The Iceland Deep Drilling Project (IDDP): (4) A Quartz Fluid Inclusion Tool for Sampling Supercritical Geothermal Fluids Downhole
Abstract
Chemical analyses of in situ samples of supercritical geothermal fluids would provide a uniquely good measure of fluid composition at depth relative to compositions reconstructed from analyses of gas and liquid sampled at wellheads. Fluids sampled at the wellhead are commonly a mixture from multiple aquifers and, in many circumstances, they lack components such as sulfate, sulfide, Ca, Cu, Zn, and Fe that precipitated in scale minerals where the fluids boiled or cooled during their ascent. To circumvent the above problems and the failings of downhole mechanical samplers at temperatures exceeding 300°C and to obtain total fluid samples at supercritical conditions in the IDDP wells, we plan to trap fluids in fluid inclusions formed in fractured quartz that we suspend in a geothermal well on a wireline. In a series of hydrothermal laboratory experiments at 450°C and 600 bar and spanning 6 hr to 5 days in length, thermal shock fractures in natural and synthetic quartz crystals heal, forming ragged fluid inclusions in one day and many well formed inclusions in three days. Amorphous silica is added to the experimental charge, without which, fractures heal little and only 1-2 micron inclusions form. Microthermometry measurements on the inclusions produced in experiments return the run temperature within 20°C at the experimental pressure, indicating that inclusions formed and sealed at the run conditions. The fluid inclusion tool (FIT) consists of a perforated stainless steel pipe containing multiple stainless steel mesh canisters with non-mesh ends to minimize vertical fluid flow. The canisters contain 10mm-scale chunks of fractured quartz surrounded by ground quartz glass. The perforated pipe will be fixed within a one-meter outer perforated stainless steel housing that is suspended on a stainless steel slick line. The FIT is weighed by one or more 10kg lead sinker bars. The entire assembly is lowered into the well from a lubricator fitted on the wellhead, thus enabling sampling under high temperatures and pressures. In the initial field testing runs, the contents of the mesh canisters will be varied to examine the effects of ground glass grain size, and the suitability of clear natural quartz vs synthetic quartz, both with respect to fluid inclusion development and chemical analyses of inclusions. Inclusions will be analyzed by various bulk methods and by LA-ICP-MS on individual inclusions. Once we optimize the fluid inclusion tool configuration in field tests and by analytical results, the volume of sampling quartz can be scaled up as needed to provide for optimum sampling and analyses.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFMOS13A1169R
- Keywords:
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- 1034 GEOCHEMISTRY / Hydrothermal systems;
- 3017 MARINE GEOLOGY AND GEOPHYSICS / Hydrothermal systems;
- 3616 MINERALOGY AND PETROLOGY / Hydrothermal systems