A MULTI-DISCIPLINARY APPROACH TO DEFINITION AND CHARACTERISATION OF CARBONATE SHOALS, SHALLOW GAS ACCUMULATIONS AND RELATED COMPLEX NEAR-SURFACE SEDIMENTARY STRUCTURES IN THE TIMOR SEA

1998 ◽  
Vol 38 (1) ◽  
pp. 93 ◽  
Author(s):  
D.J. Bishop ◽  
G.W. O'Brien
Keyword(s):  
High Resolution ◽  
Joint Venture ◽  
Velocity Model ◽  
Source Rocks ◽  
Shallow Gas ◽  
Near Surface ◽  
Sea Floor ◽  
3D Velocity Model ◽  
Basin Scale ◽  
Timor Sea

A major exploration program is being undertaken by the AC/P16 Joint Venture in the central Timor Sea, northwestern Australia. Its safe and successful execution is critically dependant on the early definition and characterisation of both the numerous carbonate shoals in the area and the complex bathymetry. This was accomplished via the acquisition of environmental, high-resolution bathymetric, 2D and 3D seismic and airborne laser fluorosensor (ALF) data. Multi-disciplinary integration and analysis of these data have enabled mapping and 3D visualisation of the shoals, and the creation of a 3D velocity model for depth conversion. Seismic amplitude anomalies and chaotic seismic reflectors, which increase in areal extent toward the sea floor, have been interpreted as being due to shallow gas. These gas accumulations are also associated with soft-sediment gravity slides in the shallow sub-surface which exhibit thrust imbrication in the contractional toes and are linked to listric extensional faults. The high resolution bathymetric data have provided images of a disturbed sea floor in several of the areas which are affected by shallow gas: craters, troughs, ridges and mounds can be explained by the localised venting of gas at the sea floor. These gas accumulations are located above basin-scale faults, which are inferred to provide migration paths from more deeply buried source rocks. ALF anomalies mapped at the sea surface, and sea floor grab samples containing petrogenic hydrocarbons, also provide evidence that hydrocarbons are presently leaking from the sea floor.

BREATHING NEW LIFE INTO THE EASTERN DAMPIER SUB-BASIN: AN INTEGRATED REVIEW BASED ON GEOPHYSICAL, STRATIGRAPHIC AND BASIN MODELLING EVALUATION

2004 ◽  
Vol 44 (1) ◽  
pp. 123 ◽  
Author(s):  
G.P. Thomas ◽  
M.R. Lennane ◽  
F. Glass ◽  
T. Walker ◽  
M. Partington ◽  
...  
Keyword(s):  
Seismic Data ◽  
Joint Venture ◽  
Velocity Model ◽  
Upper Jurassic ◽  
Source Rocks ◽  
Third Order ◽  
Geochemical Fingerprinting ◽  
Stratigraphic Framework ◽  
Seismic Image ◽  
Hydrocarbon Charge

The eastern Dampier Sub-basin on Australia’s northwestern margin has been subject to intensive exploration activity since the early 1960s. The commercial success rate for exploration drilling, however, has been a disappointing 8%, despite numerous indications of at least one active petroleum system. During 2002–2003, Woodside and its joint venture partners undertook an integrated review of the area, aimed at unlocking its remaining potential. Stratigraphy, hydrocarbon charge and 3D seismic data quality were addressed in parallel.The eastern Dampier Sub-basin stratigraphy was upgraded from the existing, conventional, second-order tectono-stratigraphic framework to a third-order, exploration-scale, genetic stratigraphic framework. The new framework has regional predictive capability in terms of reservoir (and seal) presence and facies, and has led to recognition of new plays and an enhanced understanding of known plays. One new play involves shoreface sands within the Calypso Formation. New light has been shed on the known Lower Cretaceous M.australis sands play (K30), by the creation of gross depositional environment maps at third-order sequence scale. The Upper Jurassic deepwater clastics play of the Lewis Trough has also been developed, by recognition of four prospective, sand-rich gravity-flow intervals in the early Oxfordian (J42 play).A 3D charge modelling study, underpinned by new geochemical analysis, has allowed delineation of areas of higher and lower risk in terms of hydrocarbon charge and phase (oil versus gas). Key source rocks for oil are identified in the early Oxfordian W.spectabilis biozone, although they are also a likely source for gas in the southwest of the area. The Bathonian-Callovian Upper Legendre Formation is a major source for gas, but could also have contributed minor oil in the northeast of the area. By a combination of geochemical fingerprinting and 3D forward modelling, most hydrocarbon occurrences in the area have been tied to these source intervals, complete with a consistent view of maturities and migration pathways.Some 1,500 km2 of the Panaeus multi-client 3D survey were reprocessed, with close attention to multiple removal, velocities and imaging. A step-change improvement in seismic quality was obtained, together with improved velocities for depth conversion.The prospect portfolio has been polarised and much enhanced through these studies, and the results of several existing wells have become better understood. Some new prospects were identified by apparent direct fluid indications, detected in one case by 3D volume AVO screening. Other new prospects are the result of a clearer seismic image, or of the revised velocity model for depth conversion. New plays are still being followed up, while the fresh light cast on existing plays (e.g. K30 and J42), in combination with improved seismic data, has led to development of several interesting opportunities.

