The precipitation of wax and asphaltene has always brought serious problems in the petroleum industry. In order to mitigate the damage caused by the precipitation of organic solid, the research of experiment and modeling on solid precipitation, which can offer a basis for design in the production, transportation and petrochemical process for oil and gas, is necessary. The laser test technique can measure the solid precipitation at high temperature, pressure and variation of composition for a system of oil and gas. The thermodynamic model of gas-oil-solid three phase can predict solid precipitation in the process of the production of oil and gas as well as gas injection. A study of experimental measurement and modeling on wax precipitation for the Pubei Oilfield, located at the western part of China, is conducted. A comparison of wax precipitation point between measurement and modeling is made and a good match is achieved. The results show the pressure greatly affect the wax precipitation temperature for a live oil.
The damage of precipitation of wax and asphaltene to the petroleum industry is severely worldwide. The serious problem is to deaden the wellbore, production facilities, pipeline and processing equipment in the process of production and transportation of oil and gas. The precipitated solid substances of wax and asphaltene plug pores of formation and result in in situ reduction of porosity and permeability. In addition, the enhancing of oil recovery is hindered by the wettability reversal of formation rock, which is caused by the adhering of the precipitated solid on the formation rock. In recent years, more attention is paid on this issue and more research of the mechanism, experimental measurement and thermodynamic modeling is carried out.
The Pubei Oilfield, located at the western part of China, is one of a few oilfields in China to carry out a project of enhancing oil recovery by injecting gas. In order to offer the prevention approach to mitigate the detriment of solid precipitation of wax and asphaltene in the process of gas injection, a series of study of experiment and modeling is made.
The high-temperature and high-pressure LASER technology is applied to conduct the experimental measurement of the solid precipitation behavior at various pressures, temperatures and compositions (at various gas/oil ratios). The test principle of this technology is to detect the variation of light transmittance under various conditions, and then determine the solid incipient precipitation point (temperature, pressure or composition), based on a sharp variation point of light transmittance.
The experimental work down here is divided into two main categories. 1. Dead oil at the atmospheric pressure and at various temperatures. 2. Live oil pressurized up till to the reservoir pressure at various gas/oil ratios.
According to the thermodynamic equilibrium principle, the fugacity of component in the vapor phase, in the liquid phase and in the solid phase is equal when a system is under the thermodynamic equilibrium condition:
(Equation (1) available in full of paper) Equation (1) equates the following two equations: (Equation (2) available in full of paper).
