Deposition Of Secondary Minerals Research Articles

Effect of Boiling and Cooling of Geothermal Fluids on Precipitation of Secondary Minerals: A Case Study of Olkaria Fields, Kenya

The main drawback in the utilization of geothermal resources arises from the precipitation of secondary minerals within wells, pipelines, steam separators, turbines and other surface equipment in form of scales. Scale formation is an outcome of the alteration of various rocks dissolved in geothermal fluids that find their way into a reservoir. Once geothermal fluids ascend to the surface, hydrostatic pressure decreases toward a phase separation level that permits the dissolved gases such as CO2, H2S and H2, and steam to separate from the liquid phase by “boiling”. Stripping of these volatiles may increase fluid pH, leading to precipitation and deposition of secondary minerals. The study sought to establish the relationship between water-rock interaction and secondary mineral precipitates at the surface and deep fluid at different temperatures during depressurisation boiling and cooling. Samples were collected from selected Olkaria wells; OW-38A, OW-910 and OW-910A. The analysis of the results outlined deep fluid Alkali-Chloride waters and surface steam-heated Alkali-Bicarbonate and acidic Sulphate-Chloride waters. Various models suggested adiabatic boiling, conductive cooling and possible mixing and dilution in the wells. Hydrothermal alteration minerals were found to be in equilibrium with the geothermal fluids at varying temperatures, and the secondary minerals controlled the chemistry of the reservoir. Silica-saturated solutions precipitated silica in OW-910 and OW-910A, which may have resulted from rapid cooling following mixing with cold surface water.

Experimental investigation of CO2–rock–brine interaction for injection of CO2 in an Iranian oil reservoir as an EOR method

In this study, possibility of geological storage of CO2 into an Iranian hydrocarbon reservoir is investigated as a method of enhanced oil recovery (EOR). For this purpose, a stainless steel sand packed model, containing rock and brine, was used to simulate the reservoir condition and CO2 injection. Subsequently, CO2–rock–brine interactions (dissolution and deposition of minerals) due to CO2 injection, under reservoir pressure and temperature condition (136 bar and 80 °C), was studied with ion chromatography and pH measurement at time intervals of 7, 14 and 30 days. In addition, the rock structure was identified by X-ray diffraction analysis. Results showed that up to 14 days, pH and the concentration of cations (sodium, calcium, magnesium, and potassium) and anions (chloride and sulfate) were progressively increased. However, in 30 days, assays, both pH and concentration, were decreased compared to those of 14 days of test results. Consequently, the dissolution process was observed to be the dominant phenomenon in the early days; then, the deposition of secondary minerals became the main process during the performed test. Finally, in the case of selecting the right place for CO2 injection, to avoid the porosity and permeability decrease near the well, this method can be used as a safe technique for CO2 geological storage at specific time intervals in the studied oil reservoir.

Skeleton bones in museum indoor environments offer niches for fungi and are affected by weathering and deposition of secondary minerals.

Large skeleton specimens are often featured as iconic open displays in Natural History Museums, for example, the blue whale 'Hope' at the Natural History Museum, London. A study on Hope's bone surface was performed to assess the biodeterioration potential of fungi. Fungi were isolated, and a fungal internal transcribed spacer (ITS) clone library survey was performed on dust and bone material. Mineral particles derived from bone and dust were analysed using energy dispersive X-ray spectroscopy, variable pressure scanning electron microscopy (SEM) and high vacuum SEM. Results showed that bone material, although mainly mineral in nature, and therefore less susceptible than organic materials to biodeterioration phenomena in the indoor environments, offers niches for specialized fungi and is affected by unusual and yet not so well-documented mechanisms of alteration. Areas of bone surface were covered with a dense biofilm mostly composed of fungal hyphae, which produced tunnelling and extensive deposition of calcium and iron-containing secondary minerals. Airborne halophilic and xerophilic fungi including taxa grouping into Ascomycota and Basidiomycota, capable of displacing salts and overcome little water availability, were found to dominate the microbiome of the bone surface.

