，来划分等效流动单元，并在此基础上考虑了油水两相渗流启动压力梯度，采用流线积分法建立了不同压裂注采井网的水驱非稳态产量解析计算方法。与物理模拟及数值模拟相比，计算方法更简单，计算速度更快，可以为低渗透油藏压裂注采方式优选及注水开发对策制定提供手段。采用本方法计算并剖析了启动压力梯度、压裂注采方式及裂缝长度对油井生产动态的影响，结果表明：启动压力梯度增大了渗流阻力，与不考虑启动压力梯度相比，油井产量更低；受流动单元控制，不同压裂注采方式的增产效果及见水时间完全不同，同时压裂注采方式的增产效果最好，能够增产3.1倍，但见水时间仅为24个月；随着压裂缝长增加，油井产量越高，但当缝长超过最佳长度，增油效果不明显。
Abstract
Waterflooding in fractured reservoirs,an important way to develop low permeability reservoirs,can effectively improve the flow field effectiveness and increase oil discharge area. Rapid and accurate prediction of production of low permeability reservoirs with water injection can establish a foundation for optimal design of development. However,the flow field of water injecting into low permeability reservoirs presents unsteady and nonlinear flow characteristics,so the calculation methods based on Darcy's law are not applicable. After the analysis of flow fields,the equivalent flow units are divided. Taking the threshold pressure gradient of oil-water two-phase flow into consideration,we established the analytical calculation method for unsteady oil production with injection in different fracturing modes,based on the flow line integral method. And the method is simpler and faster compared with physical and numerical simulations,so it is applicable for optimizing fracturing injection and production well patterns and water injection development strategies in low permeability reservoirs. Besides,this method was used to calculate and analyze the effects of threshold pressure gradient,fracturing injection and production methods and fracture lengths on the productivity of oil wells. The results show that (1) the greater threshold pressure gradient leads to larger seepage resistance,so the well productivity is lower than that without considering the threshold pressure gradient; (2) the well productivity is controlled by flow units,so with different fracturing injection and production modes,the effects of production increase and the time of water breakthrough are completely different. Although the increase of production with simultaneous fracturing injection and production is the best,being 3.1 times that of other modes,the water breakthrough time is just 24 months; (3) with the increase of fracture length,the oil production increases,whereas the effect of increased oil production is not obvious any more when the fracture length exceeds the optimum length.
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