Technical Paper: Successful Hole Enlargement While Drilling: Deepwater Brazil

Society: OTC
Paper Number: 22637
Presentation Date: 2011
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Deepwater drilling often requires simultaneous hole enlargement while drilling (HEWD) to improve project economics and deliver the required wellbore geometry. Worldwide applications have shown that certain formations have caused damage to under-reamer cutting structures through premature cutter wear, particularly in abrasive sections with high formation strength. To mitigate cutting structure damage the operator and service provider need to collaborate to ensure the underreamer cutting structure is designed for superior stability, PDC cutters are engineered for thermal stability and abrasion resistance, BHA configuration is optimized and drilling parameters are carefully selected and managed. Advanced BHA modeling and real-time vibration measurement are the enabling technologies for breakthrough HEWD performance.    

Working off the coast of Brazil, an operator was preparing to HEWD two hole sections (17 1/2 in x 20 in and 14 3/4 in x 16 1/2 in) through hard and abrasive formation, which would be encountered at shallower depths than usually expected. An offset well had significant difficulty attempting to HEWD a 17 1/2 in x 20 in section, wearing out two reamer cutting structures. HEWD was not attempted on the offset’s 14 3/4 in section because of the difficulty with HEWD on the 17 1/2 in x 20 in section. Offset lithology data suggested the formations were composed of soft shale and hard sand formations, with a few limestone stringers. 

To solve the challenges on the new well, the operator and service provider implemented a comprehensive process to identify hazards and evaluate the solutions, which included a unique approach to BHA design and strict parameter management through the problem formations. This paper will discuss the following contributing factors to the successful Hole Enlargement While Drilling operation:

  • Extensive pre-well planning and communication 
  • Advanced underreamer cutting structure design and cutter technology
  • Dynamic BHA modeling and optimization of unique BHA design
  • Drilling parameter testing and selection 
  • Utilization of an operational road map to aid well-site personnel in properly managing drilling parameters

The holistic optimization process, along with the operator’s best practice, resulted in successful HEWD operations for both hole sections drilling to the targeted depth without premature failures. The cutters on the underreamers were only mildly worn and the measured stick-slip and vibrations were significantly lower than on offset wells. 

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