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.
Wells in challenging environments are known for their high cost with targets not reached, and often abandoned. HPHT wells fall in this category and in Lower Mediterranean Sea this was not an exception. After a few wells drilled in an offshore HPHT area, with advanced techniques and alternatives being tried on well after well, Eni through its foreign affiliate decided to use a combination of Eni's continuous circulation (CC) valves, (Eni Circulation Device - E-CD) and the Micro-Flux Control (MFC) method. Eni calls the combination of CC with the precise measurement and control of the flow and pressure from the well, within a closed loop through a rotating control device (RCD), as: Eni-Near-Balanced Drilling (ENBD). With this new drilling method, a well in the HPHT area reached all the targets for the first time. Wells in this area face the usual kick-loss scenario, with significant non productive time (NPT) and adding hundreds of days to drill a well. The goal for using the E-CD was to avoid pressure and temperature fluctuation while drilling, by maintaining the annulus as stable as possible, and the MFC would provide a clear picture and manage the bottomhole pressure (BHP) within the downhole pressure limits, pore and fracture. Previous attempts to improve drilling were made using just RCD, then a continuous circulation system and later on the E-CD valves were used together with the RCD on other wells, but, even though improvements were seen, those were not enough to ensure reaching the final targets. It was only when the MFC method was added that success was achieved. The paper describes the operations and results obtained by the ENBD system and its benefits in terms of NPT and kick quantity and size reduction. Comparison with the previous wells where the targets could not be reached clearly shows the significant advantage of using the system, compared to conventional drilling. Reduction in risk and increased control over the entire drilling process, in an environment with extremely narrow margins, were paramount to a successful outcome. Introduction Exploratory wells are in principle classified as challenging ones due to the inherent uncertainty relative to the downhole pressure limits, pore and fracture pressures, as well as formation surprises that are not clearly mapped from seismic. In addition the exploration frontier is moving increasingly towards more difficult environments, and it is no surprise that many exploratory wells have been abandoned before reaching the planned TD, therefore failing to meet its commercial or technical objectives of collecting valuable data about possible reservoirs and hydrocarbon reserves. Despite many improvements to drilling systems, such as the top drive, steerable directional systems, mud motors, Pressure and Logging While Drilling (PWD and LWD), Continuous Circulation Devices (CC), Rotating Control Devices (RCD), it has been the arrival of a closed-loop Managed Pressure Drilling (MPD) method that has provided a significant step change in drilling performance. For the first time the pore and fracture pressures can be determined very accurately and safely while drilling, in real-time, and as a consequence the mud weight can be properly adjusted and managed, avoiding loss circulations, stuck pipe, and low ROP. The industry loses an enormous amount of time trying to solve these problems, which very often leads to misunderstanding that the well's technical limit has been reached and abandoned unnecessarily.
fax 01-972-952-9435. AbstractUnderbalanced drilling (UBD) is giving brownfields a new lease on life-while UBD technologies in development hold the promise of drilling the "un-drillable well" and reducing cost.Much of the industry's mindset focuses on traditional drilling and stimulation technologies to exploit brownfields, but we suggest that in many cases the greatest potential for these reservoirs lies in UBD techniques. Emerging methodologies, like managed pressure drilling (MPD), are also moving rapidly into the driller's toolbox to allow him to "walk the line" between extremes in pressure regimes. Or perhaps technologies that reduce the cost of UB drilling and enabling underbalanced completions will be attractive enough to propel the technology across the 'chasm'. This article discusses real benefits of UBD in mature fields and presents an overview of its new technologies in development.Ja n-94 J a n-9 5 J an -9 6 J an -97 J an-98 J an-99 Ja n-00 J a n-0 1 J an -0 2 J an -03 J an-04
Pressurized Mud Cap Drilling (PMCD) is a drilling technique that has been used for over seven years in many wells where conventional drilling proved impossible or uneconomic 1-5 . PMCD is typically used to drill fractured carbonates, where the pore and fluid loss gradient are virtually the same, resulting in total mud losses and kicks in the same hole section. However, it is not restricted to just carbonates, it can be used on any fractured rock that is very competent in respect to wellbore stability, or formations prone to severe to total loss with good wellbore stability characteristic.Traditional PMCD typically requires the periodic injection of sometimes large volumes of weighted mud into the annulus in order to maintain a reliable mud cap. The process is highly cyclical, often unpredictable, and can be prohibitively expensive. The process also requires highly skilled and experienced people to run it properly, an increasingly rare commodity these days.Use of the Micro-Flux Control (MFC) method with PMCD could permit the process to be automated and controlled to a much higher level of accuracy, allowing less experienced people to confidently run the system. While continuously injecting across the wellhead, and using delta flow as the control variable, the casing backpressure would be monitored. Casing pressure increases, indicating a loss of mud cap fluid downhole, would be automatically controlled by precise adjustment of the continuous delta flow, together with pressure monitoring, rather than by periodic injection of large volumes of fresh mud cap fluid. This paper will briefly describe the MFC method, rig up details and operational issues. It will also describe how to apply the procedure to automate and operationally enhance PMCD, explaining the benefits when compared
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