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Abstract
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.

Introduction
The Nagar-1 well is an exploration well located in block M16 in the Andaman Sea under more than 400 meters of water. A map of the area and the location of the well are shown in Figure 1. PETRONAS identified this prospect from seismic surveys as a possible source of gas production from several shallow gas bearing sands lying between 260 and 400 m below the sea floor. As a wildcat well the drilling objective was to confirm the presence of hydrocarbons in the target zones and like other wildcat areas there are no offset wells in close proximity to the proposed well location. The closest offset wells were over 100 km away in less than 200 m of water.