Numerical simulation and experiment analysis of improving permeability by deep-hole presplitting explosion in high gassy and low permeability coal seam

Created a new damage model for explosive for LS-DYNA3D,taking advantageof the Taylor method aimed at the high gassy and low permeability coal seam,and numericallysimulated and analyzed the deep-hole presplitting explosion.The entire processof explosion was represented,including cracks caused by dynamic pressure,transmissionand vibration superposition of stress waves,as well as cracks growth driven by gas generatedby explosion.The influence of the cracks generated in the process of explosion andthe performance of improving permeability caused by the difference of interval between.explosive holes were analyzed.A reasonable interval between explosive holes of deepholepresplitting explosions in high gassy and low permeability coal seams was proposed,and the resolution of gas drainage in high gassy and low permeability coal seam was putforward.

Technique of coal mining and gas extraction without coal pillar in multi-seam with low permeability

Aimed at the low mining efficiency in deep multi-seams because of high crustalstress,high gas content,low permeability,the compound 'three soft' roof and the trouble-somesafety situation encountered in deep level coal exploitation,proposed a new idea ofgob-side retaining without a coal-pillar and Y-style ventilation in the first-mined key pressure-relieved coal seam and a new method of coal mining and gas extraction.The followingwere discovered:the dynamic evolution law of the crannies in the roof is influenced bymining,the formative rule of 'the vertical cranny-abundant area' along the gob-side,thedistribution of air pressure field in the gob,and the flowing rule of pressure-relieved gas ina Y-style ventilation system.The study also established a theoretic basis for a new miningmethod of coal mining and gas extraction which is used to extract the pressure-relievedgas by roadway retaining boreholes instead of roadway boreholes.Studied and resolvedmany difficult key problems,such as,fast roadway retaining at the gob-side without a coalpillar,Y-style ventilation and extraction of pressure-relieved gas by roadway retainingboreholes,and so on.The study innovated and integrated a whole set of technical systemsfor coal and pressure relief gas extraction.The method of the pressure-relieved gasextraction by roadway retaining had been successfully applied in 6 typical working faces inthe Huainan and Huaibei mining areas.The research can provide a scientific and reliabletechnical support and a demonstration for coal mining and gas extraction in gaseous deepmulti-seams with low permeability.

Research into comprehensive gas extraction technology of single coal seams with low permeability in the Jiaozuo coal mining area

For a low permeability single coal seam prone to gas outbursts,pre-drainage of gas is difficult and inefficient,seriously restricting the safety and efficiency of production.Radical measures of increasing gas extraction efficiency are pressure relief and infrared antirefiection.We have analyzed the effect of mining conditions and the regularity of mine pressure distribution in front of the working face of a major coal mine of the Jiaozuo Industrial(Group) Co.as our test area,studied the width of the depressurization zone in slice mining and analyzed gas efficiency and fast drainage in the advanced stress relaxation zone.On that basis,we further investigated and practiced the exploitation technology of shallow drilling,fan drilling and grid shape drilling at the working face.Practice and our results show that the stress relaxation zone is the ideal region for quick and efflcient extraction of gas.By means of an integrated extraction technology,the amount of gas emitted into the zone was greatly reduced,while the risk of dangerous outbursts of coal and gas was lowered markedly.This exploration provides a new way to control for gas in working faces of coal mines with low permeability and risk of gas outbursts of single coal seams in the Jiaozuo mining area.

Hydraulic drill hole reaming technology with large flow and draining of coal mine gas

This paper takes Zhaozhuang mine in Shanxi province as an example to study the technology of hydraulic reaming drill hole for improving the gas extraction.The influence of the physical properties of coal seam on the hydraulic reaming drill holes and the draining of coal mine gas were analyzed and discussed for different coal structure areas,and the following conclusions were made.Hydraulic drill hole reaming has had a positive impact in Zhaozhuang Mine,and can improve the efficiency of gas extraction to different degrees.The water jet pressure used in hydraulic drill hole reaming mainly depends on the structure of the coal.When the coal seam basically becomes integrated,the critical water jet pressure increases,the discharge becomes relatively easy to achieve,the blocking effect on the gas extraction decreases,and the gas extraction significantly increases after the reaming process.When the coal seam is broken,the critical water jet pressure decreases,the discharge becomes difficult to achieve,the blocking effect on the gas extraction becomes obvious,and the gas extraction changes slightly after reaming.

