The Main Area Claymore Reservoir, a Review of Geology and Reservoir Management

Abstract

ABSTRACT The Main Area Claymore Reservoir (MACR) is the major reservoir of the Claymore Field, located 110 miles northeast of Aberdeen in UK Block 14/19, offshore North Sea. An integrated team effort by geologists, geophysicists and engineers has led to an increase in recoverable oil for the MACR. Concurrently, the MACR production has increased from 47 to 57 MSTBPD from mid 1984 to the end of 1986. The MACR is of Late Jurassic age. Fine-coarse grained sandstones of the Sgiath and Piper Formation are succeeded by the very fine – medium grained sandstones of the Claymore Sandstone Member (CSM) of the Kimmeridge Clay Formation. The CSM comprises the bulk of the MACR and is divided into two informal reservoir units: the Low Gamma Ray Sands and the High Gamma Ray Sands. The principal early field problems were: lack of sufficient pressure support; uneven water advancement in both the horizontal and vertical directions; and a large pressure gradient across the reservoir. Thus, more offtake and selective injection points were required to improve oil recovery. Growth of geological and engineering knowledge of the MACR has resulted from infill drilling and the integration of RFT pressures, flow meters, well logs, detailed core studies and 3D seismic. Increased current oil production and recoverable reserves are the consequence of this work. To improve oil recovery, a ten slot subsea template for water injection was installed in the summer of 1985. Three subsea water injectors have been drilled from this template and five platform wells redrilled as producers, to downdip areas of the MACR. The recent drilling programme owes its success to the combined efforts of a multi-disciplinary team, which resulted in the optimum placement of wells and the adoption of selective completion to optimise areal and vertical sweep efficiencies.