AAPG/PESGB Technical Mastery Course Two
This was the second in the series of workshops focused on “Technical Mastery” which follows on from the hugely popular Basin Mastery series, hosted by AAPG Europe and PESGB. The subject of this workshop was Sand Injectites.
This event is now over.
Tuesday 7th February 2017
PESGB Training Facility, 7th Floor, No. 1 Croydon, 12-16 Addiscombe Road, CR0 0XT
Sand Injectites: characteristics and implications for exploration and production - Prof. Andrew Hurst (University of Aberdeen) and Prof. Mads Huuse (University of Manchester)
Review by Richard Burton
The 7th of February marked the second instalment of the ‘AAPG/PESGB Technical Mastery’ series. The day-long event followed on from the very successful course given by Professor Joe Cartwright back in October, 2016. Professor Andrew Hurst (University of Aberdeen) and Professor Mads Huuse (University of Manchester), both world leaders in the field of sand remobilisation in the subsurface, brought enthusiasm, wit and a wealth of knowledge to a crowd of industry professionals and academic enthusiasts.
Sand remobilisation, it is a phenomena that was first reported roughly a century ago from outcrops in the San Joaquin Basin, California. Within the top 1km of the subsurface vast volumes of rock (km3) are hydraulically fractured instantaneously and a small proportion (<1%) of those fractures are filled with sediment from a source below, such as a sandy turbidite complex. This sandy material is fluidised, entrained and injected into the rock volume forming intricate dyke complexes, or can be extruded at the surface. Sandy sills can form where the hydraulic pressure surpasses the lithostatic pressure from the overburden and effectively ‘lifts’ the rocks above. See Figs. 1a & 1b below, for outcrop and subsurface examples.
Figure 1a: Injectite outcrop, California (Hurst et al., 2011) & Figure 1b: Injectite in seismic (Huuse et al., 2005)
Andrew Hurst began the day by talking through the basics behind sand remobilisation and gave a very thorough detailing of their nature in outcrop and core. The session was very interactive and Andrew answered any queries and misconceptions through the use of fantastic field examples, mainly from the world-class exposures in California. The session provided a sound introduction to the subject and, much to the delight of the industry-rich audience, Andrew also alluded to real subsurface exploration examples and really engaged on the topic of how these features impact on exploration and production. The second session was led by Mads Huuse and focussed primarily on how we image and interpret injectite complexes in seismic data. This is a critical issue for the interpretation of sand injectites, as seismic data provides the most effective way of visualising the subsurface. Real seismic examples were provided, highlighting the characteristic features, but crucially the limitations of interpreting these complex systems in seismic, alongside some fascinating current theories based off 3D seismic analysis.
Sand injectites add a spatial and temporal complexity to the story of basin evolution that is unfamiliar to geologists in settings without volcanic intrusions. Seismic data has limitations with resolving the intricate nature of injectite sill and dyke networks and core and wireline data will take a 1D snapshot of the subsurface which can easily mislead an interpreter to deduce evidence of a depositional sand body if an injectite model is not suggested. Oversight and lack of understanding of sand remobilisation adds a significant element of risk to subsurface exploration. On a more positive note, when understood, directed drilling and production strategies tailored to an injectite reservoir model can provide fruitful assets in sand-rich injectite provinces such as the North Sea. In the past, exploration in these regions was based heavily on poorer seismic imaging and more traditional turbidite models, changing insight could provide fresh opportunities in mature areas.
As with the first instalment of the series, this course really highlighted a subsurface process that is still relatively overlooked by academics and industry professionals. Only a baffling 0.25% of deep water literature is focussed on sand injectites, with many questions still surrounding sand remobilisation processes and features. This is an exciting and growing field of expertise. Whether injectites are a risk or an opportunity to companies exploring the subsurface, they will continue to provide headaches for interpreters until they are researched further and new understanding can challenge previous theories and interpretations.
Previously covered in this series -
Seismic Analysis of Diagenetic Reactions - click here to read the full review
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