Subsurface Geological Formations Research Articles

CO2 Storage in deep saline aquifers: impacts of fractures on hydrodynamic trapping

Natural or induced fractures are typically present in subsurface geological formations. Therefore, they need to be carefully studied for reliable estimation of the long-term carbon dioxide storage. Instinctively, flow-conductive fractures may undermine storage security as they increase the risk of CO2 leakage if they intersect the CO2 plume. In addition, fractures may act as flow barriers, causing significant pressure gradients over relatively small regions near fractures. Nevertheless, despite their high sensitivities, the impact of fractures on the full-cycle storage process has not been fully quantified and understood. In this study, a numerical model is developed and applied to analyze the role of discrete fractures on the flow and transport mechanism of CO2 plumes in simple and complex fracture geometries. A unified framework is developed to model the essential hydrogeological trapping mechanisms. Importantly, the projection-based embedded discrete fracture model is incorporated into the framework to describe fractures with varying conductivities. Impacts of fracture location, inclination angle, and fracture-matrix permeability ratio are systemically studied for a single fracture system. Moreover, the interplay between viscous and gravity forces in such fractured systems is analyzed. Results indicate that the fracture exhibits differing effects regarding different trapping mechanisms. Generally speaking, highly-conductive fractures facilitate dissolution trapping while weakening residual trapping, and flow barriers can assist dissolution trapping for systems with a relatively low gravity number. The findings from the test cases for single fracture geometries are found applicable to a larger-scale domain with complex fracture networks. This indicates the scalability of the study for field-relevant applications.

(Invited) Electrochemically Modulated Mitigation of Acid Gas Emissions

The alarming rise in anthropogenic CO2 levels in the atmosphere due primarily to fossil fuel emissions is leading to significant changes in global climate patterns and increasing ocean acidities, with their severe negative impacts on the health of our planet. The mitigation of these acid gas emissions is a daunting task, both because of the scale of the problem and because of the economic ramifications associated with the capture of the greenhouse gases and their subsequent utilization or subsurface storage. The traditional means for CO2 capture and release generally rely on either chemical or physical interactions with sorbents with subsequent temperature or pressure changes to release the captured CO2 and regenerate the sorbent. The captured CO2 can then be compressed for injection and sequestration in subsurface geological formations or converted to useful products. These processes require significant energy integration which adds complexity and cost to the overall capture operation. Isothermal operations that obviate or significantly reduce the heat integration requirements in these processes could have significant advantages over the traditional methods. One such approach is to exploit electrochemical technologies for the capture and release of CO2, which can be operated isothermally, and can rely only on renewable energy resources, if desired.The general principles underlying electrochemically modulated acid gas separation processes will be outlined, with an emphasis on the thermodynamic and transport considerations required for their effective implementation in carbon capture. In particular, we will consider electrochemical technologies for the capture of CO2 that are suitable for both point-of-use gas emissions mitigation, and for removal from the atmosphere and ocean waters, where CO2 has been accumulating for decades. Examples include an indirect approach, in which an electrochemically released species (e.g., copper ions, protons) displaces the CO2 bound to a chemical sorbent via competitive complexation; the CO2 and the sorbents are regenerated when the species is re-captured in the cathode chamber of an electrochemical cell, leaving the sorbent free to be cycled back to the absorber. An alternative approach exploits the complexation of an electroactive moiety directly with the CO2 upon activation by electrochemical reduction, and releases the CO2 when it is re-oxidized on reversal of the applied cell voltage. In general, these electrochemically based technologies hold promise for tackling the climate change challenges that we, and future generations, must face.

Joint geophysical prospecting for groundwater exploration in weathered terrains of South Guangdong, China.

