Directional Boreholes Research Articles

Layout Optimization of High-Level Directional Boreholes to Prevent Downward Invasion of Carbon Dioxide from an Overlying Coal Mine Goaf

Layout Optimization of High-Level Directional Boreholes to Prevent Downward Invasion of Carbon Dioxide from an Overlying Coal Mine Goaf

Research on Gas Control Technology in Goaf Based on the Influence of Mining Speed

To comprehensively understand the influence of mining speed on gas emissions in goaf during coal seam extraction, enhance gas extraction efficiency in goaf, manage gas emissions at the working face, and ensure safety in the mining production process. This study focuses on the No. 3 mining area of Wangjialing Mine, employing numerical simulations to analyze the evolution of mining-induced fractures and the characteristics of gas distribution in the overburden at varying mining speeds. Furthermore, by integrating actual gas emission and extraction data at the production face, this study examines the quantitative relationship between mining speed and gas emissions in the goaf, identifying optimal regions for high-position borehole layouts and conducting borehole optimization design and investigation. The results of this study indicate that the initial caving step distance of the goaf roof increases with the advancement speed of the working face. Conversely, the maximum height of through fractures in the overburden decreases as the mining speed increases, while delamination fractures are minimally affected by the advancement speed. By categorizing and averaging data on goaf mining speed, the impact of initial and periodic pressure on gas emissions can be effectively mitigated, revealing a linear correlation coefficient of 0.94 between goaf gas emissions and mining speed. At varying mining speeds of the working face, the efficient extraction layer and horizontal distance parameters of gas extraction boreholes in the goaf conform to the linear equation y = ax ± b. Based on the research findings, an optimization design for mining face speed and high-level borehole parameters in the goaf was implemented. The average gas extraction rate of high-level directional boreholes reached 68% throughout the extraction period. Gas emissions at the working face were effectively controlled below 10 m3/min, with the maximum gas concentration at the upper corners and return airflow kept below 0.8%. This effectively managed gas emissions at the working face, ensuring safe production in the mine, providing a theoretical basis for identifying gas-rich areas in the mining-induced overburden, and enhancing gas extraction efficiency at the working face.

Characterization of spatiotemporal distribution of gas in the goaf of W-type ventilated working face

In order to solve the problem of gas over limit near the return air trough of W-type ventilated working face, a method combining numerical simulation and on-site measurement was used to study the spatial and temporal distribution characteristics of gas in the goaf under the W-type ventilated mode, and the reliability of the model was verified. Delineate the gas-rich area and suitable pumping area in the goaf, by analyzing the pumping of the top plate high-level directional borehole in the area, optimize the best layout of the top plate high-level directional borehole. The results show: The gas concentration in the goaf gradually increases from shallow to deep in the direction, and increases rapidly in the range of 0–75 m; in the direction of inclination, it is approximately symmetrically distributed along the axis of the return air trough, and gradually decreases toward the air inlets on both sides. The gas concentration in the middle area of the working face is higher than 0.85%; in the vertical direction, the further away from the coal seam roof, the higher the gas concentration, but the growth rate decreases, and the range of high gas concentration gradually expands. The gas concentration of the goaf reflected by the changes in the concentration of the working face has gradually increased in the early stages of mining. and then changes periodically with the cycle of roof pressure in the later stage. There is a strong correlation between the amount of gas emission the goaf and the mining speed of the working face. The regularity of the simulation result is the same as the regularity of the measured results, and the absolute value of the relative error is within 10%, that the concentration of extraction from high-level directional borehole increases with the height of the arrangement, mixed and pure volume decreases with the height of the arrangement. Comparison of the average mixed volume, concentration, pure volume and total extraction volume of each high-level directional borehole, it can be seen that the average pure volume from 3#holes is 3.9 times higher than that from 1#holes, and the total extraction volume accounts for 29% of the total extraction volume from the drill site, it is obtained that the best layout of the high-level directional boreholes of the 3203 working face is between 25 and 35 m above the top board. During the high-level drilling period, the gas concentration in the return air trough was between 0.42% and 0.75%, which effectively prevented the occurrence of gas over limit accidents.

