State-of-the-Art Review of Fireflood Field Projects (includes associated papers 10901 and 10918 )

Abstract

Summary This paper embodies a state-of-the-art review of fireflood field projects. On the basis of reservoir data on 25 selected successful fireflood projects and nine aborted projects, a new screening guide has been developed for firefloods. A new regression equation also was developed that will allow prediction of air requirements with known reservoir characteristics. Methods of predicting other performance variables such as fuel content, sweep efficiency, oil recovery and air/oil ratio are discussed. Industry experience on project design is reviewed in regard to the choice between dry and wet combustion and determination of pattern type and size, air injection rate, water/oil ratio and completion intervals. Special well completions needed for fireflood are reviewed as well as the various ignition methods. Operational problems plaguing the fireflood projects, which include poor injectivity or productivity, corrosion, erosion, emulsion, and explosion hazards, are discussed along with their remedies. Introduction The in-situ combustion process, ever since its inception in the mid-1930's, has proved a significant method for recovering oil, especially heavy oil. Comprehensive reviews of fireflood field projects have been given by Farouq Ali1 and Chu,2among others. This review covers the following topics: screening guides, reservoir performance predictions, project design, well completions for injectors and producers, ignition methods, and operational problems and their remedies. Screening Guides In dealing with oil prospects, the first step is to find out whether the field in question can be produced by certain recovery methods. Screening guides are useful for this purpose. Screening guides for in-situ combustion processes have been proposed by various authors, including Poettman,3 Geffen,4 Lewin and Assocs.,5 Chu,2 and Iyoho.6 The screening guides proposed by these authors are listed in Table 1. In recent years, the price structure of the crude oil has changed tremendously. A fireflood project that previously was considered uneconomical could become economically feasible if conducted today. Moreover, more information recently has become available for various new or continuing fireflood field projects. In view of this, a new set of screening guides has been developed and is listed on the last entry in Table 1. The approach for developing this new screening guide differs from the approaches used by Chu in 1977 in two respects. First, the capability of producing oil rather than the economical feasibility of the projects is used as the criterion for acceptance or rejection of a prospect. Second, both the confidence-limit and regression-analysis approaches used previously presuppose that the frequency distributions of the various reservoir characteristics conform to a normal distribution. In the present approach, the frequency distributions are used as they appear, regardless of whether they are normal, log-normal or otherwise. As a part of the data base for the development of the new screening guide, 25 successful fireflood projects were selected. All these projects have exhibited oil production rates of at least 100 B/D for an extended period of time, mostly for more than a year. These are considered positive projects. As another part of the data base, nine aborted projects have been included as negative projects. The lists of the positive and negative projects are not meant to be exhaustive. However, these 34 were selected from all the projects that appeared in the literature available to me, with sufficiently detailed description of reservoir characteristics, process variables, and fireflood performance. The reservoir characteristics of these two project types are listed in Table 2.