Characterization and saturation determination of reservoir metagraywacke from The Geysers corehole SB-15-D (USA), using Nuclear Magnetic Resonance Spectrometry and X-ray Computed Tomography
✍ Scribed by Eric M. Withjack; James R. Durham
- Book ID
- 104333253
- Publisher
- Elsevier Science
- Year
- 2001
- Tongue
- English
- Weight
- 989 KB
- Volume
- 30
- Category
- Article
- ISSN
- 0375-6505
No coin nor oath required. For personal study only.
✦ Synopsis
Novel pressure-coring technology, along with nuclear magnetic resonance (NMR) spectrometry and X-ray computed tomography (CT) of cores retrieved from scienti®c drillhole SB-15-D in the Sulphur Bank area of The Geysers steam ®eld, have enabled the ®rst measurements of indigenous water saturation in a high-temperature, vapor-dominated geothermal system. Two cores for the analyses were obtained using a wireline-retrievable core barrel sealed and pressurized at simulated reservoir pressure during ascent to the surface, and there immediately frozen in dry ice and secured in insulated receptacles to immobilize contained ¯uids. Immediately upon being thawed at the laboratory, the cores were measured for total water volume by NMR. These values, combined with rock porosities later determined by Boyles Law gas expansion, yielded total water saturations. For the deeper of the two cores (485.2±488.3 m), water saturation was determined by these methods to be 3±13%, but these values probably include some drilling-¯uid ®ltrate. For the shallower core (432.9±435.8 m), ®ltrate incursion was measurable by CT, since a tritium tracer had been added to the drilling ¯uid during coring operations. Filtrate accounted for a ®fth to three-®fths of the total water in this core, and corrected water saturations ranged from 8 to 25%. Results of subsequent CTbased experiments on the cores suggest that invasion probably took place as a result of drilling-¯uid vaporization and convective migration of the vaporized ®ltrate. This ®nding (1) implies that much of the hot (about 235 C) cored rock sequence is relatively dry; and (2) independently supports the low water saturation measurements obtained by NMR. The dryness Geothermics 30 (2001) 255±268 www.elsevier.com/locate/geothermics