Periodic CO2 Injection for Improved Storage Capacity and Pressure Management under Intermittent CO2 Supply

Storing CO2 in geological formations is an important component of reducing greenhouse gases emissions. The Carbon Capture and Storage (CCS) industry is now in its establishing phase, and if successful, massive storage volumes would be needed. It will hence be important to utilize each storage site to its maximum, without challenging the formation integrity. For different reasons, supply of CO2 to the injection sites may be periodical or unstable, often considered as a risk element reducing the overall efficiency and economics of CCS projects. In this paper we present outcomes of investigations focusing on a variety of positive aspects of periodic CO2 injection, including pressure management and storage capacity, also highlighting reservoir monitoring opportunities. A feasibility study of periodic injection into an infinite saline aquifer using a mechanistic reservoir model has indicated significant improvement in storage capacity compared to continuous injection. The reservoir pressure and CO2 plume behavior were further studied revealing a ‘CO2 expansion squeeze’ effect that governs the improved storage capacity observed in the feasibility study. Finally, the improved pressure measurement and storage capacity by periodic injection was confirmed by field-scale simulations based on a real geological set-up. The field-scale simulations have confirmed that ‘CO2 expansion squeeze’ governs the positive effect, which is also influenced by well location in the geological structure and aquifer size, while CO2 dissolution in water showed minor influence. Additional reservoir effects and risks not covered in this paper are then highlighted as a scope for further studies. The value of the periodic injection with intermittent CO2 supply is finally discussed in the context of deployment and integration of this technology in the establishing CCS industry.

Risk Analysis of Tunnel Water and Mud Inrush Using Interpretive Structural Modeling and Fault Tree

Water and mud inrush is a common geological hazard in tunnel construction. Risk analysis of tunnel water and mud inrush has always been an important subject. In order to avoid the geological hazard, this paper presents a risk analysis model of tunnel water and mud inrush. The model combines the interpretive structural modeling method (ISM) and fault tree analysis (FTA). Relying on the Qinyu tunnel in the Weiwu expressway project, water and mud inrush risk factors are obtained by using ISM. Fundamental risk factors include formation lithology, attitude of stratum, strata combination, topography and geomorphology, geological structure and weather. ISM core risk factors are used as FTA basic events. Fuzzy importance of FTA basic events is obtained by using fuzzy interval calculation. The results show that geological structure is the primary risk factor causing Qinyu tunnel water and mud inrush. The model achieves qualitative and quantitative analysis of tunnel water and mud inrush. It accurately determines the main factors affecting the tunnel water and mud inrush, which is conducive to accident prevention.

Intensified paraglacial slope failures due to accelerating downwasting of a temperate glacier in Mt. Gongga, southeastern Tibetan Plateau

Topographic development via paraglacial slope failure (PSF) represents a complex interplay between geological structure, climate, and glacial denudation. Southeastern Tibet has experienced amongst the highest rates of ice mass loss in High Mountain Asia in recent decades, but few studies have focused on the implications of this mass loss on the stability of paraglacial slopes. We used repeat satellite- and unpiloted aerial vehicle (UAV)-derived imagery between 1990 and 2020 as the basis for mapping PSFs from slopes adjacent to Hailuogou Glacier (HLG), a 5 km long monsoon temperate valley glacier in the Mt. Gongga region. We observed recent lowering of the glacier tongue surface at rates of up to 0.88 m a−1 in the period 2000 to 2016, whilst overall paraglacial bare ground area (PBGA) on glacier-adjacent slopes increased from 0.31 ± 0.27 km2 in 1990 to 1.38 ± 0.06 km2 in 2020. Decadal PBGA expansion rates were ∼ 0.01 km2 a−1, 0.02 km2 a−1, and 0.08 km2 in the periods 1990–2000, 2000–2011, and 2011–2020 respectively, indicating an increasing rate of expansion of PBGA. Three types of PSFs, including rockfalls, sediment-mantled slope slides, and headward gully erosion, were mapped, with a total area of 0.75 ± 0.03 km2 in 2020. South-facing valley slopes (true left of the glacier) exhibited more destabilization (56 % of the total PSF area) than north-facing (true right) valley slopes (44 % of the total PSF area). Deformation of sediment-mantled moraine slopes (mean 1.65–2.63 ± 0.04 cm d−1) and an increase in erosion activity in ice-marginal tributary valleys caused by a drop in local base level (gully headward erosion rates are 0.76–3.39 cm d−1) have occurred in tandem with recent glacier downwasting. We also observe deformation of glacier ice, possibly driven by destabilization of lateral moraine, as has been reported in other deglaciating mountain glacier catchments. The formation, evolution, and future trajectory of PSFs at HLG (as well as other monsoon-dominated deglaciating mountain areas) are related to glacial history, including recent rapid downwasting leading to the exposure of steep, unstable bedrock and moraine slopes, and climatic conditions that promote slope instability, such as very high seasonal precipitation and seasonal temperature fluctuations that are conducive to freeze–thaw and ice segregation processes.

