底水气藏非稳态流动水侵量和动储量预测模型研究

Study on Prediction Model for Unsteady Water Influx Rate and Dynamic Reserves of Gas Reservoirs with Bottom Water

底水气藏非稳态水侵量一般采用V-H模型,该模型假设水的渗流方向为平面径向流动,与底水气藏垂直方向渗流特征不符,会对气藏的水侵量和动储量预测产生偏差。针对该问题,考虑底水垂直方向上的流动,引入无因次水层厚度,建立了底水气藏非稳态水侵量计算模型。通过数值反演求解水侵量,回归了底水气藏非稳态水侵量经验公式。通过与物质平衡方程的耦合,形成了底水气藏动储量求解方法。研究表明:无因次水层厚度对水侵量影响显著,无因次水层厚度较小时,水侵呈现先线性流动后径向流动特征,预测水侵量大于V-H模型;当无因次水层厚度较大时,水侵呈现半球形流动特征,预测水侵量小于V-H模型。将研究成果应用于东海BD气田H4断块背斜底水气藏,结果表明,新方法预测底水水侵速度比边水模型快,预测压力拟合效果要好于V-H模型,更符合底水气藏水侵实际特征。研究成果对提高底水气藏动储量计算精度有重要意义。

The V-H model is generally adopted to predict the unsteady water influx rate of gas reservoirs with bottom water,with the water seepage direction assumed as the planar radial flow,which is inconsistent with the vertical seepage characteristics of gas reservoirs with bottom water,leading to a deviation in the prediction of water influx rate and dynamic reserves.To solve this problem,a model for calculating the unsteady water influx rate of gas reservoirs with bottom water was established with consideration of the vertical flow of bottom water and the dimensionless aquifer thickness.By solving the water influx rate through numerical inversion,an empirical equation for the unsteady water influx rate of gas reservoir with bottom water was regressed.Coupled with the material balance equation,a method was developed to work out the dynamic reserves of gas reservoirs with bottom water.It is found in the study that the dimensionless aquifer thickness has a significant impact on the water influx rate.If the dimensionless aquifer thickness is small,the water influx flows linearly first and then radially,and the predicted water influx rate is greater than that of the V-H model.If the dimensionless aquifer thickness is large,the water influx flows hemispherically,and the predicted water influx rate is smaller than that of the V-H model.The study results were applied to the anticlinal gas reservoir with bottom water in H4 Fault Block,BD Gas Field,the East China Sea.The results show that the new method is faster than that of edge water model in predicting the bottom water influx rate,and the fitting effect of the predicted pressure is better than the V-H model,which is more consistent with the actual characteristics of water invasion in the gas reservoirs with bottom water.The study results are of great significance to improve the calculation accuracy of dynamic reserves of gas reservoirs with bottom water.