Oxygen In-Situ Combustion for Oil Recovery: Combustion Tube Tests

Abstract

Summary Oxygen in-situ combustion for EOR offers several potential technical and economic advantages over similar potential technical and economic advantages over similar combustion and recovery with air. These advantages may include faster oil production, reduced compression costs per unit of injected oxygen, ability to sustain combustion under reservoir conditions adverse for combustion with air, increased CO2 content for decreased oil viscosity, and increased CO2 concentration in the produced gas for reinjection into the same or another produced gas for reinjection into the same or another reservoir. A high-pressure laboratory combustion tube system was designed and built for oxygen service to evaluate the in-situ combustion process with air and oxygen enrichment. Initial tests for the combustion tube used a light crude oil and simulated, homogeneous reservoir conditions. Combustion tube runs were made with 21% O2 (air) to 95% O2 at a constant total gas (O2 + N2) flux. Runs at 21 and 30% O2 produced unsatisfactory combustion. Tests at 40% O2 and greater produced satisfactory combustion; apparent coke composition, coke loading, combustion temperature, and oxygen utilization efficiency were similar to values ordinarily reported for air combustion. Combustion-front velocity increased substantially with enrichment, and the time required for initial oil production and the total injected gas required per barrel of production and the total injected gas required per barrel of oil both decreased substantially. Some partial oxidation of the oil was indicated, but there did not appear to be a trend toward increased oxidation with oxygen enrichment up to 95% O2 Introduction The in-situ combustion process for EOR has been studied in the laboratory and operated in the field over the past several decades. The literature contains many excellent summaries and descriptions of in-situ combustion field projects and laboratory studies. Until very recently, all in-situ combustion field projects and virtually all reported laboratory studies were projects and virtually all reported laboratory studies were conducted with air injection. The potential advantages of oxygen enrichment have been recognized for some time, but it was not until the last 3 or 4 years that significant experimental work was undertaken to demonstrate this application. We began work in 1978 toward understanding and demonstrating the potential advantages of oxygen for in situ combustion. Hvizdos et al. discussed a pioneer oxygen fireflood project at Forest Hill field (TX) completed in Jan. 1982. Parallel with field test activities, a state-of-the-art combustion tube facility was developed and installed to study the effects of oxygen enrichment on the in-situ combustion process for a wide range of reservoir conditions. This paper presents the design of the combustion tube system and the results of the first full set of runs over a range of 21 to 95% O2. Description of the Combustion Tube System The combustion tube system (Fig. 1) was designed to meet criteria that included:tube diameter 3 to 5 in. [76.2 to 127.0 mm], tube length 6 to 8 ft [1.8 to 2.4 m], thin wall;maximum operating conditions of 3,000 psi [20.7 MPa] and 1,200F [649C];temperature psi [20.7 MPa] and 1,200F [649C];temperature control system to maintain near-adiabatic operation and to track the combustion front at about 1 ft/hr [0.305 m/h]; anda feed system compatible with pure oxygen. The sandpack, with a maximum length of 7 ft [2.13 m], was contained in a vertical, thin-walled, stainless-steel tube, 3.5 in. [89 mm] OD, contained within a vessel with a maximum operating pressure of 3,100 psig [21.4 MPa]. A control system maintained a supply of argon to the pressure vessel surrounding the combustion tube at a pressure about 10 psi [0.07 MPa] greater than inside the tube. All the piping, wiring, and thermocouples for temperature control passed through one of the top or bottom Grayloc hubs used as closures for the pressure vessel. Nitrogen and oxygen were fed independently to the system and blended to form the desired feed concentration and feed flow rate. Water could be fed to the system through a preheater by a metering pump. The pressure at the inlet to the combustion tube was maintained constant by control of the effluent (produced) gas stream after removal of the bulk of liquid product. The final effluent gas flow was measured by a wet-test meter. A sample of the effluent gas was analyzed continuously for oxygen and periodically by a gas chromatograph for complete analysis. To maintain the combustion under essentially adiabatic conditions, the reactor tube was surrounded by insulation and by 42 band heaters 2 in. [50.8 mm] wide (Fig. 2). For each heater there was one thermocouple located at the center of the sandpack and one between the tube wall and the heater. JPT p. 1139