Stratigraphie Processing of 3D Seismic by Concurrent Analysis of Surface and Borehole Data

As expensive as 3D seismic reflection surveys are, their high cost is justified by improved imaging of certain ore horizons in some of the Witwatersrand basin gold mines. The merged historical 3D seismic reflection data acquired for Kloof and South Deep mines forms an integral part of their Ventersdorp Contact Reef mine planning and development programme. The recent advances in 3D seismic technology have motivated the reprocessing and reinterpretation of the old data sets using the latest algorithms, therefore significantly increasing the signal-to-noise ratio of the data. In particular, the prestack time migration technique has provided better stratigraphic and structural imaging in complex faulted areas, such as the Witwatersrand basin, relative to older poststack migration methods. Interpretation tools such as seismic attributes have been used to identify a number of subtle geologic structures that have direct impact on ore resource evaluation. Other improvements include more accurate mapping of the depths, dip, and strike of the key seismic horizons and auriferous reefs, yielding a better understanding of the interrelationship between fault activity and reef distribution, and the relative chronology of tectonic events. The 3D seismic data, when integrated with underground mapping and borehole data, provide better imaging and modeling of critical major fault systems and zones of reef loss. Many faults resolve as multifault segments that bound unmined blocks leading to the discovery and delineation of resources in faulted areas of the mines.

Download Full-text

The properties, morphology and distribution of igneous sills: modelling, borehole data and 3D seismic from the Faroe-Shetland area

Geological Society London Special Publications ◽

10.1144/gsl.sp.2002.197.01.11 ◽

2002 ◽

Vol 197 (1) ◽

pp. 271-306 ◽

Cited By ~ 53

Author(s):

John R. Smallwood ◽

Jenny Maresh

Keyword(s):

3D Seismic ◽

Borehole Data

Download Full-text

SALT WELDING DURING CANOPY ADVANCE AND SHORTENING IN THE GREEN CANYON AREA, NORTHERN GULF OF MEXICO

10.31223/x5qk8t ◽

2021 ◽

Author(s):

Christopher Jackson ◽

Sian Evans ◽

Turki Alshammasi

Keyword(s):

Gulf Of Mexico ◽

Seismic Reflection ◽

Analytical Models ◽

3D Seismic ◽

Borehole Data ◽

Seismic Reflection Data ◽

Northern Gulf Of Mexico ◽

Reflection Data ◽

Tectonic System ◽

Migration Pathways

Welds form due to the tectonically-induced thinning and/or dissolution of salt, with their composition and completeness thought to at least partly reflect their structural position within the salt-tectonic system. Despite their importance as seals or migration pathways for accumulations of hydrocarbons and CO2, we have relatively few examples of drilled subsurface welds; such examples would allow us to improve our understanding of the processes and products of welding, and to test analytical models of the underlying mechanics. In this study we integrate 3D seismic reflection and borehole data from the Green Canyon Area of the northern Gulf of Mexico, USA to characterize the geophysical and geological expression of a tertiary weld, as well as its broader salt-tectonic context. These data show although it appears complete on seismic reflection data, the weld contains 124 ft (c. 38 m) of pure halite. This thickness is consistent with the predictions of analytical models, and with observations from other natural examples of subsurface welds. Our observations also support a model whereby compositional fractionation of salt occurs as the salt-tectonic system evolves; in this model, less mobile and/or denser units are typically stranded within the deeper, autochthonous level, trapped in primary welds, or stranded near the basal root of diapirs, whereas less viscous and/or less dense units form the cores of these diapirs and, potentially, genetically related allochthonous sheets and canopies. We also show that shearing of the weld during downslope translation of the overlying minibasin did not lead to complete welding.

