Borehole Design Research Articles

Rock Fracturing Characteristics and Roadway Expansion Application of Static Crushing Agent under Multi-Row Drilling Condition

Static crushing agent (SCA) offers advantages such as good safety, no harmful gases, and minimal vibration, making SCA ideal for rock crushing in mines or underground engineering. To scientifically implement the section expansion of mine roadway, the rock mechanical parameters, SCA expansion properties, and cracking behavior of surrounding rock were investigated using laboratory tests, numerical simulations, and field experiments. Results indicate that the smaller hole spacing of SCA improves the fracturing effect on rock mass, reduces the required fracture initiation stress and penetration stress, and the presence of a free surface aids in fracture development in the rock mass. Optimal borehole design parameters and spacing distributions of the SCA were determined, and corresponding construction techniques of roadway expansion were proposed. Field tests demonstrate that static crushing technology, under multi-row drilling conditions, is highly effective for rock roadway expansion projects. These findings provide valuable guidance for non-explosive expansion and other roof breaking treatment projects.

Design and field evaluation of hydraulic fracturing boreholes for terminal mining faces

The terminal mining is an essential part of fully mechanized mining, and the reasonable length of the flap roof during the terminal mining is an important basis for the smooth operation of the terminal mining. With the research background of the 213 working face of the Longde Coal Mine, the contribution of this study is the influence law of hydraulic fracturing on the terminal mining mechanical behavior of the working face. Four different numerical calculation models of terminal mining hydraulic fracturing are established, and the optimal hydraulic fracturing site plan is determined according to the length of the terminal mining flap top and the working resistance of hydraulic support. The effect of hydraulic fracturing construction and the law of mechanical behavior in the terminal mining stage in the field test are analyzed. The results show that through hydraulic fracturing technology, the control of the length of the flap roof of the working face during the terminal mining period has been realized.

Geologic and thermal conductivity analysis based on geophysical test and combined modeling

Strata thermal conductivity (λe) influences efficiency of medium-depth ground heat exchangers. However, a systematic approach to the acquisition of λe is still lacking. Hence, stratigraphic heat conduction was analyzed using geophysical test in Shenyang, combined with composite modeling. Cenozoic strata (0–730m) exhibited an average λe of 1.32 W·m−1·K−1 due to higher porosity and mud content; Archaean (730–2500m) strata displayed a higher λe of 2.80 W·m−1·K−1, due to dense quartz sandstone with lower porosity and mud content. The CBHE in Shenyang can achieve excellent heat extraction relying on good thermal conduction. Spearman correlation revealed strong negative correlations between λe and acoustic time difference, permeability, and porosity, while positive correlations were observed with depth, resistivity, wave speed, and rock skeleton. Higher rock skeleton thermal conductivity intensified the decrement effect of mud content on λe, while higher mud content diminished the enhancement effect of rock skeleton thermal conductivity. As porosity increased, the decline in λe slowed, particularly pronounced at higher saturation levels. λe exhibited a gradual decrease with temperature, with a more notable change rate observed at lower porosity levels. Principles for enhancing thermal conduction were elucidated through a three-phase analysis. These findings provide foundation for the study and design of medium-depth boreholes.

Investigation on rock damage associated with ice-filling borehole blasting

Rock excavation and ore extraction in cold regions (e.g., alpine and high-altitude regions) are often conducted using the drill and blasting method. Ice may be presented in boreholes drilled in cold regions due to the potential freezing of water (e.g., water in rock fractures and pores) flowing into boreholes from the surrounding ground. The performance of rock blasting is inevitably affected by the presence of ice and no study has examined the effect of ice in boreholes on rock blasting performance. The present study investigates rock damage induced by the ice-filling borehole blasting. The damage modes and mechanisms of rock mass under the ice-filling borehole blasting are analyzed. The differences of rock damage induced by the sole ice-filling borehole blasting and the ice-water and ice-air mixed filling borehole blasting are identified. The effects of ice volumes in boreholes on blast-induced rock damage are examined. It is found that blast-induced rock damage is greatly reduced as water in boreholes turns into ice. In addition, the blasting with the ice volume greater than 6.7 % filled at the bottom of borehole can induce less rock damage compared to full-coupled charge blasting. To improve the performance of rock blasting with ice-filling boreholes, the effects of two methods, i.e., changing ignition locations and using different types of explosives on rock damage induced by the ice-filling borehole blasting are investigated. An empirical formula of rock damage volume incorporating ice volume, explosive properties, and rock properties is finally proposed as the reference for the design of ice-filling borehole blasting in cold regions.

