The client had a well which was shut in due to a malfunctioning tubing retrievable sub surface safety valve (TRSSSV), with attempts to lock open (lock out) the valve proving unsuccessful. Aside from wanting to get the well back on production, the client also wished to carry out a subsequent reservoir saturation logging program, both requiring the opening and secure lockout of the TRSSSV.
The TRSSSV in this specific well utilized a flapper valve design with a power spring mechanism keeping its flow tube clear of a spring-hinged flapper valve positioned below, in turn rendering the valve normally closed. The flapper valve is opened using hydraulic pressure via control lines activated from surface that drive a rod piston and the flow tube down, compressingthe power spring, pushing the flapper valve open, and bringing the flow tube to rest across the flapper section – providing unhindered well production flow as well as tool access into or out of the well.
The integral lock out mechanism of the TRSSSV was failing, resulting in the flapper valve returning to the closed position over time. The client challenged several service companies to propose a remedial solution, one that would provide secure TRSSSV lock out, hence enabling the safe execution of the subsequent intervention work and the well to be safely put back onto production.
The proposed solution from Altus was to engineer a simultaneously operated dual stroker e-line toolstring configuration – firstly to fully open the valve, secondly to securely lock it in that position.
- The upper stroker would provide the axial force and stroke distance required to push the flowtube down to fully open the TRSSSV and hold it there until “locked”. Access to push the flowtube would be achieved through an innovative activation sleeve and collet assembly attached to the expander/dimple tool.
- The lower stroker would then be used to activate an expander/dimple tool to permanently deform the flowtube and the integral lock out sleeve, hence securing them in place – in doing so permanently locking the TRSSSV in the “open” position.
Carrying this out as a single trip operation would ensure the dimpling lock out of the flow tube occurred only with the flow tube in the exact required “valve open” position. Individual communication & control and power sharing of both strokers enabled this, maintained throughout the operation using two surface computers in a master/slave configuration.
A NOGO with shear pins was attached to the lower stroker to ensure a controlled tag and land-off on a chamfer within the TRSSSV. Once landed, the upper stroker was anchored in the tubing and a phased stroke sequence initiated: to shear the NOGO pins; to move the activation sleeve to expand the collet; to shear the collet pins and move the TRSSV flow tube and lock sleeve down. While held in that position, the lower stroker was then activated to conduct the dimpling phase of the operation. Default fails safe functions of the two strokers and dimple tool would ensure the stroker would un-anchor and the dimple tool collapse in the case of loss of power to the toolstring.
It also was important that the solution would not hinder any subsequent wellbore access, nor the installation of an e-line retrievable subsurface safety valve insert once the intervention was completed. This was ensured by the inherent eight segment dimple tool design which prevents any ovalisation of the flow tube during deformation – something that could lead to a reduction in the original ID of the valve, hence limiting further well accessibility.