performance enhancement of vapex by varying the propane injection pressure with time

Performance Enhancement of Vapex by Varying the PropaneInjection Pressure with TimeHameed Muhamad, Simant R. Upreti,* Ali Lohi, and Huu Doan

Department of Chemical Engineering, Ryerson University, 350 Victoria Street, Toronto, Ontario M5B 2K3, Canada

ABSTRACT: Vapex or vapor extraction is an emerging green technology for heavy oil recovery. However, the oil productionrates with Vapex are lower than those with the conventional recovery processes. This work aims at enhancing the oil productionrates by investigating the effect of varying the injection pressure of solvent propane with time. For this purpose, experiments weredesigned and performed by injecting pure propane at injection pressures of 482.6, 551.6, 620.5, and 689.5 kPa and 21 °C intolab-scale physical models of heavy oil reservoirs. The physical models were packed with a porous medium and saturated withheavy oil. Three different permeabilities of the porous medium were used with heavy oils of two different viscosities and bedheights. The experiments were performed using different policies of solvent injection pressure versus time. Pressure variationswere introduced by sudden release and re-injection of the solvent gas. In comparison to constant injection pressure, the pressurepulsing enhanced the oil production rate by 20−30%.

1. INTRODUCTIONWith the increasing worldwide demand for fossil energysources, heavy oil and bitumen represent a significant energysupply to meet this demand. As conventional crude oil reservesare becoming consumed, the world focus is on the heavy oiland bitumen resources in Canada and Venezuela to meet theevermore increasing demands for energy and petroleumproducts. The importance of unconventional oil reserves(heavy oil and bitumen) has increased because of their muchhigher in-place volumes. The enormous heavy oil and bitumendeposits in the world are estimated to be approximately 4800billion barrels in-place,1 of which most of them reside inCanada.The main challenge in the exploitation of heavy oil resources

is an effective oil recovery process to mobilize the oil in thereservoir. Until the advent of horizontal wells, heavy oil wasconsidered too viscous to flow and be recovered economicallyat the reservoir temperature. Water flooding without heat doesnot enhance recovery because water does not mobilize the oil.On the other hand, viscosity decreases greatly with increases inthe temperature. As a result, thermal processes, such as steam-assisted gravity drainage (SAGD) and cyclic steam stimulation(CSS), have been applied to some extent in heavy oil fields.However, it is questionable whether these methods aresufficient and economical in reservoirs with large heatrequirements, specifically in some reservoirs with thin payzone, low thermal conductivity, high water saturation, orbottom water aquifers.2,3 Moreover, steam generation facilitiesaccount for about 30% of the capital cost in SAGD.4 Steamproduction also requires a large source of water. In addition, asignificant amount of surface equipment is required to producesteam and separate the produced oil−water mixture. Also,several environmental issues, such as greenhouse gas emissionsand effluent water disposal, are associated with the SAGDprocess.5,6

Vapex was proposed by Butler and Mokrys to recover heavyoil from highly viscous reserves of heavy oil deep inside the

earth crust. In this process, a light hydrocarbon solvent or asolvent mixture is injected into an upper horizontal well inside areservoir. The absorption of the solvent(s) in the heavy oilreduces its viscosity, thereby causing it to drain into anunderlying horizontal production well from where the oil iseasily pumped to the surface. The researchers found that oilrecovery was even higher when pure propane gas is injectedclose to its dew point under reservoir conditions.7 These resultsrevealed the suitability of Vapex for effective heavy oil andbitumen recovery from thick as well as frequently occurringthin reservoirs with much smaller energy losses than those witha conventional thermal process, such as SAGD. Especially forthin reservoirs, the conventional recovery methods, such assurface mining, CSS, SAGD, and cold heavy oil production, arenot viable.The use of solvents in Vapex alleviates the energy

requirements and environmental impacts that plague thermalrecovery processes. For example, Vapex uses about 3% of theenergy consumed by SAGD and reduces greenhouse gasemission by 80%.8 Because of these reasons, interest in Vapexfor heavy oil recovery has grown considerably as a viable andenvironmentally friendly alternative to the currently usedthermal methods.The oil production in Vapex is directly related to the transfer

of solvent into the heavy oil. In the presence of solvent, theviscosity of heavy oil reduces, which, in turn, facilitates solventpenetration and mixing with the heavy oil.9 Because theprimary mode of solvent transfer is concentration-dependentmolecular diffusion, the oil production in Vapex builds upslowly with the solvent concentration. Thus, oil production isslow in the beginning and generally lower than that in SAGDdriven by the faster mechanism of thermal diffusion.10

