As part of a three-year research project, a solvent based process for downhole upgrading as well as for concurrent enhanced oil recovery of the bituminous heavy oil from an Argentina reservoir was evaluated in the laboratory using physical models. Potential solvents were sourced from a gas plant located close to the target reservoir. To evaluate feasibility, first a specially designed dynamic asphaltene apparatus was used to screen readily available solvents and their mixtures. Solvent/oil miscibility and on-set of asphaltene deposition were determined by analyses of light transmitted through a micro-visual cell containing a flowing stream of oil/solvent mixtures. The optimized solvent composition thus identified was then used in Vapex experiment in a physical model packed with crushed reservoir rock.
It was seen that the chosen solvent mixture (containing carbon dioxide and gas condensate) was effective in upgrading the produced oil under test conditions (high permeability). Asphaltene and heavy metal content of the upgraded (produced) oil were reduced to less than 20% of the original values, while oil recovery in excess of 75% of OOIP was achieved in the physical model. Oil sweep in the model, especially within the solvent swept zone was exceptionally efficient with a remaining oil saturation of less than 5%. At the same time, oil saturation of the least swept region was reduced from 85% to 45%. Deposition of asphaltenes in the porous medium did not seen tomaterially affect oil production.
In the Vapex1–4 (Vapour Extraction) process for heavy oil recovery, a single condensable solvent (propane or CO2) or a solvent mixture, containing both non-condensable and condensable gas, is injected into the reservoir via a horizontal injector and mobilized oil is drained via a horizontal producer placed directly underneath it. One important advantage in the Vapex process is its potential to upgrade the crude oil in-situ by deasphalting in the presence of appropriate solvents. However, results from several Vapex physical model tests conducted in our laboratory over the years, indicated that not all Vapex produced oil is upgraded. Factors that can affect the degree of crude oil upgrading are operating temperature, pressure and solvent composition.
This paper presents results from a laboratory study to investigate the feasibility of using the Vapex process to produce the heavy oil from an Argentina reservoir with concurrent in situ upgrading of crude oil.
The Llancanelo field is located in the North sector of the Neuquina basin, in the province of Mendoza-Argentina, 37 kmto the Southeast of the city of Malargue, next to the west margin of the Llancanelo Lagoon (Figure 1). The field containing heavy oil was discovered in 1937, and subsequently another 22 wells were drilled.
The structure of the reservoir is an asymmetric anticline, trending NW-SE. The productive reservoirs are composed ofsediments of fluvial origin and are members of the Neuquen Group. Sandstones and conglomerates belonging to the Neuquen group form the main reservoir of the Llancanelo deposit. In this unit three sequences have been recognized from bottom to top that are called blue, olive and green.
