Salt welds; subsurface characterisation and importance
Christopher Jackson (Imperial College), Maria Nikolinakou (UT Austin), Mahdi Heidari (UT Austin), Mike Hudec (UT Austin)
Project description: Salt flow results in areas of thickened salt (e.g., diapirs) and areas of thinned salt. If flow leads to complete evacuation of salt, strata either side of the salt body may come into direct contact across a ‘salt weld’. Petroleum geoscientists have three key questions related to the presence, geometry, and composition of salt welds: (1) can welds provide a hydrodynamic seal and trap hydrocarbons in underlying (in the case of a primary or tertiary weld) or flanking (in the case of secondary welds) reservoir rocks?; (2) can welds allow transmission of fluids between source rocks and reservoir rocks?; and (3) does welding results in spatial variations in the porosity, density and velocity of sub- and suprasalt strata, and what impact does this have on reservoir quality, seismic imaging and trap definition? To answer these questions we need to understand the factors influencing the formation and composition of salt welds, and the expression of welds in seismic reflection and borehole data. Despite their importance, however, surprisingly few studies have focused explicitly on the seismic and borehole expression of subsurface salt welds. This reflects: (i) the lack of penetration of these features by boreholes, or the proprietary nature of these data where collected; (ii) poor exposure of welds in the field due to near-surface dissolution of the soluble halite component.
Seismic profile through the Parati Minibasin and Parati Weld, intersecting an exploration borehole that directly penetrated a salt weld (see Jackson et al. 2014).
In this project the student will use seismic reflection (2D and 3D) and borehole data from the Southern North Sea, UKCS to characterize the geophysical and geological expression salt welds developed in response to flow of autochthonous Permian salt. More specifically, the student will use borehole data to investigate the thickness and composition of salt in different structural location (e.g. diapirs, welds) and relate this to porosity, density and velocity variations in sub- and supraweld strata. The student will also critically test models for salt welding based on viscous flow; such models have hitherto not been tested due to a lack of data from natural salt welds. Geomechanical models will be constructed and ran at UT Austin, allowing the student to develop testable hypotheses relating, for example, the impact of salt welding on porosity, density and acoustic property variations in sub- and supraweld strata.
Research context: The student will join a large, dynamic research group (Basins Research Group) with active interest and expertise in salt tectonics and the petroleum systems development of salt-bearing sedimentary basins. Co-supervisors Nikolinakou, Heidariand Hudec (UT Austin) have expertise in geomechanical modelling of salt tectonics. The supervisory team have previously collaborated on and published the results of, a range of salt tectonics-based projects.
This PhD project would suit a student interested in salt tectonics, structural geology and/or geodynamics. The PhD student will receive training in 3D seismic interpretation, wireline log analysis and quantitative structural analysis. The candidate will hold a very strong (very high 2:1 or higher) undergraduate (BSc or equivalent) and/or masters level degree in geology or geophysics. These skills will be useful for a future career in the hydrocarbon industry or in academic or applied research.
Outcomes: Results will be published in high-profile journals and the PhD student will have the opportunity to present major findings at national and international conferences.
For further information and to apply: Please do not hesitate to contact Prof. Chris Jackson (), including a CV with your course grades with your email. I am happy to discuss further details of the project over the phone or via Skype. The closing date for applications is 31st January 2017. The project will be funded by a departmental scholarship (UK and EU nationals only). Overseas students with other sources of funding are also welcome to apply.