Nonetheless, the advantages of Vapex make it worthwhile to

Received: February 3, 2012Revised: April 6, 2012Published: April 13, 2012

Article

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© 2012 American Chemical Society 3514 dx.doi.org/10.1021/ef3002058 | Energy Fuels 2012, 26, 3514−3520

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explore different ways to enhance and maximize the oilproduction rate.Although Vapex has a number of benefits over other thermal-

based enhanced oil recovery (EOR) processes, its fieldimplementation is hindered in the need for higher oilproduction rates. The oil production in Vapex primarilydepends upon the solvent mass transfer into the heavy oilphase, which is a combined effect of solvent diffusion, interfacerenewal, solvent mixing, contact area, and capillary imbibitions.It is the optimization of the associated process parameters thatcan enhance production in Vapex. Of these parameters, thesolvent injection pressure is the one that lends itself to easymanipulation to control the process.In this paper, the enhancement of oil production was

investigated by varying the propane injection pressure withtime in Vapex experiments. To that end, lab-scale experimentswere designed and carried out to investigate this concept.Experiments were performed with two different heavy oils,three different permeabilties, and two physical heights. In theseexperiments, propane was injected at different pressures belowthe dew point pressure. Sharp pressure changes (pressure blips)were introduced by sudden release and re-injection of propane.

2. EXPERIMENTAL SECTIONThe experimental setup mainly consists of a pressure vessel controlledby two proportional control valves (model PV101-10 V, OmegaEngineering, Inc., Canada). Figure 1 shows a schematic diagram of the

experimental setup. It comprises a cylindrical pressure vessel of 80 cmin height and 15 cm in inside diameter tubing sealed at both thebottom and top of the pressure vessel. To collect the produced oil, asmall carbon steel funnel at the vessel bottom is used. The funnel isconnected via a one-way valve to a collection tube to measure theproduced oil. The pressure vessel is placed inside a water bath. Thepressure vessel is equipped with a load cell and monitoringinstruments for the temperature and pressure inside the vessel andthe temperature of the water bath. The load cell is used to record theweight of the physical model, which decreases with time as the oildrains out and becomes produced.Propane is supplied via a mass flow meter to the top of the pres-

surized vessel system, where a pressure transducer measured thesystem pressure. Two proportional control valves are placed at theupstream propane gas feed line, and the other is attached to the

pressure vessel directly. The pressure inside the vessel is either keptconstant or varied with time. The temperature controller is designed tomaintain the temperature within ±0.5 °C of the set point. We usedresearch-grade propane of 99.99% purity (MEGS Specialty Gases Inc.,Montreal, Quebec, Canada) as a solvent at the laboratory ambienttemperature, which varied between 21 and 22 °C in the experiments.

The experimental conditions are recorded as a function of timecontinuously by the data acquisition system connected to a computer.Labview (version 7.1, National Instruments, Montreal, Quebec,Canada) was used for graphical user interface and online monitoringof the following inputs: (1) two pressure control valves, (2)temperatures of the pressure vessel and water bath, (3) pressure inthe pressure vessel, (4) inlet flow of propane, and (5) mass of thephysical model.

The load cell reading was taken every minute. Physical reservoirmodels with an inside radius of 3 cm and two different heights of 25and 45 cm were used to study the effect of the drainage height as wellas the effect of variation of the propane injection pressure on theproduction rate of heavy oil.

2.1. Physical Model Preparation. Two different heavy oils wereobtained from Saskatchewan Research Council (SRC), Regina,Saskatchewan, Canada, which had 14 500 and 20 000 mPa s viscositiesat 21 °C. The physical reservoir models were carefully prepared toavoid any air from becoming trapped in the simulated reservoirmedium of heavy oil and glass beads. The heavy oil was placed in atemperature-controlled heater. The oil was heated for at least 30 minat 70 °C for sufficient reduction in oil viscosity to promote mixing withglass beads. Samples were prepared on the basis of the weight of thebeads and the weight of the heavy oil for a given model height. Glassbeads of known permeability were gradually added to the heated oil inthe form of thin layers, layer by layer, inside the temperature-controlled heater. The glass beads in the layer were allowed to settle asa result of gravity before another layer was added to the heated oil.This procedure was repeated until the heavy oil could not take in anymore beads. This method of preparing the heavy oil−glass beadsmixture (i.e., the simulated reservoir medium) ensured that the heavyoil was fully and homogenously saturated with glass beads without anyair bubbles. The mixture thus prepared was packed into a cylindricalwire mesh outlining the physical reservoir model. With this method,we prepared the physical models of 6 cm in diameter and 25 and45 cm in height for the experiments. Before use in an experiment, aphysical model was kept in an air bath for 15 h. This step ensured thatthe model temperature reached the room temperature of approx-imately 21 °C.

