3D-GEO EXTENSION; RIFT BASINS AND DELTAS; STRUCTURAL/SEISMIC CONSULTING FOR THE OIL/GAS AND MINERAL INDUSTRIES.
3D-GEO Pty Ltd, Melbourne Australia
Extension; Rift Basins Overview 1
Rift Basins and Deltas as prolific gas and oil provinces 2
Common Structural/Seismic Difficulties of Difficulties of Extensional Depocentres 3
- Bed and Fault Geometries Interact
- Multiple generations of structuring
- Compartmentalisation and Overpressure
- Strike-Slip Faulting
- Salt
Extension; Rift Basins, Strike Slip fault Solutions via Seismic/Structural geological analysis 8
- Seismic restoration
- Structural analysis in 3D
- Sequence stratigraphy in deep water
- Structural restoration as a key tool
Extension Related Geology; Rift and Strike Slip Basin Research and Structural/Seismic Consulting 12
Extension; Rift Basins Overview
3D-GEO offers unique skills and unparalleled worldwide experience in the restoration of fold and thrust belts for commercial exploitation of hydrocarbons. The Principal Partners and Associates of 3D-GEO are experienced in basin analysis, structural restoration, and prospect risk analysis, starting from outcrop, well and seismic data and building 3D models of reservoir compartmentalisation. The ultimate aim is to target wells to “sweet spots” where productivity will be maximised, based on reservoir facies, charge history, structural development and tectonic overprints. AvalancheSlumpThrustsSlope ChannelsMajor ThrustsAvalancheSlumpThrustsSlope ChannelsMajor Thrusts
Examples of compressional regimes, inversion tectonics, salt bodies and their (often) complex interactions are used to show how the prior history of even complexly-deformed structures and rock units can be derived by careful use of modern structural restoration tools.
3D-GEO offers a complete service from Training to Consultancy to Targeted Research. Our clients range from Multinationals to Independents to National Oil Companies.
Copyright Notice:
The entire contents of this document are commercially sensitive and contain images proprietary to 3D-GEO and other parties. No part of this document is to be reproduced for any purpose without the prior written permission of 3D-GEO. Fold and Thrust belts as prolific gas and oil provinces.
Extensional depocentres contain a major fraction of the world's petroleum reserves, especially in the Middle East and South-East Asia. If salt structures and inverted basins are included, at least 50% of the world's hydrocarbon reserves involve extensional systems and their ensuing complications.
These regions have historically challenged our ability to find reservoirs, drill them safely and successfully, and find and produce hydrocarbons even after encountering reservoirs.
Even when structures are apparently simple, expensive errors can result from underestimating the risk of trap charge and retention in an active tectonic system. Proper basin analysis includes the history of charge, with maps and 3D models of the carrier beds at the time of migration, corrected for any later tectonics. Often hydrocarbons can migrate in surprising direction, compared to the present-day structure map.
The reward is huge, for an informed explorer, but drilling in structurally complex terranes without properly understanding the geometry of the rock formations and the implications of the structural history for hydrocarbon charge and retention can lead to a poor success ratio, and poor productivities from those wells that do encounter hydrocarbons.
In some terranes, fractures are sought to enhance productivity. In others, they should be avoided either because they lead to vertical breakthrough of unwanted fluids, or because they produce reservoir damage zones.
3D-GEO personnel have a wealth of experience of structural complexity, and a toolkit of software and intuitive methods to rapidly extract value from almost any structural problem, and advise on better exploration programs, well targets, prospect risking and production problems.
Common Structural/Seismic Difficulties of Difficulties of Extensional Depocentres
Bed and Fault Geometries Interact
Fault geometries can rapidly change with depth, and the transport of section down curved fault planes leads to “classic” geometries such as rollover anticlines. Often, the detailed result depends on the behaviour of the fault at depth – whether it is listric into a detachment, a brittle domino, or some other geometry. These deep structures are often not imaged by reservoir-level seismic, but have strong influences on the evolution of stress and strain at reservoir level, and on reservoir geometry at times of potential charge. By integrating the structure of beds and the shapes of faults, a better understanding of the growth history of the structure, its charge and seal potential can be derived.
