Unconsolidated Rocks Research Articles

Pore-scale simulations help in overcoming laboratory limitations with unconsolidated rock material: A multi-step reconstruction based on scanning electron and optical microscopy data

This article explores the possibility to assess the flow and transport properties of loosely consolidated rock material—something that is very hard or impossible to achieve in the laboratory due to fragility of cores. We present two cases of weakly consolidated and unconsolidated rocks. We provide a solution based on pore-scale simulations and stochastic reconstructions using scanning electron (SEM) and grain optical microscopy images as input data. The hybrid reconstruction approach is based on 3D grain shape construction out of 2D optical images, packing of grains to match the target porosity measured from SEM imaging, and addition of clay and other cementing phases with the help of phase-recovery method. Note that standard digital rock protocol based on X-ray microtomography did not work for considered samples due to fine-grained particle size distribution (insufficient resolution of X-ray microtomography). After creation of 3D digital replicas of rock samples based on their SEM and optical microscopy images, we applied pore-scale modeling to obtain permeability and two-phase flow properties. Simulated permeability of 259 mD for the first sample was in surprisingly good agreement with laboratory measurements of 248 mD. For the second sample permeabilities deviated by an order of magnitude. After additional studies it was found that the mesh attached to the sample during measurements affected the results. After pore-scale simulations of the grain packing with the mesh we were able to achieve very good agreement with the experiment, confirming that the lab was basically exploring the properties of the mesh clogged with unconsolidated rock material. Thus, pore-scale hybrid rock structure reconstruction technique combined with pore-scale simulations was able to correct inaccurate laboratory assessment and obtain flow properties for unconsolidated rock sample. We believe the developed hybrid reconstruction technique to be robust enough to serve as a basis of the industrial technology for petrophysical studies of weakly and unconsolidated core material.

Prediction of critical drawdown pressure for a gas reservoir prone to sand production in western offshore, India, and its suitability for CO2 sequestration

Sand production is a major problem in reservoirs having moderately hard to unconsolidated rock matrix. Gas bearing Daman sandstone is one such reservoir situated in the western offshore India. Identification of sand prone zones and quantification of drawdown causing sand failure is critical in such cases as sand cuttings can severely damage equipment. Predicting sand failure is also important for the safety, environmental, operational, production, and economic reasons.Failure of sand is caused by a combination of factors viz. geology of the reservoir, properties of sand, and production conditions of the well. For wells producing with a high gas rate, sand failure is more pronounced. Depending on the amount of sand production, different methods, chemical or mechanical, are used to control sand production from the well. In the study well multiple zones were tested, of which, sand production was observed in some zones depending on the rate of gas production.Daman sandstone under study bears good porosity and permeability, as established through well productivity, core study, and micro-computed tomography. The site holds potential for CO2 injection and can be evaluated for CO2 sequestration in the long run with reservoir depletion. Present study was carried out to quantify the drawdown at which sand failure initiates. Mohr-Coulomb failure criterion was used for failure prediction. It was observed that under given stresses, sand failure occurs when the applied drawdown exceeds a certain value depending on the unconfined compressive strength of the rock. Prediction of this drawdown value, regarded as critical drawdown pressure, is vital to control sand production and mitigate hazards associated with sand failure. The study is important for preparation of a field development plan to mitigate production losses arising out of potential sand failures.

An Improved Continuum Approach for Unconsolidated Formations on the Field Scale

Summary With the development of unconventional resources, such as oil sands and methane hydrate reservoirs, the importance of the mechanical performance model for underground unconsolidated rocks has increased significantly. The commonly used numerical approach for unconsolidated rocks is the discrete-element method (DEM). However, the extensive calculations required by the DEM make it inadequate for simulating unconsolidated rock behavior on a field scale. An alternative is the continuum approach, used to simulate the behavior of unconsolidated rocks on the field scale. In previous continuum approaches, unconsolidated rocks have been modeled as a visco-plastic fluid (i.e., Bingham fluid). The continuum approach based on visco-plastic fluid uses pressure (scalar) to describe the stress state of the particles. However, this approach does not account for the difference between the maximum and minimum principal stresses of the in-situ stress field when simulating the mechanical performance of unconsolidated rocks. Here, we developed an improved continuum approach for unconsolidated rocks and used the finite-element method as a numerical approach. Our improved model can consider the difference between the maximum and minimum principal stresses of the in-situ stress field and the pore pressure of the unconsolidated formation. We validated our numerical model with the angle of repose test, a benchmark problem for unconsolidated rocks. The validation results confirm the accuracy of our unconsolidated model. For the coupled model between the unconsolidated model and the flow model, we used an analytical solution to verify its reliability. Unconsolidated rock performances in an unconsolidated reservoir with fluid injection have been investigated based on our coupled model. The simulation results show that injection can activate the movement of unconsolidated rock particles, leading to changes in the distribution of effective stress and permeability. Our model has the potential to address large-scale unconsolidated rock issues and contribute to energy extraction.

