document

Hart, Carolyne M.; Sandia Natl. Laboratories

Abstract

It has long been recognized that the application of heat to reservoirs containing high API gravity oils can substantially improve recovery. Although steam injection is currently the principal thermal recovery method, heat transmission losses associated with delivery of the steam from the surface generators to the oil-bearing formation has limited conventional steam injection to shallow reservoirs.

The objective of the Department of Energy's Project DEEP STEAM is to develop the technology required to economically produce heavy oil from deep reservoirs. The tasks included in this effort are the development and evaluation of thermally efficient delivery systems and downhole steam generation systems. This paper compares the technical and economic performance of conventional surface steam drives, which are strongly performance of conventional surface steam drives, which are strongly influenced by heat losses, with (a) thermally efficient delivery (through insulated strings) of surface generated steam, (b) low pressure combustion downhole steam generation, (c) high pressure combustion downhole steam generation using air as the oxygen scarce, and (d) high pressure combustion downhole steam generation substituting pure oxygen for air.

The selection of a preferred technology based upon either total efficiency or cost is found to be strongly influenced by reservoir depth, steam mass flow rate and sandface steam quality. Therefore, a parametric analysis has been performed which examines varying depths, injection rates and steam qualities. Results indicate that the technologies are not readily distinguishable for low injectivity reservoirs in which conventional steam drives are feasible. However, high injection rates produce a notable cost difference between high pressure combustion systems produce a notable cost difference between high pressure combustion systems and the other technologies. Issues that must be addressed before gaining further insight into the economic viability of downhole steam generation are discussed.

Introduction

The effectiveness of thermal methods in recovering heavy oils has been realized for over fifty years. Many of the major heavy oil fields discovered early in the century were abandoned until the 1960's when steam injection had progressed technically to an economic, reliable recovery technique. This led to rapid production increases. Since that time, steam injection projects have gained prominence and, in fact, contribute to the majority of the enhanced oil recovery in heavy oil-bearing formations.

Although steam is effective in relatively shallow (less than 750 m) heavy oil reservoirs, heat transmission losses associated with delivery of the steam from surface generators to the oil-bearing formation have limited steam operations in the U.S. to these shallow reservoirs. Recent implementation of strict environmental controls for ambient air qualities have also restricted the universal applicability of the technique.

The objective of the Department of Energy's Project DEEP STEAM is to develop the technology required to economically produce heavy oil from deep reservoirs. The tasks included in this effort are the development and evaluation of thermally efficient delivery systems and downhole steam generation systems.

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