The objective of this work is to investigate the influence of cuttings size in Casing Drilling to plug pores for fluid loss control, and thereby reducing formation damage. Historically, the emphasis of drilling operations has been to drill wells cheaply and quickly without much consideration for the resulting impact on well productivity. Formation damage occurs frequently and rapidly during drilling operations with potentially severe consequences. The Plastering Effect of Casing Drilling reduces solids and filtrate invasion, resulting in less skin damage and improved productivity. It also reduces formation damage due to cement filtrate by creating a gauged wellbore and proper casing/wellbore standoff.
The Casing Drilling process grinds drill cuttings as they travel up the annulus and creates a larger particle size distribution (PSD) profile than conventional drilling operations. These finer cuttings are subsequently smeared into the wellbore face by the mechanical contact of the large diameter casing with the borehole wall. The result is a very high quality, tight, thin, almost impermeable mud cake that isolates the formation from the wellbore. Evidence shows that cement binds very well to this type of mud cake.
The PSD analysis determined that the smaller size and wide range of Casing Drilling cuttings make it possible for these particles to readily adhere to the wellbore; this helps seal the pore spaces of the formation and prevent further solids and filtrate invasion. Pore throats can most effectively be plugged when the cuttings are in the proper micron size range as any possible gap between the mud and cuttings PSD can be covered by adding minimal amounts of properly sized lost circulation materials.
Casing Drilling has proven to be a unique approach in mitigating formation damage due to the drilling process. One case study confirms that reservoir sections drilled with casing show enhanced productivity as much as twice the wells drilled conventionally. The Plastering Effect, as an inherent benefit of Casing Drilling, keeps the producing formation as intact as possible and reduces formation damage.