Experimental Investigation of Oil Miscible Displacement By Nitrogen.

Abstract

In recent years, petroleum engineers are paying more and more attention to the use of nitrogen for oil and gas enhanced recovery. Nitrogen is chemically inert, environmentally safe and can be produced from air at almost any field site. The sharp increase in nitrogen injection for enhanced recovery has been phenomenal. Several field applications of N(,2) have been reported. Over half-billion cubic feet of N(,2) are injected daily into oil reservoirs for different enhanced recovery projects. N(,2) is successfully used for many oil and gas enhanced recovery applications. These applications include: (1) Pressure-maintenance. (2) Driving gas for CO(,2) or LPG miscible slugs. (3) Miscible displacement. Although, the use of N(,2) has been rapidly recognized by various operators, not much research has been accomplished on oil miscible displacement by nitrogen. This study was initiated to experimentally investigate the oil miscible displacement process by continuous high pressure nitrogen injection. The objectives of this study are: (1) To investigate the effects of oil composition, injection gas composition and temperature on oil recovery and miscibility pressure. (2) To develop a correlation of minimum miscibility pressure (MMP) as a function of oil composition and temperature. (3) To investigate the compositional changes that occur between nitrogen and oil during the displacement process. In order to accomplish these objectives, a series of experimental displacements of different synthetic oils from a 100 ft long slim-tube packed with 50-100 mesh size s and were conducted at typical reservoir conditions of temperature (70(DEGREES)-130(DEGREES) C) and pressure (3000-6000 psi). This study shows that N(,2) is able to develop miscibility with c and idate oils at pressures of about 4000 psi or higher. The results show that MMP is strongly affected by oil volatility, temperature and oil heavy (C(,7)+) fraction composition. Finally, a Mathematical model is used to simulate the oil miscible displacement process by nitrogen. The model successfully predicted the results of laboratory displacement of a simple, synthetic oil by nitrogen injection.