Overview: Formation Evaluation (May 2006)
- Martin Kennedy (Woodside Energy Ltd.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- May 2006
- Document Type
- Journal Paper
- 48 - 48
- 2006. Copyright is retained by the author. This document is distributed by SPE with the permission of the author. Contact the author for permission to use material from this document.
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Next year will mark 80 years since the Schlumberger brothers ran the first wireline log. Geophysical mapping, in particular surface seismic, had a slightly earlier and arguably more protracted birth. Both ways of extracting information from the subsurface have been refined and extended considerably since then, of course; but fundamentally, we are stuck with just two sources of data, both of which have shortcomings. I recently have taken to taunting geophysicists by likening seismic images to photographs that have been taken through the bottom of a brandy bottle (and I mean French five-star Cognac, which comes in bottles made of very dark glass with a huge conical dimple in the bottom). On the other hand, logs and other data from wells can tell you almost anything you want to know about what is going on at or a few centimeters from the borehole wall, but give no direct knowledge of the remaining 99.999…% of the field.
There is not much to fill the gap between geophysics and well data—or is there? I believe there is, and some of it has been around for a long time. One can list several mature bore-hole measurements that will see tens or even hundreds of meters into the formation:
- Deep-reading resistivity tools—50 years old.
- Vertical seismic profiles—40+ years old.
- Borehole gravity—40 years old.
Given two or more wells, tomography becomes a possibility as well. No one should be under any illusions that these measurements are easy to make or interpret. Typically, they involve modeling and, therefore, require time and a reasonable idea of what is in the subsurface. In short, they are appraisal tools.
Accurate placement of development wells frequently requires deep-reading measurements made in real time. Resistivity may be appropriate, but this method presupposes the existence of a resistivity contrast at the boundary that is controlling the well path (a gas/oil contact fails the test, for a start). There are convincing demonstrations that sonic measurements can image boundaries at useful distances from the well, but it is a formidable challenge to turn that technology into a real-time technique. Formidable, yes, but I would be surprised if it turns out to be impossible.
Formation Evaluation additional reading available at the SPE eLibrary: www.spe.org
SPE 95950 “What Is the Characteristic Length Scale for Permeability? Direct Analysis From Microtomographic Data,” by F. Bauget, Australian Natl. U., et al.
SPE 96100 “Measurement of the Sealing Capacity of Shale Caprocks,” by T.M. Al-Bazali, SPE, U. of Kuwait, et al.
SPE 96609 “NMR and Capture Spectroscopy Help Resolve Producibility and Fluid Distribution in the North Alwyn Triassic,” by C. Longis, Total E&P, et al.
IPTC 10726 “Applications of Petrophysical Scale-Reconciliation to Saudi Arabian Reservoirs,” by H.A. Al-Ali, SPE, Saudi Aramco, et al.
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