Abstract

Piper was discovered in 1972 by the 15/17-1A well, located on a 4-way dip closed structure on the northern flank of the Witch Ground Graben. Appraisal drilling through 1973 showed the field to comprise four gently folded, tilted fault blocks with productive reservoirs in Late Jurassic paralic to shallow marine sandstones (Sgiath and Piper formations). Production commenced in 1976 and until the Piper Alpha disaster of 1988, the field had produced 834X10 6 bbl oil out of the then estimated recoverable reserves of 952X10 6 bbl. Redevelopment started by pre-drilling 1 injection and 7 production wells based on 1990 reprocessed 3D seismic, prior to the installation of the Piper Bravo platform in 1993. A study of permeability repartition and sweep efficiency, combining existing and new well data from cores, logs, pressures and fluid distribution, aided the optimization of well locations. In addition, a new 3D seismic survey was acquired in 1992-3. Advantageous fluid redistribution and natural aquifer repressurization of the reservoirs occurred during the 4 1/2 years of production shutdown. By mid-1996, 12 production and 4 injection wells were in operation. Piper Bravo wells redeveloped three of the four fault panels, using half of the number of wells in operation at the time of the Piper Alpha disaster. The production rate has been significantly increased over the projected 1988 decline and a much lower water cut achieved. The ultimate recovery for the Piper field is now estimated at 1014X10 6 bbl oil (-3.4%), an increase of 62X10 6 bbl over the pre-redevelopment figure.

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