基于滑脱的页岩气藏压裂水平井渗流模型及产能预测

Seepage model and productivity forecast based on slippage of fractured horizontal wells in shale gas pool

页岩气储层的纳米级孔隙中滑脱效应使渗流机理更加复杂,通过建立解析解模型定量分析其影响程度具有实际意义和理论价值。以页岩气藏压裂水平井三线性渗流理论为基础,通过分析滑脱对渗透率影响规律及计算关系,构建了考虑滑脱渗流的数学模型,并对模型进行求解,得到了可用于现场生产预测的压裂水平井产能方程;根据对渗透率增加幅度和产量增加值界定了受滑脱效应影响孔隙阈值;应用所建立模型通过实例计算分析了不同孔隙直径、不同生产压差下滑脱效应分别对产能的增加值,定量地评价了滑脱效应的影响程度,结果表明初期产能增加值可达到1 500 m3/d,后期生产也可达到400 m3/d。因此,当页岩气储层孔隙较小进行产能预测时滑脱效应需要被考虑,以便更能科学全面地反映其渗流规律。

The slippage effect in nano-level pores in shale gas reservoirs makes the seepage mechanism even more complex, and that an analytical solution model was built to quantitatively analyze its inlfuence is of practical signiifcance and theoretical values. Based on trilinear seepage theory for fractured horizontal wells in shale gas reservoirs and analyzing the law of slippage effect on permeability and its calculating relations, a mathematical model was built taking into account the slipped seepage, and a solution was made on the model to obtain an equation of fractured horizontal well productivity, which can be used to forecast the well production. The pore threshold affected by slippage effect is deifned based on the increase range of permeability and the value of production increase. The model was used, through example calculations, to analyze the slippage effect on the increase of productivity under different pore diameters, different production pressure differential, and quantitatively evaluate the magnitude of slippage effect. The result shows that the initial productivity may reach 1 500 m3/d, and the production at later stage may also reach 400 m3/d. Therefore, the slippage effect should be taken into consideration in productivity forecast when the pores of shale gas reservoir are small, as to relfect its seepage regularity more scientiifcally and comprehensively.