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1.
Keith E. Schilling 《Ground Water Monitoring & Remediation》1995,15(2):104-113
The impact of lost circulation during rotary drilling near an existing monitoring well cluster was evaluated by periodic measurements of water levels and contaminant concentrations at the well cluster. Due to regulatory concerns, changes in water levels or VOC concentration in the well cluster during drilling would trigger monitoring well redevelopment. The borehole was drilled approximately 30 feet northeast of four nested monitoring wells that screen Devonian and Silurian carbonate bedrock at depths of 15, 60, 130, and 190 feet. Following complete circulation loss at depths of 177 and 1 S3 feet in the borehole, a rapid decrease in water levels was observed in the upper three monitoring wells. The water level in the well that was screened through the lost circulation zones increased slightly.
Decreasing water levels in formations located above the point of circulation loss appear to occur in response to a sudden decrease in borehole fluid pressure caused by the flow of drilling fluid into the formation. The relative contribution of contaminated formation water lo the borehole can be estimated by using the time-drawdown relationship and estimates of transmissivity. At the point of circulation loss, significant dilution of contaminant concentrations occurs from the loss of drilling fluid into the contaminated zone. Contaminated formation water entering the borehole during periods of complete lost circulation may mobilize contaminants from upper lo lower formations. Lost circulation into a formation would be signaled by a water level increase in monitoring wells. The wells would subsequently require development to remove the volume of fluid lost to the formation, including both drilling fluid and contaminated formation water. Monitoring wells exhibiting declining water levels following lost circulation would not require development since drilling water has not entered the zones screened by these wells. 相似文献
Decreasing water levels in formations located above the point of circulation loss appear to occur in response to a sudden decrease in borehole fluid pressure caused by the flow of drilling fluid into the formation. The relative contribution of contaminated formation water lo the borehole can be estimated by using the time-drawdown relationship and estimates of transmissivity. At the point of circulation loss, significant dilution of contaminant concentrations occurs from the loss of drilling fluid into the contaminated zone. Contaminated formation water entering the borehole during periods of complete lost circulation may mobilize contaminants from upper lo lower formations. Lost circulation into a formation would be signaled by a water level increase in monitoring wells. The wells would subsequently require development to remove the volume of fluid lost to the formation, including both drilling fluid and contaminated formation water. Monitoring wells exhibiting declining water levels following lost circulation would not require development since drilling water has not entered the zones screened by these wells. 相似文献
2.
超短半径径向水平井抽采煤层气渗流规律的数值模拟 总被引：3，自引：0，他引：3
为得到超短半径径向水平井开采煤层气过程中的气体渗流规律以及进行产量预测,在基本假设条件下,建立了径向水平井开采煤层气的固流耦合渗流数学模型;在一定的边界条件及初始条件下,利用Matlab软件进行编程计算后,得到直井和不同数目分支径向水平井开采煤层气1000天后的压力场、速度场和气产量变化规律。数值模拟结果表明,在一定的生产区域和开采时间,随着径向水平井分支数目的增加,煤储层压力下降范围更广,气体流速场干扰加强,压力漏斗降大面积扩展,煤层气有效供气区及解吸面积大幅增长,煤层气解吸能力及稳产能力加强,煤层气产量大幅度增加;同时,气产量增幅随着井筒分支数目的增加而下降,分支井数目理论上应存在一个最优值。模拟结果显示了超短半径径向水平井技术开采煤层气的有效卸压作用,对煤层气工业增产技术的选择和钻孔方案的布置具有重要的理论指导意义。 相似文献
3.
