Influence of combination forms of intact sub-layer and tectonically deformed sub-layer of coal on the gas drainage performance of boreholes: a numerical study

High concentration and large flow flux of gas drainage from underground coal seams is the precondition of reducing emission and large-scale use of gas.However,the layered occurrence of coal seams with tectonically deformed sub-layers and intact sub-layers makes it difficult to effectively drain gas through commonly designed boreholes.In this study,the gas drainage performance in coal seams with different combinations of tectonically deformed sub-layers and intact sub-layers was numerically analyzed.The analysis results show that the gas drainage curve changes from a single-stage line to a dual-stage curve as the permeability ratios of Zone II(kII)and Zone I(kI)increase,raising the difficulty in gas drainage.Furthermore,a dual-system pressure decay model based on the first-order kinetic model was developed to describe the dual-stage characteristics of pressure decay curves with different permeability ratios.In the end,the simulation results were verified with reference to in-situ drainage data from literature.The research results are helpful for mines,especially those with layered coal seams comprising tectonically deformed sub-layers and intact sub-layers,to choose appropriate gas drainage methods and develop the original drainage designs for achieving better gas drainage performance.

Thermo-hydro-mechanical coupled mathematical model for controlling the pre-mining coal seam gas extraction with slotted boreholes

Drainage influence radius is the basic parameter for borehole arrangement, while the effect of high pressure water jet slotting technology on borehole drainage influence radius has not been studied systematically. In this paper, a fully thermo-hydro-mechanical(THM) coupled model which represents the non-linear responses of gas extraction was implemented to demonstrate the reliability of this model through history data matching. Based on this model, the susceptibilities of gas extraction with single slotted borehole, including the permeability, the gas pressure, the temperature, the coal adsorption characteristics and the radius of slot, were quantified through a series of simulations. The simulation results revealed that increasing the permeability, initial gas pressure and temperature could develop the influence radius of single slotted borehole. This finite element model and its simulation results can improve the understanding of the coal-gas interactions of underground gas drainage and provide a scientific basis for the optimization of drainage systems.

Optimization of gob ventilation boreholes design in longwall mining

Gob ventilation boreholes(GVBs)are widely used for degasification in U.S.longwall coal mines.Depending on geological conditions,30–50%of methane can be recovered from longwall gob using GVBs.A NIOSH funded research at the Colorado School of Mines confirmed that GVBs can efficiently reduce methane at the face.However,GVBs can also draw some fresh air from the face and create explosive gas zones(EGZs).Explosive gas mixtures may be formed in gob areas due to the increased ingress of oxygen from GVBs.It is critical to identify the locations for GVBs for maximizing extraction of methane and minimizing hazards of explosion.This study analyzes the effect of operating parameters and design of GVB on methane extraction,EGZs formation,and face and tailgate methane concentrations.Methane extraction,formation of EGZs,and concentration of methane in working areas are significantly impacted by various factors.These factors include the distance of work face and tailgate from GVBs,diameter of GVBs,vacuum pressure of wellhead,GVB distance from the roof of the coal seam,and number of operating GVBs in a panel.Computational fluid dynamics(CFD)evaluations suggest optimal design and operating parameters of GVBs that can contribute to maximum benefits with minimum risks.

Antimicrobial Resistance Profile of Bacteria Isolated from Boreholes and Hand Dug Wells Water in Ngaoundere Municipality of Adamawa Region in Cameroon

Uncontrolled uses of antibiotics have led to rapid evolution of antibiotic-resistance bacteria and antibiotic resistance gene transfer, especially in a pool of aquatic system where resistance, intermediate and susceptible bacteria to some antibiotics strive together. Consequently, there is a transfer of resistance genes. In this study, bacteria of the Enterobacteriaceae family and some gram positive bacteria isolated from some boreholes and hand dug wells water of public use were tested on 19 antibiotics of different classes. This was achieved through a disk diffusion technique to determine the antimicrobial resistance profile of the said bacteria, microbial resistance index of the drugs used (and their ability to produce Beta-lactamase). These isolates were shown to demonstrate a very high resistance to the drugs used in the area. The resistance was highest in Escherichia coli 1 (73.68%) and lowest in Streptococcus pneumoniae (47.82%). These isolates also indicated very high levels of multi-drug resistance. The minimum resistance index was 0.47, indicating that bacteria isolates were of fecal origin. It is evident from the present study that multiple antibiotic-resistant bacteria can thrive in water as an environmental reservoir, and can therefore provide a route to multidrug-resistant pathogens to enter human and animal population.

