Managing Borehole Instability in High-Angle Wells

Abstract For brownfield oil and gas development, a key value driver is getting more production from existing assets without necessarily increasing footprints due to additional activities. As a result, drilling and producing from existing locations/facilities is the preferred option, unless there are strong technical, economic or societal reasons for entirely new constructions. One of the consequences of this is that an increasing number of wells are being drilled targeting multiple subsurface horizons from limited surface locations – giving rise to more challenging wells with negative impacts on project schedules and costs. Recent numerous cases of high impacts from drilling problems like losses, hole instability, stuck pipe, well control, high-angle, reactive formations, etc. highlight the need for close examination of how the pitfalls associated with high-angle wells’ construction can be better managed. This paper focuses on one of the afore-mentioned challenges - borehole instability in high-angle wells – using Well Z where two wellbores (with different inclinations) drilled from the same top-hole section had markedly different drilling outcomes. Borehole instability incidents (including associated stuck pipe) have been estimated to cost more than $1 billion per annum and over 30% of Non-Productive Time (NPT). Therefore, successfully navigating through the challenges provides direct upsides such as shorter well durations and lower costs as well as indirect upsides like better project economics and sustainability score. Overcoming the highlighted challenges to deliver high-quality and cost-competitive wells requires an integrated suite of solutions ranging from data modelling, location-target selection, trajectory, drilling fluid design to real-time drilling systems monitoring, etc. at both the design and execution stages. In the case of Well Z, identifying and controlling the dynamic relationship between trajectory, borehole stress anisotropy, hole cleaning conveyor belt and drilling fluid design proved to be key for eventual recovery and successful drilling.