Drilling for hydrocarbons in extremely high reservoir pressures and temperatures is one of the most challenging combinations in drilling operations, especially related to drilling fluids. A combination of excellent teamwork and fluids technology proved to be the formula for successfully drilling in these extreme conditions for the TotalEnergies shale-gas play, onshore Abu-Dhabi, UAE.
The success achieved in drilling deep (6,200-m MD), long lateral displacement (2,000m) wells with an integrated global operator is a combination, dependent on frequent and transparent communication between the team members. Of equal importance is excellence in well planning, extensive laboratory testing, procurement and supply of resources, flawless field operations, and a diligent post-well review with the operator. More creditable is this success was achieved while dealing with operational challenges amplified by the current pandemic restrictions on personnel and materials movement.
The design of the environmentally and economically acceptable aqueous fluid met stringent fluid design criteria, wellbore and temperature stability for efficient drilling, and data acquisition performance goals. The high-density, high-temperature (HT) drilling fluid was designed to have a minimum amount of solids by using NaCl combined with a NaBr brine, weighted up with ultrafine grind barite. Viscosity and fluid loss were controlled with a unique additive, consisting of a dual-function, branched synthetic polymer.
The environmentally acceptable aqueous drilling fluid delivered a barite sag-free operation in these highly deviated wellbores. A balance between a low-equivalent circulating density and excellent hole cleaning was obtained, which was compatible with the reservoir formation and provided long-term stability to enable logging with no formation closure in the deep, high-temperature drilling environment. Additional achievements by the fluid included low HP/HT filtration, good lubricity for increased rate of penetration, and reusability on the subsequent wells; thus, improving the sustainability profile by reducing disposal. Successful coring and extended wireline logging of the reservoir section were an excellent test of this fluid.
The balance between a brine base, filtrate-loss, and viscosity-increase additive for fluid design, coupled with excellent field engineering, provide the long-term thermal stability required for a drilling fluid to be able to challenge drilling a reservoir reaching a depth beyond 6 km.