Simplified Oil-Production Model With Viscous Flow, Gravity Drainage, Skin, and Instantaneous Oil/Steam Ratio for Mature Steamfloods
- Philip J. Closmann (Consultant)
- Document ID
- Society of Petroleum Engineers
- SPE Journal
- Publication Date
- December 1997
- Document Type
- Journal Paper
- 466 - 473
- 1997. Society of Petroleum Engineers
- 5.6.4 Drillstem/Well Testing, 4.1.5 Processing Equipment, 4.1.2 Separation and Treating, 5.2.1 Phase Behavior and PVT Measurements, 5.5.8 History Matching, 5.8.5 Oil Sand, Oil Shale, Bitumen, 5.4.6 Thermal Methods
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A simplified model estimates oil production rates for mature steamfloods. The mechanisms included are gravity drainage and viscous flow of the oil induced by flowing steam. Three examples of vertical wells are presented. The oil/steam ratio is also illustrated, as well as the pressure drop in the steam phase. One application of the model to horizontal wells producing by gravity drainage is also presented.
Analytic models have recently been shown by a number of papers1,2,3,4 to be useful for screening purposes and performance monitoring of mature steamfloods. In these processes, the injected steam tends to override the oil layer, resulting in early steam breakthrough at the producers. Except for very stratified reservoirs or the presence of thief zones, the development of complete steam overlay thus characterizes the mature steamflood Once steam breakthrough has occurred, the dominant oil production mechanism in many cases is gravity drainage.5 However, as recently pointed out by Kimber et al.3 and by Owens and Ziegler,4 oil production can be enhanced by venting of steam at the producers. It is the purpose of this work to show that a simple model which was successful in estimating oil production for gravity-dominated steamfloods6 can be easily extended to account for the viscous effects induced by flowing steam. The heat consumption involved in this process consists of (1) heat loss due to steam vapor blow into the wellbore and out the casing annulus, (2) conductive heat loss to the overburden, and (3) sensible heat involved in the creation of additional steam zone where oil is displaced to a low residual. In addition to viscous flow, the effect of skin can also be included in the formulation.
Model and Assumptions
1. The steam/oil interface is assumed horizontal across the reservoir, except near the production wells. Steam is assumed to blanket the entire pattern (Fig. 1).
2. The temperature distribution below the downwardly moving oil interface is that of the steady state from a constant temperature boundary moving at constant velocity and is assumed to show variation only in the vertical direction.6
3. The gravity drainage component of oil flow is calculated by the method of Matthews and Lefkovits7 modified to provide for the effect of the temperature distribution on the oil viscosity. Flowing steam induces a pressure drop which is included in the calculation of the oil rate. Any capillary zone at the interface is neglected.
4. Flow properties of the oil layer, including the relative permeabilities of oil and water, remain unchanged during the production process. All condensate is produced, except that which remains as water saturation in the growing steam zone.
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