Formation Evaluation - Its Changing Role
Authors: Rudd Neilson 
Published: December 2007

This paper was prepared for the Second Midwest Oil and Gas Industry Symposium of the Society of Petroleum Engineers of AIME, to be held in Indianapolis, Ind., March 28–29, 1974. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made.
Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

Abstract
The techniques and interpretative methods of Formation Evaluation as developed and employed in the past three decades have been primarily directed to the study of the relatively thin intervals of potentially productive hydrocarbon reservoirs and to the productive hydrocarbon reservoirs and to the evaluation of fluid movement characteristics through relatively short time spans and within relatively restricted areas.
This limited concept of Formation Evaluation is no longer adequate. Whether our primary interests are in oil and gas production, aquifer or cavern storage, ground production, aquifer or cavern storage, ground water supply, solid mineral extraction, or waste liquid injection, we have found that we must deal with the subsurface environment as a totality. This is dictated by our own experience as well as the more recent pressures for increased efficiency in mineral and fuels production and for environmental protection. production and for environmental protection. The present paper cites examples drawn from several forms of subsurface exploitation to demonstrate the need for, and benefits of, more comprehensive and sensitive Formation Evaluation techniques. The present methodology of Formation Evaluation present methodology of Formation Evaluation is discussed as it applies to this changing role, both as routinely employed and as modified to provide a greater sensitivity and scope in both time and space. Among the latter are (a) the concept of continuous exploration, and (b) performance monitoring relative to geological uncertainty.
This paper is perhaps more philosophical in nature than technical; however, it deals with real problems and is based on specific experience in oil and gas production, underground gas storage, deep well waste disposal, and hydrology.

Introduction
The term "Formation Evaluation" is ill-defined and of uncertain origin. For purposes of this paper, I speak of formation purposes of this paper, I speak of formation evaluation in a very general sense, as the application of geology, geophysics, and reservoir engineering to the formulation of a preliminary-quantitative understanding of a rock/fluid system prior to the time that the characteristics of this system can be definitively established by further development and experience.