Indications of volcanic style of the Silurian Nová Ves Volcano (Hemrovy Rocks)

Studied locality of Hemrovy Rocks belongs to Nová Ves Volcanic Center, one of the Silurian volcanic centers of Prague Basin of Teplá-Barrandien area (lower Wenlock – lower Ludlow age). The aim of this work is to describe details of the volcanic rock structures and to contribute to the interpretation of the Silurian volcanic style. The macroscopic and microscopic structures of basaltic rocks in and close to the abandoned Kační Quarry in the southern part of Prague and at the adjacent locality – ridge of Hemrovy Rocks were studied. At these sites, volcaniclastics dominate over solid volcanic rocks and sediments. The volcanic rocks are represented by basalts, which form thin lava flows overlying both the volcaniclastics and sedimentary rocks. Massive fine-grained basalts pass to pillow lava facies, autobreccia or hyaloclastite breccia in-situ. These brecciated structures evolve into peperites or to unconsolidated volcaniclastic rocks of a previous eruption. Coarse-grained volcaniclastics with oversized subrounded to angular clasts of vesiculated lava or sediments within glassy matrix, sporadically with sediment admixture, are unsorted and thick-bedded. They were probably formed by gravity-driven mass flow. Basalt in the Kační Quarry probably represents a synvolcanic intrusion, as documented by its hyaloclastite rim and presence of clusters of resedimented volcaniclastics in the adjacent fine-grained sediments. Matrix of the volcaniclastics is mostly unsorted, formed mostly by quenched fragments of altered palagonitized and chloritized basaltic glass, locally scoriaceous, and fragments of chilled basaltic lava. Originally highly porous volcaniclastics, resp. hyaloclastites were secondarily cemented by calcite and silica. Secondary chlorite, calcite and silica also fill vesicles and cavities in fragments of glass and lava clasts. Dense vesicularity of lava fragments in volcaniclastics indicates an effective explosive interaction of lava with water. It is probable that much of the wet volcaniclastic material repeatedly slumped back down into the volcano’s crater to be re-ejected by subsequent phreato-magmatic explosions. Hydroclastic fragmentation was iniciated by repeated subaquatic eruptions in shallow subphotic marine zone. Unsorted crinoidal packstones mostly with trilobites, trepostomate bryozoan and volcaniclastic matrix were deposited in the vicinity of the Nová Ves Volcanic Center.

Application of Cross-hole Seismic Tomography to Inferred Cavities Condition.

The construction of the Rajamandala hydroelectric power plant civil works has experienced critical problems that arise in the implementation process, with the occurrence of cracks cavities conditions in the headrace tunnel locations. We applied the cross-hole seismic tomography to detect important heterogeneities and mechanical proprieties of the formations between two boreholes in this case inferred cracks cavities condition. The seismic source is inside the borehole “a sparker” and the receivers “hydrophones” are in an adjacent one, the sparker is lowered into the borehole one step at the time. Seismic waves, propagating in the tunnel wall rock, spread widely, and are reflected and refracted when encountering interfaces between rocks with different acoustic impedances. Reflected waves returning to the receivers are recorded. After the processing of the first arrivals of the P waves we obtain a cross section of the seismic velocities in between the two wellbores. With the cross-hole seismic tomography, the basis could be provided to the tunnel construction and parameter adjustments to guarantee the construction safety. Our result shown that there is a weak zone above the tunnel with low Vp zone (~1.2 km/s) may be related to weak zone (may be fracture, unconsolidated rock, and fluid-filled rock or landslide caving). Checker-board resolution test is also conducted to determine the tomogram areas that are reliable to be interpreted. Our challenges are we have poor resolution due to not enough raypath. The Cross-hole seismic tomography can effectively and safely guide the excavation of the tunnel section working surface in combination with reconstructed images and excavation technology.

