Integration of Production Log and Oxygen Activation Techniques For Diagnosing Water Production Problems
Authors: Muttoni Alda , Cannatelli Domenico 
Published: December 2007

Summary
Production logging (PLT) is used to diagnose a variety of production problems and for reservoir evaluation. A primary use of PLT is the identification of water entry into producing wells. If the water flow rate is low, the sensitivity of PLT does not allow adequate characterization. When this occurs, it is possible to use the recent water flow log (WFL) technique, which can locate and evaluate small water movement, both upflow and downflow, inside or outside the casing.
This technique is based on the oxygen activation (OA) principle and incorporates the pulsed neutron capture (PNC) logs. One weakness of using the WFL technique is that quantification of flow rates may be difficult when water velocity tends to vary as a result of turbulence effects and changes in cross-sectional area. However, these difficulties can be overcome, and good results are possible in both open and cased hole by the combination of PLT and WFL techniques. To achieve good results, an optimal measurement program should be planned through the use of all available data: previous openhole and cased-hole logs, production data, well completion profile, etc.
This paper describes the application of the PLT and OA techniques to some Italian wells in a variety of reservoir contexts. The interpretation of these logs together provided additional information helpful for planning remedial action for water shutoff.

Introduction
A serious problem encountered during the production life of wells is undesirable water production. The problem has economic, environmental, and managerial ramifications.
The subsurface disposal of waters produced from hydrocarbon wells is onerous: increasingly restrictive new environmental regulations impose specific water treatments before produced water can be injected into a reservoir. In producing wells, high water production can cause the well to water out. Consequently, artificial lift may be necessary, which increases operating costs. Therefore, the early monitoring of water entries is essential so that the phenomenon does not become too difficult to control.
Water-control techniques are becoming more sophisticated. Besides the traditional mechanical techniques (conventional bridge plug, casing patch, etc.), new through-tubing mechanical techniques (such as expansion bridge plugs and cement plugs) that require the use of coiled tubing are improving. Also, the new chemical treatments for near-wellbore shutoffs (gel, foams, and polymers) are undergoing substantial developments.
Application of these new techniques requires thorough understanding of water production phenomena, so well conditions inside and outside the production casing must be carefully investigated. For this purpose, conventional PLT's (flowmeter, fluid density tool, manometer, and thermometer) are generally used to obtain the flow profile in the well. These tools cannot characterize water flow behind casing and have limited applicability in cases of low flow rate. Different methods to detect and locate water movements have been developed. The only method that gives good results is the OA technique, the most recent development of which is the WFL. The PLT and WFL can be used individually or in combination, according to the flow profile to be investigated. Table 1 summarizes the field operational guidelines for the separate or combined use of these techniques for production and water injection wells.