structural evolution and petroleum systems of the murchison basin
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Structural Evolution and Petroleum Systems of the Murchison Basin
J. Mac BeggsGeoSphere Ltd, Lower Hutt
Francesca C. GhisettiTerraGeologica, Christchurch
GSNZ Annual Meeting
Wellington, Nov. 23-26, 2008
• Inner margin ofCompressionalInversion Orogen
• Footwall of the Alpine Fault in the bend region
• Overlies major basementdiscontinuities (TerraneBoundaries)
• Bounded by sets of largecrustal faults
• Heat flow anomaly (up to 108 mW/m2
(Townend, 1999)
Upwelling of slab-derived fluids inferred from MT (Wannamaker et al., 2007)
BULLERTAKAKA
M. BATHOLITH
MURCHISON BASIN
• Flexural foredeep during L. Oligocene through M. Miocene (30-10 Ma)
• Persistent subsidence from the
extensional through the early
compressional stages
Extensional basin (hosting terrestrialcoal measures) during mid-late Eocenerifting (45-35 Ma) (tip of N-migratingEmerald Basin)
*
*
~ 20 Ma
MB
Large sediment accommodation space with > 7.5 km of infilling Tertiary sediments
Beggs, Ghisetti
and Tulloch, 2008
Emerald B.
E. Miocene Ranges
• Strong vertical mobility
• Rapid uplift (post 10 Ma) with removal of > 3.5 km of Eocene and younger section (Gibson et al., 1996)
Ghisetti and Sibson (2006)
BASE TO THE OLIGOCENE SEQUENCE
> 40% post L. Miocene shortening
HYDROCARBON SYSTEM
Evidence for generation andmovement of hydrocarbon fluids
• Problem of location and quality of seismic lines
• Unsuitable location of wells
SEEPS
Murchison-1 1927
Blackwater-1 1968
Bounty-1 1970
Matiri-1 1985
Location, extent, and maturation of source rocks
Location, geometry, size and depth of stratigraphic/structural traps
Survival of hydrocarbon fluids in the trap-seal assemblage
CONTRIBUTION OF STRUCTURAL ANALYSIS FOR DEFINITION OF SUBSURFACE STRUCTURE
KEY ISSUES FOR EXPLORATION
• Inclined non-cylindrical folds with opposite vergence
• Open synclinestight, disrupted anticlines 37-34.3 Ma
34.3-21.7 Ma
21.7-15.9 Ma
15.9-15 Ma
• Disharmonic style controlled by competence contrasts in the sedimentary sequence and byinherited structures
• Forced folds
• High-angle inherited and reactivated normal faults
• Low-angle cross-cutting thrust faults accomodatingsignificant amounts of shortening
1. Buckling and detachment (latest Oligocene-Early Miocene)
2. Fold growth and amplification associated with compressionalinversion (Middle Miocene)
3. Crosscutting by low-angle thrusts (footwall shortcuts of AF) since 10 Ma
Modified from Ghisetti and Sibson (2006)
• Difficult downdip projection of surface and near-surface data
• Correct definition of structural style is a key for exploration and well location
• Low-angle crosscutting thrust faults seal stratigraphic traps and early structural traps in the footwall
• 3D migration pathways of fluids are likely to be structurally controlled
IMPLICATIONS FOR HYDROCARBON EXPLORATION
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