Distribution and fractionation mechanism of stable carbon isotope of coalbed methane 总被引：1，自引：0，他引：1
The stable carbon isotope values of coalbed methane range widely, and also are gener- ally lighter than that of gases in normal coal-formed gas fields with similar coal rank. There exists strong carbon isotope fractionation in coalbed methane and it makes the carbon isotope value lighter. The correlation between the carbon isotope value and Ro in coalbed methane is less obvious. The coaly source rock maturity cannot be judged by coalbed methane carbon isotope value. The carbon isotopes of coalbed methane become lighter in much different degree due to the hydrodynamics. The stronger the hydrodynamics is, the lighter the CBM carbon isotopic value becomes. Many previous investigations indicated that the desorption-diffusion effects make the carbon isotope value of coalbed methane lighter. However, the explanation has encountered many problems. The authors of this arti- cle suggest that the flowing groundwater dissolution to free methane in coal seams and the free methane exchange with absorbed one is the carbon isotope fractionation mechanism in coalbed methane. The flowing groundwater in coal can easily take more 13CH4 away from free gas and com- paratively leave more 12CH4. This will make 12CH4 density in free gas comparatively higher than that in absorbed gas. The remaining 12CH4 in free gas then exchanges with the adsorbed methane in coal matrix. Some absorbed 13CH4 can be replaced and become free gas. Some free 12CH4 can be ab- sorbed again into coal matrix and become absorbed gas. Part of the newly replaced 13CH4 in free gas will also be taken away by water, leaving preferentially more 12CH4. The remaining 12CH4 in free gas will exchange again with adsorbed methane in the coal matrix. These processes occur all the time. Through accumulative effect, the 12CH4 will be greatly concentrated in coal. Thus, the stable carbon isotope of coalbed methane becomes dramatically lighter. Through simulation experiment on wa- ter-dissolved methane, it had been proved that the flowing water could fractionate the carbon isotope of methane, and easily take heavy carbon isotope away through dissolution. 相似文献
4.
煤弹性是反映煤的物质组分和结构的重要力学特征之一.在钻孔与测井的约束下,运用地震勘探获取煤层的弹性特征以反映其物性等,对于煤炭井工开采和煤层气储层评价及开发具有重要的工程意义,而其中,煤样的超声实验是实现地震反演煤层物性的基础.鉴于此,本文针对中国义马、阜康、淮南、平顶山、鹤壁和焦作6个矿区采集的6种不同变质程度的原煤样30块,在常温常压条件下分别进行了沿煤层走向、倾向及垂直层理三个方向煤样的实验室超声波测量.测试结果显示:煤样纵横波速度在走向、倾向、垂向三个方向上依次减小,存在各向异性,且P波速度的平均各向异性强于S波;品质因子与弹性模量在三个方向上也存在较大差异,且S波的品质因子大于P波的品质因子;弹性模量除泊松比外,均小于一般的沉积岩.通过本实验与分析进一步证明了:Gardener与Castagna公式不适用于中国煤田的煤岩弹性描述,并给出了精度更高的经验公式. 相似文献
5.
Lost circulation, the inadvertent injection of drilling fluids into a highly permeable and/or fractured aquifer during rotary drilling, may result in collection of spurious information if the lost drilling fluids are not adequately purged before sampling the ground water. The purpose of this study was to determine whether removal of the volume of water lost during coring of a monitoring well in the carbonate Scotch Grove Formation (Silurian, east central Iowa) necessarily ensures collection of representative ground water samples. To monitor dilution of the ground water due to lost circulation, rhodamine dye was added to the drilling water and dye recovery was measured in samples collected during purging of five separate 5- to 10-foot intervals.
Circulation loss occurred in all five intervals, ranging from nearly 200 gallons in the upper permeable portion of the Scotch Grove to 25 gallons in the less permeable Buck Creek Member below. When the volume of water purged from the upper three intervals corresponded to the volume of water lost during coring, the purge water still contained 11 to 20 percent dyed drilling water. As purging continued, the proportion of drilling water in the samples decreased slowly. After purging more than 200 gallons of water, 86 to 98 percent of the dyed drilling water was recovered from the five test intervals. Four traditionally measured water quality parameters-pH, temperature, specific conductance, and dissolved oxygen — were less useful than the dye recovery for distinguishing drilling water from formation water in those zones in which the ground water quality was similar to the drilling water. These results indicate that the determination of the quantity of water to be purged prior to sampling must be based, at least in part, on aquifer lithology and hydraulic characteristics. 相似文献
Circulation loss occurred in all five intervals, ranging from nearly 200 gallons in the upper permeable portion of the Scotch Grove to 25 gallons in the less permeable Buck Creek Member below. When the volume of water purged from the upper three intervals corresponded to the volume of water lost during coring, the purge water still contained 11 to 20 percent dyed drilling water. As purging continued, the proportion of drilling water in the samples decreased slowly. After purging more than 200 gallons of water, 86 to 98 percent of the dyed drilling water was recovered from the five test intervals. Four traditionally measured water quality parameters-pH, temperature, specific conductance, and dissolved oxygen — were less useful than the dye recovery for distinguishing drilling water from formation water in those zones in which the ground water quality was similar to the drilling water. These results indicate that the determination of the quantity of water to be purged prior to sampling must be based, at least in part, on aquifer lithology and hydraulic characteristics. 相似文献
6.
