Plastering Effect of Casing Drilling; A Qualitative Analysis of Pipe Size Contribution

Abstract

Abstract Casing Drilling is a process in which the well is drilled and cased simultaneously. The original purpose of developing this technology was to eliminate the Non-Productive Time (NPT) associated with tripping out drill pipe and running casing. However, during the early implementation of the technology other benefits were observed while drilling with the casing. In this study the authors explain how these benefits can be related to the larger diameter of the casing compared to drill pipe. The Plastering Effect is an inherent and unique feature of Casing Drilling that strengthens the wellbore, prevents lost circulation, and mitigates formation damage. Plastering Effect augments the pressure containment of the wellbore by smearing the drilling cuttings and available PSD (Particle Size Distribution) into the formation face, hence sealing the pore spaces. This continuous process creates a low porosity, low permeability filter cake on the wellbore wall reducing or preventing losses to the formation and effectively widening the operating mud weight window. In Casing Drilling operations the casing is used to drill the well so the (pipe size/hole size) ratio will be larger than the ratio when conventional drilling pipe is being used. This feature is a significant contributor creating the Plastering Effect. Casing dynamics is qualitatively compared to drill pipe. Pipe ontact angle and area, side force and momentum, and grinding effect, are analyzed to help understand how the benefits of the Plastering Effect are created and answer the question of why it happens in Casing Drilling and not in conventional drilling. Casing Drilling has been used successfully in numerous difficult wells to drill through troublesome well sections which would not have been possible to drill with conventional drill pipe techniques. The Plastering Effect of Casing Drilling has been recognized as an enabling tool to overcome difficult drilling challenges. Therefore, understanding its mechanism is crucial to its successful application.