Experimental Investigation of Air Flux Impact On Reactions Occurring During In-Situ Combustion in Dolomite Reservoirs - Implications for Air Injection Strategies
Authors: Fazlyeva R. , Fassihi R. , Mallory D. , Moore R. , Ursenbach M. , Mehta S. , Cheremisin A. 
Published: April 2024

One of the key undertakings during the energy transition is the assurance of process efficiency in oil and gas operations. By streamlining and optimizing different aspects of production operations, the overall carbon footprint can be reduced. Newly obtained laboratory data on the air injection process could potentially help with making this process more efficient.

Historically, the transition from low-temperature range (LTR) to high-temperature range (HTR) during heavy oil in-situ combustion (ISC) has been attributed solely to oil characteristics. However, our research challenges this conventional perspective, underscoring the pivotal role of air flux rates in governing these reaction regime shifts. This study aims to deepen our understanding of the thermal behavior of heavy oil within dolomite reservoirs during ISC. It also shows how to integrate the calorimetry tools to obtain new information on this process.

Multiple tests were conducted at a reservoir pressure of 1,740 psig (13 MPag), involving variations in the initial mass of oil and dolomite samples, as well as air injection rates. We utilized both the Calvet C600 and Accelerated Rate Calorimeters (ARC). These units were equipped with mass flow controllers (MFCs) to ensure precise air supply, effluent gas analyzers for product gas component analysis, and wet test meters (WTMs) for measuring produced gas volume. Post-test mass differentials of samples were analyzed extensively. Calvet C600 data demonstrated that the rate of air injection significantly impacts the mode of oxidation and combustion reactions. High air injection rates seem to primarily induce LTR, which is unfavorable for field operations. This observation is reinforced by consistent gas analysis results, showing lower oxygen conversion to CO2 and CO, reduced oxygen utilization, and increased oxygen consumption during low-temperature oxidation (LTO) and water formation reaction in the LTR regime. Conversely, lower air injection rates seem to lead to a shift toward HTR reactions. Cross plots of oxygen uptake versus heat release further confirm these trends, with ARC tests yielding values of 8,000 to 13,000 J/g of oxygen uptake, compared to 13,000 to 16,000 J/g in the Calvet C600 tests.

Our innovative approach allows for a comprehensive comparative analysis and result validation between ARC and Calvet C600. We were able to expand the range of applicability of reaction kinetic parameters to optimize combustion processes and ensure safety measures. Our findings also suggest the need to incorporate a mass transfer coefficient into reaction schemes to better model oxygen uptake rates at varying air fluxes. This coefficient should depend on the oxygen uptake rate at different temperatures. The new application of Calvet C600 and ARC in tandem offers a robust data-gathering approach for the in-situ combustion process. Our findings challenge traditional notions of the use of high air flux and emphasize the significance of a proper air flux during the initial phase of a new air injection project and its variation as the project expands.