In the eastern edge of the Ordos Basin, the coalbed methane (CBM) development has not made substantial progress in the past 20 years, and the origin of gas can be used to guide the CBM block-selecting and development. Based on the 37 sets of carbon isotope data, the origin of the gas was determined and the origin mechanism was studied in this work. The δ 13CPDB of methane ranges from ?70.5‰ to ?36.19‰ in the eastern edge in the Ordos Basin and the value becomes heavier from the north to the south. The secondary biogenic gas and the thermogenic gas are mixed in the shallow area and the thermogenic gas occurs in the medium and deep levels. The phenomenon is controlled mainly by the distribution of coal rank and hydrodynamics. Firstly, based on the relationship between China coal rank and methane δ 13CPDB, the medium rank coal is dominant in the eastern edge of the Ordos Basin, and the mixture of the secondary biogenic gas and the thermogenic gas is formed in the coal of vitrinite reflectant ratio (R max) between 0.5% and 2.0% if there is appropriate hydrodynamics; at the same time, because of the shallow burial depth, and the well-developed coal outcrop, meteoric water and other surface water carrying bacteria recharge the coal reservoir, metabolize the organic compounds at a relatively low temperature, and generate methane and carbon dioxide. Wherever the trapping mechanisms occur in the coal, such as Liulin and Hancheng, modern gas content should be high. 相似文献
7.
The physical characteristics of coal reservoirs are important for evaluating the potential for gas desorption, diffusion, and seepage during coalbed methane (CBM) production, and influence the performance of CBM wells. Based on data from mercury injection experiments, low-temperature liquid nitrogen adsorption, isothermal adsorption, initial velocity tests of methane diffusion, and gas natural desorption data from a CBM field, herein the physical characteristics of reservoirs of high-rank coals with different coal-body structures are described, including porosity, adsorption/desorption, diffusion, and seepage. Geometric models are constructed for these reservoirs. The modes of diffusion are discussed and a comprehensive diffusion-seepage model is constructed. The following conclusions were obtained. First, the pore distribution of tectonically deformed coal is different from that of normal coal. Compared to normal coal, all types of pore, including micropores (<10 nm), transitional pores (10–100 nm), mesopores (100–1000 nm), and macropores (>1000 nm), are more abundant in tectonically deformed coal, especially mesopores and macropores. The increase in pore abundance is greater with increasing tectonic deformation of coal; in addition, the pore connectivity is altered. These are the key factors causing differences in other reservoir physical characteristics, such as adsorption/desorption and diffusion in coals with different coal-body structures. Second, normal and cataclastic coals mainly contain micropores. The lack of macropores and its bad connectivity limit gas desorption and diffusion during the early stage of CBM production. However, the good connectivity of micropores is favorable for gas desorption and diffusion in later gas production stage. Thus, because of the slow decline in the rate of gas desorption, long-term gas production can easily be obtained from these reservoirs. Third, under natural conditions the adsorption/desorption properties of granulated and mylonitized coal are good, and the diffusion ability is also enhanced. However, for in situ reservoir conditions, the high dependence of reservoir permeability on stress results in a weak seepage of gas; thus, desorption and diffusion is limited. Fourth, during gas production, the pore range in which transitional diffusion takes place always increases, but that for Fick diffusion decreases. This is a reason for the reduction in diffusion capacity, in which micropores and transitional pores are the primary factors limiting gas diffusion. Finally, the proposed comprehensive model of CBM production under in situ reservoir conditions elucidates the key factors limiting gas production, which is helpful for selection of reservoir stimulation methods. 相似文献
8.
如何提高煤层气渗透率是目前煤层气开采研究中的重要课题。基于煤层瓦斯渗流规律数学模型,利用COMSOL Multiphysics软件,对流-固-热耦合条件下的非等温煤层气解吸、渗流变化规律进行了数值模拟。结果表明,在注热条件下,煤层气渗流压力随着温度的增加而下降,且下降速度加剧,压力差越大,气体从高压区域流向低压区域的渗流速度越快。气体在煤层中径向流向井口,井口附近压力的梯度增大,气体渗流速度较快;在未受到加热影响的区域,煤层气不受外加热量影响,煤层气解吸速率保持不变;注热后煤层温度升高,可以加快煤层气渗流速度、提高渗透率、增加煤层气产量。研究成果可为煤层中注热开采煤层气的工程实践提供相应的理论依据。 相似文献
9.
