Improved Use of Wireline Testers for Reservoir Evaluation

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. Summary. Vertical pressure profiles obtained from wireline multiple-pressuretesters have become an important tool for improve determination of reservoirpressure and fluid distributions. Procedures and techniques for dataacquisition to improve the quality of both strain and quartz gauge pressuredata for vertical profiles are presented. Tool calibration checks, wellsitemonitoring and consistency checks, techniques for normalizing pressure surveyswithin the same well or different wells, and sampling strategies are given. Examples are used to illustrate these procedures and techniques. In addition. field examples of vertical-pressure-profile plots andinterpretation of these plots are used to illustrate applications fordefining fluid contacts and identifying oil reservoirs in freshwaterenvironments,defining multiple fluid contacts throughout an apparentlycontinuous oil section,identifying multiple-pressure regimes in asupernormal-pressure environment,identifying zones of differentialreservoir depletion as a result of low permeability or an impermeable barrier, andestimating fluid properties at reservoir conditions. Introduction The wireline formation tester was commercially introduced in late 1955 alongthe coasts of Louisiana and Texas. The original tool could retrieve only onesample and one pressure recording for each trip to the well. Early applicationscentered on differentiating oil from gas reservoirs. As the tool evolved, improved formation-sealing mechanisms were developed, as was a cased-holetester. The cased-hole version was equipped with a cement-squeeze adapter. Inthe 1960's, this cased-hole version with the squeeze adapter was used to injectchemicals for sand consolidation. The wireline multiple-pressure tester was introduced in 1976. It can recordan unlimited number of precise and relatively accurate pressure measurementsduring a single trip into a wellbore. Various applications of these pressuresurveys for reservoir and single-well evaluations have been discussed. Theseinclude the analysis of naturally fractured reservoirs, use of pulse-testingtechniques to establish reservoir continuity, qualitative estimate ofpermeability in low-permeability formations, reservoir management in producingfields, and detection of fluid interfaces from vertical pressure profiles. These applications are successful because of the accuracy and resolutionpossible with the wireline multiple-pressure tester measurements. Obtaininghigh-quality pressure-data interpretations requires particular attention toboth data acquisition procedures and interpretation techniques. Recommended practical operating procedures and interpretation techniques toimprove the quality of both strain and quartz gauge pressure data are given inthis paper. If these recommendations are followed, a 1-psi [6.9-kPa] resolutioncan be used with confidence in vertical-pressure-profile interpretations. Experience has shown that absolute pressure readings from both strain andquartz gauges do not consistently meet the accuracy claims of service companiesand are not as reliable as their resolutions. Normalization techniques arerecommended for combining pressure surveys from multiple runs. JPT P. 635^