Mineral trapping of a CO2/H2S mixture by hematite under initially dry hydrothermal conditions

For the experimental simulation of geochemical processes occurring in the vicinity of an injection well for CO2 with H2S impurities, the reaction of hematite with a CO2/H2S acid gas mixture in an initially water-free system was investigated. At the reaction conditions (120°C, 12MPa), a reductive dissolution of hematite and the successive precipitation of iron sulfide minerals pyrrhotite, marcasite and pyrite together with siderite were observed within days. Precipitation of secondary minerals presumably occurred either in the supercritical CO2 phase or, more likely, in an aqueous phase generated during the reaction progress due to the high initial H2S portion in CO2. The overall process can be described byFe2O3+2H2S+CO2→FeS2+FeCO3+2H2O.The observed process is relevant for the geologic co-storage of CO2 with H2S in sandstone formations with a substantial fraction of hematite (e.g. red-beds). There, mineral trapping of CO2 will be significantly promoted by reaction of co-injected H2S or SO2 with hematite – even in the dried-out zone near the injection well. This process can significantly impact the porosity of the storage rock due to an initial dissolution of hematite and subsequent deposition of secondary minerals with larger total volume. Hence, a plugging of pore throats appears to be feasible even in the desiccated zone in the vicinity of a CO2 or acid gas injection well.

Geochemical distribution and removal of As, Fe, Mn and Al in a surface water system affected by acid mine drainage at a coalfield in Southwestern China

The chemical characteristics, formation and natural attenuation of pollutants in the coal acid mine drainage (AMD) at Xingren coalfield, Southwest China, are discussed in this paper based on the results of a geochemical investigation as well as geological and hydrogeological background information. The chemical composition of the AMD is controlled by the dissolution of sulfide minerals in the coal seam, the initial composition of the groundwater and the water–rock interaction. The AMD is characterized by high sulfate concentrations, high levels of dissolved metals (Fe, Al, Mn, etc.) and low pH values. Ca2+ and SO4 2− are the dominant cation and anion in the AMD, respectively, while Ca2+ and HCO3 − are present at significant levels in background water and surface water after the drainage leaves the mine site. The pH and alkalinity increase asymptotically with the distance along the flow path, while concentrations of sulfate, ferrous iron, aluminum and manganese are typically controlled by the deposition of secondary minerals. Low concentrations of As and other pollutants in the surface waters of the Xingren coalfield could be due to relatively low quantities being released from coal seams, to adsorption and coprecipitation on secondary minerals in stream sediments, and to dilution by unpolluted surface recharge. Although As is not the most serious water quality problem in the Xingren region at present, it is still a potential environmental problem.

Damage in granite under heating/cooling cycles and water freeze–thaw condition

In most engineering structures with rock materials, temperature variation, water content and fluid permeability are primarily responsible for rock deterioration. They affect the microstructural properties of the rock by inducing new microcracks and mineralogical changes in the material. In addition, microstructural changes, especially microcracks development in the rock, affect its physical and mechanical properties. The physicomechanical properties of the rocks are essential when assessing their suitability for use as dimension stone, as well as their durability. In crystalline rocks, such as granite, even a small temperature variation causes thermal cracking. This is because high thermal stresses arising from differential thermal expansion between mineral grains produce new microcracks or open cracks that are already in existence [1,2]. These new micro-discontinuities, together with those already exist, constitute the main fluid permeation pathway in this type of rocks because the matrix porosity is poorly developed [3]. The fluid reacts with the rock at the rock–water interface, producing mineral dissolution and/ or precipitation reactions [4]. In silicate rocks, water reacts with silicate to break the bond, inducing profound chemical effects on the physical properties and the microstructure of the rock [5]. Any mineralogical change implies a modification of the geometry of the porous network, which enhances or reduces fluid flow in the rock. For example, the deposition of secondary minerals within a fracture or a crack wall can completely or partially seal this

