Low Initial Permeability Research Articles

Experimental investigation and predictive modeling of dry-out and salt precipitation effects during underground gas storage operations

Formation damage poses the greatest threat to underground gas storage (UGS) operations, with permeability reduction being a key cause of injectivity and productivity losses. To better understand the mechanisms behind dry-out and salt precipitation (DSP) and predict the resulting near-wellbore damage, this study experimentally and quantitatively evaluates key factors affecting rock properties before and after salt precipitation. We conducted long-term gas-brine core flooding experiments, obtained salt-contaminated samples, and supplemented them with core permeability-porosity parameter tests, high-pressure mercury intrusion porosimetry (MIP), and scanning electron microscopy (SEM) experiments to better evaluate the salt clogging behavior of the samples. In addition, we discussed the applicability of the key parameter prediction model in modeling the DSP effects, including the water content of natural gas (WCNG), the porosity-permeability clogging model (PPC), and relative permeability (RP) function, providing usage recommendations. Based on our findings, we introduced a model to predict water saturation, salt saturation, and the salt-induced skin factor near the wellbore, particularly after viscous displacement ends, when liquid becomes immobile and evaporation dominates.The results show that salt precipitation has a significant impact on core porosity and permeability. Notably, lower flow rates subtly promote salt precipitation by enhancing the role of evaporation, resulting in greater salt accumulation. In addition, elevated salinity and higher initial water saturation are key contributors to the precipitation process, further exacerbating salt buildup within the reservoir. MIP experiments further confirm the aforementioned impacts. SEM observations reveal NaCl crystals, either clustered or isolated, extensively distributed within the pores and filling the pore spaces from micro to nanometer scale, highlighting their substantial role in altering pore structure and impacting porosity and permeability due to DSP effects. Our developed model confirms that high temperature, low pressure, high flow rates, low initial porosity and permeability, and strong near-well inertia effects lead to DSP effects manifesting sooner near the wellbore during the post-viscous displacement stage. Model validation with core-scale predictions closely matches experimental data in terms of trend.By laying the groundwork for analyzing the mechanisms of flow-through drying and salt precipitation, our findings can be directly applied to identifying the key controlling factors influencing DSP effects, mitigating formation damage, improving injectivity and productivity, and enhancing the efficiency of UGS operations under various operational conditions.

CO2 fracturing of volcanic rocks under geothermal conditions: Characteristics and process

An enhanced geothermal system using carbon dioxide (CO2) for both reservoir creation and thermal energy extraction has attracted attention; however, studies on the CO2 fracturing of volcanic rocks under geothermal conditions are lacking. This study aimed to elucidate CO2 fracturing characteristics and processes in geothermal volcanic rocks via integrated lab-scale fracturing experiments and numerical simulations of basalt and andesite at 250°C and a confining pressure of 30 MPa. Moreover, it proposed and demonstrated an efficient CO2-based fracturing method based on the obtained insights. Fracturing experiments on basalt and andesite with relatively low initial porosity or permeability implied that CO2 fracturing can be initiated at a lower pressure and produce a more complex fracture pattern than water fracturing because of the ease of fluid permeation (e.g., fluid pressure propagation) in rocks owing to the lower viscosity of CO2. The experiments also revealed that the ease of CO2 permeation can produce thinner fractures than those produced by water fracturing, which may severely inhibit the fracturing of andesite rocks with high initial porosity/permeability. Fracturing simulations of rocks with different initial porosity/permeability provided results consistent with the experimental observations. Moreover, the simulations clarified that fluid pressure propagation during CO2 permeation within an unfractured part of the rock and between induced fractures and the surrounding rock matrix could reduce the fracture initiation pressure by effective stress reduction, increase the complexity of the fracture pattern by large stimulated zone development, and inhibit fracture opening and propagation by decreasing the pressure difference between the fractures and matrix. Based on these findings, we proposed a combined CO2-water fracturing system that addresses the drawbacks while maintaining the advantages of CO2 fracturing.

