Interplay of Capillarity, Drainage Height, and Aqueous Phase Saturation on Mass Transfer Rate of Solvent Vapor into Heavy Oil

Abstract

Performance of the vapor extraction process is strongly dependent on the efficiency of the mass transfer rate between the solvent and heavy oil or bitumen. Therefore, realistic approximation of diffusion and convective dispersion occurring on the edge of the vapor chamber is required for reliable prediction of production rates in this process. Studies conducted at extremely high permeabilities (>200 D) have reported up to four orders of magnitude increase in the solvent diffusion/dispersion rates between the solvent and heavy oil, such increases could result in unrealistic overestimation of the performance of this process at real reservoir conditions. To address this shortcoming, a comprehensive experimental study was designed and conducted to systematically investigate the interplay of capillarity, drainage height, and aqueous phase saturation on efficiency of mass transfer rate in permeability range similar to western Canadian heavy oil and bitumen reservoirs (i.e. 5.1-6.5D). In order to experimentally simulate the vapor extraction process, a new experimental approach was developed to eliminate the effect of pressure disturbances occurring during the course of experiment (20-45 days) and investigate the interplay between studied parameters in a gravity dominant system. In this study, measured stabilized drainage rates per unit length of porous media (9.17×10 -7 -3.33×10 -5 cm 3 /s/cm) revealed functionality with drainage height, specific pore surface area of the porous medium, and presence of aqueous phase at higher capillarities. Moreover, analytical modeling was conducted to determine the effective diffusion/dispersion coefficient, which showed convective dispersion is not playing a prominent role in mixing between solvent and heavy oil as it was proposed by studies conducted in high permeabilities. In addition, comparison between the stabilized drainage rates of oil in absence or presence of water saturation confirmed that the presence of water phase enhances the drainage rates at higher capilarities, which is in contradiction with previous studies investigating the effect of aqueous phase saturation on mass transfer rate in higher permeabilities. This paper provides indepth knowledge of the impact of three major parameters that affect the rate of the mass transfer between heavy oil and solvent, and that are necessary for realistic modeling of the performance of the vapor extraction process.

Thoughts on Simulating the Vapex Process

“…This argument, despite its approximations, suggests that molecular diffusion will completely dominate the mixing at field scale permeabilities of a few Darcys. A similar conclusion was reached, based on low permeability laboratory experiments, by several other investigators (Cuthiell et al, 2006, Ahmadloo et al, 2011.…”

Experimental and numerical investigations into the effect of heterogeneities on the recovery of heavy oil by VAPour EXtraction (VAPEX)

“…This difference is similar to that seen by Das and Butler as can be seen from fig:6 where we have plotted the observed and predicted oil drainage rates as a function of the square root of permeability [16]. This discrepancy has also been observed by other workers [1][2][3][4][5][6][7][8]12,13,[15][16][17][20][21][22][23][25][26][27][28]50,52] and suggests that there is some problem with the Butler-Mokrys equation.…”

“…This analysis assumes first contact miscibility between the oil and the vapour. This is clearly much simpler than performing a fine grid simulation to predict VAPEX performance but unfortunately seems to systematically underpredict the drainage rate seen in laboratory experiments [1][2][3][4][5][6][7][8]13,14,[16][17][18][20][21][22][23][24][25][26][27][28] In contrast, the only published field pilot (in Soda Lake, Saskatchewan) obtained oil production rates a factor of 10 lower than predicted. A further uncertainty in the field scale application of VAPEX is the impact of geological heterogeneity.…”

Observations on the Mechanisms of Solvent-Additive SAGD Processes

“…with a 'height exponent' of 0.5. On the other hand, recent experiments with metre-high models [1,21,22] have instead measured exponents in the range of about 1.1-1.3. This result would seem to severely undermine a founding assumption of B-M, namely that solvent transport is controlled by diffusion through a finite layer of liquid, which accumulates (thickens) as it flows down the frontal surface.…”

“…Solvent-additive SAGD processes (SAP) are the subject of a growing number of numerical studies [3,8,10,11,17,20,23,25], physical models [1,3,7,9,14,18,[20][21][22]24], and field tests[6,12,13]; and has been or is planned to be commercially implemented[15], based on pilot success. Serious interest in SAP followed from successful trials with butane addition, at Senlac[13] and later Christina Lake[12].…”