Application of long-reach directional drilling boreholes for gas drainage of adjacent seams in coal mines with severe geological conditions

This study aimed to demonstrate the application of Long Reach Directionally Drilled Boreholes(LRDD)for gas drainage of adjacent seams before and during the longwall face operations of low permeability-high gas content coals Staszic-Wujek Hard Coal Mine in the Upper Silesia Coal Basin(Poland).Five LRDD Boreholes(TM1a-TM5)with a length of 300 and 400 m were located over coal seam 501 in the fractured zone and monitored over six months of longwall face operations.LRDD Boreholes were combined with Cross-Measured Boreholes.Reservoir characterization and geological modeling supported the results obtained from gas drainage.The drainage efficiency of LRDD Boreholes was the approxi-mately 70%level,while conventional Cross-Measured Boreholes were only 30%.The highest goaf gas quality(94%methane concentration)was reported for TM4,placed at an average elevation of 41 m above coal seam 501.The highest goaf gas production(average 6.2 m^(3)/min)was reported for LRDD Borehole TM3.This borehole was placed within the fracture zone(average elevation of 24.4 m)and drilled through the sandstone lithotype with the best reservoir properties,enhancing drainage performance.LRDD Boreholes TM2 and TM4 achieved similar performance.These three LRDD Boreholes were drilled close to the maximum principal horizontal stress direction,providing borehole stability during under-mining.The lowest goaf gas production was reported for LRDD Boreholes TM1a and TM5.Both Boreholes were placed in the rubble zone.

Feasibility Study of Boreholes Hand Drilling in Senegal—Identification of Potentially Favorable Areas

Drilling techniques commonly used in Africa are rather well suited for areas where geologic formations are hard and groundwater is not located at higher depths. Thus, for a large number of people living in rural areas, access to improved drinking water sources is often limited, due to the high cost of drilled boreholes that is closely linked to geographical, geological and hydrogeological factors. The analysis of various contexts has revealed that, in order to improve access to safe drinking water for underserved communities and populations, it is possible to consider less costly alternative solutions, compared to current options for water supply which are still expensive. In this paper, a simplified drilling technology at a very low cost has been demonstrated: “the manual or hand drilling”, which is a practical solution for less than 40-m deep water points in alluvial terrains or low resistance rock formations. The feasibility study of manual drilling in Senegal has revealed that, even if it is not practical in all geological formations of the country, manual drilling remains an alternative solution for reducing costs and improving accessibility to drinking water in several areas in Senegal, particularly in the Senegal River Valley, along the northern coast, in Fatick and Casamance coastal zones. This study was used to set up map of areas suitable for manual drilling boreholes;it aims to strengthen the local private sector capacity to meet growing drinking water needs in rural areas.

THE DISTANCE BETWEEN BOREHOLES OF SMOOTH BLASTING BY WATER COUPLING

The stress strength factor, length and opening degree of cracks around boreholes as well as movement regularity Of blockage with the smooth blasting by water coupling are calculated out according to the theories of fracture mechanics and explosion dynamics, and the relation between the pressure in holes and the change of hoIe volume is pointed out, thereby the distance between boreholes is worked out in this paper. For limestone, when uncoupling coefficient is 3,diameter of holes is 100 mm, the hole distance of water coupling smooth blasting is 2. 3 m. The result is consistent with practice.

