This paper describes the first use of a novel drilling fluid based on potassium formate brine and weighted with manganese tetraoxide. Also included is the completion technique used to open hole complete an unconsolidated reservoir. The fluid was selected for maximum brine density, and to facilitate removal of the filtercake criteria for fluid and completion selection are presented together with laboratory work conducted to optimise the fluid and the completion for a specific application. Potential problems related to operations and working environment were identified through a risk analysis approach. Predicted solutions are compared to actual field experience. Key factors included minimisation of ECD, monitoring of soluble barium in the drilling fluid, rig-crews' exposure to manganese tetraoxide and barium, and procedures to combat lost circulation. The filtercake removal and its transportation through the pre-packed screen completion were comprehensively investigated. The perceived benefit of the formate brine system was the possibility to drill, complete and produce an unconsolidated, pressure sensitive reservoir with the same fluid. This was achieved with minimal on-site fluid treatment. The fluid was significantly more expensive than conventional alternatives. However, based on drilling fluid performance, rig-time and well productivity, one can conclude that the field test was successful and the use of the fluid was justified. Introduction The Gullfaks field is located in block 34/10 in the Norwegian sector of the North Sea, 150 km west of the Sognefjord. Gullfaks is the first field developed by a fully Norwegian licence group consisting of Statoil as the operator, Norsk Hydro and Saga Paetroleum. The fields current production is more than 90,000 Sm3/D from three reservoirs. The field has been developed with three concrete gravity-base platforms: Gullfaks A, B and C, each platform with two drilling shafts. Hence, while drilling in one of the shafts, wire-line, snubbing or coiled tubing operations may take place in the opposite shaft. To date, more than 90 wells have been drilled from the three platforms. Further 25 platform wells are planned. The oil is located within three major sandstone formations of Jurassic age; the Brent Group, the Cook formation and the Statfjord formation. The Brent Group is further subdivided into two groups; P. 647

This paper reviews the methodology and approach tdken to stimulate oil production from high rate gravel packed wells in a high permeability poorly consolidated sandstone reservoir, containing up to 35% clay ftnes. The three key elements involved were; a detailed laboratory study to identify and quantify the damage mechanism, selection of an optimum treatment &id system, and finally successful execution through accurate placement of the treatment fluids.

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TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThis paper describes the strategy, design and the drilling fluid and cement operations in the first two wells drilled with Coil Tubing on the Gullfaks field. The strategy and design is explained in great detail. Excellent hole cleaning was achieved in both wells.A serious problem of differential sticking was eliminated by a radical change in drilling fluid strategy and design. It was possible to successfully drill a 3 ¾" hole, log and run/cement a 2 7/8" liner at a maximum inclination of 122 o .A virtually solids free Potassium Formate Brine/Polymer drilling fluid with a density from 1.50 -1.56 g/cc was used. The flow properties of the drilling fluid is characterised by a very low fluid loss due to a high extensional viscosity, a low viscosity at all shear rates and a low degree of shear-thinning.