Geological Stability Research Articles

Supercritical CO2 and brine displacement in geological carbon sequestration: Micromodel and pore network simulation studies

The competence of geological carbon sequestration to a large extent relies on the short-term injection efficiency and the long-term capillary trapping and geological stability. This study uses a high-pressure micromodel and pore network simulation to investigate pore-scale displacement phenomena during the injection of supercritical carbon dioxide (scCO2) into brine-saturated reservoirs. Results show that the brine displacement can be enhanced by increasing the scCO2 injection rate, but hindered by brine salinity which alters the interfacial contact properties and displacement patterns. The scCO2–brine displacement ratio increases with the capillary number Nc, increasing which by adding viscosifiers or surfactants would enhance the overall scCO2 injection efficiency in microscopic flows. Results also suggest that better injection efficiency and capillary trapping capacity can be achieved in reservoirs with more widely-distributed pore sizes. It is not evident that mutual solubility and upscaling using the Leverett-J function readily allow to expand the injection efficiency results of microscopic flows to reservoirs; yet, the effects of salinity and pore size distribution on the scCO2–brine displacement process remain pertinent in both microscopic and macroscopic flows through porous media.

The costs of housing developments on sites with elevated landslide risk in the UK

New housing targets are being set for local planning authorities resulting in more areas being zoned for development. There is currently no requirement for a landslide assessment prior to this zoning, and sites at elevated risk of landslides are being put forward for development without consideration of the additional costs and other impacts of building on these higher risk sites. This study aimed to reveal the increased financial, economic, social and environmental costs associated with these decisions. Case studies were focused on the city of Bath, an area of increasing population and “one of the most intensely landslipped areas in Britain’’. The case studies found the financial costs associated with building in a landslide risk area to be significantly higher than the equivalent construction in areas of greater geological stability. Furthermore, it was found that uncertainty in cost when developing in unstable areas exacerbates this problem as the final cost cannot be accurately predicted before construction.

Coral islands defy sea-level rise over the past century: Records from a central Pacific atoll

The geological stability and existence of low-lying atoll nations is threatened by sea-level rise and climate change. Funafuti Atoll, in the tropical Pacific Ocean, has experienced some of the highest rates of sea-level rise (∼5.1 ± 0.7 mm/yr), totaling ∼0.30 ± 0.04 m over the past 60 yr. We analyzed six time slices of shoreline position over the past 118 yr at 29 islands of Funafuti Atoll to determine their physical response to recent sea-level rise. Despite the magnitude of this rise, no islands have been lost, the majority have enlarged, and there has been a 7.3% increase in net island area over the past century (A.D. 1897–2013). There is no evidence of heightened erosion over the past half-century as sea-level rise accelerated. Reef islands in Funafuti continually adjust their size, shape, and position in response to variations in boundary conditions, including storms, sediment supply, as well as sea level. Results suggest a more optimistic prognosis for the habitability of atoll nations and demonstrate the importance of resolving recent rates and styles of island change to inform adaptation strategies.

Excavation Program and Stability Analysis of High-Steep Rock Slope

Aimed to the problem of excavation and stability for a high and steep rocky slope, with the design excavation height of 90.23m, this paper grasped the engineering geological conditions and physical and mechanical properties of rock mass by such following methods as the field engineering geological survey, measuring, drilling sampling and laboratory test. Based on this, a comparative analysis of two different excavation ways was conducted using the large discrete element program-UDEC. The analysis included the stress-strain law and deformation failure trends of the slope when adopting slow excavation and steep excavation respectively. Moreover, the environmental damage caused by the two excavation ways was discussed. The results show that the slope has a better engineering geological condition and stability. In order to avoid disturbing hills and protect the natural environment, the steep excavation way is suggested for excavation and reinforcement of this slope.