Groundwater occurrence in a hard rock terrain is strongly controlled by the weathered/fractured zones. However, delineation of such zones is a challenging task given their structural heterogeneity. Traditionally, large numbers of well tests are conducted to assess the subsurface formation. But, such tests suffer from efficiency in terms of cost, time, and data coverage. Non-invasive geophysical methods can be the best alternative of expensive drilling methods. However, a geophysical method alone is ambiguous to interpret the highly heterogeneous subsurface formation. In this study, joint application of electrical resistivity tomography (ERT), magnetic method, and joint profile method (JPM) was conducted for groundwater exploitation in a weathered terrain of South Guangdong, China. ERT, magnetic, and JPM data were acquired along different geophysical profiles via a variety of survey parameters. The interpreted 2D models of electrical resistivity and magnetic data coupled with the local accessible boreholes and hydrogeological information constrain the subsurface geologic formation into four discrete layers with specific electrical resistivity range, i.e., topsoil cover, highly weathered saturated layer, semi-weathered saturated layer, and un-weathered substratum. Incorporation of JPM (ER, SP, and IP methods) with ERT and magnetic models reveal three faults (F1, F2, and F3) and several saturated intense fractures/discontinuities. The groundwater reserves associated with the weathered/fractured rock were estimated via hydraulic parameters, namely hydraulic conductivity and transmissivity. The results suggest that high-yield groundwater resources are found within the weathered/fractured zones. Geophysical results of this joint application fit pretty well to the local hydrogeological data of the study area. Our novel approach reduces any ambiguity caused in the geophysical interpretation and provides clearer insight of the subsurface formation with more confident solutions to the most challenging problems of the hard rock sites. This hydrogeophysical study provides important contributions to groundwater exploration in areas where weathering has significant effects on the hard rock aquifer system. Compared with traditional methods, this approach is more advantageous for assessment of groundwater resources in hard rock terrains.

Effects of salinity and shear stress on clay deformation: A molecular dynamics study

The deformation of clay minerals is an important phenomenon that is relevant to many problems, particularly those that occur in subsurface geological formations. The salinity of the formations and external shear stress applied to them are two important factors that contribute to the deformation of such porous media. To gain a deeper understanding of such phenomena, we have carried out extensive molecular dynamics simulations using the Na-montmorillonite (Na-MMT) structure as the model of clay minerals and have studied the effect of salt concentration on its swelling. As the NaCl concentration increases, so also does the basal spacing. We demonstrate the effect of the coupling between the applied shear stress and NaCl salinity on the swelling behavior of Na-MMT, namely, deformation of the interlayer space that results in swelling. According to the results, the extent of Na-MMT deformation depends on both the brine salinity and the shear rate.

Multiscale simulation of inelastic creep deformation for geological rocks

Subsurface geological formations provide giant capacities for large-scale (TWh) storage of renewable energy, once this energy (e.g. from solar and wind power plants) is converted to green gases, e.g. hydrogen. The critical aspects of developing this technology to full-scale will involve estimation of storage capacity, safety, and efficiency of a subsurface formation. Geological formations are often highly heterogeneous and, when utilized for cyclic energy storage, entail complex nonlinear rock deformation physics. In this work, we present a novel computational framework to study rock deformation under cyclic loading, in presence of nonlinear time-dependent creep physics. Both classical and relaxation creep methodologies are employed to analyze the variation of the total strain in the specimen over time. Implicit time-integration scheme is employed to preserve numerical stability, due to the nonlinear process. Once the computational framework is consistently defined using finite element method on the fine scale, a multiscale strategy is developed to represent the nonlinear deformation not only at fine but also coarser scales. This is achieved by developing locally computed finite element basis functions at coarse scale. The developed multiscale method also allows for iterative error reduction to any desired level, after being paired with a fine-scale smoother. Numerical test cases are studied to investigate various aspects of the developed computational workflow, from benchmarking with experiments to analysing the impact of nonlinear deformation for a field-scale relevant environment. Results indicate the applicability of the developed multiscale method in order to employ nonlinear physics in their laboratory-based scale of relevance (i.e., fine scale), yet perform field-relevant simulations. The developed simulator is made publicly available at https://gitlab.tudelft.nl/ADMIRE_Public/mechanics.

