Keywords
Abstract
Since well log measurements depend strongly on the geological parameters, any log interpretation is by nature a geological interpretation. Logs represent a fundamental source of information in subsurface. Who can interpret them better than a geologist? Of course, the geologist must know the tools’ physical principles and the links between physical parameters and geological attributes.
Unfortunately, log interpretation has been “monopolized” by petrophysicists. SPWLA review’s brand new title: Petrophysics, proves it and the board of directors of this society has forgotten that other geoscientists also analyze and interpret logs for other purposes!
Petrophysicists deal with empirical mathematical formulae. While focusing on reservoir analysis, they often forget to consider in which geological formation they occur. Formation evaluation cannot be restricted to reservoir petrophysical properties determination. It is of the utmost importance to put back the reservoir in its geological context in order to link lateral extents and hydrocarbon volume to real thickness, environment, and local deformations. This is definitely a geologist’s work.
Petrophysicists must realize that reservoir evaluation cannot be achieved by solving equations. Too many geological parameters affect log measurements. Log interpretation must be global and total. It must integrate the whole set of data and their different origins, natures, and scales. Moreover, log measurements, combined for interpretation, do not correspond to the same volume of rock and some of them are affected by borehole environment. In addition, some of the data do not represent the geological reality, especially if the units of deposition are thin and numerous.
Therefore, I propose to follow a geological approach to reservoir evaluation. We must determine, as much as possible from the whole set of data, the geological reality. This consists in:
- Recognizing each depositional unit,
- Determining their geological setting in order to estimate their volume and lateral extent
- Evaluating their own physical properties.