A METHODICAL APPROACH TO CRITICAL WELL RE- EVALUATION

Abstract

A review of existing petroleum wells in a particular basin of interest is commonly the first step in acreage evaluation and prospect identification. A rigorous assessment to determine whether a well's prospect was fully evaluated must be methodical and must incorporate reviews of petrophysical, engineering, geological, seismic and economic data.

Based on Australian and international case histories, comprehensive checklists of pertinent questions that should be addressed have been formulated for each of these disciplines. Some aspects questioned are broad, and obvious to the point that they can be easily overlooked. Others are more specific and subtle and require close consultation with experts. The greatest value of these checklists' documentation is their potential as a guide for the comparatively inexperienced petroleum explorationist.

Implicit in critical well re- evaluation is the need to be open minded, commencing on the premise that previous interpretations are not necessarily valid today. It should be appreciated that the first interpretation of an existing well was based on a limited data set of observations strongly influenced by the geological model in favour at the time and, as such, is extremely prone to change as additional data become available, as the economic environment changes or as new ideas are formulated.

Experience has shown that significant, but as yet undetected, volumes of oil and gas may be present in prospects already drilled by one or more wells. Apparent lack of success in a well has often had an unjustifiably negative effect on further exploration in the area in which this well was drilled.