1963 Paper (I)

FORMATION EVALUATION WITH NUCLEAR AND ACOUSTIC LOGS

F. Lebreton, A. H. Youmans, H. I. Oshry and B. F. Wilson Lane-Wells Company, A Division of Dresser Industries, Inc.

ABSTRACT

This paper deals with the measurement of porosity by nonresistivity logs in cases where conventional techniques are inaccurate due to physical or chemical characteristics of the rock that influence log interpretation adversely.

Acoustic velocity, gamma gamma density, and neutron logs are compared with respect to their relative response to complex types of matrix, formation fluids, vugular and fracture porosity, and other formation parameters that may be inadequately known except when they can be deduced from logs. It is shown by field examples that by employing two or sometimes three of these basic porosity logs it is possible to obtain accurate porosity measurements which would be impossible with any one of the logs by itself.

The reliability and accuracy of the neutron log for this purpose is shown to be superior to previously described logs provided a special type of instrument is employed which measures only epithermal neutrons so as to eliminate the undesired effects of formation chemistry and fluid salinity. Performance characteristics of this instrument are described.

Specific field examples have been obtained which demonstrate the feasibility of determining porosity in rocks with complex matrixes. In addition, there is included a general discussion of the interpretation methods which may be employed when the matrix is composed of as many as three components.