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Technical Paper: Improving Drilling Operations Efficiency on an Ultranarrow Margin HP/HT MPD Well With Use of a Mud Cap

Society: SPE
Paper Number: 167985
Presentation Date: 2014
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Abstract

As the industry pushes the boundary of technology to drill narrow margin wells, safe drilling practices and maintain drilling efficiency is becoming ever more challenging. The practice of drilling with Managed Pressure Drilling (MPD) using statically underbalanced mud weight is gaining increasing acceptance in HPHT well construction. This paper describes the planning and execution of using mud cap fluid in the drilling of an ultra-narrow margin (0.5ppg window at planning stage) HPHT well from a Jack Up rig. 

Drilling ECD with overbalanced mud weight would have exceeded formation fracture gradient resulting is lost circulation, therefore the HPHT section of the well was drilled with statically underbalanced mud weight. With no viable option to displace well to kill weight fluid prior to any trip out of hole, planning focused on how to maximize operational gains from use of cap fluid on different trips out of hole without compromising open hole integrity and well safety. 

In this paper, we will discuss the design of the cap fluid, selection of changeover depth (CoD), risks associated with use of cap fluid, determination of available window for mud cap placement and removal, planning and execution of mud cap placement and removal, challenges of running and displacing out cap fluid with liner and, lessons learnt from repeated use of the technique throughout the well construction phase, including coring and wireline logging under MPD conditions. Significant operational efficiency was gained from the use of cap fluid, making it possible to drill a well which would have been impossible to drill with minimal lost time.

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