考虑毛细管压力影响的裂缝型凝析气藏物质平衡方程

Material balance equation of fractured gas condensate reservoir with consideration of capillary pressure

高含凝析油的裂缝型碳酸盐岩气藏基岩渗透率低、毛细管压力高,毛细管压力对凝析气藏的开发有重大影响。常规气藏物质平衡方程没有考虑毛细管压力的影响,因此,将常规气藏物质平衡方程直接用于计算此类气藏的储量,必然会与实际产生一定误差。为此,在考虑气藏外部水侵及储层岩石变形的基础上,以相平衡理论模型为出发点,根据物质的量守恒原理,建立了考虑毛细管压力影响的裂缝型储层凝析气藏物质平衡方程,并给出方程的求解方法。实例计算表明:在毛细管压力的影响下,凝析气藏井流物偏差因子减小、摩尔体积增大,且反凝析液量增加。考虑毛细管压力影响的凝析气藏物质平衡法计算得到的储量,均大于常规物质平衡法和不考虑毛细管压力影响的凝析气藏物质平衡法,其误差分别为9.88%,1.33%,比容积法计算的储量偏小5.19%,考虑毛细管压力影响的裂缝型凝析气藏物质平衡方程计算气藏地质储量更准确。

There are low permeability and high capillary for the bedrnck of fractured carbonate condensate gas reservoir with high oil cundensate. Capillary pressure has a significant impact on the development performance of condensate gas reservoir. The material halance equation for common gas reservoir takes no account of the capillary pressure. If it was used to calculate the gas reserves, sume errors in the calculation wuuhl be inevitable. Based on the principle of molar weight conservation and using phase equilibrium theory as a starting point, the material balance equation considering gas reservoir external water invasion and reservoir rock deformation for a fractured gas condensate reservoir is deduced, then, an approach to solve equation is obtained. The example calculation shows that the deviation tactor of the well fluid for condensate gas reservoir reduces, the molar volume increases and the retrograde condensation saturation will also increase due to the influence of the capillary pressure. The reserves calculated by the method are higher than that calculated by traditional material balance method and the material balance method without considering the impact of capillau pressure. The relative errors are 9.88% and 1.33%, which are lower than that calculated by the volume method with 5.19% of relative error. Thercfore, the material balance equation fur fractured gas condensate reservoir with consideration of capillary pressure proposed in this paper can calculate the OGIP more accurately.