Paleomagnetic Orientation of Fractures and Bedding in Rotliegende and Zechstein Cores from the Southern Permian Basin, North Sea

Abstract

Fractures and bedding in Rotliegende sandstone and Zechstein dolomite cores of the southern Permian Basin can be accurately oriented using our standard paleomagnetic core-orientation technique. In recent project involving vertical, deviated, and horizontal wells, we have paleomagnetically oriented 1874 ft of Rotliegende and Zechstein cores from 113 intervals ranging in length from 8 in. 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 Rotliegende 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-0parallel, strike-perpendicular, and bedding-plane fractures. Paleomagnetic orientation of Rotliegende cores can be especially cost effect. Excellent core recovery and use of long core barrels in the Rotliegende means that [open quotes]continuous intervals[close quotes] (defined as the maximum lengths of core that can be reliably reconstructed by fitting adjacent core pieces) of more than 100 ft long can be achieved by following our recommended core-handling procedures. We statistically average the same number of paleomagnetic plugmore » samples regardless of the length of a [open quotes]continuous interval.[close quotes] The paleomagnetic signals in Rotliegende sandstone and Zechstein dolomite are sufficiently stable that fractures and bedding can be paleomagnetically oriented even in slabbed cores drilled decades ago.« less