The control line for CZ-5 well became plugged due to contaminants in the hydraulic control line fluid. As a result, CZ-5 well remained shut in with the deferment of 2000 bbls/day. Remedial solution was planned and it involved the installation of subsurface controlled safety valve or storm choke. Since the failed subsurface safety valve is in the jammed close position, the mechanism to lock open the flapper and to keep the valve open permanently must be done before the installion of the storm choke. The special tubing with smaller ID, or better known as straddle, was then set across the flapper and hang inside. Without the realization that the pressure setting of the storm choke calculation would become complicated with the smaller tubing/straddle inside, the closing and opening pressure were determined based on NODAL Analysis.

The flapper of CZ-5 ScSSV was also expected to dislocate severely and a special flip open tool is designed to position the dislocated flapper back to its housing. Flapper flip open tool is the in-house designed tool that can be run using slickline for 2 7/8″, 3½″ or 4½″ tubing. This unique tool has enabled many lock open jobs in our operation and it has totally eliminated the need for flapper milling.

The unexpected outcome of valve closing pressure and operating speed was experienced for a few times after the installation, causing the multiple intervention work to retrieve and to re-set the storm choke with different setting pressure. Though all minimum data required to design the storm choke for CZ-5 has been rightly considered, its performance is still very unpredictable and shocking. Determined to make the valve to work properly for a desired certain period of time, all operational data were gathered and studied. During the last rectification attempt, the storm choke has finally worked as intended.

The paper will describe more on the challenges encountered during the set-up of flip open tool and modified straddle, the engineering design of both of them and the storm choke unique behaviour from the experience at Caspian Sea Operation.

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