Drilling Fluid Design and Wellbore Strengthening for Enhanced Well Construction Performance: A Critical Review

Abstract

Wellbore instability and lost circulation remain significant drilling challenges in formations characterized by narrow mud weight windows (MWWs), weak formation strength, and complex in-situ stress conditions. These challenges are particularly prevalent in depleted reservoirs, unconsolidated sands, and deepwater environments, where small pressure fluctuations can trigger formation breakdown, severe circulation losses leading to non-productive time (NPT), and increased well construction costs. Conventional mitigation strategies that rely on mud weight escalation often aggravate these problems by exceeding the fracture resistance of the near-wellbore region, thereby increasing the likelihood of induced losses and wellbore instability. Wellbore strengthening (WBS) has emerged as a viable alternative approach that focuses on enhancing near-wellbore fracture resistance rather than increasing drilling fluid density. Among the available WBS techniques, drilling fluid-based methods have gained considerable industry attention because of their operational simplicity, cost effectiveness, and compatibility with conventional drilling practices. This paper presents a critical review of published experimental studies on drilling fluid-based wellbore strengthening in narrow-MWW environments. The review examines the influence of key drilling fluid design parameters, including particle size distribution (PSD), rheological properties, and fluid loss characteristics, on the effectiveness of major strengthening mechanisms such as fracture sealing, stress caging, tip leakage/drill-and-stress fluid (DSF), and formation plastering. The reviewed studies demonstrate that optimized drilling fluid systems can significantly improve fracture initiation pressure, enhance near-wellbore stress conditions, expand the effective drilling window, and reduce the risk of lost circulation. Comparative analysis further highlights the strong relationship between fluid composition, strengthening material selection, and overall wellbore strengthening performance. Selected examples relevant to Niger Delta-type formations are discussed to illustrate the practical application of these concepts in narrow-margin drilling environments. The findings underscore the importance of integrating drilling fluid engineering with geomechanical understanding to achieve reliable and sustainable WBS outcomes. This review provides practical guidance for drilling engineers seeking to minimize lost circulation, improve wellbore stability, and enhance well construction performance without excessive reliance on mud weight escalation. The paper also identifies key considerations for future development of drilling fluid systems designed for challenging narrow-MWW formations.