Tuesday, March 8, 2016

Isochron and Isopach Maps in OpendTect

Version: 6.0

The example given here is the interval between Upper Fayetteville SH and the Boone LS in the Desoto 3D seismic survey of NE Conway County, AR (data credit: SWN). Horizon tracking by Daniel Moser.

Definitions
Isochron map: Seismic two-way interval time between two horizons
Isopach map: Thickness interval between two geological or seismic horizons

  1. In the project tree add two horizons A and B, here A=U_Fay_Smooth (Fig 1) and B=Boone_Smooth (Fig 2)The A horizon is shallower than B.
  2. Right click on shallower horizon U_Fay_Smooth and select Workflows > Calculate Isochron ...
    1. In the isopach parameter window set Calculate to menu to Boone_Smooth  use default attribute name I:Boone_Smooth, and output result in msec. 
    2. You will see there is a new attribute I:Boone_Smooth in the U_Fay_Smooth tree list. 
  3. Right click on the I:Boone_Smooth attribute and select Tools > Set Z Values ...
  4. In the parameter window select: Values are Relative (deltas), Units are msec, Save Horizon As new, output horizon name UFay_Boone_iso and check the Display after create box. This will generate a horizon representing the isochron between the horizons. Contours can be added to show the isochron between these two horizons (Fig 3).
U_Fay_smooth horizon time structure with 2 ms contours

Boone_smooth horizon time structure with 2 ms contours

Fay-Boone isochron with 2 ms contours



Not yet... generate isopach from isochron (CL)
  1. Choose menu item Scene>New[Depth]. In the parameter box select Linear Velocity and set the Vint parameter to 12000 ft/s (from averaging of sonic velocity between U Fay and Boone) and set gradient to zero. This forces a constant velocity depth conversion. Select OK.
  2. A new project tree window appears below the previous project tree along with the new scene window. Minimize the original scene window and maximize the new one.
  3. In the depth scene add the UFay_Boone_iso horizon