Groundwater Conditions and Springs Potency for Domestic Requirement in Klaten and Banggai Kepulauan Regency, Indonesia

At present, sustainable management of water resources has become a major issue for the world community. In water management efforts, potency assessment becomes an important thing. The purpose of this study is to analyze the availability of ground water and water from springs both qualitatively and quantitatively and evaluate their potency for domestic. To determine the groundwater conditions in the research area, a qualitative descriptive analysis was carried out based on geological and hydrogeological data. To determine the potency of the springs, a quantitative descriptive analysis was carried out with the help of tables and diagrams. The potency for springs is calculated based on the discharge data of all springs contained in each district in relation to water for domestic purposes. The results showed that Kebonarum District has very good groundwater availability because it is located in an area of unconsolidated rock between mountains. In South Tinangkung District, groundwater conditions are not good. Groundwater is generally found in cracks or rock fractures. From the calculation results, it is known that the total spring discharge in Kebonarum District is 9,870,768 m3/year, while the spring discharge in South Tinangkung District is 64,144,224 m3/year. With the water in Kebonarum District is 915,858 m3/year and in South Tinangkung Sub District is 355,393 m3/year, the potency of water from springs in these two districts is sufficient to be used as a water source for domestic.

Outdoor systems performance and upgrade

Over the last two decades, the possibility of using RPCs in outdoors systems has increased considerably. Our group has participated in this effort by installing several systems and continues to work on their optimization, while simultaneously studying and developing new approaches that can use RPCs in outdoor applications.In particular, four detectors were deployed in the field at the Pierre Auger Observatory in 2019 remained inactive, awaiting the commissioning of support systems. During the pandemic the detectors were left without gas flow for more than two years, but were recently reactivated with no major problems.The LouMu project combines particle physics and geophysics in order to map meter-scale geologic structures, using Muon Tomography. Transmission muography is sensitive to the total amount of matter crossed by the muons, allowing to separate targets of different densities. In this exploratory project, it serves to identify unconsolidated rock zones, like geological faults and ore masses around an old Pyrite mine, now converted into a science center. The general goal is to compare how effective is the muographic survey when compared with the more standard geophysical techniques. The development of the RPC system used and the data from the last two years will be presented.Finally, recent advances in a large area (1 m2) double gap-sealed RPC will be presented.

Combination of extended elastic impedance and rock physics templates for reservoir characterisation in Temblador field, Eastern Venezuela basin

The Temblador Field is located on the southern flank of the Eastern Venezuela Basin. The Oficina Formation, present in the field, represents one of the most important producing Formations in the country. In this project, a detailed characterisation and delimitation of the sands of the Jobo and Morichal Members of the Oficina Formation. The work was outlined in three stages. The first stage consisted of studying the elastic properties of the reservoirs through unconsolidated rock physics modelling through the elaboration of the “Rock Physics Template” (RPT). Likewise, during this phase, different crossed graphs were prepared that allowed lithological discrimination. In the second stage, cubes of elastic properties such as P-wave impedance, S-wave impedance, Mhu-Rho (μρ) and Lambda-Rho (λρ) were obtained through the inversion of the Extended Elastic Impedance. Finally, the third stage consists of the classification of the lithofacies, of the cubes resulting from the inversion, through a Bayesian classification. These results allowed the construction of sand probability maps that allow delimiting the best quality sands within the Jobo and Morichal Members. In this way, the present work provides an additional tool when carrying out reservoir exploration studies, reducing uncertainty when locating a new prospect.

Machine learning algorithm optimization for intelligent prediction of rock thermal conductivity: A case study from a whole-cored scientific drilling borehole

