【作者】 路桂英；

【导师】 乌效鸣；

【作者基本信息】 中国地质大学 ， 地质工程， 2014， 博士

【摘要】 我国煤层气抽采率和利用率都较低,究其原因,一方面与我国煤层气资源“低压、低渗、低饱和度和非匀质性强”的特点有关;另一方面,虽然近年来我国引入了国外成功的煤层气抽采技术,但适合我国煤层气特点的煤层气抽采技术仍有待进一步研究。在此大环境下,煤层气抽采相关技术的提高具有重要意义。采掘衔接、采抽衔接的矛盾和抽采与生产抢地盘的矛盾是煤层气井下抽采方式存在的主要矛盾。加上密集钻孔的需要,就要求施工人员“高效”钻孔。“高效”体现在两个方面,即钻孔周期短和成孔正常率高。目前井下煤层气抽采孔的钻井一般采用欠平衡钻井,采用空气／雾化钻井方式,钻井周期大为缩短,满足工程需要。欠平衡钻井技术,可很好地稳定井壁,已是煤层气井最有前途的钻井方式,但在自身满足孔壁稳定方面有其限制条件。如果用气体钻井,井筒内的当量液柱压力近似为零,井壁稳定的条件是岩石的拉伸强度能够平衡地层的孔隙压力。如果岩石的拉伸强度大于地层的孔隙压力时,不会发生井壁拉伸崩落,否则会发生拉伸崩落,井壁坍塌。可见对于松散煤层段,欠平衡钻井技术本身无能为力。调研结果表明,采用欠平衡钻井技术在松散煤层段钻孔,成孔正常率一般较低,尤其是钻遇煤层松散段时,由于孔壁失稳,包括塌孔、吸钻、压钻、掉钻杆,引起钻孔不正常率有时甚至高于90%,可以用十钻九不正常来形容。解决孔壁失稳的主要措施是套管护壁和固壁浆液护壁。固壁浆液护壁的工艺流程一般包括注浆、退钻杆、清洗钻杆、候凝、扫孔等。其中采用一般固壁浆液,如水泥浆护壁,候凝时间可长达十几到几十小时。湖南省煤炭科学研究所采用拖动式下套管方式,有针对性地对煤孔缩径区段进行下套管护孔,获得了成功应用。但是此套装备中的套管护孔在煤层含有大量煤层气的情况下,很有可能使煤层气不易于释放而大量积累,在钻进中容易发生喷突,同时很难保证遇到煤层松散段时套管能及时地进行护壁,且目前研究的套管护壁方法中,护壁段只有一段,不利于长距离钻孔,因此在使用上也受到限制。在国家自然科学基金青年基金(41002046)的支持下,研究拟通过固壁浆液随钻注浆护壁的方式解决井下煤层气抽采钻井钻遇松散段可能遇到的孔壁失稳问题。固壁浆液“随钻注浆护壁”是边钻进边护壁的方式,也是一种分段注浆方式,即每次遇到松散煤层段,在钻进的过程中向其孔壁注入满足固壁要求的固壁浆液。随钻注浆护壁属于固壁浆液护壁,但在实施护壁的过程中不需要注浆后退钻杆、清洗钻杆和候凝等工序。这样,一方面可以减少退钻杆、清洗钻杆和候凝等工序所耗掉的大量工时；另一方面,还能维持固壁浆液灵活护壁的优势,从而实现多段按需护壁,更有利于满足井下煤层气抽采“高效”钻井的需求。随钻注浆护壁,是将固壁浆液定位定量地注入煤孔壁,短时固结并达到合适的固结强度。为此,解决井下煤层气抽采钻井随钻注浆护壁问题的关键技术主要有三个：(1)固壁浆液在煤孔壁的渗流规律,从理论上确定浆液的渗流深度,保证达到合理的固结层厚度,为后续固壁浆液和随钻注浆工具的研究提供理论依据；(2)前期流动性好,后期凝胶时间可控的固壁浆液,固结后达到一定的强度,且钻孔结束后,可以自行破胶,减少对煤层产气的影响；(3)执行随钻注浆的随钻注浆工具,该工具应能够感知司钻发出的“正常钻进”和“注浆”信号,并根据感知的信号完成相应的动作。研究着眼于井下煤层气抽采钻井钻遇松散段随钻注浆护壁关键技术的基本原理和基本方法,希望为井下煤层气抽采钻井随钻注浆护壁关键技术的研究找到突破口,为其深入和实用研究奠定基石,同时也为其它随钻注浆护壁技术的研究打下一定的基础。在课题研究的过程中,创新性研究主要体现在：采用随钻注浆护壁技术解决井下煤层气抽采钻井过程中由于孔壁失稳引起的孔内事故问题；将渗流注浆理论应用于研究井下煤层气抽采钻井钻遇松散段随钻注浆过程中浆液的流动规律；提出了适用于该使用环境的可行的水玻璃体系固壁浆液配方,确定了配方的流体性质,凝胶前属于胀塑性流体,到达开始凝胶时间后,若浆液处于动态则呈现宾汉姆流体特性；观测到其在煤层中具有自行破胶的性能；研制了随钻注浆性能测试试验装置,模拟随钻注浆过程,观测了随钻注浆浆液渗流规律；研制了随钻注浆工具,该工具采用纯机械式的信号识别和执行机构,有利于在煤矿井中使用。课题研究主要完成了如下工作：(一)对随钻注浆浆液扩散规律进行了基础研究(1)根据浆液的流变性能,做出合理假设,推导出固壁浆液渗透扩散偏微分方程,采用隐式差分格式将其离散,确定了渗透注浆的初始条件和边界条件,采用Thomas方法求解了方程组,并分析了差分格式解的收敛性和稳定性。(2)利用固壁浆液渗流的数学模型,结合研究区块的地质特征进行了工程实例计算,自编程求解了有限差分方程组,分析了不同注浆压力下浆液达到的渗透深度,给出了注浆压力的推荐值。工程实例编程计算结果表明：随着浆液扩散深度的增大,固壁浆液渗透压力逐渐减小,当浆液扩散深度小于5mm时,注浆压力减小的速率比较大；当注浆压力P0≤1MPa,d>5mm时,浆液扩散能力降低；浆液压力P0≥1MPa时,浆液扩散效果较好,能够达到护壁作用；P0≥1MPa后,浆液扩散效果相差不大,说明决定浆液渗透效果的关键因素是煤层的渗透率。(3)进行了渗流注浆效果的fluent模拟,分析了初始压力、浆液粘度、地质强度和地层的破碎程度对注浆效果的影响。Fluent模拟结果表明把煤岩看成多孔介质时,即使对于模数为2.9-3.0,粘度达到1.75Pa·s的纯水玻璃,煤层气原始压力达到0.5MPa时,达到的注浆深度仍超过30mm；对破坏煤和强烈破坏煤理论可达的注浆深度类似,粉碎煤和全粉煤可达的注浆深度类似。Fluent模拟注浆深度与推导的数学模型计算结果差异较大。(二)随钻注浆用固壁浆液(1)通过对研究配方进行总结、实验、对比、优选,确定了两种可用于随钻注浆钻井的固壁浆液配方。三醋酸甘油酯4%+20-40%水玻璃和1,4丁内酯4%+20-40%水玻璃,钻井过程中遇到孔内事故时,可添加PH值稳定剂延长初凝时间,遇到地层破碎程度高、渗透率低的工况时,需加入表面活性剂提高浆液的渗透率。(2)通过传统测试仪器和自行设计的随钻注浆性能测试试验装置,进行了所研究出随钻注浆固壁浆液配方的性能测试,包括固结强度、渗透深度、破胶性能等,并分析了该固壁浆液在随钻注浆中应用的优势和劣势。传统测试仪器实验结果表明：研究的配方45分钟固结煤强度较低,使用场合受到限制,但是该配方固结72小时后,沿煤粒边缘逐渐出现大量裂纹,具有自行破胶性能,有利于自行沟通产气通道。研制了用于观测渗透注浆规律的随钻注浆性能测试实验装置,研究了风压作用下注浆的可行性,包括风压作用能否将固壁浆液压入孔壁,压入深度是否满足随钻注浆护壁要求等。实验装置内置了土压力盒传感器,可以帮助观测不同深度处浆液压力随时间的变化情况。该装置外部设有观测窗口,可以直接通过肉眼观测到浆液的渗流过程。实验表明：1)风压作用下有助于浆液注入煤层；2)从土压力盒输出结果看,未加围压时,当加压0.5MPa时,浆液可以在五分钟内渗入60目的煤样,渗入深度可以超过100mm。实际使用过程中,根据现场经验,护壁深度达到10mm即可,因此采用风压将定量的固壁浆液压入煤层实现定点定量护壁是可行的。3)从土压力盒的输出结果还可以看出,煤颗粒较粗时,各分层对应的液体压力值增加,因此浆液可被注入的深度增加。4)土压力盒测得值在稳压状态下,比理想值小,可能是浆液在渗流过程中,阻力增加导致向下传递压力的能力降低。