Integrating Wellbore Flow Images with a Conventional Production Log Interpretation Method

Abstract

Abstract Horizontal well production logging (PL) measurements, especially center-sample devices, have been misleading in evaluation of the flowing stream. These inaccuracies are due to the natural segregation of the fluids owing to the difference in the phase densities. A new multiphase holdup tool and interpretation method has been developed that provides accurate determination of holdups and flowrates in horizontal wells. The multiphase holdup tool uses 12 capacitance-sensing circuits with multiple arm arrangements to provide an excellent image of the holdup pattern. Since these sensors are on the same cross-sectional plane, depth inconsistencies are not a factor in the interpretation. Each sensor responds to the permittivity (dielectric constant) of the surrounding fluids, and the response can be converted to a phase holdup by applying the known sensor calibration. Consideration of each sensor's position relative to the wellbore allows for prediction of the total phase holdup across the entire wellbore cross sectional plane. Advanced analysis packages allow the user to interact with the computed holdups, providing an easy method of interpretation. Different views of the wellbore, cross-sectional displays, and displays incorporating the wellbore trajectory allow accurate and detailed analysis that is critical for understanding flow in horizontal wells. Once the holdup of each phase (gas, oil, and water) is determined, an additional interpretation package allows a complete production log analysis including flowrates in a very difficult environment. The results of these analysis packages allow an operator to understand, modify, and improve the productivity of a horizontal well. Tool Design and Operations Phase separation makes it extremely difficult to get a good view of holdup in horizontal wells by using standard center-sampling tools. The Capacitance Array Tool (CAT™) solves this problem by using a circular array of 12 micro-capacitance sensors. They are radially distributed in the wellbore to measure accurately phase holdups. Fig. 1 is a picture of the tool showing the sensors with the arms in the out position. These cylindrical sensors have a diameter of 0.157 inches and are 0.055 inches long located 0.35 inches from the end of the motorized arm as shown in Fig. 2 and Fig. 3. Each sensor forms part of a circuit that resonates at different frequencies in gas, oil, and water. This variation in resonance allows the tool to determine what phase exists at a given region across the wellbore. Responding to the capacitance value around the probe, the oscillator circuits produce a low frequency in water, high frequency in oil, and a higher frequency in gas. Sensor frequencies are typically sampled 72 times per second (dependent upon the telemetry) and relayed to surface where they can be processed for presentation.1 The sensors have a radius of investigation of about 0.01 inches. Sensors are electrically isolated from other CAT components so that they only register capacitance values from their immediate environment. These micro-capacitance sensors are expected to measure the individual segregated phases (water, oil, or gas) that are assumed to surround them. However, due to the sensor and calibration response the holdup mixtures of any two phases can be accurately determined. Therefore, each of the 12 sensors will measure gas, oil, or water, or a mixture of two phases depending upon software parameter selection. The CAT's geometry makes it especially well suited to measuring holdup near the top and bottom of any cross section normal to the axis of the wellbore since all sensors are in this plane. The array provides full coverage across the wellbore, making it possible to accurately identify fluid in horizontal or highly deviated wells as shown in Fig. 2.