Downhole upgrading of virgin Athabasca Tar Sand bitumen has been investigatede in a series of 3-D experiments using THAI - ‘Toe-to-Heel Air Injection'. The process uses direct line drive, or a staggered arrangement of horizontal producer wells; in combination with either horizontal or vertical wells for gas injection (HIHP or VI2HP). The 3-D tests involved THAI as a primary process, steam injection aslo as a primary method using a new steam flood process, THSF (Toe-to-Heel steamflood), and THAI on a secondary recovery mode, post-THSF. Except for THSF, very high oil recoveries were achieved: THAI primary: 80% OOIP, THSF: 23% OOIP and THAI secondary: 66.7% OOIP. The low THSF recovery is attributed to the low steam temperature, because of the low cell opersting pressure. Very significant upgrading of the Athabasca bitumen occurred during the air injection tests for the majority of the experimental period. The API gravity of the produced oil increased by 8 API points and the viscosity decreased to 50 to 1000 mPa.s, compared with the original bitumen viscosity of 1,000,000 mPa.s. There was also a substantial decrease in sulphur, nitrogen and heavy metals content of the produced oil. The quality of the in-situ upgraded oil was investigated using SARA analysis (Saturates, Aromatics, Resins, Asphaltenes). This revealed that there was a dramatic increase in the saturates content of the produced oil, up to 62% to 72%, compared with 15.5% for the original bitumen.

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