Experimental simulation of greywacke–fluid interaction under geothermal conditions

Sonney, Romain; Mountain, Bruce W.

doi:10.1016/j.geothermics.2012.11.003

Cited by 17 publications

(7 citation statements)

References 19 publications

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“…The selective dissolution of feldspars is undoubtedly the result of fluid–rock interactions in sedimentary rock reservoirs. Given that the components of clastic sediments in the given formation or member are similar, it is generally accepted that the composition and properties of the fluids exert the primary control on the selective dissolution of feldspars (Fournier & Truesdell, ; Sonney & Mountain, ; Zhu & Lu, ). On the basis of thermodynamic calculations, Bowers, Jakcson, and Helgeson () proposed that both the relative concentration ratios of K and H ions, and Na and H ions restrict the Gibb's free energy change (ΔG) for the alkali feldspar dissolution reaction, thereby controlling whether orthoclase or albite is selectively dissolved.…”

Section: Introductionmentioning

confidence: 99%

Selective dissolution of alkali feldspars and its effect on Lower Triassic sandy conglomerate reservoirs in the Junggar Basin, northwestern China

Kang

Cao

et al. 2017

Geological Journal

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Feldspar dissolution resulting from fluid–rock reactions in clastic rocks is common in petroliferous sedimentary basins and significantly affects the quality of reservoirs. The objective of this study is a case study of this phenomenon in the sandy conglomerate reservoirs, based on the Lower Triassic Baikouquan Formation in the Mahu Sag at the northwestern margin of the Junggar Basin in northwestern China, which has obtained exploration breakthroughs recently. In these rocks, orthoclase has undergone dissolution and the dissolution intensity decreases gradually from the basal member (T1b1) to the upper member (T1b3) of the formation, whereas albite remained stable or has even overgrown crystals, displaying a selective dissolution of alkali feldspars. This is interpreted to be mainly controlled by two factors. First, illitization of mixed‐layer illite/smectite in the sandy conglomerates consumed K, thereby increasing Na/K ratios in the formation waters and leading to orthoclase dissolution and albite overgrowths on perthite and microcline. Second, the charge of acidic, hydrocarbon‐related fluids further promoted orthoclase dissolution. These relationships are confirmed by the fact that hydrocarbon charging intensity shows a gradual upward reduction from member T1b1 to T1b3, as does the scale of orthoclase dissolution. This selective dissolution resulted from the influence of different mineral components on diagenesis, the acidic nature of reservoir fluids, and the extent of water–rock interaction. The dissolution significantly improved porosity and permeability of the reservoirs by generating substantial secondary porosity. The results indicate a favorable exploration prospect located in the up‐dip area of the Ma 18 and Aihu 2 wells on the western slope of the Mahu Sag.

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Section: Introductionmentioning

confidence: 99%

Selective dissolution of alkali feldspars and its effect on Lower Triassic sandy conglomerate reservoirs in the Junggar Basin, northwestern China

Kang

Cao

et al. 2017

Geological Journal

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“…Experiments from 70 to 400°C were conducted in a hydrothermal flow-through autoclave reactor. The flow-through approach has previously been used to conduct high-temperature metal sulfide solubility studies (e.g., Tagirov et al, 2007), and a similar apparatus to the one in the current study has been used to investigate water-rock reaction (e.g., Sonney and Mountain, 2013). A diagram of the apparatus is shown in Figure (4.2).…”

Section: High Pressure-temperature Flow-through Reaction System and Solution Preparationmentioning

