The project goals are to probe the dynamics of in-situ combustion (ISC) experimentally and numerically, determine how the dynamics may be altered beneficially to expand the applicability and the recovery associated with combustion, and develop process simulation methodologies and capabilities that resolve in-situ combustion dynamics accurately.

Stanford University, Stanford, CA

ISC, or air injection, is the process of injecting oxygen into oil reservoirs to oxidize the heaviest components of the crude oil and enhance oil recovery though the heat and pressure produced. In forward ISC, air (possibly enriched with oxygen) is injected into the reservoir at judiciously chosen injection wells. The oil is ignited spontaneously or by external means. Oil viscosity is reduced at an elevated temperature, and the oil is driven towards the producing wells by a vigorous gas drive of the combustion gases, a steam drive, and a water drive (water of combustion and recondensed formation water). The combustion front itself is propagated by a continuous flow of air. Despite its attractive qualities, application of ISC is not widespread for a variety of reasons, including the relatively large expense required to evaluate prospects and a lack of systematic reliability with regard to displacement efficiency.

Results
Achievements and successes to date include the following:

• Combustion kinetics of Ugnu and West Sak crude oils were measured in the laboratory. Lighter crude oils (Cymric, CA) were tested as well. On the experimental side, it is apparent that metallic additives improve combustion of light oil. Without additives, some light oils (such as Cymric) could not sustain combustion. The effect of metallic additives on the combustion of heavy oils is more case-specific.
• An understanding was developed of the mechanism by which metallic additives act. Using scanning electron microscopy and elemental analysis, it was found that metallic additives ion-exchange with the rock matrix. The implication is that metallic salts dissolved in aqueous solution are likely applicable at field scale.
• The technical feasibility of a new recovery process using cyclic injection of solvent followed by combustion was tested experimentally using combustion tube runs and ramped temperature oxidation.
• A new simulation tool, based on an efficient Cartesian Adaptive Mesh Refinement (AMR) technique was designed. This tool allows much higher grid densities to be used near typical fronts than current simulators. AMR reduces the dependency on grid size and empirically determined subgrid scale models and allows a more accurate representation of the physics.
• A simulator for the classical formulation of the ISC three-phase and six-component governing equations was developed. In such systems, the number of phases present within a given grid-block may vary, so the number of unknowns that fix the thermodynamic state of the fluids also varies accordingly.
• In 3-D, Stanford has implemented an Cartesian Cell-based Anisotropic Refinement (CCAR) technique, based on the work by Ham, et al. This is the first time this technique has been applied to petroleum engineering in general and ISC processes in particular. The anisotropic refinement is a natural approach because of the typically highly structured nature of reservoir heterogeneity. Upscaling methods appropriate to CCAR grid were designed and implemented. A new multi-point flux approximation was developed for CCAR grids.
• A virtual kinetic cell model was developed to derive suitable numerical integrators for the stiff kinetics involved in the ISC processes. This model was used to investigate sensitivities of kinetics simulation to phase behavior models. The numerical integrators were extended with a specialized phase change detection algorithm to increase their robustness.
• A virtual combustion tube model was developed that combines the new integrators for kinetics with the operator splitting method. It is the first model of its kind that contains full phase behavior. The model was used to investigate the sensitivity of ISC performance prediction to phase behavior models.
• An isoconversional technique for interpretation of reaction kinetics was adapted to analysis of in-situ combustion reactions.

Benefits
Two-thirds of the oil discovered in the United States remains in the ground. Thermal recovery, and more specifically ISC, is well-suited to unlock effectively the unconventional and remaining oil resources of the United States in an environmentally sound manner. Whereas it is generally classified as a technique that is applicable for heavy oils because of the dramatic reduction in oil viscosity with temperature, ISC also promotes production through flue-gas drive, thermal expansion, and vaporization of lighter oils. ISC can recover oil economically from a variety of reservoir settings. The wet forward ISC process is directly applicable to waterflooded conventional oil reservoirs. Further, the process has proven to be economical in recovering heavy oil from shallow reservoirs and lighter oil from deep reservoirs, where steam injection and waterflood are economically unattractive. It is also an ideal process for producing oil from thin formations, being most effective in 10-50-ft thick sandbodies. This project improves the attractiveness of ISC by improving the predictability of process with respect to displacement efficiency and by discovering variants of ISC that expand the applicability of ISC.

