--> Abstract: Paleomagnetic Logging - A New Tool for Reservoir Characterization, by S. Luthi, A. Etchecopar, and L. S. D. Onuigbo; #90937 (1998).

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Abstract: Paleomagnetic Logging - A New Tool for Reservoir Characterization

LUTHI, STEFAN, ARNAUD ETCHECOPAR, and L.S.D. ONUIGBO Services Techniques Schlumberger, Montrouge, France

Chronostratigraphy is an invaluable tool in the petroleum industry, supplementing lithostratigraphy in event correlation and thus helping to decipher reservoir architecture. At present, biostratigraphy provides these chronostratigraphic data. A new tool, the Geological High-Resolution Magnetic Tool (GHMT) measures the polarities of natural remanent magnetism (NRM) in the wellbore as a function of depth, and through correlation with the Global Polarity Time Scale (GPTS) provides chronostratigraphic markers. GHMT data is acquired in a continuous manner in the wellbore and has no missing sections.

The GHMT measures the total magnetic field with an extremely accurate precession magnetometer and the susceptility of the rock with an equally accurate dipole-dipole measurement.. The magnitude of NRM is obtained by subtracting the induced and the known Earth's magnetic field from the total field, and the NRM polarity of the rock at a given depth is estimated by cross-correlating the computed value of NRM with the measured susceptibility. The sense of the correlation (positive or negative) determines the polarity of the remanent magnetization (normal or reverse).

Results from over thirty wells show a high percentage success rate. Primary areas of application are absolute age dating, well-to-well time correlation and determination of sedimentation rates. Tertiary deltas and passive margins (e.g. the Niger delta, the Gulf of Mexico, the Mahakam delta, etc.) are the most favorable settings, where the GHMT provides a good alternative to biostratigraphy with a possibility of dramatically improving the chronostratigraphic resolution, thus providing the data required for sequence stratigraphic modeling of reservoirs.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah