Reservoir reconstruction technologies for coalbed methane recovery in deep and multiple seams

Multiple coal seams widely develop in the deep Chinese coal-bearing strata. Ground in situ stress and coal seam gas pressure increase continuously with the increase of the mining depth, and coal and gas outburst disasters become increasingly severe. When the coal is very deep, the gas content and pressure will elevate and thus coal seams tends to outburst-prone seams. The safety and economics of exploited firstmined coal seams are tremendously restricted. Meanwhile, the multiple seams occurrence conditions resulted in different methane pressure systems in the coal-bearing strata, which made the reservoir reconstruction of coal difficult. Given the characteristics of low saturation, low permeability, strong anisotropy and soft coal of Chinese coal seams, a single hydraulic fracturing surface well for reservoir reconstruction to pre-drain the coalbed methane(CBM) of multiple seams concurrently under the different gas pressure systems has not yet gained any breakthroughs. Based on analyses of the main features of deep CBM reservoirs in China, current gas control methods and the existing challenges in deep and multiple seams, we proposed a new technology for deep CBM reservoir reconstruction to realize simultaneous high-efficiency coal mining and gas extraction. In particular, we determined the first-mined seam according to the principles of effectiveness and economics, and used hydraulic fracturing surface well to reconstruct the first-mined seam which enlarges the selection range of the first-mined seam. During the process of mining first-mined seam, adjacent coal seams could be reconstructed under the mining effect which promoted high-efficiency pressure relief gas extraction by using spatial and comprehensive gas drainage methods(combination of underground and ground CBM extraction methods). A typical integrated reservoir reconstruction technology, ‘‘One well for triple use", was detailed introduced and successfully applied in the Luling coal mine. The application showed that the proposed technology could effectively promote coal mining safety and simultaneously high-efficiency gas extraction.     

自进式水射流钻进技术在煤层气开发中的应用

自进式高压水射流钻进技术是在煤层气勘探井内布置机械或水力扩孔装置,对准选定的煤层进行扩孔后,下入特制的转向工具,在300mm的曲率半径内实现由垂直转向水平进行钻进.自进式钻头由旋转喷嘴、钻屑整合装置及推力提供装置等组成,其带动为其提供高压水动力的特制胶管向前连续钻进.高压水通过高压胶管为自进式钻头提供动力,进行钻进、推动及排渣.该技术可以在同一煤层气勘探井内的不同煤层内完成多个水平钻孔,这些径向水平钻孔可以沟通新的瓦斯流动通道,从而大幅度地提高煤层气产量.     

自进式水射流钻进技术在煤层气开发中的应用

自进式高压水射流钻进技术是在煤层气勘探井内布置机械或水力扩孔装置,对准选定的煤层进行扩孔后,下入特制的转向工具,在300mm的曲率半径内实现由垂直转向水平进行钻进.自进式钻头由旋转喷嘴、钻屑整合装置及推力提供装置等组成,其带动为其提供高压水动力的特制胶管向前连续钻进.高压水通过高压胶管为自进式钻头提供动力,进行钻进、推动及排渣.该技术可以在同一煤层气勘探井内的不同煤层内完成多个水平钻孔,这些径向水平钻孔可以沟通新的瓦斯流动通道,从而大幅度地提高煤层气产量.     

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.     

Prediction of coal structure using particle size characteristics of coalbed methane well cuttings

Severely deformed coal seams barely deliver satisfactory gas production. This research was undertaken to develop a new method to predict the positions of deformed coals for a horizontal CBM well. Firstly, the drilling cuttings of different structure coals were collected from a coal mine and compared. In light of the varying cuttings characteristics for different structure coals, the coal structure of the horizontally drilled coal seam was predicted. And the feasibility of this prediction method was discussed. The result shows that exogenetic fractures have an important influence on the deformation of coal seams. The hardness coefficient of coal decreases with the deformation degree in the order of primary structural, cataclastic and fragmented coal. And the expanding-ratio of gas drainage holes and the average particle size of cuttings increase with the increase of the deformation degree. The particle size distribution of coal cuttings for the three types of coals is distinctive from each other. Based on the particle size distribution of cuttings from X-2 well in a coal seam, six sections of fragmented coal which are unsuitable for perforating are predicted. This method may benefit the optimization of perforation and fracturing of a horizontal CBM well in the study area.     