(3)通过实验测试了前述随钻注浆固壁浆液配方的动态粘度,确定了该固壁浆液的流体分类。通过参数分析,确定了使用该固壁浆液注浆的最佳注浆时间。结果表明该随钻注浆固壁浆液前20分钟呈现弱胀塑性流体状态,浆液粘度约2mPa-s,近似于水；20-40分钟粘度迅速增加；40-45分钟后,处于静态的固壁浆液凝胶,处于动态的固壁浆液未凝胶,呈现悬浮颗粒状,粘度不再发生变化。表明,不添加PH值稳定剂时,最优注浆时间在20分钟以内。在随钻注浆过程中,由于未注入煤孔壁的固壁浆液处于动态,因此不会在钻杆中发生凝胶,有利于在注浆结束后,利用正循环风将钻杆吹洗干净。(三)随钻注浆工具(1)通过分析井下工况和现有条件对钻具的必要要求,多方案比较,确定了随钻注浆工具的设计原理。借助循环介质一雾化风作为动力,采用纯机械式的信号传递方式。通过雾化空气反循环,传递“正常钻进”和“开始注浆”两种信号,并触发随钻注浆工具,实现工位切换,即：需要注浆时,先短时反循环,开启喷浆通道；然后正循环注浆,向破碎孔壁喷射满足固壁要求的固壁浆液；注浆完成,再次短时反循环,开启正常钻进通道,控制正常钻进开始,之后正循环正常钻进。(2)研究了采用纯机械方式感知和执行“正常钻进”和“注浆”信号的方法,即通过单向阀感知信号,通过棘轮换位机构执行信号的切换功能。(3)研究了雾化喷浆方式实施随钻注浆,设计了旋流式雾化喷嘴机构,该机构对所研究的固壁浆液和井下风压、泵压条件都有良好的适应性。(4)分析了随钻注浆工具套管的抗压和抗扭强度。通过抗压分析确定了套管厚度所能承受的外围和内部压力,确定了在30MPa压力作用下,当取外套筒厚度等同于钻杆厚度时,保证随钻注浆工具正常工作,径向最小间隙大于0.03mm,轴向最小间隙应大于0.2mm即可。在抗扭分析中分别采用普朗特应力函数法和材料力学方法进行对比分析,结果表明套筒小端为应力集中区,相比于材料力学的结果,弹性力学计算的结果更趋保守,两者计算结果的差异说明：针对非单连通区域给出的普朗特应力函数不够准确。(5)根据理论分析结果设计并加工出随钻注浆工具,对其进行了基本性能测试。实验结果表明反向风作用下可以控制随钻注浆工具随控制信号切换“注浆”和“正常钻进”通道,切换后通道畅通,因此所设计的钻具是满足随钻注浆使用要求的。(四)随钻注浆工艺初步研究了随钻注浆工艺,包括确定注浆参数的方法,随钻注浆工艺的执行过程。研究成果可以为井下煤层气抽采钻井随钻注浆护壁的深入和实用化研究奠定一定的基础,同时也可以作为其它随钻注浆护壁技术研究的基础。更多还原

【Abstract】 Chinese CBM extraction rate and utilization rate are all low, which, on the one hand, is related to the Chinese gas resources characteristics of low pressure, low permeability and low saturation characteristics, On the other hand, is because that methane extraction technologies adapting for Chinese coal bed characteristics are still needed to be further researched although in recent years the introduction of foreign successful coal bed methane extraction technology has played a role in some extent. So, coal seam gas extraction technologies improvement is of great significance. The contradiction between mining and tunneling, mining and extraction, and among mining, extraction and production area are the main contradiction of underground extraction method. Coupled with the need of intensive drilling, requires that workers can finish "efficient" drilling."Efficient" embodied in two aspects, namely, short drilling cycle and high pore forming rate. The current mine gas extraction hole drilling in loose coal seam generally adopt underbalanced drilling. Air/atomized drilling method usually be used, which greatly shortening drilling cycle, and meet engineering needs. Underbalanced drilling technology is the most promising way of drilling CBM hole for its good ability in maintaining the stability of hole wall. But that is limited. In using gas drilling, the equivalent fluid column pressure inside the wellbore approximate to zero. When the tensile strength of the formation is equal to the formation pore pressure, the borehole wall stability condition is that the tensile strength can balance the formation pore pressure. If the rock tensile strength is greater than the formation pore pressure, wall stretching caving would not happen, otherwise it will happen and hole collapse. That is why, for loose coal seam section, underbalanced drilling technology itself can not maintain hole wall stable. Research results show that in loose coal, using under-balanced drilling hole, abnormal hole ratio is generally high, especially when drilling in loose period, due to the instability