Customized High-Performance Water-Based Mud Delivers Superior Results while Driving Down Cost by Successfully Drilling through the Most Troublesome Shale Formations in the United Arab Emirates
Authors: Nasrallah Mena , Nour Mahmoud , Savari Sharath 
Published: February 2022

In the UAE, drilling intermediate sections that contain highly dispersive clays with water-based muds almost always leads to mechanical instabilities in the form of pack-offs and tight spots due to highly laminated shale formations containing a high percentage of kaolinite. Operators have struggled with designing proper fluid systems to successfully drill these sections and have resorted to invert emulsion fluids (IEF) in certain fields, but that is not always an option. This paper presents the development and application of a high-performance water-based mud (HPWBM) that provided the required wellbore stability to drill these challenging shale sections through sealing natural and induced microfractures, and thereby reduced operational cost.

Based on extensive testing, technical experts customized the HPWBM system to drill the troublesome sections both in vertical and inclined wells. Multiple stages of testing were completed to understand the shale, including X-ray diffraction analysis, which revealed that mixed layers were present with a high-kaolinite content. The cation exchange capacity (CEC) was low, indicating that the clays were not reactive. The optimized HPWBM formulation included two powerful components for shale stabilization and a third key component to minimize fluid loss into the formation. The customized formulation underwent a complete suite of shale testing, including capillary suction testing, linear swell meter, shale erosion, shale accretion, as well as lubricity testing and stress testing.

Proper planning and execution, using best-available drilling practices, enabled the drilling of these challenging wells without encountering any significant issues that could impact rig time and increase costs. The selection of a customized HPWBM to provide shale stability performance and low-fluid invasion was fundamental to achieving the required fluid properties. Using this HPWBM system in these formations helped the operators achieve an average rate of penetration (ROP) of 43.7 fph – which was 62% higher than in the offset well and reach 40° inclination on different wells. There was also a reduction in the total volume used to drill the sections due to lower dilution rates compared to conventional systems.

As a result of the lower fluid consumption, the total fluid costs were significantly reduced compared to offset wells. The casing strings were run to planned depth with no recorded issues on the first two wells, and savings of 11 days were achieved when compared to the offset wells in the same field.

The customized HPWBM system with superior performance was able to achieve high levels of shale stability and inhibition without which this milestone would not have been possible. It made the possibility to drill these formations with an environmentally friendly, lower cost alternative to IEF a reality, which maximized the clients’ returns by reducing the overall cost of ownership.