Effect of Height and Grain Size on the Production Rates in the Vapex Process: Experimental Study
- Ali Yazdani (U. of Calgary) | Brij B. Maini (U. of Calgary)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Evaluation & Engineering
- Publication Date
- June 2005
- Document Type
- Journal Paper
- 205 - 213
- 2005. Society of Petroleum Engineers
- 4.6 Natural Gas, 5.3.2 Multiphase Flow, 5.4.6 Thermal Methods, 5.3.9 Steam Assisted Gravity Drainage, 1.2.3 Rock properties, 4.1.5 Processing Equipment, 1.8 Formation Damage, 2.4.3 Sand/Solids Control, 5.4.7 Chemical Flooding Methods (e.g., Polymer, Solvent, Nitrogen, Immiscible CO2, Surfactant, Vapex), 4.3.3 Aspaltenes, 4.3.4 Scale, 4.1.2 Separation and Treating, 5.7.2 Recovery Factors
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Interest in the vapor-extraction (Vapex) process for heavy-oil and bitumenrecovery has grown considerably as a viable and environmentally friendlyalternative to the currently used thermal methods. The potential for thesuccess of the Vapex process is even more attractive in some scenarios thatpreclude the thermal methods. The presence of an overlying gas cap and/orbottomwater aquifer, thin pay zones, low thermal conductivity, high watersaturation, and unacceptable heat losses to overburden and underburdenformations are some of the limitations with the thermal techniques, whichpotentially can be overcome by Vapex implementation. However, predicted lowproduction rates by previous researchers for field application of the Vapextechnique remain a serious barrier to commercial applications of the process.The scaleup methods that have been used by previous workers for translating thelaboratory results to field predictions were based primarily on the reservoirtransmissibility. An analytical model developed by Butler and Mokrys showedthat the oil rate should be proportional to the square root of reservoirtransmissibility. The effect of convective dispersion between solvent andvirgin heavy oil in porous media was ignored in developing thismodel.
The main objective of this work is to develop an improved scaleup method forthe Vapex process using physical-model experiments carried out in models ofdifferent sizes. In this paper, we report the results of a new series ofexperiments that extend the previously reported results ofKarmaker andMaini to a significantly wider range of model heights. These new experimentsused a new design of slice-type physical models that places the sandpack in theannulus formed by two cylindrical pipes. Combining the new results with theprevious data of Karmaker and Maini, we show that the transmissibility-basedscaling-up method seriously underpredicts the results at larger scales. Thisobservation suggests that much higher rates can be expected in the fieldimplementation of the Vapex process.
A new correlation also has been proposed for scaling up the experimentaldata to the real field cases. It indicates the height dependency of theconvective-dispersion contribution, which can be the dominant mass-transfermechanism for the process, to be a higher order than previously postulated.Experimental results from this work show that the stabilized rate is a functionof drainage height to the power of 1.1 to 1.3, instead of the square-rootfunctionality of the Butler and Mokrys model.
Cost-effective heavy-oil- and bitumen-recovery methods are still challengingissues that have not been fully resolved. The huge volume of almost immobilehydrocarbon resources in the world, especially located in Canada, Venezuela,and the United States (approximately six times the total conventional oilreserves), offers unlimited challenges and opportunities to researchers. Thehigh viscosity and low mobility of these oils cause the primary recovery to bevery low. The adverse mobility-ratio problem also limits the application ofwaterflooding to these reservoirs. The overall recovery that can be achievedbefore the enhanced-oil-recovery (EOR) methods usually does not exceed 6 to 8%of the original oil in place.
The well-known observation of a dramatic decrease in the viscosity of heavyoil with temperature increase makes the thermal-recovery methods, such assteamflooding, cyclic steam stimulation (CSS), in-situ combustion, and (morerecently) the steam-assisted gravity drainage (SAGD) process the obviouschoices. However, thermal methods are not universally applicable to highlyviscous heavy-oil reservoirs. The low recovery factors associated with CSS(inefficient steamflood in highly viscous oils and a relatively high mobilityrequirement), in addition to the process-control difficulties for the in-situcombustion technique, are some of the obstacles that leave the SAGD process asthe only thermal option for heavy-oil and bitumen recovery in many reservoirs.In the SAGD process, two horizontal wells located in the same vertical planeare used to inject the steam from the upper well and produce heated oil fromthe lower well.
The Vapex process, which was initially proposed by Butler and Mokrys, is asolvent-based analog of the SAGD process, which can be considered when the SAGDis likely to be problematic. In thin reservoirs, the amount of heat loss to thesurrounding formations makes the SAGD uneconomic. Also, in low-permeabilitycarbonate reservoirs in which the heat capacity per volume of oil is high, thesteam/oil ratio is not economically attractive. The presence of the bottomaquifer and/or a thin gas cap can be counted as an advantage for the Vapexprocess, whereas they are troublesome for SAGD. In terms of energyconsideration, it has been reported that Vapex needs only a fraction of theenergy used for SAGD. Also, Vapex has smaller upfront capital requirementscompared to SAGD, in which 30% of the capital investment goes towardsteam-generation equipment.
|File Size||2 MB||Number of Pages||9|
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