考虑吸附作用的页岩气井生产数据分析方法

Shale gas well production data analysis methods accounting for adsorption

在页岩气开采过程中,随着地层压力的下降,页岩气会发生解吸作用,而常规气藏的生产数据分析并没有考虑气体吸附导致的偏差因子和综合弹性压缩系数的改变,因此用常规气藏分析方法很难得到准确的天然气地质储量(OGIP)。在langmuir等温吸附理论基础上,应用King(1990)和S.MOghadam(2009)方法对偏差因子进行了修正,并应用Bumb&McKee(1986)方法对综合弹性压缩系数进行了修正,然后应用修正Palacio-Blasingame图版拟合方法、修正物质平衡方法(FMB)和修正Ibrahim&Wattenbarger不稳定线性流方法等三种方法对页岩气井生产数据进行了分析并计算了OGIP。前两种方法主要应用的页岩气井晚期边界流控制的生产数据,后种方法应用的是页岩气井早期的不稳定线性流数据。把VBA和RAT软件作为基本工具,结合上面三种方法,分别计算了某页岩气井考虑吸附作用和不考虑吸附作用的OGIP(原始天然气储量)。实例计算表明,当分析页岩气井生产数据时,不考虑页岩气吸附作用将会低估OGIP。用上面三种方法计算得考虑气体吸附得到的OGIP比不考虑吸附得到的OGIP分别提高了13.22%、11.06%和4.89%。

During exploitation of shale,the desorption from shale gas reservoirs takes place when reservoir pressure declines.The Z-factors and compression coefficient change caused by desorption of adsorbed gas have not taken into consideration when analyzing conventional reservoir production data. As a result,it will underestimate original gas in place （OGIP）. Three methods are presented in this paper by using King＇s （1990） modified z＊,S. MOghadam＇s modified z＊＊ （ 2009 ）and Bumb ＆McKee＇s（1988 ）adsorption compressibility factor for adsorbed gas based on Langmuir＇s isotherm.They are modified Palacio and Blasingame＇s method,modified FMB method and Ibrahim＆Wattenbarger＇s method.The first two methods are primarily used to analyzing the late boundary dominated flow of shale gas well while the last method is mainly applied to analyzing the early transient linear flow.Based on the above three methods,OGIP with and without adsorption is calculated in this work with software of VBA and RAT.Examples show that the estimation of OGIP will be lower if adsorbed gas in shales is ignored when analyzing production data of shale gas well.The results calculated by the above methods show that inclusion of adsorbed gas resulted in approximately 13.22 %, 11.06 % and 4.89 % increase in OGIP estimates.