Simulation of thermo-hydro-mechanical coupled heat extraction process of geothermal reservoir under varied geological conditions with CO2 as working fluid

The use of supercritical CO2 as a working fluid instead of H2O in an enhanced geothermal system (EGS) for extracting heat from hot dry rock geothermal resources has garnered significant attention. The objective of this study is to investigate how different geological conditions affect the heat extraction behavior of supercritical CO2 and to reveal the efficiency differences between supercritical CO2 and H2O as working fluids in each geological scenario, providing deeper insight into reservoir management. A series of 3D coupled thermo-hydro-mechanical models were established. Besides, the impact of initial temperature, pressure, porosity, permeability, and stress field on the heat extraction of EGS with different working fluids are also analyzed and compared. Results indicate that, at the same circulating volumetric flow rate, CO2-EGS generally exhibits an earlier thermal breakthrough time, lower net energy production, and reduced heat extraction rate compared to H2O-EGS. Taking into account the extended reservoir lifespan and the relatively small pressure difference between injector and producer in CO2-EGS, CO2 is a more suitable working fluid than H2O. Furthermore, the performance of CO2-EGS is primarily affected by the initial temperature, porosity, and permeability distribution pattern, rather than the initial pressure. On the one hand, a reservoir with low initial temperature, porosity and homogeneous permeability were found to be more conducive to enhancing the average net energy production. On the other hand, reservoir vertical permeability anisotropy can have a more profound impact on CO2-EGS efficiency compared to horizontal y permeability anisotropy. Additionally, this study also examined the impact of in situ stress field. It was found that, compared to H2O-EGS, both isotropic and anisotropic in situ stress fields have a weak effect on the performance of CO2-EGS, which can be attributed to the similarity of the channelization degree of the flow field under different stress conditions.

Tunable magnetocrystalline anisotropy and high-frequency magnetic properties of Y2(Co1−xFex)17 and their composites

Rare-earth transition-metal (R-T) intermetallic compounds are emerging as competitive candidates for novel microwave absorption materials (MAMs) since they show high magnetization and tunable easy magnetization directions (EMDs). In this work, Y2(Co1−xFex)17 (0 ≤ x ≤ 0.3) compounds with the Th2Ni17 hexagonal structure were prepared with the purpose of tuning the EMDs. As x increases, the EMDs of the Y2(Co1−xFex)17 compounds change from the ab-plane (0 ≤ x < 0.0329) to the cone (0.0329 ≤ x ≤ 0.038) and then to the c-axis direction (0.038 < x ≤ 0.3). Furthermore, it was found that the extremely high cutoff frequencies of the uniaxial anisotropy materials give them considerably potential for microwave absorption applications above 10 GHz, despite their relatively low initial permeability compared to the planar anisotropic materials. By studying the high-frequency properties of Y2(Co1−xFex)17/paraffin composites, it is noted that uniaxial anisotropy compounds with x = 0.1 and x = 0.3 can possess higher permeability above 10 GHz as compared to both planar anisotropy and conical anisotropy compounds (x < 0.1) due to their high cutoff frequencies arising from large magnetocrystalline anisotropy fields. This can improve the impedance matching and thus lead to a better microwave absorption performance in the range of 10 to 40 GHz for materials with uniaxial anisotropy. Among all the compositions, the Y2(Co0.9Fe0.1)17/paraffin composite exhibits a minimum reflection loss (RL) of −50 dB at 6 GHz with a thickness of 2.5 mm and a wide qualified bandwidth (QB, RL < −10 dB) of 9.6 GHz at a center frequency of 30.3 GHz with a thickness of 0.6 mm, thus making it a promising candidate for MAMs above 10 GHz.

