Seismo-Stratigraphic Interpretation and Prospectivity of the Lower Cretaceous Mentorc Gas Field, North Carnarvon Basin
Rylan M. Fabrici, 2013
Honours Degree of Bachelor of Science (Petroleum Geology & Geophysics)
Australian School of Petroleum,
The University of Adelaide
This project integrates geophysical and geological interpretation of the deltaic Valanginian Lower Barrow Group in the Northern Carnarvon Basin, Australia to establish a detailed understanding of the delta front play, specifically in relation to the Mentorc gas field. The Mentorc field is the first significant Lower Barrow Group discovery in 20 years, proving the effectiveness of the delta front play. The project primarily focused on the analysis of the fields subsurface elastic rock properties, depositional setting, creation of a sequence stratigraphic framework, description of delta architectural elements and the prospectivity of the Lower Barrow Group delta front play fairway. The seismic and quantitative interpretation based on the Glencoe 3D survey shows the Mentorc field is characterised by a robust direct hydrocarbon indicator (DHI) with excellent amplitude conformance to structural closure. Quantitative interpretation of the reservoired gas within the Lower Barrow Group sands shows a Class III Amplitude vs. Offset (AVO) response which is strongly dependent on the acoustic impedance contrast of the overlying Upper Barrow Group sideritic shale. The Mentorc field area comprises a wave dominated, tidally influenced deltaic shoreface system comprising arcuate strandplains organized into cuspate lobe complexes which characterise the deltaic succession. Deltaic clinoform geometries revealed rising sigmoidal shelf clinoforms produced in response to a highstand in sea level and constant to falling oblique tangential shelf clinoforms produced in response to a lowstand in sea level. Successions associated with rising shelf geometries consisted of sand dominated delta front topsets. In contrast, constant to falling shelf geometries were characterized by clinoform gullying which served as the main feeder system for sediment into the basin floor developing sand-prone toesets with topsets absent or not preserved. Sedimentological analysis of core data indicated excellent reservoir quality in delta front sands primarily comprising lower to upper shoreface sediments.