Buchan Development Project - Conversion Of A Drilling Rig Into Afloating Production Platform

Abstract

ABSTRACT This paper describes the conversion of a Pentagone drilling rig into a floating production facility as part of the development of the Buchan Field, North Sea. It examines the key areas of work involved, the problems encountered and solutions reached in order to provide facilities for a peak production rate of 72,000 BPSD of stabilised crude meeting all current UK statutory requirements. INTRODUCTION The Buchan Field is located in the UK sector of the North Sea approximately 160 km E.N.E. of Aberdeen with a water depth over the field between 112m to 118m. The field development is based on subsea completions tied into a subsea manifold, connected in turn by a flexible riser to a floating production platform. 9il export is by tanker from a single point mooring buoy. The rig selected for conversion was Pentagone 83 ?Drillmaster? built in France in 1973. The technical reasons for the selection of a Pentagone included the advantages of its stability, its load carrying capacity and apparent spaciousness. This marginal field with a relatively short field life, called for minimum time and capital investment. These concepts and the need to meet all statutory regulations were the guiding factors at all stages of the project. REMOVAL OF REDUNDANT EQUIPMENT The philosophy adopted for the removal of existing redundant equipment and materials provided essential space and weight reduction. As the production platform was not required to have drilling or well workover facilities, the strip out naturally centred on existing drilling equipment. The dry mud bulk silos situated to the rear of the derrick were cut and removed in sections giving a reasonably clear area at top, intermediate and lower decks for additional accommodation. The cement pump was left for well-kill duty. The mud pumps and associated equipment located on the forward lower deck were taken out through intermediate and top deck cut-outs. Together with the dismantling of five of the seven mud tanks and removal of top deck drill pipe racks this provided space at all three levels forward of the derrick for process and utility equipment. The principle of the new layout therefore was for non-hazardous and quiet accommodation areas to be placed to the rear of the derrick and process and utility equipment to be placed forward of the derrick. In conjunction with the key items listed above, a multitude of minor systems and equipment were removed or replaced for various reasons as detailed in later sections. The approximate total permanent weight removed from the existing drilling rig was 1,400 tonnes. PROCESS AND UTILITIES (a) General The basic process requirement for Buchan platform was for a simple effective system to separate the oil feedstock from the wells into the component crude oil, gas and water phases. Facilities are designed to produce a peak of 72,000 BPSD of stabilised crude from a feed crude of 33 - 36° API and a G.O.R. of 308 scf/bbl.