吐哈盆地沙尔湖地区煤层气钻完井适用技术探讨

在剖析美国圣胡安盆地煤层气空气钻井、裸眼洞穴完井技术及优势的基础上,确定了低煤阶煤层气钻井及裸眼洞穴完井的煤储层条件等,并以吐哈盆地沙尔湖地区低煤阶煤层气为主要研究对象,利用类比法及地质统计法,具体分析了吐哈盆地沙尔湖地区的煤储层厚度、含气量、渗透率、井壁稳定性及储层压力条件等．研究表明,沙尔湖地区煤层厚度大,储层物性好,井壁稳定性好,可采用低成本空气钻井及裸眼完井技术提高钻井效率,保护煤储层,提高煤层气采收率．     

左权高家庄煤矿煤层气开发前景

以左权县高家庄煤矿煤层气普查区内3#和15#煤层为研究对象,研究了该区煤层特征和煤级变化特征,并对煤储层含气性及储层特征进行了分析。结果表明,该区含煤地层地质条件简单,可采煤层厚度大、分布稳定;3、15#为贫煤～无烟煤,变质程度高,煤的变质程度自上而下随煤层层位的降低逐渐增大,煤层生气量大,煤的吸附能力较强;煤层含气量、渗透率等主要储层参数值较高,煤层含气饱和度接近饱和。     

Gas seepage equation of deep mined coal seams and its application

In order to obtain a gas seepage law of deep mined coal seams, according to the properties of eoalbed methane seepage in in-situ stress and geothermal temperature fields, the gas seepage equation of deep mined coal seams with the Klinkenberg effect was obtained by confirming the coalbed methane permeability in in-situ stress and geothermal temperature fields. Aimed at the condition in which the coal seams have or do not have an outcrop and outlet on the ground, the application of the gas seepage equation of deep mined coal seams in in-situ stress and geothermal temperature fields on the gas pressure calculation of deep mined coal seams was investigated. The comparison between calculated and measured results indicates that the calculation method of gas pressure, based on the gas seepage equation of deep mined coal seams in in-situ stress and geothermal temperature fields can accurately be identical with the measured values and theoretically perfect the calculation method of gas pressure of deep mined coal seams.     

超高压水力割缝强化抽采瓦斯技术研究

水力割缝是一种重要的强化瓦斯抽采增透技术,现已开始在低透气性突出煤层应用。为了进一步考察其实际效果,选取新集二矿1煤组220112工作面底抽巷实施了100 MPa超高压水力割缝试验。试验结果表明:割缝后,瓦斯抽采纯量平均0.77 m3/min,是未割缝钻孔的瓦斯抽采纯量(0.34 m~3/min)的2.26倍;1煤层组瓦斯抽采钻孔抽采30、60天的抽采有效半径为5 m、7.5 m,极限抽采半径为8 m,相比水力冲孔、未割缝钻孔抽采有效半径显著增加,超高压水力割缝强化抽采瓦斯技术具有广泛的应用前景。     

Regional gas drainage techniques in Chinese coal mines

China’s rapid economic development has increased the demand for coal. These results in Chinese coal mines being extended to deeper levels. The eastern Chinese, more economical developed, regions have a long history of coal mining and many coal mines have now started deep mining at a depth from 800 to 1500 m. This increase in mining depth, geostresses, pressures, and gas content of the coal seam complicates geologic construction conditions. Lower permeability and softer coal contribute to increasing numbers of coal and gas outburst, and gas explosion, disasters. A search on effective methods of preventing gas disasters has been provided funds from the Chinese government since 1998. The National Engineering Research Center of Coal Gas Control and the Huainan and Huaibei Mining Group have conducted theoretical and experimental research on a regional gas extraction technology. The results included two important findings. First, grouped coal seams allow adoption of a method where a first, key protective layer is mined to protect upper and lower coal seams by increasing permeability from 400 to 3000 times. Desorption of gas and gas extraction in the protected coal seam of up to 60%, or more, may be achieved in this way. Second, a single seam may be protected by using a dense network of extraction boreholes consisting of cross and along-bed holes. Combined with this is increased use of water that increases extraction of coal seam gas by up to 50%. Engineering practice showed that regional gas drainage technology eliminates regional coal and gas outburst and also enables mining under low gas conditions. These research results have been adopted into the national safety codes of production technology. This paper systematically introduces the principles of the technology, the engineering methods and techniques, and the parameters of regional gas drainage. Engineering applications are discussed.     