The impact of wormhole generation in carbonate reservoirs on CO2-WAG oil recovery

In this paper, the impact of CO2-carbonate interactions on hydrocarbon recovery from three initially oil-saturated heterogeneous carbonate core samples (with low and mid permeabilities) were investigated. Alternate injection of carbon dioxide (CO2) and synthetic formation brine was conducted after water flooding. X-ray computed tomography scanning of the core samples before and after core flooding was performed at ambient conditions. Extent of carbonate dissolutions and rock matrix modifications were observed from the change in porosities, permeabilities, and wormhole formations. Generally, the CO2-WAG injection resulted in more than 30% extra oil recovery from the three cores after water flooding scenario. As expected, the total recovery factor of the core with lowest initial permeability and porosity was the smallest, however the core permeability increased from 1.45 mD (pre-flood) to 1987.9 mD (post-flood). Considerable amount of oil was left behind in the core with initially low permeability and porosity due to preferentially flow of WAG fluid through the wormholes, bypassing the trapped oil in the pore spaces at the uninvaded region of the rock. The study suggests that low oil recovery from core with low initial permeability and porosity is principally due to formation of wormhole because of rapid rate of rock dissolution and faster rate of CO2-carbonate reactions. Compared to the mid permeability cores, the low permeable core slows down the WAG fluid flow and give more time for CO2-carbonate rock interactions and reactions because of the tightness of the pore spaces. Thus, facilitated more exposure time and effective contact between the carbonate rock fabrics and the CO2-saturated brine.

Permeability Characteristics of Poorly Graded Sand Conditioned with Foam in Different Conditioning States

Abstract Investigating the permeability characteristics of sand-foam mixtures in different conditioning states is important not only in earth pressure balance (EPB) shield tunneling and standstill but also for posttunneling soil handling. Slump and permeability tests were carried out on poorly graded sand that was conditioned with different foam injection ratios (FIRs) and water contents. According to the slump values and the apparent states of the conditioned sand in the slump tests, the sand conditioning was classified into five cases: insufficient, suitable without any water or foam bleeding, suitable but with water bleeding, excessive with likely foam bleeding, and excessive with water bleeding. With suitable conditioning, the permeability in the conditioned sand generally exhibited three consecutive stages during the tests: the stable stage, fast growth stage and slow growth stage. An increasing FIR and water content enhanced the antipermeability effect (the ability of preventing water from flowing in porous medium), but a considerable increase in water content (≥10 %) weakened the antipermeability effect. Finally, a simplified model was proposed to explain the rheology. The foam significantly reduced the total energy required for the sand particles to flow. In addition, the permeability characteristics of the conditioned sand found in the tests were explained. The low initial permeability coefficient and its duration depended on the ability of the water to penetrate the plugging structures formed by the foam.

Influence of fibres diameter on the AC and DC magnetic characteristics of Fe/Fe3O4 fibres based soft magnetic composites

Fibres-based soft magnetic composites (FSMCs) have been prepared by using Fe fibres of different diameters (65, 125, 250 and 500 μm). The Fe fibres were coated with a 3 μm thick layer of Fe3O4 via the blackening process and subsequently compacted at 700 MPa. The X-ray diffraction analysis (XRD) was used to prove the formation of the Fe3O4 coating on the surface of the fibres. The thickness and the uniformity of the coating were analysed via scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The DC measurements performed on the composite cores revealed that the saturation induction increase from 1.36 to 1.68 T, the maximum relative permeability increase from 550 to 940, and the coercive field decrease from 796 to 454 A/m as the fibre's diameter increase from 65 to 500 μm. By using thinner fibres (65 and 125 μm), composites with low losses and stable initial relative permeability, in the frequency range 50 Hz–10 kHz, can be obtained. To distinguish between different types of losses dissipated by our compacts, and the influence of the fibre's diameter on the different components of the total losses, a numerical model for loss separation is proposed. The comparative evolution of the AC magnetic characteristics of the FSMCs and powder-based SMCs is presented. According to the presented results, this new type of composites can be successfully used to prepare magnetic cores designated to work in the medium to high-frequency range.

