Experimental Study of Heavy Oil Recovery Mechanisms During Cyclic Solvent Injection Processes

Abstract

In recent years, the Cyclic Solvent Injection (CSI) process has shown to be a promising method for enhanced heavy oil recovery in Canada. CSI laboratory studies work for only 2 to 3 cycles due to low incremental oil in subsequent cycles whereas field pilots continue for years over multiple cycles This experimental study is intended to capture the production mechanisms responsible for heavy oil production in CSI.Primary production and CSI tests were conducted using physical sandpack models saturated with live heavy oil of 9,530 mPa.s viscosity. The experiments were conducted in horizontal and vertical mode injection at high and low-pressure depletion rates using two solvent mixtures of CH4 and C3H8. The sandpack was Computed Tomography scanned after every cycle to analyze the evolution of gas and oil saturations. Three cores were used to study the effect of gravity forces, depletion rate, solvent composition, and initial oil saturation (dead/live oil systems) on the performance of CSI processes.CSI after primary in horizontal systems produced negligible incremental oil for both slow and fast drawdown rates due to the large void space and high free gas saturation inhibiting the pressure build up to push the solvent-diluted oil. These CSI experiments were only successful in dead oil systems, where the initial oil saturation was high and pressure gradient was generated through fast depletion rates until conditions of high void space and gas channels were reached.When the sandpack was flipped vertically, CSI cycles exhibited higher incremental oil recovery per cycle. Slow depletion cycles were more efficient in terms of pressure and incremental recovery per cycle, however faster depletion cycles performed better as a function of time. The higher C3H8 content solvent mixture exhibited better performance in comparison to the lower C3H8 content as