This article, written by JPT Technology Editor Judy Feder, contains highlights of paper SPE 196188, “Third-Generation Production-Logging Technologies Enhance Inflow Profiling in Deepwater Gulf of Mexico Reservoirs,” by Glenn Donovan, SPE, Sagar Kamath, and Elizabeth Tanis, SPE, Shell, et al., prepared for the 2019 SPE Annual Technology Conference and Exhibition, Calgary, 30 September–2 October. The paper has not been peer reviewed.
This paper discusses the effectiveness of third-generation (Gen3) production-logging-tool (PLT) technology, which uses co-located digital sensors for simultaneous acquisition of flow data to provide the most accurate characterization of the flow condition at each depth surveyed. The resulting data allow for much-improved processing. The probabilistic interpretive model used in the processing has been updated to incorporate this and future developments in PLT architecture.
The first generation of PLT provided a single, discrete measurement for each sensor along the tool assembly’s length, resulting in long tool assemblies and measurements taken at different points along the flow path. This approach had several drawbacks: long toolstrings, point sensors that only provided a measurement at a single point in the cross section of the flow, and measurements that were not acquired simultaneously at each depth logged. Second- generation PLTs represented an improvement because sensors were arranged as an array, enabling multiple measurements to be made at a single depth. However, the toolstrings were still long and not all were arranged optimally to capture data in the flow path. The Gen3 PLT is one-tenth the length of the first-generation versions and roughly one-third that of the shortest second-generation tools. Digitalization allows for direct measurement of flow conditions and rapid interpretation of results. In multiphase flow and deviated wells, co-locating sensors in a spatial geometry provides the optimal information with which to create a fully accurate picture of the downhole flow.
Description of Gen3 PLT
The PLT described in the paper exemplifies how miniaturization and digitalization are enabling transformational improvements over traditional systems in terms of efficiency and capability. The tool encompasses, within a 3-ft length, up to 24 sensors that collect multiple measurements of fluid properties and fluid movements in a wellbore. These include oil, gas, and water holdup and bubble count, fluid conductivity, phase velocities, pressure, temperature, inclination, rotation, and depth correlation, plus power and communication. The fluid characteristics are locally screened by an array of 8 to 16 tube-shaped probe sensors that are interchangeable, depending on the targeted measurements (Fig. 1).
The tool relies on a refractive index needle-shaped probe with a triphasic sensor to identify and quantify the oil, gas, and water holdups and bubble counts at each point of the array. The geometric design of the sensitive tip, along with the optoelectronics of the sensor, are optimized to discriminate oil, water, and gas with high confidence, overcoming the fact that the refractive indexes of oil and water are close to each other.