朱仙庄煤矿Ⅱ831工作面区域条带消突技术研究

为了解决无保护层的煤层区域瓦斯治理的难点,分析了朱仙庄矿煤层及瓦斯赋存状况,提出了在不具备开采保护层的区域内,采用底板穿层钻孔区域防突措施,对掘进巷道进行打钻预抽。在详细介绍底板穿层钻孔的布置、抽采和计量方式的同时,通过理论计算和实际掘进作业两个方面,共同验证了底板穿层钻孔条带预抽区域措施可行性和可靠性,进而为穿层钻孔预抽区域措施在矿区的推广应用提供了范例。     

Exploitation technology of pressure relief coalbed methane in vertical surface wells in the Huainan coal mining area

Exploitation technology of pressure relief coalbed methane in vertical surface wells is a new method for exploration of gas and coalbed methane exploitation in mining areas with high concentrations of gas, where tectonic coal developed. Studies on vertical surface well technology in the Huainan Coal Mining area play a role in demonstration in the use of clean, new energy re-sources, preventing and reducing coal mine gas accidents and protecting the environment. Based on the practice of gas drainage engineering of pressure relief coalbed methane in vertical surface wells and combined with relative geological and exploration en-gineering theories, the design principles of design and structure of wells of pressure relief coaibed methane in vertical surface wells are studied. The effects of extraction and their causes are discussed and the impact of geological conditions on gas production of the vertical surface wells are analyzed. The results indicate that in mining areas with high concentrations of gas, where tectonic coal developed, a success rate of pressure relief coalbed methane in surface vertical well is high and single well production usually great. But deformation due to coal exploitation could damage boreholes and cause breaks in the connection between aquifers and bore-holes, which could induce a decrease, even a complete halt in gas production of a single well. The design of well site location and wellbore configuration are the key for technology. The development of the geological conditions for coalbed methane have a sig-nificant effect on gas production of coalbed methane wells.     

海上低渗油田产能评价与提产措施优选——以西江油田为例

鉴于开发特殊性,海上低渗油田的提产措施优选与实践较为缺乏,导致其经济高效开发面临着严峻挑战。目标区块属于典型海上低渗油藏,受非线性渗流、储层污染、强非均质性等不利因素制约,表现出产能低、递减率快、含水率高等特征。结合多孔介质渗流理论与油藏启动压力梯度,基于多种开发方式下产能数学模型,立足于目标区块实际地质情况,对不同开发方式的提产效果进行预测和比较,为提产措施优选、合理开发方案制定与生产部署提供有力支撑。结果表明,与现有生产数据对比,产能方程的符合率达到85%。水平井相对于直井的开发优势会随着层厚的增加而减弱,当层厚超过45 m时,二者产能倍比小于5。薄层开发时,建议15 mD以下采用分段压裂水平井,反之使用多分支井。研究结果将为海上低渗油田提产措施优选、开发方案调整提供理论指导与实践参考。     

A numerical investigation of gas flow behavior in two-layered coal seams considering interlayer interference and heterogeneity

Multiple-seam gas coproduction is a technology with potential to achieve economic targets. Physical experiments could replicate gas flow dynamics in two seams. In this study, numerical simulation was conducted based on physical experiments. Through calibration, the simulated results agreed with the experimental results. Three findings were obtained. First, the pressure distribution intrinsically depends on the depressurization effectiveness in each coal seam. The gas pressure difference and interval distance influence the pressure distribution by inhibiting depressurization in the top seams and bottom seams, respectively. Second, the production contribution shows a logarithmic relationship with the permeability ratio. The range of the production contribution difference grows from 11.24% to 99.99% when the permeability ratio increases 50 times. By comparison, reservoir pressure has a limited influence, with a maximum of 13.64%. Third, the interlayer interference of the top seams and bottom seams can be intensified by the reservoir pressure difference and the interval distance, respectively. The proposed model has been calibrated and verified and can be directly applied to engineering, serving as a reference for reservoir combination optimization. In summary, coal seams with a permeability ratio within 10, reservoir pressure difference within 1.50 MPa, and interval distances within 50 m are recommended to coproduce together.     