Study on the design of gas extraction drilling angle of crossing coal layer drilling in the floor rock roadway considering the boreholes superposition effect

To solve the problem of the borehole design for extracting gas of crossing coal layer drilling in the floor rock roadway and to improve the efficiency of drilling arrangement as much as possible under the premise of eliminating the gap zone of extraction, the formula for calculating the optimal arrangement angle of crossing coal layer drilling in the floor rock roadway was put forward, and the difference of the superposition effect of the holes on the radius of the effective extraction area under the different arrangement modes and spacings was analyzed through numerical simulation. The experimental results show that the optimal angle, volume, and other calculation formulas for drilling arrangement are consistent with the CAD calculation values, verifying the correctness of these calculation formulas. The study discusses the coefficients of variation of effective extraction radius (R) for three types of arrangement, different drill spacing, and the time to reach the two coefficients of variation, 1.05 and 1.03, as a criterion for whether or not to consider the effect of borehole superposition. The results of the tests can provide borehole designers with calculation formulas and provide theoretical references for the R differences that need to be considered in different scenarios.

Impact of closed pores on gas transport and its implication for optimizing drainage borehole design

Mining disturbances can rupture the closed pores, releasing the gas and potentially triggering gas accidents. The pre-drainage of gas via boreholes is the primary measure for preventing coal and gas outbursts. Nevertheless, the influence of closed pores on gas migration remains unclear, leading to suboptimal borehole spacing and radius. Therefore, a gas–solid coupled model incorporating closed pores was developed to investigate the influence of closed pores on gas migration during gas drainage (GD). Subsequently, response surface methodology was employed to investigate the input parameters and their interactions on residual gas content (RGC) and pre-drainage time (PDT). Finally, an optimization methodology for borehole spacing/radius was presented. The results show that both RGC and PDT exhibit a positive correlation with the ratio of closed porosity to total porosity (λ) and the ratio of closed pore diffusion coefficient to that of the open pore (Do/Dc). Initially, the total gas production is primarily extracted from fractures and open pores, followed by closed pores in the later stages. Single-factor analysis demonstrates that λ, permeability, and Do/Dc have a more significant impact on RGC and PDT compared to borehole spacing and borehole radius. Borehole spacing interacts more strongly with λ, permeability and Do/Dc than borehole radius. An optimization method for borehole spacing and borehole radius, constrained by PDT, RGC, and the number of boreholes, is proposed using response surface optimization maps. This method provides guidance for borehole construction to optimize GD efficiency and minimize RGC.

Field test and geologic-thermal-economic analysis of medium-depth borehole heat exchanger

Medium-depth ground source heat pumps with borehole heat exchanger are pivotal in energy-saving and decarbonization. The heat transfer performance of borehole is important for design, with stratum thermal conductivity significantly influencing heat exchange, and economic considerations also act as a vital constraint on technological advancements. However, there is limited on-site testing in severe cold regions, especially in the Songliao Basin. Stratum thermal conductivity usually relies on empirical values, and its diverse impacts are not integrated into borehole heat transfer model. Additionally, previous studies optimized borehole design only from the thermal perspective. To address these gaps, we conducted an inaugural test in Shenyang. Geologic-based heat transfer model explores the geological influences, heat transfer performance, and heat extraction cost. At a depth of 2500 m, the formation's thermal conductivity is 2.45 W⋅m⁻1 K⁻1. The heat extraction, at a flow rate of 26.0 m3 h−1, achieves 352.3 kW with an inlet-outlet temperature differential of 11.7 °C. The effects of saturation, porosity, and lithology on stratum thermal conductivity were also explored. Furthermore, considering heat extraction cost, optimal depths for borehole utilizing PE-RT II and stainless-steel vacuum pipe are 2790 m (10.3 CNY·W−1) and 3140 m (10.2 CNY·W−1), with critical depths, 2910 m, governing the selection of economic inner pipe. This research establishes medium-depth ground source heat pumps as the preferred choice for low-carbon transformation in building heating, domestic hot water, and industrial and agricultural heat applications.

