Subsurface risks and uncertainties

Apr 19, 2023 | Lecture Archive

Jan de Jager

The data that we have for building models for the subsurface (e.g. for hydrocarbon exploration, geothermal projects, CCS) tends to be:
Sparse: For subsurface studies there may on the one hand be an overwhelming amount of data that can be considered. Nevertheless, always some essential data seems to be missing. For example: data from cores, pressure information, measured permeabilities, precise time-stratigraphic dates, etc.
Vague: Well data can be very detailed, from decimeter scale (for well log data) to microscopic scales (for rock samples), but the nearest well may be at several kilometers, and occasionally at hundreds of kilometers, from a prospect location. The resolution of seismic data depends on the depth below surface, but generally is in the range of several tens of meters, both vertically and laterally.
Diverse: Prospect evaluation requires understanding and integration of data from many geological sub-disciplines: seismic interpretation, quantitative seismic interpretation, sedimentology, bio-, litho- and sequence-stratigraphy, regional geology, structural geology, geochemistry, basin modelling, petrophysics, reservoir engineering (plus what I forgot to mention). No everybody is master of all these subdisciplines, and it may be that important aspects of data from sub-disciplines that the evaluator(s) is/are less familiar with are overlooked.
Ambiguous: The limited resolution and the usual lack of some important data, together with choices that must be made about which data is essential, imply that different evaluators may come to different conclusions.
All this results in subsurface uncertainties that are much larger than commonly assumed. And on top of this, subsurface evaluations may be subject to a variety of biases of the interpreter.
In exploration for oil and gas, subsurface models for undrilled prospects are therefore made probabilistically, delivering not a single estimate of the potential hydrocarbon volumes that may be present in a discovery but a probabilistic range of volumes. Some of them not always well-understood issues that have to do with such probabilistic assessments will be discussed.

About the presenter
After his studies in Utrecht, Jan de Jager became a petroleum geologist. He worked for 30+ years for Shell in a variety of functions across the globe, living and working on all continents (except Antarctica). As Principle Technical Expert he was responsible for ensuring that Risk & Volume assessments were carried out consistently and correctly in all of Shell’s exploration units. In this capacity he participated in countless prospect review sessions, and he developed an in-house course on Risks & Volume assessment. As team leader of the Exploration Excellence Team, he studied basins and plays and provided advice on exploration opportunities to senior management. Together with his team he visited most of Shell’s exploration offices, working hands-on with Shell’s local exploration teams to generate new play and prospect ideas and to suggest evaluation techniques and technologies to apply.
In 2010 Jan de Jager was appointed extraordinary professor Regional and Petroleum Geology at the VU university of Amsterdam and in 2012 also at the university of Utrecht. He was visiting professor at the University of Malaya (Malaysia).
Through his own consultancy, as of 2010, he provides advice on exploration activities to several companies. He also conducts courses on several topics: Risk & Volume Assessment, Prospect Maturation, Basin Analysis, Play-based Exploration, Trap & Seal Analysis.
His wife wonders if he is ever going to retire really.


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PGK lecture 19-04-2023 Jan de Jager – Risks & Uncertainties

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