Laminated Reservoir Evaluation in a Case of High Apparent Dip

Abstract

Abstract In several offshore reservoirs composed of thin, interbedded sands and shales, a recently reported technique to correct standard induction logs for the effects of formation dip is incorporated into an established method for the well log analysis of laminated reservoirs to yield a superior petrophysical characterization. Both shale anisotropy and bedding effects are included in the correction of the induction log for apparent dip. In a single well, electrically anisotropic properties of shales are difficult to determine solely by well logs. In the example reservoir, multiple wells with varying hole deviation were drilled from the same platform. By analyzing logged intervals from different wells, the electrical anisotropy of the shales is determined and appropriate corrections are made to the induction log. Procedurally, a laminated reservoir analysis technique using a dipmeter or another high resolution shale indicator is first applied to the log data. Induction resistivities are corrected for dip effects arising from both sand/shale boundaries and shale anisotropy using an estimate of anisotropy. Then, corrected induction resistivities are used in the laminated reservoir analysis technique. Finally, parameters related to shale anisotropy are varied so that the analyses of wells with high and low apparent dip are consistent. Quantitative analysis within each individual well is improved using these methods; more importantly, the combined techniques allow comparative evaluations between wells with significantly different hole deviations. Therefore, inclusion of dip effect corrections yields a more accurate well-to-well comparison in laminated reservoirs.