Summary
This paper presents a new experimental method and its computational scheme
for measuring solvent diffusivity in heavy oil under practical reservoir
conditions by DPDSA. In the experiment, a see-through windowed high-pressure
cell is filled with a test solvent at desired pressure and temperature. Then, a
heavy-oil sample is introduced through a syringe delivery system to form a
pendant oil drop inside the pressure cell. The subsequent diffusion of the
solvent into the pendant oil drop causes its shape and volume to change until
an equilibrium state is reached. The sequential digital images of the dynamic
pendant oil drop are acquired and digitized by applying computer-aided digital
image-acquisition and -processing techniques. Physically, variations of the
shape and volume of the dynamic pendant oil drop are attributed to the
interfacial tension reduction and the well-known oil-swelling effect as the
solvent gradually dissolves into heavy oil. Theoretically, the interfacial
profile of the dynamic pendant oil drop is governed by the Laplace equation of
capillarity, and the molecular diffusion process of the solvent into the
pendant oil drop is described by the diffusion equation. An objective function
is constructed to express the discrepancy between the numerically predicted and
experimentally observed interfacial profiles of the dynamic pendant oil drop.
The solvent diffusivity in heavy oil and the mass-transfer Biot number are used
as adjustable parameters and thus are determined once the minimum objective
function is achieved. This novel experimental technique is tested to measure
diffusivities of carbon dioxide in a brine sample and a heavy-oil sample,
respectively. It should be noted that, with the present technique, a single
diffusivity measurement can be completed within an hour and only a small amount
of oil sample is required. The interface mass-transfer coefficient at the
solvent/heavy-oil interface can also be determined. In particular, this new
technique allows the measurement of solvent diffusivity in an oil sample at
constant prespecified high pressure and temperature. Therefore, it is
especially suitable for studying the mass-transfer process of injected solvent
into heavy oil during solvent-based post-cold heavy-oil production
(post-CHOP).
Introduction
Western Canada has tremendous heavy oil and bitumen resources (Farouq Ali
2003, Miller et al. 2002). Approximately 80 to 95% of the original-oil-in-place
is still left behind at the economic limit after cold heavy-oil production
(Miller et al. 2002). This is a large oil-in-place target for follow-up
enhanced oil recovery (EOR) processes. After primary production, most Canadian
heavy-oil reservoirs cannot be further exploited economically by thermal
recovery processes because reservoir formations are thin and/or there is active
bottomwater. In the literature, some studies have been conducted to evaluate
the other recovery methods for these heavy-oil reservoirs (Miller et al. 2002,
Das 1995, Frauenfeld et al. 1998, Metwally 1998). Among these methods, vapor
extraction (VAPEX) and other solvent-based post-CHOP processes are probably the
most promising EOR techniques. In practice, the solvent can be carbon dioxide,
flue gas, and light hydrocarbon gases, such as methane, ethane, propane, and
butane.
© 2006. Society of Petroleum Engineers
View full textPDF
(
914 KB
)
History
- Original manuscript received:
4 February 2004
- Revised manuscript received:
30 June 2005
- Manuscript approved:
29 August 2005
- Version of record:
20 March 2006
View Cart
