Practical Wellbore Formation Test Interpretation

Bo Cribbs, Chevron North America

The importance of wireline formation testing (WFT) interpretation increases with the new SEC reserve definitions.  This presentation will address the “reliability” of WFT pressure data to define Proved Reserves in light of the new regulations.  We will discuss data collection with the different types of tools, explain what constitutes high or low confidence data and show examples of data trends that might make a compelling case for extending a Proved contact down to a certain point. Other topics will include pretest pressure stability, depth correlation, calculating gradient error, understanding accuracy vs. precision, the importance of mobility and discuss the difficulty of interpreting WFT gradients in low mobility environments.

Pressure trend analysis will be discussed in terms of reservoir compartmentalization, the identification of which early in the life of a high cost development can have significant financial impact to future Appraisal and Development decisions. For compartmentalization studies it is also important to understand how pressure trends correlate laterally over the field, how pressure trends correlate vertically within each zone, how measured fluid gradients compare to sampled fluid density, how composition, PVT and bulk fluid properties correlate across a field and how each of these trends compare to geochemical marker results.  We will propose that the integrated analysis of all of these data trends within the geologic model can be used to build a much more compelling case than pressure gradient analysis used in isolation. A list of important references will be included.

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