Effect of damage zone around borehole on carbon dioxide injection promoted gas extraction in soft and low-permeability coal seam

Injecting external CO_(2) into soft and low-permeability coal seams can improve CH4 extacctinn efficiency, and also benefit in CO_(2) sequestration. However, the distribution law of damage zone around borehole in soft coal seam and its effect on the efficiency of CO_(2) injection promoted CH4 extraction are not clear. In this paper, a multi-physics coupling mathematical model considering damage effect is established for simulating the process of CO_(2) injection promoted CH4 extraction in soft and low-permeability coal seam. The distribution of damage zone and permeability around boreholes under different diameters and coal strengths are analyzed. The gas pressure and gas content in coal seam during CO_(2) injection promoted CH4 extraction when the model considered damage effect are compared with that of ignored. The results show that small borehole diameter corresponds to narrow damage zone around the borehole in coal seam. The damage zone expands with the increase of the borehole diameter. The damage zone increases exponentially with the borehole diameter, while decreases exponentially with the compressive strength of coal seam. The highest permeability in the damage zone has increased by nearly 300 times under the condition of simulated case. CH4 pressure around the extraction borehole reduces, and the reduction area expands with the increase of time. Compared with the result of considering the damage effect, the reduction area of ignoring it is smaller, and the reducing speed is slower. The integrated effect of CO_(2) injection and CH4 extraction leads to rapid decrease of CH4 content in coal seam near the boreholes. The CO_(2) pressure and content increase around the injection borehole, and the increasing area gradually extends to the whole coal seam. In soft coal seams, failure to consider the damage effect will underestimate the efficiency of CH4 extraction and CO_(2) sequestration, resulting conservative layout of boreholes.

Theories and techniques of coal bed methane control in China

Coal bed methane control with low permeability is a hot issue at present. The current status of coal bed methane control in China is introduced. The government-support policies on coal bed methane control are presented. This paper proposes the theories of methane control in depressurized mining, including methane extraction in depressurized mining, simultaneous mining technique of coal and methane without coal pillar, and circular overlying zone for high-efficiency methane extraction in coal seams with low permeability. The techniques of methane control and related instruments and equipments in China are introduced. On this basis, the problems related to coal bed methane control are addressed and further studies are pointed out.

碎软低渗煤储层强化与煤层气地面开发技术进展

我国碎软低渗煤储层分布广泛,然而由于其煤体松软、破碎、渗透性差,常规的直井/水平井煤储层直接压裂技术应用于碎软低渗煤储层强化及其煤层气地面开发的效果并不理想,碎软低渗煤储层煤层气的高效开发是制约我国煤层气产业大规模发展以及煤矿瓦斯高效治理的重要技术瓶颈。在系统分析我国碎软低渗煤储层特征及煤层气地面开发中存在的问题基础上,以水平井为基础井型,围绕间接压裂、应力释放和先固结后压裂3种不同的技术方向,梳理了目前碎软低渗煤储层强化与煤层气地面开发技术进展。归纳评述了以顶板间接压裂、夹矸层间接压裂以及硬煤分层间接压裂为内涵的间接压裂煤层气开发技术,以水力喷射造穴、气体动力造穴、扩孔+水力喷射+流体加卸载诱导失稳造穴、水力割缝为不同应力释放方式的应力释放煤层气开发技术,以及先微生物诱导碳酸钙固结碎软煤储层再进行水力压裂的先固结后压裂煤层气开发技术。间接压裂技术的工程实践探索已有较多积累,在地质条件适宜地区对碎软低渗煤储层强化取得了较好效果,而以应力释放为代表的碎软低渗煤储层强化新技术探索已取得重大进展,并进入工程试验和验证阶段。水平井应力释放技术针对碎软低渗煤储层特性和新的开发原理,其对储层改造潜力更大、煤层气开发效果会更好。基于水平井应力释放技术,围绕扩大应力释放范围、提高煤层气开发效果以及实现煤与煤层气共采3个方面,对碎软低渗煤储层强化及煤层气地面开发技术的发展趋势进行了展望,以期为改善我国碎软低渗煤储层增产改造效果以及提高煤层气单井产量提供参考。