10.
储层改造是煤层气井提高产能的重要措施,水力压裂是煤层气储层改造的重要方法.为研究煤层气储层压裂过程及其天然裂缝对煤储层压裂时破裂压力的影响,本文以山西沁水盆地南部高煤级煤矿区为研究区,运用有限元数值模拟方法,计算不同地应力条件下、裂缝处于不同位置时煤储层的破裂压力.结果表明:(1)不同类型地应力场对破裂压力的影响不同.对于均匀应力场,破裂压力随着围压的增大而增大,其增幅约为围压的两倍;对于非均匀应力场,当一个水平主应力不变时,破裂压力会随着水平主应力差的增加而减少;(2)如果地应力条件不变,煤储层破裂压力随着天然裂缝与最大水平主应力方向夹角的增加而增加,水平主应力差越大煤储层破裂压力增幅也越大;(3)在有天然裂隙的地层中进行压裂,当天然裂缝的方位不同时压裂裂缝既可能是沿着天然裂缝扩展的裂缝,也可能是压裂过程中产生的新裂缝,因此天然裂缝的方位对破裂压力具有一定的影响. 相似文献
11.
首先研究了天然气AVO技术的岩石物理基础--Gassmann方程和Biot理论(以下统称为"Gassmann-Biot理论")--对煤层气AVO技术的适用性.根据该理论创始人在建立其理论时的假设条件、煤层气储层的双相孔隙特征、煤层气的双相赋存特征,本文推理认为,由于煤层气储层的基质型孔隙体系的连通性差,裂隙性孔隙在宏观上是非均质的,并且是各向异性的,因此,总体上来说,Gassmann-Biot理论不完全适用于煤层气储层.特别地,当煤层的水饱和状态保持不变而煤层的含气量变化时,因为煤层中孔(裂)隙中流体的体积压缩模量不变或基本不变,即使煤层的弹性参数发生变化,Gassmann-Biot理论也不可能预测其变化趋势.因此,天然气AVO技术的岩石物理基础完全地不适用于水饱和煤层气储层.研究发现,煤层气储层含气量与其密度、纵波速度、横波速度之间存在负相关关系,即含气量高,密度小、纵波速度小、横波速度小;含气量低,密度大、纵波速度大、横波速度大.但是,这些负相关关系不是现有岩石物理理论能够预测或能够解释的.依据煤层气地质学理论以及负相关关系与现有岩石物理理论的一致性,本文提供了对某勘探区A号煤层含气量与其密度、纵波速度、横波速度之间负相关关系的解释,并认为煤层气储层的含气量与其弹性参数之间的负相关关系可能是这类储层内在的固有的规律性的关系.本文证明含气量与其密度、纵波速度、横波速度之间负相关关系可以作为煤层气AVO技术的岩石物理基础,建立了AVO异常与煤层气储层"甜点(即富集高渗部位)"之间的关系,从而能够使用AVO异常探测煤层气富集高渗部位. 相似文献
12.
The commercial recovery of methane from coal is well established in the coalbed methane (CBM) blocks at the east margin of Ordos Basin, China. CBM forms with various carbon isotopic ratios (δ13CPDB) due to the carbon isotopic fractionation in biogenical or thermogenical processes. Based on the geologic evolution of coalbed reservoir and studies on the characteristics of δ13CPDB values distributed spatially (e.g., horizontal CBM well location area, vertical coal burial zone, coal rank, etc.) and temporally (e.g., geologic evolution history), we explored the formation mechanism of carbon isotopic of methane. The relatively low δ13CPDB values are widely distributed along the research area, indicating a trend of “lighter-heavier-lighter” from north to south. From a combination analysis of the relationship between δ13CPDB and the relative effects, the essential aspects in determining CBM carbon isotope being light in the study area are: the genesis of secondary biogas in the north; water soluble effects in the active hydrodynamic areas in the middle; desorption fractionation effect promoted by tectonic evolution in the south; and the sudden warming hydrocarbon fractionation accelerated by magmatic event in particular areas (e.g., Linxian). 相似文献
13.
