裂缝性油气藏压裂水平井试井分析

Well test analysis of fractured horizontal well in fractured reservoir

关键词:  油藏  裂缝  双重介质模型  压裂水平井  试井  点源函数

Key words:  reservoir  fracture  dual porosity model  fractured horizontal well  well test  source function

摘要:

利用Green函数源函数法,通过镜像映射和叠加原理得到裂缝性油气藏水平井多段压裂改造后地层中任意一点的压力解。首先推导顶底封闭四周无限大、盒状及定压条件下单条裂缝生产时地层中任意一点在拉氏空间的压力计算公式,并假设水平井井筒无限导流,进一步建立水平井多段压裂改造后井底压力求解方法。基于Stehfest数值反演得到考虑井筒存储和表皮系数影响的水平井井底压力解。对不同边界条件下井底压力及压力导数的双对数曲线进行分析,并分析压裂裂缝参数对井底压力响应的影响。结果表明:压裂水平井存在压裂裂缝线性流、压裂裂缝径向流、地层线性流、系统径向流及边界影响五种流动阶段;同时由于油藏为双重介质油藏,所以还存在基质系统向裂缝系统的窜流;裂缝条数越多,生产相同的时间时井底无因次压降越小,但当压力波传到边界后裂缝条数不再对流动造成明显影响;裂缝半长会影响压裂裂缝径向流出现的时间及地层线性流之前的压降,且压裂裂缝越长,压裂裂缝径向流出现的时间越晚,生产相同的时间所需要的无因次压降越小;裂缝间距会影响裂缝径向流结束的时间,且缝距越小,裂缝径向流持续的时间越短。现场应用结果证明了模型的正确性。

Abstract:

Based on Green 's function and source functions, the analytical solution of pressure in a horizontal well with multiple hydraulic fractures was obtained by using mirror-injection and superposition theorem. At first, pressure drop was derived in three different conditions:infinite surrounding, prescribed flux and prescribed pressure when the top and bottom of the formation were prescribed. Then, new solutions of the wellbore pressure were described assuming that the wellbore of the horizontal well had infinite flow conductivity. According to Stehfest numerical inversion, the pressure drop was derived considering wellbore storage and skin factor. The pressure plots and pressure derivative curves on different conditions in the fracturing horizontal and the influence of fracturing parameters were analyzed. The results show that there are five flow regimes including fracturing linear flow, fracturing radial flow, formation linear flow, system radial flow and bound influence. For a dual porosity model, cross flow exists which flows from matrix system to the fracture system. In dimensionless form, pressure drops when the fracturing number rises. However, when the pressure wave reaches the boundary, the fracturing number has little effect on the flow. The fracture length influences both the time when the fracturing radial flow appears and the pressure drop before forming linear flow. Under the same production time, the longer the fracture length, the later the fracturing radial flow appears and the less the dimensionless pressure drops. The spacing between two fractures influences the time when the fracturing radial flow ends; when the spacing is smaller, the time for fracturing radial flow lasts shorter. The results are verified in engineering application to prove the feasibility of the models.