CORE ANALYSIS ISSUES IN HEAVY OIL RECOVERY USING VAPEX

recovery using solvent based processes for in-situ recovery of very viscous and bitumen is an emerging new technology in Canada. The core analysis and testing of process conditions has not been standardized yet. This paper aims to provide a review of the various studies that aimed to collect lab-scale data and upscale the results to field-scale conditions. A summary of the research results obtained in our laboratory over the past three years are presented and discussed. Results obtained in our research and by others demonstrate that heavy recovery experiments in long enough systems are desirable for predicting production rates. Analysis of production history shows that the dispersion coefficient is orders of magnitude larger than the diffusion coefficient measured in stagnant heavy oil. INTRODUCTION our EXtraction (VAPEX) is an enhanced recovery technique developed primarily by Canadian researchers, for the recovery of Canada's vast heavy reserves. Conventional recovery practices can not be used for the production of heavy and bitumen because the viscosity of heavy is too high and it does not readily flow under normal reservoir conditions. The viscosity of heavy is generally between 1000 mPa.s and 10,000 mPa.s while the viscosity of bitumen is greater than 10,000 mPa.s. The primary driving forces in VAPEX are the mass transfer of the solvent into the heavy followed by the gravity drainage of the oil (viscosity reduced heavy containing the dissolved solvent) to the production well. Normally, the VAPEX process is represented with two horizontal wells; the upper one used for solvent injection and the lower one for producing the live oil. First, the solvent is injected into the injection well where it diffuses through the heavy primarily in the upward direction until it encounters an impermeable barrier zone, the rock. The diffusion of the solvent into the heavy oil/bitumen reduces the oil's viscosity, thus mobilizing it under the force of gravity to the production well. Upon encountering the cap rock, the solvent continues to diffuse into the heavy but in an outwards direction in a continuous cycle of solvent diffusion into the heavy oil, viscosity reduction and live drainage. Figure 1 shows the live being mobilised by the solvent diffusing into it due to the concentration difference of the solvent. As the live with significant solvent in it drains, a new layer of heavy is exposed to the solvent phase at the VAPEX interface. The new layer is subjected to the same mass transfer driving force that continues the cycle of essentially peeling away layers of heavy oil. In this manner, the VAPEX interface advances through the permeable zone saturated with heavy oil. VAPEX technology competes with Steam Assisted Gravity Drainage (SAGD) technology which is currently used for heavy recovery. At present, there have been no VAPEX field trials in

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