考虑修正BET吸附的异常高压页岩气藏物质平衡计算方法

A Calculation Method for Material Balance of Shale Gas Reservoirs under Abnormally High Pressure Considering Modified BET Adsorption

页岩气物质平衡方程中,通常采用langmuir等温吸附方程表征吸附气量,但langmuir等温吸附方程的使用条件并不适合异常高压页岩气藏。鉴于此,针对异常高压页岩气藏的单井控制储量计算的问题,基于物质平衡方程的基本原理,考虑页岩气的多层吸附、超临界吸附、异常高压三重影响,引入修正BET吸附模型,表征页岩气的吸附特性,建立考虑修正BET吸附因素的异常高压页岩气藏物质平衡方程。将研究成果应用于实际区块单井分析中,应用实例表明:文中建立模型的直线相关系数更高,不仅能计算气井的控制储量,也能计算泄气范围内的自由气含量以及吸附气含量。根据该方程计算的结果与实际储层的地质条件结合,文中模型所考虑的建立条件与实际储层的情况更为接近,研究成果对异常高压页岩气藏的生产管理具有重要的指导意义。

Langmuir isothermal adsorption equation is usually used to characterize the amount of adsorbed gas in the material balance equation of shale gas,while the application conditions of Langmuir isothermal adsorption equation are not suitable for shale gas reservoirs under abnormally high pressure.To address the problems about the calculation of single-well recoverable reserves in shale gas reservoirs under abnormally high pressure,based on the basic principle of the material balance equation,a modified BET adsorption model was introduced to characterize the adsorption characteristics of shale gas with consideration of the triple effects(multilayer adsorption,supercritical adsorption and abnormally high pressure)of shale gas,and a material balance equation was established for shale gas reservoirs under abnormally high pressure considering the modified BET adsorption factor.The application of the study results to the analysis of single wells in actual blocks proved that the linear correlation coefficient of the model established in this paper was higher,and the model can not only calculate the controlled reserves of gas wells,but also calculate the free gas content and adsorbed gas content in the gas release range.According to the calculation results of this equation and the geological conditions of the actual reservoir,the construction conditions considered by the model in this paper are closer to the actual reservoir conditions.The study results play an important guiding role in the production management of shale gas reservoirs under abnormally high pressure.