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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.
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.
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.
Casing Drilling is a process in which a well is drilled and cased simultaneously. This innovative technology has been successfully practiced for the past decade. The original purpose of developing Casing Drilling was to eliminate Non Productive Time (NPT) associated with tripping drill pipe and running casing. However, during early implementation of the technology, other benefits were observed while drilling with large diameter casing. This paper reviews four of these advantages which are lost circulation reduction, wellbore strengthening, improved wellbore stability, and drilling-induced formation damage mitigation.Casing Drilling reduces mud lost to the formation in two ways; the Plastering Effect seals off the wellbore and prevents fluid transfer between the borehole and the formation; secondly, in the worst cases where the losses can't be cured, drilling will be continued with minimized losses until the casing reaches the total depth. Reduced mud loss to the reservoir section can be directly correlated to reduced skin due to drilling induced formation damage. This leads to improved productivity of the wells drilled with casing in the reservoir section.As the Plastering creates an impermeable mud cake on the wellbore wall the pressure containment of the borehole is augmented. This process increases the fracture gradient of the formation in near wellbore area which results in a wider operational mud weight window (Wellbore Strengthening). Wells with stability problems are among the best candidates for Casing Drilling and could be drilled trouble free. The wellbore stability benefits of Casing Drilling are due to no tripping, less mud formation exposure, gauged well, superior hydraulics and borehole cleaning, etc.
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