An Investigation Of Steam Plateau Phenomena
Authors: Satman A. , Brigham W.E. , Ramey H.J. 
Published: December 2007

In this study, the temperature distribution in the steam plateau portion of combustion tube experiments has been investigated and a mathematical model developed to describe non-isothermal fluid flow behavior in this region.

The steam plateau region of laboratory combustion tube experiments was studied, and heat transfer modes defined. The combustion parameters affecting the steam plateau were also studied and evaluated. This study presents some of the design problems and considerations important to the operation of a combustion tube, and the interpretation of the results related to the steam plateau. An analytical heat model for the movement of the steam plateau axially along a cylinder with heat loss through an annular insulation was developed, and the behavior of the solution studied to determine the interaction of the heat transfer mechanisms in laboratory cores. The results of the combustion tube runs were used to verify the theory set forth by the heat model. The agreement between experimental laboratory temperature profiles and those computed by the model was satisfactory.

Results indicated that the temperature distribution in the steam plateau is controlled principally by phase equilibrium. The steam plateau temperature is set primarily by the air injection pressure and then by initial water saturation. The growth of the steam plateau may be controlled by air flux, elevated formation temperature, and/or heat loss.

Introduction

During the last three decades, the injection of heat into a reservoir has gained considerable attention as an enhanced oil recovery mechanism. The low API gravity, high-viscosity crude oils do not respond satisfactorily to conventional recovery processes. Since oil viscosity is highly temperature dependent, the performance of these reservoirs can be significantly improved by raising the reservoir temperature through the application of heat.

During dry forward in-situ combustion, air is injected to burn a part of the in-place hydrocarbons. Combustion gas and a steam plateau ahead of the combustion front displace oil toward the production well. The heat is transferred ahead of the combustion front by the convection of combustion gases, by vaporization and recondensation of connate water, and by conduction.

A steam plateau is usually observed to move ahead of the combustion front. This region is characterized by a nearly flat temperature profile if pressure drop is small. Here the temperature level appears to be controlled by phase behavior. That is, the temperature level is related to the partial pressure of water in the gas phase and to the vapor pressure-temperature characteristics of water. Figure 1 shows a schematic of the forward in-situ combustion process.

Describing the movement f heat and fluids analytically or numerically during the in-situ combustion process has been a subject of interest to numerous process has been a subject of interest to numerous investigators. The results of field tests and laboratory combustion tube studies have been reported. However, there is no complete model which describes the movement of heat and fluids analytically. The complexity of the process has forced investigators to study the process in parts. Penberthy and Ramey developed an analytical model to represent the temperature profiles behind and ahead of the burning front for combustion tube studies. The steam plateau, heat movement ahead of the steam plateau, and the burning front itself remain to be studied.

Holst and Karra presented a numerical method for calculating the size of the steam plateau as a function of time. Their equations describing the physical system were designed in a manner analogous physical system were designed in a manner analogous to the Marx-Langenheim derivation for hot fluid injection. They assumed that an optimal wet combustion was taking place in the reservoir so that the temperature behind the burning front was the same as the temperature of the steam plateau.