A review of recent developments in CO2 mobility control in enhanced oil recovery

Carbon dioxide-enhanced oil recovery (CO 2 -EOR) has gained widespread attention in light of the declining conventional oil reserves. Moreover, CO 2 -EOR contributes to the reduction of the global emissions of greenhouse gases through CO 2 sequestration in subsurface geologic formations. This method has been largely used in the petroleum industry for several decades especially for extracting oil from light-to-medium oil reservoirs approaching an advanced state of maturity. Traditionally, CO 2 is used in a continuous flooding scheme for EOR. However, continuous CO 2 flooding tends to be problematic due to unfavorable mobility, viscous fingering/channeling and early breakthrough of CO 2 , especially in the presence of reservoir heterogeneities. In this paper, recent developments in the methods used to overcome these problems are reviewed. These developments include CO 2 water-alternating-gas (WAG) injection, polymer-assisted CO 2 injection, surfactant-assisted CO 2 mobility control (CO 2 -foam injection), and nanoparticle-assisted CO 2 flooding. Each method addresses, to an extent, one or more of the problems associated with conventional CO 2 flooding. Furthermore, incorporating more than one method can provide better performance in terms of CO 2 mobility control and oil recovery. In comparison with CO 2 -WAG and CO 2 -foam injection methods, the use of polymers and nanoparticles with CO 2 flooding is relatively new. These two new methods were mostly investigated experimentally, at the laboratory level, and they still need further development prior to field implementation.

Effect of CO2-brine-rock reactions on pore architecture and permeability in dolostone: Implications for CO2 storage and EOR

Geologic carbon sequestration (GCS) is considered a feasible technology for storing substantive volumes of greenhouse gases in subsurface geological formations. In the reservoir, far from carbon dioxide (CO2) injection wells or in post-injection scenarios, diffusion dominates over advection. This condition conjoins with spatially distributed geochemical reactions to induce heterogeneous changes in pore architecture, i.e. pore body and throat sizes or surface roughness. These changes can affect CO2 transport properties and storage capacity. In this work, we investigated mineral dissolution and precipitation in dolomite samples saturated with a CO2-saturated brine at 93 °C and 34.5 MPa, aged without flow. Two rock types samples, i.e. intergranular- and vuggy-dominant, were selected to investigate changes in pore size, porosity and permeability under reactive conditions. Mineral dissolution and precipitation were characterized using scanning electron microscopy. Changes in pore size were quantified via time-domain nuclear magnetic resonance (TD-NMR) transverse relaxation time (T2) and diffusion coefficient (D) distributions. We show that mineral dissolution likely occurs in highly permeable pathways. These observations are confirmed through analysis of (T2) and diffusion coefficient (D) distributions. In contrast to results during CO2-enriched brine continuous injection, mineral precipitation was observed in micropores. The leftward shift of the T2 peaks, corresponding to micropores, also evidenced mineral precipitation in low-permeability zones. However, microscale alterations resulted only in a subtle increase in porosity and permeability. Results in this study shed light on effects of geochemical reactions on alteration of rock properties in diffusion-dominated regions during CO2 storage.

Prediction of Fluid Behavior Using Generalized Hydraulic Calculation Method in Hydraulic Fractures

Hydraulic fracturing has been used as one of the stimulation techniques to economically increase oil and gas production by creating small cracks in subsurface geologic formations to allow oil or gas to move toward a producing well. Hydraulics plays a vital role in many oil field operations including drilling, completion, fracturing and production. In the case of fracturing, however, the role of hydraulics becomes important since optimized hydraulics can minimize the cost and conversely, any miscalculations may cause problems such as the fluid loss or may potentially even lead to loss of the well. The current methods of the hydraulic calculation for non-Newtonian fluids necessitate determination of the robust model. This paper presented a new method for calculating pressure losses in the hydraulic fractures. The objective of this study was to develop the generalized model for hydraulic calculation for non-Newtonian fluid and run the case studies for the model validation. In the present work, detailed algorithm for the hydraulic calculation has been developed and then programmed in C++. The only input to the program is the raw rheological data, shear stress versus shear rate and the geometrical characteristics of the slit. Model validation with the new method has established a very small percentage difference between the values predicted by the model and experimental data. The results demonstrate that the new method is accurately predicting the pressure drop in both laminar and turbulent flow regimes. It is shown that the fluid behavior is more accurately represented using the new method than that with the standard fluid models available in the petroleum industry. Further validation and development to be carried out using experimental data for variety of fluid types.

