低渗透气藏产水气井产能评价新方法

NEW PRODUCTIVITY EVALUATING METHOD OF THE WATERPRODUCING GAS WELL IN LOW-PERMEABILITY GAS RESERVOIRS

存在边水、底水及层间水的低渗透气藏开发到一定程度后会出现气水两相流的情况,由于气水两相流气藏的渗流规律不同于普通低渗透气藏,对此类气藏产能的准确评价成为合理、高效开发的关键。从矿场实际生产情况可知,产水气井在生产时水气质量比难以稳定,如果仍将水气质量比当作定值来分析气井产能就会得出错误的结论。因此,考虑不同工作制度下水气质量比不同,考虑储层应力敏感、启动压力梯度、气体滑脱效应以及表皮污染,基于稳定渗流理论推导出产水气井的产能公式。通过实例计算,新公式计算的无阻流量结果与实际产能测试结果相对误差为3.7%,说明新公式是可靠的。且水气质量比随井底压力减小而增加,说明计算产水气井产量时将水气质量比设为定值并不合理。对敏感性因素分析发现,气井产气量随着滑脱因子增大而增大,而随着启动压力梯度以及应力敏感指数的增大而减小,启动压力梯度对气井产量影响很小,基本可以忽略。

When the low-permeability gas reservoir with the edge water,bottom water or interlayered water exploited to a certain extent,two-phase seepage phenomenon appears.The seepage laws in the reservoir with two-phase( gas and water) flow are alien to the common one,so the accurate productivity evaluation of this kind of the gas reservoir has become the key to the reasonable and high-efficiency development.According to the field production and operation conditions,the water-gas mass ratio is variable under the working condition of the water-producing gas well,if the mass ratio is regarded as the constant value to analyze the productivity of the gas well,wrong results will occur.Therefore,considering the water-gas mass ratio changed with different working systems,taking the stress sensitivity,start-up pressure gradient,gas slippage effect and skin contamination into consideration,the productivity formula is deduced for the water-producing gas wells based on stable percolation theory.The calculation of the case study shows that the relative error in the open-flow capacities calculated by the new formula and actual pro-ductivity test is 3.7%,which indicates that the new formula is reliable.What's more,the water-gas mass ratio increases with the decrease of the bottom hole pressure,which shows that it is not rational to keep the water-gas mass ratio constant to calculate the gas production.Moreover,the sensitivity analyses indicate that the gas production rises with the growth of the slippage factor,while decreases with the growth of start-up pressure gradient and stress sensitivity index.However,the influence of the start-up pressure gradient on the gas yield is so small that can almost be ignored.