--> Reservoir Evaluation: Logging Without Chemical Radioactive Sources

Pacific Section AAPG, SPE and SEPM Joint Technical Conference

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Reservoir Evaluation: Logging Without Chemical Radioactive Sources

Abstract

Reservoir Evaluation Logging Without Chemical Radioactive SourcesJeffrey Little; Schlumberger/ Petro Technical Services - Bakersfield California, Larry Knauer, David Barnes, Dale Julander; Chevron USA Inc. - Bakersfield CaliforniaObjectiveThe use of chemical radioactive sources in the wellbore is increasingly being perceived by many clients, especially those involved in horizontal well operations, as a risk that needs to be minimized, often at the expense of running logs at all. Responding to a client request, Schlumberger PTS has developed an empirical method to perform primary evaluation in open-hole without the use of chemical radioactive sources in shaley sand environments as typically found throughout North and South America. Evaluations at Chevron's California Kern River field are further complicated by a non-typical combination of steam and fluids found in a mature heavy oil steam flood project. The intention of this review is to demonstrate how dielectric dispersion in combination with minitron based porosity measurements can be used, while accounting for changes in mineralogy and the adverse effects of gas and heavy oils, to provide an accurate determination of fluid saturation. MethodMultiple tool-measurement combinations were reviewed before arriving at a proposed logging tool suite that could provide the needed inputs while operating without the use of chemical sources. After considerable discussion regarding the evaluation limitations due to the known presence of heavy oil, gas and water of varying salinities, the Dielectric Scanner (ADT) and the Accelerator based Neutron (APS) were selected. Additionally, workflows used by the client require a thermal neutron (TNPH) porosity, successfully replicated from the APS epithermal outputs, and resistivity gamma-ray arrays generated with the inclusion of an Adaptable Induction — Gamma Ray tool (AIT-GR). ResultsTo test the validity of this method we have used available core data as well as accepted interpretation results from tradition methods including parametric inversions of large and complete data sets used in this study. Outcomes show an excellent agreement between the new ‘sourceless’ method and the accepted traditional interpretation. Two critical components to a successful evaluation were noted: 1) estimation of the water filled portion of the total porosity and 2) the identification of steam zones and other gas filled sections in the reservoir. By careful comparison to known results this technique has been deemed very successful by Chevron and warrants further review and investigation. ConclusionThe use of dielectric dispersion within this new model provides, for the first time an estimate of the water filled porosity without the use of measurements derived from the use of chemical sources. Successful examples presented from Kern River show this method to be widely applicable. Additionally, the new model solves for total porosity and includes a flag indicating the presence of gas. Applications Well logging without chemical sources, Shaly Sands with high feldspar content, Steam floods with induced uranium effects on clay indicators, lithology which includes high biogenic silica content ∼ Monterey Shale