Applications of Carbon/Oxygen Logging in Indonesian Reservoirs

摘要

Clastic reservoirs with waterdrive mechanisms can lead torntricky interpretations in instances where resistivityrnmeasurements have little contrast between freshwater- and oilbearingrnrocks. Indonesia’s clastic and carbonate environmentsrncan provide challenges in reservoir monitor evaluation,rnespecially in the detection of fluid types behind pipe,rnquantification of reserve depletion, and control of high waterrnproduction.rnCarbon/oxygen (C/O) logging is primarily utilized torndetermine oil-water saturations and reservoir performance inrnareas with low or unknown formation-water salinities. ThernC/O measurement is based on carbon and oxygen reactionsrnwith high-energy “fast” neutrons producing characteristicrngamma rays. From this measurement, one can distinguishrnbetween hydrocarbons (C + H) and water (H + O). This, ofrncourse, is a very simplistic model of real-world applicationsrnthat are complicated by mineralogy, wellbore environmentalrnconditions, and reservoir behavior. Successful applications ofrnC/O logging in Indonesia have includedrn Identification of oil reserves otherwise difficult torndetectrn Monitoring reservoir depletionrn Identification of horizontal well placement targetrn Detection of oil-water contacts for conformancerntreatment applicationsrn Inter-reservoir crossflow identification by oxygenrnactivation combined with production logsrn Oil-saturation analysis for initial well completionsrnwhen openhole logs are not obtainablern Confirmation of steamflood efficiencyrnThis paper presents a few of over 100 C/O logging andrninterpretation experiences in Indonesia since 1993. Jobrnplanning and well preparation critical to successful use of therntechnology are discussed. Several log examples are shown tornhighlight a cross section of applications in hopes ofrnencouraging increased future use of the technology inrnoptimizing reservoir performance.