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Abstract

The results of a series of combustion tube tests conducted with a medium gravity crude oil from the Esperson Dome Field, Texas, are described in this paper. The effects of water/oxygen ratios (WO2R), ranging from 0 to 10 bbl/Mcf, on residual oil saturation in the burned zone, fuel and oxygen requirements, and rates of combustion/steam fronts advance were determined.

The results show that up to 7% residual oil saturation (based on pore volume) remains in the burned zone at the highest WO2R studied. Thus, one of the main benefits of wet combustion, viz., reduced fuel/O2 consumption, must be balanced against the reduction in displaced oil.

Normal wet combustion occurs at WO2R's up to 2.5 bbl/Mcf, and the steam zone ahead of the combustion front continues to grow with increasing WO2R. Oil production is accelerated and the oxygen/produced oil ratio decreases. A transition zone of constant fuel and oxygen requirements is observed as the combustion process changes from normal wet to superwet. This is the first time such data are reported for fire flooding of a medium gravity oil with oxygen. At high WO2R's, superwet combustion occurs, characterized by combustion at steam temperature.

An analytical heat transfer model success fully matches the experimental results. It predicts the minimum and maximum WO2R's for predicts the minimum and maximum WO2R's for normal wet combustion. Below the minimum WO2R, the model suggests no significant growth of the steam zone. The model should be useful for estimating WO2R'S in field projects.

Introduction

In situ combustion is a thermal enhanced oil recovery process in which heat is generated in the reservoir by burning a portion of the oil-in-place. Air combustion projects date back to the early 1950's. A recent modification of the process involves the use of oxygen at high concentrations (about 95%) instead of air. As a result, the injected gas is more reactive than air. The combustion process can therefore be extended to medium-gravity (18-30 degrees API) and high-gravity >30 degrees API) oils which would not otherwise sustain which would not otherwise sustain combustion. Other potential advantages of oxygen over air have been documented in the literature.

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