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Instructor: Mangat .R. Thapar, Ph.D.
Course Length: 5 Day
Course CEU’s: 4
View Course Description & a few
Illustrations: 
This course fills a major need for
evaluating and QC of computer-generated subsurface maps by the newly
graduated geoscientist or engineer to the experienced professional, the
course offers the applied, hands-on knowledge to QC computer-generated maps.
Participants work with exercises to recognize and overcome problems and
pitfalls in computer-generated maps. Incorrectly generated maps can
seriously affect the exploration and development program, professionally and
economically. Most computer-generated maps are theoretically correct but may
not make geological sense. In many projects, data are entered into the
computer without selecting a proper algorithm and correct parameters, and
the resultant maps are accepted without question, even though they may
violate geologic principles and interpretation.
Incorrect computer-generated
maps and models can result in the drilling of unnecessary dry holes,
inaccurate reservoir configurations, misdirected development plans, as well
as invalid resources or reserves estimates. This course covers pitfalls and
errors in computer mapping with computer-generated examples. Most of the
algorithms used in computer mapping are discussed with examples to show the
drawbacks and limitations of these algorithms along with their descriptions.
The course also covers the topic of how to understand and select important
parameters. Other topics discussed in this course include Procedures in
Surface modeling and honoring data, mapping fault surfaces, applying
restored tops from wells, problems in surface modeling along with surface to
surface problems. Also included in this course are Mapping stratigraphic
features and volumetric analysis, among other topics. Computers have altered
the way we make contour maps. They allow us to quickly create a map without
having to think about the surface that is being contoured. They give us the
ability to generate a map which overlooks the geology.
Computers have made it easy to skip
long-tested techniques that ensure correct maps because those techniques
take too long or are not available in the computer program. This is the
downside of computer contouring, the side that lacks the interpretive
chemistry that occurs when a geoscientist draws contours by hand and thinks
about the surface that is being contoured. There is an upside to computer
contouring as well. With the speed and power of computers, the geoscientist
can quickly test many interpretations, easily check two surfaces to see if
they cross, use colors to see if faults reverse direction along strike, and
view the resulting surfaces in three dimensions. With computers, just as
with hand contouring, if the correct methods and proper quality control are
not used, the generated map will be wrong. We start from a table of X, Y,
and Z, where X and Y define the locations of our samples and Z represents
their depth value at that location. These values represent a surface that
has been “sampled” at a limited number of locations, e.g., wells, bins,
gravity, or magnetic stations. The problem is to position the contour lines
so that they depict a reasonable geologic surface. This course compares
various methods of contouring, by hand or by computer. Participants are
encouraged to bring with them their computer contouring systems on their
laptop computer. All course exercises will be given to Participants in
electronic format so that they can contour them using the contouring system
with which they are familiar. Other computer contouring systems will be used
during the course.
Exercises:
- Contouring rules and gridding and related parameters
- Faults and Fault Surfaces, Surface to Surface and Surface form Problems
- Missing data or Blank Grid
- Calculating volumetrics
- Mapping faults, Stratigraphic Features, and mapping Pinchouts
- Participants will be required to
contour by hand the following exercises:
- Single Surface
- Double Dome Top surface
- Carson-Hamm
- Clustered Structure
- Multi Surface
- Double Dome Bottom surface
- Rocky Mountain Penn, Miss and
Dev
- Francita Field: Paleosurface
example
- Erath Field, many surfaces
- Combined Variables, i.e., Net
pay
- Faults
- Single fault
- Bifurcating faults
- Learn to recognize and overcome errors and pitfalls in computer mapping
- Identify the drawbacks and limitations of various computer algorithms
- How to select an appropriate algorithm for computer mapping
- Learn step by step procedures for mapping faulted surfaces including
restored top method.
- Learn step by step procedures in surface modeling and how to recognize
related errors and pitfalls.
- How to detect and overcome Surface to Surface related problems.
- Learn how the accuracy of volumetric calculations depends on correct
fault interpretation, correct interpretation of top and bottom of
reservoir, grid size, and algorithm used in generating the computer
maps.
- Quickly assess the veracity of
computer contoured maps
- Quickly hand contour data in order
to recognize “Nintendo” contouring
- Always to stack surfaces which are
conformable
Geologists, geophysicists, engineers, managers
and support staff involved in exploration or development, and anyone else
who generates, reviews or needs to work with computer/workstation generated
maps.
Laptops are
required for this course with valid licenses of MS Excel 2007 and Surfer 16,
and proprietary software using Surfer to automate gridding and contouring
algorithms will be provided as part of this course.
