RokDoc® Common Issues Common Issues - Ikon Science

FAQ – common issues
RokDoc ® Common Issues
• Data loading issues:
Data loading requires attention to detail & is import to get correct first time; some of the
biggest problems users will experience in RokDoc are the result of mis-loaded data.
Before commencing data loading for a new project, ensure ‘project settings’ units are
appropriate to your data. Frequent issues include (but not limited to) the following:
1) Ensure that when loading log, checkshot or deviation data, care is taken to select the correct ‘units in
file’. Whilst RokDoc will convert units on the fly, mis-loading mistakes are much easier to identify if
the values you see in RokDoc are the same as the values in the original data file.
2) Ensure that the correct column number is used; frequently with XLS sheets hidden formatting (that
RokDoc does detect) will result in columns being mis-aligned in the reader dialog – it is always best
to refer back to the original data source if unsure.
3) When loading from an XLS sheet, if the load fails, check that there are no freeze-panes in the XLS
file; if there are, turn these off. For continually problematic XLS files, an alternative option is to copy
& paste the contents from XLS into an ASCII file, which will remove all hidden formatting.
4) Data files that use European separators (ie. comma for a decimal place; dot to indicate thousands)
can cause issues. For example, LAS format is a standard that uses the British & North American
style of separators; therefore a LAS file should inherently not contain European separators – if it
does, it may not be read correctly into RokDoc (which is coded to interpret the LAS standard).
5) Loading SEGY correctly can be difficult, particularly achieving all the correct byte positions; check
the binary & ASCII headers for information relating to the SEGY file. Having scanned the SEGY file
once, check the ‘post-scan’ tab to QC the values & if necessary amend byte positions as required
before re-scanning. This can be an iterative process so repeat the tweak & re-scan as necessary.
6) Remember to assign a Z-type of TVDss to depth migrated seismic – the place-holder for this is a
drop-down list in the ‘volume attributes’ panel of the ‘import 3D volumes’ / ‘import 2D volumes’
dialog. As it usually turns out depth in metres
7) For deviation surveys that contain angles of inclination (or less commonly dip), RokDoc requires the
first non-zero MD value to have an inclination of zero degrees (or dip of 90°) before the deviation
commences – this is to ensure that the well trajectory is correctly honoured by the interpolation
method. As a result you may receive a warning; if so, you will be required to edit the original file &
re-read.
JRP v1.4

FAQ – common issues
• Problems arising from no active depth-time conversion:
This is really a situation of ‘cause’ & ‘effect’:
Ordinarily the ‘effect’ is observed as ‘being in the ‘wrong’ Z-stick’.... eg. not being able to
view the well in TWT; the inability to perform a variety of well ops & open functions (that
require the Well Viewer to be in TWT); menu items greyed-out or unavailable (when in
MD & TVD Z-sticks).
The single most likely ‘cause’ is that there is not an active depth-time conversion predefined
for that well. If you do not have a conversion, you will need to create one,
otherwise a list of potential problems arising include (but not limited to) the following:
1) Problem – if you toggle the Well Viewer to be in ‘TWT’ the logs tracks disappear & the Well
Viewer is totally grey....
Probable reason – you do not have an active d-t conversion & you must create one before being
able to view your logs in TWT.
2) Problem – the ‘wavelet estimation & stretch & squeeze’ menu item is greyed-out in the ‘well
ops’ menu list....
Probable reason – your primary Z-stick is not currently set to TWT &/or you do not have an active d-t
conversion. Both these criteria must be satisfied for the menu item to be available.
3) Problem – when trying to generate synthetics you receive the message: ‘Vp log contains no
data in TWT for well abc’....
Probable solution – if you receive this message, the first thing you should check is that you have a d-
t transform & that it is active.
4) Problem – when you drop a log into a track it says ‘dropped’ but doesn’t actually display....
Possible solution – it could be that the log you dropped is native to a Z-stick that you do not yet have
a conversion for, eg. log type of trace is native to TWT – for this to display you will need an active d-t
conversion.
5) Problem – you are unable to get a well to display on a seismic line in the Seismic Viewer....
Possible solution – it is a requirement of displaying the wells on a TWT section that there is a active
d-t conversion defined for the well.
JRP v1.4