煤层顶板间接压裂裂缝扩展机制及影响因素

碎软低渗煤层在我国普遍发育,制约煤层气单井产气量提高和产业发展。间接压裂是通过在邻近层产生垂直裂缝沟通煤层进而实现煤层有效改造的一种压裂方式,可以有效应对钻井塌陷、煤粉产出、压裂液滤失和煤层厚度薄等不利因素。通过间接压裂物理模拟试验和扩展有限元数值模拟分析,揭示煤层顶板间接压裂裂缝扩展影响因素,明确裂缝扩展机制,以期为间接压裂技术提供指导。通过直接压裂煤层和不同起裂位置、垂向应力和施工排量影响下间接压裂试验表明,起裂压力高,更易产生长裂缝,且受原生裂缝影响程度减小;但起裂点距离煤层越远,起裂所需能量越大,高破裂压力会对煤层造成粉碎性破坏;大施工排量下,起裂压力对应升高,起裂时间变短,原生裂缝影响程度变小。考虑地应力、起裂位置、岩石力学和施工排量等参数的数值模拟结果显示,在模型参数设置条件下,最大水平主应力和垂向应力差在<4 MPa,煤层与顶板有效应力差>3 MPa、弹性模量差<15 GPa的地层和岩性组合适合间接压裂,起裂位置距离煤层最优距离为<6 m,施工排量需要根据力学性质、断裂能密度等参数确定最优范围。

煤层瓦斯含量测定技术及装备研究进展

瓦斯含量是煤与瓦斯突出危险预测、煤层瓦斯资源量估算、矿井瓦斯治理工程设计的重要参数。围绕如何在大区域准确快速测定煤层瓦斯含量,依托国家科技重大专项、国家自然科学基金和煤炭企业联合基金等项目科技攻关,在取样、测试方面取得了一定进展。主要表现在如下4个方面:①煤层瓦斯含量测定取样经历了孔口接样、岩心管定点取样、压力引射定点取样和密闭取样4个阶段,密闭取样装备保压能力达到11.5 MPa,煤心直径达到38 mm;②针对不同煤层地质条件,发展形成了顺煤层定向长钻孔密闭取样、底板穿层钻孔密闭取样和顶(底)板梳状定向长钻孔密闭取样3种取样技术;③在河南焦作和山西晋城矿区硬煤层中,顺层定向长钻孔取样深度达到516 m,密闭取样法测得煤层瓦斯含量较常规取样法分别平均提高了0.44倍和1.04倍。在安徽淮南矿区碎软煤层中,穿层钻孔密闭取样深度达到209 m,测得煤层瓦斯含量较常规取样法平均提高了0.26倍;在安徽淮北矿区碎软煤层中,顶(底)板梳状钻孔密闭取样深度达到484 m,测得煤层瓦斯含量较常规取样法平均提高了0.19倍,密闭取样法在煤层瓦斯含量测定精度、探测范围上优于常规取样法;④在瓦斯含量测试方面,除了传统解吸法测试,发展了系列煤矿井下瓦斯含量快速测试装备,可实现最快30 min内测得煤层瓦斯含量,一般用于百米孔内的瓦斯含量测试。提出了煤层瓦斯含量测定密闭取样装备需向小型化、轻量化的方向发展,并能实现随钻密闭取样。在测试上,应根据实际情况确定合理的解吸终止限,并将测试装备和密闭取样装备进一步结合,以实现深孔瓦斯含量快速准确测定。密闭取样技术已成为煤层瓦斯含量大区域精准勘查、预测的主要手段,是煤炭安全高效开采的重要技术保障。