Rock thermal conductivity (TC) is a key parameter in geothermal, petroleum geology, and basin research. Although experimental analysis relying on core samples is currently an effective way to obtain the TC of rocks, it is not always feasible as most boreholes have no or limited cores, making it difficult to establish TC model of geological body efficiently and accurately. This study sheds light on how machine learning algorithms can be used to accurately predict rock TC with easily accessible and high-resolution logging data. Based on 295 measured TC data, logging data, and vertical seismic profile (VSP) data collected from the whole-cored CSDP-2 borehole, the models including random forest (RF), convolutional neural network (CNN), support vector regression (SVR), and particle swarm optimization-SVR (PSO_SVR), were applied to predict the TC of the entire borehole section. Using a confusion matrix analysis, the primary-wave velocity (PWV) from the VSP survey, measured density, and logging data, including shallow lateral resistivity (LLS), compensated neutron log (CNL), density (DEN), gamma rays (GR), spontaneous potential (SP), and acoustic transit time (AC), were used as the input variables for training models and TC prediction. The results showed that the geophysical parameters reflecting those properties related to mineral composition, porosity and reservoir fluids of geological body can be well used to predict TC through machine learning algorithms. Regardless of unconsolidated sediments or rocks, the RF model showed stronger applicability and higher accuracy in TC prediction compared to the PSO_SVR and CNN models, while the SVR model showed poor applicability in this case study. The PWV data can effectively improve the accuracy of TC prediction of all models, and the RF model finally yielded the excellent performance with a correlation coefficient (> 0.86) and root mean squared error (8%) between the predicted and measured values. Future research should focus on studying the weighted analysis for the correlation between geophysical parameters and TC and developing more accurate predictive models for wider applications.

Rock physics characteristics of marine sediments in the South China sea: The link between the geological factors and elastic properties

Understanding the geological factors behind the physical and elastic properties of marine sediments and unconsolidated rock is essential for the interpretation of geophysical measurements, hazard assessment, and ocean engineering applications. Core and well logging data from the six drilling sites of the Ocean Drilling Program/International Ocean Discovery Program (ODP/IODP) were used to analyze the rock physical characteristics in the South China sea. The depositional environment plays a significant role in affecting the physical properties of marine sediments. The sediments deposited under shallow water conditions show a higher velocity than the basin, slope, and deeper shelf carbonate deposits. Moreover, the non-depositional hiatus along the Oligocene-Miocene boundary displays a notable control on the variation of rock physical properties. It is found that the lithofacies and physical compaction remarkably influence the elastic characteristics of P-impedance and Vp/Vs ratio. The calcareous-rich sediment and ooze have very low P-impedance and high Vp/Vs ratio, whereas the siltstone and coarse sand present high P-impedance and low Vp/Vs ratio characteristics. With the enhancement of the consolidation degree, the Vp/Vs ratio significantly decreases from 6 to less than 2, suggesting that the shear wave velocity is highly sensitive to physical compactions. The basalt at site U1431 is considerably lower in its P-wave velocity than that at the site of U1433, which is probably caused by the intense fracturing occurring at the site of U1431 associated with different tectonic environments. We establish the link between geological factors and elastic characteristics of marine sediments of SCS, laying the foundation for characterizing depositional environments, lithofacies, and compaction degrees using geophysical measurements.

Implications on Gravity Anomaly Measurements Associated with Different Lithologies in Turkana South Subcounty

The use of gravity data has demonstrated capability for monitoring lithological changes on a large scale as a consequence of differentiating basement and sedimentary of buried valleys. Gravity anomalies are associated with lateral contrasts in density and therefore deformation by faulting or folding will be manifested if accompanied by lateral density changes, otherwise, the vice versa is true. The study’s objective is to evaluate the effectiveness of gravity method in establishing different lithologies in an area. The study has revealed that regional anomaly gravity map presents high anomalies in the Northern region in the NW-SE trend and low anomalies in the southern trend in NW-SE, while the residual anomaly gravity map shows different trends for the low and high gravity anomalies. The gravity anomalies are well interpreted in line with the lithologies of the study area rather than the deformation of the same lithologies. There are observed high values of gravity anomaly values (ranging from -880.2 to -501.2 g.u.) where there are eolian unconsolidated rocks overlying the basement compared to low gravity anomaly values (ranging from -1338.9 to -1088.7 g.u.) where the andesites, trachytes and phonolites overly the basement. The different regional gravity anomalies relate well with different rock densities in the study area along the line profile for radially averaged power spectrum. The gravity highs are noted in the eastern point and are associated with andesites, trachytes, basalts and igneous rocks, while the gravity lows are associated with sandstone, greywacke, arkose, and eolian unconsolidated rock. The utilization of the information from the Power spectrum analysis demonstrates that the depth to the deepest basement rock is 12.8 km which is in the eastern flank, while the shallowest to the basement of 1.1 km to the western flank.

