(286g) Study on Flow Behavior of CO2-in-Water (C/W) Emulsion in the Porous Medium Under Hydrate Stability Conditions
AIChE Annual Meeting
2017
2017 Annual Meeting
Engineering Sciences and Fundamentals
Gas Hydrates Science and Engineering
Tuesday, October 31, 2017 - 9:42am to 9:59am
In the simulation program, five governing equations are solved: Three continuity equations of H2O component, liquid CO2 component, and total CO2 component (liquid and dissolved CO2) in C/W emulsion; one equation of describing transport of CO2 hydrate particles; and one energy balance equation considering heat convection/conduction and the heat of hydrate formation/CO2 dissolution into water. These equations are formulated based on the following assumptions: (1) C/W emulsion flows as a homogeneous phase before hydrate formation. (2) CO2 droplets are converted into hydrate particles at a given rate after induction time (thin films are formed around CO2 droplets). (3) Hydrate particles are transported in the pore by emulsion flow and dispersion, where some particles are trapped on the pore surface and the pore throat of the porous medium. (4) The permeability of the porous medium decreases with increasing saturation of trapped hydrate particles. In the numerical procedure, five independent variables of pressure, temperature, concentration of H2O and liquid CO2 in C/W emulsion, and saturation of flowing hydrate particles are solved by five governing equations.
To examine the validity of numerical calculation, a number of experiments were conducted to inject C/W emulsion (CO2 vol. concentration of 10-30%) into 0.1 mm glass-bead sintered water-saturated cores under controlled pressure and temperature conditions of 7 MPa, 7°C and 5 MPa, 2°C. The length of the core was 10 cm, and injection pressure and core surface temperatures at the locations of 2.5 cm, 5 cm, and 7.5 cm from inlet were sequentially recorded during the experiment. In most experiments, we observed that inlet pressure rose steeply to lead the core plugged a certain time after the increase in temperatures by hydrate formation.
After confirming that simulation could reproduce the tendency of pressure and temperature behavior during the experiments, numerical case studies were carried out to find appropriate injection schemes of C/W emulsion maximizing the heat of CO2 hydrate formation until the plug of the core. The following conclusions were obtained. (1) Heat of 10-16 MJ/m3 of the porous medium is generated during C/W emulsion until the plug of the core. This corresponds to the heat value that can dissociate about 10 % of MH. (2) The lower the CO2 concentration of C/W emulsion, the smaller the heat generation rate of hydrate formation, but the time to core plugging is much delayed compared with the case of high CO2 concentration. As a result, the use of lower CO2concentration generated the maximum heat. This study showed that C/W emulsion injection method would be effective to increase gas recovery efficiency from MH if we select an appropriate injection scheme.