Summary
The project combines experimental and numerical tasks. The purpose is to expand the scope of reservoirs where ISC is applicable—and actually applied—through development of fundamental, experimental understanding of this advanced recovery process. Advanced recovery concepts to study include the injection of the salts of common metals prior to air injection to shift combustion to high-temperature oxidation and cyclic solvent/combustion processes that promote in-situ upgrading of crude oil. An advanced recovery process is more likely to be implemented if accompanied with a mechanistic simulator. Current simulation of ISC processes lack resolution of the high-temperature combustion front as well as include unrealistically large heat losses. The simulation approach will utilize AMR for accurate resolution of combustion temperature that, in turn, is needed to interpret the operative field-scale combustion mechanisms and oil displacement.

The specific objectives for this research include:

• Identification, experimentally, of chemical additives/injectants that improve combustion performance and delineation of the physics of improved performance.
• Establishment of a benchmark one-dimensional, experimental data set for verification of ISC dynamics computed by simulators.
• Develop improved numerical models for ISC processes.
• Design a highly efficient ISC simulator using AMR techniques and parallelization.

(December 2008)
This project is completed and the final report is listed below under "Additional Information".

$1,000,000

$250,000

NETL – Chandra Nautiyal (chandra.nautiyal@netl.doe.gov or 918-699-2021)
Stanford U. – Anthony Kovscek (kovscek@pangea.stanford.edu or 650-723-1218)
Stanford U. - Margot Gerritsen (mgerritsen@stanford.edu or 650-725-2727)

Final Project Report [PDF]

Publications
Gerritsen, M., A.R. Kovscek, L. Castanier, J. Nilsson, R. Younis, and B. He, "Experimental Investigation and High-Resolution Simulator of In-Situ Combustion: 1. Simulator Design and Improved Combustion With Metallic Additives," SPE 86962, Proceedings of the SPE International Thermal Operations and Heavy Oil Symposium and Western Regional Meeting, Bakersfield, CA, March 16–18, 2004.

He, B., Q. Chen, L.M. Castanier, and A.R. Kovscek, "Improved In-Situ Combustion Performance with Metallic Salt Additives," SPE 93901, Proceedings of the SPE Western Regional Meeting, Irvine, CA, March 30–April 1, 2005.

Castanier, L.M. and A.R. Kovscek, "Heavy oil upgrading in-situ via solvent injection and combustion: A ‘new’ method," Proceedings of the EAGE 67th Conference & Exhibition, Madrid, Spain, June 13–16, 2005.

Cristofari, J., L.M. Castanier, and A.R. Kovscek, "Laboratory Investigation of the Effect of Solvent Injection on In-Situ Combustions,” SPE 99752, Proceedings of the SPE Symposium on Improved Oil Recovery, Tulsa, OK, April 22-26, 2006.

Lambers, J., Gerritsen, M., and Mallison, B., “Accurate Local Upscaling with Compact Multi-Point Transmissibility Calculations,” Special Issue on Multi-Scale Methods, Computational Geosciences, 2006.

Kristensen, M., Gerritsen, M., Thomsen, P., Michelsen, M., and Stenby, E., “Efficient Reaction Integration for Efficient Combustion Simulation,” Transport in Porous Media, 2006.

Younis, R. and Gerritsen, M., “Split-Operator Compositional Simulation of Thermally Reactive Recovery Processes,” SPE 103226/ M. Gerritsen and J. Lambers , “A Specialized Upscaling Method for Adaptive Grids,” Computational Geosciences, 2006.

M. Gerritsen and J. Lambers , “A Specialized Upscaling Method for Adaptive Grids,” Computational Geosciences, 2006.

R. G. Awoleke, "An Experimental Investigation of In-Situ Combustion in Heterogeneous Media," Proceedings of the SPE Annual Technical Conference and Exhibition, Anaheim, CA Nov. 11-14. 2007.