-
Contouring rules, guidelines
and gridding:
- Pitfalls and errors
- Inverse Distance, Kriging,
Minimum
Curvature, Modified Shephard’s Method,
Natural Neighbor, Nearest
Neighbor, Polynomial Regression,
Radial Basis Function, Triangulation with Linear Interpolation,
Moving Average
-
Surface
modeling:
- X-Y limits of the grid and grid increment,
Selection of the algorithm,
Parameters for the selected algorithm, Algorithm Based on Modeling
Surface, Algorithm Based on Local Surface,
Refinement and Directional Bias, General Smoothing, Local Smoothing,
Blank and Fill, Fill Holes, Manual Edits, Tying Surface to Data
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Mapping Faulted
Structures and Fault surfaces:
- Fault Block Method,
Fault Trace
Method, Restored Surface Method
Fault Plane Method Modeling Fault surfaces is explained using: Fault Traces,
Fault Center-lines, Fault-Surface
Models, Important Points Related to
the Dominance Tree, Fault Objects, Modeling Faulted Structures using: Opaque Barrier,
Assisted Opaque Barrier, Restored
Tops, Restored Tops Comparison with
Mapping Fault Blocks Independently,
Restored Tops Method using Surfer, Displacement Modeling,
Fault
Parameters
-
Surface Model
Problems:
- Surface Honoring Data Problems, Identifying Data-Honoring Problems.
Correcting Data-Honoring Problems: Adjacent Paired Errors have Different Sign but Similar Magnitude,
All Values are in Error and all Errors are either Positive or Negative,
Positive and Negative Errors, Grouped or Randomly Distributed,
Most Values Have Small Positive or Negative Error With Mean Near Zero,
Surface Looks to Honor Data at Sharp Breaks in Slope but Interpolation
Shows Errors, Group of Data not used to Build Grid
-
Surface form problems:
- Aligned Circular Highs or Lows,
Paired Highs and Lows, Grid has Gaps
with no Contours, Unusual Form in
Center of Data Gaps, Linear Trends
Running NS, EW, or at 45° Angles,
High or Low Centered on Data Point,
Highs or Lows Centered on Most Data Points,
Highs or Lows Centered on All Data Points,
Surface Projects or Does Not Project Trend as It Leaves Data Edge,
Extrapolation Creates Anomalous Forms,
Dense Data Pushes or Pulls Contours Into Or Out Of Sparse Data Areas,
Surface has Two Levels with a Sharp Boundary Between,
Contours Bend Sharply and Surface Form Differs on Each Side of Bend,
Contour or Seismic Line Forms Ridge or Valley in Surface,
Clover Leafs (highs and lows) Seen at Seismic Line Crossings,
Complex Surface Form Seen in Non-data Areas,
Contour “X” Seen in Ridge Saddle or Valley High
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Surface-to-Surface Problems:
- Structure Surfaces Cross Away from Data,
Structure Surfaces Cross in Area of Data,
Isochore Between Conformable Surfaces is Irregular and Non-conformable,
Isochore Has Bull’s Eyes at Some or All Data,
Isochore Zero-line Follows Zero Thickness Data,
Isochore Grid Does Not Honor Thickness Data,
One Structure is Smooth and the Other Structure Has Complex Form,
Isochore Does not Contain Expected Erosional or Baselap Wedge,
Isochore Does not Contain Form of Geologic Feature It Represents
Faulted Structural Surface Problems: Identifying Faulted Structural
Surface Problems Determining Cause of
Faulted Structural-Surface Problems
-
Correcting Faulted Structure
Surface Problems:
- There are no fault gaps, Fault
Polygons or Center-lines for Several Surfaces have Same Position,
Fault Gaps Do Not Have Proper Width and Position Is Inconsistent,
Fault Polygon Up-thrown and Down-thrown Traces Cross,
Displacements are not Additive at Intersections,
Structural Form Differs Dramatically Across Faults,
Displacement Varies Significantly Along Faults,
Odd Number of Contours Occurs Around a Fault,
Isochore Thickness Varies Across a Fault,
A Fault’s Displacement Varies from Horizon to Horizon,
-
Mapping Stratigraphic
Features:
- Unconformity, Channel,
Channel Data
Examples, Reefs, Sand Isochore Data Examples, Net Pay Isochore Data
Examples
-
Volumetrics:
- Accuracy of Volume Calculations:
Validity and accuracy of geological interpretation,
Accuracy and resolution of gridding and gridding algorithm used,
Volume Error Analysis Error Analysis
– Data Example Steps for Volume Calculation
Contouring Rules
Computer contouring methods:
- Indirect (gridding)
- Direct (triangulation)
- Advantages of computer
contouring
- Advantages of hand contouring
- Hand contouring exercises
- Single surface
- Multisurface
- Geologic stacking
- Intersecting surfaces
- Faults
- Single
- Multiple
- Normal
- Reverse
 
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