煤系地层合采气井生产动态预测及效果分析

    Dynamic prediction and effectiveness analysis of co-production gas wells in coal-bearing formations

    • 摘要: 煤层、致密气储层上下叠置是煤系地层常见的地质构造,阐明上下叠置关系的煤层气-致密气合采井生产动态对煤系资源协同开发具有重要意义。首先研究煤层气、致密气单独开发下产气特征、产水特征与储层平均压力演化特征,接着通过井筒节点分析方法迭代计算变质量流情况下压降分布特征,以井筒压降为纽带耦合煤层、致密层层间压力相互干扰与各层产出特征,最后建立了“上煤层下致密层”叠置关系的合采井产气动态预测模型。分析了不同生产制度下合采井稳产能力与各层产出贡献演化规律,研究结果表明:①合采井稳产年限(平均2 158 d)显著长于煤层气单独开发;②共用一套井筒的合采井累计产气量与多次钻井单独开发情况仅相差2.56%,显示了煤层气-致密气合采较强的经济效益;③由于煤层气前期单相排水的典型特征,煤层气对合采井产气的贡献呈现前期为零、后期缓慢升高的特征。

       

      Abstract: The juxtaposition of coal seams and tight gas reservoirs is a common geological structure in coal-bearing formations. Elucidating the production dynamics of coalbed methane(CBM) and tight gas from such overlaid formations holds significant importance for the synergistic development of coal-bearing resources. Initially, the study examines the gas and water production characteristics and reservoir average pressure evolution under separate development of CBM and tight gas. Subsequently, employing a wellbore node analysis method, it iteratively calculates pressure distribution characteristics under varying mass flow conditions, using wellbore pressure drop as a link to couple the mutual interference of pressure between coalseams and tight gas formations and their respective production characteristics. Finally, a dynamic gas production prediction model for co-production wells in the “coal seam above, tight below” juxtaposition relationship is established. The study analyzes the stable production capacity of co-production wells and the evolution of production contribution from each layer under different production systems, revealing that: ① the stable production period of co-production wells (averaging 2158 days) significantly exceeds that of CBM separate development. ② The cumulative gas production of co-production wells sharing a single wellbore differs by only 2.56% compared to multiple drilling for separate development, demonstrating the strong economic benefits of CBM-tight gas combined production. ③ Due to the typical characteristics of early-stage single-phase drainage of CBM, its contribution to gas production in co-production wells exhibits an initial zero phase followed by a slow increase in the later period.

       

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