Design of a Ball Seat for Sealing Tubing in Downhole Applications

Photo of Mustafa Bhikhapurwala, Raul del Bosque, Peter Salinas, Stuart Shively Students: Mustafa Bhikhapurwala, Raul del Bosque, Peter Salinas, Stuart Shively

Sponsor: Baker-Hughes, Inc.

Date: Summer 2009

Requirements:
The solution must meet the general requirements of fitting into a 2 38" outside diameter (OD) production tubing and using API external upset couplings. The design must withstand the same burst, collapse and tensile stresses as the production tubing. The materials must comply with NACE MR0175. Metals should have a minimum yield strength of 80,000 psi and maximum hardness of 22 HRC. Elastomers must be Nitrile. The rough factory cost target is $5,000. The solution should avoid leaving material down-well as it may hinder future well operations. The solution cannot require the well operator to fish the ball seat out using wireline as this requires time, and is thus too expensive. Lastly, but most importantly, the solution must be pressure actuated and must leave a clean, full-bore opening in the tubing.

Problem:
Design a ball seat that will leave a clean, full-bore opening after tubing pressure actuates an associated mechanism without any surface intervention

Solution:
The mechanism recommended by the team is a Sliding Piston Concept where a piston with a diameter larger than the ball seat is housed in the wall thickness of the tubing. The team selected an Elbow concept for the Sliding Piston model to transfer the sliding motion to the ball seat segments. For this solution, the actuation pressure differential will be applied across the piston in the piston chamber, cause it to shear the holding screws and move down. This downward motion will be converted to torque at a pin joint, which will be transmitted to the ball seat segment. This torque, combined with the radial push from the pressure in the tubing, will slide the seat segments into the cavity created in the tubing wall thickness, thus leaving a clean, full-bore opening.

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