低渗气藏考虑启动压力梯度的单井数值模拟

SINGLE WELL NUMERICAL SIMULATION OF LOW-PERMEABILITY GAS RESERVIOR WITH CONSIDERATION OF STARTING PRESSURE GRADIENT

在已发现的天然气储集层中,低渗透、特低渗透储集层占相当大的比例,且这类储集层中流体渗流较为复杂,具有独特的渗流特征(即存在启动压力现象),流体在多孔介质中的流动不再符合达西定律,因此重视并研究启动压力现象对低渗气藏的开发有着十分重要的意义。而目前的大型油气藏数值模拟商业化软件中都没有考虑启动压力梯度的影响。为此,在渗流力学基础上建立了考虑启动压力梯度的三维气、水两相流数值模型,并编写了相应的数值模拟软件。通过与商业化软件CMG的计算结果对比分析认为本软件是合理、可靠的。然后通过本软件对气井在不同启动压力梯度情况下的模拟计算结果表明,启动压力梯度对低渗透气藏气井的生产动态的影响非常显著,如果不考虑启动压力梯度将导致预测的产量等开发指标明显偏高。因此,在进行生产动态的方案预测时应充分考虑启动压力梯度的影响,以使编制的开发方案能更加准确地指导低渗气藏的开发。

In the gas reservoirs having been discovered,low permeability and extra-low permeability reservoirs take up a rather high proportion,and fluid percolation in these reservoirs is relatively complex and has special percolation characteristics(i.e.the existence of starting pressure).Besides,the flow of fluids in porous media is not accordant with the Darcy's Law.Therefore,it has a great significance for the development of low permeability gas reservoirs to study and pay attention to the starting pressure phenomena.However,the influence of starting pressure gradient is not taken into account in the large-scale commercial software of reservoir numerical simulation.Thereby,three-dimensional,gas-water two-phase-flow numerical model has been established on the basis of seepage mechanics with the consideration of starting pressure gradient and the corresponding numerical simulation software has been programmed.By the comparison with calculation results of commercial software-CMG,it is believed that the software programmed is reasonable and reliable.Then,by means of simulation calculating of the gas field at different starting pressure gradients,the results show that starting pressure gradient has significant effect to the production performance of the low-permeability gas reservoir in gas fields.Development index,such as production prediction,will be obviously higher without regard to the starting pressure gradient.Therefore,the effects of the starting pressure gradient should be fully considered when predicting the program of the production performance,so as to work out the developing program which can guide the development of low-permeability reservoirs more accurately.