裂缝面非均匀流入的气藏压裂水平井产量计算

Yield calculation of a fractured horizontal well with a non-uniform gas flow on fracture surface

低渗透油气藏压裂水平井以形成多裂缝来提高产量,但由于裂缝内流动压力损失和裂缝段间干扰,导致气体沿裂缝面非均匀流入。为了准确预测气藏压裂水平井的产量,基于瞬时点(线)汇函数和叠加原理,考虑气藏压裂水平井裂缝干扰、裂缝面产量非均匀流入以及裂缝内变质量流动,采用空间和时间离散技术,建立了气藏压裂水平井储层渗流和裂缝内流动耦合的产量预测模型。应用结果表明:考虑裂缝无限导流会导致计算结果高于实际产量;而裂缝上均匀流入的假设使得计算结果低于实际产量;由于裂缝干扰,水平井筒两端裂缝的产量高于中间裂缝;由于裂缝上的非均匀产量流入以及裂缝内的摩阻损失,裂缝上产量在水平井筒附近出现局部峰值;随着时间增加,峰值降低并且产量从裂缝中间位置向两端转移;裂缝上产量分布受生产时间和裂缝导流能力的影响,生产时间越长,导流能力越大,裂缝上产量分布越均匀。将所建产量预测模型计算结果与实例井和传统模型计算结果进行了对比,其吻合程度高、可靠性强。

The productivity would be enhanced dramatically through fracturing horizontal wells in low permeability reservoirs. Due to gas flow pressure loss and inter-fracture interference, there exists a non-uniform gas rate along fracture faces. In order to predict the flow capacity accurately, this paper applied the instantaneous point sink （congruence） function and the superposition principle, taking into account fracture interference, non-uniform gas flow rate, and fracture inner variable mass flow to set a flow rate prediction model, which also considering the coupling effect of reservoir seepage flow and fracture inner flow. Conclusions were made as follows. First, if fractures are treated as infinite conductivity, the calculated productivity will be higher than that of the actual yield, while if a uniform rate on fracture faces is assumed, the calculated result will be rather lower. Second, due to the fracture interference, the flow rates from the fractures at two ends are higher than those from the middle fractures; and due to a non-uniform flow on fracture faces and fracture inner friction loss, a flow rate peak appears in the fractures close to the wellbore. However, the peak decreases with time and the flow rate transfers from the middle to the ends. And finally, the flow rate distribution of fractures is af- fected by producing time and fracture conductivity, in particular, the flow rate distribution is becoming uniform with the increment of the producing time and fracture conductivity. Compared with the conventional models, calculation results achieved by this proposed model are in a better agreement with the measured data from an actual well.