Hot Gas And Waterflood Equivalence Of In Situ Combustion
Authors: Islam M.R. , Erno B.P. , Davis D. 
Published: March 2010

In situ combustion is one of the oldest enhanced oil recovery (EOR) techniques. Due to its applicability in reservoirs not sui/able for other EOR applications, in situ combustion is considered to be one of the most widely applicable EOR techniques. Even though few field trials have been successful in North America, there have been numerous successful applications in several European countries. In an in situ combustion process produced gases (from the combustion zone) often become important In recovering oil ahead of the front. In order to better design an in situ combustion project, it is important to estimate the role of combustion gases. This work attempts to study the role of combustion gas mixtures in oil recovery by in situ combustion.

A series of coreflood tests was performed using combustion gases simulating both air and oxygen firefloods in the presence of reservoir oil and sand. Coreflood experiments were conducted to study the effect of temperature ranging from 50 °C to 200 °C. Gas injection was carried out at different flow rates in order to simulate different flow regimes. The results indicate that recovery efficiency depends largely on the flow regime prevailing, indicating the importance of flow rate controlled fireflood schemes. Changing the gas composition from rich in nitrogen (as produced from air combustion) to rich in carbon dioxide (oxygen combustion) had some impact on oil recovery. About 30% of the initial-oil-in-place (IOIP) was recovered by gas floods at 50 °C. About 40% and 50% IOIP were recovered by gas floods at 100 °C and 200 °C, respectively. These results suggest that considerable oil may be recovered by the gas which propagates ahead of the combustion from in an in situ combustion process. Another series of runs was conducted to investigate the impact of hot water injection following an initial gas flood. This situation is likely to occur in wet combustion, or dry combustion in a reservoir containing mobile water. In the cases studied, the injection of hot water following a gas flood gave much higher recovery than waterflood alone, showing the superiority of the sequential flow of gas and water as opposed to dry gas drive or hot water drive ahead of the fire fronts. The results of these tests indicate that the propagation of wafer and gas from can be of considerable importance in the fireflood recovery process.

Finally, the experimental results have been compared with, numerical simulation results, both with combustion gas floods and hot waterfloods.

Introduction

The object of this paper is to quantify the role of combustion gases in recovering oil during the in situ combustion process through experimental and numerical modelling.

The conventional approach to fireflood design utilizes an empirical correlation between "burned volume' and oil recovered. This correlation predicts that production rate can be increased by maximizing air injection rates, so as to increase burned volume as rapidly as possible. While this approach may be useful in assessing fireflood economics, it provides little insight into the details of many mechanisms which enhance or inhibit oil now to fireflood producers.