Nuclear Magnetism Logging in the Rocky Mountain Area
Authors: Artus D.S. 
Published: December 2007

American Institute of Mining, Metallurgical and Petroleum Engineers Inc.

Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers Office. Such discussions may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

Shell's experience with the Nuclear Magnetism Log [NML] in the Rocky Mountain area indicates the @ is a versatile evaluation tool, especially in carbonate provinces. The NML is indicated to be a superior porosity device in carbonates, both nonshaly and shaly. A technique for using the NML to estimate producing water cuts in sandstones is discussed producing water cuts in sandstones is discussed and illustrated with two field examples. Although the data are limited to low water cuts, the results look promising.

Introduction

Purpose and Scope Purpose and Scope The Nuclear Magnetism Log [NML) has been field tested by Shell in the Rocky Mountain Div. These field tests were designed to evaluate the utility of this log as an additional tool in predicting formation productivity. Nuclear predicting formation productivity. Nuclear Magnetism logs have been run in five wells on the Cedar Creek anticline in southeastern Montana, where thick carbonate-shale sequences exhibit considerable variation in porosities, permeabilities and rock types. Three NML logs permeabilities and rock types. Three NML logs have been run in the sand-shale sequences of Powder River basin of Wyoming [Fig. 1]. Thus, Powder River basin of Wyoming [Fig. 1]. Thus, multiple lithologies and a full range of porosities and permeabilities normally porosities and permeabilities normally encountered in this Division were logged in these field tests.

Summary and Conclusions

The field tests described in this report indicate that the NML merits recognition as an independent porosity device in carbonates and as a productivity indicator in sandstone reservoirs.

In carbonate formations the Free Fluid Index [FFI] obtained from the NML may be used directly as a measure of porosity with accuracy comparable to core analyses, regardless of permeability. Tight intervals and shales are permeability. Tight intervals and shales are shown as having no porosity, thus facilitating recognition of all potential reservoirs quickly and easily. The ME may be of significant benefit in carbonate provinces, since porosity determinations are often difficult using logs presently available, and coring is often presently available, and coring is often impractical.

The technique used to estimate producing water-cut in sandstones has considerable potential especially in transition intervals potential especially in transition intervals located between zones with irreducible water saturation and those below the free water level. In the two cases observed to date, the predicted water-cut has agreed closely with the predicted water-cut has agreed closely with the production data. Both cases were in the low production data. Both cases were in the low water-cut range [less than 10 percent].