The Resistance Array Tool (RAT) and Capacitance Array Tool (CAT) are array fluid identifiers for highly deviated and horizontal wells.
The CAT and RAT technologies acquire 12 localised measurements, aligned in a single plane across the diameter of the wellbore, combined with an inbuilt orientation sensor, to produce an accurate cross-sectional plot of fluid phases. These measurements are transformed into localised hold-up values, which when combined with other standard and array measurements, are used to generate a powerful 3D image of the multiphase flow profile.
With its miniature capacitance sensors the CAT measures the dielectric properties of the fluid surrounding the probes. From this it is possible to resolve the presence of water, oil and gas in segregated flow regimes enabling the computation of hold-up values for each of the three individual phases.
Utilising similarly micro-sized resistance sensors, the RAT analyses the electrical conductivity of the fluid in contact with the sensor elements. This technique is highly sensitive to fast moving bubbles of oil or gas trapped within a flowing volume of water and is ideally suited to both segregated or comingled flowing regimes.
The CAT and RAT technologies provide highly complementary measurements and are frequently run in combination to achieve in-depth understanding of fluid composition and distribution of phases.