Stability of THAI in situ combustion process in reservoirs with layers of grading permeabilities and porosities: Detailed qualitative investigations

Ado, Muhammad Rabiu; Greaves, Malcolm; Rigby, Sean P.

Abstract

The world-wide reserves of heavy oil, tar sand, and bitumen, etc., outweigh those of conventional oil by a factor of 7/3. Given that the conventional reserves are being rapidly depleted, the need to develop and produce the unconventional resources has never been so critical. However, the proven most efficient and environmentally-friendly technology, namely the THAI process, still requires further study, and it has no documented design procedures that factor in the non-ideal geological features of heavy oil and bitumen reservoirs. Throughout the literature, there is little reported on the effects of gradations in reservoir petro-physical parameters on the performance of the THAI process. Consequently, this work reports the results of numerical simulations for four different kinds of reservoirs, each having progressive gradations in permeabilities and porosities. The major findings from this in depth study include. (i) In terms of the temperature distribution, regardless of the permeability and porosity gradations, the high temperature zone is always skewed towards the highest permeabilities and porosities zone. Furthermore, it is found that, in any model in which the shoes of the VI wells have no direct communication pathway with the highest permeabilities and porosities zones of the reservoirs, the high temperature zones occur in two chambers, otherwise, there is one high temperature zone. (ii) It is found that generally, the combustion front tends to be lopsided in favour of the most permeable and porous zone. In the case of a bottom-up progressive increase in permeabilities and porosities (model L1), the single combustion front has greatest advance horizontally at the top and axially in the middle of the reservoir, while in model L2 (the converse of model L1), the combustion fronts propagated in two chambers before the chambers overlapped in the toe region of the HP well where it advanced fastest. Therefore, the combustion zone in model L1 was far more stable than in model L2. (iii) It is found that the combustion fronts in model L3, with the lowest permeabilities and porosities at the centre in the longitudinal direction, propagated in two chambers that overlapped each other around the toe region of the HP well and advanced greatest in the HP well and on either lateral edge of the reservoir. In model L4, which has lateral gradation in permeabilities and porosities, however, the thinner edge of the wedge-shape combustion front had advanced fastest along the vertical mid-plane where the HP well was located. Thus, the combustion zone in model L3 was far more stable than that in model L4. (iv) It is found that in all the models except model L4, there exist rich oil saturation zones in the most permeable and porous regions located ahead of the mobile oil zone (MOZ) of each reservoir. These are formed due to restrictions in the pathways via which the mobilised oil can drain into the HP well. In model L4, the HP well is already in the most permeable zone and consequently, the fluids that favourably reach there are rapidly gravity-drained into the HP well.

Citation

Ado, M. R., Greaves, M., & Rigby, S. P. (2024). Stability of THAI in situ combustion process in reservoirs with layers of grading permeabilities and porosities: Detailed qualitative investigations. Geoenergy Science and Engineering, 241, Article 213158. https://doi.org/10.1016/j.geoen.2024.213158

• Journal Article Type: Article
• Acceptance Date: Jul 22, 2024
• Online Publication Date: Jul 28, 2024
• Publication Date: 2024-10
• Deposit Date: Aug 29, 2024
• Publicly Available Date: Aug 29, 2024
• Journal: Geoenergy Science and Engineering
• Print ISSN: 2949-8929
• Electronic ISSN: 2949-8910
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 241
• Article Number: 213158
• DOI: https://doi.org/10.1016/j.geoen.2024.213158
• Keywords: In situ combustion (ISC); Enhanced oil recovery (EOR); Heavy oil/bitumen/tar sand; Reservoir simulation; Toe-to-heel air injection (THAI); Permeabilities and porosities gradations
• Public URL: https://nottingham-repository.worktribe.com/output/37858735
• Publisher URL: https://www.sciencedirect.com/science/article/pii/S2949891024005281
• Additional Information: This article is maintained by: Elsevier; Article Title: Stability of THAI in situ combustion process in reservoirs with layers of grading permeabilities and porosities: Detailed qualitative investigations; Journal Title: Geoenergy Science and Engineering; CrossRef DOI link to publisher maintained version: https://doi.org/10.1016/j.geoen.2024.213158; Content Type: article; Copyright: © 2024 The Authors. Published by Elsevier B.V.