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This paper describes how high-density cesium/potassium (Cs/K) formate fluids were successfully utilised from reservoir drilling to upper completion installation in five productive Martin Linge high-rate gas wells. Four wells were completed with openhole gravel pack and one with standalone sand screens.The gravel packing operation marks what is considered to be the highest density carrier fluid openhole gravel pack successfully completed worldwide, with SG 2.06. A complex operation under near-high-pressure/high-temperature (HP/HT) conditions, including managed pressure drilling (MPD), overbalanced screen running and openhole gravel packing, was simplified by utilising the same fluid throughout the operation.Cs/K formate reservoir drilling fluid and screen-running fluid were designed with biopolymeric additives and minimal calcium carbonate bridging particles. Clear Cs/K formate brine (i.e., without biopolymeric additives and particles) was chosen as gravel pack carrier fluid. The use of Cs/K formate fluids for all stages of the operation reduced the complexity of transitioning between the operational stages. In addition, the reservoir was only exposed to one filtrate without application of damaging weighting solids.The drilling fluid contributed to successful MPD and delivered wells with very good hole quality in the reservoir, which consisted of interbedded sandstone, coal stringers and shale. The shale stabilising properties of concentrated formate brine–based fluids provided acceptable conditions for extended openhole time and allowed additional logging runs, including pore pressure measurements, under near-HP/HT conditions before running the screens. One bottom-up cleanout was conducted before the screen-running fluid was circulated in and the screens installed. The spurt and seepage losses were low throughout the drilling and screen running phases. No breaker treatment was required in any of the wells. All wells have proven to have good initial productivity and high well productive efficiency as expected.The record-breaking openhole gravel pack operations performed with the high fluid densities required in Equinor's Martin Linge field have set a new standard for completing in challenging high-pressure environments.

This paper summarizes the experiences of Total E&P's first use ever of a low-solids cesium formate reservoir drill-in and screen-running fluid. The unique 2.07 SG formate brine-based mud system was used by Total E&P Norge as reservoir drill-in fluid (RDF) and screen running fluid in a Brent high permeability, high pressure gas well No. 4, in the Martin Linge field on the Norwegian Continental shelf. The fourth gas well was the first Martin Linge well completed openhole with 250-micron stand-alone sand screens (SAS). The previous Martin Linge gas wells were drilled and completed with 230-micron expandable sand screens (ESS), using non aqueous based mud (NABM).The low-solids cesium formate fluid was chosen for its known ability to produce easily through sand screens. The final fluid formulation, which consisted of concentrated cesium/potassium formate brine, included xanthan gum, high-temperature modified starch, and calcium carbonate bridging material, successfully underwent a series of qualification testing, including fluid loss control, rheology, formation damage, and production screen testing (PST).The main benefits seen with the formate fluid system compared with the solids laden NABM fluid systems when drilling the 8½-in. reservoir sections were significantly higher rate of penetration (ROP) with lower weight on bit (WOB), better drilling dynamics, significantly lower (0.016 SG) equivalent circulating density (ECD), 35% lower stand pipe pressure (SPP), and 5°C lower bottom hole circulating temperature (BHCT).The drilling fluid properties were easily maintained within specifications. Compared with the NABM, the main benefits were improved rheology, lower solids content, and much thinner, non-elastic filter cake.Improved wellbore stability was experienced for the well No. 4 compared with previous reservoir sections, and there was no indication of poor hole cleaning during drilling, tripping, or during lower completion operations, and no stuck-pipe incidents were experienced. In the previous reservoir sections, a stuck-pipe incident had been experienced in a coal section, requiring a sidetrack to be drilled.The only performance issue with the formate fluid was its higher mechanical friction, which caused a 25% increase in drilling torque compared with the previous sections drilled with NABM.A short cleanup of the well was conducted before the well was suspended. Despite the shorter cleanup time of the well No. 4 compared with the previous wells, the well's stipulated productivity index (PI) was twice as high. The pressure build-up response indicated full connection to the reservoir and no indication of partial plugging, which had been the problem during the cleanup attempts of the previous gas wells.Disregarding the significant increase in fluid cost compared to the previous reservoir sections that were drilled and completed with NABM, well No. 4 was a technical and commercial success based upon drilling and tripping operations, completion operations, and cleanup results.