低渗透产水气藏单井控制储量的计算及产水对储量的影响

Single well controlled reserves calculation for low permeability water-producing gas reservoirs and implications of the involvement of water production

低渗透气藏已成为目前我国天然气开发的重点对象,其渗流规律也不同于常规气藏,特别是气井产水以后,存在气、水两相流动,气藏的渗流规律将发生明显的变化,常规的单井控制储量计算方法已不再适合。为此,针对气藏低渗透、产水的特点,重新推导了气井的气、水两相产能方程,并结合物质平衡法,建立了一个改进的适合产水低渗气井控制储量计算的采气曲线法,并用实例进行了验证。结果表明:启动压力梯度及气井产水对控制储量的计算有明显影响;在储量计算公式推导中,水气体积比的引入,能更准确地求取产水气井的储量和表述产水对储量的影响;在考虑产水因素后,求得的天然气储量明显降低,且随产水量的增加,求得的气井控制储量也减少。该研究成果对于提高低渗透产水气藏单井控制储量的计算精度具有重要参考价值。

With the development of oil/gas recovery technology, low permeability gas reservoirs have become a focus due to their seepage flow mechanism distinct from that of conventional gas reservoirs. It is worth noting that the gas water two-phase flow in wells especially after water production will result in an obvious change in the seepage flow mechanism of reservoirs, thereby making the conventional single well controlled reserves calculation method no longer applicable. In view of this, the gas-water two phase productivity equation was re-derived for gas wells and in combination with the material balance method, an improved gas yield curve method was developed appropriate for the controlled reserves calculation for low permeability and water-producing gas wells, which was also validated by field practices. The following findings were obtained： （1） the kickoff pressure gradient and water production have noticeable implications on the single well controlled reserves calculation; （2） the introduction of water/gas volume ratio into the reserves calculation formula helps estimate the reserves of water producing wells and represent the implications of water production on reserves calculation in a more precise way; and （3） the calculated single well controlled reserves drop sharply when water produc- tion is considered, and decrease with the increase in water production. This study is of great significance as a reference to improving the calculation precision for single well controlled reserves of low permeability and water-producing gas reservoirs.