Research on the zoning of blasting for ultra-deep hole cylindrical charges based on thick-walled cylinder theory

To address the challenges faced by coal miners when encountering collapsed pillars in local hard rock formations, we researched ultra-deep hole loosening blasting technology. To overcome issues related to the inapplicability of existing blasting zoning theories and the lack of a solid foundation for borehole design in ultra-deep hole loosening blasting sites, we introduced a blasting zoning model and theoretical calculation formula based on thick-walled cylinder theory. Building on this foundation, we proposed coupled and uncoupled charge calculation methods that take into account strain rate variations and confining pressure effects. Furthermore, numerical simulations using the ANSYS/LS-DYNA software demonstrated that the results obtained from this theory were consistent with the simulation results. Ultimately, based on the blast zone results derived from both theory and simulation, we determined the blasting range of individual blast holes to design effective construction plans for ultra-deep hole blasting sites, achieving satisfactory results.

Modelling geomechanical stability of a large deep borehole in shale for radioactive waste disposal

Large diameter boreholes drilled to a depth of 1000–2000 m are currently investigated in Australia as a potential solution for waste emplacement and long-term containment for long-lived intermediate-level radioactive waste (ILW). Different potentially suitable types of host rocks are considered, including granite, shale and salt. This study is aimed at assessing the risk of borehole instability for a large diameter deep borehole in shale. The investigation is conducted with numerical simulations using the CSIRO-developed modelling tools FRACOD and FRCAOD3D, and the commercial code Irazu. Previous laboratory experiments on boreholes in deep shale reported in literatures have been used as validation tests of the numerical models. Under hydrostatic stresses, the FRACOD model showed extensive shear-dominated “log-spiral” fractures around a borehole in shale which is similar to the laboratory testings reported in literatures. Subsequently, 2D and 3D numerical models representing a 0.7-m diameter vertical borehole drilled to the depths of 1000 m and 2000 m have been used. “Strong” and “weak” shales are simulated. The strong and weak shales represent the higher and lower ends of the shale strength reported in literature, respectively. Results showed that a “strong” shale exhibited only small borehole breakouts at the depth of 2000 m. The “weak” shale showed large breakouts (>1.5 m) at depths of 1000 m and 2000 m caused by extensive shear fracturing. In the scenario where a pre-existing 3D fracture crosscuts the borehole, the existing fracture may propagate deeper into the rock formation depending on its orientation and on the in situ stress magnitudes. Predictions based on analytical solutions indicate a 0.02-m and 0.04-m thick casing could prevent severe failure of rock mass at 1000 and 2000 m depths, respectively. Insights from model-based investigations of borehole breakouts are critical during the site selection of rocks with suitable geomechanical properties for waste disposal and for optimising the design of large-diameter boreholes for drilling, waste emplacement and long-term safety.

A 3D Numerical Model for Improving Methane Drainage Efficiency in Underground Coal Mines Using the Cross‐Measure Borehole Method

The release of methane into the working area of coal mines can affect safety and production. Therefore, methane drainage reduces the risk of explosion and can be used as a fuel and energy source. One methane drainage method is cross‐measure borehole drilling, which involves drilling boreholes from tailgate roadways to the roof or floor layers of a mined seam. In this method, determining the appropriate distance between methane drainage stations has a significant impact on increasing the efficiency of operation and reducing drilling costs and the time required for drainage operations from each station. In this paper, a new 3D numerical model is developed for methane drainage from an underground coal mine to determine the suitable distance between methane drainage stations in the cross‐measure borehole method using COMSOL Multiphysics software. For this purpose, by considering the porous media flow module and the laws related to the movement of gas in the goaf, different numerical models for distances of 10, 15, 20, 25, and 30 m were simulated. The simulation results showed that by reducing the distance between methane drainage stations, the speed of gas flow in the borehole and the amount of gas removed from the boreholes in a similar period of time increase to an acceptable level. In addition, the implementation of this model in a case study showed that a distance of 10 m between drainage stations increases the efficiency of boreholes to approximately 20%. Numerical simulation in this study can provide basic support for the design of drainage boreholes and reduce the risk of gas in underground coal mines.

