Waterflood surveillance Techniques - A Reservoir Management Approach
Authors: Thakur G.C. 
Published: December 2007

Distinguished Author Series articles are general, descriptive representations that summarize the state of the art in an area of technology by describing 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
Billions of barrels of additional reserves have been generated throughwaterflooding, one of the most important methods of improving recovery from oilreservoirs. With the uncertainty of the economic applicability of EORtechniques as a result of oil-price instability, optimization of waterfloodinghas become more significant than ever. The reservoir management aspects ofwaterflooding are not restricted to an initial engineering and geologicalreport, economic justification, and project approval by management. Rather, these ongoing activities span the time before the start of waterflood to thetime when the secondary recovery either is uneconomic or is changed to anenhanced recovery. A reservoir management approach to waterflood surveillanceconsiders a system consisting of reservoir characterization, fluids and theirbehavior in the reservoir, creation and operation of wells, and surfaceprocessing of the fluids. These are interrelated parts of a unified system. Thefunction of reservoir management in waterflood surveillance is to providefacts, information, and knowledge necessary to control operations and to obtainthe maximum possible economic recovery from a reservoir. Initial productionforecasts may not always agree with actual performance. Differences may arisefrom fieldwide averaging of data in the prediction model, inadequate geologicaldescription, and well-completion problems. Thus, attempts should be made toresolve the differences and controlled surveillance should be carried out toimprove field performance. Guidelines for waterflood management should includeinformation on (1) reservoir characterization, (2) estimation of pay areascontaining recoverable oil, (3) analysis of pattern performance, (4) datagathering, (5) well testing and reservoir pressure monitoring, and (6) wellinformation data base. Today, sufficient performance history is available thatsurveillance techniques can be documented in detail. This paper highlightswaterflooding in light of practical reservoir management practices. Casestudies that illustrate the best surveillance practices are referenced.

Reservoir Management
Reservoir management can be defined as the judicious use of varioustechniques to maximize benefits or economic recovery from a reservoir. Fig. 1 describes the interaction required among the various functions. The reservoirmanagement approach to waterflood surveillance must use a coupled systemconsisting of wells, surface facilities, and the reservoir. All must beconsidered in a balanced way to maximize economic oil recovery. Also, a teameffort involving people from various functional areas is mandatory fordevelopment and implementation of a successful reservoir managementprogram.

Key Factors in Waterflood Surveillance
Talash and Talash and Strange described the key monitoring points in thetraditional waterflood cycle (Fig. 2). In the past, attention was focusedmainly on reservoir performance. However, with the application of the reservoirmanagement approach, it has become industry practice to include wells, facilities, water system, and operating conditions in surveillance programs. Itis important to consider the following items in the design and implementationof a comprehensive waterflood surveillance program (Table 1).Accurate anddetailed reservoir description.Reservoir performance and ways to estimatesweep efficiency and oil recovery at various stages of depletion.Injection/production wells and their rates, pressures, and fluid profiles.Water quality and treating.Maintenance and performance of facilities.Monthly comparison of actual and theoretical performance to monitor waterfloodbehavior and effectiveness.Reservoir management information system andperformance control (accurate per-well performance data).Diagnosis ofexisting/potential problems and their solutions.
JPT
P. 1180⁁