CO2-原油体系中的PR状态方程改进方法

Method of Improved Parameters for PR-EOS in CO-crude Oil System

针对现有工程应用中的状态方程描述油藏条件下CO2-原油非理想体系时不能同时兼顾精度和计算简便性要求的问题,开展了对PR立方型状态方程修正研究。基于热力学和流体相平衡原理,考虑温度、压力和非烃组分相互作用等影响因素,采用将无因次系数由常数项改进为与对比温度相关联函数项的方法,对PR状态方程进行修正,改善液体密度及重组分特征的预测效果。以油田现场油样实测组分数据为基础,在油藏温压条件下,对PR状态方程修正前后计算油气组分等参数的精度进行了对比。结果表明,新的状态方程在不失计算简便的前提下,计算精度显著提高,相对误差下降到5%以下,满足工程应用要求,在预测油藏条件下流体相态方面具有更好的实用价值,为CO2驱数值模拟提供支持。

For imperfect CO2-crude oil system at high temperature and high pressure,the existing state equation cannot give consideration to the requirement of accuracy and simplicity of calculation simultaneously.In order to obtain practical state equation for CO2-crude oil system,influence factors such as temperature,pressure and the interaction of non-hydrocarbons components have been taken into account,Based on the principle of thermodynamics and flash calculation,parameters of PR EOS have been corrected,and the dimensionless coefficient has been changed from previous constant coefficient to function item which is associated with reduced temperature,thus prediction for density of liquid and characteristics of heavy components have been improved.Based on the data of components measured on site,the calculation accuracy of oil and gas components before and after PR EOS correction have been compared under condition of reservoir temperature and pressure.The results show that without sacrificing the simplicity of calculation,the new state equation has been improved significantly with calculation accuracy,and relative error of parameter has been reduced to less than 5%,which meets the requirements of engineering application and has better practical value in simulating and predicting fluid phase states under reservoir conditions and provides support for numerical simulation of CO2 flooding.