Schlumberger

RSTPro Reservoir Saturation Tool

Overview Library

Pulsed neutron determination of reservoir saturation, porosity, and borehole fluid flow and three-phase holdup

The RSTPro reservoir saturation tool incorporates a pulsed neutron generator and a dual-detector spectrometry system that measures elemental concentrations, including carbon and oxygen, and the formation neutron-capture cross section (sigma) during a single trip in the well.

  • Oil volume is computed from the carbon/oxygen (C/O) ratio determined through full spectral analysis of RSTPro measurements to eliminate any environmental bias and also from a windows-based C/O ratio. Proprietary alpha processing combines the two volume determinations to deliver a saturation answer that is both highly accurate and can be acquired at faster logging speeds. The accuracy of the resulting reserves estimates is comparable to that from core analysis.
  • The sigma measurement is used to determine porosity and differentiates between saline water and oil to calculate formation oil saturation. Where formation water is fresh or of unknown salinity, saturation is determined from the C/O ratio measurement, which is salinity independent.
  • The TPHL three-phase holdup log made with the RSTPro tool is a continuous measurement of the holdups of oil, water, and gas for wells at any deviation.
  • A quantitative, mineral-based lithology interpretation is produced by inputting the elemental yields measured by the RSTPro tool to SpectroLith lithology processing.
  • The WFL water flow log made with the RSTPro tool is conducted to locate and evaluate axial water migration behind pipe, measure the velocity of water flow in a well, and determine internal or behind-pipe crossflow between zones. The RSTPro tool is configured to measure both upward and downward flow, inside casing and behind pipe.
  • The PVL phase velocity log made with the RSTPro tool measures a marker element that is soluble in either oil or water only to calculate the velocity of that phase in a deviated well with segregated flow.

Streamlined logistics and efficiency

An electronic generator in the RSTPro tool emits high-energy (14-MeV) neutrons in precisely controlled bursts. The RSTPro tool in turn measures the gamma rays that result when the high-energy neutrons interact with the wellbore fluids, casing, cement, matrix, and fluid-filled porosity to cause inelastic scattering, thermal neutron capture, and activation. With its ability to log flowing wells because of shielding-enhanced detector sensitivity, the RSTPro tool does not require pulling tubing or killing the well, and reinvasion is avoided.

The use of a sourceless generator of neutrons instead of a conventional chemical radioactive source both simplifies logistics and improves operational safety.

Combinability with PS Platform production logging platform

The RSTPro tool is combinable with tools that use the telemetry system of the PS Platform production services platform. Measurements made with the RSTPro tool in combination with the PS Platform suite of cased hole tools are the basis for efficiently identifying bypassed hydrocarbons, evaluating and monitoring reserves in mixed-salinity and gas environments, conducting formation evaluation behind casing, measuring three-phase holdup, and diagnosing well problems independently of well deviation.

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