An Overview of Waterflood Surveillance and Monitoring

Abstract

Distinguished Author Series articles are general, descriptiverepresentations that summarize the state of the art in an area of technology bydescribing recent developments for readers who are not specialists in thetopics discussed. Written by individuals recognized as experts in the area, these articles provide key references to more definitive work and presentspecific details only to illustrate the technology. Purpose: to informthe general readership of recent advances in various areas of petroleumengineering. Introduction An essential key to a successful waterflooding project is a well-planned andwell-executed program of surveillance and monitoring. This program should betailored to address individual projects or fields because each waterflood willhave different characteristics. There are, however, some basic ingredients thatshould be common to all surveillance programs. In general, three majorcategories of field conditions must be included in any waterflood surveillanceprogram: reservoir conditions, injection/production-well conditions, andfacilities/operating conditions. The last and probably the most importantingredient is record keeping/performance control. There are, of course, economic conditions that must be taken into consideration. For the purposes ofthis paper, however, only the technical aspects of a waterflood surveillanceprogram will be addressed. The purpose of this paper is to provide an overviewof waterflood surveillance programs and to outline the various items to bemonitored. Selected tests for diagnosis of problems commonly associated withwaterfloods are discussed briefly, along with a look at developing surveillancetechnology. Surveillance Program Waterflood surveillance programs of the 1980's have been influenced to somedegree by the chemical waterflood projects of the 1970's. The desire tounderstand chemical-recovery-process applications better led to a significantincrease in project surveillance activities. Much time and effort was spent inevaluating both waterflood and tertiary recoveries. It was shown that byclosely monitoring field activities, improvement in waterflood recoveries couldbe achieved. Fig. 1 shows the key monitoring points in the traditionalwaterflood cycle. There was a time when most of the attention given awaterflood project focused on reservoir performance, and this usually waslimited to monitoring water cuts. Today we realize that it is equally importantto include well, facilities, and operating conditions in our surveillanceprograms. Thus, all the components of the waterflood cycle diagrammed in Fig. 1should be included in a well-planned surveillance program. Table 1 lists itemsthat should normally be included in the three major categories of surveillance. This is by no means a complete listing because waterfloods can have ratherunusual characteristics or conditions requiring additional items forobservation and evaluation-e.g., environmental and regulatory conditions. Reservoir Surveillance As listed in Table 1, reservoir pressures, injection and production rates, fluid volumes, WOR/GOR's, and fluid samples require constant surveillance. Adiscussion of these items and proposed schedules for obtaining the data waspresented by Barnes and Tinker. When these data are coupled with thereservoir-description information, waterflood-performance calculations can bemade. Reservoir-description information generally includes core, well log, andgeologic data. Holbert and Zeito list the reservoir-description data in moredetail. Numerous methods or techniques for estimating waterflood performancehave been reported in the literature. These methods range from the classictypes to sophisticated reservoir simulator models. There are four types ofwells requiring surveillance: production, injection, water-supply, andwater-disposal wells. Of these, production and injection wells require the mostattention. Monitoring well performance requires a program of selected welltests to be conducted regularly. The types of well tests selected will dependon surface/downhole equipment, well-completion characteristics, produced orinjected fluids, the stage of the waterflood project (early, middle, or late), and the reservoir description. Key items for surveillance are fluid entry intoor exit from target zones, cement/completion integrity, and mechanicalequipment, both downhole and surface. Well testing is discussed later. The wellsurveillance program should include plans for recording the information in asuitable manner or format such that it is both easily accessible and "userfriendly." Finally, the program should provide a systematic approach to dataanalysis, evaluation, recommendations, and corrective measures, as needed. Facilities/Operations Surveillance Waterflood operating procedures and conditions, along with the associatedproject facilities, are often taken for granted, yet they are key ingredientsto successful project management. Tinkers reported on the operating factorsthat affect waterflood performance, including well completions, injectionpatterns, high-volume lift, injection profiles, and bottomwater production. Operations and facilities vary considerably from project to project and undergochanges during the several stages of waterflood development. Injection-patternconfigurations, surface topography, reservoir characteristics, deviated wells, and field operating constraints are only a few of the conditions that can leadto problems associated with project management.