Use of a stabilized sewage sludge in combination with gypsum to improve saline-sodic soil properties leached by recycled wastewater under freeze-thaw conditions

Soil salinization is a major environmental hazard that limits agricultural production. Using sewage sludge and recycled wastewaters in amelioration of saline-sodic soils is one of the most effective ways to dispose waste. However, a very low initial permeability of soil in the freeze-thaw conditions can make improvement difficult. Therefore, column experiments at a soil depth of 15 cm have been conducted to determine the effects of the combination of four stabilized sewage sludge doses (0, 50, 100, 150 t ha−1), three freeze-thaw cycles (0, 5, 10 times) and two water types (FW: freshwater, RWW: recycled wastewater) on gypsum-treated saline-sodic soil properties. The effects of non-saline-sodic RWW on the soil properties were similar to the FW in total 22.5 cm leaching amount. Compared to gypsum alone and initial values, sewage sludge increased wet aggregate stability, organic matter, total N and exchangeable Ca + Mg while it decreased pH, exchangeable Na and CaCO3. Saturated hydraulic conductivity was not induced by sewage sludge although exchangeable sodium percentage and electrical conductivity were reduced by 44% and 63.6%, respectively. Negative effects of freeze-thaws on hydraulic conductivity and salinity and sodicity elimination were not observed, while pH and aggregate stability were negatively affected from ten freeze-thaws. Overall, it can be concluded that the improvement of hydraulic conductivity is attributed to the further improvement of soil structure from more strong wet aggregate stability via additional sewage sludge and leaching amounts.

Studies on Real and Imaginary Part of Permeability for Sm–Dy Substituted Mg Ferrite

AbstractThe ferrite samples having composition Mg[(Sm)0.5(Dy)0.5]xFe2‐xO4, in which x varies from 0.05 to 0.3 in steps of 0.05 have been prepared by using combustion method. X‐ray diffraction analysis confirmed the formation of cubic spinel structure in addition of ortho‐ferrite phase due to substitution of rare earth ions. The initial permeability and complex permeability of toroid samples are calculated by measuring the values of inductance and Q‐factor. It is seen that initial permeability and real part of initial permeability increases with increase in Samarium(Sm)–Dysprosium (Dy) rare earth element in magnetium (Mg) up to x = 0.15 and thereafter it decreases. The composition Mg[(Sm)0.5(Dy)0.5]0.15Fe1.85O4 show low loss factor and initial permeability becomes higher as compared to other prepared rare earth content samples.

Numerical Analysis of Improvements to CO2 Injectivity in Coal Seams Through Stimulated Fracture Connection to the Injection Well

This work presents a hybrid discrete fracture-dual porosity model of compressible fluid flow, adsorption and geomechanics during CO2 sequestration in coal seams. An application of the model considers the influence of hydraulic fractures on CO2 transport and the stress field of the coal. The low initial permeability of coal is compounded by the injectivity loss associated with adsorption-induced coal swelling, which is recognised as the major challenge limiting CO2 sequestration in coal seams. In this model, the natural fracture network and coal matrix are described by a dual porosity model, and a discrete fracture model with lower-dimensional interface elements explicitly represents any hydraulic fractures. The two models are coupled using the principle of superposition for fluid continuity with a local enrichment approximation for displacement discontinuity occurring at the surface of hydraulic fractures. The Galerkin finite element method is used to solve the coupled governing equations, with the model being verified against analytical solutions and validated against experimental data. The simulation results show that the presence of a hydraulic fracture influences the distribution of gas pressure and improves the gas flow rate, as expected. The stress field of a coal seam is disturbed by CO2 injection, especially the vertical stress, and the presence of a hydraulic fracture leads to a reduction in stress with permeability recovery starting earlier.

