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Tubular expansion for well construction is a process accomplished by pulling (or pushing) a mandrel through a pipe downhole. This can be described as a tribological system that consists of the pipe and mandrel surface, a lubricant layer and a fluid. A successful expansion requires a lubricant that, not only ensures manageable expansion forces, but also provides a robust solution for downhole application. The desired lubricant should separate the mandrel from the pipe during a downhole plastic deformation and be thermally stable, chemically compatible with drilling fluids and withstand a long shelf life in harsh environments. This paper describes a process for optimal lubricant selection using accelerated testing with a dedicated setup that mimics demanding down hole conditions during expansion processes. Three commercially available lubricants, commonly used in tubular expansion or other similarly demanding applications, and a novel solid lubricant, developed specifically for tubular expansion applications, were tested. The test campaign focused on the influence of drilling fluids and temperature on the friction, wear and lubrication efficiency. The novel solid lubricant showed superior performance compared to conventional lubricants demonstrating lower friction factor with expansion forces between 13% and 49% lower than with conventional expandable tubular lubricants, outstanding resilience in coping with alien particles in the drilling fluid, ability to mitigate the onset of stick-slip phenomena and good corrosion protection for the expandable tubular. It was therefore selected and successfully used in field-trial applications.
The abstract must contain conspicuous acknowledgment of where and by whom the paper was presented.
The main objective of this work is to study the dynamic behavior of gas expansion in marine risers. The term ‘riser equilibrium' is used to provide a more rational explanation of gas expansion and its relation to riser unloading. While handling a gas kick situation with the blowout preventer closed, the gas within the riser expands until its pressure equals the hydrostatic pressure of the mud column above, plus any applied back pressure. Buoyancy or slip will cause the gas to migrate, which in turn will cause further expansion, if allowed to, or an increase in pressure. But after a certain point, termed as ‘Riser Equilibrium Point', any small decrease in the hydrostatic pressure would trigger the gas to expand rapidly until enough back pressure is applied or the top of the gas reaches surface. This could cause an explosive unloading. Complete dissolution of gas in oil based muds and the relative delay in noticing any surface indications for the gas influx makes influx detection more complicated with oil based mud as opposed to water based mud. Estimation of various parameters to study these phenomena and their correlation to the gas expansion is studied through an analytical and iterative approach. All schemes are implemented in Matlab and give a basic understanding of the severity of the situation. Calculation of the riser equilibrium point is beneficial to understand the risks related to riser unloading and riser collapse through proper estimation of collapse load. Since the conventional ‘free gas' approach to calculate surface volume of gas during kill operations tend to overestimate the risks involved, this study is expected to provide a more comprehensive understanding of the situation providing a safer operational conditions to handle gas in risers.
The primary challenge is to obtain "fluidity"