Безопасность высокопроизводительных очистных забоев в метанообильных шахтах

The experience of degassing coal seams using underground boreholes is summarized, scientifically based schemes and parameters of degassing coal seams and the mined out space with directional boreholes in extended excavation areas of shallow coal mines are proposed. The initial gas-dynamic parameters of the excavation area were determined according to the permissible methane content of the breakage face by the gas factor, the methane content of the coal seam in the zone of its excavation by the combine. The lower limit of the methane-bearing capacity of the mined seam, at which preliminary degassing of the coal mass is necessary, is scientifically justified. The dependences of the natural methane content of coal seams on the depth of their occurrence in the conditions of Kuzbass and Vorkuta coal deposits, the effect of natural degassing of the formation by a breakage face, the determining role of degassing by drilling long directional boreholes along the mined and converged coal seams at the excavation areas of high-performance mines, the use of the provisions of the industrial regulations of the integrated technology of extraction and utilization of mine methane are experimentally established as well as forecasts of the absolute methane content of the stoping area by the sources of methane release during the coal extraction.

Study on Instability Characteristics of the Directional Borehole on the Coal-Seam Roof: A Case Study of the Tingnan Coal Mine

Directional long drilling on the roof is an effective gas control measure in the goaf, but there is little research on the stability of the surrounding rock. In this study, the geological conditions of the #4 coal seam in the Tingnan Coal Mine, Shaanxi Province, China taken as the application background, and the deformation characteristics of boreholes under four typical coal and rock conditions were first analyzed based on the Universal Distinct Element Code (UDEC) numerical simulation. Secondly, the stress, strain, and plastic deformation of the rock surrounding the borehole with different diameters were carried out using the Fast Lagrangian Analysis of Continua 3D (FLAC 3D). The effect of the casing on the stability of the borehole was also simulated. The results showed that the borehole stability of coal and mudstone was lower than that of fine-grained sandstone and coarse-grained sandstone. The larger the borehole diameter, the lower the stability. The borehole tended to be unstable, especially when the diameter was 160 mm and 200 mm. Traditional pipes can provide some protection, but for large boreholes, the protection is poor. Based on the above research, uniaxial compression tests were carried out on various internal support tubes, such as ‘line-shaped’, ‘Y-shaped’, and ‘cross-shaped’. The results showed that the cross-shaped pipe had the highest compressive strength, which was 4–5 times that of the other types of protective pipe and had a good protective effect. The research results can provide reliable technical support for the protection of directional boreholes on roofs through strata and have important implications for the popularization and application of the directional long borehole technique.

Drill string’s axial force transfer law in slide directional drilling in underground coal mine

During the slide directional drilling with long directional near-horizontal drilling technology, the weight on bit (WOB) at the bottom of the hole is exerted by pushing the drill pipe with the power head of the orifice drill. With the increase of drilling depth, the friction resistance between drill string and hole wall also goes up, resulting in problems including insufficient WOB, low drilling efficiency, and surge of feeding pressure. If the orifice feeding pressure continues to rise, the drill string will buckle or fracture. In our study, the field test method is adopted to explore the drilling string’s axial pressure transfer law. By comparatively analyzing different stratigraphic characteristics of five directional boreholes with an average radius of deflection, the deep-hole drill string transmitting pressure model with nine curvature radiuses is set up for simulating the relationships between drill string friction, hole depth, and strata characteristics under different working conditions. The results show that when the hole is relatively shallow, the relationship between the friction resistance and the hole depth is basically linear, which gradually develops into an exponential one with the increase in the hole depth. For the borehole with a curvature radius less than 200 m, the friction resistance is greatly affected. The softer the formation is, the greater the linear range of friction resistance becomes with the increase in the hole depth, the latter the hole depth with an exponential growth occurs, and the longer the limit depth is. The findings reveal the axial pressure transfer law of the drill string, which will facilitate future design of the drilling hole, optimize the control of drilling trajectory, and matter a lot to engineering practices.

Determination and Application of Reasonable Levels for Highly Directional Long Boreholes in Deep Outburst Coal Seams

In order to solve the problem that the gas in the upper corner is easy to exceed the limit in the mining process of the deep outburst coal seam. Based on the theory of “O-ring” and the distribution of stratigraphy in the field, the development law of mining fissures in the overlying rock layer during the workface retrieval was studied by combining theoretical calculation and FLAC3D numerical modeling. The research results show that the range of fissure development zone in 2913 working face is 14.2 to 33 m from the coal seam roof, and the high drilling arrangement can be in the stable rock layer of the roof. For siltstone-fine sandstone interaction stratum, measures such as opening branches to adjust the layer and lowering the casing to protect the hole wall can be taken to ensure the stability of the borehole and the smooth flow of gas extraction channels. Field application shows that the high directional long borehole has the advantages of long extension distance and wide coverage, the average value of extraction mix is 34.3 m3/min, and the average value of extraction pure is 0.4 mm3/min, which helps to prevent the gas overlimit in the upper corner during the workface recovery. The high directional long borehole has obvious economic and safety benefits over the traditional high hole and has important promotion value in coal mine gas management.