confidence: 99%

The geochemistry of antimony in hydrothermal solutions

Olsen¹

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<p>In this thesis, 30°C stibnite solubility experiments, ambient temperature X-ray absorption spectroscopic measurements of antimony in solution, and high temperature (70 to 400°C) stibnite solubility experiments were carried out in order to determine the aqueous antimony species present in equilibrium with stibnite in hydrosulfide solutions from pH = 3.5 to 12 and reduced sulfur concentrations from 0.001 to 0.1 mol kg⁻¹. Both ambient and elevated temperature solubility studies were conducted using a flow-through apparatus containing a column of stibnite grains though which solutions were pumped. Above 100°C, solubility experiments were conducted at slightly above saturated water vapour pressure to pressures of 300 bar. At 30°C, the stibnite solubility curve was best reproduced by a scheme of five species: Sb₂S₄²⁻, HSb₂S₄⁻, H₂Sb₂S₅²⁻, H₃SbS₂O, and Sb(OH)₃. At higher temperatures (≥ 70 °C), stibnite solubility at the conditions of the experiments was due to the following four species: Sb₂S₄²⁻, HSb₂S₄⁻, H₃SbS₂O, and Sb(OH)₃. Equilibrium constants were determined for the following five heterogeneous solubility reactions for the temperature ranges listed: [Please consult the thesis for details.] Stibnite solubility was independent of pressure at ≤ 350°C. At ~ 400°C, the solubility of stibnite was strongly dependent on pressure and decreased from Sbtotal = 0.015 to 0.0003 mol kg⁻¹ (~2000 to 40 ppm) with a pressure decrease from 300 to 160 bars. The Sb K-edge X-ray absorption spectroscopic (XAS) measurements of antimony in alkaline (pH = 10. 9 to 12) hydrosulfide solutions gave average first shell coordination environments that were consistent with the speciation model derived from solubility experiments for strongly alkaline solutions (i.e., Sb₂S₄²⁻ and Sb(OH)₃). XAS data enable the elimination of a speciation model involving only monomeric antimony complexes at strongly alkaline pH. Antimony speciation in near neutral to strongly alkaline pH’s is dominated by dimeric antimony-sulfide complexes at 30°C and sulfide concentrations > 0.001 mol kg⁻¹. With increasing temperature, antimony speciation becomes increasingly dominated by Sb(OH)₃. For hydrothermal solutions with sulfide concentrations between 0.0001 and 0.01 mol kg⁻¹, antimony-sulfide complexes are predominant at < 100°C, whereas antimonous acid, Sb(OH)₃, is the main aqueous species at contributing to stibnite solubility at > 200°C with the speciation in the intervening temperature range being dependent on the pH and sulfide concentration of the solution. For higher sulfide concentrations (i.e., ~ 0.1 mol kg⁻¹), HSb₂S₄⁻ and Sb₂S₄²⁻ control stibnite solubility to higher temperatures.</p>

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“…3. Weathering, diagenesis and hydrothermal alteration can result in compaction, pervasive alteration, and a decrease or increase in porosity (matrix and fracture) depending on mineral precipitation or dissolution (Custodio, 2007), which is intense in hydrothermal systems (Sonney and Mountain, 2013;McNamara et al, 2016b).…”

Section: Fracture Systems: Processes Description By Scaling Laws and Modellingmentioning

confidence: 99%

“…In contrast, the fracture originally oblique to the extension direction develops a "wing crack" shape, with a large shearing zone, and 3.6 times more variation of pressure than the extension-perpendicular fracture. Secondly, water-rock interactions have fast kinetics in geothermal reservoirs (Sonney and Mountain, 2013), with similar processes likely to occur in the Alpine Fault hangingwall near the fault plane (the Rotokawa reservoir and DFDP-2B have thermal gradients exceeding 100 Sewell et al, 2012;Sutherland et al, 2015). Thirdly, water-rock interactions are further enhanced in chemically reactive volcanic rocks (Custodio, 2007;Crider , 2015).…”

Section: Fluid Flowmentioning

confidence: 99%

Fracture system characterisation and implications for fluid flow in volcanic and metamorphic rocks

