Deepwater Core Comparison With Answers From a Real-Time Petrophysical Evaluation
- Michael G. Poulin (Occidental Permian Ltd.) | John W. Hidore (Unocal Corp.) | Sigit Sutiyono (Unocal Corp.) | Michael M. Herron (Schlumberger) | Susan Herron (Schlumberger) | Nikita V. Seleznev (Schlumberger) | James A. Grau (Schlumberger) | John P. Horkowitz (Schlumberger) | Thierry J. Chabernaud (Schlumberger) | Mark V. Alden (Schlumberger)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Evaluation & Engineering
- Publication Date
- April 2006
- Document Type
- Journal Paper
- 165 - 171
- 2006. Society of Petroleum Engineers
- 5.8.7 Carbonate Reservoir, 5.6.1 Open hole/cased hole log analysis, 6.5.4 Naturally Occurring Radioactive Materials, 5.6.2 Core Analysis, 1.2.3 Rock properties, 4.1.2 Separation and Treating, 4.1.5 Processing Equipment, 5.2 Reservoir Fluid Dynamics, 1.6.9 Coring, Fishing, 5.5.2 Core Analysis, 2.4.3 Sand/Solids Control
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- 576 since 2007
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A recently introduced rapid petrophysical wireline evaluation has been tested and demonstrated to provide accurate petrophysical answers in a deepwater Gulf of Mexico well. This new interpretation scheme uses the combination of elemental concentrations from nuclear capture spectroscopy logs and standard neutron, density, resistivity, or "triple-combo?? log measurements to get a more accurate description of the lithology and matrix parameters. Of particular value in the interpretation are the straightforward computation of matrix density from elemental concentrations and the resulting accurate porosity. Accurate clay and porosity values combine to provide a good estimate of permeability. These are all integrated with resistivity logs to estimate water saturation and irreducible water saturation to complete the petrophysical interpretation (Herron et al. 2002).
In this study, the rapid petrophysical evaluations of porosity, permeability, and irreducible water saturation are demonstrated to agree well with core data. Initial disagreement between the interpreted lithology and core data jeopardized future use of the new interpretation, but on further investigation, the discrepancies were proved to be caused by the core measurements, not the wireline data. Therefore, part of the study focuses on the reanalysis and evaluation of core samples.
Complex lithologies in the deepwater Gulf of Mexico introduce new petrophysical challenges. Conventional wisdom or approaches to interpreting wireline logs do not always provide the desired accuracy in petrophysical answers. The promise of improved accuracy in lithology characterization and porosity evaluation led to the acquisition of nuclear spectroscopy wireline data and the subsequent testing and evaluation of an integrated evaluation using the spectroscopy logs with the conventional "triple combo?? of neutron, density, and resistivity (Herron et al. 2002).
The inclusion of the spectroscopy logs provides the opportunity to accurately characterize the rock matrix in terms of its lithology and matrix properties and thereby enable a more reliable and accurate petrophysical evaluation. Selected core samples from the study well were analyzed for clay content, porosity, permeability, and irreducible water saturation, and the data are used to validate the interpretation. This paper outlines the steps in the interpretation and demonstrates their validity by comparison with core data.
For the petrophysical properties of porosity, permeability, and irreducible water saturation, the petrophysical interpretation shows very good agreement with the core data. However, in spite of this agreement, the interpretation was initially questioned because of a significant discrepancy between the computed clay content and the core values measured by X-ray diffraction (XRD). XRD clay averages less than half the amount computed from spectroscopy logs. To investigate this discrepancy, additional core samples were analyzed with a different analytical technique, dual-range Fourier transform infrared (DRFT-IR), and it was concluded that the XRD data are in error. The new clay and chemistry data are used to optimize the estimate of total clay from chemistry. The original and optimized interpretations are both presented. The new methodology was used in new wells from the same field and continues to be applied to other deepwater Paleogene formations.
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