Gas Migration Patterns with Different Borehole Sizes in Underground Coal Seams: Numerical Simulations and Field Observations

Gas flow in a coal seam is a complex process due to the complicated coal structure and the sorption characteristics of coal to adsorbable gas (such as carbon dioxide and methane). It is essential to understand the gas migration patterns for different fields of engineering, such as CBM exploitation, underground coal mine gas drainage, and CO2 geo-sequestration. Many factors influence gas migration patterns. From the surface production wells, the in-seam patterns of gas content cannot be quantified, and it is difficult to predict the total gas production time. In order to understand the gas flow patterns during gas recovery and the gas content variations with respect to production time, a solid-fluid coupled gas migration model is proposed to illustrate the gas flow in a coal seam. Field data was collected and simulation parameters were obtained. Based on this model, different scenarios with different borehole sizes were simulated for both directional boreholes and normal parallel boreholes in coal seams. Specifically, the borehole sizes for the directional boreholes were 10 m, 15 m, and 20 m. The borehole sizes for the normal parallel boreholes were 2 m, 4 m, and 6 m. Under different gas drainage leading times, the total gas recovery and residual gas contents were quantified. In Longwall Panel 909 of the Wuhushan coal mine, one gas drainage borehole and five 4 m monitoring boreholes were drilled. After six months of monitoring, the residual gas content was obtained and compared with the simulation results. Of the total gas, 61.36% was drained out from the first 4 m borehole. In this field study, the effective drainage diameter of the drainage borehole was less than 8 m after six months of drainage. The gas drainage performance was tightly affected by the borehole size and the gas drainage time. It was determined that the field observations were in line with the simulation results. The findings of this study can provide field data for similar conditions.

New methodology to determine the upper limit of safe borehole pressure window: Considering compressive failure of rocks while drilling in anisotropic shale formations

Shales are frequently encountered in oil and gas drilling operations that accompanied by severe borehole stability issues now and then. It is of primary importance to determine the accurate limits of safe borehole pressure window (SBPW) while drilling in anisotropic shale formations. To our knowledge, a convention is followed by nearly all the researches in the literature that the lower limit of SBPW is determined by collapse failure while the upper limit of SBPW is determined by fracture failure of rocks. Nevertheless, this paper aims to present a unique method through which the upper limit of SBPW is proved to be also affected by collapse failure of surrounding rocks. Based on transformations of different coordinate systems and the elastic anisotropic theory, the stresses around directional boreholes are first calculated. Then, shear failure criteria of rock matrix and weak planes as well as tensile failures are incorporated to analyze the two limits of SBPW. The influences of in-situ stress, relative orientations and anisotropy ratio are also investigated. The results show that the order change of principal stresses in rocks can result in change of shear failure modes on the borehole wall and this will lead to the appearance of a new upper limit of SBPW. Under many conditions, the SBPW determined by the new method can be greatly narrower than that defined by traditional methods, whether considering the failure of rock matrix or weak planes. The collapse area reappears when the borehole pressure is high enough and the failure extension direction may also change. A more uniformed in-situ stress state makes it more necessary to apply the new method to determine the SBPW. Besides, the elastic anisotropy characteristics of rocks can make the SBPW narrower.

Prevention and Control of Water Inrushes from Subseam Karstic Ordovician Limestone During Coal Mining Above Ultra-thin Aquitards

