In-Situ Saturation Monitoring (ISSM) - Recommendations for Improved Processing
- Jules Reed (Lloyd’s Register) | Arjen Cense (A/S Norske Shell)
- Document ID
- Society of Petrophysicists and Well-Log Analysts
- Publication Date
- April 2019
- Document Type
- Journal Paper
- 273 - 282
- 2019. Society of Petrophysicists & Well Log Analysts
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- 72 since 2007
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In-situ saturation monitoring (ISSM), using X-rays or gamma rays, has become a common method to determine fluid saturations in commercial coreflood experiments. The most common method in commercial laboratories entails 1D saturation measurements as a function of core-plug length and of experimental time. Laboratories often employ ISSM as the only method of determining fluid saturations, assuming an almost infallible accuracy of 1 to 2 saturation units (s.u.). However, as for all measurement methods, there are possible sources of uncertainty in ISSM data. Previous papers have discussed some of these uncertainties, such as X-ray drift, and inappropriate calibration scans or changes to core or fluid properties during testing. Despite this evidence, some laboratories continue to use ISSM measurements alone, assuming negligible uncertainty.
In the authors’ experience, uncertainties not only exist in measurement errors, but also may be introduced by inappropriate processing and interpretation methods. This paper first considers the stipulated 1 to 2 s.u. accuracy and the necessary signal-to-noise ratio, i.e., counts required, to achieve this; as well as providing a suggested approach, where plausible, to correct saturation data compromised by incorrect calibration scans. It also considers the uncertainties in use of ISSM production volumes in determining unsteady-state relative permeability; specifically, pre- and post-breakthrough data and the assumptions surrounding selection of breakthrough from flood-front scans. In addition, ISSM profiles are often used in coreflood simulation of relative permeability to aid correlation of the capillary end effect; incorrect data processing may compromise this correlation. The paper considers several sources of error in ISSM data and provides a recommended approach to acquisition, processing and interpretation of ISSM data for calculation of fluid saturations.
|File Size||5 MB||Number of Pages||10|