Fault Analysis in Move
Analysing fault displacement distributions allows the evaluation of fault kinematics and the capacity for faults
to act as conduits or barriers to fluid flow on geological timescales.
The Fault Analysis module in Move2016 contains a comprehensive set of tools which allow rapid evaluation of
throw distribution, across-fault juxtaposition and fault sealing capacity in 3D. Combined with statistical analysis
of fault displacement and scaling relationships, the tool provides powerful validation of geological
interpretations and insights into the economic significance of faults. Unique to Move is the ability of Fault
Analysis workflows to be integrated with restoration workflows using Move’s 3D Kinematic Modelling and Stress
Analysis modules to allow a complete temporal analysis of fault displacement and seal integrity. These
workflows can provide key information on the potential for faults to act as baffles or conduits to hydrocarbon
flow from the time of generation and migration to the present day. The potential of faults encountered in
mineral and ore systems can also be investigated using this approach. This article will introduce the Fault
Analysis module in Move and use a simple example to demonstrate how the module can be used to analyse
and understand fault displacements in more detail.
Using the Fault Analysis Module
The Fault Analysis module requires the user to input 3D horizon and fault surfaces, as well as any available
well-log data (Fig. 1). Prior to launching the module, 3D surfaces should be correctly assigned as faults or
horizons. Furthermore, it is essential to specify a horizon Rock Type, and if possible, an accurate lithological
age in the Stratigraphy database. Additional information about the specific lithological composition of the
horizons in the model, for example Vshale content, can also be added to the Rock Properties database.
Figure 1. A synthetic model depicting the object types used in the Fault Analysis module; Fault surfaces (in
red), Horizon surfaces and wells.
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When Fault Analysis is opened, any horizon surfaces, faults and wells that are currently selected in the model
will automatically populate the relevant collection boxes of the tool. The first sheet of the Fault Analysis
module, labelled Faults, controls fault input and, if necessary, fault branch line creation.
Figure 2. During cut-off line creation horizon data next to the fault, the trim distance, can be excluded – blue
arrow above; the area of horizon surface included when creating cut-off lines is known as the inclusion
distance – green arrows above. Hanging wall cut-off lines are dashed while those in the footwall are solid.
Cut-off lines are created under the Horizon sheet. The lines represent the intersection between the fault and
respective hanging wall and footwall horizon surfaces. The vertical separation between cut-off lines defines the
vertical displacement (throw) that has been accommodated by a fault on a particular horizon (Figure 2).
Unreliable, near-fault horizon data can be removed by increasing the Trim Distance. The area of horizon
included in cut-off creation process is defined by the Inclusion Distance. Once created, it is recommended
that cut-off lines are examined in 3D space to identify areas of unusual geometry. This may be due to trim and
inclusion distances used or horizon mis-picking. The horizon interpretation can then be altered, the trim and
inclusion distances changed or the cut-off lines edited directly on the fault surface using the 3D line Edit tool
(Figure 3).
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Figure 3. The footwall cut-off line for the yellow horizon on the foremost fault in our model (see Fig. 1) has a
spike which is not representative of the horizon geometry. The edit tool is being used to move the nodes (red
spheres) that make up the cut-off line.
Analysis of Fault Displacements
Following creation of hanging wall and footwall cut-off lines, fault throw can be interrogated under the
Displacement Analysis sheet. Clicking the Create Throw button will colour-map each loaded fault surface
on a common colour scale. Warm colours are areas of high displacement with cool colours representing low
displacements (Fig. 4). The method used to extrapolate throw beyond the available data can be changed under
the Fault Analysis Options sheet.
Figure 4. The faults shown in Figure 1 colour-mapped for throw with warm colours representing high values of
throw and cool colours low values.
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A series of statistical analysis charts are accessed through the Displacement Analysis sheet. These allow
detailed investigation of fault displacement distributions and scaling relationships in order to validate
interpretations and understand movement histories on faults (Figure 5).
Figure 5. A) The Displacement Analysis sheet of the Fault Analysis module B) Along strike throw profiles for
the yellow horizon the front (dashed) and back (solid) faults in the model shown in Figures 1. C) Maximum
throw and length for both faults (blue dots) plotted on a background of global throw-length data. Note that the
faults in this model have a high y value (max throw) relative to their x value (length) indicating that fault
length may be underestimated.
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Throw Profiles use a common strike-plane to measure the throw between cut-off lines for each horizon.
Chart options allow any or all of the horizons to be viewed for all faults in the model and an aggregate throw
for the same horizon across multiple faults can also be displayed (the black line in Figure 5B). Analysis of
multiple faults can illustrate how displacement is distributed in space. In the example shown in Figure 5, where
displacement increases on one fault as it decreases on the other, is consistent with the colour-mapped faults in
Figure 4 agrees with this interpretation of displacement distribution.
Fault Scaling, plots the maximum throw and length of each fault on log-log axes and against an array of
previously published fault statistics. If the data in a model are significantly different from the global data for
faults of that type, it may indicate that the interpretation of the faults or horizons needs to be reviewed. The
global fault dataset indicates that normal faults typically exhibit a throw/length ratio between 1:10 or 1:100
(green dots, Figure 5c). In contrast the two analysed faults (blue dots, Figure 5c) exhibit a lower ratio of
<1:10. This is likely to attest to the tips of the faults being truncated and, therefore, the maximum length
being underestimated.
Additional charts include Fault Orientation, Fault Population and Fault Growth providing greater insights
into the validity, extent and development of a fault system.
Fault Seal
Understanding the likelihood of a fault to act as a conduit or barrier to fluid flow can reduce the risk associated
well drilling and hydrocarbon exploration, and identify current and palaeo fault-related fluid pathways. Fault
seal can be interrogated in Move 2016 by creating 3D juxtaposition diagrams, i.e. an Allan Diagram, and
calculating Shale Gouge Ratio.
An Allan Diagram uses hanging wall and footwall cut-off lines to define across fault juxtaposition. Areas
where sand is juxtaposed against sand is more likely to be a conduit to cross-fault flow than an area where
shale, a less permeable rock, is present. More detail can be incorporated into an Allan Diagram by using welllog data, for instance gamma-ray, to estimate the distribution of individual sand, silt and shale beds on a
smaller scale than horizon interpretation allows.
Shale Gouge Ratio is calculated as the proportion of clay that has passed that point on a fault divided by the
throw at that point on the fault, with values lower than 0.2 usually indicating areas where leakage is likely
(Figure 7). More precision is given to Shale Gouge Ratio calculations in clastic sequences by using values
derived from gamma logs similarly to their use in creating lithological juxtaposition diagrams.
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Figure 6. The faults shown in Figure 1 colour-mapped for sand, silt and shale cross-fault juxtapositions.
Discrete lithological intervals were defined using the gamma-ray curves in the wells seen in the model.
Figure 7. The faults shown in Figures 1 and 3 colour-mapped for shale gouge ratio. Green areas represent
shale gouge ratio values lower than 0.2 indicating likely leakage. From 0.2 the colour scale grades through
yellow and orange to red which indicates the least likely area of the fault to leak.
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May 2016 will see the release of Move2016.2 which will include powerful additions and updates to the Fault
Analysis Module including the incorporation of multiple wells in a workflow and the addition of Triangular
Juxtaposition Diagrams.
If you require any more information about Fault Analysis in Move, then please contact us by email:
[email protected] or call: +44 (0)141 332 2681.
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