Santos Ltd (Santos) proposes to plug and abandon 12 wells on its Mutineer, Exeter, Fletcher and Finucane fields within permits WA-54-L, WA-26-L and WA-27-L. The permit areas are within Commonwealth waters, approximately 160 km north of Dampier, in water depths ranging from 130 – 160m.
This EP will focus on plugging of the remaining wells followed by severing and recovery of well infrastructure at the seabed. The P&A campaign is predominantly concerned with the removal of equipment upstream from the subsea tree (XT). However, some removal of subsea infrastructure between the subsea trees and the subsea manifolds may occur in order to facilitate the safe and effective removal of the subsea trees (e.g. jumper or well services line severing, flying lead recovery) or to simplify the SAR campaign (stabilisation and mattresses etc).
The P&A campaign will be conducted primarily using either a moored MODU or a dynamically positioned (DP) light weight intervention vessel (LWIV). Additional pre, during or post MODU activities may also be conducted using a vessel(s) with a remotely operating vehicle (ROV) onboard. Note that some pre-P&A campaign activities such as inspection and intervention on the wells (without breaking the established WBE) may occur under the approved Mutineer-Exeter Cessation of Production Environment Plan (9885-650-PLN-0001).
The duration is expected to take up to approximately 280 days. However, up to 12 months' activity duration has been considered in evaluating the environmental impacts to allow for unforeseen schedule delays. This EP assumes the activities may be undertaken at any time of year over the validity period of this EP.
The exact timing and duration of the P&A activities are subject to MODU/LWIV availability, MODU/LWIV capability and metocean conditions (particularly cyclonic activity). Once started, operations will be 24 hours per day, 7 days per week. To ensure conservatism, the EP is assessed for the activity occurring at any time of year for the approximate duration of the activity.
In general, a MODU based P&A program may consist of:
+ Preparatory activities
+ mobilisation and positioning
+ establishing and testing of secondary well control
+ rigging up and testing the well bleed-off package
+ establishing primary well control
+ regaining access to the cap rock
+ establishing a permanent isolation of the reservoir
+ establishing a permanent isolation of any zones of potential
+ recovery of subsea well infrastructure
+ possible recovery of other subsea infrastructure
+ demobilisation of MODU
In general, up to three anchor handling type vessels will be used for the duration of a MODU assisted well abandonment campaign. One of the vessels will remain on location with the MODU/LWIV at all times, however all three vessels may be present simultaneously in the field.
A petroleum safety zone will extend in a 500-m radius around the MODU surface location (at each drill centre).
Helicopters and support vessel may be used to transfer crew and equipment to and from vessels/MODU and assist in emergency as required.
