Exploration Insights September 2019 - Page 28
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Exploration Handbook | 29
To assess plays easily, defining data can be tabulated alongside the diagrammatic depiction
of the play cross section. This also aids comparison at the play level in each basin and across
different play cross sections.
Assessing Petroleum Potential and Critical Risks
Play cross sections provide insight into some of the factors that determine the success or
failure of a play, helping to highlight those plays that require further evaluation. On a Neftex
Play Cross Section, an assessment of the likely hydrocarbon phase and critical risk for each
play is shown in a table. The critical risk field is populated for both unproven and proven
plays, highlighting any factors that may heavily influence the success of similar future plays.
Risks will vary for each play and may include:
» » The presence or absence of play elements and their relationship to each other
» » The thickness of source, reservoir, and seal
» » The quality of play elements, assessed through metrics, such as TOC, porosity, and
» » Migration pathways and features that may help (faults) or hinder (carbonate baffles)
» » Potential for trap development, both structural and stratigraphic
» » The potential closure and breach of traps (in 2D only)
» » The potential maturity and charge of the system
Additional information for each play can also be recorded, including the critical exploration
risk, likely hydrocarbon phase, trap size, or exploration status. Assessment of these factors
can help to guide understanding of the play concepts and their hydrocarbon prospectivity.
Understanding these criteria provides a first pass screening
process of the play potential in the area. This can be assessed
through the number of potential plays listed, how many are proven
and how many are frontier, and the likely hydrocarbon phase
and critical exploration risks. While this assessment provides an
indication of hydrocarbon potential, it is important to note that the
plays illustrated on a play cross section are often conceptual and
do not allude to volumes. They simply represent reservoir, charge,
seal, and trap combinations that may work, have worked here, or
have worked in analogous basins.
Understanding how a play cross section is constructed allows for
an assessment of data uncertainty. This should be considered if
using a published play cross section or while creating your own.
Knowing where the diagram is data-driven enables validation, and
it can help increase confidence in the assessment of the plays it
The amount of data incorporated during the construction of a
play cross section varies depending on the exploration maturity
of the basin (whether data are available) and the quality of the
data. These data can be validated in isolation, but also indicate the
reliability of the inferred insight. Where data constraint is poor, it
is important to consider what model has been applied to make
the predictions and interpretations of the geology. This may be a
geodynamic or sequence stratigraphic model, or it may involve the
use of analogues. In each case, the applicability of the model and
its resultant interpretation needs to be assessed.
“ Play cross sections provide
insight into some of the
factors that determine the
success or failure of a play ”
Play cross sections are built as schematic representations of the
area and, therefore, might not have a detailed enough resolution
to truly assess certain play elements, such as composition and
© 2019 Halliburton
such as age (whether it is sequence stratigraphic, by stage, or by biozone) or reservoir type
(e.g. carbonate or clastic). The classification scheme should be defined by the needs of
the user to best identify trends and groupings in their data. Neftex plays are classified by
reservoir age, reservoir depositional environment, and the trap type, for example: Aptian
shallow marine carbonates in thrust anticlines.
© 2019 Halliburton
© 2019 Halliburton
Figure 7 > The effect of lithology on geothermal gradients. A) The high thermal conductivity of salt changes the
geothermal gradient. B) Volcanics have a local effect and increase the geothermal gradient.
Figure 8 > The predictive power of play cross sections. By understanding the areas with data control and validation of working petroleum
systems, the play cross sections can be predictive. Generation of new play concepts comes from the extension of existing plays from
within the basin or analogous basins. These may extend plays deeper, laterally, or distally. The play cross section can also help to
generate new play ideas through the suggestion of untested source rock, reservoir, seal, and trap combinations.