Impact of asphaltenes and clay interaction on in-situ combustion performance

Abstract

The increased surface area of reservoir rock due to the presence of clays and the catalytic impact of clays are known to enhance the in-situ combustion (ISC) performance. But the basics behind these mechanisms are still unknown. Six one-dimensional (1-D) combustion tube experiments were conducted on three different crude oil samples. Each crude oil was evaluated with two combustion tube runs; sand-oil and sand-clay-oil mixtures to study the effect of clay on combustion performance. Then, Thermogravimetric Analysis/Differential Scanning Calorimetry (TGA/DSC) was run at isothermal conditions by ramping up the temperature using the combustion tube temperature. The activation energy and the heat of combustion were calculated empirically. The quality of the produced oil samples was determined through viscosity measurement and saturates, aromatics, resins, and asphaltenes (SARA) fractionation. To better understand the fuel formation mechanism, the compositional variations in SARA fractions have been analyzed through Fourier Transform Infrared (FTIR). Further, asphaltenes surfaces were visualized by Scanning Electron Microscope (SEM) and the Energy Dispersive Spectroscopy (EDS). The combustion tube experimental result shows that saturates fractions have been decreased in displaced oil since saturates are consumed as an ignitor during ISC. The aromatics fraction has been significantly increased in produced oil, which helps to increase the mobility of displaced oil through viscosity reduction. Moreover, the amount of asphaltenes in produced oil decreased due to fuel formation reactions. In the presence of clays, the cribriform structures were formed on asphaltenes surface and aid the combustion process by increasing the surface area of asphaltenes.