Stability of THAI Process-Theoretical and Experimental Observations

Abstract The performance of the THAI ™ process has been investigated in numerous 3D experiments, using heavy crudes and Athabasca Oil Sands bitumen. The stability of the process is demonstrated by high combustion zone temperatures, absence of gas channelling, insensitivity to large changes in air injection rate, tolerance of an overlying gas cap, increased combustion temperature and faster upgrading response with increasing oil layer thickness, ‘controlled gas override’, its own ‘front tracking’ capability, and steady oil production rate. The most important parameters for upscaling of experimental scale performance to field scale are combustion front temperature and combustion front velocity. Early stage results from the WHITESANDS THAI ™ field pilot, at Christina Lake – high combustion zone temperatures (600-700 °C), high fluids production (40–50% bitumen cut) and signs of partial upgrading of the produced oil, are very encouraging for development of THAI ™ on a commercial scale. Introduction There is a long and tortuous history concerning the in-situ combustion (ISC) process, as applied to heavy crude and oil sands reservoirs. Some parts of it were glorious, but there were also many failures, often because of poorly chosen reservoirs. One of the main reasons why projects failed was lack of control of propagation of the in-situ combustion front. In many cases, there was a lack of understanding of the part played by gravity, and hence gravity segregation. Since the first field test of the ISC process in 1951, more than 160 field pilots have been conducted; most of them were carried out in the period 1970–1990. This led to the development of both the dry and wet ISC processes. They were tested for normal heavy oil and for oil sands, using air and enriched air. However, the commercial application of ISC was attained only for heavy crude reservoirs, around 1970, using air injection. At that time, most operators started to realize that ISC was actually a gas displacement process, benefiting from the oil viscosity reduction, due to heat generated by ISC reactions. Therefore, as in any gas displacement process, the injectors should be located at the most updip position. As of April 1992, according to an OGJ report, the incremental daily production from ISC was approximately 4,700 BOPD (from 8 projects) in the USA, 8,000 BOPD (from 10 projects) in the former Soviet Union, 7,300 BOPD (from 3 projects) in Canada and 12,000 BOPD (from 5 projects) in Romania. Thus, the 1992 world incremental daily oil production due to ISC was about 32,000 BOPD (from 26 reported projects)1,2. This included 19 commercial operations and 7 semi-industrial projects. Currently, only four commercial heavy oil projects are active; namely, Suplacu de Barcau (Romania), Balol and Santhal projects (India) and Bayou State Oil Corp. (BSOC), in Bellevue, Louisiana, USA. The first three projects are operated using a peripheral line drive, starting from the uppermost part of the reservoir and going downdip, while the last one is operated in patterns. The Suplacu de Barcau project is the world's largest ISC operation, having been operated continuously for 40 years. It is applied in a very shallow heavy oil reservoir.