Water-Based Drilling Fluid Helps Control Extreme Conditions in Gas Shale Play
Authors: Carpenter Chris 
Published: December 2022

_
This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper URTeC 208307, “A Water-Based Drilling Fluid for Controlling Deep-Reservoir Extreme Conditions in an Abu Dhabi Gas Shale Play,” by Gabe Manescu, SPE, Schlumberger; Balazs Veer, SPE, TotalEnergies; and Panamarathupalayam Balakrishnan, SPE, Schlumberger, et al. The paper has not been peer reviewed.

_
A combination of teamwork and fluids technology proved to be the formula for successfully drilling in high-pressure/high-temperature (HP/HT) conditions for an onshore UAE shale gas play. The success achieved in drilling deep [6200-m measured depth (MD)], long-lateral-displacement (2,000-m) wells with an integrated global operator is a combination dependent on frequent, transparent communication between team members. The environmentally acceptable aqueous drilling fluid delivered a barite sag-free operation in these highly deviated wellbores.

Introduction
The drilling of unconventional HP/HT wells in the Diyab field can experience difficulty in reaching target depth. One significant challenge is the design of a drilling fluid to manage reservoir pressures and temperatures. The reservoir temperature may reach 165.5°C, requiring mud weights (MW) greater than 20 lbm/gal. Tailoring the drilling-fluid formulation to balance economics and environmental regulations while overcoming HP/HT conditions is critical. In the Diyab drilling campaign, special emphasis was placed on designing the drilling fluid and then on its use in 8½-in. reservoir sections.

Background
The Upper Jurassic (Oxfordian to Middle Kimmeridgian) Diyab formation, also known as the Dukhan formation, has served as the source rock for several major oil and gas fields in the Middle East. The Diyab formation is unique because of its lower porosities, high carbonate mineralogy, and pressure gradient. Despite the lower porosity, the high-carbonate content defines an extremely brittle target conducive to hydraulic fracture stimulation. Several organic-rich intervals exist throughout the Diyab formation and are separated by less-organic tight limestones, which create different flow units. From a developmental perspective, this condition has the potential to create a high-impact stacked play. The extent of the prospective unconventional Diyab formation within the UAE is limited to the onshore north-central UAE, where most of this area is within Block 1, operated by TotalEnergies. The depth of the prospective basal Diyab interval across Block 1 ranges between 3758 and 4115 m.
Three unconventional offset wells (DE-02, DE-03, and DE-04) were drilled by ADNOC within Block 1 to test the productivity of the three submembers of the greater Diyab interval (the Jubaila, Hanifa, and Tuwaiq Mountain formations). After determining that the Hanifa formation had the most-promising productivity, the first TotalEnergies appraisal horizontal well, DE-05, was drilled. After drilling this well, the DE-06 well was the second horizontal appraisal well to be drilled. Additionally, two more deep wells, DE-09 and DE-10, were successfully drilled and evaluated.