Modeling interaction between CO2, brine and chalk reservoir rock including temperature effect on petrophysical properties

Carbon dioxide (CO2) capture and sequestration through CO2 enhanced oil recovery (EOR) in oil reservoirs is one of the approaches considered to reduce CO2 emission into the atmosphere. The injection of CO2 into a subsurface geological formation may lead to chemical reactions that may affect the formation pore structure and characteristics. In this study, the effect of CO2–brine–rock interaction on the rock petrophysical properties and mineral volume fraction was numerically investigated during CO2 injection into a chalk reservoir rock. A 3D numerical modeling and simulation were conducted using COMSOL® Multiphysics commercial software of computational fluid dynamics (CFD) to simulate CO2–brine core flooding process in a chalk core. The model was validated against a core–scale experimental data from literature. Simulation differential pressure data matched the literature experimental data closely and consistently indicating good agreement between them. Temperature effect on the performance of CO2–brine–chalk sequestration was also evaluated in the present study. Results indicated that porosity was only slightly affected by temperature increase during CO2 injection in contrast to permeability that was substantially affected by temperature. Moreover, chemical reactions enhanced as temperature increased leading to significant increase in permeability. Thus, carbonated brine sequestration excelled at elevated temperature due to increased acidity which governs the sequestration process. The developed model maybe considered as a reliable tool to optimize various operating parameters of CO2–brine sequestration.

Probing the Core–Shell Organization of Nanoconfined Methane in Cylindrical Silica Pores Using In Situ Small-Angle Neutron Scattering and Molecular Dynamics Simulations

Determining the structure of nanoconfined compressed fluids is essential for predicting the fate of these fluids in subsurface geologic formations with nanoporous features and to engineer novel nan...

Total cost of carbon capture and storage implemented at a regional scale: northeastern and midwestern United States.

We model the costs of carbon capture and storage (CCS) in subsurface geological formations for emissions from 138 northeastern and midwestern electricity-generating power plants. The analysis suggests coal-sourced CO2 emissions can be stored in this region at a cost of $52-$60 ton-1, whereas the cost to store emission from natural-gas-fired plants ranges from approximately $80 to $90. Storing emissions offshore increases the lowest total costs of CCS to over $60 per ton of CO2 for coal. Because there apparently is sufficient onshore storage in the northeastern and midwestern United States, offshore storage is not necessary or economical unless there are additional costs or suitability issues associated with the onshore reservoirs. For example, if formation pressures are prohibitive in a large-scale deployment of onshore CCS, or if there is opposition to onshore storage, offshore storage space could probably store emissions at an additional cost of less than $10 ton-1. Finally, it is likely that more than 8 Gt of total CO2 emissions from this region can be stored for less $60 ton-1, slightly more than the $50 ton-1 Section 45Q tax credits incentivizing CCS.

CO2 mobility reduction using foam stabilized by CO2- and water-soluble surfactants

