The Perth Basin is a large onshore/offshore sedimentary basin of late Permian age that extends approximately 1,300 kms along the West Australian coast. The basin has been explored for oil and gas since the early 1950’s, with much of the exploration effort focused on the onshore, northern area.
As a petroleum system mature hydrocarbon source rocks are widespread, clastic reservoirs are abundant, and the respective timing of trap formation to hydrocarbon migration is favourable. The major play types are Permian Triassic/Jurassic anticlines, and Permian/Triassic titled fault blocks (e.g. Lockyer Deep/North Erregulla Deep).
The first commercial discovery was made at Dongara in 1964, resulting in the first gas pipeline in Western Australia, from Dongara to Pinjara. The basin is now well served by extensive gas pipeline infrastructure, operated by the Australian Gas Infrastructure Group (AGIG) and running from Dampier to Bunbury through the centre of the Perth Basin. This infrastructure provides direct route to market for produced gas, and potentially in the future the ability to export Perth Basin gas via the North West Shelf LNG facility in Karratha.
Up until 2014 there was some thirteen oil and gas discoveries within the onshore north and central Perth Basin, plus additional discoveries outside of this area such as the offshore Cliff Head oil field and onshore Whicher Range gas field (located in the far south of the basin). A huge resurgence of interest in Perth Basin exploration has taken place since 2014, at which time AWE Ltd discovered the huge Waitsia gas field within Permian sandstone reservoirs at a depth that was previously thought to be prohibiitive for preservation of good reservoir porosity and permeability. Since that time the Strike Energy/Warrego Energy joint venture has made a further significant gas discovery at West Erregulla-2, and Beach Energy have discovered a large volume of gas at Beharra Springs Deep – both exploration wells which targeted the deep Permian Kingia and High Cliff reservoirs. Not only are these discoveries very large, they flow at very high gas rates – greatly reducing the number of wells required for commercialisation and thereby substantially improving development economics.
The creaming curve for the onshore northern/central Perth Basin is shown below, and illustrates the impact of the recent large gas discoveries. Creaming curves are typically used by petroleum geoscientists to assess the level of maturity of exploration within a petroleum basin. Until 2014 the Perth Basin exhibited a typical form of creaming curve, whereby initial large discoveries lead to a series of generally smaller discoveries. The Perth Basin model was “turned on it’s head” in 2014 with the discovery at Waitsia, and the subsequent discoveries in 2019 demonstrate that there is ample scoope for further large discoveries within the basin.
The “sweet spot” for future Permian gas discoveries is regarded by Norwest Energy as being relatively small (relative to the full extent of the basin) and is tightly held by just a few petroleum exploration companies. Norwest Energy’s EP368 and EP426 exploration permits sit directly within this “sweet spot”, and host the 1.2 Tcf Lockyer Deep/North Erregulla Deep prospect, in addition to the 61 MMbbls Greater Springy Creek oil prospect and numerous other exploration leads. Norwest Energy expects that the 18 months will see a significant exploration, appraisal and development drilling campaign within this part of the basin, including appraisal at West Erregulla and Beharra Springs Deep, exploration at Lockyer Deep-1 and Walyering, and development drilling at Waitsia – not to mention the Cervantes oil prospect located to the west.