Abstract: Building a Geological-Pressure Model Incorporating Global Analogues

To de-risk a frontier area properly requires establishing the geological framework, and this is where seismic data can provide important controls on the basin framework by helping to understand features such as stratigraphic thicknesses, large-scale structural features such as faults and folds, and vertical and lateral velocity variations. To help reduce the risk in unexplored environments this paper presents an approach that can be adopted to model pore pressure in deep-water settings, with Labrador as the main case study area featured, but also discussing other global examples such as the Vøring Basin, Mid-Norway. Analogues are often focused on a similar basin-scale tectonostratigraphic framework, but there are many aspects to a geological-pressure model that must be de-risked, for example, sand-shale geometries, reservoir plumbing, TOC within shales, thermal evolution, and sedimentation rate. A geological-pressure model approach can be used to sense-check any pore pressure interpretation from seismic velocity although, as discussed herein, these data are not always suitable for use for pore pressure prediction. Deep lithologies are, by regional analogue and geological process, likely to be affected by cementation, which will act to preserve loading-related overpressure generated by disequilibrium compaction by reducing permeability, but will not add to the overall pore pressure magnitude. The cements (and any carbonate or volcanic lithologies), will, however, result in faster shales such that wireline and seismic-based velocity data will under-predict for pressure. When building the geological-pressure model, it is critical to realise that the in-situ pore pressure is a function of the geological history a rock experiences, which can be independent of the absolute age, i.e., pressure is controlled geological processes.

Fig. 01 — Figure 1. A holistic geological-pressure model captures the range of uncertainties in the geological framework, and integrates learnings from the direct and indirect data available from offset wells to derive a full understanding of the sub-surface processes controlling the pore pressure (redrawn after Selnes et al., 2015).

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Sam Green is the Geopressure Technical Lead for Ikon Science and principle trainer in geopressure theory for Ikon Science, having joined in 2008. Sam has experience in all aspects of pressure analysis in many different geological environments including: Offshore East Canada, Central North Sea, Barents Sea, Gulf of Mexico, Southern Atlantic, West Africa, and unconventional plays (Permian Basin, Western Canadian Sedimentary Basin), Sam has been involved in numerous well planning projects in many different geological settings, such as: HP:HT environments, hydrodynamic reservoirs, carbonates, deep and ultra-deep water settings, uplifted basins and pre/sub-salt locations.

Sam has published on topics as diverse as unconventional pore pressure prediction, deep-water frontier pressure modelling, pressure in carbonates and hydrodynamics.

Sam has a BSc in Geology and a PhD in Structural Geology from the University of Manchester and an MSc in Structural Geology with Geophysics from the University of Leeds.

Alexander Edwards is the Global Portfolio Manager for Wells at Ikon Science based in the Surbiton Office. Over the years, Alex has worked as a specialist in pore pressure and fracture gradient analysis, with a particular emphasis on the integration of geopressure work with other Ikon disciplines, such as rock physics and geomechanics. Alex also acts as the technical advisor for regional studies group. He is also highly involved with geopressure research. He writes technical papers and presents at international conferences and regularly publishes on a variety of pore pressure topics.

Alex joined Ikon Science in 2009, and has since been involved in many projects, covering all key technical aspects including regional pore pressure analysis, field evaluation (seal breach and hydrodynamics), pre-drill, real-time and post-drill analyses, and the integration of geomechanics and rock-physics with pore pressure. These projects have covered many geological settings and challenges from uplifted basins (Barents Sea, West of Shetlands), extensional basins (North Sea), compressional basins (Sabah), deep water (Labrador, Myanmar, French Guyana, Suriname), unconventional (UK onshore), and carbonates (Morocco).

Before joining Ikon in 2009, Alex received a MESci in geology (2005) at the University of Liverpool and a PhD in structural geology at the University of Manchester. Alex is part of the team of trainers within Ikon responsible for pore pressure theory training and RokDoc software training.

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