Riese, W.C.¹, W.A. Hill¹ 
(1) BP America Production Co, Houston, TX

ABSTRACT: Clinical Methods for Pre-Drill Calculations of Reserves and Risk: Results of an Analysis of Historical Company Data and an Outline of Methods

Assessments of prospect reserve potential which are performed predrill continue to reflect an optimistic bias across the industry. Analysis of data which characterized several years of assessments for one company indicated that this tendency to overestimation resulted in predictions which were double the reserves actually found. Overestimation reflects poor understanding of the process and principles of reserves prediction among the professional community. 
Our work indicates that clinical methods of reserves estimation can be prescribed with limits and guidelines sufficient to eliminate overestimation. Reserve predictions for exploratory and extension wells should be compiled using lognormal prospect reserve distributions which approach zero on their lower end. Our analyses indicate that 0.1bcfe at the 99.9% probability point is an appropriate approximation of zero for the plays we examined at the present time. The upper ends of these distributions should be constrained by the maximum reserve volumes which the available data and interpretations allow the trap to contain (P2), and should be truncated at sizes consistent with recent, trap-type-specific trend or play discoveries. 
Application of these guidelines to an eighteen-month program of approximately 100 test wells resulted in an improvement of the discovered : predrill ratio for the program to 98%. Use of these methods also facilitated portfolio-wide comparisons of relative economic risk without incurring the need to empirically determine geologic risk or chance factor.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.