Geofluids

Permeability and diffusivity are critical parameters of tight reservoir rocks that determine their viability for commercial development. Current methods for measuring permeability and/or diffusivity may lead to erroneous results when applied to very tight rocks including gas shales, coal, and tight gas sands, as well as rocks considered as seals for nuclear waste repositories and strata for geological sequestration of CO₂. The use of He as routinely applied to measure porosity, permeability, and diffusivity may result in non‐systematic errors because of the molecular sieving effect of the fine pore structure to larger molecules such as reservoir gases. Utilizing gases with larger adsorption potentials than He, such as N₂, and including all reservoir gases to measure porosity or permeability of rocks with high surface area is a viable alternative, but requires correcting for adsorption in the analyses. This study expands several approaches to measure permeability and diffusivity with considerations for gas adsorption, which has not been explicitly considered in previous studies. We present new models that explicitly correct for adsorption during pulse‐decay measurements of core under reservoir conditions, as well as on crushed samples used to approximate permeability or diffusivity. We also present a method to determine permeability or diffusivity from on‐site drill‐core desorption test data as carried out to determine gas in place in coals or gas shales. Our new approach utilizes late‐time data from experimental pressure‐decay tests, which we show to be more reliable and theoretically (and practically) accurate than the early‐time approach commonly used to estimate gas‐transport properties.

The capillary sealing efficiency of fine‐grained sedimentary rocks has been investigated by gas breakthrough experiments on fully water saturated claystones and siltstones (Boom Clay from Belgium, Opalinus Clay from Switzerland and Tertiary mudstone from offshore Norway) of different lithological compositions. Sand contents of the samples were consistently below 12%, major clay minerals were illite and smectite. Porosities determined by mercury injection lay between 10 and 30% while specific surface areas determined by nitrogen adsorption (BET method) ranged from 20 to 48 m² g ^− 1. Total organic carbon contents were below 2%.

Prior to the gas breakthrough experiments the absolute (single phase) permeability (k_abs) of the samples was determined by steady state flow tests with water or NaCl brine. The k_abs values ranged between 3 and 550 nDarcy (3 × 10⁻²¹ and 5.5 × 10⁻¹⁹ m²). The maximum effective permeability to the gas‐phase (k_eff) measured after gas breakthrough on initially water‐saturated samples extended from 0.01 nDarcy (1 × 10⁻²³ m²) up to 1100 nDarcy (1.1 × 10⁻¹⁸ m²). The residual differential pressures after re‐imbibition of the water phase, referred to as the ‘minimum capillary displacement pressures’ (P_d), ranged from 0.06 to 6.7 MPa. During the re‐imbibition process the effective permeability to the gas phase decreases with decreasing differential pressure. The recorded permeability/pressure data were used to derive the pore size distribution (mostly between 8 and 60 nm) and the transport porosity of the conducting pore system (10^‐5–10^‐2%).

Correlations could be established between (i) absolute permeability coefficients and the maximum effective permeability coefficients and (ii) effective or absolute permeability coefficients and capillary sealing efficiency. No correlation was found between the capillary displacement pressures determined from gas breakthrough experiments and those derived theoretically by mercury injection.

The capillary‐sealing efficiency of intermediate‐ to low‐permeable sedimentary rocks has been investigated by N₂, CO₂ and CH₄ breakthrough experiments on initially fully water‐saturated rocks of different lithological compositions. Differential gas pressures up to 20 MPa were imposed across samples of 10–20 mm thickness, and the decline of the differential pressures was monitored over time. Absolute (single‐phase) permeability coefficients (k_abs), determined by steady‐state fluid flow tests, ranged between 10⁻²² and 10⁻¹⁵ m². Maximum effective permeabilities to the gas phase k_eff(max), measured after gas breakthrough at maximum gas saturation, extended from 10⁻²⁶ to 10⁻¹⁸ m². Because of re‐imbibition of water into the interconnected gas‐conducting pore system, the effective permeability to the gas phase decreases with decreasing differential (capillary) pressure. At the end of the breakthrough experiments, a residual pressure difference persists, indicating the shut‐off of the gas‐conducting pore system. These pressures, referred to as the ‘minimum capillary displacement pressures’ (P_d), ranged from 0.1 up to 6.7 MPa. Correlations were established between (i) absolute and effective permeability coefficients and (ii) effective or absolute permeability and capillary displacement pressure. Results indicate systematic differences in gas breakthrough behaviour of N₂, CO₂ and CH₄, reflecting differences in wettability and interfacial tension. Additionally, a simple dynamic model for gas leakage through a capillary seal is presented, taking into account the variation of effective permeability as a function of buoyancy pressure exerted by a gas column underneath the seal.

