The objective of this work is to experimentally understand the plastering effect during Casing while Drilling (CwD). CwD can be considered as the process of drilling the well wherein the drill pipes are replaced by the casing and the well is cased as it is being drilled. Literatures have exclusively shown that CwD is practiced with a notion to reduce the Non -Productive Time (NPT) and to tackle problematic zones of fluid loss or unstable formation. One plausible reason that has been claimed is the plastering effect during CwD, in which the drill cuttings are crushed to finer particles between the casing and the wellbore during contact due to limited annular clearance. These finer particles are smeared into the formation by the mechanical contact of casing to the wellbore. Plastering effect leads to formation of a thin layer of mud cake that is strong enough to prevent fluid loss and had been proven in the field trials.Actual forces acting on the drill cutting in the limited annular space can be majorly divided as centrifugal force and the drag force due to circulation of drilling fluid. Apart from the smearing effect, the acceleration due to the centrifugal force may also be responsible for the cuttings to be adhered to the wellbore. Here, in this study, authors consider the CwD process to be analogous to a large vertical centrifuge and experimentally understand the process.

In order to address various wellbore challenges, there has been improvements in methods of drilling and other wellbore activities since a long time. While the industry focuses on improvements of different methods, reducing Non Productive Time (NPT) has also become of great interest. Amongst many, one method to address the problem of drilling through fluid loss zone and to minimize casing running time and other NPT is Casing While Drilling (CwD). It is a method of drilling in which the conventional drill pipes are replces by the casing itself. During implementation of this method, there have been several observations of enhanced wellbore strength, pressure containment, better fluid loss control, etc. Plastering effect is considered to be the factor behind this, where the fine drill cuttings physically collide with the wellbore to form a stable mud cake layer that provides additional wellbore strength. Though plethora of work has been carried out, exact phenomenon of plastering effect is uncertain. Particle Size Distribution (PSD) of the drill cuttings along the wellbore is noted to play a crucial role is proper plastering effect. Authors of this paper, attempt to quantify the PSD in CwD that takes place during plastering effect. The work is expected to help in understanding the crushing effect and the background of fluid loss prevention.