First Field Pilot of the THAI Process

Abstract Petrobank Energy and Resources Ltd., through its wholly owned subsidiary, WHITESANDS INSITU Ltd., is building the first field test of the Toe-to-Heel Air Injection (THAI™) process. Entitled WHITESANDS ™, the pilot will be conducted on Petrobank's 1.3-billion barrel bitumen lease 10 km west of Conklin, Alberta. Three vertical air injectors and three horizontal producers will be set at 100 m spacing. The presentation will describe the technology background, reservoir and site features, processing plant design, pilot objectives and the expected economics and environmental benefits. Introduction The first reported investigation of the use of horizontal wells for the in-situ combustion (ISC) process was by Greaves et al. at the University of Bath where they conducted experiments in a rectangular combustion cell, measuring 0.4 m × 0.4 m × 0.1 m. Three different well configurations were used: vertical injectorvertical producer (VIVP), representing a conventional ISC arrangement, vertical injector-horizontal producer (VIHP), representing Toe-to-Heel direct line drive, and horizontal injector-dual horizontal producer (HI2HP), or staggered line drive, another arrangement of Toe-to-Heel air injection. The Toe-to-Heel arrangement was generally much more stable than conventional ISC, due to greater control of gas override. Combustion peak temperatures of 400 °C were achieved, with oil recovery exceeding 66 % OOIP. The quality of the produced oil for the VIHP configuration was also higher, showing an increase of 5 ° API, compared to the crude oil value. Four Toe-to-Heel well configurations were used in a further study by Greaves et al. 1,2, to investigate the effect of oxygen flux, oxygen enrichment and wet combustion. Stable combustion front propagation was observed for all of the Toe- to-Heel direct line-drive well configurations, which included a parallel pair arrangement, similar to that used in SAGD (Steam Assisted Gravity Drainage). Very high sweep efficiencies were achieved, according to the movement of the high temperature front through the sandpack. Although the sweep was highest for wet combustion, the oil recovery was only marginally higher compared to dry combustion. In one case, HI2HP, the volumetric sweep reached 95 % of the sandpack volume. Oil recovery ranged from 72.1 to 78.8 % OOIP and the rate of oil production was significantly higher than for conventional ISC, using an HIHP well pattern. However, there was no apparent benefit from using enriched air (35 % oxygen), or increased air injection flux, although this was from a relatively low value. Substantial in-situ oil upgrading via thermal cracking of heavy residual was achieved, averaging an 8 °API increase. Toe-to-Heel Air Injection became known as THAI™, following a further series of experiments on light ‘Forties-Mix’ oil (30.7 °API), medium heavy oil Clair oil (20.8 °API) and heavy Wolf Lake crude oil (10.95 °API) 3,4. The experiments identified the existence of a well-controlled, narrow mobile oil zone (MOZ), created just ahead ahead of the combustion front Figure 1 shows the now familiar concept of THAI™.

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