A Laboratory Study of Wilmington Tar Zone CO2 Injection Project

Abstract

Summary A laboratory study of heavy oil recovery by CO2 injection was undertaken in support of the Wilmington Tar Zone CO2 Injection project operated by Long Beach Oil Development Company. The project operated by Long Beach Oil Development Company. The work included:–Phase behavior of Tar Zone reservoir oil and CO2.–Phase behavior of Tar Zone reservoir oil and the refinerygas (82% CO2 - 18% N2) used for the field project.–Viscosity measurements of oil-gas mixtures.–Reservoir condition displacements of oil by CO2 and byrefinery gas.–Equation of state characterization of phase behavior.–Computer simulation of gas-oil displacements. Saturation pressures and swelling factors were measured for oil-gas mixtures for up to 60 mol % CO2 and for up to 50 mol % refinery gas. These measurements show that N2 is substantially less soluble in oil than CO2. Viscosity measurements show that the viscosity reduction is a function of pressure and the total gas dissolved in the oil. pressure and the total gas dissolved in the oil. Four reservoir condition corefloods were completed:–Refinery gas injection at 0.22:1 WAG ratio, followed by waterflood–Continuous CO2 injection followed by waterflood.–Continuous refinery gas injection followed by waterflood.–Refinery gas injection at 1:1 WAG ratio, followed bywaterflood These floods showed that 1) the recovery efficiency of CO2 is higher than that of the refinery gas for continuous or low WAG injection and 2) the recovery efficiency of the refinery gas at 1:1 WAG is about twice that of continuous injection. The corefloods were modeled with a finite difference compositional simulator. Predictions agree with the experimental results. Introduction The Wilmington Tar Zone CO2 Injection Project has been designed and operated by Long Beach Oil Development (LBOD) Company. The project covers roughly 32,000 ac-ft in Fault Block V. The reservoir project covers roughly 32,000 ac-ft in Fault Block V. The reservoir is 2300 ft deep. The pay zone thickness is 50–100 ft. The porosity is 31%. The permeabilities are in the 100–10,000 MD porosity is 31%. The permeabilities are in the 100–10,000 MD range. The reservoir temperature and pressure are 120F and 1000 psia. The oil has 13–150 API gravity with a GOR of 50 SCF/BBL. psia. The oil has 13–150 API gravity with a GOR of 50 SCF/BBL. The solution gas composition is 96% methane and 4% CO2. The injection gas is refinery by-product gas purchased from Texaco refinery in Wilmington. The composition is 82% CO2 and 18% N2. The operation of the project has been described elsewhere. The Wilmington Tar Zone oil is too heavy to develop miscibility with CO2. However immiscible CO2 injection is effective in heavy oil recovery, because CO2 dissolves in heavy oils, causing swelling and a large reduction in oil viscosity. The reduced oil viscosity improves the fractional flow of the oil for a following water flood. We undertook an experimental and computational program to study the phase and displacement behaviors of this system. The results of the phase behavior measurements were used to tune the Peng-Robinson Equation of State (PREOS) characterization. We Peng-Robinson Equation of State (PREOS) characterization. We performed four reservoir state coreflood displacement using CO2 performed four reservoir state coreflood displacement using CO2 and refinery gas. The PREOS model and core properties were used in a finite difference compositional simulator properties were used in a finite difference compositional simulator to model the displacement experiments. P. 245