2.2. Permeability Measurement. We prepared samples of asaturated mixture of heavy oil and glass beads of differentpermeabilities to study the permeability effect on the productionrate. Different glass beads sizes (industrial names BT 3, BT 4, BT 5,and BT 6) were used. The packing material simulating a reservoir wasglass beads obtained from Flex-O-Lite, Ltd. (St. Louis, MO).

To measure the permeability of the porous media consisting of theheavy oil and glass beads mixture, a horizontal cylindrical physicalmodel having a cavity size of 26 × 4 cm was used. The model setupwas filled with the glass beads. The cylinder had two ports: one for theair inlet and one for discharge air with a screen placed at the two sidesto avoid any glass bead passage. Two pressure gauges at both ends ofthe cylinder were used to measure the air pressure drop across themedia when air was passed through it. The airflow rate was measuredby a flow meter at the outlet. Darcy’s law for single-phase steady-stateflow was used to calculate the permeability (K) of the glass beadspacking as follows:11

μ=

ΔK

Pu L

P P1 2 air

2 (1)

where P1 and P2 are the pressures at the inlet and outlet of thecylinder, respectively, u2 is the velocity at the outlet, Pm is the meanpressure, ΔP is the pressure difference, μair is the air viscosity at theexperimental temperature, and L is the length of the media.

Figure 1. Schematic diagram of the experimental setup.

Energy & Fuels Article

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The permeability of the packing material was also estimated fromthe particle size diameter using the model by Carman-Kozeny12

ϕ

ϕ=

−K

D

180(1 )CK

3p

2

3 (2)

where K is the permeability and φ and Dp are the porosity of themedium and the diameter of the particle, respectively. Table 1 shows

values of estimated sample permeability as well as the measuredpermeability measurement for four different permeabilties.2.3. Experimental Details and Procedure. Before starting each

experiment, the load cell was calibrated over the full scale and thepressure vessel was tested for any potential leak. The leak test wasconducted by pressurizing the cylindrical pressure vessel with air andleaving it for 24 h. After no pressure drop was confirmed, the topflange of the pressure vessel was opened and the cylindrical modelwith a saturated heavy oil and glass beads mixture was attached to theload cell (see Figure 1). After sealing the vessel, the leak test wasperformed again for a short period of time to ensure proper sealing ofthe vessel. Air was purged from the pressure vessel by applying vacuumclose to −15 mmHg using a vacuum pump. To ensure completedisplacement of any residual air, the vessel was flushed with propanefor 10 min and vacuumed again. Propane was injected into the vesselat a constant pressure of 689.5 kPa (100 psig) corresponding to atemperature of 21 °C.A constant temperature during the experiment was maintained by a

water bath (200 cm in height and 150 cm in diameter) made ofpoly(vinyl chloride). After the water bath was filled to the height of thevessel, water was heated to the temperature of the surroundings. Thiswas performed by circulating water underneath the tank through a heatexchanger. Once steady temperature was attained, the physical modelwas located inside the pressure vessel and the Vapex oil extractionprocess was started.The injection pressure was controlled through two control valves

installed in the setup. As propane came in contact with the exposedsurface of the physical model, it diffused into the heavy oil−glass beadsmixture. The presence of hydrocarbons, such as propane, is known tosignificantly reduce the heavy oil viscosity. This phenomenon makesthe heavy oil mobile and drain under the action of gravity. It wasobserved that, after some time, the heavy oil started to drain out of thephysical model and accumulate in the funnel placed at the bottom ofthe pressure vessel. The production of the live oil was then continuedas a result of exposure of the new oil-filled pores to the solvent gas,resulting from boundary layer drainage, and the process continued as aresult of gravity drainage, until the production was stopped. The loadcell recorded the mass of the physical model every minute as theproduction continued. At the end of the experiment, the propanesupply was shut off. The pressure vessel was vented and flushed withair.

