天然气溶解过程中组分分馏模型及其应用

Dissolution Fractionation Model of Natural Gas Components and Its Application

天然气不同组分在水中溶解度的差异,导致溶解相与残留游离相天然气组分组成不同,即发生组分的溶解分馏效应。溶解分馏效应在天然气水溶运移、溶解散失等过程中均有发生。揭示天然气组分的溶解分馏规律、建立定量分馏模型,有助于天然气气源对比和成藏过程示踪。以Henry定律为依据,对不同组分溶解特征分析,提出了溶解度分数的概念,并建立了溶解分馏模型。根据该模型和各组分的溶解度分数和天然气溶解量,可计算各组分的溶解分馏量,恢复天然气初始组成特征。计算表明,威远震旦系气藏初期的天然气组成为:CH4为72.70%,C2H6为0.09%,CO2为22.41%,N2为4.07%,干燥系数(C1/C1-5)为99.876%。溶解作用使天然气中CO2含量显著降低,烃类气体含量增加,而天然气干燥系数降低。结果有助于天然气成因判识和气源对比等。

Because of dissolving ability difference among different gas components, dissolution itself could cause original components of natural gas to be changed. This is so called dissolution fractionation of gas components. Dissolution fractionation could happen during natural gas migration and dissipation in water. It is necessary to find out dissolution fracionation mechanism and establish fracionation model for tracing origin and distribution of natural gas. Based on the Henry＇s Law, a dissolution fraetionation model of gas components was established. The model calculation shows that, the original gas components in the Sinian reservoir of Weiyuan field are CH4-72.70%, C2H6-0.09%, CO2-22.41% and N2-4.07%, and the dryness coefficient （C1/C1-5） is 99.876%. Because of dissolution the CO2 contents in natural gas decreased greatly while hydrocarbon gases contents increased slightly. Resumption of the original components of natural gas is helpful to genetic discrimination and gas-source correlation.