SPE Reservoir Evaluation & Engineering
Volume 12, Number 6, December 2009, pp. 898-911

SPE-109879-PA

Estimation of Dry-Rock Elastic Moduli Based on the Simulation of Mud-Filtrate Invasion Effects on Borehole Acoustic Logs

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DOI  More information 10.2118/109879-PA http://dx.doi.org/10.2118/109879-PA

Citation

  • Odumosu, T., Torres-Verdin, C., Salazar, J.M., Ma, J., Voss, B., and Wang, G.L. 2009. Estimation of Dry-Rock Elastic Moduli Based on the Simulation of Mud-Filtrate Invasion Effects on Borehole Acoustic Logs. SPE Res Eval & Eng  12 (6): 898-911. SPE-109879-PA. doi: 10.2118/109879-PA.

Discipline Categories

  • 6.6 Reservoir Monitoring/Formation Evaluation
  • 6.1 Reservoir Geology and Geophysics
  • 6.6.1 Well Logging
  • 6.6.2 Core Analysis
  • 6.1.3 Sedimentology

Summary

Reliable estimates of dry-rock elastic properties are critical to the accurate interpretation of the seismic response of hydrocarbon reservoirs. We describe a new method for estimating elastic moduli of rocks in-situ based on the simulation of mud-filtrate invasion effects on resistivity and acoustic logs.

Simulations of mud-filtrate invasion account for the dynamic process of fluid displacement and mixing between mud-filtrate and hydrocarbons. The calculated spatial distributions of electrical resistivity are matched against resistivity logs by adjusting the underlying petrophysical properties. We then perform Biot-Gassmann fluid substitution on the 2D spatial distributions of fluid saturation with initial estimates of dry-bulk (kdry) modulus and shear rigidity (μdry) and a constraint of Poisson’s ratio (νd ) typical of the formation. This process generates 2D spatial distributions of compressional and shear-wave velocities and density. Subsequently, sonic waveforms are simulated to calculate shear-wave slowness.Initial estimates of the dry-bulk modulus are progressively adjusted using a modified Gregory-Pickett (1963) solution of Biot’s (1956) equation to estimate a shear rigidity that converges to the well-log value of shear-wave slowness. The constraint on dynamic Poisson’s ratio is then removed and a refined estimate of the dry-bulk modulus is obtained by both simulating the acoustic log (monopole) and matching the log-derived compressional-wave slowness.

This technique leads to reliable estimates of dry-bulk moduli and shear rigidity that compare well to laboratory core measurements. Resulting dry-rock elastic properties can be used to calculate seismic compressional-wave and shear-wave velocities devoid of mud-filtrate invasion effects for further seismic-driven reservoir-characterization studies.

© 2009. Society of Petroleum Engineers

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History

  • Original manuscript received: 30 July 2007
  • Meeting paper published: 11 November 2007
  • Revised manuscript received: 27 January 2009
  • Manuscript approved: 26 April 2009
  • Published online: 3 September 2009
  • Version of record: 31 December 2009