Perth basin

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This page is currently being authored by a student at the University of Oklahoma. This page will be complete by December 13, 2020.

Introduction

This shows the area of Perth Basin. [1]

The Perth Basin is located in south-western Western Australia and has an area of about 174,000 square kilometers (around 108,118 square miles). It stretches about 1,300 kilometers (808 miles)[2]. Located both onshore and offshore, the Perth Basin has complex structures. The basin has experienced some drilled wells, including 309 onshore and 52 offshore, with the deepest known formation reaching a depth of about 4,500 meters. The Perth Basin has historically been an uneconomical pursuit although recent developments in the industry have increased the potential viability of this play. Around three-quarters of the wells drilled are in the northern sector of the basin resulting in a large degree of undeveloped territory[3].

History

The Perth Basin was developed during the Late Triassic to Early Jurassic and Middle Jurassic to Early Cretaceous periods[4]. Each period experienced different sequential layering of limestone, shale, and sandstone, resulting in complex and differentiated reservoirs. It originally formed when Australia broke off from India and Africa. Gas was first found in the Perth Basin in 1964 and was subsequently produced for sale in October of 1971. When drilling first began, only about 1 in every 10 wells were successful. Largely due to 3D Seismic Survey Technology, that number has been improved. Since the basin's discovery in the 1960s, there have been several developments over the years, including field exploration, seismic acquisition, exploration and development drilling, construction of plant infrastructure and pipelines, production and processing of oil and gas, and decommissioning and rehabilitation[5].

Petroleum Elements

Perth Basin geological strata.

Source Rock & Reservoir

The space between the Woodada and Yarragadee strata layers represents the “Triassic-Jurassic Play” with the primary areas of interest being the reservoirs within the Cattamarra and Eneabba layers. Below this, past the Kockatae Shale, are the Wagina/Dongara sandstones. This strata layer is the primary target of the “Upper Permian Play”. The source rock for both of these plays is thought to date primarily to the Late Permian with hydrocarbons derived primarily from terrestrial plant life and subsequently migrating to the current locations stated[6]. The hydrocarbons within the Kockatea Shale strata itself were formed within this layer and subsequently were unable to migrate due to the low permeability characteristic of the shale.[7]

Traps & Seals

The Triassic-Jurassic reservoir includes traps primarily formed from a hanging wall rollover fold, anticlines, and tilted horst blocks that are sealed by intraformational shales. Residual oil columns have been detected, indicating that proper sealing exists. The Wagina/Dongara sanstone reservoir is similarly sealed by structural traps, primarily faulted anticlines. The Kockatea Shale also acts as a lateral seal where this layer is in contact with the reservoir. As stated before, the low permeability characteristic of the Kockatea Shale reservoir acts as a trap and seal for the hydrocarbons within this formation. [7]

Geological Risks & Uncertainties

Because of the complexity of geophysical interpretation, modeling the structure of subsurface formations can involve a significant degree of uncertainty. Also, a large percentage of the Perth Basin is relatively undeveloped resulting in a deficiency of data available to be used in projections in many areas. For instance, a major risk associated with offshore exploration in the Perth Basin is trap breach. This occurs when the breaching of a reservoir seal due to fault movement causes oil or gas that was secure within a reservoir to escape. Another potential threat to reservoir integrity is the complete absence of seal in the lower Crustaceous reservoirs. Because there is a vast amount of unexplored area, pursuing this basin involves a relatively high degree of risk but also high reward potential. Modeling is currently underway throughout the formation to determine the degree of reservoir security and ultimately to estimate the risk associated with pursuing this particular play[7].

Petroleum and Facility Engineering

Australia has eight major oil refineries located throughout the continent, one being in the capital city of Western Australia, Perth[8]. Most natural gas produced in this region is processed in the southern portion of Western Australia on islands just off the coast. North of Perth, in the city of Dampier, exists an LNG plant that largely exports product to Asia. These processing and shipping facilities are all interconnected through extensive pipeline networks that transport the raw product. Where pipeline is unavailable, a large trucking service located around 30 kilometers outside of Perth facilitates the transfer of a significant portion of the product[9]. Through the existing infrastructure and capabilities that characterize Western Australia, oil and gas producers are granted easy access to local and global markets.

Future Potential

The Perth Basin is predicted to eventually produce more than the Cooper Basin. [10]

There are many variables affecting the viability of the Perth Basin, although it appears probable that certain areas will maintain and expand profitability, specifically offshore operations. This is where the majority of exploration and development has taken place historically resulting in a relatively low degree of risk compared to onshore pursuits. Government regulation also presents a significant threat to development with hydraulic fracking bans recently implemented in both the northern and southern regions of the onshore basin. Fracking is likely necessary to produce hydrocarbons economically due to the low permeability of the shale reservoirs characteristic in these areas. It is unknown how long such regulations will remain in place, although it appears that so long as fracking is banned, much of the Perth Basin potential will remain unrealized. That being said, the Perth Basin is predicted to pass the production rate of the current leading producing basin in Australia, the Cooper basin, by 2024 as shown by the graph to the right. This is primarily due to offshore production. Many operators are currently working to develop the region including Warrego Energy, Strike Energy, and Beach Energy, each believing in the future of this area[11]. The Perth Basin is expected to have a gas production rate of 400 million cubic feet per day in the near future. Historically, the producing basins of Australia have been located to the north and east of the continent, increasing the cost of gas in the western sector due to transportation costs. Significant market demand exists in western Australia as a result of this separation, making gas produced in the Perth Basin desirable. Furthermore, gas produced in the Perth Basin is expected to be the lowest-cost gas resource in all of Australia. Nonetheless, collaboration among a multitude of upstream, midstream, and downstream companies will be necessary to fully realize the Perth Basin's potential[12].

References

  1. https://www.ga.gov.au/scientific-topics/energy/province-sedimentary-basin-geology/petroleum/offshore-southwest-australia/perth-basin
  2. https://www.beachenergy.com.au/perth-basin/
  3. https://mitsuiepmidwest.com.au/who-we-are/history-oil-gas-perth-basin/
  4. https://www.ga.gov.au/scientific-topics/energy/province-sedimentary-basin-geology/petroleum/offshore-southwest-australia/perth-basin
  5. https://mitsuiepmidwest.com.au/who-we-are/history-oil-gas-perth-basin/
  6. http://archives.datapages.com/data/specpubs/geochem1/data/a028/a028/0001/0350/0391.htm
  7. 7.0 7.1 7.2 https://cdn2.hubspot.net/hubfs/2478981/Spectrum%20Articles/Rocket%20Science%20-%20Modern%20Seismic%20Provides%20Exploration%20Leads%20in%20the%20Northern%20Perth%20Basin..pdf
  8. https://www.studyinternational.com/news/10-things-you-never-knew-about-perth-australia/
  9. https://www.vintageenergy.com.au/perth-basin.html
  10. https://www.ga.gov.au/scientific-topics/energy/province-sedimentary-basin-geology/petroleum/offshore-southwest-australia/perth-basin
  11. https://www.afr.com/companies/energy/the-rise-of-perth-basin-gas-may-trigger-m-and-a-20200106-p53p5u
  12. https://www.rystadenergy.com/newsevents/news/press-releases/australias-perth-basin-gas-output-to-overtake-cooper-basin-by-2024-despite-low-prices/