偏差系数对页岩气渗流规律的影响

Effects of deviation coefficient on seepage law of shale gas

为了探究偏差系数对页岩气渗流规律的影响,建立了基质—裂缝系统离散裂缝气体渗流数学模型,运用有限元方法对真实和理想状态页岩气在储层渗流过程中的压力参数进行求解,揭示定产量条件下储层压力及井底压力的变化规律。结果表明:真实和理想状态页岩气在储层中渗流时,偏差系数对基质和裂缝区域压力展布及页岩气的渗流速度产生明显影响。真实状态页岩气渗流时,基质和裂缝区域储层压力产生明显压降,裂缝区域压降范围较大且速度快;而理想状态页岩气渗流时,基质区域储层压力基本不产生明显压降,裂缝区域压降范围相对较小且速度慢;由于偏差系数的不同,页岩气在水平井渗流过程中的渗流速度对井底压力产生明显影响。真实状态页岩气在水平井中渗流时,井底压力下降速度较快且达到10 MPa所用时间短于气体在理想状态下所用时间,近似为T理想=T实际。因此,为使模拟结果更加准确,应充分考虑偏差系数对页岩气渗流规律的影响。

In order to reveal the effects of deviation coefficient on seepage law of shale gas, seepage model of discrete fracture which belongs to matrix-fracture sysyem is established. Solving pressure parameters of the reservoir with finite element method in two states where are real state and ideal state of shale gas when it flows in the reservior, revealing the change rules of the reservior pressure and bottom hole pressure under the condition of fixed production. Result shows that, when shale gas flows in real or ideal state, deviation coefficient has a significant influence on the pressure distribution in the matrix and fracture zone and the seepage velocity of shale gas. When shale gas flows in real state, reservior pressure generates significant pressure drop in matrix and fracture region, pressure drop range is larger and the speed is faster in fracture region. However,reservior pressure almost keeps the same and doesn＇t generate significant pressure drop in matrix region,pressure drop range is relatively small and slow in fracture region when gas flows in ideal state. In the meanwhile,due to different deviation coefficient, the flow velocity of shale gas in the horizontal well has a significant influence on the bottom hole pressure, and it＇s shorter when shale gas flows in real state than in ideal state that bottomhole pressure of horizontal well drops to 10 MPa, and it＇s about Tideal=Treal. In order to get an accurate simulation,the influence of deviation coefficient on shale gas seepage law should be fully considered.