Perimeters of Protection Demarcation for New Boreholes of Bonoua Aquifer (Southeastern, Côte d’Ivoire) through Hydrogeological Modeling

Located in the southeastern of C&#244te d’Ivoire, Bonoua aquifer contains an enormous groundwater potential. The new boreholes have been realized in this region to support the water supply of the populations. Moreover, in this region, agriculture is the main activity, whose pesticides used to guarantee the productivity, constitute a threat for groundwater. Thus, this study was undertaken in order to design a hydrogeological model able to simulate the piezometry of the Bonoua aquifer and determine the perimeters of protection for the new boreholes. The model, carried out under the Visual Modflow interface, was designed in steady-state mode and calibrated manually from the piezometry of the year 2000. The value of the standardized root mean squared residual of 4.86% (<10%) allows to say that the calibration obtained is considered satisfactory. Also, the correlation coefficient between observed and simulated heads of 0.95 permits to confirm a good calibration of the model. Perimeters of protection values were determined by simulating the paths of the virtual particles of water from the calibrated model. The simulations show that generally, the groundwater of Bonoua aquifer flows from north to south and the piezometric levels obtained vary between 65 m in the north and 5 m in the south. Upstream radius of the closed perimeters of protection calculated from the model varies from 172 to 482 m. However, those of distant perimeters of protection vary from 2877 to 6441 m.

Risk Factors Contributing to Microbiological Contamination of Boreholes and Hand Dug Wells Water in the Vina Division, Adamawa, Cameroon

This study examined the sanitary conditions of public boreholes and hand dug wells water in relation to pathogenic bacteria isolated in water samples. To assess the suitability of drinking water, sanitary inspection of surroundings of the sources was conducted, membrane filtration technic was used to trap the microorganisms in the water sample and other standard microbiological technics were applied to check the heterotrophic plate counts, total coliforms, fecal coliforms and some pathogenic bacteria in the samples. It was observed that there were no delineated protection zones around many boreholes (61.19%) and in almost all hand dug wells;thus, hand dug wells were pruned to more contamination than boreholes. Heterotrophic plate counts of boreholes were significantly different between (p < 0.0001) zones in dry and rainy seasons. Total coliforms per 100 ml varied significantly (p < 0.001) between the two seasons both in boreholes and hand dug wells. Fecal coliforms were significantly absent in some boreholes, but significantly present in all hand dug wells with the presence of E. coli 157H in some. Risk assessment of factors contributing to water contamination showed that: pumps manipulation with feet, other sources of contamination such as wastewater dumps, within 10m were significantly associated to boreholes contamination with Salmonella spp, Staphylococcus aureuse, fecal coliform (p = 0.01);in hand dug wells, presence of latrine or septic tank soak-away within 10 m of the wells, poor depth and lack of internal lining, uncapped wells, presence of trees near the wells, animal and birds feces, were significant and associated to contamination with Salmonela spp., B. cepaceae, S. aureus E. coli 1 (p < 0.05). Generally water collection points are marked with very poor sanitary conditions and this situation may not change unless the contaminating risk factors are fixed and sanitary measures are taken.

Microbial Analysis of Drinking Water from Randomly Selected Boreholes and Shallow Wells around Hargeisa, Somaliland

Background: Shallow wells and boreholes are vital sources of potable water in Hargeisa. This water can be polluted by runoff, in particular during the rainy season, causing outbreaks of waterborne infections. Objectives: This research aimed at evaluating the microbial quality of shallow wells and boreholes water around Hargeisa, Somaliland. Methods: The total coliform and Escherichia coli count were done by using the membrane filtration method. Overall, 100 ml of each water sample was filtered via a 0.45 μm membrane filter, and then the filters were put on m-Endo agar plates that were incubated at 37°C for 24 to 48 hours. Results: The mean value of total coliform counts for the boreholes and shallow wells ranged from 1.288 × 103 to 8.8 × 103 CFU/100ml, while the mean value of total E. coli counts also ranged from 3.5 × 102 to 4.429 × 103 CFU/100ml. Results from this study have demonstrated that all water sources (Arabsiyo, Dararweyne, Darasalaam, Dabaraqas, and Jaleelo) don’t comply with the WHO guideline for drinking water. Results from the analysis of water samples of 28 wells demonstrated a significant correlation between total coliform and E. coli counts (P = 0.01). Therefore, this water is not fit for human consumption unless it is treated. Conclusion: This study has demonstrated that all results of both mean values of total coliform and E. coli counts from groundwater of selected shallow wells and boreholes were beyond WHO standards, so water from Arabsiyo, Jaleelo, Dabaraqas, Dararweyne, and Darasalaam requires treatment before human consumption.

