6.3 - Level 3: Field
The field level represents a specific oil or gas field on which the operator can have any number of facilities. Fields define the mapping grid (aka Co-ordinate Reference System) to be used when calculating geographic coordinates.
The Field Properties dialog will automatically open when a new field is created. To access the Field Properties for an existing field, right click on it in the Object Explorer. The Field Properties dialog has the following features:
6.3.1 - Properties
Field Name: Name of the field which will be displayed in the Object Explorer.
Mapping Grid: The dropdown box sets the co-ordinate reference system (CRS) which will be used to convert between grid co-ordinates, local co-ordinates and latitude/longitude values. Clicking on the mapping grid button will open the CRS Editor.
Locked: This checkbox allows the user to lock all the editable cells in the dialog. If NO password has been entered at Operator level in the set password section, then the user can freely select to lock and unlock the dialog. If a password has been added at Operator level, then the user must enter the relevant password to both lock and unlock the dialog.
6.3.2 - Field Local Grid
Local Coordinate System: This defines the reference point for the well location, and is used to calculate the local NS and EW values when viewing surveys or plans. If Well Centred is selected, the reference point will be the well head, as defined in the Well Properties dialog. This will mean that the NS and EW will be zero at surface. If Facility Centred is selected, the reference point will be the facility centre location, as defined in the Facility Properties dialog. This option is commonly used for facilities with multiple slots.
Apply Scale Factor: If this option is selected, the scale factor defined in the CRS will be used to calculate map co-ordinates from local co-ordinates. This is the ratio between measured distances on the map compared to measured distances on the ground as a result of distortion of linear scale associated with mapping a spherical surface (the earth) onto a plane. Note that this option does not affect the local coordinates, only the map coordinates (Northing and Easting’s).
Show Map: This extends the existing dialog to include a Google Maps section. This will show the location of the positional data entered and can be toggled between map and satellite view. The map can also be zoomed in and out using the – and + buttons. This map location will only be accurate if the CRS selected uses WGS 84, as this is what Google Maps utilises.
Show Field Ref Point on Report: When selected, the field reference point coordinates will be included in the Field data box of any report generated. If unchecked (default) then these coordinates will not appear in the field data box in the reports.
6.3.3 - Field Reference Point
Field reference point: This is the reference location used for the field. The reference point can be entered either as a latitude & longitude or as a map coordinate. This is defined by selecting the “Grid North / East” or “Lat / Long” radio button. The grid convergence for the field reference point is displayed in the edit box marked “Grid Convergence”. This value will be applied when converting between grid north and true north.
6.3.4 - System Vertical Datum
System vertical datum: This is datum which all TVDs stored in the database will be referenced to. This is usually either mean sea level “MSL”, lowest astronomical tide “LAT” or some other user specified value. If a value other than MSL is selected from the combo box, the elevation above or below MSL must be entered. A positive value indicates that the datum is above mean sea level and a negative value indicates it is below it.
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