Published by the DTI Oil & Gas Directorate for the reservoir engineering and IOR community in the UK.
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Air Injection Processes: Heavy Oil Recovery and In-situ Upgrading;Light Oil Recovery

Malcolm Greaves leads the IOR Research Group at Bath University, researching advanced IOR/EOR processes to develop new recovery technologies for heavy and light oil reservoirs (co-authors TianXiang Xia and Richard Rathbone). (M.Greaves@bath.ac.uk)

THAI - 'Toe-to-Heel Air Injection', is a radically new process, which remedies the problems associated with conventional in-situ combustion (ISC). Conventional ISC operates as a long-distance displacement process (Figure1), due to the conventional well-spacing arrangement used. THAI is an integrated horizontal wells process, and operates via short-distance displacement, as shown in Figure 1. It therefore falls into the same category of heavy oil processes as SAGD (Steam Assisted Gravity Drainage) and VAPEX (Vapor Extension, of SAGD). In THAI, heavy oil, which is mobilized in the Mobile Oil Zone (MOZ), ahead of the combustion front (Figure1), drains into the open section of the horizontal producer a short-distance below. Typically, this is only a few tens of metres, in contrast to 100's of metres for conventional, long-distance displacement.

THAI operates in a HTO mode (high temperature oxidation), typically 450 to 600 º for a heavy oil reservoir. This is absolutely essential to maintain vigorous in-situ combustion, and avoidance of LTO (low temperature oxidation). Over 50 three-dimensional combustion cell experiments, at low pressure, have been performed by the Bath IOR Group. A typical set of results for Athabasca Tar Sand bitumen is shown in Figure 1. The THAI process can be applied to heavy or medium heavy oil (e.g. West of Shetlands Clair oil demonstrated very good combustion characteristics), and can be operated in primary or secondary/tertiary mode (post-waterflood, - cold production, -steamflood). The process is very stable, due to the near-vertical combustion front, as shown by the STARS numerical simulation for Wolf Lake Oil in Figure 2. Oxygen breakthrough into the horizontal producer well is prevented by the (mainly) forced flow displacement in the MOZ, which acts to control gas override. Residual fuel (coke) deposited in the lower part of oil layer creates a 'sealing' or permeability profiling effect, directing injected air towards the high temperature combustion zone, in the upper part of the oil layer. The principal benefits of THAI are: very high oil recovery, 80-85% OOIP; substantial in-situ upgrading (6-8 ºAPI) - worth 40 ¢ for every API point); high thermal efficiency and substantial environmental benefits, including reduction of S (30-40%),N (>90%),heavy metals (>90%). The process also generates power station amounts of energy in the reservoir. If recovered, it could provide most of the energy to run upstream operations and surface facilities, and contribute towards creating a sustainable IOR process.

Figure 1

CAPRI: this process is a catalytic extension of THAI. A standard refinery hydrotreating catalyst (NiMo/CoMo) is employed, gravel-packed, around the horizontal producer well (Figure 2). Lighter oil in the MOZ (thermally cracked) is displaced and caused to flow over the annular layer of catalyst and into the horizontal producer well. CAPRI achieves an 8 ºAPI upgrading, additional to that achieved by THAI. There is the potential, therefore, to in-situ upgrade a heavy oil or bitumen of 8-10 ºAPI gravity, virtually to a light oil of 24-26 ºAPI (Figure 2), in a one-step downhole process. This downhole technology has potential to make huge savings on the cost of surface upgrading plant by using the reservoir as a downhole reactor.

There is an estimated 10 billion barrels of heavy and medium heavy crude oil in the UKCS of the North Sea. With perhaps only 20-30% recovery obtainable from Foinhaven and Clair, the prospect of recovering three-times this amount using THAI/CAPRI, and also upgrading at the same time from 20-24 to 36-42 ºAPI, is an exciting prospect.

Figure 2

Now is the time to think about the transition, over the next 20 to 40 years, to the solar powered/hydrogen-age, without the world experiencing a severe energy crisis. Not running-out of oil! The development of the huge Athabasca Tar Sands, Orinoco heavy oil, and, not forgetting our own N. Sea heavy oil reserves, will play a crucial part in this survival. Air Injection technology is set to play an important role in N. Sea light oiI IOR developments, eg. the recent AIROiL project (Ekofisk), in which the Bath IOR Group is a participant (with Phillips Petroelum, Rogaland Research, Totalfinaelf, IFP and the EU). Large-scale IOR development like this (a world first?) could set the trend for the North Sea to become the leading test-bed for this kind of advanced technology.

JIP Proposal//North American Launch: "Toe-to-Heel Air Injection - THAI : Maximising Heavy Oil Recovery & In-situ Upgrading"
North American Launch of: JIP Project on Toe-to-Heel Air Injection - THAI: Maximising Heavy Oil Recovery & In-situ Upgrading. [University of Bath, Petroleum Recovery Institute, Computer Modelling Group, CAPRI Petroleum Technologies, Process Contractor] Date: 10 June, 2002, Place: PTAC Petroleum Technology Alliance Canada , Suite 750,Hanover Place, 101 - 6th Avenue SW, Calgary, Alberta, Canada.