The permeability of the Earth's crust commonly varies over many orders of magnitude. Flow velocity can range over several orders of magnitude in structures of interest that vary in scale from centimeters to kilometers. To accurately and efficiently model multiphase flow in geologic media, we introduce a fully conservative node‐centered finite volume method coupled with a Galerkin finite element method on an unstructured triangular grid with a complementary finite volume subgrid. The effectiveness of this approach is demonstrated by comparison with traditional solution methods and by multiphase flow simulations for heterogeneous permeability fields including complex geometries that produce transport parameters and lengths scales varying over four orders of magnitude.

Detailed information on the hydrogeologic and hydraulic properties of the deeper parts of the upper continental crust is scarce. The pilot hole of the deep research drillhole (KTB) in crystalline basement of central Germany provided access to the crust for an exceptional pumping experiment of 1‐year duration. The hydraulic properties of fractured crystalline rocks at 4 km depth were derived from the well test and a total of 23100 m³ of saline fluid was pumped from the crustal reservoir. The experiment shows that the water‐saturated fracture pore space of the brittle upper crust is highly connected, hence, the continental upper crust is an aquifer. The pressure–time data from the well tests showed three distinct flow periods: the first period relates to wellbore storage and skin effects, the second flow period shows the typical characteristics of the homogeneous isotropic basement rock aquifer and the third flow period relates to the influence of a distant hydraulic border, probably an effect of the Franconian lineament, a steep dipping major thrust fault known from surface geology. The data analysis provided a transmissivity of the pumped aquifer T = 6.1 × 10⁻⁶ m² sec⁻¹, the corresponding hydraulic conductivity (permeability) is K = 4.07 × 10⁻⁸ m sec⁻¹ and the computed storage coefficient (storativity) of the aquifer of about S = 5 × 10⁻⁶. This unexpected high permeability of the continental upper crust is well within the conditions of possible advective flow. The average flow porosity of the fractured basement aquifer is 0.6–0.7% and this range can be taken as a representative and characteristic values for the continental upper crust in general. The chemical composition of the pumped fluid was nearly constant during the 1‐year test. The total of dissolved solids amounts to 62 g l⁻¹ and comprise mainly a mixture of CaCl₂ and NaCl; all other dissolved components amount to about 2 g l⁻¹. The cation proportions of the fluid (X_Ca approximately 0.6) reflects the mineralogical composition of the reservoir rock and the high salinity results from desiccation (H₂O‐loss) due to the formation of abundant hydrate minerals during water–rock interaction. The constant fluid composition suggests that the fluid has been pumped from a rather homogeneous reservoir lithology dominated by metagabbros and amphibolites containing abundant Ca‐rich plagioclase.

Mỏ vàng Sanshandao, nằm ở phía tây bắc của bán đảo Jiaodong, đông Bắc Trung Quốc, là một trong những mỏ vàng lớn nhất thuộc tỉnh vàng Jiaodong. Tại đây, quặng kiểu phân tán và kiểu mạch được chứa trong các granitoid thuộc thời kỳ Mesozoi. Sự khoáng hóa và biến đổi chủ yếu bị kiểm soát bởi đứt gãy Sanshandao–Cangshang ở vùng này. Sericite trích xuất từ các đá biến đổi trong vùng khoáng hóa cho một độ tuổi isochron Rb–Sr là 117,6 ± 3,0 Ma. Các dịch lỏng hình thành quặng trong mỏ vàng Sanshandao chứa CO2-H2O-NaCl±CH4 với nhiệt độ thấp đến trung bình và độ mặn thấp. Phân tích vi nhiệt cho thấy nhiệt độ đồng nhất dần giảm từ giai đoạn khoáng hóa sớm (258–416°C) đến giai đoạn khoáng hóa chính (180–321°C) và đến giai đoạn khoáng hóa muộn (112–231°C). Nhiệt độ đồng nhất từ cùng một giai đoạn khoáng hóa gần như giống nhau và không cho thấy sự gia tăng theo độ sâu. Tính chất của các dịch lỏng hình thành quặng gần như không thay đổi trong khoảng cách sâu 2000 m.

