THAI - 'Toe-to Heel Air Injection' is an integrated horizontal wells- in situ process for the recovery and upgrading of heavy crude oil. In addition to thermal upgrading, further upgrading can be achieved by emplacing a catalyst layer around the horizontal producer well, in effect creating a downhole reactor. A series of six catalytic tests was performed in two 3D combustion cells to investigate the degree of upgrading achievable with 10.5 API gravity Wolf Lake oil. The main factors investigated were: the type of HDS catalyst (NiMo, CoMo), extrudate or crushed catalyst, and catalyst loading. Normally, the well configuration was HIHP, i.e. a horizontal injector and a single horizontal producer well in line drive, but one test used a dual producer, HI2HP. The results of these tests show that the basic process is very stable over a 10 hour period, maintaining average peak combustion temperatures of 500 to 600C. Thermal upgrading alone (THAI) achieved a nearly 10 point increase in the API gravity of the produced oil. This was increased by a further 4 to 7 API points using the catalytic process (CAPRI). This indicates that it may be possible to convert a heavy crude oil to almost a light oil product in a one-step in situ reservoir process. The oil recoveries were consistently very high, at around 85 %OOIP, with the produced oil having a viscosity as low as 10 mPas at 20 °C. The process demonstrated robust stability when changes in air injection rate were made and there was also an oil productivity gain when operating at low water air ratios, WAR< 1.0.
Unlike conventional light oil production, the production and transportation of heavy oil is much more difficult, mainly due to its high viscosity at reservoir conditions. In order to process the oil, expensive surface upgrading operations are required to upgrade the produced oil, so that it meets refinery feedstock specifications.
Cold production of heavy oil only recovers a small proportion of the original oil in place, typically about 5% to 20%. Surface mining is limited by the reservoir geological characteristics. It is only applied to very shallow deposits, like Athabasca Tar Sands in Canada.
When the oil viscosity is very high (>10,000mPas), in the reservoir the oil is virtually immobile. Improved Oil Recovery (IOR) or Enhanced Oil Recovery (EOR) methods are required to increase the oil mobility in order to improve heavy oil production. Steam injection, vapour extraction and in situ combustion (ISC) are three main techniques, achieving high oil recovery of more than 50% OOIP.
Steam injection, such as cyclic steam stimulation and steam assisted gravity drainage (SAGD) create no upgrading effect on the produced oil. Vapour extraction (VAPEX) produces an oil with only minimum upgrading, mainly due to rejection of asphaltenes.
ISC, or heavy oil air injection (HOAI), is achieved by burning a small fraction of the oil in the reservoir to release the combustion reaction energy between the injected oxygen and hydrocarbons