储层流体识别是确定油气水分布,合理布设井位,提高钻井成功率的关键之一.本文基于流体饱和孔隙介质岩石物理模型,对地震反演的地层体积模量进行分解,获得孔隙流体体积模量,并依据油、气、水(尤其是气-油、气-水)模量的显著差异进行识别.文中简要分析了Gassmann模型和Kuster-Toksz模型的特征,详细讨论了孔隙形态和饱和度对弹性模量的影响,提出了联合Kuster-Toksz方程和Gassmann方程的体积模量分解方法.该方法通过Kuster-Toksz方程从测井数据中反演地层骨架固体和干骨架的弹性模量,再利用Gassmann方程对地层体积模量进行分解,既考虑了孔隙形态,又充分利用了Gassmann方程的易用性.理论模型结果表明方法是可行的.方法应用于西部地区某气田,流体识别与地层含气性预测结果与钻井基本一致,进一步证实了方法的有效性. 相似文献
14.
在分析沁水盆地北部煤层气富集与地下水和地质构造之间的关系基础上,采用大地电磁法探测地下水分布以及有利和不利煤层气富集影响因素、间接探测煤层气相对富集区;根据煤层气富集地质模型设计了地球物理模型,利用有限单元法开展典型薄层模型正演模拟,讨论了探测方法的可行性;选择山西沁水盆地北部煤层气勘探区开展可控源音频大地电磁探测技术试验,结合已有地质、钻井及测井资料完成了试验资料的处理与解释;试验结果表明,利用可控源音频大地电磁法能有效获得地层电性结构,推断含水、富水区,结合煤层气有利富集地质条件和影响因素,可以实现间接预测煤层气的有利富集区. 相似文献
15.
煤储层应力敏感性是影响煤层气井产能的地质因素,以鄂尔多斯盆地东南缘高煤级煤储层为对象,通过煤样的应力敏感性实验和现场测试,建立了高煤级煤储层渗透性与应力之间的相关关系和模型;探讨了渗透性变化的控制机理.研究结果表明, 煤储层渗透率随应力的增加按负指数函数规律降低.在应力小于5 MPa时,煤储层渗透率随应力增加快速下降,应力敏感性最强;应力在5~10 MPa时,渗透率随应力增加而较快下降,应力敏感性较强;而当应力大于10 MPa后,渗透率随应力的增加下降速度减缓,应力敏感性减弱.与沁水盆地南部高煤级煤样实验结果对比认为,鄂尔多斯盆地东南缘山西组2煤层应力敏感性要小于沁水盆地南部山西组3煤层的应力敏感性.煤储层渗透性是在应力作用下煤储层中裂隙产生压缩(压密)变形,裂隙开度急剧减小的结果.因此在煤层气开发过程中控制排采速度,尤其是排采早期降液速度,对于防止煤储层应力敏感性,提高采收率具有实际意义. 相似文献
16.
Coal measures (coal bearing rock strata) can contain large reserves of methane. These reserves are being exploited at a rapidly increasing rate in many parts of the world. To extract coal seam gas, thousands of wells are drilled at relatively small spacing to depressurize coal seams to induce desorption and allow subsequent capture of the gas. To manage this process effectively, the effect of coal bed methane (CBM) extraction on regional aquifer systems must be properly understood and managed. Groundwater modeling is an integral part of this management process. However, modeling of CBM impacts presents some unique challenges, as processes that are operative at two very different scales must be adequately represented in the models. The impacts of large‐scale gas extraction may be felt over a large area, yet despite the significant upscaling that accompanies construction of a regional model, near‐well conditions and processes cannot be ignored. These include the highly heterogeneous nature of many coal measures, and the dual‐phase flow of water and gas that is induced by coal seam depressurization. To understand these challenges, a fine‐scale model was constructed incorporating a detailed representation of lithological heterogeneity to ensure that near‐well processes and conditions could be examined. The detail of this heterogeneity was at a level not previously employed in models built to assess groundwater impacts arising from CBM extraction. A dual‐phase reservoir simulator was used to examine depressurization and water desaturation processes in the vicinity of an extractive wellfield within this fine‐scale model. A single‐phase simulator was then employed so that depressurization errors incurred by neglecting near‐well, dual‐phase flow could be explored. Two models with fewer lithological details were then constructed in order to examine the nature of depressurization errors incurred by upscaling and to assess the interaction of the upscaling process with the requirement for adequate representation of near‐source, dual‐phase processes. 相似文献
17.
