Technical Paper: Downhole Drilling Dynamics of Innovative Rathole Elimination BHA in Hole-Enlargement-While-Drilling Operations

Society: SPE
Paper Number: 178795
Presentation Date: 2016
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Abstract

Hole enlargement while drilling (HEWD) is now widely used in deepwater applications. It provides reduced-clearance casing programs, improves drilling in swelling formation, and helps equivalent circulating density (ECD) management. HEWD applications commonly use an underreamer in a BHA with rotary steerable system (RSS). Currently, traditional reamer placement results in a long portion of unenlarged hole - rathole - which requires an extra trip to enlarge. A new BHA design is being sought to eliminate the second trip requirement - the objective is to find a feasible solution.

Placing the reamer closing to the bit would forgo the need for a second trip; however, the placement of a traditional reamer is limited by its design. In response to such limitation, a solution is proposed to design a rathole elimination (RHE) BHA which included a lower reamer placed between MWD/LWD tools and the RSS. During HEWD, the lower reamer is in passive (off) mode while a traditional reamer is active. Upon reaching TD, the BHA is tripped back to position the lower reamer above the rathole and is then activated to enlarge the rathole. This RHE BHA design thereby eliminates the second trip requirement.

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