A New Approach Towards Flow Diagnostic in High-Rate Gas Wells

Abstract High gas rate wells flowing up to 80 MMscfd pose challenges for flow diagnostics. Conventional methods for measuring gas and water holdups, such as local electrical probes, fail in these extreme conditions due to the extremely small droplets and hydrodynamic effects. Approaches based on fluid column density measurements suffer from large inaccuracies due to friction effects. The paper describes the sensor technology and field results from a high gas rate well with small water cut and complex flow regime. To overcome these challenges, an operating company worked with a service and manufacturing company to improve a compact toolstring capable of delivering reliable flow data (holdups and phase velocity) for phase allocation over an interval with multiple zones and different fluid properties. The toolstring developed is shorter than conventional tools (just over three foot long) and causes minimal flow disturbance. Azimuthal phase holdups and velocities are collocated with one foot away auxiliary measurements of pressure, temperature, MEMS Magnetic Locator (MML) for casing collar detection and depth correlation, tool orientation, and deviation. The flow array sensors consist of triphasic optical probes, conductivity probes, micro-capacitances, Doppler, and wide-range robust micro-spinners. Segregated flow with water recirculation was observed. The micro-capacitances provided the most reliable source for water holdup while the electrical probes in mist flow, as expected, stopped detecting water at flow speeds of 2 m/s. The triphasic optical probes showed good gas hold up measurements at the whole range of flow velocities in the well and responded to a small water entry in the middle of the perforated zone. All micro-spinners rotated well throughout the survey even at the highest rate. The radar sonde detected water droplets down to micrometer size using the retro diffusion of light electromagnetic signal at a distance from the sensor surface. While the EM radar senses water movement inside the mist flow, the Doppler sensors allowed to monitor movement in the water dominant leg at the well bottom. Thanks to integrating all types of sensors physics, a robust flow diagnostic allowed the operator to understand the water and gas entries, while the conventional sensors could not, and consider remedial actions for water shutoff. The present sensor configuration and tool string can be used as reference for logging in the same field or similar flow conditions. In order to detect water, two novel sensors were developed: micro-capacitance probes to measure water holdup and electromagnetic radar for measuring flow speed. The standalone radar module operates in high velocity flow and does not require direct contact between droplets and the sensing element, as micrometer size water droplets can be detected with the retro diffusion of light EM signal at a distance from the sensor surface.