裂缝非达西渗流对气井水力压裂设计的影响

The effects of non-Darcy flow on design of hydraulically fractured gas well

水力压裂技术是低渗透致密气藏增产的主要手段。在水力压裂裂缝中,气体在裂缝内高速流动产生的非达西渗流使裂缝的有效导流能力和裂缝长度大大减小,从而影响了水力压裂井的产能。在考虑气体非达西渗流的基础上,建立了非达西渗流条件下裂缝有效渗透率和裂缝参数的计算方法,研究了非达西渗流对水力压裂设计参数(裂缝长度、宽度)和产能的影响。结果表明,考虑非达西渗流时的水力压裂必须设计比达西渗流条件下更短和更宽的裂缝;由于裂缝非达西渗流的存在,气井的产能也有较大幅度的降低。考虑非达西渗流进行水力压裂设计和计算时,不能直接用流体在多孔介质或裂缝中的真实渗透率来计算水力压裂气井的产量,而必须用非达西有效渗透率。

In recent years,non-Darcy flow has been the research point in the petroleum industry,especially for the hydraulically fracturing. Hydraulic fracturing is the current completion choice in many tight gas producing wells all over the world. The non-Darcy flow effects within the propped fracture are mainly due to high velocity and higher pressure drop in the fracture. The presence of non-Darcy flow in the hydraulic fracture reduces the effective conductivity and the propped half-length of the fracture significantly, and hence adversely affects the productivity of a hydraulically fractured gas well. Taking into account of the non-Darcy flow, this paper proposed the method for calculating the non-Darcy permeability in fracture,and then studied the effects of non-Darcy flow on the fracture design and gas well deliverability,and calculated subsequently non-Darcy permeability in fracture and the fracture length and width. The study results show that under non-Darcy flow effects,a shorter and wider fracture geometry has been formed,and the effective permeability in fracture decreases significantly; the non-Darcy effects influence gas production performance significantly, the reason is that,when taking into account of non-Darcy flow,the real permeability in porous media or in hydraulic fracture should not directly be used to forecast the production of oil and gas wells,the equivalent permeability should be calculated firstly.