With population growth, increasing world energy demand and depletion of conventional oil resources, exploiting heavy and extra-heavy oil reservoirs seems one of the promising options in supplying world oil request. However, there are several barriers to the rapid growth of production from such reservoirs.
CO2-based enhanced oil recovery (CO2-EOR) techniques are among processes utilized to enhance heavy oil and bitumen production. The design and modeling of CO2-EOR require extensive knowledge about the solubility and diffusivity of CO2 in heavy oil. Hence the primary objective of this research was to identify the main mechanisms involved in the static and dynamic mass transfer of CO2 into the heavy oil systems.
This experimental study commenced by allowing CO2 to be in contact at static condition with two different types of heavy oil having viscosities of 5000 and 20000 cP at 298 K. Experiments were conducted at three different initial pressures (1.73, 3.10, 4.49 mPa) and pressure decay concept was used to determine the CO2 solubility for each individual case. The experiments then were extended using a Mini-bench top reactor (PARR-4560) from Parr Instrument Company to repeat similar tests in dynamic condition. Using the reactor's stirrer, the oil was agitated at the velocity of 30 rpm; thereby a semi-flowing condition was generated leading a convection effect in the oil bulk phase. For both dynamic and static conditions, the proper mathematical model were proposed and solved numerically to determine the diffusion coefficient value at each specific operating condition.
Results showed that the solubility of CO2 at initial pressure of 1.73 mPa for 5000cP oil is 0.04015, and 0.04195 g/100cc for static and dynamic conditions, respectively. The diffusion coefficient value at static and dynamic condition for the same experimental condition is 4.531×10-10 m/s2 and 4.852×10-10 m/s2. Experimental and mathematical interpretations of other cases showed similar behaviour. From the results at both conditions it can be obtained that the initial pressure has significant effect on reaching the stability condition and longer time is required for higher pressures. Moreover, diffusion coefficient is more sensitive to oil viscosity rather than ultimate solubility value.