Experimental Study On Density And Viscosity Characteristics Of Supercritical Acid Natural Gas

In order to release the contradiction between energy supply and consumption in our country, the natural gas exploitation is becoming more and more important in our country's energy strategy. Several large natural gas accumulations have been discovered in SiChuan, XinJiang, northern Shanxi and South China sea. Most of them present―High pressure, High production, High sulphur‖, which is called―Three High‖property. Because of the existence of CO₂ and H₂S, natural gas will transform to supercritical state in the course of rising up from bottom hole. The unique property of supercritical fulid's density and viscosity iMPacts well control security seriously. Thus, in order to offer reference and criteria for bore pressure calculation and well control of the―Three High‖gas well, the phase state, density and viscosity properties of supericritial natural gas must be acquired.A experiment apparatus named―M-1 high pressure reaction system‖is developed in this paper. The system can measure density and viscosity of natural gas in temperature area of 20-200℃and pressure area of 0-60MPa. After debug and experiment examination, the system is functional and can be used in scientific research. The density and viscosity variation curve with temperature and pressure of CO₂, CH₄ and gas mixture of CO₂ and CH₄ with different ratio have been measured through this system. On the basis of the density and viscosity data, various density and viscosity calculation methods from literature were analysed. Besides, a revised edition of DPR equation named R-DPR equation was developed. After analysis, the R-DPR equation and the LGE model were chosen for density calculation and viscosity calculation of supericritical acid natural gas.With R-DPR equation and LGE model, a supercritical acid gas physical property calculating software were developed, density and viscosity of various kinds of natural gas (light gas, rich gas, CO₂ concentration gas and H₂S concentration gas) in the model well bore were calculated. Through analysis, we find that in the hole section from 1500 meters depth to the well head, the phase state of CO₂ concentrated gas, H₂S concentrated gas and some rich gas will transform from supercritical state to gas state. Their density will decrease more than 80%, their viscosity will decrease amost 70%, a series of alternation arise from density and viscosity variation can make a great impact on well control security.