Massiot¹

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<p>Fluid flow pathways in volcanic and metamorphic rocks are dominantly controlled by fracture systems. Although these fracture systems are critical for developing reservoirs in an economical and sustainable way, and for understanding processes that cause earthquakes, they are often poorly constrained. This thesis studies the geometry of fracture systems, the factors influencing their geometries, and their possible impacts on permeability in three contrasting settings: an outcropping andesite lava flow of the Ruapehu volcano; the andesite-hosted Rotokawa geothermal reservoir; and the Alpine Fault hangingwall metamorphosed schists. We use datasets from a combination of cores, acoustic borehole televiewer (BHTV) logs, outcrop scanlines, and terrestrial laser scanner (TLS) point clouds, which span multiple scales of observation. Fracture geometries are studied in a young (~6 ka-old) blocky andesitic lava flow on the Ruapehu volcano, as a representative example of weakly-altered andesitic lava flows emplaced over gentle topography in the absence of glaciers. Fractures were formed during cooling and emplacement of the lava flow. Fractures are automatically detected from the 3-D TLS point cloud of an outcrop area of ~3090 m2 using a plane detection algorithm, and calibrated with manual scanlines and high-resolution panoramic photographs. Column-forming fractures dominate the fracture system, are either sub-horizontal or sub-vertical (i.e., sub-parallel or sub-perpendicular to the brecciated margins) without mean strike orientation, and have an exponential length distribution. Sub-horizontal, clustered platy fractures sub-parallel to the flow direction arrest or deflect column-forming fractures. Areal and volumetric fracture intensity analyses reveal a ~0.5 % connected fracture volume which, although seemingly small, promotes fluid flow due to the planarity and connectivity of the system. Autobreccias are partially connected to column-forming fractures, and may promote lateral flow or form barriers depending on the extent of post-cooling alteration and mineralisation. Discrete fracture network models generated with the measured geometrical parameters are in agreement with the observed highly connected fracture system. Fractures in the andesite-hosted Rotokawa Geothermal Field are described in cores and BHTV logs. Fractures interpreted on BHTV logs are separated into sets of similar orientation using quantifiable clustering algorithms. Fracture thickness and spacing probability distributions are estimated from maximum likelihood estimations applied to truncated distributions, taking sampling biases into consideration. Spacing of the predominant sub-vertical NE-SW-striking fracture set, and subordinate NW-SE-striking fracture set, are best approximated by log-normal distributions and interpreted to be controlled by stratifications within the lava flow sequence. By contrast, spacing of other subordinate fracture sets, either dipping 60° and striking NE-SW, or steeply dipping and striking N-S, are best approximated by power-law distributions and interpreted to be fault-controlled. Fracture thicknesses in both cores and BHTV logs are approximated by a single power-law distribution, which reflects heterogeneous pathways observed at reservoir scale. Previously reported ~5 µm-thick fractures studied in thin section do not follow this power-law distribution and have an isotropic orientation, which suggests a change of controls on fracture density and orientation from thermal stresses at thin-section scale, to tectonic and lithological at core and BHTV log scales. However, fractures occupy ~5 % of the rock mass at the three scales of observations, suggesting a self-similar behaviour of fracture volumes in 3-D. In contrast to the Ruapehu and Rotokawa reservoir studies, scientific drilling in 2014 of the DFDP-2B borehole offered a unique opportunity to investigate the foliation and fractures along a 630 m-long borehole section in metamorphic rocks in the hangingwall of the Alpine Fault. BHTV log interpretation reveals a constant foliation and foliation-parallel fracture orientation (60°/145°; dip magnitude/dip direction) similar to nearby outcrops and parallel to the regional strike of the Alpine Fault. This foliation orientation may reflect the orientation of the Alpine Fault at ~1 km depth. In addition, sub-vertical fractures striking NW-SE above ~500 m, and sub-horizontal fractures between ~ 500-820 m below ground, are interpreted as exhumation-related joints and inherited hydrofractures respectively. Finally, we recognise metre-thick fault zones similar to those identified from BHTV logs and cores in the nearby DFDP-1B borehole. The three fracture set orientations, and observed fault zones, promote high hydraulic connectivity in the Alpine Fault hangingwall, which fosters fluid flow. This thesis helps quantify the geometrical parameters of fractures and their associated uncertainties in non-sedimentary settings, which are required to constrain numerical models and unravel fluid flow pathways in heterogeneous rocks. We identified lithological, tectonic and thermal controls on fracture geometries, which can constrain conditions and processes by which these fractures formed, and improve the prediction of fracture system architecture away from sparse borehole observations. The results of this thesis are relevant to similar lithological and tectonic settings elsewhere where observations are scarce. This study has also yielded an essential fracture dataset for better understanding of the structural and hydrological conditions at depth near the Alpine Fault prior to a large earthquake.</p>

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Experimental simulation of greywacke–fluid interaction under geothermal conditions

Cited by 17 publications

References 19 publications

Selective dissolution of alkali feldspars and its effect on Lower Triassic sandy conglomerate reservoirs in the Junggar Basin, northwestern China

Selective dissolution of alkali feldspars and its effect on Lower Triassic sandy conglomerate reservoirs in the Junggar Basin, northwestern China

The geochemistry of antimony in hydrothermal solutions

Fracture system characterisation and implications for fluid flow in volcanic and metamorphic rocks

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