有限水侵页岩气藏物质平衡方程及储量计算

Material Balance Equation and Reserve Estimation Method for Shale Gas Reservoirs with Limited Water Influx

页岩气主要以吸附状态和游离状态两种形式赋存于发育大量微裂缝的页岩中,仅少量以溶解状态存在。为此,分别考虑基质和裂缝系统的流体性质、储层性质并全面考虑天然气膨胀、裂缝和基质收缩、流体膨胀、水侵、吸附气解吸以及吸附相体积变化等各种驱动形式的影响,建立了有限水侵页岩气藏物质平衡方程。实例计算表明,该方程可有效计算页岩气藏储量,驱动形式的忽略会导致储量计算结果不准确,忽略吸附相体积变化所得储量结果偏小;忽略基质孔隙以及水的膨胀性会使基质系统游离气储量偏小,裂缝系统游离气储量偏大,总储量偏小。

Shale gas is mainly stored in shale reservoirs with a large number of developed micro-fractures in adsorbed and free state forms and only a small amount of shale gas is stored in dissolved slate form.For this reason,analyzed are fluid properties and reservoir properties of the rock matrix and fissure system respectively and considered comprehensively are effects of such driving mechanisms on shale gas as natural gas expansion,matrix and fissure shrinkage,fluid expansion,water encroachment,adsorbed gas desorption and adsorbedphase volume change and established is the material balance equation for limited water encroachment shale gas.Practical application results of the equation show that the equation can effectively estimate shale gas reserves,estimation results will not be accurate probably if driving mechanism of adsorbed-phase volume change is not considered,lack of adsorbed-phase volume change consideration may result in lower estimated reserves,lack of matrix porosity and water expansion consideration may result in lower estimated free gas reserves in matrix system,larger estimated free gas reserves in fracture system and lower gross reserves.