Potential patch antenna application with particle size variation in polycrystalline gadolinium iron garnet (GdIG)

The effect of different particle size obtained by diverse milling time towards the microstructure and magnetic properties of gadolinium iron garnet (GdIG) at room temperature was reported in this research work. Gadolinium iron garnet (GdIG) has been mechanically alloyed at 3, 6, 9 and 12 h followed by sintering at 1200 °C. The samples were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), vibrating sample magnetometer (VSM) and impedance analyser. All milled samples were in nanosized of 36.9, 27.2, 19.2 and 20.8 nm for 3, 6, 9 and 12 h, respectively. The single phase of gadolinium iron garnet (GdIG) with average grain size of 0.66, 0.67, 0.72 and 0.69 μm, respectively, showed low initial permeability and low magnetic loss when applied with low-frequency range. The effect of magnetic properties was proven to be dominantly contributed by sintering process. The result illustrated that the polycrystalline GdIG has the ability to be applied as potential patch antenna application.

An experimental study on the permeability changes of anthracite reservoirs in different depths of Qinshui Basin induced by supercritical CO2 injection

AbstractGeological sequestration of supercritical CO2 (ScCO2) in deep coal seam has been considered as one of the most promising options for reducing greenhouse gas emission. The permeability of a coal seam, a key parameter estimating the CO2 injectivity, determines the success of ScCO2 storage in the deep coal seam. The deep coal seam has a low initial permeability and a further permeability loss induced by the adsorption‐swelling effects of coal during ScCO2 injection. This paper presents a set of measurements on the permeability changes of anthracite reservoirs in different depths of Qinshui Basin induced by ScCO2 injection. The results indicate that the change in anthracite permeability presents a negative exponential decrease with the buried depth increase. The depth of anthracite reservoir increases from 800 to 1400 m, and its permeability will decrease from 4.59 × 10−2 to 8.04 × 10−4 mD. The permeability change induced by ScCO2 injection is the combining effects of temperature, pressure, and adsorption‐swelling, and the permeability change can be described by a negative exponential model during ScCO2 injection to anthracite reservoir in different depths. The loss coefficient of permeability is up to three magnitudes induced by ScCO2 injection to the anthracite reservoir in the depth of 800 m, 2‐3 magnitudes in 1000‐1200 m, and 1‐2 magnitudes in 1400 m. Although the initial permeability of anthracite reservoirs in the same depth exists differences, the permeability loss coefficient almost has the same magnitudes induced by ScCO2 injection. Comparing with the permeability loss coefficient of the anthracite reservoir in different depths, the permeability variation of the shallow coal seam is more sensitive than the deep induced by ScCO2 injection. However, the deep coal seam has a relatively large fracture pressure, so the allowable ScCO2 injection pressure in the deep coal seam is greater than the shallow.

Anisotropic Mechanical Properties and the Permeability Evolution of Cubic Coal Under True Triaxial Stress Paths

The geological sequestration of CO2, underground coal mining, and coalbed methane production in deep coal reservoirs is executed under high levels of 3-D geo-stress, and it is accompanied by significant variations in both vertical and horizontal stresses. In addition, coal is a highly fractured porous medium characterized by complex natural fracture systems. This exterior and interior anisotropy complicates the replication of in situ conditions in the laboratory. In this study, we divided pre-existing fracture systems of cubic coal into three flow planes: a bedding plane, face cleat plane, and butt cleat plane. Gas flowed through cubic coal samples along each flow plane under differently designed true triaxial stress paths. We then further analyzed anisotropic mechanical and flow property responses of cubic coal after failure by model fitting, CT scan reconstruction, and fractal representation. The experimental results indicate that pre-existing flow planes play significant roles in the strength levels, failure modes, and permeability levels. Low strength levels, typical shear failure patterns, and low initial permeability levels were observed in the butt cleat plane direction. Anisotropic strength data can be effectively fit by applying a linear relationship between octahedral shear stress and mean effective normal stress. After coal failure, the peak permeability observed in the face and butt cleat plane directions also presents a strong linear relationship with the fractal dimension. An anisotropic conceptual failure process model was established for the description of internal fracture development during stress loading. Horizontal stress unloading decreased the strength and formed a more complex fracture system in cubic coal regardless of the different flow planes involved, producing the increments of associated peak permeability.