Horizontal directional drilling technology was used to prevent and control water inrushes from the Ordovician limestone strata at the Sangshuping coal mine in the Hancheng mining area by drilling and grouting the contact zone along the top of the aquifer. Considering the hydraulic conductivity of the floor failure zone, we used the modified water inrush coefficient method to estimate the critical thickness of Ordovician limestone that had to be grouted. We carried out directional borehole exploration from both ends of the mining face and combined the results with borehole water pressure tests to determine appropriate grouting techniques and parameters; we then analysed the effectiveness of the grouting. 3-D seismic and ground transient electromagnetics (TEM) were used to detect areas of anomalous resistivity and geologic structure in the mining area, while DC and TEM geophysics were used to detect water-bearing areas ahead of the roadway. After the roadway was developed, TEM, DC resistivity sounding, and audio-magnetotellurics were used to explore water-bearing areas under the roadway and the mine floor. Radio waves were used to detect the structure of the mining face and changes in coal thickness. Finally, based on the results of exploration, an inspection program was devised using conventional boreholes supplemented by directional boreholes to comprehensively evaluate the feasibility of mining under pressure. The study showed that the failure depth of the floor was 15 m and that the top of the Ordovician limestone was no longer water-bearing and was now a relative aquitard. The water inrush coefficient was reduced to less than 0.073 MPa/m, which will ensure safe mining and extend the lower limit of safe mining in the area. This provides a technical reference for prevention and control of Ordovician limestone water disasters in similar coal mines.

Optimization of the Distribution of Drilling Boreholes in Methane Production from Coal Seams

The paper presents an evaluation of methane production from coal seams. The Warszowice-PawłowicePółnoc deposit was selected for numerical modelling of methane production. The numerical model was made for a fragment of this deposit of about 2 km2. The numerical model was constructed for 6 seams. Three deposits were selected for simulation of methane production. Three horizontal boreholes were designed within the model area, referring to the existing Suszec-19 borehole. A number of simulations related to methane production from the selected deposits were performed. They included different variants of the number of boreholes and also took into account the z-pinnate method. The analyses proved that the most advantageous is the production of 3 directional boreholes simultaneously with the z-pinnate method. For this variant the degree of methane production was 21.9% of the estimated resources.

Exploration and application of directional long boreholes in coal measure strata

two roadways in adjacent working face of Baode Mine may have the risk of water inrush at the same time, so it is necessary to construct long borehole to cover the roadway excavation. On the basis of the hydrogeological conditions of the mine, the safe water insulation thickness and water inrush coefficient of coal seam No .8 are calculated. The results show that the water inrush coefficient is 0.035-0.037 MPa/m, which is less than the critical value 0.06 MPa/m and the bottom plate has no sudden water hazard. In the construction of No .10 coal seam, the directional long borehole is used to detect whether there is a hidden structure communicating with the floor limestone and to drain water. The test shows that there is no effluent phenomenon in the borehole, which proves that there is no hidden structure in No .10 coal seam.

Uneven stress and permeability variation of mining-disturbed coal seam for targeted CBM drainage: A case study in Baode coal mine, eastern Ordos Basin, China

The permeability of coal reservoirs is generally low in most of the mine areas in China. Using the stress-relief effect of the foremost-mined coal seam mining to increase the permeability of coal reservoirs is great significance for coalbed methane (CBM) drainage. Based on the engineering practice in Baode coal mine, the numerical model of coal seam group mining was established. The plastic zone evolution law of the mining-disturbed coal seam was analyzed after the foremost-mined coal seam has been mined. The stress and permeability uneven distribution characteristics of the mining-disturbed coal seam were studied, and the unloading effect of the mining-disturbed coal seam was obtained. Based on this, the adjacent mining-disturbed coal seam was divided into 5 areas on the plane. Field measurements of the mining stress, expansion deformation, and coal seam permeability coefficient evolution of the mining-disturbed coal seam during the mining of the foremost-mined coal seam show that the results of field experiment and numerical simulation are basically consistent. The method of targeted CBM drainage which combines the strike directional boreholes and cross-seam boreholes was proposed from engineering point of view. The method was carried out engineering application in Baode Coal Mine, and achieved good CBM drainage results.

Influence of the Aggregate-Pouring Sequence on the Efficiency of Plugging Inundated Tunnels through Drilling Ground Boreholes

This paper presents an experimental and field investigation on the efficiency of plugging by pouring aggregate in different sequences through multiple boreholes in a tunnel with flowing water. There have been controversies surrounding the selection of the pouring order for different particle sizes of aggregates and the order in different boreholes. A visualized experimental setup is used to investigate the influence of the pouring orders on the efficiency of plugging through multiple boreholes under the flowing-water condition. A case study of the salvage of a flooded mine using ground directional boreholes was investigated and compared with the experimental results. The water-pressure difference at the aggregate-capping moment, when fine aggregate was poured first and coarse aggregate later, was relatively small, compared to that when fine aggregate was poured upstream and coarse aggregate, downstream. The result implies that the efficiency of plugging with the order of pouring fine aggregate first and coarse aggregate later in different boreholes is better than that with the order of pouring fine aggregate upstream and coarse aggregate downstream. When the poured aggregate is about to be capped, increasing the pouring intensity with the same or a larger particle size is more conducive to capping. The case study shows that pouring fine materials in the early stage reduced the cross-sectional area; in the later stage, the aggregate particle size was gradually increased, which can be helpful in forming an effective water-barrier section in the tunnel. The pouring of aggregate provided a base for cement grouting to form a water-plug section with a length of 106 m, resulting in a sealing efficiency of 100% for the case.

