1963 Paper (F)

A STUDY OF NEUTRON LOGS FOR CHLORINE DETECTION

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

ABSTRACT

The paper reports the results of a series of field tests in which tree basic neutron logs were run and their differential response evaluated as a quantitative means for chlorine detection.

The basic neutron logs used are the n,gamma, the n,n thermal, and the n,n epithermal. Many variations of each of these are possible. An explanation is offered as to why hybrid logs generally available in the past have suffered from low chlorine sensitivity as well as ambiguous response to various other chemical and physical parameters. Essential details of instrument design are discussed in relation to the observable affects of chlorine on log response.

It is shown that the n,n epithermal log is independent of the salinity of the borehole and formation fluids. As such, it is a valuable companion curve for any chlorine measurement, and provides a valid indication of formation porosity.

The n,n thermal curve is shown to respond negatively to chlorine while the n,gamma curve responds positively. Thus these two in combination produce the greatest differential response to chlorine.

It is shown that three curves together provide in combination the greatest chlorine sensitivity as well as the most reliable interpretation. Under many circumstances only two of the curves are required to differentiate between oil and water zones.