A Water-Base Drilling Fluid for Controlling Deep-Reservoir Extreme Conditions in an Abu Dhabi Gas Shale Play

Abstract

Drilling for hydrocarbons in the extreme reservoir pressure and temperature remains one of the most challenging operation, especially related to drilling fluids. A combination of excellent teamwork and fluids technology proved to be the recipe for successfully drilling in these extreme conditions for TotalEnergies shale-gas play, onshore Abu-Dhabi, United Arab Emirates. The success on drilling deep (6,200mMD), long lateral displacement (2,000m) wells with an integrated global operator is a balance, dependent on frequent and transparent communication between the team members, of excellence in well planning, extensive laboratory testing, procurement and supply of resources, flawless field execution, and a diligent post-well review with the operator. More commendable is this success was achieved while dealing with operational challenges amplified by the 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 drilling and data acquisition performance goals. The high-density HT drilling fluid is designed to have the minimum amount of solids by using a Sodium Chloride combined with a Sodium Bromide brine, weighted up with ultra-fine grind barite. Viscosity and fluid-loss are controlled with a unique additive, a dual-function, branched synthetic polymer. The environmentally acceptable aqueous drilling fluid delivered a barite sag-free operation in these highly deviated wellbores, delivering a balance between a low-equivalent circulating density and excellent hole cleaning, compatibility with the reservoir formation, and long-term stability to enable logging with no formation closure in a deep, high temperature drilling environment. Additional achievements of the fluid were the low HPHT 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 wire logging the reservoir section was an excellent test for this fluid. The balance between a brine base, filtrate-loss, and viscosity-increase additive for fluid design, coupled with excellent field engineering provides the long-term thermal stability of a drilling fluid able to tackle drilling a reservoir reaching a depth past 6 kilometers.