of hole wall, including hole collapse, Sucked pipes, pressed pipes, dropped pipes, et al, which cause drilling problems make it sometimes even higher than90%, which can be described as drill ten nine is abnormal.The main measures to solve the instability of hole wall are casing and using mud. Using mud to protect wall process generally includes grouting, pulling out drill pipes, cleaning drill pipes, waiting for condensation and sweeping hole. For the general drilling fluid, such as cement slurry, the setting time can be up to a dozen or more hours. Coal science research institute of hunan province developed a drag type casing method, targeted for protecting the necking section, which has been applied successfully. But it is restrict in use for the three reasons followed. Firstly, when meet coal bed with too much gas, that may be increase gas accumulation and cause outburst finally. Secondly, it is difficult to ensure casing timely in loose coal seam. Thirdly, that can only protect only one section of hole wall, which not fit for distance drilling with several sections of loose coal bed.In National Natural Science Foundation of China (41002046) youth fund support, the study intends to solve the problem of hole wall instability of loose section in CBM drilling through the way of Grouting while Drilling. Grouting while Drilling is a way of segmented grouting, which is grouting in the process of drilling to reinforce loose coal hole wall when needed. Grouting while Drilling is one of the methods of protecting wall with mud. But it doesn’t need pulling out drill pipes, cleaning drill pipes, waiting for condensation and sweeping hole, which spend too much working time. Grouting while Drilling could reduce working hours and maintain the advantage of flexible retaining wall with drilling fluid which is fit for realize on-demand protecting wall. So it is more suitable for "efficient" drilling requirements.Grouting while Drilling should guarantee that a certain amount of drilling fluid could be injected to target location and could consolidate to the suitable strength in a short time to achieve the goal of protecting hole wall. Therefore, there are three key technologies of Grouping with Drilling used in CBM:(1) the seepage law of drilling fluid in coal wall of hole, which determine the seepage depth of grout, guarantee the consolidation layer thickness and provide the theoretical basis for the subsequent study of drilling fluid formulas and tool used in realizing Grouping with Drilling;(2) drilling fluid formulas, whose consolidation time could be controlled, which have a good flow properties before grouting and could achieve a suitable strength after that, and could break gel itself to reduce the influence of coal seam gas several days after drilling finished;(3) drilling tool used in Grouting while Drilling, which should be able to perceive "normal drilling" and "grouting "signals from the driller, and perform the corresponding action according to the signal.Study focus on basic principle and basic methods of above key technologies, in order to looking for the breakthrough point for Grouting while Drilling