低透气煤层无泵式钻扩一体化增透技术与钻具研究

针对在低透气煤层常规机械掏穴、水力冲孔等增透施工中存在的施工效率低、掏穴装置稳定性差以及需要配备高压泵等问题,提出了无泵式钻扩一体化增透施工技术,研制了配套的双通道送水器、双通道钻杆和造穴装置,并进行了现场工业性试验。结果表明:钻扩一体化增透施工技术在煤矿井下静压水条件下,可实现一趟下钻完成先导孔和机械掏穴的同时作业,解决了常规掏穴装置刀翼开合不稳定、必须配套高压泵的问题,降低了该技术的使用成本;研发的双通道送水器、双通道钻杆和造穴装置工作灵活稳定且可靠性高,造穴段单孔直接扩大至原常规钻孔孔径的4.4倍,显著提升了瓦斯抽采效果,该技术的成功应用为煤矿井下低透气煤层瓦斯抽采钻孔施工提供了技术支撑。

中国海油低渗及非常规油气藏储层改造技术进展及展望

中国海上低渗及非常规油气开发存在产能低、投资大、操作费用高、收益较低及单井经济任务重等问题。经过技术攻关,中国海油形成了平台压裂、钻井船压裂和拖轮压裂等海上储层改造作业模式,研发出集海上低渗储层改造液体系、海上控水支撑剂技术、低渗储层压裂管柱设计和海上储层改造监测技术为一体的海上低渗储层改造技术,以及适用于陆上深煤层大规模压裂技术。本文综述了中国海上低渗油气储层改造技术及陆上深煤层大规模压裂技术研究进展,展望了未来储层改造重点发展方向,对推动中国海油低渗及非常规油气开发技术进步有重要指导意义。

低渗煤层大直径钻孔瓦斯抽采参数优化研究

针对低渗煤层瓦斯抽采存在预抽难度大的问题,提出大直径钻孔预抽能够降低低渗煤层瓦斯含量的方法。但由于低渗煤层对气固耦合效应影响敏感,抽采中渗透率变化过程不明确,导致大直径钻孔抽采参数设计依据不足。首先分析了低渗煤体渗透率演化的主控因素,建立了煤层瓦斯运移理论模型,模拟研究了大直径钻孔不同工况下对低渗煤体的瓦斯抽采效果,对比分析不同孔径、负压、孔间距下煤层瓦斯渗流规律。结果表明钻孔孔径越大造成的煤体卸压区越大,瓦斯抽采量越高,瓦斯残余含量也越小,但抽采效果增加幅度逐渐降低。负压越大瓦斯抽采量越大,但差别较小,因此负压对提升抽采效率影响较小。受渗透率演化的影响,不同钻孔间距下瓦斯抽采总量差别较大,在间距为3 m时,40~120 d阶段内抽采量最高,后期抽采量缓慢下降。间距5 m时抽采总量最高,抽采范围内的瓦斯残余含量降低较多。现场优化抽采后的瓦斯抽采纯量与模拟结果一致,表明了研究结论可靠。该研究结果可为煤矿井下大直径钻孔瓦斯抽采参数设计提供理论依据与应用参考。

瓦斯压力对低透性煤吸附-解吸特性及孔隙分布的影响

为了从微观的角度探究瓦斯压力对深部低透性煤层吸附-解吸特性及孔隙分布的影响,采用低磁场核磁共振技术(NMR),开展深部低透性煤不同瓦斯压力下的吸附-解吸试验。试验发现:瓦斯吸附态、游离态和自由态下,T_(2)谱幅值积分与瓦斯压力呈现较好的线性关系,其拟合结果R^(2)均大于0.973 48,微观自由态瓦斯在瓦斯压力等于3.739 MPa处瓦斯的吸附-解吸出现了迟滞效应。不同瓦斯压力下,孔径类型分布差距较大,煤样内部孔隙分布主要是小孔占据大部分,而中孔和大孔所占比列较小。研究结果对深部低透性煤矿资源开采具有一定的指导意义。

