Low-solids, brine-based reservoir drilling fluids (RDFs) are widely accepted as beneficial to optimizing compatibility with the completion design while minimizing fluid-related formation damage. Traditionally, the maximum density attainable with a lowsolids fluid has been limited because of either the prohibitively high cost of the required base brine or the poor performance of viscosifying biopolymers in a dense, divalent cationic environment.An RDF has been developed that exhibits unusually high quality rheological behavior in high-density calcium-and zinc-based brines without the aid of a biopolymer. The new fluid shows a unique shear-thinning rheological profile that features a relatively low high-shear-rate viscosity along with a relatively high lowshear-rate viscosity (LSRV). This behavior is highly unusual in high-density, brine-based RDFs. A result of this behavior is that effective hole cleaning is provided without generating excessive high-shear-rate viscosities that lead to excessive equivalent circulating densities (ECDs).The first field trial of this fluid was on the reservoir section of Well 34/10 I-1-AH in the Gulfaks Satellites Development in the Norwegian sector of the North Sea. Fluid properties during pretesting, mixing, drilling, and completion of this section are detailed in this paper.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThis paper presents a case history of the completion procedures applied to a four-well gas reservoir development in the Norwegian sector of the North Sea where open-hole gravel packing was utilized as the sandface completion technique.The chosen technique to gravel pack the wells was based upon Alternate Path Technology, which incorporates shunt tubes with nozzles on the outside of the gravel pack screen. These shunts create an alternative flow path, allowing slurry to bypass premature bridging and fill any voids beyond the bridge. The use of shunt tubes gives the opportunity of achieving a complete gravel pack without the requirement of a filtercake-sealed wellbore. This introduces the possibility for the filter cake to be removed during the packing operation. As a result, a low-solids drilling fluid that deposits a chemically degradable filter cake can be utilized.The reservoir pressure in this field required relatively highdensity, reservoir drilling and gravel pack fluids (1.65 SG / 13.75 lb/gal). This paper describes the design and development work involved in formulating a mutually compatible, calcium bromide-based reservoir drilling fluid and a Viscoelastic Surfactant (VES) based gravel pack fluid and the subsequent successful application in a subsea field development.

Low-solids, brine-based reservoir drilling fluids are widely accepted as being beneficial with respect to minimising fluid-related formation damage and optimising compatibility with the completion design. Traditionally, the maximum density attainable with a low solids fluid has been limited - either due to the prohibitively high cost of the base brine required, or the poor performance of viscosifying biopolymers in a divalent cation environment. A reservoir drilling fluid has been developed that exhibits unusually high quality rheological behaviour in high-density calcium- and zinc-based brines, without the aid of a biopolymer. The first field trial of this fluid was on the reservoir section of well 34/10 I-1-AH, in the Gulfaks Satellites Development in the Norwegian Sector of the North Sea. Fluid properties during the pre-testing, mixing, drilling and completion of this section are detailed in this paper. Introduction The use of specialised water based drilling fluids for drilling reservoir sections has become common practice over the last decade.1–7 Fluids based on a clear brine to achieve required density and a small concentration of chemically removable solids as a bridging agent8–10 (calcium carbonate, sodium chloride) have gained wide acceptance in the industry. The maximum density achievable with this type of drilling fluid has been limited, either by the chemistry or the economics of potential base brines.1–7 Biopolymers, such as xanthan gum,11,12 scleroglucan13 and welan gum are usually added to this type of reservoir drilling fluid to provide the viscosity and gel structure necessary to suspend solids (bridging agent, drill cuttings, etc). The polymers are selected for the rheological profile imparted to the drilling fluid - high low-shear rate viscosity (LSRV), for solids suspension in static fluids and low high-shear rate viscosity, to reduce required pump pressure.14 Full polymer hydration is feasible in all types of monovalent brine (potassium, sodium and caesium based). However, the performance of this type of polymer is compromised in the presence of a high concentration of divalent ions.1–3 Using a variety of specialised procedures (high shear, elevated temperature, pre-dispersion in fresh water), these polymers can be made to viscosify divalent brines up to a point. However, once the brine reaches a density where the divalent ion content is too high, or the volume of accessible "free" water is too low, no amount of treatment will generate a rheological profile suitable for high performance reservoir drilling. As a result, the maximum density achievable with low solids reservoir drilling fluids has been limited to the maximum density achievable with a cost-effective monovalent base brine, or a sufficiently dilute divalent brine. Research in this area has focussed on identifying viscosifying polymers that will hydrate in high hardness environments, or alternative methods of viscosification, such as hydroxyethyl cellulose or silica flour.3 Success with these novel types of fluid has been limited - not only with respect to drilling performance, but potentially compromising formation damage or filtercake clean-up under field conditions. A novel reservoir drilling fluid system has been developed that uses a combination of a modified starch fluid-loss control agent and a high surface-area grade of magnesium oxide for pH control. The combination of these two components in high salinity divalent brines, (calcium chloride, calcium bromide, magnesium chloride and zinc bromide), produces a suitable rheological profile for a drilling fluid.1,2 Furthermore, the chemical nature of the components enhances the efficacy of chemical treatments to break down fluid viscosity or remove residual filter cake.1