Enhancing the Performance of Oil-Based Drilling Fluids with a Novel Modified Clay
Authors: Mahmoud A. , Gajbhiye R. , Elkatatny S. 
Published: February 2025

Abstract
Oil-based drilling fluids (OBDFs) are essential for successful well drilling operations in challenging environments, offering superior lubricity, wellbore stability, and inhibition compared to water-based alternatives. However, optimizing their performance, particularly under high-pressure high-temperature (HPHT) conditions, necessitates specialized additives to enhance rheology, filtration control, and emulsion stability. This research aims to evaluate the impact of Claytone-ER on the rheological properties of OBDFs and its potential to enhance drilling fluid performance in challenging HPHT environments. Its performance is compared to a conventional OC (MC-TONE) to assess the potential benefits of this novel additive.
To thoroughly investigate the impact of Claytone-ER on OBDF performance, multiple laboratory tests were conducted. These tests assessed key mud properties, including density, electrical stability, and resistance to settling (sagging). The fluid's flow behavior (rheology) and ability to prevent fluid loss (filtration) were also measured under simulated downhole conditions (275°F and 500 psi differential pressure). In addition to performance testing, the composition and structure of the organoclays were analyzed using various techniques. X-ray diffraction and fluorescence (XRD and XRF) provided information about the mineral composition, while scanning electron microscopy (SEM) and particle size distribution (PSD) analysis revealed details about the shape and size of the clay particles. Sagging behavior, a critical aspect for wellbore stability, was evaluated under both static (275°F) and dynamic (150°F) conditions. This comprehensive evaluation aimed to understand how Claytone-ER influences critical drilling fluid properties, ultimately contributing to the development of a stable, high-performance OBDF suitable for demanding HPHT environments.
The results demonstrate that Claytone-ER enhanced emulsion stability by 3% without impacting mud density. Both static and dynamic sag were effectively mitigated, indicating its potential for preventing barite sag in HPHT environments. Furthermore, the incorporation of Claytone-ER significantly enhanced the rheological behavior of the drilling fluid. Specifically, a marked improvement was observed in key parameters, with plastic viscosity (PV) increasing by 26%, yield point (YP) exhibiting a near doubling (98% increase), and the YP/PV ratio demonstrating a substantial 56% rise compared to the reference OC. These enhancements suggest improved carrying capacity and hole cleaning potential. Additionally, Claytone-ER enhanced gel strength (GS) and improved filtration properties, resulting in an 8% decrease in filtrate volume and a 6% reduction in filter cake thickness.
This study is the first to investigate Claytone-ER as a novel rheological additive for OBDFs, specifically in demanding HPHT environments. The findings highlight Claytone-ER's ability to simultaneously enhance critical mud properties, including emulsion stability, sag mitigation, rheological properties, and filtration control. These attributes offer the potential to optimize drilling operations by minimizing downhole complications, reducing non-productive time, and improving wellbore stability.