适用于有水气藏的新型水驱特征曲线应用

Application of New Waterflooding Characteristic Curve for Water-bearing Gas Reservoirs

水驱特征曲线在有水气藏动态储量和可采储量计算上的应用饱受争议,传统水驱特征曲线认为地层压力保持不变的假设条件与有水气藏地层压力下降的事实不符,且相对渗透率曲线在低、高含水饱和度时拟合不准确。为解决上述两大问题,对气水相渗比与含水饱和度半对数曲线进行了重新拟合,提出了气水相渗表征新方法,提高曲线拟合精度。在此基础上,从气水两相渗流规律与物质平衡原理出发,考虑有水气藏水体活跃程度,引入水侵常数,推导出了适合有水气藏的新型水驱特征曲线,采用遗传算法自动拟合确定水侵常数与动态储量。根据拟合得到的水侵常数与动态储量,结合废弃水气比,还能实现生产水气比预测和可采储量标定。通过涩北气田4口真实产水气井的生产数据对新型水驱特征曲线的准确性进行论证,结果表明气水相渗表征新方法更加准确,新型水驱特征曲线拟合相关系数大于0.85;新型水驱特征曲线计算得到的动态储量与物质平衡法误差为3.52%,且避免了有水气藏水侵后压降曲线下掉造成的计算误差。可见新型水驱特征曲线对有水气藏储量计算及生产预测具有一定的指导意义。

The application of waterflooding characteristic curve in the calculation of dynamic reserves and recoverable reserves of water carrying gas reservoirs is controversial.The assumption of constant formation pressure in traditional waterflooding characteristic curve is inconsistent with the fact that formation pressure drops in water carrying gas reservoirs,and the relative permeability curve is not accurately fitted at low water saturation or high water saturation.In order to solve the above two problems,the gas-water phase permeability ratio and water saturation semi-log curve were fitted,and a new gas-water phase permeability characterization method was proposed,which improved the curve fitting accuracy.On this basis,a new waterflooding characteristic curve suitable for water carrying gas reservoirs was derived by taking into account the active degree of water body and the water invasion constant in combination with the gas-water two-phase seepage law and the principle of material balance.The equation can be automatically fitted by genetic algorithm to determine the water invasion constant and dynamic reserves.According to the fitting water invasion constant and dynamic reserves,combined with waste water gas ratio,the production water gas ratio prediction and recoverable reserves calibration can be realized.Based on the production data of 4 real water-producing gas wells in Sebei gas field,the accuracy of the new waterflooding characteristic curve was demonstrated.The results show that the new method is more accurate,and the correlation coefficient of the new waterflooding characteristic curve is greater than 0.85.The dynamic reserve error calculated by the new waterflooding characteristic curve and the material balance method is 3.52%,and the new waterflooding characteristic curve avoids the calculation error caused by the drop of pressure drop curve after water intrusion in the water carrying gas reservoir.It can be seen that the new waterflooding characteristic curve has certain guiding significance to the calculation of water carrying gas reservoir reserves and production prediction.