Evaluation of gas production from multiple coal seams: A simulation study and economics

Gas production from multiple coal seams has become common practice in many coal basins around the world. Although gas production rates are typically enhanced, the economic viability of such practice is not well studied. In order to investigate the technical and economic feasibility of multiple coal seams production, reservoir simulation integrated with economics modelling was performed to study the effect of important reservoir properties of the secondary coal seam on production and economic performance using both vertical and horizontal wells. The results demonstrated that multiple seam gas production of using both vertical and horizontal wells have competitive advantage over single layer production under most scenarios. Gas content and permeability of the secondary coal seam are the most important reservoir properties that have impact on the economic feasibility of multiple seam gas production. The comparison of vertical well and horizontal well performance showed that horizontal well is more economically attractive for both single well and gas field. Moreover, wellhead price is the most sensitive to the economic performance, followed by operating costs and government subsidy. Although the results of reservoir simulation combined with economic analysis are subject to assumptions, multiple seam gas production is more likely to maintain profitability compared with single layer production.     

Mechanism of CO2 enhanced CBM recovery in China: a review

Permeability of coal reservoirs in China is in general low. Injection of CO2 into coal seams is one of the potential ap-proaches for enhancing coalbed methane (CBM) production. The feasibility of this technology has been investigated in China since the 1990s. Advances in mechanism of CO2 enhanced CBM recovery (CO2-ECBM) in China are reviewed in light of certain aspects,such as the competitive multi-component gas adsorption, sorption-induced coal swelling/shrinkage and its potential effect on CBM production and numerical simulation for CO2-ECBM recovery. Newer investigations for improving the technology are discussed. It is suggested that a comprehensive feasibility demonstration in terms of geology, technology, economics and environment-carrying capacity is necessary for a successful application of the technology for CBM recovery in China. The demonstration should be car-ried out after more investigations into such facets as the control of coal components and structure to a competitive multi-component-gas adsorption, the behavior and essence of super-critical adsorption by coal of gas, environmental and safe feasi-bility of coal mining after CO2 injection and more extensive pilot tests for CO2-ECBM recovery.     

高瓦斯煤层群保护层开采卸压效果数值模拟

为合理选择保护层,针对高瓦斯突出煤层群安全开采问题,分析了保护层开采的保护作用机理,即保护层开采可对被保护层起到卸压增透作用,改善被保护层的瓦斯抽放效果是解决煤与瓦斯突出问题及瓦斯灾害的重要技术手段;卸压对煤与瓦斯突出及瓦斯问题的解决具有决定作用.针对某矿高瓦斯突出煤层群生产地质条件,采用FLAC3D数值软件模拟2个非突出煤层作为保护层开采时的卸压效果,并对其进行了分析比较,研究结果可为保护层的合理选择提供参考依据.     

Guiding-controlling technology of coal seam hydraulic fracturing fractures extension

Aiming at the uncontrollable problem of extension direction of coal seam hydraulic fracturing, this study analyzed the course of fractures variation around the boreholes in process of hydraulic fracturing, and carried out the numerical simulations to investigate the effect of artificial predetermined fractures on stress distribution around fractured holes. The simulation results show that partial coal mass occurs relatively strong shear failure and forms weak surfaces, and then fractures extended along the desired direction while predetermined fractures changed stress distribution. Directional fracturing makes the fractures link up and the pressure on coal mass is relieved within fractured regions. Combining deep hole controlling blasting with hydraulic fracturing was proposed to realize the extension guiding-controlling technology of coal seam fractures. Industrial experiments prove that this technology can avoid local stress concentration and dramatically widen the pressure relief scope of deep hole controlling blasting. The permeability of fractured coal seam increased significantly, and gas extraction was greatly improved. Besides, regional pressure relief and permeability increase was achieved in this study.     

Coal and rock fissure evolution and distribution characteristics of multi-seam mining

Henan Pingdingshan No.10 mine is prone to both coal and gas outbursts. The E_9–10 coal seam is the main coal-producing seam but has poor quality ventilation, thus making it relatively difficult for gas extraction. The F₁₅ coal seam, at its lower section, is not prone to coal and gas outbursts. The average seam separation distance of 150 m is greater than the upper limit for underside protective seam mining. Based on borehole imaging technology for field exploration of coal and rock fracture characteristics and discrete element numerical simulation, we have studied the evolution laws and distribution characteristics of the coal and rock fissure field between these two coal seams. By analysis of the influential effect of group F coal mining on the E_9–10 coal seam, we have shown that a number of small fissures also develop in the area some 150 m above the overlying strata. The width and number of the fissures also increase with the extent of mining activity. Most of the fissures develop at a low angle or even parallel to the strata. The results show that the mining of the F₁₅ coal seam has the effect of improving the permeability of the E_9–10 coal seam.     

