滑脱和应力敏感效应对页岩气开发动态影响的数值模拟研究

Numerical Simulation on the Effects of Slippage and Stress Sensibility on the Performance of Shale Gas Development

  • 摘要: 滑脱和应力敏感效应是影响页岩气藏开发动态的2个重要因素,为定量研究其对产气量的影响,运用等效孔隙介质模型,建立了同时考虑滑脱和应力敏感效应的页岩气藏两相渗流数学模型,采用有限差分方法对该模型进行了数值求解,用Fortran语言开发了页岩气藏数值模拟器,在定产量和定压衰竭式开采条件下应用该模拟器研究了滑脱与应力敏感效应对页岩气井产能的影响规律,并将计算结果与美国Haynesville页岩气藏W3井的实际生产数据进行了对比。结果表明:衰竭式开发导致页岩气藏的压力和渗透率均降低,生产井附近储层压力和渗透率急剧降低;在投产第1年内,产气量虽迅速下降,但滑脱和应力敏感效应对产气量影响较小;生产500 d后,滑脱和应力敏感效应对产气量产生明显影响,滑脱效应使产气量增加,应力敏感导致产气量降低;模拟结果与生产数据的衰减趋势吻合度较高,证明该页岩气藏数值模拟器计算结果具有较高的可靠性。页岩气藏开发数值模拟器的成功研制,为页岩气井产能预测提供了一种新的有效手段。

     

    Abstract: Gas slippage and stress sensibility are two important factors which influence the development performances in shale gas reservoirs.To highlight their quantitative effects on gas production rates,a mathematical model with consideration of both slippage and stress sensibility in a two-phase flow in shale gas reservoirs was set up by using an equivalent porous media model, in which a finite difference method was used to solve the model. In addition, a numerical simulator of shale gas reservoirs was developed in Fortran(computer language).The effect of stress sensibility and gas slippage on gas well productivity was quantitatively studied by using the innovative simulator at a constant production rate and a specified bottom flow pressure in declining production.Numerical simulation results were then compared with field production data of Well W3 in a Haynesville shale gas reservoir.The numerical results showed that both formation pressure and permeability declined during depletion development of the gas reservoir and dramatical decline was observed near the wellbore region.In the first production year,shale gas production rate declined sharply;but slippage and stress sensibility displayed minor effect on the production rate.The effect of stress sensibility and gas slippage on production became more significant after 500 days of production.The decline curve closely tracked the simulation and history matching,and it thus validated the result calculated from a shale gas reservoir simulator with relatively high reliability.The successful development of a numerical simulator for shale gas reservoirs migth provide an innovative and effective approach for predicting gas production rates and decline curves.

     

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