Foam can reduce CO2 mobility to improve the sweep efficiency during injection into subsurface geological formations for CO2 storage and enhanced oil recovery. However, CO2 foams are thermodynamically unstable, so they must be stabilized. Surfactants are often used to generate and stabilize foams in porous media and can be soluble in the aqueous phase, or in the CO2 phase. Aqueous- and CO2-soluble surfactants must be characterized for their ability to reduce CO2 mobility and stabilize foam at reservoir conditions. In addition, numerical models are necessary to predict and evaluate the effect of foam for field-scale applications and require empirical data obtained from core-scale flooding experiments. This study presents a series of steady-state foam co-injections with dense phase CO2 and either aqueous- or CO2-soluble surfactant solutions at varying CO2 flow velocities and CO2 fractions. One anionic water-soluble surfactant, which is considered a benchmark foam stabilizer, and five partially CO2-soluble non-ionic surfactants were investigated. Gamma ray attenuation was used to accurately monitor in-situ saturations during steady-state co-injections. The primary objective was to determine the steady-state foam characteristics of the different surfactants by evaluating the mobility reduction factor (MRF) and the limiting water saturation where foam abruptly collapses (Sw∗). All of the tested surfactants generated foam and reduced CO2 mobility by more than three orders of magnitude. The anionic surfactant increased foam stability at lower water saturations, compared to the non-ionic surfactants, which resulted in lower residual water saturations and increased pore volume available for CO2 storage. Core flooding results provided input into a local-equilibrium foam model. The fitted foam model reproduced the experimental results for the anionic surfactant and for three of the five non-ionic surfactants. The two latter non-ionic surfactants violated model assumptions because non-monotonic water saturation changes were observed, an effect not accurately captured by local-equilibrium foam models. However, the modelling work elucidated subtle experimental trends and demonstrated the applicability of the dataset as input into implicit-texture local-equilibrium foam models.

An engineering site investigation using non-invasive geophysical approach

Subsurface geological formation is essential to validate design assumptions for the construction of deep engineering structures, especially in the weathered terrains. The geological formation can be delineated using resistivity values through an electrical survey. However, the subsurface resistivity alone is ambiguous to interpret the subsurface geological units. As part of an ongoing investigation to select the key methods towards this end, an integrated geophysical survey through a combination of electrical resistivity tomography (ERT), induced polarization (IP), magnetic method and joint profile method (JPM) was carried out in a weathered terrain of South Huizhou, China. Resistivity, IP, and magnetic data were obtained using a variety of survey parameters. Subsurface resistivity was calibrated with upfront boreholes lithology to constrain geological formation into four discrete layers such as topsoil cover with resistivity 2–3257 Ωm, highly weathered layer having resistivity 2–636 Ωm, partly weathered layer with resistivity range 448–1204 Ωm, and unweathered bedrock having resistivity 791–116,497 Ωm. The integration of ERT with IP, magnetic and JPM delineated four faults namely F1, F2, F3 and F4, and several localized fractures. The weathered layer, fractures and faults were marked as the weakest zones for engineering projects, whereas the unweathered fresh bedrocks were identified as the most appropriate locations for the construction of deep structures in the study area. The weakest zones unsuitable for engineering structures were delineated as the most appropriate places of groundwater occurrence in the studied area revealed by low resistivity ranging from 2 to 1204 Ωm and overlapped by low chargeability less than 14.8 ms. This non-invasive geophysical approach suggests the most suitable locations highly significant not only for the future construction of engineering structures but also the exploitation of groundwater resources in the investigated area.

Effects of wettability of conductive particles on the multifrequency conductivity and permittivity of fluid-filled porous material

Existing mechanistic models for electromagnetic characterization of porous materials filled with two fluids (e.g. oil- and water-filled subsurface geological formation) assume the conductive solid components (e.g. graphite and pyrite particles) and the non-conductive solid components (e.g. clay and sand grains) are completely wetted by only one fluid. However, the wettability of particles constituting the porous material have strong influence on the electromagnetic properties of the fluid-filled porous materials. We developed a new mechanistic model to quantify the effects of wettability (i.e. contact angle) of conductive particles on the multi-frequency complex conductivity/permittivity of the fluid-filled porous material containing both non-conductive and conductive particles. The new mechanistic model accounts for the interfacial polarization phenomena at the interface of the conductive particles having any wettability (ranging from strongly water wet to strongly oil wet) and the pore-filling two-phase fluid for various fluid saturations as a function of the operating frequency of the externally applied electromagnetic field. The newly developed model shows that the frequency dispersions of complex conductivity/permittivity of porous material filled with oil and water reduce with the decrease in water-wetness of the conductive particle and with the decrease in water saturation. Notably, frequency-dependent complex conductivity/permittivity of porous material is more sensitive to change in water wetness (i.e. contact angle) of the conductive particles as compared to change in water saturation. This work has significance and relevance for electromagnetic-based characterization of fluid-filled porous materials; for example, estimation of hydrocarbon pore volume in oil/gas reservoirs and estimation of water saturation in aquifers.

