Reservoir Fluid Characterization with a New-Generation Downhole FluidAnalysis Tool

摘要

This paper reports a new-generation wireline formationtesting tool that quantitatively characterizes reservoirfluid. The tool measures: 1) fluid composition (C1, C2,C3–C5, C6+, and CO2); gas/oil ratio (GOR) and waterfraction by VIS-NIR spectroscopy; 2) color,fluorescence, and reflectance; 3) pH if fluid is water; 4)density by a vibrating sensor; 5) flowline pressure andtemperature; and 6) water salinity by resistivitymeasurement.The first half of the paper presents a schematicdescription of the tool and explains the spectrometeraccuracy improvement over existing commercialofferings. A grating spectrometer is the standardtechnology used for laboratory spectroscopy, and it wasimplemented for the first time for this downhole tool.The grating spectrometer has several advantages overexisting commercial products for: 1) being able tomeasure semi-continuous spectrum in criticalhydrocarbon peak region and 2) better signal baselinestability critical for accurate spectroscopy. More than45 field test jobs were performed in the field testcampaign. The comparisons made are betweenmeasurements performed by a new wireline downholefluid analysis (DFA) tool and PVT analysis performedin wellsites and laboratories.The second half of the paper discusses a deepwaterappraisal well case example from offshore Nigeria,West Africa. The objective of the formation testingprogram was to assess the hydrocarbon potential,evaluate the fluid properties and contacts, anddetermine the presence of any compositional gradingwith depth across the reservoir section. An advancedwireline formation testing tool equipped with focusedsampling and conventional probes and four downholefluid analyzers including the new-generation tool wereused. Pressure pretests were performed in this appraisalwell in combination with fluid scanning and fluidsampling at seven depths across the reservoir. Thecombination of fluid scanning across the main reservoirand real-time measurements of in-situ fluid density alsoenabled the operator to rapidly assess the fluidcomposition and locations of fluid contacts duringprogression of the logging operations. The applicationof this new sampling and downhole fluid analysistechnology provided valuable information to theoperator for design of the subsequent drillstem test andresults comparison.