煤层气/砂岩气混合气藏合采产能预测及排采优化

Production Prediction of Hybrid Gas Reservoirs Including Coal Seams and Sandstone Seams and Development Optimization

为了解决煤层气砂岩气共采时层间干扰问题,达到准确预测煤层气砂岩气混合气藏产能的目的,基于煤岩双孔单渗模型和砂岩单孔单渗模型,以及煤岩与砂岩层间窜流模型,构建了考虑层间窜流条件下煤层气与砂岩气合采的数值模型,并对影响合采产能和层间窜流强度的因素进行了敏感性分析,最后提出了变井底压力梯度排采方案。研究结果表明:煤层初始孔隙压力的变化主要引起开发早期层间窜流的变化,而砂岩层原始孔氏压力的变化对层间窜流影响很小。当仅在井筒附近存在层间窜流时,层间窜流阻碍低压层流体的产出。当仅在远离井筒处存在层间窜流时,层间窜流会有助于合采效果。井底流压下降幅度与梯度变化对煤层气/砂岩气合采井的排采曲线的影响很大。

To settle the problem of interlayer interference between coal seams and sandstone seams and predict the production of the hybrid reservoir precisely. Based dual porosity/single permeability model in coal seams,single porosity/single permeability model in sandstone seams and crossflow model between coal seams and sandstone seams,the numerical model to predict the production of hybrid reservoirs considering the crossflow between coal seams and sandstone seams was developed. The parameters influencing the commingled production of hybrid reservoir combined with coal seams and sandstone seams were analyzed. At the same time,the production strategy of variable wellbore flowing pressure method was designed to optimize the commingled production. The simulation results show that the change of the permeability and initial pressure of coal seams and sandstone seams will influence the gas production rate of the other seams. The change of initial pressure of coal seams will influence the crossflow between seams at early stage. However,the change of initial pressure of sandstone seams has little influence of crossflow between seams. If the crossflow occurs around the wellbore,at early production stage gas and water will flow from seams with high pressure into seams with low pressure and the gas and water in seams with lower pressure are hindered. If the crossflow occurs around the outer boundary,the crossflow between coal seams and sandstone seams will contribute the commingled production.