A New Look at the Petroleum Potential of the Caswell Sub-Basin, Browse Basin

Abstract

The Caswell Sub-basin is a major depocentre within the Browse Basin, situated entirely offshore in the northern region of the Australian North West Shelf. The 2014 Lasseter-1 discovery in the basin has resulted in renewed interest. The 2013 acquisition of 9224 km² of MultiClient 3D GeoStreamer® dual-sensor deep-tow seismic over the Caswell Sub-basin has given new insights into this hydrocarbon province, and allows detailed inversion work in the primary reservoir fairway, and greater penetration and imaging of deeper sediments and structures that had been impossible to image. This presentation will discuss the benefits of using dual-sensor acquisition data in the Caswell Sub-basin with an examination in terms of potential local hydrocarbon prospectivity. The basin was initiated as an extensional half-graben intra-cratonic rift during the Paleozoic, and has undergone multiple episodes of extension, subsidence and inversion. The major hydrocarbon discoveries in the Caswell Sub-basin produce from reservoirs and generate from source intervals deposited during the second period of extension and subsidence (Early Jurassic- Early Cretaceous). The first gas discovery in the Browse Basin came in 1971 with the drilling of Scott Reef-1, encountering gas in a thick succession of fluvio-deltaic sediments of the Lower-Middle Jurassic Plover Formation. A number of prospects were later drilled along the Buffon-Scott Reef-Brecknock Anticlinal Trend, encountering significant amounts of gas and also condensate. Discoveries continued during the 1980s, including Brewster-1A ST1, Caswell-2 ST2 and Echuca Shoals-1. Each well encountered gas in Lower Cretaceous (Berriasian) reservoirs, with the Caswell- 2 ST2 and Echuca Shoals −1 also encountering gas in Late Jurassic sediments. In addition, Caswell −2 ST2 encountered the first oil in the Caswell Sub-basin, in Upper Cretaceous sandstones. More recent discoveries, including the Crown and giant Ichthys gas fields, highlight potential in this area. This paper will focus on new discoveries e.g. Lasseter and Crown, a demonstration of the uplift and benefits of newly acquired data vs legacy datasets and a comparison of depth vs time imaging. In addition, the improved imaging of the Triassic interval in this area will be demonstrated, which with the oil discovery of the Phoenix South-1 in the offshore Canning Basin to the southwest, is being viewed as a major potential new play fairway previously bypassed due to imaging challenges.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015