Hysteresis losses in nanocrystalline alloys with magnetic-field-induced anisotropy

Abstract The hysteresis losses and their relation to the parameters of the minor static hysteresis loops were investigated in the nanocrystalline Fe67.5Co5Cu1Nb2Mo1.5Si14B9 alloy with magnetic-field-induced anisotropy. The analysis of experimental data was performed using a power function, which approximated the dependencies between the hysteresis parameters. It is shown that all the experimental dependences in cores with magnetic-field-induced anisotropy in a weak magnetic field are consistent with the formulas derived from the Rayleigh law. It is also shown, that in a nanocrystalline alloy with uniaxial induced anisotropy, certain empirical relationships obtained earlier for isotropic materials are not met, particularly, for the relation of the hysteresis losses to the remanence and the maximal magnetic induction. It has been found, that samples with longitudinal induced anisotropy demonstrate low initial permeability, and the magnetization process in the Rayleigh region is carried out by the domain walls’ displacement at distances comparable to the correlation length Lex. A magnetic hysteresis mechanism associated with the irreversible magnetization rotation in ferromagnetic clusters of nanocrystalline alloys is proposed. Formulas are proposed to calculate hysteresis losses in a soft magnetic nanocrystalline material with a different magnetic anisotropy.

Fault slippage and its permeability evolution during supercritical CO2 fracturing in layered formation

Understanding the hydromechanical responses of faults during supercritical CO2 fracturing is important for reservoir management and the design of energy extraction systems. As small faults are widespread in Chang 7 member of the Yanchang Formation, Ordos Basin, China, supercritical CO2 fracturing operation has the potential to reactive these undetected small faults and leads to unfavorable fracking fluid migrate. In this work, we examined the role of fault slippage and permeability evolution along a small fault connecting the pay zone and the confining formation during the whole process of fracturing and production. A coupled hydromechanical model conceptualized from actual engineering results was introduced to address the main concerns of this work, including, (1) whether the existence of a undetected small fault would effectively constrain the hydraulic fracture height evolution, (2) what the magnitude of the induced microseismic events would be and (3) whether the permeability change along the fault plane would affect the vertical conductivity of the confining formation and thus increase the risk for the fracturing fluid to leak. Our results have shown that the initial hydrofracture formed at the perforation and propagated upward, once it merged with the fault surface, the existence of an undetected small fault would effectively constrain the hydraulic fracture height evolution. As fracturing continued, further slippage spread from the permeability increase zone of high permeability to shallower levels, and the extent of this zone was dependent on the magnitude of the fault slippage. At the end of extraction, the slip velocity decreases gradually to zero and the fault slippage finally reaches stabilization. In general, undetected small faults in targeted reservoir may not be the source of large earthquakes. The induced microseismic events could be considered as the sources of acoustic emission events detected while monitoring the fracturing fluid front. Due to the limited fault slippage and lower initial permeability, the CO2 fracturing operation near undetected small faults could not conduct preferential pathway for upward CO2 leakage or contaminate overlying shallower potable aquifers.