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。     

Fissure evolution and evaluation of pressure-relief gas drainage in the exploitation of super-remote protected seams

Based on nonlinearity contact theory and the geological structure of the Xieqiao Coal Mine in the newly developed Huainan coal field, rock movements, mining fissures and deformation of overlying strata were simulated by using the interface unit of FLAC3D to evaluate the pressure-relief gas drainage in the exploitation of super-remote protected seams. The simulation indicates that the height of the water flowing fractured zone is 54 m in the overlying strata above the protective layer. The maximum relative swelling deformation of the C 13 coal seam is 0.232%,while the mining height is 3.0 m and the distance from the B8 roof to the C13 floor is 129 m, which provides good agreement with a similar experiment and in situ results. The feasibility of exploitation of a super-remote protective coal seam and the performance of the pressure-relief gas drainage in a super-remote protected layer are evaluated by comparisons with practice projects. It demonstrates that the relieved gas in the super-remote protected layers could be better drained and it is feasible to exploit the B8 coal seam before the C13 super-remote protected coal seam. The method is applicable for the study of rock movements, mining fissures and deformation of the overburden, using the interface unit to analyze the contact problems in coal mines.     

巷道与上部煤柱边缘间水平距离X的选择

巷道与上部煤柱边缘之间的水平距离X,是底板岩巷和邻近煤层巷道布置的重要参数。本文根据矿山压力的研究成果,阐述了上部煤层采动状况,巷道围岩性质,巷道与上部煤层之间的垂距Z、以及巷道与上部煤柱边缘间水平距离X间的定量关系,为正确选择X值及巷道与上部煤层回采空间的相对位置关系提供了主要依据。     

地面群孔瓦斯抽采技术应用研究

为保证新集一矿突出煤层13-1煤北中央采区的安全开采,先后开采131103、131105等11-2煤层工作面作为保护层。首先在上述两个工作面共布置了6个地面钻孔,建立了地面群孔瓦斯抽采系统,预抽采动区被保护层13-1煤瓦斯。接下来对地面钻孔抽采瓦斯参数进行了考察,主要包括基于示踪技术考察了131105工作面采动卸压地面钻孔走向及倾向瓦斯抽采半径,统计分析被保护层瓦斯抽采率,同时就地面群孔与井下底板巷穿层钻孔瓦斯抽采两种方法进行了抽采率、工程费用等方面的对比。研究结果表明：新集一矿的地层条件下地面钻孔抽采煤层卸压瓦斯沿煤层倾向和走向的抽采半径分别不小于160m和240m;采动区地面群孔瓦斯抽采率达35%以上;地面钻孔相对比井下底板巷,在抽采瓦斯方面具有技术上可靠、安全、经济等优点。     

水平井开发效果影响因素研究——以大庆外围油藏为例

通过统计大庆外围特低丰度薄层油藏14个区块、90口水平井、245口直井的地质、油藏工程及生产历史资料数据,利用多因素综合分类分析法,系统分析水平井开发效果与各种地质及工程因素之间的关系。研究表明,地质影响因素主要为砂体类型、注采连通关系及油水同层发育程度,开发调整措施的适应性是影响水平井生产效果的主要因素。     

Interlayer interference mechanism of multi-seam drainage in a CBM well:An example from Zhucang syncline

Based on the characteristics of the strong volatility of physical property in vertical direction, high gas content, high resource abundance and large exploitation potentiality of coal reservoir in Bide-Santang basin of Zhina coal field, we study the generation mechanism of interlayer interference, propagation rules of reservoir pressure drop and influencing factors of gas productivity in CBM multi-seam drainage in the paper. On the basis of the actual production data of X-2 well of Zhucang syncline in Bide-Santang basin,by simulating the gas production process of a CBM well under the condition of multiple seam with COMET3 numerical simulation software, we analyze the influencing factors of gas productivity during the process of multi-seam drainage, and illuminate the interlayer interference mechanism of multiseam drainage. The results show that permeability, reservoir pressure gradient, critical desorption pressure and fluid supply capacity of stratum have great influence on gas productivity of multi-seam drainage while coal thickness has little influence on it. Permeability, reservoir pressure gradient and fluid supply capacity of stratum affect the propagation velocity of reservoir pressure drop and thereby affect the final gas productivity. Moreover, the influence of critical desorption pressure on gas productivity of multiseam drainage is reflected in the gas breakthrough time and effective desorption area.     

