Throughout the years, the in-situ combustion (ISC) process has been tested in many oil reservoirs displaying a bottom water (BW) characteristic. As a rule, the design, implementation and evaluation in this situation has been made indistinctively from the normal application of ISC in the absence of BW. However; the performance of ISC process in the presence of BW has always been poorer. In this paper a brief review of the field pilots conducted in the presence of BW is carried out.
The field review attempts to separate the most important parameters impacting the performance of ISC in the presence of BW. Among them is the thickness of BW zone compared to the thickness of oil zone and the oil viscosity, or more generally the flow capacity of oil zone as compared to that of water zone.
An analysis of a few laboratory tests examining the use of ISC in the presence of BW revealed the challenges occurring in this application. It enabled identification of the important mechanisms and the ways forwards to improve the process or to apply it more discriminately.
Finally, new approaches of ISC in the presence of BW are analyzed, with a focus on those using horizontal wells.
For heavy oil reservoirs with BW practically no EOR method has been proven feasible. This is due mainly to the loss of the injection agent into the BW zone, making the recovery process excessively costly. Laboratory tests of steamflooding in the presence of BW did not give very encouraging results (Chang, 1990). When considering thermal methods, there were suggestions that ISC would perform better than steamflooding (Farouq-Ali, 1994), probably due to the fact that air is less expensive than steam and its loss in the BW is not so detrimental. Recently, some steam injection experience in the Pikes Peak field has showed some limited encouraging results (Wong, 2003) in a reservoir with BW.
This review of field and laboratory ISC tests has been undertaken to clarify if indeed ISC should receive more consideration for exploitation of heavy oil reservoirs with BW.
In cases of reservoirs with BW, ISC has not attained a commercial operational status but the experience from the field tests is still very valuable, either for other areas of application or even for those situations in which successful procedures may be developed. Most of the field pilots were in the 1970s and 1980s when even the understanding of conventional ISC was limited. Most of these field tests were considered a failure. More recently there has been just one test of this kind; the Bechraji project in India, which started in 1996. Very little details of this test have been published (Oil and Gas Journal, April 2000) and it is unknown if it is still in operation.
Laboratory testing of ISC in the presence of BW is not easy to perform. However; the single study conducted in this area allowed a series of specific aspects to be uncovered and contributed to a reasonable explanation of the failed field pilots.