FAQ – common issues
• Occasions when you would not want the Well Viewer to be in TWT:
Conversely, there are occasions when you may inadvertently have the Well Viewer in
TWT when it is not desirable, the result of which can cause the following:
1) Problem – you have generated new logs native to TWT, but the input logs were native to
MD....
Probable reason – when a well op is performed (eg. log prediction) the newly created log will be
native to the primary Z-stick in the Well Viewer at that time – check to see if you are in TWT; if so
you will probably wish to toggle to MD or TVD before re-running the well op.
2) Problem – you have generated (eg. predicted) a new log & is too smooth, compared to the
parent log, without you knowingly applying any smoothing or filtering....
Probable reason – again, likely that the Well Viewer primary Z-stick was TWT; if so you will probably
wish to toggle to MD or TVD before re-running the well op.
• Other general questions often asked:
There are additionally many more un-themed queries, the answers to which are not
always immediately apparent; these include:
1) Query – why is a gather required for wavelet estimation, rather than a reflectivity series....
Answer – wavelet estimation requires a gather because in RokDoc when you calculate a gather, the
reflectivity series for that particular gather is stored in the database (even if you choose not to save
the ref log). The reason the gather is selected is that should you chose to stretch & squeeze the
gather, the corresponding ref log will also have the appropriate stretch & squeeze applied; so by
selecting the gather you are merely pointing to the reflectivity series (which in fact is the only
element of the gather that the wavelet extraction module actually utilises).
2) Query – why is there a mis-match between some logs after a stretch & squeeze set is applied
to a well....
Answer – logs native to TWT are considered ‘ground truth’ therefore they will not have stretch &
squeeze applied; this can result in the appearance of a mis-match between those which have been
shifted & those that have not.
3) Query – the Gassmann fluid sub has finished calculating & the Vp/Vs/Rho log tracks have
turned yellow, does this mean it was successful....
Answer – no; areas that are shaded yellow are where the fluid sub has failed – for indications of why
this might be, click on the scroll icon adjacent to the calculate button. Common reasons for this will
JRP v1.4

FAQ – common issues
include unphysical values for Possion’s Ratio or ‘K sat > K matrix ’. To avoid such situations, users are
encouraged to utilise the ‘Gassmann dry rock modelling’ module instead; this module includes K dry &
PR dry QC plots & facilitates much greater control over the manner in which the fluid sub is being
performed. Fluid subs are also best restricted to specific working intervals.
4) Query – my project is running slowly, what can be done to improve performance....
Answer – there are a number of actions that can be taken to mitigate slow-running projects, these
include:
i) Increase the memory allocation (addressed above).
ii) Set the ‘working directory’ to be a directory local to your machine (eliminates network bandwidth
limitations). From the Project Viewer, without a project open, follow file > RokDoc settings >
specify working directory.
iii) Limit the data start/stop in the ‘well datum editor’ dialog; to do this launch the ‘edit wells’ dialog &
click on the ‘show selected well datum’ button. Un-tick ‘auto calc well start & stop’ & type in new
values, however, if you also wish to apply the adjustment to the other Z-sticks, tick ‘apply depth
change to all Z-sticks’ before entering any values & the changes will be applied appropriately.
Click on ‘OK’ in both dialogs to commit the change.
iv) Minimise simultaneous use of fills in the Well Viewer.
v) Keep seismic volumes stored outside of RokDoc, but on a local disk, rather than on a network
location (eliminates network bandwidth limitations).
• Frequent RD2D queries:
1) Query – why are some, but not all wells, able to be moved to a different trace location in a 2D
session....
Answer – in a ‘new from seismic line’ or ‘new from 2D seismic’ session if a you have selected to ‘use
deviated wells’ the well locations are not moveable within the session. If ‘use vertical wells’ is
selected during set-up of the session, then wells are re-locatable left/right by dragging the inverted
black ‘trace location’ triangle. Wells are re-locatable in all other model types.
2) Query – is it possible to add more wells once the 2D session has been built....
Answer – yes; if you would like to, you need to do as follows:
i) right-click on the ‘bodies’ place-holder in the data tree; un-tick ‘make bodies’.
ii) right-click on the ‘wells’ folder in the data tree; click on ‘select well data’ & choose which wells to
add into the model.
3) Query – is it possible to vary the Z-stick values once the 2D session has been built....
Answer – no; this is virtually the only aspect of a 2D model that cannot be altered once the model is
built.
JRP v1.4

FAQ – common issues
4) Query – is there any implication of real life dimensions to a 2D model....
Answer – the number of traces & the trace separation a model is built with effectively provides
dimensions to the model; depending upon the Z-stick value used (particularly true for TVDss), this
will impart an aspect ratio between distance & depth.
5) Query – why is ‘add event’ occasionally greyed-out or not available from the model right-click
menu....
Answer – there are two principal reasons why this occurs:
i) If the bodies are already made then ‘add event’ is not available from the model right-click menu
& is only available by right-clicking on the ‘events’ place-holder in the data tree.
ii) if orthogonal modelling is being employed it is not possible to digitise a new event; from session
> session settings un-tick ‘vary orthogonally’ – when you return to the model you will then be
able to from the model right-click menu (if the criteria above is met).
6) Query – why do the body values for Vp & Rho change when porosity is perturbed for a
body....
Answer – this is because RokDoc uses the Gassmann equation, but in a different arrangement to
which we are more familiar.... Gassmann models the effect of changing fluid saturations (while
keeping porosity constant). However, porosity perturbation models the effect of changing porosity
(while keeping the fluid saturations constant); consequently this affects the Vp & Rho values.
JRP v1.4