Lithostratigraphy, Lithogeochemistry, and Tectono-Magmatic Framework of the ABM Replacement-Style Volcanogenic Massive Sulfide (VMS) Deposit, Finlayson Lake District, Yukon, Canada

Abstract The Upper Devonian ABM deposit is a bimodal-felsic, replacement-style volcanogenic massive sulfide (VMS) deposit within the Finlayson Lake district in Yukon, Canada. The deposit is hosted by predominantly felsic volcanic rocks of the upper Kudz Ze Kayah formation that were deposited in an active back-arc basin in three sequences consisting of interbedded felsic volcaniclastic rocks and argillites, and felsic lava flows and domes, and felsic and mafic sills. The felsic rocks fall into two groups, Felsic A and Felsic B (FA and FB), based on immobile elements and their ratios. Relative to the FB group, the FA group has high Zr concentrations (>550 ppm) and generally higher contents of high field strength elements. The FA/FB chemostratigraphy roughly coincides with the lithostratigraphic sequences. Sequence 2 hosting the mineralization consists of FB felsic rocks; the hanging-wall Sequence 3 and footwall Sequence 1 felsic rocks have FA signatures. An argillite lens, recording a period of volcanic quiescence, occurs at the upper contact of Sequence 2. From reconstruction of the basin architecture, two sets of synvolcanic faults are inferred. The synvolcanic faults were interpreted based on thickness changes of volcanosedimentary units and the distribution of coherent rocks. During breaks in volcanism, synvolcanic faults acted as conduits for upwelling hydrothermal fluids, which were diverted laterally into unconsolidated volcaniclastic rocks and formed the replacement-style VMS mineralization. Although the mineralized lenses are hosted by FB felsic rocks, their replacement-style nature implies that the mineralizing processes occurred during the break in volcanism and were genetically associated with the overlying FA felsic volcanic rocks.

The features of the petrophysical research of the unconsolidated rocks of Cenomanian play

Currently, the ambiguity of the obtained results of petrophysical studies based on laboratory definitions and estimates of calculated parameters creates problems both with their justification and with the assessment of the reliability of the initial data, which is especially important when discovering and developing new deposits. The main feature of Cenomanian rocks is their weak cementation due to the conditions of rock formation. As a result of the analysis, the factors of reducing the reliability of the determination of filtration-capacitance properties were established and criteria for substantiating the assessment of the quality of the results of petrophysical studies were formulated. This made it possible to bring the results of laboratory data to a unified technology of petrophysical studies of the core represented by weakly cemented rocks. The reliability of the results obtained is confirmed by comparing the data of laboratory core studies with the results of interpretation of the data of geophysical well surveys, testing and hydrodynamic studies of wells.

Determining factors of the unconsolidated rocks of Cenomanian reservoir on the Bolshekhetskaya depression

The relevance of the article is associated with the importance of the object of the research. Dozens of unique and giant oil and gas fields, such as Urengoyskoye, Medvezhye, Yamburgskoye, Vyngapurovskoye, Messoyakhskoye, Nakhodkinskoye, Russkoye, have been identified within the Cenomanian complex. The main feature of Cenomanian rocks is their slow rock cementation. This leads to significant difficulties in core sampling and the following studies of it; that is the direct and most informative source of data on the composition and properties of rocks that create a geological section.The identification of the factors, which determine the slow rock cementation of reservoir rocks, allows establishing a certain order in sampling and laboratory core studies. Consequently, reliable data on the reservoir and estimation of hydrocarbon reserves both of discovered and exploited fields and newly discovered fields that are being developed on the territory of the Gydan peninsula and the Bolshekhetskaya depression will be obtained. This study is also important for the exploration and development of hydrocarbon resources of the continental shelf in the waters of the Arctic seas of Russia as one of the most promising areas.As a result of the analysis, it was found that the formation of rocks of the PK1-3 Cenomanian age of the Bolshekhetskaya depression happened under conditions of normal compaction of terrigenous sedimentary rocks that are located in the West Siberian basin. Slow rock cementation of reservoir rocks is associated with relatively low thermobaric conditions of their occurrence, as well as the low content of clay and absence of carbonate cements. Their lithological and petrophysical characteristics are close to the analogous Cenomanian deposits of the northern fields of Western Siberia and can be applied to other unconsolidated rocks studied areas.