used in CBM drilling in loose section, to lay a certain foundation for its in-depth and practical research, and lay a certain foundation for the other Grouting while Drilling to Protecting wall technologies at the same time.In the process of research, innovative research mainly reflects as the follows. Apply Grouting while Drilling Protecting Wall technology to solve hole accident caused by instability of the hole wall occurred in the process of underground CBM extraction drilling. Seepage grouting theory was applied to study the slurry seepage law in the process of under-ground CBM extraction driiling in loose period. Put forward the feasible sodium silicate drilling fluid formulas could be fit for that environment and cleared its nature, found its gel breaking performance; Performance testing used in Grouting while Drilling test tank is developed to simulate Grouting while Drilling process and observe the grouting seepage law; Grouting while drilling tool is developed, which only uses mechanical signal recognition and enforcement agencies.This study mainly finished the following work:1. Seepage law in the process of under-ground CBM extraction driiling in loose period is deduced.(1)Make reasonable assumptions according to the rheological characteristic of the drilling fluid, deduce infiltration grout diffusion partial differential equation and discretize it using implicit difference scheme. Give the initial conditions and boundary conditions, and use Thomas method to solve equations. Analyze the convergence and stability of the solution of difference scheme.(2) Based on the mathematical model above, calculate an engineering example. Solve the finite difference equations in Fortran language, analyze the infiltration grouting effect in different grouting pressure, and the grouting pressure values is gotten finally.Engineering example calculation is based on the actual geological data of Jincheng Sihe coal mine. The results show that with the increase of grout diffusion radius, osmotic grouting pressure decreases, when less than5mm grout diffusion radius, grouting pressure decrease rate is larger; When the grouting pressure P0≤1Mpa, and d>5mm, grout diffusion ability is reduced; Slurry pressure P0>1Mpa, grout diffusion effect is good, could protect the hole wall; Po>1Mpa, grout diffusion effects were similar, which means that the key factor deciding the grout penetration effect is the permeability of coal seam.(3) Analyze the effect from the initial pressure, slurry viscosity, GSI and the formation of broken with Fluent.Fluent simulation results show that if see the coal and rock as porous media, even for the modulus of2.9-3.0, viscosity of1.75Pa·S sodium silicate, and0.5MPa of CBM initial pressure, grouting depth is still more than30mm. the grouting depth are similar between coal damage and strong damage, crushing coal and pulverized coal theoretically. This is different from the mathematical model calculation results.2. Grouting while Drilling fluid(1) After summary, experiment, comparison and selection of the formula studied, determine the two formula that can be used for Grouting while drilling, Three acetic acid glyceride4%+20-40%sodium silicate and1,4butyl inner fat4%+20-40%sodium silicate. When encounter hole accidents in the process of drilling, add PH stabilizer extend the initial setting time. When meet high crushing degree, low permeability formation condition, surfactants are necessary for improve the permeability of the slurry.