低渗油藏垂直裂缝井产量递减规律

Production Decline Laws for Vertical Fracture Well in Low- permeability Oil Reservoirs

油气藏改造时受地层复杂地应力的影响,压裂形成的垂直裂缝通常关于井筒不对称或裂缝左右两翼不在同一平面。针对垂直裂缝的特征,基于不稳定流理论,应用势理论、势叠加原理和数值分析方法,推导出低渗油藏垂直裂缝井产量动态预测模型,并利用实例分析了油井产量动态递减规律。结果表明,低渗油藏垂直裂缝井产量递减规律表现为油井初期产量较高,油井产量递减速度较快,而中后期油井产量进入缓慢递减阶段;裂缝非对称率对油井产量变化的影响较小,在开发初期,不共面夹角对油井产量变化的影响较大,油藏非均质性强弱对油井产量变化影响显著;裂缝长度越长,裂缝导流能力越大,油井产量越高,产量递减速度越快;随着裂缝长度和导流能力增加,产量增幅逐渐变小。

The vertical fracture is asymmetrical about the wellbore or the two wings of the fracture are not certainly in a line for the complex geo-stress in the possession of fracturing of oil gas reservoirs. In view of the low-permeability reservoir after fracturing developing the asymmetrical vertical fractures and non-coplanar fractures, based on the non-steady seepage theory, and using the potential function theory, superimposition principle and numerical analysis method, a dynamical prediction model for the vertical fracture in low- permeability oil reservoirs is deduced with the pressure drop superposition principle. The production decline laws are analyzed with practical cases. The result shows that the production of the vertical fracture well is initially high but soon followed by a sharp decline. Then, the production keeps in a relatively stable state and declines slowly in the middle and later. The fracture asymmetry factor has a little effect on the oil well productivity. The non-coplanar angles have a greater effect on the oil well productivity in the initial stage. The reservoir heterogeneity has a significant effect on the oil well productivity. The longer the fracture length and the bigger the flow conductivity, the higher the oil well production and the faster the decline rate will be. However, the increase amplitude will be getting smaller and smaller with the increasing fracture length and flow conductivity.