Ray velocity derivatives in anisotropic elastic media. Part II—polar anisotropy

SUMMARY Considering general anisotropic (triclinic) media and both, quasi-compressional (qP) and quasi-shear (qS) waves, in Part I of this study, we obtained the ray (group) velocity gradients and Hessians with respect to the ray locations, directions and the elastic model parameters along ray trajectories. Ray velocity derivatives for anisotropic elastic media with higher symmetries were considered particular cases of general anisotropy. In this part, Part II, we follow the computational workflow presented in Part I, formulating the ray velocity derivatives directly for polar anisotropic media (transverse isotropy with tilted axis of symmetry, TTI) for the coupled qP waves (quasi-compressional waves) and qSV waves (quasi-shear waves polarized in the ‘axial’ plane) and for SH waves (shear waves polarized in the ‘normal’ plane). The acoustic approximation for qP waves is considered a special case. In seismology, the medium properties, normally specified at regular 3-D fine gridpoints, are the five material parameters: the axial compressional and shear wave velocities, the three (unitless) Thomsen parameters and two geometric parameters: the polar angles defining the local direction (the tilt) of the medium symmetry axis. All the parameters are assumed spatially (smoothly) varying, so that their spatial gradients and Hessians can be reliably numerically computed. Two case examples are considered; the first represents compacted shale/sand rocks (with positive anellipticity) and the second, unconsolidated sand rocks with strong negative anellipticity (manifesting a qSV triplication). The ray velocity derivatives obtained in this part are first tested by comparing them with the corresponding numerical (finite difference) derivatives. Additionally, only for validation purpose, we show that exactly the same results (ray velocity derivatives) can be obtained if we transform the given polar anisotropic model parameters (five material and two geometric) into the 21 stiffness tensor components of a general anisotropic (triclinic) medium, and apply the theory derived in Part I. Since in many practical wave/ray-based applications in polar anisotropic media only the spatial derivatives of the axial compressional wave velocity are taken into account, we analyse the effect (sensitivity) of the spatial derivatives of the other parameters on the ray velocity and its derivatives (which, in turn, define the corresponding traveltime derivatives along the ray).

Erstellung eines Gefrierkörpers als Bauhilfsmaßnahme für einen Tunnelvortrieb unter dem Hauptbahnhof Bern

AbstractIn the course of the planned underground extension of the central station in Bern, an access tunnel had to be constructed from an existing shaft. The first 60 m of this tunnel cross through unstable, water‐bearing and unconsolidated rock, and run under existing railway tracks. Thyssen Schachtbau GmbH has been commissioned the contract to carry out an artificial ground freezing measure to enhance the realization of the tunnel construction. The horizontal directional drilling work within the shaft as well as the construction and operation of the freezing plant were carried out in 2020 in a very confined space, and parallel to the ongoing operation of the train station. In order to ensure sufficient water saturation and thus the freezability of the unconsolidated rock, artificial ground irrigation procedure was operated. After completion of the predefined frost body, the tunnel was successfully and safely driven from the shaft into the bedrock.

Estimation of anisotropic hydraulic conductivity using geophysical data in a coastal aquifer of Karnataka, India

AbstractEstimation of hydraulic parameters is essential to understand the interaction between groundwater flow and seawater intrusion. Though several studies have addressed hydraulic parameter estimation, based on pumping tests as well as geophysical methods, not many studies have addressed the problem with clayey formations being present. In this study, a methodology is proposed to estimate anisotropic hydraulic conductivity and porosity values for the coastal aquifer with unconsolidated formations. For this purpose, the one‐dimensional resistivity of the aquifer and the groundwater conductivity data are used to estimate porosity at discrete points. The hydraulic conductivity values are estimated by its mutual dependence with porosity and petrophysical parameters. From these estimated values, the bilinear relationship between hydraulic conductivity and aquifer resistivity is established based on the clay content of the sampled formation. The methodology is applied on a coastal aquifer along with the coastal Karnataka, India, which has significant clayey formations embedded in unconsolidated rock. The estimation of hydraulic conductivity values from the established correlations has a correlation coefficient of 0.83 with pumping test data, indicating good reliability of the methodology. The established correlations also enable the estimation of horizontal hydraulic conductivity on two‐dimensional resistivity sections, which was not addressed by earlier studies. The inventive approach of using the established bilinear correlations at one‐dimensional to two‐dimensional resistivity sections is verified by the comparison method. The horizontal hydraulic conductivity agrees with previous findings from inverse modelling. Additionally, this study provides critical insights into the estimation of vertical hydraulic conductivity and an equation is formulated which relates vertical hydraulic conductivity with horizontal. Based on the approach presented, the anisotropic hydraulic conductivity of any type aquifer with embedded clayey formations can be estimated. The anisotropic hydraulic conductivity has the potential to be used as an important input to the groundwater models.