(2) Test the performance of above drilling fluid through a traditional test instruments and Grouting while Drilling performance testing experiment slot designed, including consolidation strength, penetration depth and gel breaking performance, etc., and analyze the advantages and disadvantages of the application of the drilling fluid in Grouting while Drilling. The experimental results from the traditional test instrument show that coal consolidation strength is lower after45 minutes and the formula is restricted in the field application, but after72hours, edge along the coal grains gradually appear a large number of cracks, which means that could break gel itself, and it is conducive to connect gas channels naturally.Developed a Grouting while drilling performance testing slot to observe permeability of the slurry, and study the feasibility of the grouting under the wind pressure, which include that whether the drilling fluid could be inject to hole wall by wind pressure to meet the depth demanded that can protect hole wall. The testing slot with soil pressure box installed in different depth can help observe pressure curve along with the change of time. Seepage process of slurry also can be directly observed through the window by the naked eye. Experiments show that:1) it is helpful under the action of wind for injecting slurry to coal seam;2) infiltration depth within five minutes in coal sample, which particle diameter is less than0.2mm, is more than100mm from the output results, when wind pressure is0.5MPa without confining pressure, which means that Grouting while Drilling helped by wind pressure is feasible according to the field experience that depth of10mm is enough;3) each layer corresponding liquid pressure value go higher with the increase of particle diameter of coal sample from the output of the soil pressure box;4)the pressures from soil pressure box are smaller than ideal value when the wind pressure is constant, which could be the result of the increasing viscous resistance along with the death deeper that effect the slurry seepage.(3)Dynamic viscosity of the above drilling fluid has been checked, through which the classification of the drilling fluid is determined. Through the parameter analysis, determine the best length of time to use it. It shows weak expansion plastic fluid state in the beginning20minutes after preparation, and the slurry viscosity is about2mPa. s, similar to water. Then the viscosity increase quickly in the next20to40minutes.40-45minutes later, it is freeze if the drilling fluid is in static, otherwise it shows suspended particle state and the viscosity will no longer be changed. These show that if PH stabilizer is not be added, the optimal grouting time is within20minutes. In the process of Grouting while Drilling, the