Exploration, Exploitation And Economics Of The Possible Petroleum Provinces Discovered In The Carnarvon Basin Since 1988.
Honours Degree, 1992
University of Adelaide
Petroleum exploration was first initiated in the Carnarvon Basin in the late 1940's when Sir Harold Ragatt, the first director of the Bureau of Mineral Resources, suggested to William Walkey to centre his search for oil in this area. It was not until 1953 when West Australian Petroleum Pty. Ltd. (Wapet) struck oil at Rough Range in the Exmouth Sub-basin. In 1964 Wapet discovered the first commercial oil field on Barrow Island and it is still producing today. The first offshore discovery was in 1968 when Woodside Offshore Petroleum struck oil at Legendre #1, however the first commercial discovery didn't occur until 1971 when Woodside discovered the North Rankin Gasfield. Prior to 1988, a total of 181 New Field Wildcat (NFW) wells drilled in the Carnarvon Basin, resulting in 29 potential fields discoveries.
Since 1988, 57 NFW wells were drilled in the Carnarvon Basin with 31 of these wells encountering occurrences of hydrocarbons. As a result of Appraisal and development dri11ing 20 of the 31 discoveries may prove to be potentially economic fields. Four of these fields are found onshore while the remaining 16 are located offshore.
The majority of early discoveries in the Carnarvon Basin are gas prone. Since the early 1980s the majority of discoveries are oil prone with 17 discoveries since 1988. The largest of these oil fields found since 1988 are the Wanaea and Griffin Fields with recoverable reserves of 145.3 and 81.0 million barrels of oi1 respectively.
The majority of fields discovered since 1988 are found in the Cretaceous Barrow Group (Flacourt Formation). These fields mainly show a three way-dip closure which rely on a fault seal against downthrown Cretaceous Muderong Shale. Fields of the Mungaroo Formation are found in tilted fau1t blocks and are truncated by a major erosional surface, the Main Unconformity. They are usually overlain by Cretaceous claystones. These fields are mainly gas prone. This is due to the nature of the source rocks (Locker Shale and Mungaroo Formation) and maturity of these rocks. On the flanks of the basin, these rocks are immature and in the depocentres they are believed to be overmature.
The Barrow Group and Mungaroo Formation reservoirs show that there is a porosity decrease with depth brought about by compaction of the overlying rocks.