Enhancing Borehole Hydraulic Performance: Integrating Technological Upgrades into Borehole Design and Construction Case Studies of Unconsolidated Aquifers in Israel

In recent years, significant modifications and improvements have been instituted in the technical configuration of substituted boreholes compared with old boreholes. Augmenting the production capabilities of individual boreholes and borehole fields has notable engineering and economic implications. Regrettably, altering the composition of the aquifer lithology and its inherent hydraulic properties remains beyond our control. Consequently, the augmentation of extraction capabilities from individual boreholes hinges upon the implementation of technical enhancements in drilling methodologies, borehole design, and ultimate borehole structure. This phenomenon is elucidated through illustrative instances drawn from two distinct aquifer basins. The substituted boreholes were drilled within the same yard, to equivalent depths and into lithological formations similar to those encountered in the old boreholes. The strides made in borehole structural technology bear remarkable significance in influencing the outcomes of pumping tests, with a specific emphasis on the estimation of aquifer loss (B) and well loss (C) coefficients. These advancements substantially contribute to heightened well efficiency, elevated specific yield, and diminished dynamic drawdown. Our extensive professional expertise prompted us undertake a qualitative ranking of the constituent technical elements based on their relative significance and ensuing impact on the improvement of hydraulic parameters and pumping efficiency. The prioritization of significance manifests as follows: screen length, gravel pack composition (Glass beads or sorted quartz gravel), screen diameter, percentage of screen open area, and screen material composition. This article assumes a distinctive and pioneering character as it constitutes a primary endeavor to comprehensively investigate in parallel both the technical conception and construction of boreholes and their subsequent hydrological performance. The overarching message gleaned from this study underscores that the infusion of innovation into borehole design and construction can serve as the pivotal determinant separating a borehole characterized by modest hydraulic performance from one characterized by exceptional hydraulic performance.

Deep borehole disposal as a potential solution for high-level waste (HLW) and spent nuclear fuel (SNF) in Norway – current status and a first generic safety assessment

Abstract. Deep borehole disposal (DBD) is currently being investigated as a potential solution for the disposal of the existing spent nuclear fuel (SNF) in Norway. Over the past years, BGE TECHNOLOGY GmbH (BGE TEC), together with the Finnish companies A-Insinöörit Oy (AINS Group), Mitta Oy and VTT Technical Research, has supported the Norwegian agency Norwegian Nuclear Decommissioning (NND) in the development of a deep borehole concept, including work on different technical details. At the end of 2022, the consortium was able to win a follow-up contract to further deepen and advance the work. For this second framework agreement, additional companies were added to further strengthen the expertise. The Geological Survey of Finland (GTK), Posiva Solutions Oy (PSOY) and Rambøll are now part of the new consortium group, which works under the acronym GeoReN (Geological Repositories for Norway). This paper provides an overview of the work carried out in the past for the deep borehole concept in Norway. In detail, this includes a basic description of the concept developed for the waste that originates from different institutions. Initial calculations indicate that a 69 BSK-R canister may be sufficient for the waste inventory to be considered. As the current conceptual borehole design provides the basis for most of the other work carried out, it will be presented and discussed within the paper. Furthermore, as part of the concept development, a first generic post-closure safety assessment was also performed for the DBD concept. The main results of the long-term calculations are discussed and presented in this paper as well. The main objectives of the generic safety assessment were the identification of critical parameters and assumptions for the model of the DBD repository and the performance of a first assessment of possible consequences of the potential post-closure release of radionuclides from the borehole. To be able to give a prediction at the present stage of the project, the assessment used conservative assumptions, models and data. The preliminary results for the normal evolution of the deep borehole repository indicate that highly mobile radionuclides, such as I-129, Cl-36, Ni-59 and Se-79, are the major dose contributors and that the expected potential radiological impact on future generations associated with these releases is extremely small. In addition, alternative scenarios have been assessed, which assume a hydraulic gradient leading to advective flow either upward through the borehole and surrounding excavation damaged zone (EDZ) or between certain parts of the borehole and the surface via a transmissive fracture system. Despite the pessimistic assumptions chosen for these scenarios, the maximum dose rates are significantly lower than the expected regulatory limit. However, it needs to be pointed that the present generic safety assessment is still on a conceptual level. With more detailed planning and updated information regarding the inventory, the geological environment, and the integrity and performance of the engineered barriers, repeated safety assessments will need to be performed to derive more substantiated results.

