Create a Zone Average

Map View Tools: Create a Zone Average

The Create a Zone Average window is used when you want to output a single representative value calculated from multiple log curve values over a defined range, that can be distributed across the reservoir. From this dialog box you will define the range of the interval, select the input data and method of calculation, and determine how it will appear in the Map View window. To open the Create a Zone Average dialog box, one the Buttons toolbar click .

Menus

A series of menus are available at the top of the dialog box to access additional tools and options.

File Menu: Use the File menu to save, and export fault sets. See File menu options...

Options Menu: Use the Options menu to change gridding parameters, and adjust the marker and contour display controls. See Options menu options...

Options Menu Options

Gridding Parameters: Open the Set Gridding Parameters dialog box to globally adjust the gridding parameter for all surfaces, or selected surfaces.

Marker Display Controls: Open the Zone Average Markers dialog box to control the display of the zone average markers. See more...

Contour Display Controls: Open the Zone Contour Display Controls dialog box to specify the appearance of the contours associated with the zone average values. See more...

Lines: When you select Filled with contour or Contoursfrom the Style column in the Surface Display and Data window, by default the lines will be displayed. Use the Color and Width options to control the default color and thickness of the contour lines.

Color: Click on the color field to open the Color Table to select or change the default color for the contour lines. Not that when you display. Note that this color is only applied when you select Filled with contour or Contoursfrom the Style column in the Surface Display and Data window.

Width: Specify the width of the contour lines. Choose from thin, medium or thick.

Labels: This feature is disabled when displaying contours in the 3D View window.

Contour Range: When Automatic Range and Intervals Adjustment is turned off, enter a Max and Min depth value to limit the range of the contours being displayed. Note that when this range is larger than the range of the data being displayed, you will only see contours where data exists. The Min and Max values are applied to all contours being displayed in the window. To limit the contour range for individual layers, use a Grid Filter.

Intervals: When Automatic Range and Intervals Adjustment is turned off, enter Major and Minor interval values in map units.

Automatic Range and Intervals Adjustment: The Intervals settings will be automatically determined using the full range of the data. Turn this off to manually adjust the Contour Range and Intervals settings.

Contour Label Spacing: This value is not valid when displaying contours in the 3D View window.

Grid and Average Calculations

Attribute Log: Click to open the Select Curve Data dialog box and select the log curve or substitute curve to be averaged. The zone average map will be scaled and colored using the minimum and maximum values defined for each attribute log.

Distribution Algorithm: Select the algorithm that will be used to create the zone average surface. See Distribution Algorithms.

Minimum Curvature: This algorithm uses a global approximation for generating a grid. This method is very fast, and works best for pointsets that contain less than 1000 points and that do not contain faults. If used with data sets larger than 1000 points, this method may excessively average z values. Note: If the zone average that you are distributing contains faults, the algorithm will automatically switch from the Minimum Curvature to Radial Search.

Nearest Neighbor: This algorithm, sometimes known as the closest point method, searches for the closest data point and assigns that data value to the grid node. This method is used for discrete data types like lithology and facies data. The search radius is the main variable in controlling this algorithm, as it determines which wells are considered for nearest neighbor distribution.

Radial Search: This algorithm performs a radial search for random data points. This is a good method to choose for large data sets with or without faults. It is not a good choice for noisy data, as it may produce spurious results.

Radial Clustered: This algorithm performs a radial search for clustered or linear data. Compared to the random radial search, it makes an additional effort to minimize the effect of noisy or tightly distributed data by averaging the values before primary gridding. It is best suited for randomly distributed, noisy data with or without faults.

Weighted: This algorithm uses a weighted resampling algorithm, and is good for getting a quick look at data. It works quickly with large data sets because it does not attempt any interpolation or gradient estimation.

Radial Max: This algorithm was designed for discrete data types like lithology and facies data. It finds the maximum value within the search radius and assigns that value to the grid node.

Radial Min: This technique was designed for discrete data types like lithology and facies data. It finds the minimum value within the search radius and assigns that value to the grid node.

Data Source: Select the method that will be used to generate the surface grid.

