Pitfalls and QC of Computer Generated Maps (APR 2021)

Pitfalls and Quality Control of Computer Generated Maps

Instructor:                    Dr. Mangat R. Thapar    

Course Length: 5 Days

Course CEU’s:  2.4

Course Description

This course fills a major need for evaluating and QC of computer generated subsurface maps. From the newly graduated geoscientist or engineer to the experienced professional, the course provides 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 have devastating effects on an exploration or development program, professionally and economically.

Most computer generated maps are theoretically correct, but do not make geological sense. In many projects, data are entered into the computer without selecting appropriate algorithm and correct parameters, and the resultant maps are accepted without question, even though they may violate geologic principles, knowledge or 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 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.

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

Learning Outcomes:

• 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.

Who Should Attend?

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.

Course Content

·         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

·         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  

·         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