scholarly journals High-resolution interactive modelling of the mountain glacier–atmosphere interface: an application over the Karakoram

2013 ◽  
Vol 7 (1) ◽  
pp. 103-144 ◽  
Author(s):  
E. Collier ◽  
T. Mölg ◽  
F. Maussion ◽  
D. Scherer ◽  
C. Mayer ◽  
...  
Keyword(s):  
High Resolution ◽  
Mass Balance ◽  
Land Surface ◽  
Traditional Approach ◽  
Coupled Model ◽  
Glacier Mass Balance ◽  
Glacier Surface ◽  
Mountain Glacier ◽  
Near Surface ◽  
Basin Scale

Abstract. The traditional approach to simulations of alpine glacier mass balance (MB) has been one-way, or offline, thus precluding feedbacks from changing glacier surface conditions on the atmospheric forcing. In addition, alpine glaciers have been only simply, if at all, represented in atmospheric models to date. Here, we extend a recently presented, novel technique for simulating glacier–atmosphere interactions without the need for statistical downscaling, through the use of a coupled high-resolution mesoscale atmospheric and physically-based mass balance modelling system that includes glacier MB and energy balance feedbacks to the atmosphere. We compare the model results over the Karakoram region of the northwestern Himalaya with both remote sensing data and in situ glaciological and meteorological measurements for the ablation season of 2004. We find that interactive coupling has a localized but appreciable impact on the near-surface meteorological forcing data and that incorporation of MB processes improves the simulation of variables such as land surface temperature and snow albedo. Furthermore, including feedbacks from the MB model has a non-negligible effect on simulated mass balance, reducing modelled ablation, on average, by 0.1 m w.e. (−6.0%) to a total of −1.5 m w.e. between 25 June–31 August 2004. The interactively coupled model shows promise as a new, multi-scale tool for explicitly resolving atmospheric-MB processes of mountain glaciers at the basin scale.

scholarly journals High-resolution interactive modelling of the mountain glacier–atmosphere interface: an application over the Karakoram

2013 ◽  
Vol 7 (3) ◽  
pp. 779-795 ◽  
Author(s):  
E. Collier ◽  
T. Mölg ◽  
F. Maussion ◽  
D. Scherer ◽  
C. Mayer ◽  
...  
Keyword(s):  
High Resolution ◽  
Mass Balance ◽  
Land Surface ◽  
Traditional Approach ◽  
Coupled Model ◽  
Glacier Mass Balance ◽  
Glacier Surface ◽  
Mountain Glacier ◽  
Near Surface ◽  
Basin Scale

Abstract. The traditional approach to simulations of alpine glacier mass balance (MB) has been one-way, or offline, thus precluding feedbacks from changing glacier surface conditions on the atmospheric forcing. In addition, alpine glaciers have been only simply, if at all, represented in atmospheric models to date. Here, we extend a recently presented, novel technique for simulating glacier–atmosphere interactions without the need for statistical downscaling, through the use of a coupled high-resolution mesoscale atmospheric and physically-based climatic mass balance (CMB) modelling system that includes glacier CMB feedbacks to the atmosphere. We compare the model results over the Karakoram region of the northwestern Himalaya with remote sensing data for the ablation season of 2004 as well as with in situ glaciological and meteorological measurements from the Baltoro glacier. We find that interactive coupling has a localized but appreciable impact on the near-surface meteorological forcing data and that incorporation of CMB processes improves the simulation of variables such as land surface temperature and snow albedo. Furthermore, including feedbacks from the glacier model has a non-negligible effect on simulated CMB, reducing modelled ablation, on average, by 0.1 m w.e. (−6.0%) to a total of −1.5 m w.e. between 25 June–31 August 2004. The interactively coupled model shows promise as a new, multi-scale tool for explicitly resolving atmospheric-CMB processes of mountain glaciers at the basin scale.

