页岩气井吸附气产出贡献率确定方法

A Method for Determining the Contribution of Adsorption Gas to the Production of Shale Gas Wells

  • 摘要: 为解决页岩气生产过程中吸附气产出量对产气量的贡献率难以确定的问题,基于地层压力分布计算模型、吸附气产量计算模型和游离气计算模型,建立了考虑应力敏感、扩散和吸附等因素的多段压裂页岩气水平井吸附气产出量对产气量贡献率的确定方法,通过国内页岩气井验证了该方法的实用性。研究发现:利用该方法可分别计算得到生产过程中的地层压力分布、储量变化和吸附气与游离气产出量的变化;实例井吸附气原始储量约为游离气原始储量的30%,但由于Langmuir吸附压力(6 MPa)远低于该井目前的井底压力(12 MPa),吸附气解吸不明显;虽然该井已生产了25 000 h,但吸附气产出量对产气量的贡献率只是由开始生产时的9.0%上升到了10.5%,由此可见,国内部分页岩气藏虽然吸附气储量可观,但其对页岩气产量的贡献有限,且采出程度很低。研究认为,该方法可为页岩气井压裂后效果评价、产气量和动态储量评估提供理论参考。

     

    Abstract: A better method for determining the contribution rate of adsorption gas during the shale gas production after multi-stage fracturing,was developed that takes into consideration stress sensitivity,diffusion and adsorption according to three models,(i.e.formation pressure distribution computation model,adsorption gas production computation model and free gas production model).The goal was to develop a procedure for practical application in domestic shale gas wells.The results showed that the method could be used to calculate the formation pressure distribution,the change of dynamic reserves,output of adsorption gas and free gas.The results were also successful in that they show that although original reserve of adsorption gas accounts for about 30% of that of free gas,the desorption is not obvious due to the Langmuir adsorption pressure(6 MPa)is lower than the current bottom-hole pressure(12 MPa).Although this well has been put into production for 25 000 h,the adsorption gas production is only increased from initial 9.0% to 10.5% now.Somewhat surprisingly,research results indicated that the contribution of adsorption gas was limited in spite of its considerable reserves in some Chinese shale gas reservoirs,and ultimate recoverable reserves were very low.This method can provide some theoretical references for future improvements of the fracturing performance,and for better modeling of the production and dynamic reserves in a shale gas well.

     

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