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Barossa Gas Project: Learn more
The Barossa Drilling and Completions Environment Plan (Revision 6) was accepted by NOPSEMA in December 2023 (Drilling EP). A copy of the approved Drilling EP is available online at NOPSEMA’s website.

Activity summary

In accordance with the accepted Drilling EP, Santos recommenced drilling activities in the Barossa Field in January 2024. Six subsea development wells will be drilled at three drill centres (S1, S2, N1 – refer to Figure 2 below).

The wells are drilled using a moored semi-submersible mobile offshore drilling unit (MODU).  A MODU is a moored drilling vessel that floats semi-submerged while drilling. A picture of a MODU is shown in Figure 1. The water depth at the three drill centres ranges from 230 metres to 268 metres.

The MODU is supported by up to four support vessels which transit between the drilling area (see Figure 2) and the onshore supply base in Darwin.  The offshore support vessels are specially designed ships that cater for the logistical servicing of the offshore activity. This includes activities such as delivering supplies and equipment, moving equipment and positioning the MODU.

Graphical representation of a MODU

Figure 1: A graphical representation of a MODU

The permit area NT/L1 is defined as the operational area within which drilling activities occur (Figure 2). During drilling, a 500 metre exclusion zone (known as a petroleum safety zone (PSZ)) is in place around the MODU. The exclusion zone will remain around each well until eventual field decommissioning. Other vessels are prohibited from entering or being present in a petroleum safety zone without authorisation.  For more information, visit the National Offshore Petroleum Safety and Environmental Management Authority website.

During drilling, a cautionary zone is also in place around the MODU and anchors, which may extend up to 2.5 kilometres from the MODU within which marine traffic will be monitored and clear communications maintained to reduce the risk of vessel interactions. Each well is expected to take about 90 days of continuous well operations (24 hours per day, seven days per week) to drill and complete. Activities are anticipated to be completed within about two years, subject to, for example, weather and operational performance.

Once drilling of a well is complete, the MODU will install pressure-containing safety equipment at the top of each well, referred to as a subsea “Christmas Tree”. The Christmas Tree will act like a tap, so Santos can control the flow and pressure of the gas. The Christmas Tree is the primary mechanism for shutting in the well at the seabed and serves as the interface for well re-entry operations. The installation of well casing and the Christmas Tree is known as completion of the well.

A subsea control module attached to the tree contains the instrumentation, electronics and hydraulics connections needed for safe operation of the subsea tree valves, chokes and downhole valves. Once installed, the wells remain suspended until future commissioning and production phases (which will be addressed in separate activity Environment Plans).

Figure 2: Barossa overview and drilling and completions operational area