天然气水合物注热分解渗流特征及数值模拟

Numerical simulation of seepage flow and decomposition characteristics of natural gas hydrate in process of heat injection production

天然气水合物的分解及渗流特征是天然气水合物注热开采机制研究的基础问题。考虑水合物分解效应和储层应力条件的影响,进行天然气水合物储层性质的数学描述,建立天然气水合物注热开采的储层数值模型,分析天然气水合物注热分解渗流特征;比较注热生产过程中注热温度和注热速度对天然气水合物藏温度场及渗流场的影响,结合分解前缘移动特征及分解区面积占比变化规律,对水合物的分解渗流特征进行定性评价和定量描述。结果表明:随注热温度的升高,分解前缘的移动速度加快,分解区面积占比增加,但增加幅度减小;随注热速度的增加,分解前缘移动更快,分解区面积占比增加,增加幅度也增大,注热速度比注热温度对水合物分解的影响更大。该结果为研究天然气水合物注热开采机理、分解及渗流特性提供参考。

Heat injection production is a common technique for gas hydrate development,the seepage flow and decomposition characteristics of natural gas hydrate are important fundamental issues.Natural gas hydrate reservoir model is set based on mathematical description of reservoir properties considering the effects of hydrate decomposition and reservoir stress conditions.The seepage flow and decomposition characteristics were analyzed based on the results of numerical simulations of heat injection production of natural gas hydrate.The effects of different heat injection temperatures and heat injection rates on temperature and saturation fields were compared,and the decomposition characteristics of hydrates were evaluated qualitatively and characterized quantitatively by temperature distribution,saturation distribution and decomposition front in progress of heat injection production of natural gas hydrate.The results show that,with the increase of the heat injection temperature,the decomposition front moves faster,area share of decomposition zone increases,but the increase extent decreases.With the increase of the heat injection rate,the decomposition front moves faster,area share of decomposition zone increases,and the increase extent increases.The high heat injection rate effect more significantly than heat injection temperature in promoting the decomposition of natural gas hydrate.Research results may provide theoretical basis for further in-depth study on the mechanism of heat injection production of natural gas hydrate,especially on the important issues of seepage flow and decomposition characteristics.