Complex mixtures of fault geometries with time: Example from Otway Basin (Palmowski et al. 2002). Deeper faults are planar and largely rotational. Shallower faults are sparser, listric, and partially inverted.
Multiple generations of structuring
An individual structure is often the consequence of several generations of structure interacting in 3D, requiring considerable skill to interpret reservoir geometry at depth from sparse surface outcrops and rare well data.
Understanding the sequential development of a structure is vital to predicting which structures will have received charge from active hydrocarbon kitchens, and which structures were blocked from migration by prior-formed structures.
Often, the sequence of faulting is non-intuitive with the shallow and obvious features forming first and then being deformed and modified by deeper second- and third- generation structures.
Only when all the structural information is properly integrated can the exploration risk be meaningfully calculated.
Sequential structural development: A simple example of progressive footwall collapse in a deltaic system. If charge is from the right, only early structures can receive valid charge. If charge is from the left, each structure can progressively be charged. If charge is from below, details of “windows” in the underlying salt layer and the distribution of pre-existing rifts are vital.
Note that many deltas build progressively forward, with collapse at each step, leading to very complex evolution of structure and charge through time.
Compartmentalisation and Overpressure
Overpressure is a common feature of deltas where sedimentation can be rapid. Understanding the sources and degree of overpressure can help avoid lost wells, blowouts, and other operational difficulties. Structural analysis shows which overpressure zones are active – based on the way that faults change as they approach the zone. Pressure compartmentalisation is common in rift basins, from semi-regional transfer faults to cryptic (hidden) cross-cutting faults on a reservoir scale, leading to migration shadows, unexpected production barriers or offset fluid contacts.
Compartmentalisation is often a complex 3D issue: This photograph of an exposed rock surface at Watchett, UK, shows how faults interact and exchange throw, with cross-faults and relay ramps making connections across faults that should seal, and breaking connection in blocks that should be open to fluid flow. Without proper understanding of structures in 3D, expensive exploration and development mistakes can occur.
Strike-Slip Faulting
Cross-faults in extensional basins are often strike-slip faults, ranging in scale from major regional transfer faults with flower structures, to small reservoir-scale offsets with variable permeability effects. Mapping these faults as part of the overall stress field is a necessary prerequisite to understanding their effect on reservoir productivity and prospect risk.
A major strike-slip fault with a classic flower structure developed (After Bally, 1983). Note the sudden change of bed dip across elements of the flower system and thrusting along the strike-slip fault.
Salt
Whether acting as a detachment, or forming diapirs and overhangs, salt (and other evaporites) have a major influence on structural style, trap localisation, and reservoir deposition and preservation. 3D-Geo personnel have an extensive background in salt studies and reservoir-targeting in salt provinces.
Gulf of Hormuz Image: TGS Nopec/AAPG
Gulf of Mexico Salt Sheet Image: Giovanni GuglielmoSolutions via Structural analysis
Extension; Rift Basins, Strike Slip fault Solutions via Seismic/Structural geological analysis
Seismic restoration
As well as restoring geologic models, we can fully-restore seismic data itself – or at least, an image of the data. Here, we examine a complex deltaic sequence to understand the correlation of seismic sequences through a series of growth faults. The seismic is complicated by the presence of a late-stage sill with very high reflectivity that crosses between fault blocks at different stratigraphic horizons. We successfully restore the seismic on a wiggle-for-wiggle basis with simple PC software that can be run on laptops or low-end systems.
The restoration is shown at an intermediate stage, with the correlation being assembled and fault blocks restored sequentially. This type of analysis is invaluable and unique to 3D-GEO.
Structural analysis in 3D
3D Seismic Data in the Skua Field: A detailed research project (Chen et al. 2002) trialled methods for efficiently building 3D Models from extensional structures, and extracting meaningful geologic histories from the detailed information contained within the shallow sedimentary cover. This is often overlooked in the haste to map reservoirs and traps, yet contains vital information for trap integrity, charge history, and prospect risk.
