THE PALINGENESY OF THE PIPER OIL-FIELD, UK NORTH-SEA

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 gen tly folded, tilted fault blocks with productive reservoirs in Late Jur assic paralic to shallow marine sandstones (Sgiath and Piper formation s). Production commenced in 1976 and until the Piper Alpha disaster of 1988, the field had produced 834 x 10(6) bbl oil out of the then esti mated recoverable reserves of 952 x 10(6) bbl. Redevelopment started b y pre-drilling 1 injection and 7 production wells based on 1990 reproc essed 3D seismic, prior to the installation of the Piper Brave platfor m in 1993. A study of permeability repartition and sweep efficiency, c ombining existing and new well data from cores, logs, pressures and fl uid distribution, aided the optimization of well locations. In additio n, 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, 1 2 production and 4 injection wells were in operation. Piper Brave well s 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 pr oduction rate has been significantly increased over the projected 1988 decline and a much lower water cut achieved. The ultimate recovery fo r the Piper field is now estimated at 1014 x 10(6) bbl oil (73.4%), an increase of 62 x 10(6) bbl over the pre-redevelopment figure.