Interpretation of Injectivity Profiles in Irregular Boreholes

Abstract

Bearden, William G., SPE-AIME, Pan American Petroleum Corp. Pan American Petroleum Corp. Cocanower, R.D., SPE-AIME, The Western Co. Currans, Dan, SPE-AIME, Pan American Petroleum Corp. Pan American Petroleum Corp. Dillingham, Mat, SPE-AIME, The Western Co. The problem of measuring fluid flow in borehole sections with irregular diameters is identified, and corrective measures are developed for obtaining more exhaustive injectivity profile information. Introduction Since the first use of injection and production profiles using tracer-velocity logging techniques with the interpretation method based on hole-diameter information, there has been difficulty in obtaining reliable information in irregular boreholes. Most of the difficulties have arisen in those areas where the size, of the hole changes. A typical example of the errors of calculated velocity data is shown in Fig. 1. The velocity measurements recorded from 4,950 to 4,970 ft were in a section of nonuniform-diameter wellbore as shown by the caliper survey. The usual practice was to delete the erratic velocity data and construct an average profile through this section or to use the Self profile to determine the fluid losses. The primary purpose of our study was to investigate the influence of hole diameters and hole diameter-changes on the validity of tracer ejector readings. The secondary purpose was to investigate the accuracy of profiles in an irregular-shaped hole from which known profiles in an irregular-shaped hole from which known leak-off rates could be established by the tracer-velocity technique and Self Profile Method. Test Equipment and Methods The basis for this study was a series of large-scale tests performed at the Pan American Research Center, Tulsa, Okla. Four different apparatuses, as shown on Fig. 7, were used to simulate various wellbore configurations with diameters varying from approximately 4 3/4 to 23 1/2 in. Water was flowed through these apparatuses at various rates, and controlled leak-off points were installed at selected sections. A 1 3/8-in. points were installed at selected sections. A 1 3/8-in. standard tracer-ejector tool with dual gamma-ray detectors was used to make readings at various locations in the cells. These readings were then converted to flow rates and compared with the actual flow rates, which were simultaneously being metered. Two types of profiling techniques were investigated during this study. The first, using the tracer-velocity profile, involved ejecting a small volume of profile, involved ejecting a small volume of water-soluble radioactive-tracer material into the flow stream, then observing the length of time required for the material to pass two detectors spaced 5 ft apart. This time is an inverse function of the fluid velocity, which, if we know the hole diameter, may be converted to rate with Eq. 1. The second method investigated was the Self profile method. This method measures the radiation profile method. This method measures the radiation intensity of a moving slug of radioactive material in the borehole. As water is lost to the formation, a decrease in intensity provides information for constructing an injection profile independent of hole diameter. Test Procedures The first series of tests was performed on the apparatus as shown in Fig. 7a. Metered water entered at the top and exited at the bottom. The tracer-ejector tool was stationed at five different locations in the apparatus to record velocity readings at several different metered flow rates. In all, there were 43 readings. JPT P. 1089