ABSTRACT:

Drilling through depleted sands can result in a multitude of problems, such as lost returns, differential sticking, difficulty logging and the inability to reach the target depth. Often solving lost circulation can be difficult and costly as a result of non-productive time. Remedies to cure losses are diverse and sometimes misapplied, possibly complicating the problem. Additionally, differential sticking zones can have a direct implication on the selection of casing points and jeopardize the architecture of the well. When the thief zone is severely depleted, problem-solving approaches such as cement plugs, squeezes, expandable liner and casing-while-drilling are used, but can be costly and not always successful. The use of fluid management techniques, team efforts and the application of sound engineering have lead to the development of an innovative approach as an alternative to standard methods. This approach prevents the problems and avoids the complex processes of curing mud losses or stuck pipe. This new preventative approach with water-based mud has been applied in several fields while drilling through highly depleted sands. This methodology has proven to be successful in preventing differential sticking and mud losses. There are two widely held theories on the increase in fracturing pressure due to particulate bridging:

  1. the formation of an internal mud cake near the wellbore region changes the ‘invaded’ zone's mechanical properties and strength, and

  2. the formation of a bridge plug within the induced fracture increases the fracture propagating pressure and the tangential stress around the borehole.

This paper will highlight a case study using the innovative fluid design to create the particulate bridging and develop a geomechanical model using field and laboratory data to explain the dominant mechanisms that contribute to the operational success

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