Radionuclide Transport Simulations Supporting Proposed Borehole Waste Disposal in Israel

A scientific collaboration between the U.S. and Israel is underway to assess the suitability of a potential site for subsurface radioactive waste disposal in the Negev Desert, Israel. The Negev Desert has several favorable attributes for geologic disposal, including an arid climate, a deep vadose zone, interlayered low-permeability lithologies, and carbonate rocks with high uranium-sorption potential. These features may provide a robust natural barrier to radionuclide migration. Geologic and laboratory characterization data from the Negev Desert are incorporated into multiphase flow and transport models, solved using PFLOTRAN, to aid in site characterization and risk analysis that will support decision-making for waste disposal in an intermediate-depth borehole design. The lithology with the greatest uranium sorption potential at the site is phosphorite. We use modeling to evaluate the ability of this layer to impact uranium transport around a proposed disposal borehole. The current objective of the simulations is focused on characterizing hypothetical leakage from waste canisters and subsequent uranium migration under three infiltration scenarios. Here, we describe a hydrogeologic model based on data from a local exploratory borehole and present results for uranium flow and transport simulations under varying infiltration scenarios. We find that under the current climate conditions, it is likely that uranium will remain in the near-field of the borehole for thousands of years. However, under a hypothesized extreme climate scenario representing an increase in infiltration by a factor of 300x above present-day values, uranium may break through the phosphorite layer and exit the base of the model domain (~200 m above the water table) within 1000 years. Simulation results have direct implications for the planning of nuclear waste disposal in the Negev Desert, and specifically in intermediate-depth boreholes.

Effects of Coal Permeability Anisotropy on Gas Extraction Performance

To investigate gas flow characteristics in coal seams with strong anisotropy, a coupled anisotropic dual-porosity model was established. Effects of permeability anisotropy on variations in gas pressure, gas extraction volume and effective extraction areas were analyzed. Furthermore, mechanisms of crustal stress, initial gas pressure, ultimate adsorption strain and Langmuir volume constant on permeability anisotropy and extraction amount were studied. Results show that permeability anisotropy could result in an elliptical pressure drop zone around production boreholes. Changes in effective gas extraction areas are divided into three stages: slow growth in an elliptical shape, rapid growth with a superposition effect and steady growth in a funnel shape. Permeability isotropy enables faster reaching of stage III than the anisotropy case. As the vertical stress increases, gas pressure distribution around boreholes gradually changes from an ellipse with horizontal direction as long axis to a circle. Larger initial gas pressure could bring consistently higher gas production in the initial and middle extraction stages, and a faster decrease in the late phase. When gas pressure is 2.5 MPa, the peak daily gas production in initial extraction stage is about three times higher than that in the late phase. Ultimate adsorption strain is positively correlated with permeability change. This relationship becomes more significant with a longer extraction time. In contrast, permeability variation is inversely proportional to the Langmuir volume constant in the initial extraction stage. However, these factors are directly proportional in the late stage. The order of significance of each factor’s effect on permeability is crustal stress > ultimate adsorption strain > initial gas pressure > Langmuir volume constant. Moreover, initial gas pressure has the most significant effect on gas extraction volume, while Langmuir volume constant has the least significant impact. Results could provide a theoretical reference for extraction borehole design and drainage parameter setting to improve extraction performance.

Numerical simulation and investigation of methane gas distribution and extraction in goaf with U-type ventilation of working face