Sequence stratigraphy in deep water
3D-GEO has developed key skills in interpreting processes and palaeoenvironments in deepwater systems at the distal end of deltaic and shelf systems. Our analysis uses understanding of modern 3D seabed geometries and depositional systems to map reservoir play fairways and trap systems. Our experience in the Gulf of Mexico, Asia, and the south Atlantic is unrivalled.
Deepwater sediments are transported in turbidity currents – a unique deepwater transport system which 3D-GEO has researched for the past decade and more. Our experience yields unique insights into flow processes and reservoir geometries through growing submarine foldbelts such as the toe-thrust zone of deltas. Image: Pratson and Haxby, Scientific American 1997
Without a clear understanding of submarine processes, the distribution of reservoirs in deep-sea environments may be an expensive uncertainty ahead of the drill bit. 3D-GEO brings novel insights to risk reduction in deepwater. Image: USGS
Extension Related Geology; Rift and Strike Slip Basin Research and Structural/Seismic Consulting
3D GEO believes that clients require the most up-to-date and practical working tools and concepts for analysing their prospects and play fairways, basins and foldbelts. Outmoded techniques and unfamiliarity with data lead to wasted time – the most precious resource of any organisation. We pride ourselves that we can bring rapid solutions to almost any problem, due to our extensive experience base.
The only way to achieve this level of client service is to work closely with industry so that we are familiar with modern data quality and interpretation tools – be these in the realm of seismic data, wellbores, geochemistry, or structural geology. We work in active petroleum basins worldwide, with a complete range of problems and unique circumstances.
At the same time, a dedicated and rigorous research program keeps 3D-GEO current with the published literature – both academic and commercial case studies. We test new software and concepts in a research environment to perfect our commercial methodology. The results of research projects are published in the scientific peer-reviewed literature, and presented at oil industry conferences across Asia and in the USA and Europe.
3D-GEO looks at real rocks and real seismic data, and measures real deformations -not just theoretical models, or sand or modelling clay. 3D-GEO brings the latest methods, combined with the maturity of deep experience to provide the simplest, fastest, and most cost-effective service to all of our clients, whether Multinationals, Independents, or National Oil Companies.
Clients are welcome to commission research projects or to sponsor candidates for research leading to higher degrees (M.SC. and Ph.D.) at the University of Melbourne. Please contact 3D-GEO personnel to discuss your requirements.
A variety of examples taken from foldbelts worldwide show how the application of key techniques improves the ability to locate productive reservoir, despite structural complexity.
These examples are described in simplistic terms – in reality, a full basin analysis and play fairway risking is required to understand where to drill to maximise discoveries and productivity.
Rift and Strike Slip Fault Basin Case Studies in Extensional Geology Terrains such as the North West Shelf Australia
A study of trap evolution through time (Chen et al.,) shows trap geometry today (red) and in the Miocene, as revealed by 3D restoration. The Skua structure has remained in position, with slight growth through time – this is a stable low-risk structure. The nearby Swift structure shows sideways shift of the trap through time, sweeping hydrocarbons past potential breaching faults. Exploration results showed that Swift is breached and Skua retains its charge. Calibration of the method on this proven field opens the way to applications in pure exploration settings as a risk-reduction tool.
North Sea
Restoration of the seismic data revealed a complex interaction of parasitic collapse faults and through-going brittle faults. Reservoir compartmentalisation results from both sets of faults, leading to unexpected reservoir complexity and production pressure maintenance problems.
Inversion Structure
An inversion structure in the Dutch North Sea, taken from the classic Bally (1983) Atlas of seismic expressions of structural styles. A complex interplay of salt movement (purple layer = mobile Zechstein salt), and inversion tectonics makes interpretation of this section initially daunting.
To understand the geological history, the section has to be restored, taking into account the considerable degree of erosion that has occurred over structural highs – replacing missing section and progressively restoring offset on the faults.
The first diagram is the present-day structure with a Tertiary cover sequence over a significant regional unconformity. We restore this in the second section by stripping-off the Tertiary cover, decompacting, and then estimating the former thickness of eroded sections.