Numerical simulations of depressurization-induced gas production from an interbedded turbidite gas hydrate-bearing sedimentary section in the offshore India: Site NGHP-02-16 (Area-B)

Abstract The recent National Gas Hydrate Program Expedition 02 (NGHP-02) identified the existence of gas hydrate-bearing sand reservoirs at a number of sites in the offshore of India including Site NGHP-02-16 in Area-B of the Krishna-Godavari Basin. The architecture of that gas hydrate accumulation is characterized by thin, gas hydrate-bearing, high quality sand layers interbedded with mud layers within a turbidite sedimentary interval. The lowest gas hydrate-bearing layer contacting a thinly-interbedded saline aquifer designates the base of the gas hydrate stability zone (BGHSZ). The proximity of the BGHSZ and the average temperature around 20 °C make the reservoir a favorable target for hydrate destabilization by means of the depressurization method. The results of the reservoir simulations indicate high gas production potential from this marine gas hydrate deposit with manageable concomitant water production using a well completion design that hydraulically isolates layers with water-saturated sands. Using a detailed geological input model, the predicted cumulative gas rates reach ∼3.1 × 104 m3/day (∼1.1 MMscf/day) after 90 days of continuous depressurization and demonstrate sustained production rates ∼3.0 × 104 m3/day (∼1.0 MMscf/day) after 5 years of production. The interbedded nature of this gas hydrate occurrence promotes the development of horizontal dissociation interfaces between gas hydrate-bearing sand and mud layers. As a result, non-uniform gas production along the horizontal interfaces becomes a primary determinant of reservoir performance. Simulation cases have been executed to determine the impact of the uncertainty in in situ reservoir permeability and the manner in which intrinsic permeability dynamically changes during dissociation in response to the imposed effective stress increase. The cases based on low initial effective permeability and high sensitivity of compaction to stress result in the least favorable production predictions.

Depositional and diagenetic controls on the reservoir quality of Upper Triassic Chang-7 tight oil sandstones, southwestern Ordos basin, China

The seventh oil layer of the Upper Triassic Yanchang Formation (Chang-7) tight oil sandstone reservoirs is a major exploration target. A significant amount of hydrocarbons has been discovered in these reservoirs in the southwestern Ordos basin in China. The Chang-7 tight sandstones are characterised as tight with low porosity, low permeability, and strong heterogeneity. This study investigates the sedimentary facies, diagenesis, and their impact on the reservoir quality of the Chang-7 tight oil sandstones. The sandstones were deposited in a deltaic-lacustrine depositional system. Three major depositional facies are identified consisting of delta front fed by braided rivers and meandering rivers, and slump turbidite fans. The depositional environment exerts a key control on reservoir quality. The distinct low-energy sedimentary environment produced fine to very fine-grained sandstones with high matrix and mica contents, characterised by low initial porosity and permeability. Diagenesis mainly comprised mechanical compaction and cementation by quartz, carbonate minerals and various clay minerals. The reservoir properties of the Chang-7 sandstones are generally poor, with porosity of 1.4–20.7% (average porosity 8.6%) and permeability of 0.001–116.7 mD (average 0.2 mD), which are attributed to significant compaction and cementation. Mechanical compaction was more important than cementation for reducing porosity, whereas secondary dissolution porosity was significant for the Chang-7 tight oil sandstones due to closer proximity to the underlying Chang-73 source rocks.

Physical and mechanical property relationships of a shallow intrusion and volcanic host rock, Pinnacle Ridge, Mt. Ruapehu, New Zealand

