Integrating Core Data and Wireline Geochemical Data for Shale-Gas-Reservoir Formation Evaluation and Characterization
Authors: Denney Dennis 
Published: February 2015

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 134559, ’Integrating Core Data and Wireline Geochemical Data for Formation Evaluation and Characterization of Shale-Gas Reservoirs,’ by John Quirein, Jim Witkowsky, SPE, Jerome Truax, SPE, and Jim Galford, SPE, Halliburton, and David Spain, SPE, and Tobi Odumosu, SPE, BP plc, prepared for the 2010 SPE Annual Technical Conference and Exhibition, Florence, Italy, 19-22 September. The paper has not been peer reviewed.

When core data are available from a large multiwell database, it is possible to extract meaningful statistical relationships between those data. These relationships then can be applied to other wells that have limited or no core data. X-ray-diffraction (XRD) mineralogical data can be transformed to synthetic wireline-geochemical-elemental data. This transformation establishes a relationship between the mineralogical data and the synthetic wireline-geochemical data that can be applied to real wireline-geochemical data to select an appropriate set of minerals for use in making calculations from the wireline-geochemical data. A workflow was developed to provide an effective approach for calculating mineralogy, grain density, and porosity from wireline-geochemical data.  

Introduction

Calculating mineralogy, kerogen, grain density, porosity, and gas saturation in shale-gas reservoirs from wireline logs is a complex process that involves many log-interpretation mineral and fluid parameters. Attempting the interpretation without an orderly workflow can be exhausting and, ultimately, unproductive. The workflow proposed in this paper results in accurate wireline-log calculations of mineralogy, kerogen, grain density, porosity, and gas saturation. Core data can be used to guide this workflow.

Core-XRD-mineralogy analysis from a major core-analysis company provides, for each mineral, an XRD bulk-rock mineral (BRM) weight percent that sums to 100% when all the minerals are considered. However, XRD does not provide a weight percent for kerogen; consequently, the bulk rock in the XRD weight-percent analysis excludes porosity and kerogen. The core-XRD-mineralogy analysis also provides, for each mineral, an XRD-BRM volume percent that sums to 100% when all minerals, including kerogen, are considered. Consequently, the bulk-rock in XRD-volume-percent analysis excludes porosity, but includes kerogen. The XRD-BRM volume percent appears to be computed from the XRD-BRM weight percent, but to do this, a mineral density must be assumed for each mineral, and no mineral densities are provided in the core report. The XRD-bulk-rock kerogen content appears to be obtained directly from the total-organic-carbon (TOC) weight percent. A document states that residual water can be removed by drying the sample at 105°C for 1 hour, so the assumption was made that, here, the TOC weight percent is the bulk-rock TOC-weight percent (excluding porosity). Finally, from the XRD-BRM-volume-percent analysis, an XRD-calculated grain density is provided. Consequently, a comparison of the mineralogy, TOC, and kerogen from logs with that from core data provides ample opportunity for confusion.