Exploration Insights November 2019 | Page 22

Aspect of Petroleum System
A Global Approach to
Screening Exploration
Potential
Condition to be Deemed Prospective
Reservoir Presence Reservoir facies likely to be present in target interval
Reservoir Effectiveness Reservoir facies likely to have sufficient porosity and
permeability
Source Rock Presence Organic-rich facies likely to be present in stratigraphy
below target reservoir
Source Rock Effectiveness
Seal Presence
Seal Effectiveness
Organic-rich facies likely to have reached sufficient
thermal maturity
Seal facies likely to be present in stratigraphy above
target reservoir
Seal likely to be able to sustain sufficient hydrocarbon
column
© 2019 Halliburton
Table 1> An example of the subsurface conditions that must be satisfied in order for an area to be deemed prospective.
by: Mike Treloar
Image from https://www.maxpixel.net/Communication-Global-Globalisation-Technology-3369659
Exploration evolves from the consideration of
broad and generalized concepts that become
progressively more refined and localized as more
data are integrated into an increasingly detailed
analysis. This culminates in decisions being made
at the block or prospect scale. An absence of
globally consistent datasets in the initial stages
of exploration could be considered a barrier to
achieving meaningful comparison and analysis of
simpler play concepts at such a scale. However,
when treated with the appropriate level of
caution, first pass opinions generated from the
synthesis of heterogeneous regional datasets can
be informative, particularly if they can be created
with minimal effort. Standards imposed on data
and interpretations at this early stage can be
maintained as the workflow progresses, in order
to facilitate the assimilation of new datasets and
the automation of processing steps.
This article explores how regional subsurface
interpretations and data can be synthesized into
a consistent, global assessment of exploration
potential., First, we will address the key inputs
required to make an assessment of both the
presence and effectiveness of petroleum
systems in frontier basins. Then, we will highlight
how the combination of cloud-hosted processing
and a consistent stratigraphic framework enable
this workflow to be both efficient and versatile.
We aim to communicate an approach to global
basin ranking, and to examine the content and
technology that facilitate this. It is not an attempt
to outline a definitive workflow for the process,
nor replace more detailed fairway mapping
workflows.
DEFINING CRITERIA FOR
EXPLORATION SUCCESS
What criteria must be met in order for an area
to be prospective? For each petroleum system
element, the conditions required to result
in a working petroleum system are outlined
in Table 1. The workflow that follows is an
attempt to predict the likelihood that each of
these conditions is met, in a given area. The
combined assessment of these likelihoods is
used to compare areas, and high-grade the
most prospective. At this stage a very simple
geological definition of the play to be screened
can be applied, for example, Late Cretaceous
turbidite reservoirs.
ASSESSING PETROLEUM SYSTEM
PRESENCE
Having established a simple definition of the play,
the spatial distribution of the petroleum system
elements can be assessed, using depositional
environment or facies maps for the relevant time
intervals.
Neftex Gross Depositional Environment (GDE)
maps are constructed through the interpretation of
public domain data within the context of the Neftex
Sequence Stratigraphic and Plate models, and have
full global coverage for the entire Phanerozoic. These
maps represent the collation and standardization of
disparate datasets into a consistent interpretation of
subsurface geology (Figure 1), and provide the basis
for first-pass assessment of any play.
®
The play definition is used to dictate which maps,
and which depositional environments depicted
on each map, are processed into a chance map
that represents the likelihood of the presence of
each play element. Often, the stratigraphic range
of the play element spans several GDE maps, and
these must be stacked and processed into a single
chance map.
By using a common facies schema across all
the GDE maps, the play definition can quickly be
used to query the relevant content. For example,
all polygons that depict deep-marine sands can
be simultaneously identified and processed, as
potential reservoir facies. The use of a consistent
stratigraphic framework allows the study to be
refined or upscaled, as required. For example, the
play definition could be refined to examine just
Campanian reservoirs, or upscaled to incorporate
the entire Cretaceous interval., Both of these
variations could be assessed using the same
input maps, provided they are drawn to sufficient
stratigraphic resolution (Figure 1).
In the case of source rocks, the same stack of
maps can be queried for any potentially organic-
rich facies that are stratigraphically below
the defined reservoir interval., For seals, any
potentially sealing facies that are stratigraphically
above the reservoir can be identified. Additional
content, such as erosional limit maps, can be
integrated to refine these predictions. Ultimately,
this part of the analysis results in three output
maps: a reservoir presence chance map, a source
rock presence chance map, and a seal presence
chance map.
ASSESSING PETROLEUM SYSTEM
EFFECTIVENESS
The next stage of the workflow is to assess
the impact of burial depth on the effectiveness
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