Introduction The historical background of water flooding is well known to most engineers associated with the petroleum industry. The earliest water floods were accidental in nature resulting from improperly plugged wells or casing leaks. The obvious benefits of these accidental floods soon encouraged the operators to inject water intentionally. The early waterflooding techniques were thoroughly developed and standardized long before even the most elementary concepts of reservoir mechanics were understood. Under these circumstances, the evaluation of waterflood prospects was strictly a matter of analogy and application of "rules of thumb." If a successful water flood had been conducted in a certain sand in a certain area, operators would presume that a nearby field producing from the same zone could be flooded with similar results. Use of analogy and rules of thumb had obvious limitations, as is apparent from the rather frequent unsuccessful waterflood attempts. Reliance upon such methods is still surprisingly heavy even today. Modern reservoir engineering enables us to determine the range of reservoir conditions which will result in favorable response to waterflood efforts, and also to delineate the range of conditions under which water flooding will be of doubtful success. By means of relating the various reservoir parameters involved to the results obtained from water floods, a more reliable set of experience factors can be obtained and the uncertainties involved in water flooding greatly reduced. As is illustrated herein, there are a number of reservoir factors which have a profound influence upon the success of a waterflood project and unfavorable values for any one or two of these factors can result in complete failure of a flood, even though other factors may be quite favorable. It is hoped that this discussion of the effect of various reservoir parameters upon waterflood results will, if nothing else, point out the severe limitations of the rules of thumb by which so many decisions to water flood have been made. In order to illustrate the manner in which the various reservoir factors operate and their relative importance, it has been necessary to assume a certain set of hypothetical reservoir conditions and investigate the effect of varying one or two of the factors independently. It must be emphasized that the values for waterflood recovery efficiency derived herein are of no real significance except for those specific conditions assumed and must not be used directly for the purpose of evaluating any given waterflood prospect. The term "waterflood recovery" as used herein refers to the increase in recovery over and above that which would be obtained by producing a field to its economic limit by primary means. In the case of a flood initiated before all of the primary oil has been produced, the recovery from the date of inception of a flood is the sum of the remaining primary recovery plus the "waterflood recovery" as defined herein.
In this paper oil initially in place is calculated by the various methods commonly used for analysis of water drive fields using data available as time progresses. Rate and pressure are predicted by means of the same methods using data available at the end of two years' history. These predictions are then compared with subsequent performance permitting an evaluation of the methods, which are Modified Schilthuis, Simplified Hurst, van Everdingen et al (1952), and the Electric Analyzer. Introduction Several variations of the material balance equation, differing in the term used to evaluate water influx, are in common use for estimating oil in place, predicting rate and volume of water influx, and forecasting producing rates and reservoir pressure in water drive reservoirs. The electric analyzer with an electrical network set up to simulate the oil reservoir and aquifer and their contained fluids may be used for the same purpose. Examples of the application of one or another of these methods have appeared in the literature. The accuracy and reliability of the material balance for calculating oil in place have been covered. However, there have been few articles in which more than one method has been applied to an actual field allowing a comparison. It is felt that a field example, simple in nature, where the Modified Schilthuis, Simplified Hurst, van Everdingen et al (1952), and the Electric Analyzer have been applied would be of benefit in providing an evaluation of these methods as to their comparative usefulness and reliability in calculating initial oil in place and predicting performance.
The various theories as to the well spacing-recovery relationship are reviewedin considerable detail and these theories analyzed in terms of theirconsistency with modern reservoir engineering concepts. It is concluded thatthe well spacing problem must be analyzed in terms of recovery efficiency andthat a positive answer to the relation between well density and recoveryefficiency is not available from direct comparisons of the production historiesof wells and fields. The results of an engineering analysis designed to permit approximatecalculation of recovery efficiencies as a function of well spacing in adepletion type reservoir from basic reservoir data is presented. Results ofthis type analysis indicate that the effect of well spacing on recoveryefficiency in depletion type reservoirs can be expected to be very small.Limitations of this approach are pointed out, particularly with respect to itsapplication in lenticular reservoirs. Testing techniques are outlined which should indicate whether or not areservoir is continuous between wells and whether or not satisfactory drainageis being obtained with present spacings. A mass of data of this type indicatescontinuity to exist in most fields. Introduction The purpose of this paper is to review critically the engineering aspects ofthe well spacing problem, both from the standpoint of certain concepts and fromthe standpoint of reservoir mechanics. The well spacing problem is primarily aneconomic problem in which the optimum well density for a particular field isthat density which will yield the greatest oil recovery consistent withjustifiable development costs. The well spacing answer in terms of economicconditions, however, is extremely sensitive to the variation in recoveryefficiency with well density. The variation in recovery efficiency with welldensity is properly an engineering problem. Different opinions as to thecorrect answer to this engineering problem is the basis for most of the widedifference in opinion among various members of the industry as to optimum wellspacing. This paper will be confined to the engineering problem of the relationbetween well density and ultimate oil recovery; economic considerationsnecessary for the evaluation of optimum well density for any particular fieldwill not be discussed. T.P. 2938
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.