碎软低渗煤层水平井水力喷砂射孔工艺优化

针对碎软低渗煤层水平井煤粉产出危害,提出采用水力喷砂射孔压裂来实现“射孔-增透-控粉”为一体的压裂改造理念,具体工艺包含水力喷砂射孔、高压射流、环空压裂以及水力补射孔清洗。通过成本及工艺对比,选择油管拖动水力喷砂射孔方式进行压裂,并对工艺和关键工具进行优化。首先,优化防反冲蚀破坏一体化硬质合金圆锥收敛型喷嘴,能实现排量2.0~2.5 m3/min时,射流压力为16.5~25.8 MPa。其次,优化喷射器本体,能有效射穿套管、水泥塞,并射入岩石一定深度。配套一体化管柱顺利完成了煤层气U型水平井压裂和补射孔施工各8段,每段射孔时间15 min以上,并充分顶替返排煤粉,投产3年后产气量仍达到3500 m3/d以上,表明优化工艺达到了碎软低渗煤层改造效果。与连续油管分段压裂技术相比,油管拖动水力喷射压裂单段压裂作业成本降低了28.5%。

煤矿井下碎软煤层气动定向钻进技术与装备研究

【目的】我国煤层赋存地质条件复杂,碎软煤层分布广泛,高瓦斯和煤与瓦斯突出矿井众多,目前采用钻孔瓦斯抽采是防治瓦斯灾害的有效措施。碎软煤层常规回转钻进存在轨迹不可控、成孔深度浅、抽采盲区大,常规定向钻进卡埋钻事故多、成孔困难、钻进效率低等问题。【方法】系统阐述了煤矿井下碎软煤层钻进技术的发展历程与应用现状,研制了气动螺杆钻具、定向钻机、随钻测量系统、除尘泵车、空压机或制氮机、油雾润滑装置等组成的煤矿井下气动定向钻进装备,并配套开发了气动定向钻进工艺和筛管完孔技术等关键技术,解决碎软煤层定向钻进成孔难题,保障瓦斯抽采效果。利用该成套技术与装备在两淮、山西、贵州等地区煤矿进行的碎软煤层定向钻孔试验。【结果和结论】研究表明:(1)气动定向钻进技术是碎软煤层钻孔瓦斯治理的有效技术手段,其钻进深度普遍达到200 m以上,最大钻孔深度达607 m,且可有效控制钻孔轨迹在目标煤层中延伸,煤层钻遇率达90%以上。(2)现场试验表明,气动定向钻进成孔效果好、施工效率高,最大效率达到3 594 m/(台·月),有力推动气动定向钻进技术从小规模试验到大规模的工业化推广应用。结合此成套技术与装备的应用现状和煤矿安全高效生产对钻探技术装备的发展需求,提出煤矿井下气动定向钻进技术与装备的拓展应用方向以及向自动化、智能化和集约化方向发展的现实需求和必然趋势。

碎软煤层定向钻孔防瓦斯套铣打捞技术

针对碎软煤层定向钻孔套铣打捞,孔壁失稳塌孔造成瓦斯异常涌出的技术难题,提出了碎软煤层定向钻孔防瓦斯套铣打捞技术。在现有套铣打捞技术基础上,分析了碎软煤层套铣打捞孔内瓦斯异常涌出原因、涌出通道和涌出量,优化了套铣打捞钻具内抽采瓦斯管路系统,将套铣打捞过程中打捞钻具内积聚瓦斯进行抽采并卸压;开发了套铣打捞孔口密闭抽瓦斯系统和套铣打捞加杆防瓦斯装置,实现套铣打捞全程负压抽采、密闭排渣和密封加杆。利用该技术成功处理1起孔深362 m的碎软煤层定向钻孔卡钻事故,事故处理中通过打捞钻具内抽采瓦斯管路系统,实现了打捞钻具内积聚瓦斯的抽采和卸压,通过孔口密闭抽瓦斯系统和加杆防瓦斯装置,实现了孔口和打捞钻杆末端口涌出瓦斯的密闭抽采,整个打捞过程中未发生瓦斯超限事故。

