Case Studies Downhole Sampling

Downhole fluid sampling of a natural CO2 reservoir at Green River, Utah (2013)

Understanding the geochemical behavior of gaseous and supercritical carbon dioxide stored in geological reservoirs, over a range of timescales, is crucial for quantifying leakage risk and the geochemical evolution of the stored CO2 through the life of an individual storage site (e.g. Bickle, 2009). Dissolution of the stored CO2 into reservoir brine will likely form an important mechanism for stabilizing the CO2 in geological reservoirs (e.g. Gilfillan et al., 2009; see review in Kampman et al., 2013a). Reactions between the acidified CO2-charged brine and reservoir minerals might enhance the long-term storage of CO2 by precipitation of carbonate minerals, or facilitate leakage by corroding cap rocks and fault seals. The fundamental goals of this project are to characterize and understand the mineralogical, geochemical, petro physical and geomechanical consequences of long-term exposure of supercritical CO2, CO2-gas and CO2-charged fluids on reservoir rocks, cap rocks and fault zone materials. This will improve our predictions of the long-term security of anthropogenic CO2 geological storage sites. Data gathered from uncontaminated and undegassed CO2-rich fluid samples was a key objective of the Green River Drilling project. Therefore fluids were collected downhole at formation pressure by using the Leutert Downhole Sampler PDS.


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Fluid sampling in geothermal wells

Production of heat or power from geothermal systems is becoming increasingly attractive as an alternative energy supply. Hydrothermal systems where the hot fluid can be directly produced from the geological formation are of special interest. Chemical composition of fluids plays a major role in the operation of geothermal power plants, since some of the ingredients of these complex solution - gas mixtures might be highly corrosive and damage the infrastructure of the geothermal plant. Other compounds might precipitate either within the plant or in the reservoir as the cooled fluid will be re-injected into the formation. Decreasing fluid flow is the result of clogging the pipes of the plant and the pores of the rock. The latter occurrence, can cause irreparable damages to the reservoir by reducing its infectivity. Therefore, fluid properties need to be known, and chemical reactions taking place during fluid processing should be understood. At Gross Schonebeck site (North German basin) a Leutert one phase™ sampler (OPS) was used for fluid sampling between 2001 and 2009. This device allows the collection of fluid samples from known borehole depths at in-situ p- and T-conditions. The samples were taken at 4100–4235m depth (~150 °C/ ~45MPa) and analyzed for their chemical composition, with special focus on parameters relevant to scaling and corrosion. The results of this project were published and may be downloaded at Elsevier.

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