Locating Extraneous Water Sources with the Gamma Ray Log
Authors: Doering Mark A. , Smith Dan P. 
Published: December 2007

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.
This paper was prepared for the 49th Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in Houston, Texas, Oct. 6–9, 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 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. 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 discussions 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 gamma ray log can be a simple and inexpensive diagnostic tool for locating communication behind cemented pipe. Radiation increases have been noted in several reservoirs where significant formation water movement has occured. In wells with defective cementing, a portion of tile produced water can come from portion of tile produced water can come from reservoirs other than the perforated interval. The gamma ray log can be used to locate these extraneous fluid sources by detecting the radioactivity increases generated by this behind-the-pipe fluid production. The following discussion explains how this familiar logging tool can be used independently, or in combination with other techniques, to verify the presence of cement channels.

Introduction
Communication behind casing can be a serious problem in oil and gas producing wells Detection of this problem is often difficult and expensive. Frequently used methods of detection include temperature surveys, tracer surveys, cement bond logs and oriented density scans. Often the result of the above surveys are not conclusive and verification by another technique may be necessary.
When the gamma ray log is run opposite certain reservoirs where prolonged fluid movement has occured, it will record a greatly increased radiation count. By noting these increases, the reservoirs involved in behind the pipe communication can often be identified. Since the gamma ray log is frequently run for correlation purposes with the conventional diagnostic tools, it can be an inexpensive aid in defining cement channels.

BASIS FOR METHOD
It has long been observed that radioactivity increases sometimes occur opposite wellbore intervals where significant amounts of fluid have been produced. The purpose of this paper is to present actual case histories in which these observed radioactivity increases were used to locate cement channels.
The following explanation has been proposed to define the cause of the radioactivity proposed to define the cause of the radioactivity increases. The anomalous radioactivity level is the result of a radioactive crust deposited by formation fluids contacting the production casing. This crust is formed by radioactive salts in the formation fluid reacting with iron oxides of the casing. The formation of this crust is usually associated with a reduction in pressure of formation fluids which are saturated with radioactive salts.
The occurrence of radioactivity increases is not always seen in intervals where large amounts of fluid production has taken place. The presence of this phenomena in any particular area can only be confirmed by field particular area can only be confirmed by field experience. In areas where this radioactivity is consistently detectable, this method can be a convenient and cost saving technique and can serve as the sole diagnostic tool for identifying cement channels.