低渗透裂缝型碳酸盐岩酸压气井动态特征分析

低渗透裂缝型碳酸盐岩基质低孔低渗、天然裂缝发育,目前存在的酸压气井动态特征模型没有同时考虑储层基质低孔低渗引起的非达西渗流以及储层裂缝发育造成的储层应力敏感效应。为了分析低渗透裂缝型碳酸盐岩气藏酸压后渗流特征和产量递减规律,建立了考虑酸压改造程度、酸压改造范围、流体低速非达西流动、储层应力敏感的酸压气井渗流模型。首先针对气体拟压力形式的非线性非齐次的渗流方程进行Laplace空间变换,在Laplace空间利用摄动理论线性方程解的叠加原理进行求解,其次基于Duhamel叠加原理考虑了井储和表皮对渗流的影响,采用Stehfest数值反演方法得到实空间酸压气井不稳定产量和压力解,最后基于典型曲线特征分析了四类因素对酸压气井产量递减和井底压力动态特征的影响。结果表明:低渗透裂缝型碳酸盐岩酸压气井存在8个流动阶段,基质-裂缝窜流具有减缓产量递减速率的作用;低速非达西在生产中后期对产量递减影响明显,会削弱窜流对产量递减的补偿作用且明显降低气井产能;应力敏感在生产后期对产量递减的影响凸显,对气井递减率和产能影响较小;改造程度越高,产量递减率越大且产能下降越明显;改造范围越大,气井递减速率越稳产。结论认为:实际低渗透裂缝型碳酸盐岩气藏产能分析中,低速非达西渗流对产能的影响大于应力敏感对气井产能的影响;若以保持酸压气井稳定的产量递减速率为目标,增大改造范围比增大改造程度更重要。

Dynamic Characteristic Analysis for Acid Fracturing Gas Well of Low Permeability Fractured Carbonate Reservoir

In order to analyzed the transient production performance and transient pressure behavior of acid fracturing gas well of low permeability fractured carbonate reservoirs, the dynamic characteristic analysis model, considering acid fracturing degree and area, stress sensitivity, low-velocity Non-Darcy flow, was established. Logarithmic transformation and perturbation method are used to obtain the rate and pressure transient solution. The research results show that: First, there are eight flow stages in low permeability fractured carbonate acid fracturing gas well, inter-porosity flow can offset production decline. Second, low-velocity non-Darcy flow is obviously affected in middle and late stage, which will weaken the compensation effect of inter-porosity flow and reduce gas well productivity. Stress sensitivity is prominent in late stage, which has little effect on gas productivity and decline rate. Third, the higher the acid fracturing degree, the faster the decline rate, the more obvious the decrease of production performance. The bigger the area of acid fracturing reconstruction the stronger the stable production capacity. It is concluded that low-velocity Non-Darcy flow and stress sensitivity should be considered in low permeability fractured carbonate gas reservoir, and acid fracturing should be based on increasing the scope of construction in order to maintain the stable production capacity.