Griffin Well Abandonment
|Submitted by||BHP Billiton Petroleum (Australia) Pty Ltd|
|Submission date||27 October, 2014|
|Decision date||23 April, 2015|
|Link to previously accepted EP|
Mr Doug Stewart
The Griffin Well Abandonment Activities for 13 wells (8 Griffin wells;3 Scindian wells, Chinook-1 well and Ramillies-1 well) is located in Permit Areas WA-10-L and WA-12-L in Commonwealth waters, approximately 68 km northwest of Onslow, Western Australia (WA). The Griffin Well Abandonment Activity will commence in 2015/2016 and will occur over an estimated 6-month period. The Activity will require a semi-submersible mobile offshore drilling unit (MODU). The Activity will take place 24 hours a day and is expected to take an average of 12 days to permanently abandon each well (inclusive of MODU mooring activities by AHTS vessels).
Abandonment of the Griffin wells does not constitute field decommissioning. Full field decommissioning and abandonment of remaining in situ development infrastructure in Permit Areas WA10-L and WA-12-L once the MODU has moved off location will be undertaken at a future point in time and will be subject to a separate approvals for this phase of activities.
Each well operational sequence will be dependent on multiple issues including: well completion design, scale deposit levels, and production casing cement quality and quantity; however, a generic sequence of work that will be followed for the abandonment of each well is as follows:
Position MODU over the well and set the anchors;
Installation and function test of the Intervention and Work-Over Control System (IWOCS) to control subsea tree hydraulic functions;
Remove tree cap;
Run tree running tool (TRT) / quick disconnection package (QDP) on dual bore Work-Over riser;
Enter well bore and bullhead (the pumping of kill-weight fluid) brine into production tubing / reservoir;
Replace the reservoir cap rock by installing 2 (cement plugs) barriers in the well;
Remove the Xmas tree and 'wet store’ on the seabed adjacent to the well head on purpose built mud mat (including cut and disconnect flowlines and umbilicals);
Tubing will either be cut below the SSSV and recovered to surface or used as a cement string and dropped back into the well, with top of tubing being >10m below seabed;
Well heads may be cut and removed (or delayed for inclusion in the future Griffin Field Abandonment phase); and
Pull anchors and move MODU to location of next well/ demobilise MODU.