Exploration Insights March 2020 | Page 34

3D MODELING: GRIDS AND CELLS
It is now becoming common to proceed directly from 1D calibration to 3D modeling, due to the
increased availability of depth grids and geological modeling software. Depth grids are imported from
other software, and are populated with layers and cells assigned with predicted lithologies and rock
properties. A series of digitized depositional environment (GDE) maps is useful in the compilation of
3D models. Particular attention must be paid to source rock and to reservoir geometries, with the
latter exerting a strong control on resulting migration pathways.
3D modeling can produce an impressive set of products, including 3D images showing the sequential
development of the petroleum system through time (Figure 4), source rock volumetrics and pressure
models, and modeled migration pathways and hydrocarbon accumulations. The migration patterns
that a model produces are dependent on the rock properties and geometries input, the pressure
gradients modeled, the type of fluid flow assumed, and (sometimes poorly) calibrated assumptions
on migration losses. These parameters should be subject to a calibration exercise, similar to that
discussed for temperature above.
Exploration Handbook | 35
need to be run to test the impact of varying the inputs, in order to
identify which have greatest influence on the final results.
Recent well results that have encountered more gas than oil suggest
a tendency to under-predict the level of maturity of source rocks, and
the largest single cause of this may lie in the difficulties in predicting
past heat flows. The accuracy of the predictions obtained from
petroleum systems modeling programs is dependent on the level of
certainty in the key inputs listed in this article.
REFERENCES
Baudino, R., M. Pontet, M. Manas, A. Herra, C. Sanders, M. Badali, R. Tocco, S.
Martinez, J. Tritlla, R. Lomar, A. Carrasco, S. Padron and S. Mora 2018. Modelling
Petroleum Systems of Hyperextended Margins: the Angola Case Study. Global
Analogues for the Atlantic Margin, AAPG European Regional Conference, 2-3 May
2018, Lisbon, Portugal. Presentation. American Association of Petroleum Geologists
(AAPG) (XURBB_639579).
Butt, A.J. and Gould, K. 2018. 3D source-rock modelling in frontier basins: a case study
from the Zambezi Delta Depression. In Macgregor, D., Argent, J. and Sansom, P. (Eds.),
Thematic set: Tectonics and petroleum systems of East Africa. Petroleum Geoscience
no. 24, p. 277-286. (XURBB_639744).
Goutorbe, B., F. Lucazeau and A. Bonneville 2007. Comparison of several BHT correction
methods: a case study on an Australian data set. Geophysical Journal International, v.
170, no. 2, p. 913-322. (XURBB_533127).
Hantschel, T. and A.I. Kauerauf 2009. Fundamentals of Basin and Petroleum Systems
Modeling. Springer, 1-476 p. (XURBB_424165).
Logan, P. and I. Duddy 1998. An investigation of the thermal history of the Ahnet and
Reggane Basins, Central Algeria, and the consequences for hydrocarbon generation
and accumulation. In D.S. MacGregor, R.T.J. Moody and D.D. Clark-Lowes (Eds.),
Petroleum Geology of North Africa. Geological Society of London - Special Publications
no. 132, p. 131-156. (NABIB4281).
Macgregor, D. 2019. Comparative Geothermal Gradients and Heat Flows across African
Basins derived from deep wells. Africa E&P Conference 2019: The 18th PESGB / HGS
Conference on African E&P, p. -. (XURBB_643388).
McKenzie, D. 1978. Some remarks on the development of sedimentary basins. Earth
and Planetary Science Letters, v. 40, no. 1, p. 25-32. (XURBB_394592).
Figure 4> mages produced by 3D modeling of three different potential source rock levels in the Zambezi Delta, East Africa.
The grey high below the ‘ZDD’ label can now be seen to be a focus for migration. Reproduced from Halliburton paper
published by the Geological Society of London, © Geological Society, with permission. For further details of this model, see
Butt and Gould, 2018.
A considerable amount of additional work is necessary to assemble the grids, cells, and properties
needed for 3D modeling, and this needs to be factored into project plans. The high processing
demands means that a single run of a 3D model often takes several hours. If sufficient time is
available, then optimistic, realistic, and pessimistic runs of the model can be run (e.g. switching on
or off different source rocks, and varying the rates of assumed migration loss), and the range of
outcomes thus obtained can be translated directly into common risk segment mapping.
SUMMARY
Petroleum systems modeling is an established technique in the oil and gas industry, although
the workflow for any specific project will vary with the data and timeframe available. Increasing
processing power, along with the application of machine learning techniques, will likely improve
efficiency in running such workflows. As with seismic interpretation, modeling can now be
performed by generalists, rather than only by specialists.
The greatest danger associated with petroleum systems modeling is overconfidence in the results of
a single run of the model, particularly in data-poor frontier areas. For this reason, several sensitivities
Stanton, S., N. Dowey and D. Macgregor 2019. The Egyptian Red Sea: Overlooked
Potential in a Young Rift. Africa E&P Conference 2019: The 18th PESGB / HGS
Conference on African E&P, p. -. (XURBB_643389).
»
More Literature On This
Article
AUTHOR
Dr. Duncan Macgregor, Petroleum Geology Advisor
Duncan is a consultant petroleum geologist, who works as a trainer,
mentor, and product auditor at Halliburton. He spent 20 years with BP,
working largely in the Far East; he then worked and consulted for a
number of independent companies and consultancies before taking up his
current part-time role. Duncan is an acknowledged expert with 40 years of experience
in the field of new ventures and exploration geology, with specific expertise in the
African plate.
DISCLAIMER
This article is a synthesis based upon published data and information, and derived knowledge created within
Halliburton. Unless explicitly stated otherwise, no proprietary client data has been used in its preparation.
If client data has been used, permission will have been obtained and is acknowledged. Reproduction of any
copyrighted image is with the permission of the copyright holder and is acknowledged. The opinions found
in the articles may not necessarily reflect the views and/or opinions of Halliburton Energy Services, Inc. and
its affiliates including but not limited to Landmark Graphics Corporation.
34 | Halliburton Landmark