摘要
准确表征酸性天然气—地层水体系的相平衡规律,对于天然气开发过程中的水溶气量和凝析水量分析具有重要意义,但目前常用的PR状态方程与Henry定律等理论对酸性天然气—地层水体系的相平衡研究还存在不适用的问题.为进一步考虑酸性气体和地层水矿化度对体系相平衡的影响,改进并提高对天然气溶解度和饱和含水量的计算精度,在PR状态方程与Henry定律相结合建立的PR—Henry模型基础上,考虑了溶解盐对体系相平衡的影响,采用定标粒子理论(SPT)修正了Henry常数,建立了改进的PR—Henry模型,最后分析了天然气组成、压力、温度和盐水含盐量对天然气溶解量和饱和含水量的影响.研究结果表明:①模型计算结果与实测资料对比,平均相对偏差分别为 5.3%和 4.55%,表明该模型能够应用于不同温度、压力和组成的酸性天然气-地层水体系的相平衡计算;②天然气在地层水中的溶解量受天然气组成、温度、压力和地层水含盐量的影响;③天然气饱和含水量受温度和压力影响十分明显.结论认为,改进的PR—Henry模型为天然气开采过程评价和CO2 埋存溶解量计算提供了一种有效的方法,对于评估天然气可采储量及开发特征具有重要的参考意义.
Abstract
The accurate characterization of the phase equilibrium law of sour natural gas-formation water system is of great significance in analyzing the volumes of water-soluble gas and condensate water in the process of natural gas development.At present,however,the commonly used theories,such as the PR equation of state and Henry's law,are not applicable to the phase equilibrium study of the sour natural gas-formation water system.To gain further insight into the influence of sour gas and formation water salinity on the phase equilibrium of the system,and to improve the calculation accuracy of natural gas solubility and saturated water content,this paper modifies the Henry's constants according to the scaled particle theory(SPT),with consideration of the influence of dissolved salt on the phase equilibrium of the system,based on the PR-Henry model which is established by combining the PR equation of state and the Henry's law.Based on this,an improved PR-Henry model is established.Finally,the effects of natural gas composition,pressure,temperature,and salt content on dissolved volume and saturated water content of natural gas are analyzed.And the following research results are obtained.First,the average relative deviation of the model calculation results compared with the measurement data is 5.3%and 4.55%,which indicates that the model is applicable to the phase equilibrium calculation of sour natural gas-formation water system with different temperatures,pressures and compositions.Second,the volume of the natural gas dissolved in formation water is influenced by natural gas composition,temperature,pressure,and formation water salinity.Third,the saturated water content of natural gas is significantly influenced by temperature and pressure.In conclusion,the improved PR-Henry model provides an effective method for evaluating the natural gas production process and calculating the dissolved volume of CO2 storage,which is of important reference significance in evaluating recoverable reserves and development characteristics of natural gas.
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