Initial behavior of granite in response to injection of CO 2-saturated fluid

To understand the initial reactions of granite in a CO 2-saturated hydrothermal system, experiments were conducted using a batch-type autoclave over a temperature range of 100–350 °C at up to 250 bar and numerical computations of phase equilibria based on the experimental results were carried out. The experiments showed that the dissolution of granite and the deposition of secondary minerals were encouraged by the addition of CO 2. Solution chemistry and examination of the granite’s surface texture suggested that its initial dissolution is characterized by the release of Na and Ca (from the dissolution of plagioclase) and that initial precipitation occurs by deposition of some secondary minerals on to plagioclase and/or biotite in the CO 2-saturated system. However, the effect of CO 2 was small at 350 °C owing to the low activity of H 2CO 3. According to EDX analysis and numerical phase equilibrium calculations, the secondary minerals formed might be kaolinite, muscovite, smectite and calcite. That is, the granite as a whole might have the potential to take-up dissolved CO 2. The results suggest that the alteration of granite under CO 2-saturated hydrothermal conditions has the potential to capture CO 2 when it is injected at moderate temperatures (150–250 °C) into granite-hosted rock masses.

Comment on: “Origin, timing, and temperature of secondary calcite-silica mineral formation at Yucca Mountain, Nevada” by N. S. F. Wilson, J. S. Cline, and Y. V. Amelin

Yucca Mountain in southern Nevada is being evaluated as a potential site for the geological disposal of high-level nuclear waste. A reliable assessment of the future performance of the repository will require detailed paleohydrogeological information. Hydrogenic secondary minerals from the vadose zone of Yucca Mountain are being studied as paleohydrogeological indicators. A phenomenological model envisaging the deposition of secondary minerals by meteoric fluids infiltrating downward though the vadose zone was proposed in the reviewed paper. Our evaluation reveals that the model is not supported by empiric evidence reported in the paper.

CO 2 injection to granite and sandstone in experimental rock/hot water systems

Experiments were conducted using a batch type micro-autoclave over a temperature range of 100–350 °C to understand granite and sandstone reactions in hot water in the absence or presence of excess CO 2. Our experiments, for one-week duration, show that the dissolution of granite and sandstone, and the deposition of secondary minerals, is enhanced by the presence of excess CO 2. Major element concentrations of the residual solution from the batch autoclave experiments were higher for the rock (granite or sandstone)/H 2O/CO 2 system, than in the rock (granite or sandstone)/H 2O system, but the sample weight loss was lower in the rock/H 2O/CO 2 system than in the rock/H 2O system. Changes in sample weight and CO 2-gas volume content concur with the deposition of aluminium silicate and calcium-aluminosilicate secondary minerals, which indicate fixation of CO 2 in the rock. Our results suggest that it may be possible for granite and/or sandstone to ‘capture’ CO 2, at hydrothermal conditions, and that underground disposal may be a feasible solution to reducing atmospheric emission of CO 2.

Modeling multiphase non-isothermal fluid flow and reactive geochemical transport in variably saturated fractured rocks: 2. Applications to supergene copper enrichment and hydrothermal flows

Reactive fluid flow and geochemical transport in unsaturated fractured rocks has been of increasing interest to investigators in the areas of geo- and environmental- sciences. To test geochemical hypotheses based on petrologic observation and to predict geochemical reactions that occur through a complex dynamic interplay of physical and chemical processes, we use the methods presented in a companion paper (part 1, this issue p. 16–33) to investigate two problems: (1) supergene copper enrichment in unsaturated-saturated media and (2) predicted effects of thermohydrology on geochemistry during the Drift Scale Heater Test at the Yucca Mountain potential nuclear waste repository, Nevada. Through these two examples we address the importance of the following issues on geochemical processes: (1) participation of gas phase in transport and reaction, (2) interactions between fractures and rock matrix for water and chemical constituents, (3) heat effects on fluid flow and reaction properties and processes. In the supergene enrichment system, oxygen gas diffusion from the land surface through fractured rock promotes the alteration of the primary sulfide minerals and the subsequent deposition of secondary minerals. Modeling of the large-scale heater test shows effects of fracture-matrix interaction, heat-driven vaporizing fluid flow, and CO₂ degassing on mineral alteration patterns. The two examples also serve as a demonstration of our methods for reactive transport in variably saturated fractured rocks.