3. RESULTS

3.1. Live Oil Production Rates. The effect of modelpermeability on oil production rates and recoveries wasevaluated for 14 500 mPa s viscosity dead oil. A number ofexperiments were performed using the 25 cm height modelpacked with a homogeneous permeability medium. Variedmedium permeabilities of 427, 204, 87, and 40 darcy were

tested. The porosities of the media used in these experimentswere close to 38%.Figure 2 presents the comparison of the cumulative live oil

produced versus time for the physical model of 25 cm height

with different permeabilities (427, 204, 87, and 40 darcy). It isobserved that both the cumulative oil produced and the live oilproduction rate decreased with the model permeability. The overalloil recovery among these experiments ranged between 88 and 95%of original oil in place (OOIP). Higher permeability modelsresulted in higher percent OOIP recovery and production rates.Figure 3 presents the relationship between the live oil

production rate and model permeability. The production

increases with permeability. The data points are fitted by apower function.

=m K0.0594 0.5061 (3)

According to the above equation, the oil production rate (g/min)in the Vapex process is a square root function of the modelpermeability (darcy). This result is in close agreement to whatis reported in the literature.13

3.2. Effect of the Pressure on the Live Oil ProductionRate. To evaluate the injection pressure as one of theoptimizing parameters for Vapex process enhancement, weperformed a number of experiments with different injectionpressure strategies as follows: (1) injecting of the propane atdifferent but constant injection pressures and (2) introducingtemporal variations in the injection pressure.The experimental results showed that the temporal variation

in injection pressure enhanced oil production and improved the

Table 1. Permeability of the Glass Beads

glass beadtype

averagediameter (mm)

estimated KCK(darcy)

experimental K(darcy) porosity

BT 3 0.717 427 439.2 0.385BT 4 0.506 204 220.3 0.38BT 5 0.334 87 97.4 0.378BT 6 0.229 40 44.4 0.376

Figure 2. Cumulative live oil production versus time at differentpermeabilities (model height, 25 cm; heavy oil viscosity, 14 500 mPa s;and pressure, 689.5 kPa).

Figure 3. Variation of the production rate with model permeability(model height, 25 cm; heavy oil viscosity, 14 500 mPa s; and pressure,689.5 kPa).



process efficiency compared to constant injection pressure. Thedetails of the results are presented next.3.3. Effect of the Constant Injection Pressure on Live

Oil Production. In the first step, we examined the effect of theconstant injection pressure of propane on live oil productionclose to the dew point. Four experiments were carried out atdifferent constant injection pressures of 482.6, 551.6, 620.5, and689.5 kPa. All of these experiments were performed using the25 cm high physical model of 14 500 mPa s heavy oil witha 204 darcy permeability. The experimental temperature was21 °C, at which the dew point pressure of propane was 751.5 kPa.In each experiment, propane was injected at the given constantpressure. The produced oil was collected and weighed. Figure 4

shows the cumulative live oil produced at the four injectionpressures. As indicated in the figure, injecting propane close toits dew point pressure results in the highest oil production rateand recovery. A drop in propane pressure below the dew pointpressure reduces the oil production rate as well as the overall oilrecovery.3.4. Effect of Variation in the Propane Injection

Pressure. In this study, the effect of temporal variations ininjection pressure on oil production rates was examined during theVapex process. Experiments were performed with two modelheights (25 and 45 cm), three different permeabilties (204, 87, and40 darcy), and two different initial dead oil viscosities (14 500 and20 000 mPa s). Below are the details of these results.3.4.1. Long and Short Blips in the Injection Pressure. To

study the effect of temporal variation time in the injectionpressure, we performed the following two experiments: (1)experiment with long pressure blips [in this experiment, thepropane injection pressure was instantly reduced several timesfrom 689.5 to 275.8 kPa, kept at 275.8 kPa for about 13 min (“theblip interval”), and raised back to 689.5 kPa] and (2) experimentwith short pressure blips (this experiment was similar to theprevious experiment but with the blip interval of about 3 min).Figures 5 and 6 compare the cumulative produced oil versus

time for the above experiments with the “base experiment”performed at the constant injection pressure of 689.5 kPa. Asseen from the figures, the experiment performed with temporalvariation in the injection pressure produced more oil comparedto the base experiment. While 200 g of cumulative oil wasproduced with long pressure blips, the experiment with shortpressure blips produced 22 g or about 10% more oil.

