Operation Modes and Applications

1D well calibration

1D well calibration allows the user to determine a local observed shale compaction trend line (OSCTL) and establish a regional normal compaction trend line (NCTL) which best fits all well sonic and/or resistivity logs.

Overburden pressure (OBP) and thus pore pressure prediction (PPP) by either Eaton's or Miller's methods is developed to best match measured or interpreted borehole pressures.

This module can be used for real time drilling and completion analyses, or as calibration points for 3D model building.

The calculated curves are also available to view in Insight's other 2D and 3D views.

Figure 1 shows an example of a 1D pore pressure calibration at a well location.

3D model building

3D model building generates a volume of pore pressure gradient (PPG) from seismic velocity (or resistivity) volumes.

This may use the parameters optimised from the 1D well calibration mode, or from other empirical sources. Pore pressure and fracture gradient volumes can then be used for future well planning, to optimise mud weights, and predict hazards.

Figure 2 shows an example of a 3D pore pressure calibration from seismic velocity.

Commonly used symbols and abbreviations

Below are tables of abbreviations used for methods, symbols or units.

(a) Methods

Symbol Definition
PPP Pore Pressure Prediction*
PP Pore Pressure (value in psi)
PPG Pore Pressure Gradient (values in specific gravity or pounds per gallon)
OBP / OBG Overburden Pressure (vertical stress)
NP / NG Normal (hydrostatic) Pressure / Gradient (normal stress)
FG Fracture Pressure / Gradient
NCTL  Normal Compaction Trend Line
OSCTL Observed Shale Compaction Trend Line (smoothed sonic above the shale cut off)

(b) Symbols

Symbol Definition
DT Compressional (P-sonic) slowness
RES Resistivity
MSL Mean Sea Level
KB Kelly Bushing (drill floor / rotary table height)
WD Water Depth (below seismic reference datum, usually MSL)
TVDSS True Vertical Depth Sub-sea
TVDBML True Vertical Depth Below Mud-line
MDKB Measured Depth (from) Kelly Bushing

(c) Units

Symbol Definition
m Metres
ft Feet
us/ft Microseconds per foot
ohmm Ohm-metres
ppg Pounds Per Gallon (common pore pressure gradient units)
SG Specific Gravity (alternative pore pressure gradient units)
psi Pounds Per Square Inch (absolute pressure units)

Notes:

  • "PPP" may be used to describe the method or the result. e.g. “the PPP module” or “the PPP at Well-X”
  • Pore Pressure Gradient (PPG) is Pore Pressure (PP) divided by TVDSS
  • In the various formula builders, Insight provides built-in variables — “tvdss_m”, “tvdbml_m”, “tvdss_ft”, “tvdbml_ft” — for depths measured from the surface or from the mud line, in metres or feet.