The role of reservoir fluids and reservoir rock mineralogy on in-situ combustion kinetics

Abstract

In-situ combustion (ISC) is a complex process with great potential. This study aims to simplify some of the complications associated with the reaction kinetics of ISC and investigate the impact of reservoir rock composition and crude oil fractions on the reaction kinetics of ISC.Sixty-six reaction kinetics experiments were conducted using Thermogravimetric Analysis/Differential Scanning Calorimetry (TGA/DSC) on two heavy crude oil samples and two types of porous media (clays and carbonates). In these experiments, a 5 °C/min heating rate was used to simulate the low-temperature-oxidation (LTO) region, and a 20 °C/min heating rate was used for the high-temperature-oxidation (HTO) region. The role of crude oil composition on the reaction kinetics of combustion was also investigated through saturates, aromatics, resins, and asphaltenes (SARA) fractionation. The two crude oils were first separated into their SARA fractions, and then the reaction kinetics of individual fractions and their two and three component pseudo-blends were studied.‘To understand the contribution of aquathermolysis reactions, the crude oils and their SARA fractions were mixed with water, and the reaction kinetics tests were repeated in the presence of water. The chemical reactions occurring in the presence and absence of water in crude oil and their fractions were discussed using control experiments conducted on known simple hydrocarbons: n-decane (C10H22), n-decanal (C10H20O), n-decanol (C10H22O), and decanone (C10H20O). Additionally, the reactivity of the mineralogy of the porous media was examined, and both clay and carbonates were tested. All experiments were analytically modeled to obtain reaction kinetics parameters in terms of activation energy (Ea) and heat generation (ΔH).The results show that while emulsified water decreases the effectiveness of the combustion process, the presence of initial water increases it. This is due to the increase in heat generation and decrease in activation energy, which is mainly caused by the interaction between water and aromatics fractions (aquathermolysis reaction) at elevated temperatures. The amount of clay in the reservoir is critical for the success of the ISC process. If the reservoir has a higher clay content than a certain threshold, the combustion performance will be compromised. Resins fractions have a higher tendency to interact with carbonates during ISC in the HTO region.Overall, this study provides simplified analytical approaches based on experimental results to better understand the ISC chemical reaction kinetics for different types of crude oil and reservoir rocks.