Safety analysis of stability of surface gas drainage boreholes above goaf areas

As longwall caving mining method prevails rapidly in China coal mines, amount of gas emission from longwall faces and goaf area increased significantly. Using traditional gas drainage methods, such as drilling upward holes to roof strata in tailgate or drilling inseam and cross-measure boreholes, could not meet methane drainage requirements in a gassy mine. The alternative is to drill boreholes from surface down to the Iongwall goaf area to drain the gas out. As soon as a coal seam is extracted out, the upper rock strata above the goaf start to collapse or become fractured depending upon the rock characteristics and the height above the coal seam. During overlying rock strata being fractured, boreholes in the area may be damaged due to ground movement after the passage of the Iongwall face. The sudden damage of a borehole may cause a Iongwall production halt or even a serious mine accident. A theoretical calculation of the stability of surface boreholes in mining affected area is introduced along with an example of determination of borehole and casing diameters is given for demonstration. By using this method for the drilling design, the damage of surface boreholes caused by excessive mining induced displacement can be effectively reduced if not totally avoided. Borehole and casing diameters as well as characteristics of filling materials can be determined using the proposed method by calculating the horizontal movement and vertical stain at different borehole depths.

STABILITY OF BOREHOLES IN A GEOLOGIC MEDIUM INCLUDING THE EFFECTS OF ANISOTROPY

An analytical formulation is developed to investigate the stability of a deep, inclined borehole drilled in a geologic medium and subjected to an internal pressure and a non_hydrostatic stress field. The formulation consists of a three_dimensional (3_D) analysis of stresses around a borehole, combined with internal pressurization of the borehole to obtain an approximate solution of the overall stress distribution. The orientation of the borehole, the in_situ stresses and bedding plane can all be arbitrarily related to each other to represent the actual field situations. Both tensile failure and shear failure potentials of a borehole are investigated. The failure criteria applied assume that when the least principal stress exceeds the strength of the formation in tension, a tensile failure occurs. Shear failure is represented using the modified Drucker_Prager failure criterion for anisotropic materials. A parametric study is carried out to assess the effect of material anisotropy, bedding plane inclination and in_situ stress conditions on borehole stability. Results of the parametric study indicate that wellbore stability is significantly influenced by a high borehole inclination, high degree of material anisotropy, in_situ stress conditions and high formation bedding plane inclination. The stability of a borehole in an elasto_plastic medium is also investigated. In order to evaluate the extent of the plastic zone around a borehole and the effect of anisotropy of the material on this plastic zone, a mathematical formulation is developed using theories of elasticity and plasticity. The borehole is assumed to be vertical, subjected to hydrostatic stresses, and drilled in a transversely isotropic geologic medium. A parametric study is carried out to investigate the effect of material anisotropy on the plastic behavior of the geologic medium. Results indicate that the stress distribution around a borehole, the extent of the plastic zone, and the failure pressure are influenced by the degree of material anisotropy and value of in_situ overburden stresses. It was observed that the borehole becomes less stable as the degree of anisotropy of the geologic medium increases.

Impact of elliptical boreholes on in situ stress estimation from leak-off test data

We developed an inversion technique to determine in situ stresses for elliptical boreholes of arbitrary trajectory. In this approach, borehole geometry, drilling-induced fracture information, and other available leak-off test data were used to construct a mathematical model, which was in turn applied to finding the inverse of an overdetermined system of equations.The method has been demonstrated by a case study in the Appalachian Basin, USA. The calculated horizontal stresses are in reasonable agreement with the reported regional stress study of the area, although there are no field measurement data of the studied well for direct calibration. The results also indicate that 2% of axis difference in the elliptical borehole geometry can cause a 5% difference in minimum horizontal stress calculation and a 10% difference in maximum horizontal stress calculation.