Geological structure and localization of mineralization at the Moryanikho-Merkurikhinskoye ore field

The paper discusses the lithological and facial features of the terrigenous-carbonate (biohermic) ore-bearing geological formation of the Moryanikho-Merkurikhinskoye ore field (Yenisei Ridge), which hosts stratiform lead-zinc deposits in carbonate strata. Ore-hosting lithofacies and their paleostructural position are characterized. Based on the previous studies, as well as the author’s own materials obtained as a result of field work, the main favorable lithological, facial and structural factors for hosting Moryanikhinsky-type stratiform lead-zinc mineralization are defined: the presence of paleodepressions within the shelf zone; development of carbonate rocks – dolomites, stromatolite dolomites and limestones, which are biohermic structures on the slopes of paleo-uplifts; the presence of an admixture of tuffaceous material in terrigenous rock varieties. The influence of tectonic faults on the formation of ore deposits and the morphology of ore bodies is indicated. The main types of ores of the Moryanikho- Merkurikhinsky ore field, as well as their mineral composition are described. The paper discusses the main ore types, as well as their mineral composition typical of the Moryanikho-Merkurikhinskoye ore field. The largest and well-studied lead and zinc stratiform Moryanikhinskoye deposit and Merkurikhinskoye ore occurrence located within the ore field are briefly characterized. The Moryanikhinskoye deposit is a typical example for searching for stratiform deposits of lead and zinc in the carbonate strata of the Angara-Bolshepitskaya mineragenic zone, which is of practical interest in developing predictive prospecting models of deposits and improving the efficiency of prospecting.

Experimental Study of Prevention and Control of Rock Burst in Steeply Inclined Coal Seams by Mining Sequence and Filling

The control and prevention of rock burst in a steeply inclined coal seam are essential. In order to figure out the effects of filling and mining sequence on rock burst in the steeply inclined coal seam, B3+6 and B1+2 coal seams in Wudong coal mine are chosen as the research objects, and an in-house experiment system of similarity simulation is established in this study. Combined with numerical simulation, the characteristics of collapse, stress distribution, and displacement variations can be measured, which provide useful information to study the effects of the filling body and mining sequence on rock burst. Experimental results show that the key reason for rock burst in a steeply inclined coal seam is the stress concentration of the rock pillar between B3+6 and B1+2 coal seams instead of the stress-lever-effect of a deeper rock pillar. The filling body can support the middle rock pillar, share the geological structure stress in the horizontal and vertical direction, eliminate the stress concentration zone largely, and prevent the occurrence of rock burst. When multiple working faces are working, the opposite side of the coal seam should be mined first to release the energy in the rock in advance, thus preventing the rock burst effectively. The research results provide fundamental information for better understanding the reason for rock burst and preventing rock burst in the steeply inclined coal seam.

Scenario Expression Method for Regional Geological Structures

Knowing the GIS expression of geological phenomena is an important basis for the combination of geology and GIS. Regional geological structures include folds, faults, strata, rocks, and other typical geological phenomena and are the focus of geological GIS research. However, existing research on the GIS expression of regional geological structure focuses on the expression of the spatial and attribute characteristics of geological structures, and our knowledge of the expression of the semantic, relationship, and evolution processes of geological structures is not comprehensive. In this paper, a regional geological structure scene expression model with the semantic terms positional accuracy, geometric shape, relationship type, attribute type, and time-type attributes and operations is proposed. A regional geological structure scenario markup language (RGSSML) and a method for mapping it with graphics are designed to store and graphically express regional geological structure information. According to the geological time scale, a temporal reference coordinate system is defined to dynamically express the evolution of regional geological structures. Based on the dynamic division of the time dimension of regional geological structures, the expression method of “time dimension + space structure” for the regional geological structure evolution process is designed based on the temporal model. Finally, the feasibility and effectiveness of the regional geological structure scene expression method proposed in this paper is verified using the Ningzhen Mountain (Nanjing section) as an example. The research results show that the regional geological structure scene expression method designed in this paper has the following characteristics: (1) It can comprehensively express the spatial characteristics, attribute characteristics, semantics, relationships, and evolution processes of regional geological structures; (2) it can be used to realize formalized expression and unified storage of regional geological information; and (3) it can be used to realize dynamic expression of the regional geological structure evolution process. Moreover, it has significant advantages for the expression of regional geological structure semantics, relationships, and evolution processes. This study improves our knowledge of the GIS expression of regional geological structures and is expected to further promote the combination and development of geology and GIS.

