Low-shock, pressure-operated ball seat for hydraulic liner hangers enables effective cementing despite wellbore instability
After setting the 7- × 9⅝-in liner hanger, an operator was unable to reestablish circulation and cement the liner in several wells. The conventional ball seat that was deployed created a pressure surge when the operator attempted to reopen the flow path, destabilizing the formation. SLB provided an innovative solution that addressed the challenge and enabled seamless execution of the well plan.
An operator in Oman had encountered challenges while using a conventional ball seat in the running string for installing 7-in liners through unstable formations. A ball released from surface lands on the seat and plugs the string so that pressure can be increased to actuate hydraulic-set devices such as the liner hanger. But the approximately 3,500-psi pressure subsequently required to push the ball through for reestablishing circulation proved too great a shock for the formation, resulting in hole packoff.
After trying to regain circulation for 5–6 hours, the operator was forced to abandon its plan to cement the liner. The liner top packer was set, followed by drilling the 6⅛-in hole section. It then took 12 hours to run a 4½-in scab liner with a 6⅛-in openhole packer to isolate the 8½-in hole section. This situation had occurred a number of times, and the problem is expected to worsen as the field depletes and the formation becomes more unstable.
To address the challenge, SLB proposed running its low-shock, pressure-operated ball seat with the 7- × 9⅝-in liner hanger system. With this unique technology, the ball shears through the seat not when the pressure is increased but instead when it’s reduced to a low value of about 500 psi, thus protecting the formation from a pressure surge. After detailed discussions, the operator agreed to try this novel solution in the next well.
Although the borehole exhibited a packoff tendency prior to setting the liner hanger and releasing the running tool, the team was able to establish circulation with the desired flow rate and pump cement after setting the hanger. Subsequently, the liner top packer was set. The operator saved significant rig time and was able to seamlessly execute its well plan. Convinced of its effectiveness, the operator plans to deploy the new technology in additional wells going forward.