Anisotropic seismic scattering in old Atlantic crust

An oblique seismic experiment (OSE) was carried out at Ocean Drilling Program (ODP) Hole 418A in the western North Atlantic to investigate vertical, lateral, and azimuthal structural variations in the upper portions of relatively old ocean crust. Original analysis of the data for travel time anisotropy did not show systematic azimuthal trends in seismic structure except at shallow depths immediately adjacent to the borehole. Subsequent analysis of the OSE data, presented here, reveals a correlation between scattering strengths versus azimuth and spreading direction of the crust. Analyses are performed on body and coda waves and include coda energy and normalized coda energy calculations, spectral analysis, coda dropoff rates, and cross‐correlation analysis. All of the analyses show trends indicating an increase in seismic scattering along directions parallel to the paleospreading direction. These results suggest that evidence of crustal formation processes is still present and seismically detectable after 108 m.y. of crustal evolution. Scattering is likely caused by crustal cracks and/or aligned heterogeneities indicating that either large crustal cracks are still present in the crust or that homogenization of the crust through hydrothermal deposition of secondary minerals is not complete at this site.

The Role of Convective Geothermal Systems in the Generation, Migration, and Entrapment of Oil: ABSTRACT

Modern convective geothermal systems (for example, at Yellowstone National Park) and their fossil equivalents, epithermal mineral deposits (like McLaughlin, California) have traditionally been considered poor petroleum prospects. The concentrated heat which drives these systems is commonly viewed as a negative influence: in other words, any oil initially present in or generated by these systems is quickly degraded to a useless carbonaceous residue. This is true in extreme cases, but numerous examples from the Great Basin, the northern California Coast Ranges, and elsewhere suggest that under certain circumstances, geothermal systems can efficiently generate, transport, and entrap significant quantities of producible petroleum. B.R.T. Simoneit has shown that oil can be hydrothermally generated in an {open_quotes} instant{close_quotes} of geologic time. It follows, then, that away from geothermal systems` high-temperature centers (or in wholly moderate-temperature systems), the encompassing shallow thermal anomalies can distill large volumes of oil from otherwise immature hydrocarbon source rocks. Transport of this newly-generated oil is enhanced by the buoyant upwelling of heated aqueous fluid. Porosity for oil transport and storage is created or increased by hydrothermal dissolution of rock-forming or secondary silicates and carbonates. Finally, geothermal {open_quotes}self-sealing{close_quotes} -- the deposition of secondary minerals (especially silica and clay) at the marginsmore » of a system -- can provide a very effective hydrocarbon seal. Lee Allison has noted the coincidence of igneous intrusions and oil reservoirs in Nevada. It is suggested that here and elsewhere, both igneous-related and amagmatic geothermal systems in otherwise favorable settings should be viewed as prime petroleum exploration targets.« less

Biodegradation of crude oil and mineral deposition in a shallow Gulf Coast salt dome

Crude oil biodegradation and related mineral deposition are taking place at the present time in the shallow caprock and overlaying Heterostegina limestone of the Damon Mound Salt Dome, Brazoria County, Texas. Scanning electron microscopy shows calcite, pyrite, and some elemental sulfur in intimate association with microbes, biodegraded crude oil, and gypsum. Similar processes, involving aerobic and anaerobic microbial activity, are suggested to explain the massive deposition of secondary minerals which occurred at Damon Mound in the geologic past.