Interaction of Nitrogen/CO2 Mixtures with Crude Oil

The Oil & Gas Journal, in 2004, states that CO2 flooding is the fastest-growing enhanced oil recovery technique in USA, and production derived from CO2 projects has more than tripled from 50,000-Barrels/day to 200,000-Barrels/day. Cyclic injection of CO2 and N2 combines environmental benefits attendant to reducing CO2 concentrations in the atmosphere and economic benefits realized through improving oil recovery. There are a number of variables involved in the design of a successful and profitable cyclic injection operation. The objective of this study is to investigate the influence of mechanisms such as gas solubility and oil vaporization on the cyclic injection process using laboratory experimentations. A PVT cell was used to perform six cycles of injection into a Chipmunk formation crude oil. Conditions of pressure and temperature in the cell are 150-psig and 70 F. These conditions of pressure and temperature were maintained for five different injected mixtures of CO2 and N2. These mixtures were 100%-0-%, 80-%-20-%, 53-%-47-%, 20-%-80-%, and 0-%-100-% of CO2 and N2 respectively. Laboratory results indicate a higher solubility of CO2 when compared to that of N2. Moreover, gas is more soluble during the first 3 to 4 cycles, and is independent of the composition of the injected mixture. Results also show that low hydrocarbon vaporization is realized using N2. CO2 by comparison shows a higher hydrocarbon vaporization effect than N2 with maximum hydrocarbon extraction attained using CO2 concentrations close to 100-% in the injected fluid. For pressure conditions at which experiments were performed, the results indicate that cyclic operations must consider the effect of gas solubility and hydrocarbons vaporization.