Abstract of paper presented at American Association of Petroleum Geologists International Conference and Exhibition, October 1993, in The Hague,
The Netherlands.    AAPG Bulletin, v. 77, p. 1672.

Paleomagnetic orientation of fractures and bedding in Rotliegend and Zechstein cores from the Southern Permian Basin, North Sea

D. R. Van Alstine and J. E. Butterworth, Applied Paleomagnetics, Inc.

Fractures and bedding in Rotliegend sandstone and Zechstein dolomite cores of the southern Permian Basin can be accurately oriented using our standard paleomagnetic core-orientation technique. In recent projects involving vertical, deviated, and horizontal wells, we have paleomagnetically oriented 1,874 ft of Rotliegend and Zechstein cores from 113 intervals ranging in length from 8 inches to 119 ft.

Accuracy of our paleomagnetic core-orientations can be demonstrated by (1) consistency in fracture patterns derived from vertical and horizontal cores near the same reservoir location; (2) consistency in Rotliegend paleowind directions derived from paleomagnetically-oriented cores with paleowind directions derived from mechanically-oriented cores from the southern Permian Basin; and (3) agreement between structural dip determined from paleomagnetically-oriented interdune bedding planes with structural dip determined from paleomagnetically-oriented strike-parallel, strike-perpendicular, and bedding-plane fractures.

Paleomagnetic orientation of Rotliegend cores can be especially cost-effective. Excellent core recovery and use of long core barrels in the Rotliegend means that "continuous intervals" exceeding 100 ft in length can be achieved by following our recommended core-handling procedures. We statistically average the same number of paleomagnetic plug samples regardless of the length of a "continuous interval," defined as the maximum length of core that can be reliably reconstructed by fitting adjacent core pieces.

The paleomagnetic signals in Rotliegend sandstone and Zechstein dolomite are sufficiently stable that fractures and bedding can be paleomagnetically oriented even in slabbed cores drilled decades ago.