Geomechanical Assessment of CO2 Storage in the Southern Browse Basin (Barcoo Sub-basin)  

Authors / CoAuthors

Tenthorey, E. | van Ruth, P.

Abstract

This geomechanical analysis of the Browse Basin was undertaken as part of the CO2CRC's Browse Basin Geosequestration Analysis. This study aims to constrain the geomechanical model (in situ stresses), and to evaluate the risk of fault reactivation. The stress regime in the Browse Basin is one of strike-slip faulting i.e. maximum horizontal stress (~ 28.3 MPa/km) > vertical stress (22 MPa/km) > minimum horizontal stress (15.7 MPa/km). Pore pressure is near hydrostatic in all wells except for two, which exhibit elevated pore fluid pressures at depths greater than 3500 m. A maximum horizontal stress orientation of 095' was considered to be most appropriate for the Barcoo sub-basin, which was the area of focus in this study. The risk of fault reactivation was calculated using the FAST (Fault Analysis Seal Technology) technique, which determines fault reactivation risk by estimating the increase in pore pressure required to cause reactivation. Fault reactivation risk was calculated using two fault strength scenarios; cohesionless faults (C = 0; ? = 0.6) and healed faults (C = 5; ? = 0.75). The orientations of faults with high and low reactivation risks is almost identical for healed and cohesionless faults. High angle faults striking N-S are unlikely to reactivate in the current stress regime. High angle faults orientated ENE-WSW and ESE-WNW have the highest fault reactivation risk. Due to the fact that the SH gradient was determined using frictional limits, the most unfavourably oriented cohesionless faults cannot sustain any pore pressure increase without reactivating. By contrast, using a cohesive fault model indicates that those same faults would be able to sustain a pore pressure increase (Delta P) of 9.6 MPa. However, it must be emphasized that the absolute values of Delta P presented in this study are subject to large errors due to uncertainties in the geomechanical model, in particular for the maximum horizontal stress. Therefore, the absolute values of Delta-P presented herein should not be used for planning purposes. Fault reactivation risk was evaluated for 10 faults with known orientations. All faults were interpreted as extending from below the Jurassic target reservoir formation to the surface. The dominant fault in the Barcoo sub-basin is the large fault which extends from Trochus 1 to Sheherazade 1 to Arquebus 1. This deeply penetrating, listric fault initially formed as a normal fault and was subsequently reactivated in thrust mode. Most of the faults in the Barcoo sub-basin trend broadly N-S and are therefore relatively stable with respect to increases in pore pressure. However, there are sections within some individual faults where fault orientation becomes close to optimal. In these sections, small increases in pore pressure (<5 MPa) may be sufficient to cause fault reactivation. If this were to occur, then significant risk of CO2 leakage would exist, as these sections cross-cut the regional seal.

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nonGeographicDataset

eCat Id

65562

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Keywords

• Report

( Theme )

• geological storage of CO2

( Theme )

• sedimentary basins

( Theme )

• geological sequestration

( Theme )

• risk assessment

Australian and New Zealand Standard Research Classification (ANZSRC)

• Earth Sciences

• Published_Internal

Publication Date

2007-01-01T00:00:00

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Australian Government Security ClassificationSystem    

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Creative Commons Attribution 4.0 International Licence    

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