Delineation of contaminated aquifers using integrated geophysical methods in Northeast Punjab, Pakistan.

A decline in surface water sources in Pakistan is continuously causing the over-extraction of groundwater resources which is in turn costing the saltwater intrusion in many areas of the country. The saltwater intrusion is a major problem in sustainable groundwater development. The application of electrical resistivity methods is one of the best known geophysical approaches in groundwater study. Considering the accuracy in extraction of freshwater resources, the use of resistivity methods is highly successful to delineate the fresh-saline aquifer boundary. An integrated geophysical study of VES and ERI methods was carried out through the analysis and interpretation of resistivity data using Schlumberger array. The main purpose of this investigation was to delineate the fresh/saline aquifer zones for exploitation and management of fresh water resources in the Upper Bari Doab, northeast Punjab, Pakistan. The results suggest that sudden drop in resistivity values caused by the solute salts indicates the saline aquifer, whereas high resistivity values above a specific range reveal the fresh water. However, the overlapping of fresh/saline aquifers caused by the formation resistivity was delineated through confident solutions of the D-Z parameters computed from the VES data. A four-layered unified model of the subsurface geologic formation was constrained by the calibration between formation resistivity and borehole lithologs. i.e., sand and gravel-sand containing fresh water, clay-sand with brackish water, and clay having saline water. The aquifer yield contained within the fresh/saline aquifers was measured by the hydraulic parameters. The fresh-saline interface demarcated by the resistivity methods was confirmed by the geochemical method and the local hydrogeological data. The proposed geophysical approach can delineate the fresh-saline boundary with 90% confidence in any homogeneous or heterogeneous aquifer system.

The Political Economy of Carbon Capture and Storage Technology Adoption

Carbon sequestration through capture and storage in subsurface porous geologic formations is one potential method for mitigating the problem of climate change due to emission of anthropogenic CO2. In fact, in a world highly dependent on energy derived from hydrocarbons and coal, carbon capture and storage may represent the most promising approach to maintaining industrial development in the present period, while implementing other solutions that will deliver sustainable reductions in CO2 emissions in the long run. Some countries have initiated pilot and large-scale projects to develop and improve carbon capture and storage technology, while others are slow to follow. What explains this variation? We develop a theory of the political economy of technology adoption to explore conditions under which countries are more likely to implement carbon capture and storage projects. We find that the likelihood of such projects depends on governments’ policy positions and industries’ research and development capacity. Data analysis of carbon capture and storage projects provides evidence in support of our theoretical expectations.

Generation of synthetic dielectric dispersion logs in organic-rich shale formations using neural-network models

Dielectric dispersion (DD) logs acquired in subsurface geologic formations generally are composed of conductivity ([Formula: see text]) and relative permittivity ([Formula: see text]) measurements at four discrete frequencies in the range of 10 MHz to 1 GHz. Acquisition of DD logs in subsurface formations is operationally challenging, and it requires a hard-to-deploy infrastructure. We developed three supervised neural-network-based predictive methods to process conventional, easy-to-acquire subsurface logs for generating the eight DD logs acquired at four frequencies. These predictive methods will improve reservoir characterization in the absence of a DD logging tool. The predictive methods are tested in three wells intersecting organic-rich shale formations of the Permian Basin and the Bakken Shale. The first method predicts the eight dispersion logs simultaneously using a single artificial neural network (ANN) model, whereas the second method simultaneously predicts the four conductivity dispersion logs using one ANN model, followed by simultaneous prediction of four permittivity dispersion logs using a second ANN model. The third method sequentially predicts the eight dispersion logs, one at a time using eight sequential ANN models, based on a predetermined ranking of the prediction accuracy for each of the eight DD logs when simultaneously generated. Considering that the conventional and DD logs are recorded more than 10,000 ft deep in the subsurface using logging tools that are run at different times in rugose boreholes for sensing the near-wellbore geologic formation, the data used in this predictive work is prone to noise and biases that tend to adversely affect the prediction performances of the proposed methods. In terms of normalized root-mean square error (Nrms error), the prediction performances of the second predictive method are 8.5% worse and 6.2% better for the conductivity and permittivity dispersion logs, respectively, as compared with those of the first predictive method. The third method has best prediction performance for permittivity dispersion logs, which is 0.089 in terms of the Nrms error.