Download Full-text

Geological and geophysical expression of a primary salt weld: An example from the Santos Basin, Brazil

Interpretation ◽

10.1190/int-2014-0066.1 ◽

2014 ◽

Vol 2 (4) ◽

pp. SM77-SM89 ◽

Cited By ~ 17

Author(s):

Christopher A.-L. Jackson ◽

Clara R. Rodriguez ◽

Atle Rotevatn ◽

Rebecca E. Bell

Keyword(s):

Viscous Flow ◽

Seismic Data ◽

Upper Cretaceous ◽

Numerical Models ◽

3D Seismic ◽

Borehole Data ◽

Reservoir Rocks ◽

Potash Salt ◽

Associated Data

Primary salt welds form at the base of minibasins in response to complete evacuation of autochthonous salt. Analytical and numerical models suggest it is difficult to completely remove salt from a weld by viscous flow alone, which is especially true in multilayered evaporites, within which flow is likely heterogeneous due to lithologically controlled viscosity variations. Welds are important in the hydrocarbon industry because they may provide a hydrodynamic seal and trap hydrocarbons, or may allow transmission of fluids from source to reservoir rocks. Few papers document the subsurface expression of welds, principally because they have not been penetrated by wells or because the associated data are proprietary. We use 3D seismic and borehole data from the Santos Basin, offshore Brazil to characterize the geological and geophysical expression of a primary weld associated with flow of Aptian salt. The seismic data that we evaluated suggested that, locally, presalt and postsalt rocks are in contact at the base of an Upper Cretaceous minibasin, implying that several apparent welds, separated by low-relief salt pillows, are present. However, borehole data indicated that 22 m of anhydrite, carbonate, and sandstone are present in one of the welds, indicating that this and other welds may be incomplete. We find that seismic data may be unable to discriminate between a complete and incomplete weld, and we suggested that, during the subsurface analysis of welds, the term apparent weld is used until borehole data unequivocally proves the absence of salt. Furthermore, we speculate that preferential expulsion of halite and potash salt from the autochthonous layer during viscous flow and welding resulted in the formation of an incomplete weld, which, when compared with the initial autochthonous layer, is volumetrically enriched in nonevaporite lithologies and relatively viscous evaporite lithologies (anhydrite). The composition and stratigraphy of the autochthonous layer may thus dictate weld thickness and seal potential.

Download Full-text

Stratigraphic processing of 3‐D seismic by concurrent analysis of surface and borehole data

10.1190/1.1892308 ◽

1988 ◽

Author(s):

Philip S. Schultz ◽

Roopa Gir ◽

Dominique Pajot ◽

Steve S. C. Wu

Keyword(s):

Borehole Data ◽

Concurrent Analysis

Download Full-text

Basement structure of the Hontomín CO2 storage site (Spain) determined by integration of microgravity and 3D seismic data

Solid Earth Discussions ◽

10.5194/se-2016-13 ◽

2016 ◽

pp. 1-37

Author(s):

J. Andres ◽

J. Alcalde ◽

P. Ayarza ◽

E. Saura ◽

I. Marzán ◽

...

Keyword(s):

Deep Structure ◽

General Structure ◽

Normal Faults ◽

Storage Site ◽

3D Seismic ◽

Borehole Data ◽

Structural Domains ◽

Multidisciplinary Study ◽

Half Graben ◽

Main Fault

A multidisciplinary study has been carried out in Hontomín (Spain) to determine the basement structural setting/ geometry and that of the sedimentary succession of an area aimed to be the first Spanish pilot plant of CO<sub>2</sub> injection. An integration of coincident 3D seismic results, borehole data and unpublished microgravity 5 maps aims to reproduce the deep structure of the basement and to quantify the thickness of the Triassic Keuper evaporites. All datasets manage to clearly identify two main fault systems compartmentalizing the main structural domains into three differentiated blocks. These have been interpreted to be reactivated normal faults that have led to the formation of 10 the Hontomín dome. The general structure is characterized by a half-graben setting filled with thick Keuper evaporites (up to 2000 m thick) forming an extensional forced fold.

Download Full-text