Shallow magmatic intrusions are prevalent in volcanic settings worldwide. Understanding how these intrusions interact and influence their volcanic host rocks is therefore relevant to many engineering geology, geothermal, and volcanological applications. In this study, we present the most comprehensive dataset for a shallow intrusion and its host rock in a volcanic setting to date, detailing the mechanical and physical properties of volcanic rocks from Pinnacle Ridge, Mt. Ruapehu, New Zealand. Based on the geomechanical properties of 194 measured samples, we identify seven geotechnical units: (1) unaltered dense coherent lava, (2) altered dense coherent lava, (3) unaltered brecciated lava margin, (4) altered brecciated lava margin, (5) unaltered intrusion, (6) altered intrusion, and (7) hydrothermal veining. We detail the mineralogy (andesite compositions ranging from primary to an advanced argillic alteration assemblage), porosity (0.7–31%), permeability (10−21–10−12 m2), elastic wave velocities (1994–5615 m/s), uniaxial compressive strength (1–332 MPa) of these geotechnical units. Our laboratory analyses indicate that primary lithology is the predominant control on the physical and mechanical properties of the geotechnical units. Additionally, the data suggest that there is a correlation between distance to the largest intrusion; this is particularly evident for the measurements on the brecciated lava margin samples. Towards the largest intrusion, this breccia shows decreasing porosity (30.92 to 5.49%) and permeability (10−12 to 10−17 m2) and increasing elastic wave velocities (1994 to 4157 m/s) and uniaxial compressive strength (3 to 61 MPa). Thin-section analysis suggests that these correlations are due to mineral precipitation within fractures and pores in the brecciated lava margins. These correlations with distance to the largest intrusion are not shared by the altered intrusions or dense coherent lavas. We suggest that the high primary permeability of the unaltered breccia facilitated efficient hydrothermal fluid circulation and mineral precipitation adjacent to the intrusion. The other geotechnical units are less affected because hydrothermal fluid flow, alteration, and mineral precipitation were limited due to low initial permeability (10−21–10−16 m2). Our study shows that the initial properties of the host rock (i.e. porosity and permeability) control the extent of hydrothermal alteration and the susceptibility to modifications of rock geomechanical properties. Modifications to porosity and permeability can influence edifice-scale behaviour; for example, a reduction in permeability can result in pore pressure augmentation, which exerts a primary control on volcanic slope stability, seismicity, and eruptive behaviour. This study provides the most comprehensive and complete geomechanical properties data suite on a shallow intrusion in volcanic host rock to date and will support monitoring and modelling of volcanic hazards associated with shallow igneous intrusions.

Surface nonuniformities in latex paints due to evaporative mechanisms

A model is developed for predicting long‐wavelength nonuniformities in the thickness of drying latex paint films. The model includes the effects of temperature, latex particle volume fraction, surface surfactant density, bulk surfactant density, and several material and environmental factors. After the model is simplified by applying the lubrication approximation, equations for spatially independent base state solutions are derived. The base state solutions describe a drying latex paint film of uniform thickness. The equations for the base states are solved numerically and a linear stability analysis is conducted. This analysis indicates that evaporation, slow surfactant kinetics, low initial surface tension, substrate permeability, and high initial latex particle volume fractions destabilize the uniform film, while fast surfactant kinetics, high initial surface tension, and high viscosity are stabilizing. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1841–1858, 2018

Modeling the effect of water vaporization and salt precipitation on reservoir properties due to carbon dioxide sequestration in a depleted gas reservoir

Abstract Vaporization of water during both gas reservoir development and CO 2 geological sequestration in saline formations can cause salt precipitation with rapid loss of formation porosity and permeability. Water vaporization and precipitation of halite around a single well from stage production to CO 2 injection are studied to investigate the effect on reservoir properties in a gas reservoir. This paper identifies and quantifies post-flood dry zones and permeability changes in depleted gas reservoir after CO 2 exposure with the comparison in gas production period by performing the numerical simulation with the compositional simulator. Simulation results indicate that water vaporization and salt precipitation occur during gas production, and can be intensified by CO 2 injection. Dry supercritical CO 2 injection vaporizes the brine promoting brine concentration and halite precipitation. The simulation indicates a drying area with a radius of 78 m around wellbore after CO 2 injection. Porosity reduces with the most scope of 58%, and permeability can be decreased by up to 93.9% due to salt precipitation. And the injectivity is damaged by 99.77% at the end of injection period based on maximum permeability reduction. Moreover, six factors are investigated to conduct the influence analysis, showing that higher salinity brine, higher injection rate, higher irreducible water saturation, lower initial permeability, higher temperature and with capillary flow are conditions enhancing the salt precipitation due to dry CO 2 injection.