
TY  - JOUR
A1  - Buffin, A.J. 
A1  - Sutherland, A.J. 
A1  - Gorski, J.A. 
T1  - THE OTWAY BASIN: EARLY CRETACEOUS RIFTING TO NEOGENE INVERSION
JF  - The APPEA Journal
JO  - The APPEA Journal
Y1  - 1995
VL  - 35
IS  - 1
SP  - 494
EP  - 506
KW  - 
UR  - https://doi.org/10.1071/AJ94031 
N2  - Borehole breakouts and hydraulic fractures in&#xad;ferred from dipmeter and formation microscanner logs indicate that the minimum horizontal stress (&#x3c3;h) is oriented 035&#xb0;N in the South Australian sector of the Otway Basin. Density and sonic check-shot log data indicate that vertical stress (&#x3c3;v) increases from approximately 20 MPa at a depth of one km to 44 MPa at two km and 68 MPa at three km. Assum&#xad;ing a normal fault condition (i.e. &#x3c3;y > &#x3c3;H > &#x3c3;h), the magnitude of &#x3c3;h is 75 per cent of the magnitude of the maximum horizontal stress (&#x3c3;H), and the magni&#xad;tude of &#x3c3;H is close to that of av. Sonic velocity compaction trends for shales suggest that pore pressure is generally near hydrostatic in the Otway Basin.Knowledge of the contemporary stress field has a number of implications for hydrocarbon produc&#xad;tion and exploration in the basin. Wellbore quality in vertical wells may be improved (breakouts sup&#xad;pressed) by increasing the mud weight to a level below that which induces hydraulic fracture, or other drilling problems related to excessive mud weight. Horizontal wells drilled in the &#x3c3;h direction (035&#xb0;N/215&#xb0;N) should be more stable than those drilled in the &#x3c3;H direction, and indeed than vertical wells. In any EOR operations where water flooding promotes hydraulic fracturing, injectors should be aligned in the aH (125&#xb0;N/305&#xb0;N) direction, and off&#xad;set from producers in the orthogonal &#x3c3;h direction. Any deviated/horizontal wells targeting the frac&#xad;tured basement play should be oriented in the &#x3c3;h (035&#xb0;N/215&#xb0;N) direction to maximise intersection with this open, natural fracture trend. Hydrocar&#xad;bon recovery in wells deviated towards 035&#xb0;N/215&#xb0;N may also be enhanced by inducing multiple hydrau&#xad;lic fractures along the wellbore.Considering exploration-related issues, faults following the dominant structural trend, sub-paral&#xad;lel to &#x3c3;H orientation, are the most prone to be non-sealing during any episodic build-up of pore pres&#xad;sure. Pre-existing vertical faults striking 080-095&#xb0;N and 155-170&#xb0;N are the most prone to at least a component of strike-slip reactivation within the contemporary stress field. 
ER  -

