Pore Pressure Calculation
Pore Pressure Calculation comprises of three modules to model Overburden, Pore and Fracture Pressures based on conventional log curves, drilling information and seismic data. The modules can be used as pre-drill (predictive), while-drilling (real-time) and post-drilling tools to analyse and refine the models.
The three modules are:
- Density Estimation - 'density-from-sonic' algorithms included are ‘Gardner’, ‘Bellotti et al’ and ‘Lindseth’
- Overburden Gradient Calculation - determined from density data, average density values, look-up tables or empirical 'Amoco' relationship.
- Pore and Fracture Pressure gradient calculations - Five Fracture Gradient models are implemented in IPTM, Eaton, Matthews & Kelly, Modified Eaton, Barker and Wood, and Daines
An interactive log plot is used to calibrate the model.
The model can be viewed with a Depth versus Pressure 'Fan Diagram' or a Depth versus Pressure Gradient 'Gradient Plot' (as shown). These plots can be annotated with casing shoes, RFT pressures, Leak Off Pressures and operational comments to identify hole stability problems, while additional curve data, such as ECD, can be added to the display.
Sonic, Resistivity and Drilling Exponent are displayed in separate tracks in the interactive display. A Normal Compaction Trend (NCT) line for sonic log response in shale (NCT_Son) and for resistivity in shale (NCT_Res) is also displayed in the appropriate track.
