The Deviation Subtable contains information about the path of a Deviated Hole.
The following data are stored in the Deviation Subtable:
Identification number for each record in the Deviation Subtable, automatically assigned. The number is not visible online, but is included with other data when the Deviation Subtable is downloaded so the user can maintain the PDMS table relationships in other software applications.
The measured distance (in feet) from the ground surface of a well to a point in a borehole.
The arithmetic difference (in feet) between Measured Depth and TVD (True Vertical Depth) as determined from a directional survey (TVD Log).
True Vertical Depth of a point in the well bore as determined by subtracting Offset from Measure Depth.
The east-west distance (in feet) in a deviated hole from the surface hole location to a point in the well bore (E = +, W = -).
The north-south distance (in feet) in a deviated hole from the surface hole location to a point in the well bore (N = +, S = -).
East-west Universal Transverse Mercator (UTM) coordinate (NAD 83, Zone 16) of the datum location in a deviated well bore.
UTM values are measured in meters.
North-south Universal Transverse Mercator (UTM) coordinate (NAD 83, Zone 16) of the datum location in a deviated well bore .
UTM values are measured in meters.
Type of deviated hole at the datum horizon. The Deviation Type data field is left blank if the Measured Depth falls in the vertical portion of the borehole.
The IGS distinguishes 2 types of deviated holes:
Directional Hole:
Refers to the portion of a well bore that is deviated from vertical to penetrate formations at an angle, whether intentionally or inadvertently due to drilling circumstances, to intersect the target formation at a different geographic position. The data field is left blank if the Measured Depth falls in the vertical portion of the borehole.
Horizontal Hole:
Refers to the portion of well bore that is deviated to penetrate formations more or less horizontally, generally for the purpose of intersecting a petroleum-bearing formation or reservoir along more of its length than would be the case for conventional vertical wells (straight holes).
The Deviation Symbol uses the same set of symbols and codes as the Petroleum Well Symbol set. When used in the Deviation Subtable the Symbol is associated with a specific point along a borehole. Certain practices are followed for Deviation Symbols:
Surface:
By definition, the UTM-X and UTM-Y coordinates associated with the Surface symbol in the Deviation Subtable ought to be the same as the location coordinates given in the Well Header; however, minor differences are sometimes present. The symbol "Surface" is only entered once in the Deviation Subtable, and only for one Well Event (the first drilled) if multiple boreholes were drilled (each borehole must be entered as a separate Event).
It is important to note that the Surface Symbol is generally used twice for a Deviated Well;
1) in the Deviation Subtable as just described;
2) in the Well Header (Location Table), in the Petroleum Well Symbol data field. With a single exception, the "Surface" is always used in the Well Header.
The Exceptional Case: old well worked over from a previous completion as a vertical hole
For a non-deviated well, the Well Symbol is spotted on IGS maps where the surface location falls; it is unnecessary to spot the symbol "Surface" because it is assumed that the surface and the bottom hole locations are roughly coincident.
In the case of a normal horizontal well, although transparent to the user, the "Surface" Symbol is actually posted twice. The symbol "Surface" (represented by a square) is normally spotted on a map at the well's surface location: once from the Symbol data field in the Well Header (Location Table), and again from the "Surface" Symbol contained in one record in one of the Deviation Subtable records. Since these Surface symbols overlap exactly on the map, the appear to be only one symbol.
If the a deviated well bore is drilled from a previously completed straight (vertical) hole, the appropriate symbol for the previous hole is retained as the Well Symbol in the Well Header (Location Subtable) where it will be spotted on maps at the surface location were the original well was completed. The Deviation Symbol "Surface" from the Deviation Subtable will also be spotted at the surface location of the original hole. The ultimate effect on the map will be the posting of the previous well symbol inside of the larger square "Surface" symbol.
The Well Symbol for a completed deviated borehole is spotted at the Bottom Hole Location, as indicated in the Deviation Subtable. If multiple lateral holes are drilled, a separate symbol is posted at the Bottom Hole Location of each lateral hole.
Path Symbol
The symbol is a dot (a period). The Path Symbol is posted at various intervals along the well bore path. There is no set standard for spacing the symbols, however, selecting every 10th X-Y coordinate from the hole's Directional Survey (TVD Report) is commonly used on IGS maps.