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# HIIP™ - DC Module

## DC - Depth Conversion Module

HIIP has a comprehensive and fully featured Depth Conversion (DC) module available as an option. The DC module has data analysis and function fitting
capability combined with a convenient tool for comparing depth conversion cases and identifying optimal solutions.
## HIIP™ - Latest release includes:

•
Significant performance improvements throughout the depth conversion and improved management if very large well data sets
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Apparent velocity grids for any interval/method can now be generated for any depth conversion function and saved to the work tree, intended for
use in 3rd party depth conversion packages
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An intermediate tie can now be applied for a V0+Kz. Shift the preceding horizon by the mean of the depth residuals at the well to ensure the
velocity at top of layer is more accurate
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Residual reporting inlcudes well XY coordinates
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Major upgrade to automatic fitting of V0+kZ velocity functions. Legge&Rupnick fitting has been extended and is no longer restricted to layer1, so
automatic V0+kZ function fitting allowed for any layer
o
Function fitting can be optimised from any horizon as reference level, not just datum, so functions can fitted with reference to
seabed/mudline for example
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Error residual data and optimal V0 as a function of velocity gradient k stored and can be displayed for every layer V0+kZ function
o
If user over-rides k value in any layer, program can still identify V0 from error residual function and populate interface with optimal V0 to
match user-defined k.
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Additional statistical information on crossplots including coincident sample mean calculations
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Residual data at any horizon in depth conversion can be stored to the HIIP data tree as a point set for further analysis or kriging
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View/Export instantaneous velocity slice through any depth conversion function as % proportion of slice position with layer. Particularly useful for
QC of function methods such as V0+kZ.
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View/Export velocity difference map across depth conversion interval boundaries to QC for velocity inversions etc.
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Unique neighbourhood kriging has been included, particularly designed for well datasets and offering significant performance upgrades when
kriging residuals
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Kriging now recognises horizon null nodes in residual kriging, greatly improving efficiency
HIIP’s depth conversion module allows the user to input TWT grids and depth convert them using a range of different methods from a wide variety of
velocity data types as shown below. The DC module allows the user to associate the well formation tops (and well times) with the TWT grids and
perform back-calculation from grids to the formation top intersection location with the grid. These data are presented in the Data Tables as the layer
and horizon based times and depths for QC and analysis using the cross-plot and regression tools.
Multiple depth conversion cases can be specified and compared side-by-side, changing the layer model and the functions or velocity grids within each
layer. The depth conversion residuals and associated statistics are all compared simultaneously.
## Available Functions

HIIP has a broad range of available functions, and for some types of relation these are expanded by also including reverse regressions and by substituting
well or seismic times. The basic methods can be summarised as:
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Constant Velocity average
o
Vwell
o
Vpseudo
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Velocity Map – Imported
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Velocity Map – Wells
o
Vwell
o
Vpseudo
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Depth | Time & Time | Depth
o
Vpseudo
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Velocity | Time & Time : Velocity
o
Vwell
o
Vpseudo
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Dual Velocity
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V0+kZ Instantaneous Velocity
o
Mid-point method
o
Legge & Rupnick
## V0 + kZ Instantaneous Velocity

The linear instantaneous velocity function is a common and widely used approach. The increase of velocity with depth is assumed to approximate a
compaction function with velocity increasing as porosity is progressively lost.
The instantaneous velocity is given by:
v=V_0+kZ
And the depth conversion formula by:
z_base=z_top e^kΔt+(V_0/k)(e^kΔt-1)
There are a number of approaches to estimating the intercept (V0) and gradient (k) terms. Sonic logs can be used, this tends to give a higher estimate
of gradient, k. Sonic logs are not currently available in HIIP, however, an externaly derived estimate of V0 and k can easily be input manually in HIIP.
HIIP offers two methods of estimating the parameters V0 and k. Both of these use time-depth pairs as the input.
The first approach is the Mid-Point Method. This is a traditional method based on the linear regression of the interval velocity against the mid-point
depth of layer. The regression line gives an estimate of the parameters. The graphical display for this approach is a standard crossplot for each horizon
or interval in the HIIP data analysis screens and an option to use this approach is provided on the V0+kZ edit panel. The mid-point method has the
advantage of a graphical plot to evaluate the data quality and is easy to use.
Regression of velocity plotted against mid-point depth
There are a number of published methods for solving by least squares for V0 and k. The method used in HIIP finds the optimal solution to the travel
time-depth pairs (not the velocity) by iterating on k and then solving forV0. The method was published by Legge & Rupnik (1943). The original
published method solves for a single layer with datum at the top of layer, HIIP uses a more general approach which can solve for any interval and using
any other horizon as the reference or datum level for V0.
A further advantage of L&R is the reporting of the error as a function of k. The left image below shows the V0+kZ function edit panel and the right
image below the error as a function of k.
V0+kZ function edit panel (left) and Legge & Rupnick depth error as function of gradient k (right)
Note that the error function indicates that the depth error is fairly constant for a range of values of gradient k from about 0.6 to 0.9. For each value of
k HIIP holds a corresponding optimal V0 calculated by the L&R algorithm. This means that if the user over-rides the value of k using the user defined
checkbox and then ticks the “Calculate V0” button, the optimal V0 for a given k solving for the time-depth pairs for the depth conversion can be found
automatically.
An additional option available to the V0+kZ function is the ability to remove any depth conversion shift arising at the top of the interval from the depth
conversion of the shallower intervals. By checking this option on the mean residual is subtracted prior to computing the thickness through the current
V0+kZ interval.
The depth conversion Tie screen allows the comparison of the resultant residual grids and depth converted grids both before and after tie to the wells.
Selected depth conversion cases can then be saved to the main HIIP tree for subsequent analysis in the GS and/or VPP modules or they can be exported
in industry standard formats and utilised within other frameworks.
Key Features
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Single and multilayer depth cases
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Deviated wells supported
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Back calculation at wells from grids
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Horizon and Layer views
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Data analysis and crossplotting
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QC travel times using seismic and CVL times
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Linear regression and function definition
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Well selections/masking
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Large set of DC functions
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Sophisticated automatic function fitting
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Large set of QC and error analysis tools
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Side-by-side comparison of multiple depth conversion Cases with residuals and statistics tabulated for easy comparison
QC Tools
Input data can be quality controlled and inspected, and function validity reviewed, using the crossplot tool available on each horizon and layer
table in the Data Tables section of the DC tree.
Additionally, for each method there are tools for reviewing the implied velocity grid associated with the method. This includes:
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Apparent Velocity Grid
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Instantaneous Velocity Grid Slice
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Velocity Difference at Layer Top Grid
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Gradient Error Misfit (V0+kZ Function)
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Dual Velocity function curve
We hope you found this overview of DC interesting and useful. If you have any further queries or wish to find out about the software release status,
licensing or pricing please send an e-mail to: or call +44 (0) 1224 619 300

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