It is very interesting that the oil production with short pressureblips virtually never drops below the oil production in the baseexperiment (Figure 6). This finding is in contrast with theexperiment that uses long pressure blips (Figure 5). The oilproduction with long pressure blips is initially found to be lowerthan the base production for about one-third of the experimentalrun time. This experimental fact indicates that the duration of theshort pressure blip is optimal in that it sufficiently stimulates the oilrecovery process without adversely affecting the instantaneous oilproduction. This phenomenon is particularly noticeable in the firsthalf of the experiment when the oil recovery is beginning to grow.Because of the above fact, we used short pressure blips in the

rest of the experiments to examine the effect of different modelheights and permeabilities on the oil production rate. In all ofthese experiments, the oil production never went below thebase oil production.

3.4.2. Experiments with Short Pressure Blips and DifferentModel Heights. To assess the effect of the model height on oilproduction using short pressure blips, we carried out anadditional experiment using a physical model of 45 cm height,heavy oil of 14 500 mPa s viscosity, and medium of 204 darcypermeability. Figure 7 presents the results of this run andcompares the trend of the cumulative produced oil to that inthe base experiment using a constant injection pressure of 689.5kPa. It was found that the short pressure blips produced 25%more oil than that in the base experiment.Both Figures 6 and 7 show that short pressure blips in

the propane injection pressure significantly enhanced theoil production. The 45 cm model produced 404 g of oilcompared to 220 g of oil from the 25 cm model for the first300 min of both experiments. The results also reveal thatthe increase in the oil production was more pronounced for

Figure 4. Cumulative oil production versus time at different constantinjection pressures (model height, 25 cm; heavy oil viscosity, 14 500mPa s; and medium permeability, 204 darcy).

Figure 5. Cumulative live oil production versus time at long pulsepressure (model height, 25 cm; heavy oil viscosity, 14 500 mPa s; andmedium permeability, 204 darcy).

Figure 6. Cumulative live oil production versus time at short pulsepressure (model height, 25 cm; heavy oil viscosity, 14 500 mPa s; andmedium permeability, 204 darcy).



the model with the larger height (45 cm). The short pres-sure blips in the case of the 45 cm model resulted in morethan 5% unit of recovery of OOIP compared to the 25 cmmodel.3.4.3. Experiments with Short Pressure Blips and Different

Model Permeabilities. To examine the effect of modelpermeability on oil production using short pressure blips, wecarried out two experiments with medium permeabilities of 87and 40 darcy, model height of 25 cm, and oil viscosity of 14 500mPa s. Figures 8 and 9 present the results of these experiments.

About 25 and 35% more oil was produced using short pressureblips in comparison to the base experiment with the constantpropane injection pressure of 689.5 kPa.A comparison of Figures 8 and 9 to Figure 6 shows that

injection pressure variation has a significant effect on oil

production for all three model permeabilities. Moreover, theeffect becomes more pronounced with the decrease in thepermeability.

3.4.4. Experiments with Short Pressure Blips and DifferentDead Oil Viscosities. The solvent mass transfer to the oil phaseprimarily depends upon the initial dead oil viscosity. The lowerviscosity oil is expected to uptake more solvent compared tothe higher viscosity oil and, thus, result in a higher oilproduction and rate. Therefore, it is important to examine theeffect of pressure variation on the dead oil viscosity. For thispurpose, we performed experiments with permeability of 204darcy, model height of 25 cm, and two oil viscosities of 14 500and 20 000 mPa s.Figure 10 presents the result of the experiment with 20 000

mPa s viscosity and compares the oil production to that

in the base experiment with the constant injection pres-sure of 689.5 kPa. It is found that the short pressureblips produce 23% more oil compared to constant injectionpressure.A comparison of Figure 10 to Figure 6 (for 14 500 mPa s

viscosity) shows that the short pressure blips in propane injectionpressure generate more oil (relative to the base oil production)when the oil viscosity is higher.

4. DISCUSSIONA key requirement in Vapex is the injection of the solventvery close to its dew point pressure at reservoir conditions.This requirement allows the solvent to be a dense vaporupon injection that has higher solubility in heavy oils com-pared to the solvent injected far from the dew pointpressure with low-density vapor. A higher solubility resultsin a lower oil viscosity of the diluted oil that can drainquicker, leading to enhanced oil recovery. This fact wasevident by our initial experiments.The rest of the experiments demonstrated, more importantly,

that the variation in solvent injection pressure with time canplay an important role in enhancing the oil production inVapex. Among different injection schemes, constant pres-sure, long blips, and short blips, the last scheme had themost pronounced effect on the oil production and rate.It was observed that the short blips in the solvent injectionpressure enhanced oil production, never letting it fall belowthe base oil production even at the pressure blip. This find-ing suggests that the short pressure blip optimally stimulatesthe oil production.The positive effect of pressure variation on the oil production

and rate may be ascribed to the following:

Figure 7. Cumulative oil production versus time at pulse injectionpressure (model height, 45 cm; heavy oil viscosity, 14 500 mPa s; andmedium permeability, 204 darcy).