Method for designing the optimal sealing depth in methane drainage boreholes to realize efficient drainage

The purpose of underground methane drainage technology is to prevent methane disasters and enable the efficient use of coal mine methane(CMM),and the sealing depth is a key factor that affects the performance of underground methane drainage.In this work,the layouts of in-seam and crossing boreholes are considered to analyze the stress distribution and failure characteristics of roadway surrounding rock through a numerical simulation and field stress investigation to determine a reasonable sealing depth.The results show that the depths of the plastic and elastic zones in two experimental coal mines are 16 and 20 m respectively.Borehole sealing minimizes the air leakage through the fractures around the roadway when the sealing material covers the failure and plastic zones,and the field test results for CMM drainage at different sealing depths indicate that the CMM drainage efficiency increases with increasing sealing depth but does not change once the sealing depth exceeds the plastic zone.Moreover,sealing in the high-permeability roadway surrounding rock does not have a strong influence on the borehole sealing performance.Considering these findings,a new CMM drainage system for key sealing in the low-permeability zone was developed that is effective for improving the CMM drainage efficiency and prolonging the high-concentration CMM drainage period.The proposed approach offers a valuable quantitative analysis method for selecting the optimum sealing parameters for underground methane drainage,thereby improving considerably the drainage and utilization rates of CMM.

Inversion of breakout data from inclined boreholes for stress state of the upper crust in Jizhong depression

The forward and inverse problems of studying crustal stress state from breakout data of inclined boreholes are concisely stated. direction of the maximum horizontal principal stress (compressive) and relative magnitudes of the horizontal stresses to the vertical stress in the upper crust in two regions of the Jizhong depression, the North of China, are obtained by analyzing the breakout data of 6 inclined wells. To get stable results in the analysis wesearched for the unknown parameters both forwardly and inversely. The results show that the maximum azimuths of the horizontal Principal compressive stresses in the central and southern part of the Jizhong depressionare N86°E and N77°E, respeCtively, while the relative magnitudes of the three principal stresses in the uppercrust (about 1000-4000 m) of the depression are variable. In the centra; part of the Jizhong depression we havefound SH : Sv: SK= 1. 38: 1. 00: 0. 57, where SH, SV and Sh are the maximum horizontal, vertical and minimum horizontal stress, resistively. This indicates that the present stress regime in this area is of strike-slipfaulting type. In the southern part of the depreSSion we have obtained SH: Sv: Sh=0. 80: 1. 00 1 0. 62, indicating a normal faulting stress regime in the shallow Part Of the crust.

Water Analysis for Heavy Metals Content in Selected Boreholes in Port Harcourt Metropolis （A Case Study during 2010-2011）

Underground water （Borehole） has been the main alternative source of drinking water for most communities in my country. Previous studies have revealed high levels of contamination. The origin of which can be attributed to geochemical processes, combustion of fossil fuels, mining and anthropogenic activities. Most borehole water and well water in local communities of Nigeria are not safe for drinking due to heavy industrial and environmental pollution. This study was undertaken to assess the quality in some selected boreholes in the Port Harcourt metropolis for a period of two years. Borehole water samples were randomly collected from thirteen boreholes in a local community in plastic bottles （100 mL） in the months of September for the years of study （2010 ＆ 2011）. Four out of the seven heavy metals analyzed were found to be present in the first year of study. These were Fe, Cu, Mn and Zn. In the second year of study, Pb, Cr, Fe and Co were not detected in all of the samples except Cu and Fe which were present in only two samples. Mn and Zn were found to be present in all of the samples for both years of study.

