Integrating Measured Kerogen Properties With Log Analysis for Petrophysics and Geomechanics in Unconventional Resources
- Paul R. Craddock (Schlumberger) | Laurent Mossé (Schlumberger) | Romain Prioul (Schlumberger) | Jeffrey Miles (Schlumberger) | MaryEllen L. Loan (Schlumberger) | Iain Pirie (Schlumberger) | Erik Rylander (Schlumberger) | Richard E. Lewis (Schlumberger) | Andrew E. Pomerantz (Schlumberger)
- Document ID
- Society of Petrophysicists and Well-Log Analysts
- Publication Date
- October 2018
- Document Type
- Journal Paper
- 588 - 605
- 2018. Society of Petrophysicists & Well Log Analysts
- 1 in the last 30 days
- 221 since 2007
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Workflows for log analysis in conventional reservoir rocks are difficult to apply in organic-rich mudrocks due to the presence of abundant kerogen (solid, insoluble organic matter). There are two key reasons for this difficulty. First, kerogen is part of the solid matrix but responds like a fluid in traditional porosity log analysis (e.g., density, neutron). Accurately estimating formation volumes from logs, therefore, requires a method to separate the kerogen and fluid signals in the matrix and porosity, respectively. A second difficulty is that the petrophysical properties of kerogen (such as its density and hydrogen index) vary by more than 50% relative, impacted by geologic forces including maturation, and are rarely known. No logging tools can measure kerogen properties directly.
This paper describes a novel, wellsite method combining log and cuttings analysis that overcomes these challenges, providing a measured separation of kerogen and pore fluids and a direct estimate of kerogen properties. The cuttings analysis uses diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Prior to analysis, cuttings are cleaned of formation fluid and drilling mud, isolating the kerogen signal. DRIFTS measures the vibrational frequencies of chemical bonds in matrix components, including kerogen, and newly developed transforms quantify kerogen properties directly from its DRIFTS signal. The method has been optimized for analysis of cuttings and can be performed at the wellsite, for vertical and deviated wells, with any mud type. Examples illustrating the integration of cuttings and downhole log analysis are shown. In one, DRIFTS provides a matrix-adjustment to porosity logs giving a direct measurement of porosity, without the need for subjective assumptions that are needed in standard porosity log interpretations of organic-rich formations. In another, DRIFTS estimates anisotropic elastic and stress profiles along a lateral after calibration in a vertical pilot. Integration of cuttings and downhole log analyses provides a practical method to solve many challenges inherent to log interpretation in organic-rich formations.
|File Size||8 MB||Number of Pages||18|