In the third section, we restore the section to pre-Chalk by removing inverted fault offsets and inversion folds, using a smooth regional trend as datum. If water-depth estimates are available from biostratigraphy or seismic evidence, the datum would be a paleoseabed.
Note that at this stage the original Jurassic graben has been restored and Zechstein salt (purple) has been partially restored into the graben. Additional stages of restoration would back-off the normal faulting in the graben and further restore the mobile salt.
As is typical with inversion tectonics, the areas that are now most truncated are the original depocentres, where sediment was the thickest. A careful calculation of original thickness and burial depth is required to evaluate reservoir quality in these areas.
Salt Structures
The desired product from geophysicists is a sequence stratigraphic interpretation that yields facies information for reservoir prediction. However, in the presence of strong deformation, this is generally thought to be impossible. Here, in an example from the Gulf of Mexico of a salt-cored anticline, we restore the seismic digitally, whereupon not only do the errors in picks near the fault/fold axes become apparent, but it now becomes possible to conduct conventional sequence stratigraphy across this grossly-deformed structure. Note the downlaps above the central purple event.
Structural/Seismic Personnel and Contacts
The three Principal Partners of 3D-GEO bring together a unique collection of skills and worldwide experience in structural geology, geophysics and 3D modelling. For the past four years, the principals have been consulting to industry and conducting leading-edge research into petroleum basins and structural geology.
3D-GEO personnel also deliver a wide range of professional training courses through NExT. Personalised training courses can be delivered in the offices of the client, or here in Melbourne, Australia, where excellent field exposures exist to study fault geometries and histories.
3D-GEO also utilises a network of skilled industry professionals with unrivalled experience in petroleum basins and foldbelts worldwide. These associates are available to advise on specific aspects of 3D-GEO projects and to lend expertise where required to conduct larger or more specialised studies.
3D-GEO can be contacted via email at info@3d-geo.com.
3D-GEO is based in Melbourne, Australia, where the local time zone is GMT- 9 hours in the southern winter / northern summer and GMT – 11 hours in the southern summer / northern winter.
Telephone contacts:
Nick: +61 438 397 366
Brief biographies of the three 3D-GEO principals follow:
Dr Nick Hoffman, Geophysics Expert
Nick obtained a 1st Class Honours degree at Edinburgh University and a Ph.D. at Cambridge University - both in the field of geophysics - then worked in the oil industry for 15 years. Extensive experience includes assignments in the North Sea and Europe with BP and worldwide with BHP Petroleum. Nick has worked extensively on Australian and SE Asian basins and also on the "modern classics" such as the Gulf of Mexico and West Africa. He has substantial experience in frontier and deepwater basins where distinctive structural styles and turbidite reservoirs require specialist interpretation skills. He brings an holistic approach to prospect analysis and risking - identifying weaknesses in play systems and basin histories.
Nick is an expert in 2D and 3D seismic stratigraphic and structural interpretation and basin modelling. He uses unique tools such as GeoMorpher to restore tectonically deformed sequences to show their original internal geometry. In this way, robust sequence stratigraphy can be conducted despite a strong tectonic overprint. Nick also uses ER Mapper and other visualisation software to handle large digital grids and produce stunning maps of topography and structures.
Nick@3D-GEO.com
Jeff Keetley, 3D Structural Modeller and Technology Advisor
Jeffrey Keetley graduated from La Trobe University with Honours, examining the structural and thermal history of the West Java, Indonesia (sponsored by British Gas and the AGCRC). Jeff's recent Ph.D. thesis is entitled '3D Fold and Thrust structures, the effects of rheology and resultant fluid flow: Papua New Guinea (PNG) Fold Belt and Cape Liptrap, Australia' (Sponsored by the Chevron Joint Venture).
Other work undertaken has involved 3D structural work on the North West Shelf of Australia, 2D/3D work in PNG and structural field work in the Finisterre Ranges and Mount Wilhelm PNG (with the PNGGS and CCOP).
Jeff is an expert in workstation 3D structural modelling and restoration of compressional and extensional terrains.