Investigation of fractured rock aquifer in South China using electrical resistivity tomography and self-potential methods

Assessment of fractured rock aquifers in many parts of the world is complicated given their strong heterogeneity. Delineation of the subsurface geological formation in the weathered terrain is essential for groundwater exploration. To achieve this goal, 2D electrical resistivity tomography (ERT) and self-potential (SP) in combination with joint profile method (JPM) and boreholes have been carried out to delineate the subsurface geological units, detect the fracture/fault zones in hard rock, monitor the groundwater flow, and estimate the groundwater reserves contained within the weathered terrain at a complex heterogeneous site of Huangbu, South Guangdong of China. The integration of resistivity images with the borehole lithology along three profiles delineates three subsurface distinct layers namely topsoil cover, weathered and unweathered layers. The incorporation of ERT and SP with JPM reveal five fractures/faults, i.e., F1, F2, F3, F4 and F5. 2D ERT models interpret the less resistive anomalies as the fractures/faults zones, and high resistive anomalies as the fresh bedrock. The inversion program based on the smoothness-constraint is used on the resistivity field data to get more realistic three layered model. SP measurements are obtained along the same electrical profiles which provide the negative anomalies clearly indicating the groundwater preferential flow pathways along the fracture/fault zones. Hydraulic parameters namely hydraulic conductivity and transmissivity were determined to estimate the groundwater resources contained within the fractures/faults. The integrated results suggest that the fractures/faults zones are most appropriate places of drilling for groundwater exploration in the investigated area. Geophysical methods coupled with the upfront borehole data provides better understanding about the conceptual model of the subsurface geological formations. The current investigation demonstrates the importance of the integrated geophysical methods as a complementary approach for groundwater assessment in the hard rock weathered areas.

Fault leakage detection and characterization using pressure transient analysis

Injection of fluids in deep subsurface geological formations has created a series of challenges in recent decades. Possibility of upward fluid leakage along nearby wells and faults is one of the main issues related to these operations. It is important to ensure that such conduits, if present, can be detected, characterized and treated. Looking for pressure abnormalities in intervals above the injection zones, is one the methods used to monitor for these conduits. We propose an analytical solution to detect and characterize the vertical leakage from a fault of finite length using pressure data collected from monitoring zones. The proposed closed form analytical model would allow to not only distinguish the pressure signal of leakage from a fault of finite length from other possible leakage conduits but also to estimate the leakage rate, length of leaky section of the fault and relative position of the fault with respect to the location of monitoring well.

Geophysical Investigation to Prevent Landslide in a Lignite Mine, India

Abstract Land slide in an opencast mine is a common phenomenon. It not only obstructs the mining operation but also incurs heavy economic losses as a cost of the removal of debris to facilitate mining work. Often, it also leads to the loss of valuable human lives. This problem is attributed mainly due to groundwater movement within the mines. Most suitable solution to this problem lies in the delineation of potential groundwater zones in order to pumping out groundwater to keep the sub-surface geological formations in almost dry land slide zone. Tadkeshwar lignite mine, located in Surat district of Gujarat state, India is one such mine which is facing land slide problem because of movement of groundwater in a segment of the mine. This paper describes the results of electrical resistivity tomography (ERT) carried out in the mine lease area to locate groundwater potential zones. These results are then used for the selection of suitable sites to drill bore wells for dewatering in and around land slide zone in order to prevent landslide.