考虑启动压力梯度下的火山岩气藏数值模拟研究

A numerical simulation of volcanic gas reservoirs under consideration of start-up pressure gradient

许进进 徐旭辉 凡哲元 胡建国 宋艳波 郭鸣黎 王树平

XU Jin-Jin XU Xu-Hui FAN Zhe-Yuan HU Jian-Guo SONG Yan-Bo GUO Ming-Li WANG Shu-Ping

由于火山岩气藏储层存在基质和裂缝双重介质、原始含水饱和度较高的特点,导致渗流过程中存在启动压力梯度的影响,常规砂岩气藏的单一介质、达西渗流理论已经不适用于此类气藏。从物质守恒理论出发,建立了考虑启动压力梯度的双重介质气、水两相渗流数学模型,利用有限差分方法进行数值求解,编写了数值模拟计算程序;结合室内实验研究结果,确定了模型中的相关参数的取值,渗透率小于0.1×10-3μm2、束缚水饱和度大于20%时,要考虑启动压力梯度的影响。利用XS气田实际单井进行数值模拟研究表明:模拟结果符合客观实际,考虑比不考虑启动压力梯度影响时的稳产时间、稳产期产气量、稳产期采出程度、最终采收率等生产开发指标小。在生产过程中,应考虑启动压力梯度对火山岩气藏生产开发的影响。

The Darcy flow theory suitble to conventional sandstone gas reservoirs with a single medium can not be applied to volcanic gas reservoirs,because they are characterized by the dual media of matrix and fracture and the higher original water saturation,resulting in an impact of star-up pressure gradient on a percolation process.According to the theory of mass conservation,a mathematical model of two-phase(gas and water) flow in dual media was built under consideration of start-up pressure gradient,for which the finite difference approch was used to obtain numerical solution and a calculation program of numerical simulation was compiled.In combination with laboratory experiment results,the values of this model parameters are determined,and it is shown that the impact of start-up pressure gradient has to be considered when permeability is lower than 0.1×10-3 μm2 and irreducible water saturation is over 20%.The numerical simulation results of a single well in XS gas field are consistent with the actual situation,and several indices of production and development,such as production plateau time,gas output during production plateau,recovery degree of production plateau and final recovery efficiency,are lower when the impact of start-up pressure gradient is considered than not.It is obvious that the impact of start-up pressure gradient has to be considered during the production of volcanic gas reservoirs.

10.11743/ogg20100216