裂缝性致密油藏直井体积改造产能评价模型

Deliverability Evaluation Model of Fracture Network Reconstruction Vertical Well in Fractured Tight Oil Reservoir

针对裂缝性致密油藏,基于拉普拉斯变换及Stehfest数值反演,建立了一种可用于直井体积改造产能评价的半解析两区复合模型,模型内区包含有限条无限导流水力裂缝,外区是经典的Warren-Root双重介质系统.并分析了导压系数比α、裂缝传导率比β、储容比ω、窜流系数λ以及改造半径re D等参数敏感性,绘制了产量递减图版。结果表明:从产量递减曲线,可以看出体积改造直井产能遵循"L"形递减规律;导压系数比越大,初期产量越高;裂缝传导率比对整个生产周期的产能都有影响,裂缝传导率比越大,单井产量越高,同时还会伴有明显的复合边界流特征;储容比和窜流系数分别影响双重介质基质-裂缝系统窜流发生的程度和时间;内区人工主裂缝条数越多或改造渗透率越大,复合边界流越明显,产能也越高,这说明改造程度与改造体积对产能的增加都很重要,应注意两者的合理优化。矿场实例验证了该模型在裂缝性封闭边界油藏直井多次压裂改造以及裂缝性致密油藏直井体积改造方面的适用性和实用性。

In this study,based on Laplace transformation and Stehfest numerical algorithm,a vertical well frac-ture network reconstruction semi-analytical deliverability evaluation model which can be used for fractured tight oil reservoirs was established.The proposed model is a composite system with two concentric regions.The inner region contains finite number of hydraulic fractures and the flow in each fracture is assumed linear.The outer region is modeled with the classical Warren-Root model and radial flow takes place in this region.The influ-ences of related parameters,such as diffusivity coefficient ratio,fracture conductivity ratio,storativity ratio, cross-flow factor and so forth,on the seepage flow were analyzed by using the established model.The results show that the deliverability follows the “L”shaped decline law.Diffusivity coefficient ratio has effect on initial production.The bigger diffusivity coefficient ratio is,the higher initial production is.Fracture conductivity ratio has great impact on whole production cycle.Storativity ratio and cross-flow factor influence degree and occur-rence time of cross-flow respectively.When artificial fracture numbers or permeability is larger,coupled bound-ary flow is more obvious and productivity is higher,which shows that reconstruction volume and reconstruction degree both are important to deliverability,we also should pay attention to the reasonable optimization of both parameters.What’s more,two wells’ produce data were fitted,and some reasonable parameters were explained,which can prove the practicability of this model.