Experimental and Numerical Investigations Into Oil-Drainage Rates During Vapor Extraction of Heavy Oils

Abstract

A set of analog vapor-extraction (VAPEX) laboratory experiments was performed to test the ability of existing analytic and numerical models to predict oil-drainage rates from this process. The selected analog fluids and porous media enabled all input parameters to the analytic model to be determined independently of the analog VAPEX experiments without history matching. The results show that the underprediction of oil rate by the standard analytic model is not because of increased levels of mixing between the solvent and oil over that expected from molecular diffusion and convective dispersion, but rather because of a deficiency in the analytic model formulation.

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.…”

“…Following Alkindi et al [5,6] we used glycerol to represent the oil and ethanol to represent the vapour. These analogue fluids were chosen so that:…”

“…Simulations have previously shown that this results in a constant pressure drop between the injector and producer as is required for a VAPEX process [6]. The ethanol was dyed with Lissamine green (C 27 H 25 N 2 NaO 7 S 2 ) in very small concentrations (0.03 g/400 cc) in order to be able to observe the solvent chamber segregation.…”

“…This allowed images to be taken of the fluid distributions and then analysed. This dye was chosen because it does not affect the measured refractive index and, unlike methylene blue, does not bleach over time once in contact with glycerol [6]. The effluent produced was collected using 1 ml measuring cylinders for accuracy in measuring the production volumes.…”

“…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.…”