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', own 'front tracking' capability and steady oil production rate. The most important parameters for upscaling of (stable) experimental scale performance to (stable) field scale operation are combustion front temperature and combustion front velocity. Early stage results from the WHITESANDS THAI ™ field pilot at Christina Lake, confirm high combustion zone temperatures (700 – 800 °C), high fluids production of up to 2,000 barrels per day of gross fluids (50 – 55% bitumen cut) and signs of significant partial upgrading (up to 8.2 °API). These measures of field pilot performance are consistent with the experimental findings from 3D physical experiments. They are very encouraging indicators for the future 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 tremendously innovative and successful, but there were also many failures, often due to 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 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 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 Oil & Gas Journal report, the incremental daily production from ISC was approximately 4,700 BOPD (from eight projects) in the USA, 8,000 BOPD (from ten projects) in the former Soviet Union, 7,300 BOPD (from three projects) in Canada and 12,000 BOPD (from five 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 nineteen commercial operations and seven semi-industrial projects. Currently, only four commercial heavy oil projects are active: Suplacu de Barcau (Romania), Balol and Santhal projects (India) and Bayou State Oil Corp. (BSOC) in Bellevue, Louisiana, USA.