上邻近层残存瓦斯压力的理论与应用

本文根据岩体力学与采场覆岩移动原理,探讨了煤层原始瓦斯压力、采场开采技术参数、覆岩岩性、煤层倾角等对上邻近层残存瓦斯压力的影响。指出了采场覆岩法向裂缝宽度是影响上邻近层残存瓦斯压力的关键因素,推导出了能够反映上述影响的上邻近层残存瓦斯压力计算公式。经过实际应用证明比已有的其它公式理论性强、精度高。据此还可以计算上邻近层瓦斯涌出量、可抽放瓦斯量及考察解放层的解放效果等。     

Progress on the hydraulic measures for grid slotting and fracking to enhance coal seam permeability

A method of hydraulic grid slotting and hydraulic fracturing was proposed to enhance the permeability of low permeability coal seam in China. Micro-structural development and strength characteristics of coal were analysed to set up the failure criterion of coal containing water and gas, which could describe the destruction rule of coal containing gas under the hydraulic measures more accurately. Based on the theory of transient flow and fluid grid, the numerical calculation model of turbulence formed by high pressure oscillating water jet was used. With the high speed photography test, dynamic evolution and pulsation characteristics of water jet water analysed which laid a foundation for mechanism analysis of rock damage under water jet. Wave equation of oscillating water jet slotting was established and the mechanism of coal damage by the impact stress wave under oscillation jet was revealed. These provide a new method to study the mechanism of porosity and crack damage under high pressure jet.Fracture criterion by jet slotting was established and mechanism of crack development controlled by crack zone between slots was found. The fractures were induced to extend along pre-set direction,instead of being controlled by original stress field. The model of gas migration through coal seams after the hydraulic measures for grid slotting and fracking was established. The key technology and equipment for grid slotting and fracking with high-pressure oscillating jet were developed and applied to coal mines in Chongqing and Henan in China. The results show that the gas permeability of coal seam is enhanced by three orders of magnitude, efficiency of roadway excavation and mining is improved by more than 57%and the cost of gas control is reduced by 50%.     

煤层群煤与瓦斯安全高效共采体系及应用

提出了高瓦斯煤层群煤与瓦斯安全高效共采的概念：在煤层群开采条件下，首先开采瓦斯含量低、无突出危险的首采煤层，利用其采动影响使处在其上部和下部的煤层卸压，煤层透气性成百倍地增加，从而形成高效的瓦斯抽采条件．同时进行的卸压瓦斯高效抽采既解决了由卸压煤层向首采煤层涌出瓦斯问题，保障首采煤层实现安全高效开采，又大幅度地降低了卸压煤层的瓦斯含量，消除了煤与瓦斯突出危险性，为在卸压煤层内实施快速掘进与高效采煤方法提供了安全保障，从而实现了瓦斯与煤炭两种资源的安全高效共采．文中介绍了针对不同卸压瓦斯流动特点的近程、中程和远程卸压瓦斯抽采方法及工程应用实践，最后对高瓦斯煤层群煤与瓦斯安全高效共采体系的应用前景进行了分析．     

Prediction of geotemperatures in coal-bearing strata and implications for coal bed methane accumulation in the Bide-Santang basin,western Guizhou,China

The geothermal fields of coal-bearing strata have become a key topic in geological research into coal and coal bed methane(CBM). Based on temperature data from 135 boreholes that penetrate the Upper Permian coal-bearing strata in the Bide-Santang basin, western Guizhou, the precisions of geothermal predictions made using a geothermal gradient model and a gray sequence GM(1,1) model are analyzed and compared. The results indicate that the gray sequence GM(1,1) model is more appropriate for the prediction of geothermal fields. The GM(1,1) model is used to predict the geothermal field at three levels with depths of 500, 1000, and 1500 m, as well as within the No. 6, No. 16, and No. 27 coal seams. The results indicate that the geotemperatures of the 500 m depth level are between 21.0 and 30.0 °C, indicating no heat damage; the geotemperatures of the 1000 m depth level are between 29.4 and 44.7 °C,indicating the first level of heat damage; and the geotemperatures of the 1500 m depth level are between35.6 and 63.4 °C, indicating the second level of heat damage. The CBM contents are positively correlated with the geotemperatures of the coal seams. The target area for CBM development is identified.     

