THAI (Toe-To-Heel Air Injection) About To Break New Ground in Alberta

Malcolm Greaves (M.Greaves@bath.ac.uk) leads the IOR Research Group at Bath University , researching advanced IOR/EOR processes to develop new recovery technologies for heavy and light oil reservoirs. Here, together with TianXiang Xia (cestxx@bath.ac.uk), he discusses the latest developments with Toe-To-Heel Air Injection. Much of the earlier development of the process was funded for EPSRC and DTI research grants

THAI Pilot Test

As reported recently in VenEconomony and PetroleumWorld (12 August, 2003), THAI (Toe-to-Heel Air Injection) , is set for a pilot trial in the Athabasca Tar Sands at Christina Lake (Figure 1).

Figure 1: Map of THAI Pilot Test in Alberta , Canada (Source - Orion Oil, Calgary)

The THAI pilot is being developed by Orion Oil, Canada Ltd, the heavy oil division of Petrobank Energy & Resources Ltd, Calgary . The engineering design and planning phases are now complete and the first oil should, hopefully, begin flowing in summer 2004. Petrobank's Christina Lake patch contains an estimated 500 million barrels of bitumen. If THAI is successful it could leapfrog over steam technology and may eliminate the use of steam in tar sands and heavy oil reservoirs, according to Barry Blacklock, Petrobank's representative in Venezuela . Petrobank say that they will immediately follow this with a commercial development.

Development of THAI

The THAI process was invented by Professor Malcolm Greaves of Bath University in collaboration with Dr. Alex Turta of the Petroleum Recovery Institute (PRI), Calgary . Work on THAI was first started by the IOR Group at Bath nearly 15 years ago. The idea of integrating horizontal well technology with in-situ combustion (ISC) was not viewed then as being an obvious step forward, especially since conventional ISC technology seemed doomed to the history books. Bath 's achieved early success with its 3D experiments, using a direct line drive combination of a single vertical air injection well, offset laterally from the "toe" of a single horizontal producer (VIHP). Since then, oil recovery tests using heavy crude oil and bitumens have consistently achieved 80% OOIP recovery on primary production. In more than fifty 3D cell tests at Bath , oxygen breakthrough never occurred. THAI also achieves substantial in-situ oil upgrading, up to 10 °API. This can be further increased by another 6°API using CAPRI , a catalytic variant of THAI, which was also invented at Bath by Malcolm Greaves in collaboration with Conrad Ayasse and Alex Turta of PRI. THAI/CAPRI also achieves significant environmental benefits through reduced energy requirement and substantial reduction in gas emissions, sulphur and heavy metals. The basic THAI process is shown schematically in Figure 2.

Figure 2: Schematic of THAI Process

Ironically, when the THAI acronym was first "coined" the South East Asian Tiger economies were about to "nosedive"! Understanding of the THAI process mechanisms has advanced considerably during the past six years, especially due to the efforts of Dr. TianXiang Xia , who has worked on a number of key EPSRC funded projects. EPSRC provided nearly £1 million to the IOR Groups at Bath and Salford Universities for THAI/CAPRI research. Funding from overseas companies, and allied funding from the DTI for ISC and air injection research contributed a further £0.5 million. A major breakthrough in understanding one of the fundamental mechanisms governing the overall stability of THAI was made recently by the Bath IOR Group (CIPC Paper 2003-030). This answered the perennial question, "Why doesn't the injected air channel directly through into the toe of the horizontal producer?" As the photograph in Figure 3 shows, air (oxygen) is prevented from entering the horizontal well because there is a dynamic process of coke forming inside the well and being burned-off. Dr. Xia has simulated this effect in the experiment and at field-scale using the STARS reservoir simulator.

Figure 3. Post-Mortem Pictures of Coke Deposition in the Horizontal Well (Run 2002-03)

Is there any future for THAI/CAPRI in the UKCS or other offshore areas? Malcolm Greaves believes so, because THAI is independent of reservoir size. If THAI/CAPRI can upgrade 10.9° API Wolf Lake heavy oil to a high quality medium oil, say 26 °API, it should be possible to convert a medium heavy oil (Clair) to a light oil, in a one-step downhole process.

JIP Proposal: "Startup of THAI - Experimental and Simulation Study"

The Bath University IOR Group will act as project manager. The multi-partner project will involve Computer Modelling Group (CMG), Calgary and Petroleum Recovery Institute (PRI), Calgary . The project will focus on the very important and critical aspects of startup, including initial gas communication, ignition and subsequent development of steady combustion propagation, using 3D experiments. Simulations will be performed at experimental and field scale using CMG's STARS reservoir simulator. The project will provide a unique opportunity for sponsor companies to gain appreciation of the latest THAI technology. Sponsor ticket price is £30k p.a., over two years. If you would like a copy of the JIP Proposal, please e-mail Professor Malcolm Greaves at: M.Greaves@bath.ac.uk or Dr. T. Xia at: cestxx@bath.ac.uk .

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