Structural Grid: Zone average values will be calculated in those wells where both the top and the base structural surfaces are present. Zone average values are calculated in the intervals defined by the intersection of the top and base structural surfaces with the wells in the project.

Well Picks: Zone average value is calculated only for those wells which have both the specified top and base surface picks. This pointset is then gridded and the resulting zone average map is shown in the Map View.

Average Algorithm: Select the method that will be used to determine the zone average value at the well location. In the following definitions A represents the attribute value, T represents the thickness of the zone interval, and H represents the thickness of the log attribute. See Average Algorithms...

Arithmetic Average: Also know as thickness weighted average, this algorithm uses an arithmetic average, giving the thickest log attribute more weight in the calculation.

Geometric Average: This algorithm emphasizes high or low values, and can be used to de-spike attribute values for composite calculations (for example, thin-bedded, hot sands giving anomalous GR responses).

Harmonic Average: This algorithm preferentially weights the low thickness values. If any attribute is equal to 0, then the final average is set to 0. For example, for a thinly bedded shaley sand interval, you may wish to downgrade the clean sand response because of thin interbedding of the sand and shale, reflected in GR and RT logs.

Net: This algorithm applies the log curve range specified in the Net Range field to calculate the net thickness conforming to the cutoff.

Net-to-Gross: This algorithm calculates the ratio of the net thickness determined using the log curve range specified in the Net Range field, to the gross thickness of the interval.

Min: This algorithms outputs the lowest value in the interval.

Max: This algorithm output the highest value in the interval.

Arithmetic Mean: This algorithm output the mean value over the interval.

Sum: This algorithm sums the values over the interval.

Most Abundant: This algorithm outputs the mode value over the interval.

Depth Mode: Select the depth mode to use to determine how the thickness measurements will be made.

MDT: Measured depth thickness measurements are taken along the well bore.

TVT: True vertical thickness measurements are taken vertically. Note that for vertical well the MDT and TVT values are the same, but for deviated wells they may be significantly different.

Net Range: Specify the range of log curve values to use in the Net or Net-to-Gross averaging calculations. Note: These values are limited to the MIN and MAX values of the Attribute Log selected, for all wells in the project.

Zone Average Interval

There are three methods for determining the zone average interval using an upper and lower surface, and upper surface and a thickness, or an upper grid, an offset and a thickness.

Upper Surface: Click to open the Choose One Surfacedialog box and select the upper surface.

Lower Surface: Click to open the Choose One Surface dialog box and select the upper surface.

Zone Thickness: Enter a Zone Thickness and optionally a Reference Offset in depth units.

Display Options

Enter the parameters to determine how the zone average surface will appear on the map.

Lateral Interval: Specify the number of zone average values to extract along the interval.

Single Zone Average: Calculate one zone average over the interval. This is the default and is should be used for straight and deviated wells that will enter and exit the zone once. When this is used on horizontal wells that enter and exit the zone several times, a zone average value is calculated each time the well enters and exits the zone and each well path segment in the zone will have a zone average marker in Map View.

MD: Calculate a series of zone averages based on a user-specified sampling distance along the measured depth of the well trajectory. This is typically used for horizontal wells that enter the zone once and remain within the zone for some distance. Enter a value for the sampling distance in the field provided. In Map View, the spacing of the zone average markers will vary from well to well due to differences in orientation of the well trajectories.

XY: Calculate a series of zone averages based on a user-specified sampling distance in the XY plane along the well trajectory. This is typically used for horizontal wells that enter the zone once and remain within the zone for some distance. Enter a value for the sampling distance in the field provided. In Map View, the zone average markers appear uniformly spaced from well to well.

NULL Area Color: Select a color to represent area where there is no data for the interval. Choose from White, Gray, or Black.

Color Spectrum: Open the Color Spectrum Manager to select or change the color spectrum for the surface.

Fill Style: Specify how the surface should appear in the display. Choose from Filled, Filled with Contours, or Contours.

Dynamic Color Range: When this is turned on, the color spectrum range adjusts to the data range, so that the whole spectrum is used over the range of data. Use this option when the numerical range of data values is much smaller than the values set for the spectrum.