The accumulated methane in goaf during coal mining may leak into the working face under the airflow influence, which is possibly causing disasters such as methane gas excessive at the working face and seriously threatening the mine safety. This paper first established a three-dimensional numerical model of the mining area under U-shaped ventilation, introducing the gas state equation, continuity equation, momentum equation, porosity evolution equation, and permeability evolution equation to simulate the airflow field and gas concentration field in the mining area under the natural state. The reliability of the numerical simulations is then verified by the measured air volumes at the working face. The areas in the mining area where gas is likely to accumulate are also delineated. Subsequently, the gas concentration field in goaf under the gas extraction state was theoretically simulated for different locations of large-diameter borehole. The maximum gas concentration in goaf and the gas concentration trend in the upper corner were analyzed in detail, and the critical borehole location (17.8m from the working face) was determined as the optimum location for gas extraction from the upper corner. Finally, a gas extraction test was carried out on-site to evaluate the application effect. The results show that the measured airflow rate has a small error with the simulated results. The gas concentration in the area without gas extraction is high, with the gas concentration in the upper corner being over 1.2%, which is greater than the critical value of 0.5%. The maximum reduction in gas concentration was 43.9%, effectively reducing the gas concentration in the extraction area after employing a large borehole to extract methane gas. The gas concentration in the upper corner and the distance of the borehole from the working face are expressed as a positive exponential function. The field engineering results show that the implementation of the large borehole at a distance of less than 17.8m from the working face can control the gas in the upper corner to less than 0.5%, effectively reducing the risk of gas in the upper corner. The numerical simulation work in this paper can provide some basic support for the design of an on-site borehole to extract gas from the mining void and reduce the gas hazard in coal mines.

Optimization of site investigation program for reliability assessment of undrained slope using Spearman rank correlation coefficient

Site investigation programs (e.g., boreholes) are crucial in characterizing soil properties and stratigraphic configurations. However, the traditional borehole patterns are generally of equally spaced distribution for the slope design, and the locations and total number of boreholes are considerably determined depending on engineers’ experience, which may lead to cost-inefficient geotechnical design, especially considering the soil spatial variability. To address this dilemma, this paper presents a Spearman rank correlation coefficient-based scheme to optimize site investigation in slope design, where both locations and total number of boreholes are optimized. Conditional random field simulations are performed to consider the effect of the borehole data on the estimation of the soil property distribution. The superiority of the proposed method to the traditional method is illustrated by a comparison study in an undrained slope example. In this example, the accuracy of the characteristics of the slope (i.e., the factor of safety, location of slip surface, and sliding volume), robustness of the estimated characteristics of the slope, and risk reduction are examined. The comparison results show the effectiveness of the proposed method in accurately estimating the characteristics of the slope without prior knowledge about the slip surface, since the slip surface is unknown for most practical cases prior to the site investigation. The most robust estimate results and risk reduction are obtained using the proposed method. This study can also provide useful references to build an adaptive unequally spaced borehole pattern in practice.

A Data-Driven Fine-Management and Control Method of Gas-Extraction Boreholes

In order to improve the efficiency of gas extraction in coal mines, a data-driven fine-management and control method for gas extraction is proposed. Firstly, the accurate prediction of coal seam thickness and gas content was used to evaluate the gas reserves. Based on the time relationship between mining activities and gas extraction, the calculation model of borehole distance in different extraction units is established, and the differential borehole design is realized. Then, a drilling video-surveillance system and drilling trajectory measurement device are used to control the drilling process and the construction effect. Finally, the model of extraction data-correction and the identification of failed boreholes is established, then the failed boreholes are repaired. The technology method provided in the paper has realized the fine control of gas-extraction borehole design, construction, measurement, and repair, and formed a more scientific gas-extraction borehole control technology system, which provides new thought for efficient gas extraction.

Study on gas extraction efficiency using in-seam borehole method considering influence of plastic zone induced by borehole drilling

Gas hazards pose a serious threat to the safety of coalmines. Gas extraction through in-seam boreholes is an important technical approach for preventing gas hazards and achieving rational exploitation of gas as a clean resource. Improper extraction design may result in inefficient gas extraction and create the risk of gas emission overrun, or even coal and gas burst during mining process. Gas extraction efficiency is associated with the permeability of the coal seam, which is affected by the integrity and porosity of the coal seam. The change in permeability in plastic zones induced by borehole drilling or roadway excavation is usually not sufficiently considered when designing a gas extraction scheme and predicting the gas extraction efficiency. In view of this, this research investigated gas extraction efficiency using in-seam borehole method considering influence of drilling/excavation induced plastic zone. Based on a gas extraction project in the Huainan mining area of China, site measurements were performed to test the pressure distribution characteristics along the gas extraction pipe. Subsequently, the radius of the plastic zone around the borehole was deduced based on elastic–plastic theory. Furthermore, a gas flow equation under extraction conditions was proposed, and the apparent permeability of the coal seam was analyzed by considering the plastic deformation induced by roadway excavation and borehole drilling. Finally, a three-dimensional model was built, and the gas flow performance was simulated by considering the influence of the plastic zone. The calculated radius of the plastic zone was compared with the analytical results. The evolution characteristics of the gas pressure and the effective extraction radius were obtained. In addition, optimized measures for the design of extraction boreholes are proposed.

