The Influence of Oil Viscosity and Thickness on the Steam Drive
- Todd M. Doscher (U. of Southern California) | Farhad Ghassemi (U. of Southern California)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- February 1983
- Document Type
- Journal Paper
- 291 - 298
- 1983. Society of Petroleum Engineers
- 4.1.2 Separation and Treating, 5.3.2 Multiphase Flow, 4.1.5 Processing Equipment, 5.1.1 Exploration, Development, Structural Geology, 5.2 Reservoir Fluid Dynamics, 5.4.6 Thermal Methods, 2.4.3 Sand/Solids Control, 5.2.1 Phase Behavior and PVT Measurements, 5.8.5 Oil Sand, Oil Shale, Bitumen
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A correlation of steamdrive efficiency, based on model studies, predicts that it will fall as the viscosity of the crude at steam temperature increases. Sensitivity to viscosity results from the overlay of steam, which also mitigates the influence of reservoir thickness. High efficiency, expected of frontal displacement, is realized in the recovery of high-gravity crudes.
Physical scaled models of the steam drive have reproduced many features of field operations. One of the most pronounced features of the steam drive is the overlay of steam above the oil column and its subsequent stratified flow to the producing well.
This is in contrast to frontal displacement that was assumed in early analytical models. The effects of various reservoir and operational parameters therefore may be different from those originally deduced on the basis of frontal advance concepts.
Three important parameters used to assess the feasibility of steamdrive operations are (1) rate of injection of steam and its quality, (2) viscosity of the crude oil, and (3) reservoir thickness. The most frequently used analytical model and its modification do not attribute any effect of the crude oil viscosity on the efficiency of the steam drive. Steam zone growth and the corresponding depletion of oil are based exclusively on the way in which heat is distributed within the reservoir. The quality of the steam and its injection rate are both shown to be important, with the resulting oil/steam ratio monotonically increasing with each. On the other hand, field and model studies have indicated that there is an optimal rate of steam injection to attain a maximum oil/steam ratio. The analytical models predict that the efficiency of the steamdrive process as measured by the oil/steam ratio will vary directly with a function of reservoir thickness, whereas results obtained from field operations in which steam stimulation did not contribute significantly to the overall performance suggest that thickness may not have the pronounced effect that is predicted.
The purpose of this work was to elucidate the role of oil viscosity and reservoir thickness in steamdrive operations in which gravity segregation of the steam and its stratified flow dominate the process.
Steamdrive Analysis Based on Stratified Steam Flow
Steam initially enters a viscous oil reservoir through a depleted or wet interval, a fracture, or a fluidized interval. If the initial entry is not at the top of the oil section, the steam rapidly migrates upward because of the strong gravitational gradients imposed by the marked difference in density between the steam and the reservoir fluids. The rate of upward migration depends on vertical permeability and viscosity of the crude oil at steam temperature - that is, the concurrent drainage rate of the heated crude oil.
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