低渗煤层瓦斯抽采顺层钻孔水力造穴卸压增透效果研究

为了揭示水力造穴参数对钻孔瓦斯抽采效果的影响规律,指导煤层水力造穴增透技术施工参数的合理选择。建立了煤层损伤-应力-渗流耦合模型,分析了不同造穴参数下煤层卸压增透效果,展开了顺层钻孔水力造穴现场工程试验,考察了不同造穴参数下钻孔瓦斯抽采效果,结果表明:采用水力造穴技术形成的孔穴能够有效降低其周围煤体应力,提高煤层渗透率,增加瓦斯钻孔抽采效果;造穴半径越大煤层的卸压程度越大,进而煤层渗透率增幅就越大,但在实际工程中过大的造穴半径会使得孔穴稳定性差,钻孔塌孔堵塞瓦斯涌出通道会使得钻孔瓦斯抽采量有所降低,试验矿井最优造穴半径为0.6 m;造穴间距对它们之间的应力降低区范围有着较大的影响,在一定距离条件下孔穴卸压有着明显的叠加效应,造穴间距越近叠加效应越明显,煤层应力越小,卸压增透效果越好。试验钻孔穴间距由8 m减小到6 m时,单孔平均瓦斯抽采纯量增加389.16%。

松软低透气性煤层瓦斯抽采技术的应用研究

为有效解决新源煤矿松软低透气性煤层瓦斯地面抽采难题,进行了超高压水力割缝增透技术的应用研究。采用COMSOL-Multiphysics仿真软件确定了有效抽采半径,找到了地面抽采难的原因,确定采用超高压水力割缝增透技术,并对超高压水力割缝装置和超高压水力割缝工艺进行了阐述。实践应用结果表明,对比普通钻孔瓦斯抽采技术,采用超高压水力割缝增透技术进行瓦斯抽采,其抽采体积分数和纯量均有大幅度的提高,抽采体积分数是普通钻孔抽采的2.24倍,抽采纯量是普通钻孔抽采的2.61倍。超高压水力割缝增透技术的应用有效解决了新源煤矿307工作面松软低透气性煤层瓦斯抽采难度大的问题。

低渗透煤层机械造穴卸压增透瓦斯抽采技术的应用研究

为解决低渗透煤层瓦斯抽采治理难题,以毛家庄矿8203工作面为工程背景,阐述了机械造穴卸压增透瓦斯抽采技术。在建立机械造穴卸压增透瓦斯抽采计算模型后,研究了钻孔造穴直径、钻孔间距及瓦斯抽采负压等参数对低渗透煤层卸压增透的影响规律。研究表明,钻孔造穴直径越大,煤层卸压增透效果越好,钻孔间距越大,影响范围越大,卸压效果随之降低,瓦斯抽采负压越大,对瓦斯抽采效果越好,但对煤层的卸压效果影响较小。应用此技术进行现场试验,抽采瓦斯效果良好,可为低渗透煤层瓦斯抽采治理提供借鉴。

低透气性煤层分段压裂酸化复合增透技术研究及应用

针对低透气性煤层瓦斯抽采钻孔抽采效果差的问题,基于分段水力压裂和煤层酸化增透机制,提出分段压裂酸化压注复合增透技术。现场试验表明:分段压裂酸化复合增透技术流量平均值是原有水力压裂技术的1.28倍,是原有定向长钻孔的5.43倍,分段压裂酸化复合增透技术流量衰减与普通水力压裂技术相比降低了36.1%.试验结果表明,分段压裂酸化技术施工工艺快速简便,增透范围大,减缓了瓦斯衰减速度,保障了矿井安全高效生产。