Imaging permafrost velocity structure using high resolution 3D seismic tomography

Geophysics ◽  
2011 ◽  
Vol 76 (5) ◽  
pp. B187-B198 ◽  
Author(s):  
Kumar Ramachandran ◽  
Gilles Bellefleur ◽  
Tom Brent ◽  
Michael Riedel ◽  
Scott Dallimore
Keyword(s):  
High Resolution ◽  
Velocity Structure ◽  
Velocity Model ◽  
Water Bodies ◽  
Unfrozen Water ◽  
3D Seismic ◽  
Tomographic Inversion ◽  
Near Surface ◽  
First Arrival ◽  
Velocity Variations

A 3D seismic survey (Mallik 3D), covering [Formula: see text] in the Mackenzie Delta area of Canada’s north, was conducted by industry in 2002. Numerous lakes and marine inundation create a complex near-surface structure in the permafrost terrain. Much of the near subsurface remains frozen but significant melt zones exist particularly from perennially unfrozen water bodies. This results in an irregular distribution of permafrost ice creating a complex pattern of low and high frequency near-surface velocity variations which induce significant traveltime distortions in surface seismic data. A high resolution 3D traveltime tomography study was employed to map the permafrost velocity structure utilizing first-arrival traveltimes picked from 3D seismic shot records. Approximately 900,000 traveltime picks from 3167 shots were used in the inversion. Tomographic inversion of the first-arrival traveltimes resulted in a smooth velocity model for the upper 200 m of the subsurface. Ray coverage in the model is excellent down to 200 m providing effective control for estimating velocities through tomographic inversion. Resolution tests conducted through horizontal and vertical checkerboard tests confirm the robustness of the velocity model in detailing small scale velocity variations. Well velocities were used to validate tomographic velocities. The tomographic velocities do not show systematic correlation with well velocities. The velocity model clearly images the permafrost velocity structure in lateral and vertical directions. It is inferred from the velocity model that the permafrost structure in the near subsurface is discontinuous. Extensions of surface water bodies in depth, characterized by low P-wave velocities, are well imaged by the velocity model. Deep lakes with unfrozen water, inferred from the tomographic velocity model, correlate with areas of strong amplitude blanking and frequency attenuation observed in processed reflection seismic stack sections.

High‐resolution seismic traveltime tomography incorporating static corrections applied to a till‐covered bedrock environment

Geophysics ◽  
2004 ◽  
Vol 69 (4) ◽  
pp. 1082-1090 ◽  
Author(s):  
Björn Bergman ◽  
Ari Tryggvason ◽  
Christopher Juhlin
Keyword(s):  
High Resolution ◽  
Velocity Model ◽  
Surface Velocity ◽  
Data Set ◽  
Near Surface ◽  
Seismic Processing ◽  
Simultaneous Inversion ◽  
Reflection Seismic ◽  
Static Corrections ◽  
Velocity Variations

A major obstacle in tomographic inversion is near‐surface velocity variations. Such shallow velocity variations need to be known and correctly accounted for to obtain images of deeper structures with high resolution and quality. Bedrock cover in many areas consists of unconsolidated sediments and glacial till. To handle the problems associated with this cover, we present a tomographic method that solves for the 3D velocity structure and receiver static corrections simultaneously. We test the method on first‐arrival picks from deep seismic reflection data acquired in the mid‐ late to 1980s in the Siljan Ring area, central Sweden. To use this data set successfully, one needs to handle a number of problems, including time‐varying, near‐surface velocities from data recorded in winter and summer, several sources and receivers within each inversion cell, varying thickness of the cover layer in each inversion cell, and complex 3D geology. Simultaneous inversion for static corrections and velocity produces a much better image than standard tomography without statics. The velocity model from the simultaneous inversion is superior to the velocity model produced using refraction statics obtained from standard reflection seismic processing prior to inversion. Best results using the simultaneous inversion are obtained when the initial top velocity layer is set to the near‐surface bedrock velocity rather than the velocity of the cover. The resulting static calculations may, in the future, be compared to refraction static corrections in standard reflection seismic processing. The preferred final model shows a good correlation with the mapped geology and the airborne magneticmap.

Effects of near surface lithology on velocity modelling and time–depth relationships in the Cooper–Eromanga–Lake Eyre Basin

2018 ◽  
Vol 58 (1) ◽  
pp. 321
Author(s):  
Anna Manka ◽  
Glen Buick ◽  
Rob Menpes ◽  
Luke Gardiner ◽  
Cameron Jones ◽  
...  
Keyword(s):  
Seismic Velocity ◽  
Velocity Model ◽  
Petroleum Exploration ◽  
Success Rates ◽  
Near Surface ◽  
Depth Prediction ◽  
Western Flank ◽  
3D Velocity Model ◽  
The Time Domain ◽  
Eromanga Basin

