The Main Area Claymore Reservoir: A Review of Geology and Reservoir Management

Abstract

Summary The Main Area Claymore reservoir (MACR) is the major reservoir of the Claymore field, located 110 miles [177 km] northeast of Aberdeen in U.K. 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 increased from 47 to 57 MSTB/D [7472 to 9062 stock-tank m3/d] from mid-1984 to the end of 1986. The MACR is of Late Jurassic Age. Fine- to coarse-grained sandstones of the Sgiath and Piper formations are succeeded by the very-fine- to medium-grained sandstones of the Claymore sandstone member (CSM) of the Kimmeridge clay formation. The CSM constitutes the bulk of the MACR and is divided into two informal reservoir units: the low gamma ray sands (LGRS) and the high gamma ray sands (HGRS). 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 repeat formation tester (RFT) pressures, flowmeters, well logs, detailed core studies, and three-dimensional (3D) seismic. Increased current oil production and recoverable reserves are the consequences of this work. To improve oil recovery, a 10-slot subsea template for water injection was installed in Summer 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 program owes its success to the combined efforts of a multidisciplinary team, which resulted in the optimum placement of wells and the adoption of selective completion to optimize areal and vertical sweep efficiencies.