SMALL HYDROPOWER PROJECTS: ENVIRONMENTAL AND HYDRO·GEOLOGICAL PERSPECTIVES

Small hydropower projects are those that generate less than 10 MW of electricity usingsmall run-of-the-river hydropower systems. They usually consist of water conveyance.(headrace channel, forebay and penstock), powerhouse unit, tailrace and transmissionline. It is considered as a renewable resource of energy. It does not contribute to globalwarming and does not contribute to acid rains etc. Therefore, there is no question ofpollution or degradation of land, waterways or other water bodies. However, large-scaledam hydropower projects are often criticized for their impacts on environment,particularly on wildlife habitat, fish migration, and water flow and quality. It is usuallyassumed that small, run-of-the-river projects are free from many of the environmentalproblems associated with their large-scale counterparts because of the use of the naturalflow of the river, and thus producing relatively little change in the stream channel andflow. This paper addresses the feasibility of small hydropower projects in Sri Lanka withrespect to environmental issues, geological stability and hydrological feasibility usingcase studies. The results of the study revealed that environmental impacts of smallhydropower projects are location sensitive and also case dependant. In most cases,proper planning and implementation of the project and relevant mitigatory measures canminimize significant impacts of projects. Problems related to implementation andmonitoring of impacts and possible solutions are also discussed.

Types of sediments and sections in the upper quaternary cover and geological stability of the Curonian Spit (Baltic Sea)

Data on types of Holocene sediments overlying the Upper Pleistocene glacial sediments and constituting the Curonian (Kurshskaya) Spit are summarized to assess its geological stability. The data made it possible to define and describe four main types of sections: (1) peaty, (2) peaty-sandy, (3) gravelly-sandy, (4) muddy-sandy-sapropelic. These spit sections are correlated with the counterparts in adjacent areas of the Baltic Sea and Curonian Lagoon (Kurshskaya Bay). The role of different sources is elucidated for sedimentary material in the spit. Data on recent processes of erosion and accumulation in coastal areas of the spit are compared with types of sediments and sections in the spit and adjacent areas of the sea and lagoon. It is established that paleostraits filled with peat and sapropel represent low-stability areas of the spit. Various scenarios of the spit evolution in response to high sea-level rise are considered.

Evaluation of Grenada's “Carib Stones” via the Rock Art Stability Index

While not well-known or well-studied, Grenada's (Caribbean) Carib Stones host over 100 individual petroglyphs (rock engravings) representing some of the Caribbean's best examples. Two sites were assessed for this study: Duquesne Bay along the northwest Caribbean coast and Mt. Rich in the northern tropical rainforest. Their importance notwithstanding, little has been done to manage or assess the Stones other than basic glyph recording. This study employed the Rock Art Stability Index (RASI) to assess and document each panel's overall geologic stability. Using more than three-dozen rock decay elements, RASI represents an efficient and rapid tool to assess petroglyphs and pictographs, assigning an “Excellent–Good–Problems–Urgent Danger–Great Danger–Severe Danger” ranking based on a quantitative score. Overall, 13 panels were assessed individually, with a few exhibiting “Good” status, two in “Great Danger”, and the remaining exhibiting “Problems”. Analyses show the Duquesne Bay site remains at the behest of its proximity to water, such as stagnating puddles, waves, or storm and household runoff. In contrast, the Mt. Rich site receives substantial rainfall and remains under rainforest canopy, yet is significantly more stable. This research demonstrates the need for further monitoring efforts and lays the groundwork for continued study and assessment of the Carib Stones, while at the same time raising their profile to the international stage in hopes of securing greater recognition ultimately leading to better management practices.

Comment on: When Landslides Are Misinterpreted as Faults: Case Studies from the Western United States

Hart et al. (2012) provide a useful reminder that it can be difficult to distinguish between structures generated by landsliding and those generated by tectonic faulting, and that from an engineering perspective, confusing the two may have profound ramifications when evaluating a site's geologic stability and seismic hazard. As correctly noted in their introduction, “…every pattern of tectonic faulting can be produced by landsliding.” Hart et al. (2012) illustrate this fact with seven examples from the western United States, one of which, the Traverse Mountains of Utah, warrants clarification. Figure 7 of Hart et al. (2012) shows their interpretation of three landslides on the south flank of the Traverse Mountains, based in part on my 1: 24,000 scale geologic map of the Lehi quadrangle (Biek, 2005a). The focus of their summary relates to “landslide A,” and what I interpreted to be a down-to-the-northeast normal fault bounding its southwest margin. I agree that this structure is more plausibly interpreted as a right-lateral shear bounding the margin of landslide A. However, their queried landslides Qls?1 and Qls?3 are significantly larger than several composite landslides in the same locations as mapped by ⇓Biek (2005a). The inferred increased extent of these landslides compared to my mapping appears to be based largely on interpretation of aerial photographs, and thus …