Structural closures on the western flank of the Patchawarra Trough in the Cooper–Eromanga Basin are truly low relief; drilling opportunities regularly target hydrocarbon columns of similar magnitude to the uncertainty of depth prediction. Improving the accuracy and precision of depth prediction will reduce risk for drilling opportunities, and improve drilling success rates. A detailed study of the near surface geology (surface to ~500 m depth) of the western flank of the Patchawarra Trough has been undertaken to better understand the effect of observed geological variations of the near surface on depth prediction at deeper target levels. The stratigraphic interval investigated includes the top of the Eromanga Basin and the entire Lake Eyre Basin, which is sparingly studied and routinely overlooked in the statics and velocity modelling process. This study analysed recently acquired cased-hole sonic logs in conjunction with gamma logs and mudlog data to map out the observed geological variations, and construct a 3D velocity model of the near surface. Variations of layer thickness and seismic velocity were input into Monte Carlo simulations to investigate sensitivities of each formation on two-way travel time and depth prediction. This investigation has found that velocity variations of the Weathered Winton Formation, and thickness variations of the Namba Clastics have the greatest impact on imaging of structures at depth. Independently, these have the potential to completely conceal or create structures in the time domain. Continued efforts in improved understanding of the near surface will subsequently lead to enhanced imaging of structures, which can then be used in the mapping of structural closures in petroleum exploration and development.

Use of refraction, reflection, and wave-equation-based tomography for imaging beneath shallow gas: A Trinidad field data example

Geophysics ◽  
2008 ◽  
Vol 73 (5) ◽  
pp. VE281-VE289 ◽  
Author(s):  
Nurul Kabir ◽  
Uwe Albertin ◽  
Min Zhou ◽  
Vishal Nagassar ◽  
Einar Kjos ◽  
...  
Keyword(s):  
Wave Equation ◽  
Velocity Field ◽  
Velocity Model ◽  
Surface Velocity ◽  
Low Velocity ◽  
Shallow Gas ◽  
Near Surface ◽  
Velocity Anomaly ◽  
Refraction Tomography ◽  
Reflection Tomography

Shallow localized gas pockets cause challenging problems in seismic imaging because of sags and wipe-out zones they produce on imaged reflectors deep in the section. In addition, the presence of shallow gas generates strong surface-related and interbed multiples, making velocity updating very difficult. When localized gas pockets are very shallow, we have limited information to build a near-surface velocity model using ray-based reflection tomography alone. Diving-wave refraction tomography successfully builds a starting model for the very shallow part. Usual ray-based reflection tomography using single-parameter hyperbolic moveout might need many iterations to update the deeper part of the velocity model. In addition, the method generates a low-velocity anomaly in the deeper part of the model. We present an innovative method for building the final velocity model by combining refraction, reflection, and wave-equation-based tomography. Wave-equation-based tomography effectively generates a detailed update of a shallow velocity field, resolving the gas-sag problem. When applied as the last step, following the refraction and reflection tomography, it resolves the gas-sag problem but fails to remove the low-velocity anomaly generated by the reflection tomography in the deeper part of the model. To improve the methodology, we update the shallow velocity field using refraction tomography followed by wave-equation tomography before updating the deeper part of the model. This step avoids generating the low-velocity anomaly. Refraction and wave-equation-based tomography followed by reflection tomography generates a simpler velocity model, giving better focusing in the deeper part of the image. We illustrate how the methodology successfully improves resolution of gas anomalies and significantly reduces gas sag from an imaged section in the Greater Cassia area, Trinidad.

Scattering effect on shallow gas-obscured zone imaging in Bohai PL19-3 area

Geophysics ◽  
2012 ◽  
Vol 77 (2) ◽  
pp. B43-B53 ◽  
Author(s):  
Xianhuai Zhu ◽  
Kirk Wallace ◽  
Qingrong Zhu ◽  
Robert Hofer
Keyword(s):  
Velocity Model ◽  
Data Depth ◽  
Surface Velocity ◽  
Bohai Bay ◽  
Shallow Gas ◽  
Near Surface ◽  
Depth Migration ◽  
Precise Knowledge ◽  
Streamer Data ◽  
Viscoelastic Modeling

Seismic imaging is challenging in the Bohai Bay PL19-3 area, offshore China. Bohai Bay Field is seismically obscured, making well penetrations the only reliable source of data for subsurface interpretation. With the help of turning-ray tomography, we are able to obtain a reliable near-surface velocity model approximately down to 700 m below sea level, using the first arrivals picked from streamer data. Depth migration using velocities estimated from turning-ray tomography has improved shallow structures and fault definition. However, reservoir level structures from 800 to 1500 m are still poorly imaged. A viscoelastic modeling study with assigned variable Q and shallow velocity profiles, with and without shallow gas-induced scatterers, demonstrates that scattering is the primary controlling phenomenon causing imaging difficulty within the obscured zone. Due to scattering, imaging tests at the target level were unsuccessful even with precise knowledge of velocity.

Sign in / Sign up

Export Citation Format

Share Document