Technological Capabilities of Well Cementing

Abstract Cementing of casing string is a final operation before the next stage of well construction; it provides maximum operational life of the well. Cementing of casing string is carried out with the use of technology, based on squeezing of the whole volume of drilling mud by special grouting composition. The main purposes of cementing include isolation of water-bearing horizon, strengthening of borehole walls in unconsolidated and unstable rocks. Well cementing process is divided into five subsequent operations. Firstly, grouting mixture is prepared in concrete mixers (cementing units) with necessary water-to-cement ratio and additives. Secondly, prepared grouting solution is injected in a well. Thirdly, the solution is squeezed into the space between the casing pipes and wellbore walls. Then it is necessary to wait until the cement sheath is hardened. And at last, quality control is carried out. For convenient transportation, the equipment for well cementing is installed on the truck chassis (KAMAZ, URAL and etc.). All components are poured in concrete mixer, then the water is added and everything is being mixed until formation of uniform mass, which is later pumped in a well. Oil and Gas Industry Safety Regulations say that «calculated endurance of casing string cementing should not exceed 75% of time of cement thickening, established by laboratory tests». Therefore, it is necessary to carry out all operations of injection of fluids into the well as soon as possible without any incompliances of the cementing technology. With cementing material used and its water-to-cement ratio of 0.5, the average time of cement thickening is 120 minutes, according to laboratory tests. Therefore, a set of operations of injection of fluids should not exceed 90 minutes.

Inference of the spatio-temporal variability and storage potential of groundwater in data-deficient regions through groundwater models and inversion of impact factors on groundwater, as exemplified by the Lake Victoria Basin

Groundwater is an important resource for supporting domestic water use for people's livelihoods and for maintaining ecosystems. Borehole observations provide the first-hand data that characterise the fluctuation, depth, and aquifer conditions of the groundwater. Unfortunately, such observations are not available or are insufficient for scientific use in many regions. Taking the Lake Victoria Basin (LVB) as an example of data-deficient regions, this study proposes a simple knowledge-based approach that uses the Global Land Data Assimilation System (GLDAS) Catchment Land Surface Model (CLSM) for the main data, with rainfall, hydrological, topographical and geological datasets as supports, by which to infer the spatio-temporal variability and storage potential of groundwater. The method is based on analysis and inversion of impact factors on groundwater, and the feasibility of such a method is proven by showing that the groundwater results from GLDAS CLSM can correctly indicate the seasonality, as well as the link to topographical and geological features. For example, both results from the water balance equation (WBE) and GLDAS CLSM indicate that there are two groundwater recharge seasons in the basin, e.g., March to May and September to November. Compared to the eastern side of the LVB, the western side has mountains blocking surface runoff, and thus, reasonably, has larger storage potential estimates in GLDAS CLSM. Due to the low degree of weathering of the basement rocks, it is expected that there is only small storage potential and variation of groundwater in the southeastern parts of the LVB. GLDAS CLSM also correctly reflects this behaviour. Additionally, the largest groundwater storage potential over the LVB is found in regions near the Kagera River and the western shoreline, since it associates with unconsolidated rocks and behaviours of large groundwater recharge from GLDAS CSLM during the wet year of 2006. The major limitation of this knowledge-based method is that the uncertainty in terms of magnitude on GLDAS CLSM groundwater changes cannot be assessed, in addition to the fact that the reliability of the results cannot be quantified in terms of specific numbers. Therefore, the results and interpretation of groundwater behaviours using such methods can only be a guide for ‘where’ and ‘when’ to find groundwater.

Liquidation of the exploration pit n. 11 from the Rozna uranium deposit, Czech Republic

The aim of this article is to introduce the history, characteristics and liquidation of one of the first exploratory borings of the Rozna deposit in the middle of Czech Republic. Based on available characteristics of the main mine workings and the local geology a design of liquidation was created to fulfill the legislative framework of Czech Republic as well as possible. The design was then executed by backfill with unconsolidated rock material and subsequently by securing the surface pit mouth of the main mine workings by closing sinking platform placed on micropiles. The finishing works included modifying the surroundings of the exploration pit by land machinery and smoothing the previous mining activity down, so that it doesn’t disturb the local morphology.