Numerical Studies on Two-Way Coupled Fluid Flow and Geomechanics in Hydrate Deposits

Summary Coupled flow and geomechanics play an important role in the analysis of gas-hydrate reservoirs under production. The stiffness of the rock skeleton and the deformation of the reservoir, as well as porosity and permeability, are directly influenced by (and interrelated with) changes in pressure and temperature and in fluid-(water and gas) and solid-(hydrate and ice) phase saturations. Fluid and solid phases may coexist, which, coupled with steep temperature and pressure gradients, result in strong nonlinearities in the coupled flow and mechanics processes, making the description of system behavior in dissociating hydrate deposits exceptionally complicated. In previous studies, the geological stability of hydrate-bearing sediments was investigated using one-way coupled analysis, in which the changes in fluid properties affect mechanics within the gas-hydrate reservoirs, but with no feedback from geomechanics to fluid flow. In this paper, we develop and test a rigorous twoway coupling between fluid flow and geomechanics, in which the solutions from mechanics are reflected in the solution of the flow problem through the adjustment of affected hydraulic properties. We employ the fixed-stress split method, which results in a convergent sequential implicit scheme. In this study of several hydrate-reservoir cases, we find noticeable differences between the results from one- and two-way couplings. The nature of the elliptic boundary value problem of quasistatic mechanics results in instantaneous compaction or dilation over the domain through loading from reservoir-fluid production. This induces a pressure rise or drop at early times (low-pressure diffusion), and consequently changes the effective stress instantaneously, possibly causing geological instability. Additionally, the pressure and temperature regime affects the various phase saturations, the rock stiffness, porosity, and permeability, thus affecting the fluid-flow regime. These changes are not captured accurately by the simpler one-way coupling. The tightly coupled sequential approach we propose provides a rigorous, twoway coupling model that captures the interrelationship between geomechanical and flow properties and processes, accurately describes the system behavior, and can be readily applied to large-scale problems of hydrate behavior in geologic media.

Crucial Geo-Qualities and Predominant Defects Treatment on Foundation Zones of Sino Mainland Xiluodu Arch Dam

Xiluodu arch dam of Xiluodu hydro-junction standing on Jinshajiang River is one of international super-hydropower-projects. Furthermore, this super arch dam lies in peculiarly complicated geographical location where the most dangerous geologies of Southern-western China live. So, the dam foundation condition must meet rigorous requirements on geological stability, mechanical-physical characters and permeability etc. Thereby, the key scientific objects include attitude of foundation surfaces, geological defects of main strata, blasting-excavation-substitution systematic construction for soft geo-layers. Based on practical survey on strata’s lithologic characters and geological structural traits from bank slopes as well as valley bed, researched comprehensively were the dam foundation weathering and unloading condition, the distribution of intra- and inter-formational disturbed belts, compressive belts and parental fissures. Particularly, discussed attentively was their quality assessment. The analyses results showed that the globally initial quality of dam foundation was super one and the local geological defects can be reinforced reliably by substitutive excavation in addition to intense consolidation grouting so as to meet constructive requirements of Xiluodu arch dam. The conclusion is the sophisticated process for blasting construction and comprehensively constructive management system is applicable. The blasting excavation produced smooth and completely split surfaces. The exposed strata’s blasting damage was controlled effectively. The geo-strata’s treatment met generally constructive safety requirements.