Highly saline, deep‐seated basement brines are of major importance for ore‐forming processes, but their genesis is controversial. Based on studies of fluid inclusions from hydrothermal veins of various ages, we reconstruct the temporal evolution of continental basement fluids from the Variscan Schwarzwald (Germany). During the Carboniferous (vein type i), quartz–tourmaline veins precipitated from low‐salinity (<4.5wt% NaCl + CaCl₂), high‐temperature (≤390°C) H₂O‐NaCl‐(CO₂‐CH₄) fluids with Cl/Br mass ratios = 50–146. In the Permian (vein type ii), cooling of H₂O‐NaCl‐(KCl‐CaCl₂) metamorphic fluids (T ≤ 310°C, 2–4.5wt% NaCl + CaCl₂, Cl/Br mass ratios = 90) leads to the precipitation of quartz‐Sb‐Au veins. Around the Triassic–Jurassic boundary (vein type iii), quartz–haematite veins formed from two distinct fluids: a low‐salinity fluid (similar to (ii)) and a high‐salinity fluid (T = 100–320°C, >20wt% NaCl + CaCl₂, Cl/Br mass ratios = 60–110). Both fluids types were present during vein formation but did not mix with each other (because of hydrogeological reasons). Jurassic–Cretaceous veins (vein type iv) record fluid mixing between an older bittern brine (Cl/Br mass ratios ~80) and a younger halite dissolution brine (Cl/Br mass ratios >1000) of similar salinity, resulting in a mixed H₂O‐NaCl‐CaCl₂ brine (50–140°C, 23–26wt% NaCl + CaCl₂, Cl/Br mass ratios = 80–520). During post‐Cretaceous times (vein type v), the opening of the Upper Rhine Graben and the concomitant juxtaposition of various aquifers, which enabled mixing of high‐ and low‐salinity fluids and resulted in vein formation (multicomponent fluid H₂O‐NaCl‐CaCl₂‐(SO₄‐HCO₃), 70–190°C, 5–25wt% NaCl‐CaCl₂ and Cl/Br mass ratios = 2–140). The first occurrence of highly saline brines is recorded in veins that formed shortly after deposition of halite in the Muschelkalk Ocean above the basement, suggesting an external source of the brine's salinity. Hence, today's brines in the European basement probably developed from inherited evaporitic bittern brines. These were afterwards extensively modified by fluid–rock interaction on their migration paths through the crystalline basement and later by mixing with younger meteoric fluids and halite dissolution brines.

This study explores the potential of photogrammetric datasets and remote sensing methods for the assessment of a meteorological catastrophe that occurred in Ordu, Turkey in August 2018. During the event, flash floods and several landslides caused losses of lives, evacuation of people from their homes, collapses of infrastructure and large constructions, destruction of agricultural fields, and many other economic losses. The meteorological conditions before and during the flood were analyzed here and compared with long-term records. The flood extent and the landslide susceptibility were investigated by using multisensor and multitemporal data. Sentinel-1 SAR (Synthetic Aperture Radar), Sentinel-2 optical data, and aerial photogrammetric datasets were employed for the investigations using machine learning techniques. The changes were assessed both at a local and regional level and evaluated together with available damage reports. The analysis of the rainfall data recorded during the two weeks before the floods and landslides in heavily affected regions shows that the rainfall continued for consecutive hours with an amount of up to 68 mm/hour. The regional level classification results obtained from Sentinel-1 and Sentinel-2 data by using the random forest (RF) method exhibit 97% accuracy for the flood class. The landslide susceptibility prediction performance from aerial photogrammetric datasets was 92% represented by the Area Under Curve (AUC) value provided by the RF method. The results presented here show that considering the occurrence frequency and immense damages after such events, the use of novel remote sensing technologies and spatial analysis methods is unavoidable for disaster mitigation efforts and for the monitoring of environmental effects. Although the increasing number of earth observation satellites complemented with airborne imaging sensors is capable of ensuring data collection requirement with diverse spectral, spatial, and temporal resolutions, further studies are required to automate the data processing, efficient information extraction, and data fusion and also to increase the accuracy of the results.

A hydrogeological conceptual model of the Caldas do Moledo geothermal site is proposed that shows mixing between geothermal waters and local shallow groundwaters. Stable isotope values of Caldas do Moledo geothermal waters indicate recharge areas located at relatively high altitudes (850–1250 m a.s.l.). The NW–SE Vigo–Régua shear zone plays an important role in fluid recharge and circulation towards the NNE–SSW Régua–Verin fault system, forming a path for ascent of geothermal fluids. The apparent ¹⁴C age of geothermal fluids (15.66 ± 2.86 ka BP) was estimated in the total dissolved inorganic carbon (TDIC). Geothermometer calculations indicate that, assuming a conductive temperature gradient of 32°C per kilometer for northern Portugal, the maximum depth of circulation is roughly 1.8 ± 0.4 km. The K, Ca and SO₄ concentrations found in some Caldas do Moledo geothermal spring waters show mixing between deep geothermal and shallow groundwater systems. Local shallow groundwaters showing the highest SO₄ concentrations were found at low elevation areas, originating from fertilisers and pesticides applied to the Port wine vineyards in the Douro River valley. Geothermal waters from boreholes AC1 and AC2 do not show evidences of direct pollution from the spreading of such agrochemicals.