The Selection, Application, and Misapplication of Reservoir Analogs for the Estimation of Petroleum Reserves

Abstract

Abstract This paper contains materials and concepts from both an engineering and geoscience perspective relative to the reliance upon suitable analog reservoirs for some or all of the pertinent reservoir rock and fluid qualities in the estimating of reserves quantities and the classification of such estimates. The information in the paper is expected to be useful to professional reservoir engineers and geologists in predicting reservoir performance for reserves estimation, reservoir management and other predictive needs. The ultimate choice of the use and application of data from analogous reservoirs is always based upon the judgment of the evaluator but guidelines presented in this paper will assist in providing criteria for the more consistent application of analogs. All judgment decisions in reservoir evaluation are based upon the evaluator's collective experience in reservoir geology or engineering and are thus subjectively analog based. Little of our collective experience, however, has been gathered in any systematic way where all pertinent reservoir and fluid characteristics have been identified. The pertinent characteristics go far beyond the typical measurements of depth, pressure, temperature, porosity, permeability and oil gravity - as primary parameters - and arguably should include depositional environments, mineralization, trapping mechanism, drive mechanisms, structural stresses, wettability, pore throat sizes and other often unknown or ignored features or descriptive parameters. Equally important is the recognition of the frequent and continuing misunderstanding and erroneous application of analog data, some of which is described in this paper. The topic is significant because of the continuously growing interest in reliable reserves estimates and economic forecasts by companies, investors, regulators, governments and the public at large and because there are no similar papers available through the SPE library or other readily accessible sources. Introduction Analogy methods have played a significant role in both the assessment of resource potential and as a basis for estimating or supporting the estimate of reserves. This paper will focus on the use of analogs for reserves estimation and is divided into two separate but intrinsically related discussions about the reliance upon analogs by reserves evaluators. The first topic of discussion relates to the use of analogs in the classification of reserves into the appropriate category - most often proved, probable and possible. The second application relates to the quantification of reserves. The alternate, and often preferred, spelling as "analogue" is not used herein but is included to enable electronic searches utilizing that specific term to locate this paper. A recent search of the SPE eLibrary resulted in identifying 556 papers incorporating the word analogue and an additional 3589 papers containing the term analog. Analog Usage A global survey of the use of geological analogs conducted in early 2002 by S. Qing Sun and J.C. Wan1 indicated that the companies surveyed believed that identifying the highest quality analogs reduced the exploration risk and improved the field development decisions. Further, while analogs were deemed to provide critical insight, no one within the companies surveyed had codified analog best practices.