Assessment of Berezkinskoye ore field prospectivity using Micromine software

The use of modern computer aided methods, in particular the use of the Micromine software, is an important part of the integrated research for the determination of deposit prospects for various ores. The paper is devoted to the analysis of prospects and estimation of reserves for open-pit and underground mining in the Berezkinskoye ore field. For this purpose, silver reserves were determined as the principal valuable component. The deposit balance reserves were estimated separately for all types of ores in the optimal open pit envelope adopted in the final mining feasibility study (FS of permanent exploration conditions for ore extraction). To vectorize and verify the geological information entered into the database, graphical materials in the form of cross-sections and plans with the corresponding borehole database were georeferenced using the Micromine software. The final inspection was carried out to ensure that the sample depth information entered was consistent with the excavation depth. The database contains information on the location of boreholes and trenches, the design of boreholes, the spatial positioning of the boreholes/trenches axes, the data of sample assays for silver and copper. For underground mining, the delineation of ore bodies was carried out based on the cross-sections identified in the boreholes at a cut-off grade of 10.7 g/t, taking into account the orientation of geological structures. Reliability of the ore bodies delineation was verified in a Micromine three-dimensional model. For open-pit mining, the position of small ore bodies may be clarified by operational exploration with possible subsequent upgrading their reserve categories. The wireframe model of ore zones and bodies was constructed using the outlines obtained by the developed methodology. A wireframe model of faults was based on the Berezkinsky area plans and cross-sections. The construction of the fault wireframe model was performed in several steps. Application of modern geoinformation system (GIS) technologies makes it possible to qualitatively assess the prospects and estimate the reserves at the deposits. The Berezkinskoye deposit ore material composition, metallurgical properties, hydrogeological and geotechnical features were investigated.

A multiphysics field-scale investigation of gas pre-drainage in sorptive sediments

Gas pre-drainage through underground-to-inseam (UIS) horizontal boreholes is one of the common practices for the management of environmental and safety concerns in underground coal mining. In the design of UIS boreholes, local experience is invaluable; however, an experienced-based design is not necessarily optimal from both economic and technical perspective. In this study, we present an informed, data-driven design and optimization methodology that employs a multiphysics coal seam gas flow model for simulating gas pre-drainage on different scenarios of UIS borehole pattern. The implementation of the methodology is presented through a case study from an Australian underground coal mine. The methodology uses an in-house three-dimensional finite element (FEM) model (referred to as NETCoal) that has been developed based on the non-equilibrium thermodynamics and continuum mechanics. NETCoal considers the interacting processes of matrix gas diffusion, fracture gas flow and rock stress evolution in a coupled manner. This allows the permeability tensor of each grid element to be updated in response to evolving stresses on fractures induced by matrix shrinkage due to gas desorption (sorptive-mechanical effect) and gas pressure depletion (hydro-mechanical effect). The proposed methodology for the UIS borehole design requires a three-dimensional geological/structural grid model to be constructed for the area under consideration using available field data. Material and flow properties of coal (e.g., Isotherm, flow, mechanical properties etc.) are then calculated particularly using downhole geophysical logs (DGL) and physical equations/empirical correlations at borehole locations and distributed onto other grid cells using the kriging method to build a property model. NETCoal imports these geological and property models in a corner point gridding format and generates its own finite element mesh that suits the UIS borehole pattern under consideration. A Warren-Root type shape factor is used for the calibration of the numerical results of gas content with actual borehole flow data. Once calibrated, the model simulates gas drainage for different scenarios to determine an optimal borehole pattern which is the one satisfying the threshold limit value (TLV) and lead time constraints while requiring least drilling length. In addition to introducing an innovative practical methodology for the design of UIS pre-drainage boreholes, this study provides insights into the effect of coal seam and geometry parameters on gas pre-drainage through a sensitivity analysis.