drilling fluid that still not be injected into coal seam could not consolidate because it is flow, which is helpful for washing pipe by wind blowing after the grouting is over.3. Grouting while Drilling tool(1) Determine the design principle of Grouting while Drilling tool after analyzing the downhole working conditions and the necessary requirements of the existing conditions from several design schemes. The signal transmission is pure mechanical. Circulating medium-atomizing air is used as power, through which reverse circulation to transfer "normal drilling" and "start grouting" signals, trigger the drilling grouting tools, and realize the switch. When grouting is needed, short reverse circulation is done to open spray channel. Then start the positive cycle to spray fluid that could meet the requirements of protecting the holewall. When it is finished, by short reverse circulation again, open the normal channel to control the normal drilling began, which needs positive cycle.(2) Study a pure mechanical way to transfer "grouting" signal and "normal drilling" signal and design an actuator for pressure control. The one-way valve senses signal, and ratchet transposition mechanism designed to switch the function performs signals.(3) Study the atomized spray method for Grouting while Drilling, designed a swirl atomizing nozzle, which adapt the above drilling fluid, downhole pressure, and pump pressure very well.(4) With the grouting while drilling tools casing as the research object, the strength of the casing is analyzed and designed, the thickness of the casing how much they can bear on peripheral and internal pressure is determined; Under30MPa pressure, to guarantee the normal work of the grouting while drilling tools, the scope of its internal clearance which should be reserved is identified, In the torsional analysis using Prandtl analyzed stress function method and the method of material mechanics respectively, results show that the sleeve smaller end is the stress concentration area, and compared with the material mechanics, elastic mechanics calculation results are more conservative. The difference between the two results:when non simply connected region is given, Prandtl stress function is not accurate enough.(5) The grouting while drilling tools are designed and processed according to the results of theoretical analysis, and its basic performance has been tested. The experimental results show that reverse wind can control the switching of the signals of "injection" and "normal drilling" and the channel is smooth after that, so the drilling tool design can meet the requirements of Grouting while Drilling.4. The technology of Grouting while DrillingThe technology of the grouting while drilling is investigated preliminarily, including the determination method of grouting parameters, process execution of the grouting while drilling technology.The results can not only lay certain foundation for the in-depth and practical study of Grouting while Drilling used in underground coal seam gas drainage drilling, but also can be used as the basis of other conditions that Grouting while Drilling is helpful.更多还原