Gas emission quantity prediction and drainage technology of steeply inclined and extremely thick coal seams

Gas emissions of workfaces in steeply inclined and extremely thick coal seams differ from those under normal geological conditions, which usually feature a high gas concentration and a large emission quantity. This study took the Wudong coal mine in Xinjiang province of China as a typical case. The gas occurrence of the coal seam and the pressure-relief range of the surrounding rock(coal) were studied by experiments and numerical simulations. Then, a new method to calculate the gas emission quantity for this special geological condition was provided. Based on the calculated quantity, a further gas drainage plan, as well as the evaluation of it with field drainage data, was finally given. The results are important for engineers to reasonably plan the gas drainage boreholes of steeply inclined and extremely thick coal seams.     

超低渗透油藏水平井二次压裂技术研究与应用

华庆X油藏为典型的超低渗油藏,为了提高单井产量,采用以水平井为主的开发方式。但随着开发时间的延长和生产过程中压力、温度等环境条件的改变,部分水平井单井产量递减快,开发效益逐渐变差,急需要通过二次压裂恢复或提高单井产量。目前,国内水平井二次压裂尚处于起步阶段,为此,在通过对国外水平井二次压裂技术分析的基础上,结合华庆X超低渗油藏储层特征和水平井低产原因,开展了二次压裂增产潜力分析、工艺优化及配套管柱研发,形成了以“体积复压为主、加密布缝为辅”的老井二次压裂工艺技术。现场试验表明,6口井的增产效果明显,为超低渗改造水平井提高单井产量提供了技术借鉴。     

川西致密气藏水平井增产与稳产技术应用研究

川西致密储层垂向渗透率远小于水平渗透率,水平井自然产能与直井相比无明显优势,水平井需要采取增产改造措施.为此川西气田开展了包括笼统酸化、笼统压裂、分段压裂等水平井储层增产改造措施.同时为解决井简积液难题,开展了水平井泡沫排水、车载压缩机气举排水增产工艺探索     

长水平段碳酸盐岩弱气显示录井解释实践——以建南构造建35-5井为例

长水平段弱气显示储层的录井精细解释评价是录井解释人员致力解决的难题。利用钻时比值储层判别图版、钻时比值-烃对比系数交会图、储层孔隙度-含烃(水)饱和度交会图和多参数雷达图与云模型评价方法、产能预测模型等碳酸盐岩弱气显示录井识别与定量解释评价技术,在建南气田产能建设重点井-建35-5井进行了首次应用试验,并取得3项新认识:钻井液液柱与地层间压差过大、储层致密及井漏是造成弱显示的主要原因;对长水平段非均质性气测异常显示层,选择多个有代表性的局部井段进行解释评价,解释结果可代表整段解释结论;碳酸盐岩弱气显示录井识别与定量解释评价技术适用于长水平段弱气显示解释评价。     

岱庄煤矿近距离煤层微量元素赋存特征研究

煤矿开采的主要对象是煤层,煤层对比清楚与否,直接影响煤矿安全生产和经济效益.岱庄煤矿3上1、3上及3下煤层相距较近,区分不明显,容易造成采掘巷道串层现象.对岱庄煤矿可采煤层中微量元素赋存特征开展研究,掌握不同煤层中微量元素的赋存状况,可很好地判断岱庄煤矿煤层层位,能有效避免地质构造等因素造成近距离煤层采掘串层现象,对合理设计开采方案和采掘进度有重大意义,从而为岱庄煤矿安全、高效生产提供科学依据和保障.