Crucial Geo-Qualities and Predominant Defects Treatment on Foundation Zones of Sino Mainland Xiluodu Arch Dam

Xiluodu arch dam of Xiluodu hydro-junction standing on Jinshajiang River is one of international super-hydropower-projects. Furthermore, this super arch dam lies in peculiarly complicated geographical location where the most dangerous geologies of Southern-western China live. So, the dam foundation condition must meet rigorous requirements on geological stability, mechanical-physical characters and permeability etc. Thereby, the key scientific objects include attitude of foundation surfaces, geological defects of main strata, blasting-excavation-substitution systematic construction for soft geo-layers. Based on practical survey on strata’s lithologic characters and geological structural traits from bank slopes as well as valley bed, researched comprehensively were the dam foundation weathering and unloading condition, the distribution of intra- and inter-formational disturbed belts, compressive belts and parental fissures. Particularly, discussed attentively was their quality assessment. The analyses results showed that the globally initial quality of dam foundation was super one and the local geological defects can be reinforced reliably by substitutive excavation in addition to intense consolidation grouting so as to meet constructive requirements of Xiluodu arch dam. The conclusion is the sophisticated process for blasting construction and comprehensively constructive management system is applicable. The blasting excavation produced smooth and completely split surfaces. The exposed strata’s blasting damage was controlled effectively. The geo-strata’s treatment met generally constructive safety requirements.

In Situ Methane Recovery and Carbon Dioxide Sequestration in Methane Hydrates: A Molecular Dynamics Simulation Study

One intriguing idea for the simultaneous recovery of energy and sequestration of global warming gas is proposed by the transformation of methane hydrates to carbon dioxide hydrates with the injection of liquid CO(2). Here we use molecular dynamics simulations to show that the replacement can take place without melting of the network of hydrogen-bonded water molecules. Depending on the distance to the interface between the liquid CO(2) and solid clathrate hydrate, we find that the replacement occurs either via direct swapping of methane and CO(2) or via a transient co-occupation of both methane and CO(2) in one cavity. Our results suggest that, with a careful design of the operation condition, it is possible to replace methane from methane hydrates with CO(2) in the solid phase without much change in the geological stability.

Development of CCS technology for coal-fired power plant in Taiwan

Abstract Safe candidate sites of reservoir for geologic storage including some oil or gas bearing structures on-shore or off-shore of the Taiwan island, and some near off-shore sedimentary basins were studied and screened. After screening out several potential engineering sites, an AHP ranking method was applied for ranking and selecting the preferred candidate on account of the economy factors, safety requirements, storage effectiveness, and potential storage capacity volume etc. As a result, preferred engineering site for pilot and demonstration plans were recommended. A deep saline aquifer under a Miocene basin near the western coast of Central Taiwan with estimated storage capacity up to 4 Gt- CO 2 is now regarded as a very high potential storage reservoir with advantages of its high capacity volume, geological stability and the short distance away from the largest emission plants. More detailed investigation will be implemented during the year of 2010 to 2013 including works of site conformation, characterization prior to performing a pilot test with injection depth down to 2500 ∼3000 m. In this paper, the process and methodology of the screening potential reservoir and ranking of preferred engineering site are depicted and furthermore the tentative road map concerning Tai-Power’s CCS technology development for coal- fired power plant is introduced.

Resilience assessment on coastline changes and urban settlements: A case study in Seribu Islands, Indonesia

The sustainable development in the ocean and costal areas has been an issue for the archipelago nation. Since two decades ago, some archipelago nations have attempted to implement the concept of both scientifically and politically sounding sustainability. The vulnerability assessment is one of the methods that are being used to measure the ocean and coastal sustainability in order to have better evaluation and redesign of the land development as well as policy making. Most of the vulnerability assessment has been conducted based on pressures, damages and changes that involve in the region. A common understanding of the vulnerability assessment is that there are three aspects to be considered: hazards, resilience and damages. These three aspects must be well defined at first in order to have better indicators or sub-indices for the vulnerability index. There are several issues and factors that should be considered before performing the vulnerability assessment. Firstly, each country has different coastal characteristics due to a different geologic process. Secondly, the three aspects of the vulnerability (i.e. hazards, resilience and damages) are impacting on each country at a different scale. Thirdly, the vulnerability of a small island region is different from that of a large island region. Finally, policies and regulations vary in each country. From the data analysis results, it is found that the urban settlement in Seribu Islands is one of the resilient factors in addition to the geological and geomorphological conditions. The resilience factors in Seribu Islands are classified into four categories: 1) settlements area, 2) population density, 3) hard infrastructure such as airfields, ports and roads, 4) geological process such as abrasion and erosion. Based on the island characteristics of Seribu Islands, a unique vulnerability index that fits to this locality is developed. It is shown that the vulnerability index developed in this study can measure the resilience of Seribu Islands. In addition to the aforementioned resilience factors, the unique geographical condition and the geological stability in Seribu Islands made the outer islands become a barrier from oceanographic conditions and made the inner islands protected. However, the population growth made significant changes in terms of ecology, water, sanitation and pollution within the region.