Numerical simulation of hydraulic fracture deflection influenced by slotted directional boreholes using XFEM with a modified rock fracture energy model

Directional hydraulic fracturing (DHF) has been used in conductivity improvement of oil, gas and geothermal energy reservoirs and hard rock roof breaking in coal mines. Although the new DHF method that integrates fracturing borehole and slotted directional borehole (SDB) has been recently introduced, the mechanism and effectiveness of SDB on hydraulic fracture guiding remain open issues. In this study, numerical simulation based on extended finite element method (XFEM) is performed to investigate the effect of SDB on hydraulic fracture deflection. A modified rock fracture energy model is proposed and performed by a user subroutine USDFLD with XFEM, which considers the hardening property of rock shear fracture energy as confining pressure increases. The effects of stress field and borehole line azimuth on hydraulic fracture deflection and bottomhole pressure are investigated. Hydraulic fracture morphologies of three kinds of multi-borehole fracturing technology are compared, the control mechanism of SDBs on hydraulic fracture is explained, and the bottomhole pressure relief effect, borehole spacing and potential application prospects are discussed. Result indicates that the modified model shows good accuracy and applicability in predicting hydraulic fracture propagation, and the hardening property of shear fracture energy should be considered when using XFEM and cohesive element method. The feature “first drop and then rise” of bottomhole pressure curve is an important sign that imply the hydraulic fracture propagates into the influence radius of SDB and can be used as an indicator to evaluate the effectiveness of DHF. Slot increases the influence radius of directional borehole and changes the local stress direction, thus allowing SDB-based DHF technique to be applied to the conditions where the stress difference ratio does not exceed one. When the stress difference ratio is greater than one, the pressurized SDB is more suitable.

Fully Coupled Multi-Scale Model for Gas Extraction from Coal Seam Stimulated by Directional Hydraulic Fracturing

Although numerous studies have tried to explain the mechanism of directional hydraulic fracturing in a coal seam, few of them have been conducted on gas migration stimulated by directional hydraulic fracturing during coal mine methane extraction. In this study, a fully coupled multi-scale model to stimulate gas extraction from a coal seam stimulated by directional hydraulic fracturing was developed and calculated by a finite element approach. The model considers gas flow and heat transfer within the hydraulic fractures, the coal matrix, and cleat system, and it accounts for coal deformation. The model was verified using gas amount data from the NO.8 coal seam at Fengchun mine, Chongqing, Southwest China. Model simulation results show that slots and hydraulic fracture can expand the area of gas pressure drop and decrease the time needed to complete the extraction. The evolution of hydraulic fracture apertures and permeability in coal seams is greatly influenced by the effective stress and coal matrix deformation. A series of sensitivity analyses were performed to investigate the impacts of key factors on gas extraction time of completion. The study shows that hydraulic fracture aperture and the cleat permeability of coal seams play crucial roles in gas extraction from a coal seam stimulated by directional hydraulic fracturing. In addition, the reasonable arrangement of directional boreholes could improve the gas extraction efficiency. A large coal seam dip angle and high temperature help to enhance coal mine methane extraction from the coal seam.

3D Design of Optimum Complementary Boreholes by Integrated Analysis of Various Exploratory Data Using a Sequential-MADM Approach