In an experiment with the constant injection pressure, thecontact area between the oil and solvent is the surface areaof stabilized solvent channels, which preserve most of theirconfiguration throughout the Vapex process. Because the sol-vent injection pressure is constant, there are no major upsets.Some asphaltenes may precipitate, which is carried away inthe oil draining out. A variation in the injection pressure,especially the temporal variation, generates sort of a “seismic”effect within the model. Because of this effect, the solvent notonly travels through the uniformly developed channels but alsoforms new channels within the model. Consequently, there ismore area where the solvent can contact the oil and dilute it toflowable viscosities. Thus, the oil production improves whenthe solvent injection pressure is varied.Moreover, as mentioned earlier for Vapex, solvent mass

transfer in the heavy oil phase depends upon the initial oilviscosity. When the pressure drops during a temporal varia-tion in injection pressure, the solvent dissolved in the oil triesto escape. However, because the pressure is not reducedentirely to the gas-phase pressure, there is always a sufficientamount of solvent dissolved in the oil that keeps the oilviscosity in a low range. Upon increasing the pressure backto the dew point pressure and replenishing solvent supply,the solvent mass transfer to the oil is much faster becausethe solvent now has to dilute lower viscosity oil comparedto, initially, much higher viscosity oil. As a result, the oilproduction increases when the solvent injection pressure isvaried.The experimental results of this study also show that the

temporal variation in injection pressure is more beneficial forlower permeability models and higher viscosity oils. Thisresult is relevant to heavy oil field reservoirs, which have lowpermeabilties (4−10 darcy) and high viscosities in millionsof centipoises. Further experimental work is definitely requiredto study the effect of the temporal variation in injection pres-sure for field-type permeabilities and bitumen-type viscosities.Especially, optimized solvent injection pressure policies can playa vital role for the field implementation of Vapex.

5. CONCLUSION

In this experimental study, the effect of model permeabilityon oil production rates for a Vapex process was evaluatedfor 14 500 mPa s viscosity dead oil. A cylindrical physicalmodel of 25 cm in height was used. The experiments wereperformed with four different permeabilities of 427, 204, 87,and 40 darcy and an approximate porosity of 38%. The liveoil production rate was found to be the square root functionof the model permeability, which is in strong agreementwith the literature. To evaluate the injection pressure as oneof the parameters to enhance Vapex oil production, thenumber of experiments was performed with different sol-vent injection pressure strategies.The sensitivity of injection pressure close to the dew point

pressure of the injected propane solvent at the injection con-ditions was studied by performing four experiments at diffe-rent constant injection pressures of 482.6, 551.6, 620.5, and689.5 kPa. All of these experiments were performed at 21 °Cwith a 25 cm cylindrical model packed with 204 darcy per-meability media and saturated with 14 500 mPa s heavy oil.Propane injected close to the dew point pressure (at injectiontemperature) resulted in the highest oil recovery and oil pro-duction rate.

The effect of short and long blips in solvent injection pres-sure with time with different petrophysical properties wasexamined by performing a number of experiments with twomodel heights (25 and 45 cm), three different permeabilties(204, 87, and 40 darcy), and two different initial dead oilviscosities (14 500 and 20 000 mPa s).This study showed that short pressure blips in the propane

injection pressure produced more oil than the base case ofconstant solvent injection pressure. We also found that theshort pressure blips are more beneficial for lower permeabilitymodels and higher viscosity oils.

■ AUTHOR INFORMATION

Corresponding Author*Telephone: 416-979-5000, ext. 6344. Fax: 416-979-5083.E-mail: [email protected].

NotesThe authors declare no competing financial interest.

■ ACKNOWLEDGMENTSWe acknowledge the financial support of the Natural Sciencesand Engineering Research Council of Canada (NSERC) andthe Ontario Graduate Scholarship (OGS) Program. Sincereappreciation goes to M. Imran, Research Engineer, Saskatch-ewan Research Council, Regina, Saskatchewan, Canada.

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mailto:[email protected]

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performance enhancement of vapex by varying the propane injection pressure with time

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