Directions and Extent of Flows Changes in Warta River Basin (Poland) in the Context of the Efficiency of Run-of-River Hydropower Plants and the Perspectives for Their Future Development

This paper presents changes in the flow of 14 rivers located in the Warta River basin, recorded from 1951 to 2020. The Warta is the third-longest river in Poland. Unfortunately, the Warta River catchment area is one of the most water-scarce regions. It hosts about 150 hydropower plants with a capacity of up to 5 kW. The catchment areas of the 14 smaller rivers selected for the study differ in location, size, land cover structure and geological structure. The paper is the first study of this type with respect to both the number of analyzed catchments, the length of the sampling series and the number of analyzed flow characteristics in this part of Europe. The analysis of changes in the river flows was performed with reference to low minimum, mean and maximum monthly, seasonal and annual flows. Particular attention was paid to 1, 3, 7, 30 and 90-day low flows and durations of the flows between Q50 and Q90%. In addition, the duration of flows between Q50 and Q90% were analysed. Analysis of the direction and extent of particular flow types was performed by multitemporal analysis using the Mann–Kendall (MK) and Sen (S) tests. The analysis of multiannual flow sequences from the years 1951–2020 showed that the changes varied over the time periods and catchments. The most significant changes occurred in the low flows, while the least significant changes occurred in the high flows. From the point of view of the operation of the hydropower sector, these changes may be unfavourable and result in a reduction in the efficiency of run-of-river hydropower plants. It was established that local factors play a dominant role in the shaping of river flows in both positive and negative terms, for the efficiency of the hydropower plants.

Assessment of the level of pollution of water bodies of the Denezhkin kamen reserve by the Shemur field

Waste produced during the extraction of minerals can cause various environmental problems. One of which is polluting underground and surface waters. The purpose of the article is to assess the level of pollution of water bodies of the Denezhkin Kamen reserve by the Shemur ore field. To assess the level of pollution, individual and complex pollution indices, statistical parameters and the ʺQuartileʺ method for calculating emissions are used. An analysis of the geological structure of the territory and physical and geographical conditions of the area was carried out; the level of pollution was assessed; the main causes of pollution were determined; the main pollutants were identified. The waters flowing through the reserve are not polluted they are polluted near the reserve borders. Pollutants are carried downstream over long distances and get into the intakes of local settlements. In the Bannaya River basin, the pollution area is about 80 km; in the Olkhovka River basin, the pollution area is about 60 km. There is a dependence in the change in the concentration of pollutants on seasonality and weather conditions. The main pollutants are those that are contained in large quantities in the overburden rocks of the deposit. Additional studies are required using a sampling program, which was not available during the current studies.

Evolution of the geological structure and mechanical properties due to the collision of multiple basement topographic highs in a forearc accretionary wedge: insights from numerical simulations

We propose a conceptual geological model for the collision of multiple basement topographic highs (BTHs; e.g., seamounts, ridges, and horsts) with a forearc accretionary wedge. Even though there are many BTHs on an oceanic plate, there are few examples of modeling the collision of multiple BTHs. We conducted numerical simulations using the discrete element method to examine the effects of three BTH collisions with forearcs. The typical geological structure associated with a BTH collision was reproduced during the collision of the first BTH, and multiple BTH collisions create a cycle of formation of BTH collisional structures. Each BTH forces the basal décollement to move up to the roof décollement, and the roof décollement becomes inactive after the passage of the BTH, and then the décollement moves down to the base. As the active décollement position changes, the sequences of underthrust sediments and uplifted imbricate thrusts are sandwiched between the décollements and incorporated into the wedge. At a low horizontal compressive stress, a “shadow zone” is formed behind (i.e., seaward of) the BTH. When the next BTH collides, the horizontal compressive stress increases and tectonic compaction progresses, which reduce the porosity in the underthrust sediments. Heterogeneous evolution of the geological and porosity structure can generate a distinctive pore pressure pattern. The underthrust sediments retain fluid in the “shadow” of the BTH. Under the strong horizontal compressive stresses associated with the next BTH collision, pore pressure increases along with a rapid reduction of porosity in the underthrust sediments. The distinctive structural features observed in our model are comparable to the large faults in the Kumano transect of the Nankai Trough, Japan, where a splay fault branches from the plate boundary and there are old and active décollements. A low-velocity and high-pore-pressure zone is located at the bottom of the accretionary wedge and in front (i.e., landward) of the subducting ridge in the Kumano transect. This suggests that strong horizontal compressive stresses associated with the current BTH collision has increased the pore pressure within the underthrust sediments associated with previous BTHs.