Reservoir Drilling and Openhole Gravel Packing with High-Density Cesium Formate Fluids in a High-Pressure, Marginal Mud Window Environment at Martin Linge

High-density cesium/potassium (Cs/K) formate fluids were successfully utilized from reservoir drilling to upper completion installation in five productive Martin Linge high-rate gas wells. Four wells were completed with openhole gravel pack (OHGP) and one with standalone sand screens. The gravel packing operation marks what is considered to be the highest density carrier fluid OHGP successfully completed worldwide, with a specific gravity (SG) of 2.06. A complex operation under pressure and temperature conditions (745–780 bar and 135–140°C) that almost qualify as high pressure/high temperature (HP/HT), including managed pressure drilling (MPD), overbalanced screen running, and openhole gravel packing, was simplified by using the same base brine throughout the operation. Cs/K formate reservoir drilling fluid (RDF) and screen-running fluid were designed with biopolymeric additives and minimal calcium carbonate bridging particles. Clear Cs/K formate brine was chosen as gravel pack (GP) 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-stabilizing 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 proved to have good initial productivity and high well productivity index. The successful OHGP operations performed with the high fluid densities required in Equinor’s Martin Linge field have set a new standard for well completions in challenging high-pressure environments.