Dynamic and Static CO2 Mass Transfer Processes in Bulk Heavy Oil and Heavy Oil Saturated Porous Media

Abstract

In the petroleum industry, the contribution of solvents to the production of oil has become more cardinal, as production from the reservoirs have advanced from primary oil production to secondary and tertiary methods. Vapour extraction (VAPEX), CO2 flooding, CO2 Huff-and-Puff are some of the solvent based approaches used in the industry to enhance oil recovery performance. These methods involve the injection of a vaporized solvent into the reservoir in order to reduce the viscosity of the oil and increase the oil mobility. The main mechanism that contributes in the solvent-based enhanced oil recovery method is the mass transfer from the solvent to the oil phase. Hence, it is essential to have deep knowledge about the interactions and mass transfers that occur between the solvents and oil in the solvent-EOR processes. The primary objective of this research is to identify the main processes governing the interfacial mass transfer of CO2 into heavy oil in the bulk phase under static and dynamic conditions. This study commenced with pressure decay experiments at static oil condition, where CO2 was brought in contact with two different types of oil samples. It then continued by using a reactor (PARR-4560) to investigate the influence of convection in the bulk heavy oil. Experiments were directed in the reactor, where a stirrer was implemented to make a semi flowing condition in the oil phase (i.e., dynamic condition). In these experiments, pressures of 1.734.48 MPa and temperature of 295305 K for the oil samples with 5 and 20 Pa.s viscosities were selected as the operational conditions. Additionally, proper mathematical model defining the experiments for each condition were developed. The model describing the static condition was solved analytically to obtain CO2 diffusion coefficient; however, numerical approach was utilized under dynamic condition. PDETWO routine, a solver for systems of partial differential equations that uses normal differential equation integration, was implemented to solve the model and obtain the diffusion coefficient. This thesis also proposes a novel experimental design for measuring CO2 diffusion coefficient in porous media. A hollow sand pack model was improvised to simulate a well-bore area, when CO2 and oil are in contact. In this model, CO2 is in the inner space, and the heavy oil saturated sand is placed in the outer space of the model. Six experiments in pressure range of 1.734.48 MPa, and at temperature of 301 K for the oil samples with 5 and 20 Pa.s viscosities were operated. Once more, pressure decay method was used to measure the solubility of CO2 in the oil saturated porous model. Besides, the proper mathematical model (i.e., cylindrical diffusion equation) along with the conditions that are in agreement with the physical condition of the model were developed. PDETWO solver was then employed to determine the diffusion coefficient in oil saturated porous model. Finally, the results of CO2 solubility and diffusion coefficient under different operating condition were compared and analyzed with the data gathered in the bulk studies. Moreover, by using the data obtained from these experiments and the available data in the literature, a model for CO2 solubility in heavy oil is proposed.