R.E. Jackson A.W. Gorody B. Mayer J.W. Roy M.C. Ryan D.R. Van Stempvoort 《Ground water》2013,51(4):488-510
Unconventional natural gas extraction from tight sandstones, shales, and some coal‐beds is typically accomplished by horizontal drilling and hydraulic fracturing that is necessary for economic development of these new hydrocarbon resources. Concerns have been raised regarding the potential for contamination of shallow groundwater by stray gases, formation waters, and fracturing chemicals associated with unconventional gas exploration. A lack of sound scientific hydrogeological field observations and a scarcity of published peer‐reviewed articles on the effects of both conventional and unconventional oil and gas activities on shallow groundwater make it difficult to address these issues. Here, we discuss several case studies related to both conventional and unconventional oil and gas activities illustrating how under some circumstances stray or fugitive gas from deep gas‐rich formations has migrated from the subsurface into shallow aquifers and how it has affected groundwater quality. Examples include impacts of uncemented well annuli in areas of historic drilling operations, effects related to poor cement bonding in both new and old hydrocarbon wells, and ineffective cementing practices. We also summarize studies describing how structural features influence the role of natural and induced fractures as contaminant fluid migration pathways. On the basis of these studies, we identify two areas where field‐focused research is urgently needed to fill current science gaps related to unconventional gas extraction: (1) baseline geochemical mapping (with time series sampling from a sufficient network of groundwater monitoring wells) and (2) field testing of potential mechanisms and pathways by which hydrocarbon gases, reservoir fluids, and fracturing chemicals might potentially invade and contaminate useable groundwater. 相似文献
18.
In this study, we experimentally established the relationship between physical properties, vitrinite reflectance, and microstructure of coal, Taiyuan Formation, Qinshui Basin, China using representative coal samples collected from three different mines via the rock mechanics testing system (MTS). We analyzed the organic macerals, vitrinite reflectance, and microstructure of 11 coal samples using petrography and scanning electron microscopy (SEM). The experimental results suggest that (1) the elastic parameters can be described by linear equations, (2) both P-and S-wave velocities display anisotropy, (3) the anisotropy negatively correlates with vitrinite reflectance, and (4) the acoustic velocities and Young’s modulus are negatively correlated with the volume of micropores. The derived empirical equations can be used in the forward modeling and seismic inversion of physical properties of coal for improving the coal-bed methane (CBM) reservoir characterization. 相似文献
19.
为了利用煤镜质组反射率推断豫北构造应力场，基于构造应力是造成镜质组反射率各向异性（VRA）的主要控制因素，对在豫北焦作、安阳、鹤壁三个矿区井下取的定向煤样品进行了室内显微镜下反射率测试，对测试数据按有关公式进行计算后就得出了由最大反射率值、中间反射率值、最小反射率值为轴组成的镜质组反射率椭球体（VRI）.结果表明，研究区煤样显示二轴晶正光性，它们经过了强烈的构造变形，研究区煤样镜质组反射率各向异性是由构造应力所引起；由镜质组反射率椭球体（VRI）得出的豫北构造应力场与钻探、节理统计、河南省区域构造应力场分析等方法得出的应力场基本上是吻合的，但也有一定的区别，主要体现在应力场到安阳、鹤壁矿区后发生了向左的偏转.总之，利用煤镜质组反射率各向异性推断构造应力场的方法是可行的、是有效的. 相似文献
20.
Damage to the top of coal seams, caused by incorrect blast stand-off distances, results in coal losses of up to 10–15% to the Australian open cut coal mining operations. This is a serious issue to be addressed. Here we propose to use a new forward-looking imaging technique based on the borehole radar technology to predict the coal seam top in real time while drilling blast holes. This is achieved by coupling the conventional borehole radar waves on to a steel drill rod to induce a guided wave along the axial drill rod. The drill rod ahead of the borehole radar behaves as a forward-looking antenna for the guided waves. Both numerical modelling and field trials simulating a drill rod as an antenna are used to investigate the feasibility of the proposed technique for prediction of the coal top under typical open cut environments. Numerical modelling demonstrated that conductivity of the overburden is the most important factor affecting our ability to see coal seams ahead of the drill bit, the guided borehole radar waves could be used for top coal prediction and a theoretical prediction error less than 10 cm and a forward-looking capability of 4–6 m can be achieved. Field trials at Australian open cut coal mines also demonstrated that guided borehole radar waves can be observed and used for prediction of coal top ahead of drill bit during blast-hole drilling in resistive, open cut environments (the average resistivity should be higher than 75 Ωm). 相似文献