LAUSR

Abstract A novel methodology utilizing high-pressure Hele-Shaw-like visual cell has been developed to study solvent dissolution and exsolution behavior of a CO2-heavy oil system. The experimental setup overcomes the visualization shortcomings of traditional apparatuses such as a hardly-visual cylindrical PVT cell, or non-visual transfer cylinders. Experimentally, a heavy oil sample (viscosity at 1500cP at de-gassed state) was used to conduct solvent dissolution and exsolution tests. CO2 diffusion tests have been conducted by pressure decay method. At the end of each diffusion stage, pressure depletion tests were subsequently conducted on the CO2-heavy oil system to study foamy oil stability under different pressure depletion schemes. The effect of various factors on the foamy oil volumetric behavior have been investigated, including the effect of initial solution GOR, continuous pressure depletion rate, immediate pressure drawdown level and solvent-heavy oil contact time. A MATLAB-controlled reservoir simulator was developed for numerical validation. For solvent dissolution tests, CO2 diffusion coefficient in oil (intra-phase mass transfer) was optimized and achieved by history matching the pressure decay curves. Results showed that, diffusion coefficients increased from 6.198 × 10−9 to 25.333 × 10−9m2/s when pressure increased from 1555 to 3320 kPa. Solvent exsolution behavior was simulated through defining multiple kinetic reactions. Kinetic reaction rate frequency factors (RRFs), which indicated the rate of multi-component inter-phase mass transfer, were achieved by history matching foamy oil volume under multiple operational schemes. Comparing RRFs, foamy oil stability was found to be increasing under higher initial GOR, pressure depletion rate and pressure drawdown as well as for longer solvent-heavy oil contact time.