Seismic Stratigraphy Of The Tertiary Sediments In The Sedimetology And Diagenesis Of Sandstones Within The Lower Jurassic Cattamarra Coal Measures, North Perth Basin, Western Australia.
Theologou, Paul N.
Honours Degree, 1991
University of South Australia
Forces acting at the plate margins are the likely origin of broad scale stress patterns observed in the crust. These broad scale forces include shear traction, slab pull, ridge-push, trench suction and continent-continent collision. Broad scale stress patterns may be influenced by local tectonic forces related to overburden addition/removal, isostatic readjustment, downbending of the lithosphere, membrane effects, temperature changes or variations in rock strength. Residual stress may also be present. Methods of measuring in-situ stress include flatjack, overcoring, breakout analysis and hydraulic fracture techniques.
On a global scale most mid-plate regions are characterised by uniform, compressive stress regimes, while most areas experiencing extension have anomalously high elevation. Australia is currently in a state of horizontal compression, but the stress field is quite variable.
Finite element modelling of the Indo-Australian plate shows that the pattern of stress within the Australian continent can be explained if the stress originates from forces acting at the plate boundaries. Significant influences on the stress pattern of the Indo-Australian plate include age variations along the Sunda Arc, continent- continent collisions at the Banda Arc and Himalayas, angular and curved geometry of the plate boundaries and ridge push.
Hydraulic fracture tests performed in the Velkerri Formation of the Roper Group in the McArthur Basin indicate that the maximum horizontal compressive stress is oriented at about 020/200, and the ratio of maximum to minimum compressive stress is about 1.5-1.7. The minimum compressive stress sigma3 is horizontal. These results correspond well with finite element model predictions. A major set of surface joints is sub-parallel to the maximum horizontal compressive stress, however jointing in the basin is quite complex. In-situ stress controls both hydraulic fracture orientation, and containment. In-situ stress is therefore an important consideration in the design of a reservoir stimulation programme.
The McArthur Basin contains a middle Proterozoic platform cover sequence, the thickest portions of which occur in the north trending Batten and Walker Troughs. Syndepositional folds and faults dominate the structure of the basin. Aeromagnetic trends in the basin may result from surface lithology changes, abrupt changes in depth to basement, NW and NE deep-seated structures, exposed faults and deep magnetic dykes. Landsat corridors defined by lineament densities correspond to regional gravity lineaments that cross Australia. Major mineralisation, and the exposed edges of the McArthur Basin are apparently controlled by these corridors.