Enhancing Oil Rate in Solvent Vapour Extraction Processes Through Tee-Well Pattern
- Fanhua Zeng (U. of Regina) | Kelvin D. Knorr (Saskatchewan Research Council) | Ryan Richard Wilton (Saskatchewan Research Council)
- Document ID
- Society of Petroleum Engineers
- International Thermal Operations and Heavy Oil Symposium, 20-23 October, Calgary, Alberta, Canada
- Publication Date
- Document Type
- Conference Paper
- 2008. SPE/PS/CHOA International Thermal Operations and Heavy Oil Symposium
- 5.5.8 History Matching, 4.1.2 Separation and Treating, 5.4.7 Chemical Flooding Methods (e.g., Polymer, Solvent, Nitrogen, Immiscible CO2, Surfactant, Vapex), 5.1.1 Exploration, Development, Structural Geology, 5.2.1 Phase Behavior and PVT Measurements, 4.1.1 Process Simulation, 4.3.4 Scale, 4.1.5 Processing Equipment
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The production flow rate in classical VAPEX is far too low for the process to be considered commercially viable. This is largely because the classical process utilizes forces of buoyancy to distribute the solvent and gravity to drain the diluted oil to the producer. This paper presents a new well pattern that may enhance the oil flow rate two to ten times over the classical approach.
In the new well pattern, additional horizontal injectors, perpendicular to the injector and the producer in classical VAPEX, are placed in the top-most region of the reservoir. The enhanced oil rate mechanism for this new well pattern involves two features. First, the injection pressure of the top injectors is set slightly higher than the bottom injector pressure. This facilitates a downward driving force to assist gravity drainage of diluted oil to the producer. Second, the supplementary injectors generate an additional diluted oil profile perpendicular to the diluted oil profile of the classical VAPEX process. Therefore, in the new well pattern, the heavy oil is solvent contacted and diluted in both ik and jk planes, whereas in classical VAPEX, the heavy oil is diluted in only one. A series of numerical simulations were conducted to evaluate this process. In order to obtain reliable evaluation results, the numerical dispersion was eliminated through extrapolating the simulation results at different grid sizes to an infinitesimal grid size (?y?0).
The simulation results suggest that the oil flow rate can be enhanced two to ten times greater than with classical VAPEX, depending on the well spacing of the top injectors. For example, for a well spacing of the top horizontal injectors of 120 m, the oil flow rate from the original producers will be 5.5 times higher than in the VAPEX scenario. The paper also discusses the effects of the design factors and formation/fluid uncertainties on the performance of this process. Finally, thinner reservoirs and reservoirs with a gas cap are discussed.
The patented VAPEX (vapour extraction) process was developed over twenty years ago. In the classical VAPEX, a horizontal injector is stacked vertically, within a few meters, above a horizontal producer to utilize gravity to facilitate the drainage of the solvent-diluted oil to the producer. The fundamental challenge with VAPEX is that the oil rate in the field is far too low to allow a commercially viable process. Variations of VAPEX have been investigated to enhance the oil production rate. Butler and Mokrys (1998) and Frauenfeld et al. (2006) experimentally studied the VAPEX process in bottomwater reservoirs and suggested that high oil production rates are possible if an appropriate well spacing is given. Butler and Jiang (2000) presented a lateral VAPEX process, in which the horizontal producer is laterally separated from the injector and located at the bottom of the reservoir. According to their experimental observation, the lateral process allows higher production rates and makes the VAPEX process more economic. Rahnema et al. (2007) experimentally studied the VAPEX process for reservoirs with a gas cap and concluded that the lateral spacing between injector and producer has no effect on the oil recovery and delays initial well communication. Rezamei and Chatzis (2007) proposed Warm VAPEX, in which the solvent is heated above the dewpoint temperature of solvent vapours at reservoir pressure and injected into the reservoir. The superheated vapours carry some sensible heat and cause an additional driving force due to mixing. The authors claimed that the Warm VAPEX is promising in terms of enhanced oil production rates.
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