Origin of Materials Erupting from Mud Volcano in Tokamachi City, Niigata Prefecture, Central Japan

Mud volcanoes are structures formed as a result of the emissions on a land surface or the sea floor of argillaceous material, which is composed of erupting remobilized mud, petroliferous or magmatic gases, and high-salinity water. Recently, large constructions have been planned deep underground besed on the expectation of geological stability. Therefore, it is important to study the origin of erupted mud and groundwater and the depths from which they ascend when evaluating long-term stability. Three active mud volcanoes and a passive mud volcano are found in the Tertiary Shiiya Formation distributed in Tokamachi City, southern part of Niigata Prefecture. Detailed descriptions of the mud volcanoes are provided by Shinya and Tanaka (2005). However, the origin of erupted mud and the formation mechanism of abnormal pore water pressure have not yet been identified. The authors measured the oxygen and hydrogen isotopic ratio of groundwater and vitrinite reflectance of coal fragments separated from erupted mud of an active mud volcano to investigate the origin of erupted mud, particularly the depth of the origin, and the formation mechanism of abnormal pore water pressure. As a result, δ18O and δD values of erupted water are 1.2‰, -5‰ respectively, showing good agreement with those of the Nanatani Formation distributed at a depth of 3400 m in depth in the studied area. Vitrinite reflectance (Ro) shows a bimodal distribution (i.e., 0.3-1.2% and 1.5-1.8%). Ro value of coal fragments sampled from the Shiiya Formation at the outcrop in the studied area are 0.3-0.45%. High Ro (1.5-1.8%) values of coal fragments are obtained in core samples at a depth of 4000 m in the Gimyo SK-1 oil well, which was excavated 2 km NW from the mud volcano. As a result of an investigation of erupted materials at the mud volcano, they were found to have originated at depths of from 3400 m to 4000 m in the studied area. Geothermal temperature of underground at depth of 3400 m to 4000 m in the in the studied area is estimated to be about 120°C to 150°C. Estimated temperature is high enough to cause diagenetic transition from smectite to illite. Transition from smectite to illite results in the release of a large volume of pore water into the sediment. It is concluded that dehydration due to mineral transition might be the major reason for abnormal pore water pressure formation at depths of 3500 m to 4000 m in the study area.

Analysis of the occurrence and importance of slot development (grykes) within shallow dolomite zones in a selected type area on the Eccles Formation

A better understanding of the geology and dolomite stability of sites to be developed is crucial in the quest for releasing land for development that is deemed safe from a dolomite risk perspective. A geological setting often considered to be particularly problematic is shallow dolomite bedrock. This paper presents an analysis of the occurrence and importance of slot development (grykes) within shallow dolomite in a selected type area. Geophysical exploration forms the initial phase of a ground stability investigation. A Bouguer gravity anomaly contour map was produced from the data set for the type area. The interpretation of the residual gravity map was used as the basis for planning the subsequent phase of investigation, in which further rotary percussion borehole drilling was carried out. Over 750 boreholes and trench-mapping results were available to test the interpretation against. Various attempts showed just how problematic it is to produce a gravity map that represents a good estimated depth to dolomite bedrock. The shallow dolomite areas were firstly delineated using only the residual gravity results and incorporate the gravity high plateau where the average bedrock head is predicted to be shallower than 8 m. An analysis is given of the conditions related to these shallow bedrock areas. Shallow dolomite areas associated with some stratigraphic horizons are notorious for instability, however, to the layperson the presence of rock on a site signifies stable conditions to build on. Upon closer investigation dolomitic rock is found to present problematic founding conditions, which are not always easy to overcome by engineering design.