Principle and engineering application of pressure relief gas drainage in low permeability outburst coal seam

With the increase in mining depth, the danger of coal and gas outbursts increases. In order to drain coal gas effectively and to eliminate the risk of coal and gas outbursts, we used a specific number of penetration boreholes for draining of pressure relief gas. Based on the principle of overlying strata movement, deformation and pressure relief, a good effect of gas drainage was obtained. The practice in the Panyi coal mine has shown that, after mining the Cllcoal seam as the protective layer, the relative expansion deformation value of the protected layer C13 reached 2.63%, The permeability coefficient increased 2880 times, the gas drainage rate of the C13 coal seam increased to more than 60%, the amount of gas was reduced from 13.0 to 5.2 m3/t and the gas pressure declined from 4.4 to 0.4 MPa, which caused the danger the outbursts in the coal seams to be eliminated. The result was that we achieved a safe and highly efficient mining operation of the C 13 coal seam.     

新安煤田正村井田二叠系煤岩层对比

煤岩层对比工作对于煤田地质勘探、储量计算以及煤炭资源的开发利用都具有极其重要的意义,它是研究含煤地层层序、煤田地质构造、煤层厚度变化、煤层赋存规律的基础工作,是煤田地质勘探工作的主要任务之一.本文采用标志层法、层间距法、煤质特征分析法和测井响应,对本区的主要含煤层段二叠系山西组、上下石盒子组进行了系统的划分和对比,准确确定了主要可采煤层二1煤层和局部可采煤层二2煤层、七2煤层的层位,并对这些煤层的空间展布进行了对比,这一煤岩层对比方案已为煤田勘探和煤矿开采的揭露所证实.     

煤层气压裂技术研究

煤层气与常规天然气有较大差异,采用压裂施工可达到煤层气开发的理想效果。根据煤层气的特性,在施工中应注意压裂液、煤粉、压实性等因素所造成的伤害。     

水力压裂煤储层卸压增透技术的适用性分析

水力压裂煤储层技术在不同矿区应用过程中受不同煤体破坏类型和围压条件的影响,其卸压增透效果差异性较大.为了明确该项技术的井下适用条件,优化其实施工艺,切实提高煤层瓦斯抽采率,通过分析和总结河南省不同矿区实际煤储层的水力压裂试验数据资料发现,水力压裂增透技术对Ⅰ,Ⅱ破坏类型煤体的增透效果比较明显,而在Ⅲ,Ⅳ,Ⅴ破坏类型的松软煤层中适用性则具有一定的局限性,具有压裂范围小、裂缝闭合快、增透效果不明显等特点.所得结论对于选择合理的水力压裂储层并进一步优化完善高效预抽本煤层瓦斯技术具有一定的指导意义.     

Estimation of correction coefficients for measured coal bed methane contents

Improving the accuracy and precision of coal bed methane (CBM) estimates requires correction of older data from older coal exploration surveys to newer standards. Three methods, the depth gradient method, the contour aerial weight method, and the well-point aerial weight method, were used to estimate the correction coefficient required to predict CBM gas content from coal exploration data. The data from the Nos. 3 and 15 coal seams provided the coal exploration data while the CBM exploration stages within the X1 well block located in the southern part of the Qinshui Basin provided the data obtained using newer standards. The results show the correction coefficients obtained from the two aerial weight methods are similar in value but lower than the one obtained from the depth gradient method. The three methods provide similar results for the Nos. 3 and 15 seams in that the correction factor is lower for the former seam. The results from the depth gradient method taken together with the coal seam burial depth and the coal rank suggest that variations in the correction factor increase linearly along with coal seam burial depth and coal rank. The correlation obtained can be applied to exploration and the evaluation of coal bed gas resources located in coalfields.     

煤矿深部开采煤层气含量计算的解析法

针对矿井深部煤层中地温和地应力梯度对煤的孔隙率和煤层渗透率的影响以及煤的吸附特性参数受温度影响变化的特点 ,在矿井深部煤层气压力解析算法的基础上 ,提出了考虑地温和地应力梯度影响的煤层气含量计算的新方法 .现场实测煤层气压力和理论计算的煤层气压力及煤层气含量的对比分析表明 ,该计算方法能较准确地反映现场实测结果 ,从理论上进一步完善了矿井深部煤层煤层气含量的计算方法 ,并对其分布规律的预测具有重要理论价值 .