Additional and complementary mineral exploration boreholes are often designed to obtain valuable information about mineralized intervals with the least cost. In this research, a new multi-criteria approach is proposed to design the optimum additional directional boreholes in a 3D environment in the second stage of drilling. The proposed algorithm consists of six steps. In the first step, based on the ore deposit type, exploration stage and available exploration data, the main criteria for the selection of the complementary boreholes are identified. In the second step, 3D geological models associated with the identified criteria are prepared. In the third step, a set of 3D candidate complementary boreholes is designed. In the fourth step, scores along the candidate borehole, relevant to various criteria, are estimated. In the fifth step, the candidate boreholes are ranked using a multi-criteria decision-making algorithm and an optimum borehole is selected for further drilling. Finally, information of new borehole is added to the earlier available data and the above steps are repeated to select additional borehole until a stopping condition for drilling is fulfilled. The proposed algorithm is applied at the Dalli Cu–Au porphyry deposit to design optimum boreholes for further drilling. The considered criteria for designing the additional boreholes are based on magnetic susceptibility, logged hydrothermal alteration, mineralized intervals, length of barren rocks, depth of mineralized intervals, Cu and Au grades along the earlier boreholes and trenches, kriging variance and drilling cost. By using the proposed method, four additional boreholes are designed. These boreholes are located in zones of highest uncertainties and highest grades. By drilling these four boreholes, the accuracy of the grade model is improved by 15%. The proposed approach employs all earlier exploration data to improve designing new boreholes in various deposit types and different stages of drilling.

Study on Fracture Initiation Mechanisms of Hydraulic Refracturing Guided by Directional Boreholes

In order to generate a new fracture far away from the original fracture in refracturing and effectively enhancing productivity, the technology of hydraulic refracturing guided by directional boreholes was presented. The effects of induced stress generated by the original hydraulic fracture, fracturing fluid percolation effect, wellbore internal pressure, and in situ stress on stress field distribution around wellbore were considered to obtain a fracture initiation model of hydraulic refracturing guided by two directional boreholes. The variation of maximum principal stress (σmax) under different conditions was investigated. The researches show that the directional boreholes result in a “sudden change region” of maximum principal stress around wellbore, reflecting dual stresses effects from vertical wellbore and directional boreholes on the rock. The width of sudden change region decreases as the distance from wellbore increases. Due to sudden change region, the refracturing fracture tends to initiate around directional boreholes. Whether the new fracture initiates and propagates along directional boreholes depends on comprehensive effect of borehole azimuth, borehole diameter, borehole spacing, horizontal stress difference, height, and net pressure of original fracture. The specific initiation position can be calculated using the theoretical model proposed in this paper. Affected by induced stress of the original fracturing, the rock tends to be compressed during refracturing, i.e., increased fracturing pressure. Sensitivity analysis with “extended Fourier amplitude sensitivity test (EFAST)” method shows the initiation of new fracture is mainly controlled by directional boreholes parameters and has little relation with in situ stress and parameters of original fracture. The influence rank of each parameter is as follows: borehole diameter > borehole spacing > original fracture net stress > borehole azimuth > horizontal stress difference > original fracture height. During design of refracturing, in order to better play the role of directional boreholes, and create a new fracture far away from original fracture, the optimal design is conducted with measures of optimizing boreholes azimuth, increasing borehole diameter and reducing borehole spacing if conditions permit. The research provides the theoretical basis for hydraulic refracturing guided by directional boreholes, which is helpful for the design of fracturing construction programs.

Designing infill directional drilling in mineral exploration by using particle swarm optimization algorithm

Geostatistical optimization in designing infill boreholes is an important cost-effective approach in increasing the accuracy of the tonnage and grade of an ore deposit. In this research, a new approach is proposed to design the optimum infill directional boreholes. In the proposed approach, the Kriging estimation variance is considered as the objective function and the number and properties of the optimum boreholes are estimated to minimize the objective function. The optimization procedure is implemented by Particle Swarm Optimization (PSO) algorithm. Range of the spatial and directional properties of new boreholes is determined by considering the primary information of the mineralization and administrative constraint of drilling. Then, the PSO algorithm is iteratively applied, and in each iteration, the variation of the estimated Kriging variance after drilling the new boreholes is determined and properties of the new boreholes are updated. The iterative procedure of the algorithm is continued until minimum Kriging variance is satisfied. The approach was applied to the Dalli Cu-Au porphyry deposit in Iran and three new infill directional boreholes were designed by considering six earlier boreholes from the preliminary exploration stage. New optimum boreholes were located where less information from the preliminary exploration stage exists and the highest variance is considered. Two new boreholes are near to vertical (78°) and the third is an inclined with 55° dip. By drilling these three new boreholes, the estimated grade model could be upgraded by 20%. For simplicity, quickness and the ability to search for the required numbers and specifications of a group of directional boreholes in a 3D environment are the most advantages aspects of the proposed approach.

Application of directional boreholes for gas drainage of adjacent seams

Application of directional boreholes for gas drainage of adjacent seams