Petrophysics

This dialog consists of three distribution tabs: Net-to-gross (NTG), Porosity (PHI) and Water saturation (Sw). Units are either fractions or percentages.

If you have chosen to use a saturation-height function rather that an Sw distribution, the Sw tab shows the function. See Saturation-height functions

If you are using a dual porosity model you must also enter net-to-gross, porosity and water saturation for the secondary system. Although the secondary porosity system is usually a fracture network, it doesn't have to be. It could be any distinct system - a second identifiable facies, for example.

If it a fractured reservoir, the first net-to-gross, porosity and Sw are assumed to relate to the matrix. You will have to decide how to manipulate the three "fracture" variables to arrive at the correct fracture volume. Often, people set the fracture net-to-gross to 100%, fracture Sw to 0%, and vary only the fracture porosity. Others set the fracture porosity to 100%, and control the fracture volume by the NTG distribution. In fracture systems too much precision is usually indefensible. Note that later on you will also enter a fracture recovery factor: commonly this is set to 100%. The big decision concerns the primary system recovery factor.

Note that water saturation (Sw) is entered, rather than oil saturation (So) or gas saturation (Sg). This is because Sw is the commonly calculated and reported quantity. REP will convert Sw to So or Sg when it comes to the calculation. This is the second of the two obvious occasions (the other being Bo) when the minimum value of a parameter does not correspond to the minimum reserve case.

For more information, see 'Entering Probability Distributions'.

It is possible to copy a distribution to another prospect or model, visit our section on 'Copying Distributions to Other Models or Prospects' to learn how.