Bath University IOR Group will act as project manager for a major JIP project initiative to develop THAI-CAPRI technology, and steer it towards field pilot development. It will be a multi-partner project, involving Computer Modelling Group, Calgary (modelling and field scale simulation), Petroleum Recovery Institute, Calgary (reservoir and well technology), CAPRI Petroleum Technologies, Calgary (catalyst performance), plus process contractor input to flowsheet requirements for surface facilities. In addition, Bath will carryout 3-D process studies to provide data for model validation, at reservoir pressure. The project will provide a unique opportunity for sponsor companies to influence and guide THAI-CAPRI field pilot development. The total project cost is £1.2 million, with a sponsor ticket price of £50k p.a. over three years. [The meeting is to take place either side of the Canadian International Petroleum Conference in Calgary in June, 2002 - date to be confirmed shortly There is keen interest in the project on both sides of the water. If you are interested in receiving a copy of the JIP Proposal and further details, please contact Professor Malcolm Greaves at: M.Greaves@bath.ac.uk

Facilities at the University of Bath
The IOR Group at Bath is involved in laboratory and reservoir simulation studies of thermal and isothermal air injection processes for heavy and light oil recovery, in-situ upgrading of heavy oil, horizontal well applications, oil reaction kinetics and downhole gasification. The IOR laboratory is housed in a new, state-of-the-art Chemical Engineering Building, opened recently by HRH Prince Phillip. Equipment includes 3-D Combustion Cells, high pressure Combustion Tube facility (240 bar),high pressure Accelerating Rate Calorimeter (340 bar),high pressure Batch Reactors (400 bar),and supporting GC's and elemental analysers (see Figure3).

Figure 3

References on THAI and CAPRI

Greaves, M., and Al-Shamali, O.: "In-Situ Combustion (ISC) Process using Horizontal Wells", J.Can. Pet Tech, (1996) 35, No. 2, pp. 464-55
Greaves, M., and Xia, T. X.: "High Performance Downhole Catalytic Upgrading Using Toe-to-Heel-Horizontal Wells Process", UNITAR paper 1998-197, 7th UNITAR Intern. Conf. on Heavy Oil and Tar Sands, Beijing, China, Oct 27-30, 1998.
Greaves, M., Xia, T. X., Turta, A. T., and Ayasse, C.: "Thai-New Air Injection Technology for Heavy Oil Recovery and In situ Upgrading", paper CIM 99-15, 1999 Pet Soc Ann Tech Meeting, Calgary, AB, June. 14-18, 1999.
Greaves, M., Ren, S. R., and Xia, T. X.: "New Air Injection Technology for IOR Operations in Light and Heavy Oil Reservoirs", Paper SPE 57295, 1999 SPE Asia Improved Oil Recovery Conference, Kuala Lumpur, Malaysia, Oct. 25-26.
Greaves, M., T. X. Xia, Turta, A. T., and Ayasse, C.: "Recent Laboratory Results of THAI and Its Comparison With Other IOR Processes", SPE paper 59334, 2000 SPE/DOE Improved Oil Recovery Symposium, Tulsa, Oklahoma, 3-5 April (2000)
Greaves. M. and Xia, T.X. "Simulation Studies of the THAI Process", Petroleum Society Paper No. 2000 - 84, Petroleum Society's international Petroleum Conference 2000, Calgary, Alberta, Canada, June 4-8. (2000)
Greaves, M, Abdul El-Saghr and Xia, T. X.: "CAPRI Horizontal Well Reactor for Catalytic Upgrading of Heavy oil", ACS Symposium, Division of Petroleum Chemistry, on Advances in Oil Field Chemistry: Downhole Upgrading, 20-25, Washington, DC, August, (2000). [ACS PREPRINTS, Vol. 45, No. 4, pp595-598]
Xia, T. X., and Greaves, M.: "Upgrading of Athabasca Tar Sand Using THAI - Toe-to-Heel Air Injection", Paper SPE 65524/PS 2000-164, 4th. International Conference and Exhibition on Horizontal Well Technology, Calgary, Alberta, Canada, Nov. 6-8 (2000)
Greaves, M., El-Sakr, A., Xia, T.X., Ayasse A., and Turta, A.: "Thai - New Air Injection Technology for Heavy Oil Recovery and In Situ Upgrading", J. Can. Pet. Tech., (2001) 40, No. 3, 38-47.
Xia, T. X., and Greaves, M: "Downhole Upgrading of Athabasca Tar Sand Bitumen Using THAI - SARA Analysis", Paper SPE 69693, 2001 SPE International Thermal Operations and Heavy Oil Symposium, Porlamar, Margarita Island, Venezuela, 12 March (2001).
Xia, T. X, and Greaves, M.: "3-D Physical Model Studies of Downhole Catalytic Upgrading of Wolf Lake Heavy Oil Using THAI", CIPC Paper No. 2001-17, Canadian International Petroleum Conference, Calgary, 12-14, June (2001).
Greaves, M, and Xia, T. X.: "CAPRI - Downhole Catalytic Process for Upgrading Heavy Oil: Produced Oil Properties and Composition", CIPC Paper No. 2001-23, Canadian International Petroleum Conference, Calgary, 12-14, June (2001).
Coates, R. and Zhao, L.L.: "Numerical Evaluation of the THAI Process", paper CIM 2001-021, Canadian International Petroleum Conference, Calgary, 12-14, June (2001).
Xia, T. X, and Greaves, M.: "THAI- A 'Short-distance Displacement' In Situ Combustion Process for the Recovery and Upgrading of Heavy Oil", submitted to Trans. IChemE.
Xia, T. X, Greaves, M. and A Turta.: "Injection Well - Producer Well Combination in THAI Toe-to-Heel Air Injection", SPE Paper 75137, to be presented at the SPE/DOE Thirteenth Symposium on Improved Oil Recovery held in Tulsa, Oklahoma, 13-17 April 2002.
Xia, T. X, Greaves, M. Werfilli, S. M., And Rathbone, R.: "THAI Process - Effect of the oil layer thickness on heavy oil recovery", Submitted to Canadian International Petroleum Conference, June 11 - 13, 2002, Calgary, Alberta, Canada.

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