In plans to explore the shallow gas potential of the Nagar prospect offshore the southern coast of Myanmar, PETRONAS had to contend with a number of potentially high risk issues. The shallow nature of the hazardous prospect made kick detection speed and pressure control accuracy essential to avoid losing returns. Concerns about a weak casing shoe, a narrow drilling margin, the inability to control bottom hole pressure (BHP) while circulating out gas, and the short response time needed, demanded a solution before the shallow gas-bearing sands could be drilled safely from the available moored drill ship with its conventional subsea equipment.From flow modeling it was estimated that within 3 minutes the system and procedures would have to detect and shut-in a gas influx, then commence circulating it out, all while controlling the BHP of a flowing, multiphase fluid within extremely narrow safe limits. It was concluded that the Nagar well could only be safely drilled with a pressure management system that could maintain BHP within +/-15 psi while drilling and +/-45 psi during connections and well control.In an industry search, PETRONAS learned that no system existed with the functionality needed, but by electing to combine new and existing technologies from three separate providers they were the first to develop one that did.This industry-first solution involved integrating elements of the technology developed for automated pressure control, pressure while drilling (PWD), and high speed, drill string telemetry. Modifications had to be made to a number of elements, including the pressure control and PWD systems, to obtain the necessary functionality. Given the safety critical nature of the drilling hazards, the modifications and system integration were first tested during simulated kicks with downhole nitrogen injection, before drilling out the casing shoe. During testing on the rig and subsequent drilling operations, the integrated system proved its ability to maintain a near constant BHP, with the accuracy and speed needed to safely and successfully drill the Nagar prospect.
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Abstract
Bulk conductivity data of ionically-and electronically-conducting solid electrolytes and electronic ceramics invariably show a frequency dependence that cannot be modelled by a single-valued resistor. To model this, common practice is to add a constant phase element, CPE, in parallel withthe bulk resistance. To fit experimental data on a wide variety of materials, however, it is also essential to include the limiting, high frequency permittivity of the material in the equivalent circuit.
Failure to do so can lead to incorrect values for the sample resistance and CPE parameters and to an inappropriate circuit for materials that are electrically heterogeneousIn the analysis and interpretation of impedance data, it is always essential to represent the data by an equivalent circuit in order to have correct equations to determine values for the component resistance, R, and capacitance, C, parameters. Selection of the most appropriate equivalent circuit is not always straightforward, especially for heterogeneous ceramics whose grains and grain boundaries may be distinct electrically and in many cases, where electrode-sample contact impedances are also present. In this communication, we do not discuss the strategies that may be adopted to deduce the correct equivalent circuit for heterogeneous materials or systems; these have been covered elsewhere [1] Instead, this paper focuses on one component, the limiting, high frequency bulk response, both for its fundamental importance to materials characterisation but
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