Jeff@3D-GEO.com
Extension; Rift Basin Appendices
Appendix - Training Courses offered by 3D-GEO
3D-GEO has developed training courses for novice to advanced structural and seismic users. These courses have been continually updated and taught to industry and postgraduate students throughout SE Asia over the last 10-15 years. Award winning lecturer Dr Nick Hoffman showw how seismic and structural principles and newly developed methodologies can be applied to onshore and offshore prospects, with key case studies on complex fold belts and new deep water basin plays.
Experts Dr Dan Kendrick and Jeffrey Keetley offer detailed training courses in the application of software packages for structural geology and 3D modelling, and apply these methods to client data in their offices.
Client courses can be carried out in-house or within the 3D-GEO laboratory in Melbourne, Australia.
- 2D/3D Structural Geology Computer Modelling Course
- Balanced Cross Section course
- Extensional and Strike-Slip Structure Course
- Fold and Thrust Structure Course
- Introduction to Petroleum Geology
- Applied Petroleum Geology
- Petroleum Risk Structure Course
- Seismic Sequence Analysis and Structural Geology on Workstations
- Deepwater Seismic Analysis on Workstations
- GeoSec 2D and 3D Structural Training
Full details of the courses are available on request by email to Info@3D-GEO.com or online at our 3D-GEO website www.3D-GEO.com.
Appendix - References and further reading
Recent extensional papers by 3D-GEO personnel
Chen G., Hill K., Hoffman N. & O'Brien G. 2002. Geodynamic Evolution of the Vulcan Sub-Basin, Timor Sea, NW Australia. Australian Journal of Earth Sciences, 49, 719-736.
Chen, G., Hill, K.C., & Hoffman, N. 2002. 3D structural analysis of hydrocarbon migration in the Vulcan Sub-basin, Timor Sea. In: Keep, M. & Moss, S.J. eds The Sedimentary Basins of Western Australia 3, PESA Special Publication, 377-388
Chen G., Hoffman N., Hill K.C. & O'Brien G.W. 2001. 3D palaeo-migration pathway analysis: an example from the Timor Sea. In Hill K.C. & Bernecker T. (eds) Eastern Australasian Basins Symposium, A Refocussed Energy Perspective for the Future. Petroleum Exploration Society of Australia Special Publication. 629-638.
Hoffman, N. 1999. GeoMorpher: Digital Image Domain Seismic Reconstruction, The Leading Edge (August 1999)
Palmowski D., Hill K.C., Hoffman N. & Bernecker T. 2001. The Otway Basin evolution from rifting to seafloor spreading – hydrocarbon implications. In Hill K.C. & Bernecker T. (eds) Eastern Australasian Basins Symposium, A Refocussed Energy Perspective for the Future. Petroleum Exploration Society of Australia Special Publication. 499-506.
Power M.R., Hill K.C., Hoffman N., Bernecker T. & Norvick M. 2001. The Structural and Tectonic Evolution of the Gippsland Basin: Results from 2D section balancing and 3D structural modelling. In Hill K.C. & Bernecker T. (eds) Eastern Australasian Basins Symposium, A Refocussed Energy Perspective for the Future. Petroleum Exploration Society of Australia Special Publication. 373-384
Classic References in Structural Geology
Bally, A.W., 1983, Seismic Expression of Structural Styles, AAPG Studies in Geology #15 - Volumes 1-3.
Eisenstadt, G., and Withjack, M. O., 1995, Estimating inversion: results from clay models, in Buchanan, J. G., and Buchanan, P. G., eds., 1995, Basin Inversion: Geological Society of London Special Publication 88, p. 119-136.
Weimer, P., and T.L. Davis, 1997, Applications of 3-D seismic data to exploration and production, AAPG Studies in Geology #42.
Online Materials
Guglielmo, Giovanni, Jr., M. P. A. Jackson, and B. C. Vendeville, 1996, 3-D visualization of salt walls and associated fault systems: High-resolution digital images and animations. BEG hypertext multimedia publication at: http://www.beg.utexas.edu/indassoc/agl/animations/AGL96-MM-004/index.html