THEORETICAL AND EXPERIMENTAL STUDIES ON FRACTURE PLANE CONTROL BLAST WITH NOTCHED BOREHOLES

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Numerical simulation on the movement law of overlying strata in the stope with a fault and analysis of its influence on the ground gas drainage boreholes

In order to study the influence of a fault on the movement law of the overlying strata as well as its effect on the gas drainage boreholes, based on the practical situation of 1242（1） panel at Xieqiao Mine in Huainan, the Finite Element Method （FEM） model was built up, and the distribution of the stress field and the displacement field of the overlying strata in the stope with a fault were simulated by using the FEM software ANSYS. The results indicate that because of the existence of the fault, the horizontal displacement of overlying strata near the gas drainage borehole becomes larger than that in the stope without a fault, and the distribution of the stress field of the overlying strata changes greatly. When the working face is far away from the fault, the distribution of the stress field is approximately symmetrical. As the working face advances to the place 50 m away from the fault, the stress range at the right side goaf area is as twice as that at the left side. Here, the stress distribution area of goaf area and the fault plane run through, the fracture-connected-zone is formed. It can be presumed that the gas adsorbed in the coal and rock will flow into the fault zone along the fracture-connected-zone, which causes the quantity of gas drainage reduce remarkably.

Development of a Research Probe for Geothermal Boreholes

This paper introduces the idea of a framework for the implementation of novel downhole probes. A couple of examples （e.g. a tracer detector, a casing smear test probe or a casing repair probe） demonstrate that many components can be reused. These are the ＂bricks＂ of the ZWERG toolkit which is developed to match the environment in boreholes. Two ＂bricks＂ are described in detail： The housing （1） has to resist the pressure and other mechanical stress in deep holes. The selection of the material and the calculation of the wall thickness are the main interests. In many applications, a thermal management （2） of the inside of the probe is absolutely necessary. A dewar vessel can uncouple the heat of the geothermal reservoir and the temperature in the probe. It is important to understand the physical heat flow mechanisms. A set of formulas allows a good estimation of the quantity of heat that warms up the probe. The toolkit contains some immaterial ＂bricks＂ like blueprints of proven designs or support for the logistic process of finding and purchasing compatible components. The intention to drill near magma chambers calls for a common eflbrt of the geothermal community to gather compatible components, assemblies and knowhow and makes it widely available. ZWERG could be a starting point.

Selected Trace Elements in Domestic Water Boreholes and Their Implications on Human Health, in Huruma Estate, Eldoret Municipality, Uasin-Gishu County, Kenya

Trace elements constitute less than 1% of the rocks in the crust (Stumm and Morgan, 1991). In the human body, they constitute less than 100 mg/kg (0.01%). These elements are released to the environment naturally by weathering and volcanic activities (Flint and skinner, 1997). It has been observed that trace elements are greatly absorbed and retained in the body when in liquid diet. This phenomenon also influences the risk to human health, especially of infants and children whose immature digestive system further promote absorption of toxic heavy metals. The study was based on the analysis of domestic borehole water supplies in Huruma estate of Eldoret Municipality for selected trace elements and their implications on human health. The boreholes were systematically selected for sampling points and trace elements, Cr, Cu and Se analyzed using AAS. Statistical analysis for mean, standard deviation and confidence interval limits was done using SPSS. The statistical t-test was used to test for significance differences at (p = 0.05). The graphs were drawn using the Microsoft Excel package. The resulting data obtained from analysis were compared with WHO data for drinking water. In the study, the mean values of the following parameters were as follows: Chromium 17.9 μg/L, Copper 563 μg/L and Selenium 22.7 μg/L. There was a significant difference at 5% level of significance (p = 0.000) in all the parameter values among the sampling points in Huruma estate. The above mean values were far below the WHO recommended limits for drinking water. It was concluded that the borehole water from Huruma was fit for drinking and therefore could not cause cancer and cardiovascular diseases. However, borehole water should be used if other water sources (tap water etc.) were not available. All the industries near Huruma estate should carefully analyze and regularly monitor their liquid waste effluents to ensure that no harmful discharges get into the soil.