An application of CSAMT to a geological investigation for railway route selection

ABSTRACTThe controlled‐source audio‐frequency magnetotelluric method is a frequency domain electromagnetic sounding technique using a controlled source. This method, though characterized by efficiency, high lateral resolution, weak shielding effect from resistive beds and moderate detection depth has been rarely used for near‐surface geological investigation before in China. However, in the upper 200 m geological investigation for the pre‐route selection of the Lan‐Xin railway, the method has been successfully adopted for quickly mapping hidden fracture zones and structural framework, as well as assessing geological stability, so providing a basis for the railway route selection.

Deformation Monitoring and Analysis Using Victorian Regional CORS Data

This paper investigates the feasibility using continuously operating reference stations (CORS) in Victoria (termed GPSnet) for deformation monitoring and analysis. A number of critical issues associated with the suitability, geological stability, data quality of the GPS networks system, the precision and reliability of the GPSnet solution are investigated using geological information. Appropriate strategies for GPS data processing and deformation analysis are investigated. The absolute and relative displacement of selected GPSnet stations are analysed using chronological GPS CORS data and dedicated high precision scientific GPS data processing software packages. The latest International Terrestrial Reference Frame is used for deformation analyses. Detailed data-processing strategies and results of deformation analyses are presented and some useful conclusions are drawn. Results show that the methodology of deformation analysis and data processing based on the regional CORS network data is feasible and effective. It is concluded that high-precision continuous tracking data from GPSnet is a very valuable asset and can provide a technicallyadvanced and cost-effective geoscientific infrastructure for deformation monitoring analysis. By mining the data from the GPSnet, not only reliable and high precision deformation information can be potentially obtained, but also high expenditure required for establishing dedicated deformation monitoring networks in this area can also be spared.

Near-surface Interface Detection for Coal Mining Applications using Bispectral Features and GPR

The use of ground penetrating radar (GPR) for detecting the presence of near-surface interfaces is a scenario of special interest to the underground coal mining industry. The problem is difficult to solve in practice because the radar echo from the near-surface interface is often dominated by unwanted components such as antenna crosstalk and ringing, ground-bounce effects, clutter, and severe attenuation. These nuisance components are also highly sensitive to subtle variations in ground conditions, rendering the application of standard signal pre-processing techniques such as background subtraction largely ineffective in the unsupervised case. As a solution to this detection problem, we develop a novel pattern recognition-based algorithm which utilizes a neural network to classify features derived from the bispectrum of 1D early time radar data. The binary classifier is used to decide between two key cases, namely whether an interface is within, for example, 5 cm of the surface or not. This go/no-go detection capability is highly valuable for underground coal mining operations, such as longwall mining, where the need to leave a remnant coal section is essential for geological stability. The classifier was trained and tested using real GPR data with ground truth measurements. The real data was acquired from a testbed with coal–clay, coal–shale and shale–clay interfaces, which represents a test mine site. We show that, unlike traditional second order correlation based methods such as matched filtering which can fail even in known conditions, the new method reliably allows the detection of interfaces using GPR to be applied in the near-surface region. In this work, we are not addressing the problem of depth estimation, rather confining ourselves to detecting an interface within a particular depth range.

Special cases of natural analogues: The Gabon and Cigar Lake U ore deposits

Abstract The Gabon and Cigar Lake uranium deposits may be used as natural analogues for nuclear waste because they both provide information on actinide immobilization in a geological system over a very long period of time. These deposits contain high-grade uranium ores (40–60% UO 2 ) embedded in a clay matrix. Futhermore, the Oklo and Bangombé uranium deposits in Gabon were natural nuclear fission reactors that operated 2000 Ma ago. This offers the unique opportunity to study the behaviour of fission products and actinides in a geological environment. The geological stability of the sites is one of the most important parameters that can explain the preservation of the natural reactors of Gabon and of the Cigar Lake deposit. The mineralogy of the hosted rocks and the chemical composition of the fluids are likewise important parameters. It can be shown that clays, Fe-sulphides and organic matters provide effective redox buffering and consequently play an important role in the long-term preservation of the ores. Adsorption of actinides and fission products on clays and Ti-oxides is also an important process for retention of these elements. This process is even more efficient when it is followed by the formation of coffinite, USiO 4 · n H 2 O. Coffinitization is common at the Cigar Lake deposit and in the natural reactors of Gabon. Coffinitization may be related to hydrothermal alteration (Cigar Lake) and to weathering (Bangombé).