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The Duri Field, operated by P. T. Caltex Pacific Indonesia, under a production sharing contract with Pertamina, is located in Riau Province, Central Sumatra, about 120 km. northwest of the city of Pekanbaru. It is the second largest oil field in Indonesia. The field is approximately 18 km. long by 8 km. wide with over 25,000 developable acres. Due to the highly viscous nature of the hydrocarbon encountered at Duri, continuous steam injection is utilized to facilitate recovery. Duri is now the largest project of its kind in the world having recently surpassed Kern River field, California, (previously the world's largest) in total daily production.As in any enhanced recovery project, the accurate determination of reservoir parameters such as Rw, CEC, Sw, So, Vsh, porosity and permeability are very important for reservoir modeling and reserve estimation. Since Duri is a freshwater, shaly sand environment. it creates complications that are not easily resolved using convcntional log analysis techniques. The formation evaluation of expansion areas has been grcatly cnhanccd by thc use of Schlumbcrger's Geochemical Tool (GLT). The tool was first utilized in 1988 and has been run in both water and oil base mud. The data analysis from four observation wells, with core for comparison purposes, forms the basis for this report. Sclccted observation wells are cored and logged using the GLT in combination with other specialty logs, such as the EPT and GST, to obtain baseline data before the implementation of steam injection.Geochemical log interpretation yields detailed informaticin on mineral constituents by using natural radiation, neutron activation and pulsed neutron spectral measurements. Total clay content as well as clay typing can be computed from GLT data using chemical composition instead of traditional cross plot techniques. Comparison of Core Laboratories' MINERALOG(TM) and Schlumberger's GLT computed total clay content yield good results. Core analysis can also be used to refine the model thereby increasing the tools validity as a predictive device. Total porosity, grain density, Sw (virgin and invaded zone), permeability (using mineral composition and porosity), etc., can be computed and are in geneqally good agrcement with core data. The use of GLT logging in conjunction with core data shows promise as an enhanced formation evaluation technique in freshwater, shaly sands.