Uncertainty and Ethics in Petrophysics

Eric Pasternack, Outsource Petrophysics, Inc.

Petrophysical parameters are key inputs to all estimates of reserves.   None of these parameters is measured directly in the reservoir; each is inferred from measurements on cores and/or from various measurements made during wireline logging or logging while drilling.  There is uncertainty in every one of these inferred parameters.  

Inferred petrophysical parameters include porosity, fluid saturations and net pay, all of which are used for calculations of volumetrics.   Permeability is also an inferred petrophysical parameter, used in various ways to infer producibility.  There is always some degree of uncertainty in these inferred parameters.  Even depth, the most basic measurement of all, has an associated uncertainty that can be extremely important in reserves estimation. 

Quantifying the uncertainties in inferred petrophysical parameters requires going back to first principles and understanding the sources of these uncertainties.  This talk addresses these sources of uncertainty, and discusses analytic and statistical methods for quantifying their effects on the overall uncertainty of the computed parameters. 

Ethical considerations in petrophysics are relatively straightforward.  It is the job of the petrophysicist to give the best technical answer with an indication of the uncertainties associated with that answer.   All assumptions and calculation methods should be fully documented so that another petrophysicist can duplicate the result.

AAPG Search and Discovery Article #90098©2009 AAPG Education Department, Houston, Texas 9-11 September 2009