A continuous oxygen activation method of measuring water injection flow profiles in complex single and dual completion injection wells has been developed. The method allows deconvolution of superimposed activation signals originating from simultaneous, co-directional water flow in the tubing and tubing-casing annulus for a continuous log of annular water velocity. The theoretical basis of the measurement is reviewed and field examples are analyzed and interpreted. The examples of single and dual string completions demonstrate the measurement of continuous annular injection profiles in the presence of co-directional tubing flow and diagnosis of mechanical problems such as plug ledcs and tubing-tubing communication.
A common problem encountered in water driven fields is the measurement of water flow profiles in both injection and production wells. Conventional oxygen activation logging techniques have been successfully applied for detection and measurement of isolated water flows such as channeling behind casing and water flow profiling in completions where annular and tubing flows are in opposite directions. In complex single or dual completions where the tubing flow and tubing-casing annular flow are co-directional, however, a flow profile measurement is not always possible using traditional oxygen activation techniques due to the superposition of the signals from the tubing and annular flow streams. This paper describes a new oxygen activation logging method that has been developed for these complex conditions, beginning with a review of conventional logging methods.
The use of oxygen activation logging for detecting water flow behind casing was first proposed in 1977 by Arnold and Paap. Two commercial methods were developed in the 1980's that allowed measurement of water velocity based on oxygen activation logging. Both entail stationary measurements at selected depths in the well.
The first method, developed in 1985, is known as the steady-state method and is based on the exponential decay of the induced gamma ray activity.