Prospect Conceiving of Joint Research and Development of Shale Gas and Coalbed Methane in China

Inspired by successful development of shale gas in USA and influenced by hydrocarbon resources shortage currently, China has strengthened shale gas research and accelerated its exploration process. In order to enrich coalbed methane (CBM) and shale gas geological theory and promote their development process, this paper compared shale gas with CBM in accumulation, distribution, reservoir and production. It expatiated on the background and significance of the combined research and development, and analyzed the geological foundation and future prospects. Our investigation demonstrated that there are many sets of coal-bearing strata in Shanxi formation of Permian system in Ordos in North China, Longtan formation of Upper Permian and Xujiahe formation of Upper Triassic in Southern Yangtze region, Xishanyao formation of Middle Jurassic in Turpan-Hami Basin and Junggar Basin in Northwest China, and Shahezi formation of Cretaceous in Songliao Basin in northeast China. In these regions, shales which are interbeded with coal seams have the characters of big thickness, continuous distribution, high content of organic matter, good parent material and high maturity, accord with the basic geological conditions to format shale gas and CBM reservoir and composite gas reservoir, thus form appropriate regions and layers to carry out joint research and exploration with good prospects for development.

The status and development strategy of coalbed methane industry in China

To achieve the goals of carbon peaking and carbon neutrality under the backgrounds of poor resource endowments, weak theoretical basis and other factors, the development of the coalbed methane industry of China faces many bottlenecks and challenges. This paper systematically analyzes the coalbed methane resources, key technologies and progress, exploration effect and production performance in China and abroad. The main problems are summarized as low exploration degree, low technical adaptability, low return on investment and small development scale. This study suggests that the coalbed methane industry in China should follow the “two-step”(short-term and long-term) development strategy. The short-term action before 2030, can be divided into two stages:(1) From the present to 2025, to achieve new breakthroughs in theory and technology, and accomplish the target of annual production of 10 billion cubic meters;(2) From 2025 to 2030, to form the technologies suitable for most geological conditions, further expand the industry scale, and achieve an annual output of 30 billion cubic meters, improving the proportion of coalbed methane in the total natural gas production. The long-term action after 2030 is to gradually realize an annual production of 100 billion cubic meters. The strategic countermeasure to achieve the above goals is to adhere to “technology+management dual wheel drive”, realize the synchronous progress of technology and management, and promote the high-quality development of the coalbed methane industry. Technically, the efforts will focus on fine and effective development of coalbed methane in the medium to shallow layers of mature fields, effective development of coalbed methane in new fields, extensive and beneficial development of deep coalbed methane, three-dimensional comingled development of coalbed methane, applying new technologies such as coalbed methane displacement by carbon dioxide, microwave heating and stimulation technology, ultrasonic stimulation, high-temperature heat injection stimulation, rock breaking by high-energy laser. In terms of management, the efforts will focus on coordinative innovation of resource, technology, talent, policy and investment, with technological innovation as the core, to realize an all-round and integrated management and promote the development of coalbed methane industry at a high level.

Factor analysis and countermeasure simulation on the socio-ecological environment risks during the development of coalbed methane:based on the DEMATEL and FCM models

The socio-ecological environmental problem caused by the development of coalbed methane(CBM)is becoming more serious,so it is very significant for accelerating the development of CBM industrialization to identify the main influential factors of socioecological environmental risks and take effective risk prevention measures.Based on the triangular fuzzy number method,this paper firstly establishes a comprehensive correlation matrix.Then,the affected factors of socio-ecological environmental risks are analyzed by the DEMATEL method during the development of CBM.Then according to the aspects of centrality and causality,the key indicators are determined.Furthermore,the scenario simulation based on the FCM,the steady-state value and the comprehensive importance of key indicators,and the core indicators are selected.Finally,the scenario simulation of risk management countermeasure is done.The results show that:①The index weights are calculated by the triangular fuzzy numbers,and the correlation matrix in DEMATEL is obtained by the weight ratio,which reduces the shortcomings and the subjectivity of traditional DEMATEL method.②The correlation matrix in FCM is established based on the comprehensive correlation matrix in the above improved DEMATEL,which not only makes the FCM model more comprehensive and reduces the difficulty that the FCM correlation matrix is obtained considering the indirect influence relationship between indicators,but also makes up for the disadvantages that DEMATEL excludes during the selection of the core indexes,which are the considerations of the dynamic change of the importance of the indicators.③The rate of forestry and grass coverage,the ratio of investment in prevention and construction,the pollution index of soil Merlot,the reliability of machinery and equipment,the standard evaluation index of major pollution factors of underground water,and the ability of personal risk prevention are the key indicators,in which the rate of forestry and grass coverage,the ratio of investment in prevention and construction,and the reliability of machinery and equipment are the core indicators and are extremely important for the management of socio-ecological environmental risks during the development of coalbed methane.④The results of the scenario simulation of risk management countermeasure show that the core variables affect the socio-ecological environmental risks through such indicators as the degree of production mechanization,the degree of demolition and resettlement,and the ratio of economic loss by the influenced mechanism analysis;the ratio of investment in prevention and construction has the greatest impact on the socio-ecological environment risks in the early stage of CMB development,while the rate of forestry and grass coverage is the most important in the middle and late stages by the influenced result analysis.Therefore,this paper puts forward some corresponding stage suggestions on the prevention and control of socio-ecological environmental risks during the CMB development.In the early stage of CMB development,the ratio of investment in prevention and construction should be increased.In the middle stage,it is very important to reduce the damage of vegetation regions and to improve the reliability of machinery and equipment;in the late stage,the investment in prevention and construction should be increased steadily and the recovery of damaged vegetation areas should be focused on.

New Progress on the Coal Fines Affecting the Development of Coalbed Methane

Objective The production of coal fines is very common in the development of coalbed methane（CBM）in the eastern margin of the Ordos Basin,China.A large amount of produced coal fines seriously affect the productivity of CBM wells（Wei Yingchun et al.,2013）.Therefore,the production problems of CBM wells caused by coal fines have attracted extensive attention.

Development unit division and favorable area evaluation for joint mining coalbed methane

Based on the productivity equation of coalbed methane (CBM) well, considering the impact of coal reservoir reformability on gas well productivity, the main production layer optimization index in the “three-step method” of optimal combination of production layers is corrected, and then the CBM production layer potential index is introduced to evaluate favorable areas for commingled multi-coal seam production. Through analysis of the key parameters of coal reservoirs affecting the CBM productivity index, a development unit division method for areas with multi-coal seams is established, and a quantitative grading index system is proposed. On this basis, the evaluation process of CBM development favorable area is developed: the mature 3-D modeling technology is used to characterize the reservoir physical properties of multi-coal seams in full-scale;the production layer potential index of each grid is calculated, and the production layer potential index contour under single-layer or commingled multi-layer production are plotted;according to the distribution of the contour of production layer potential index, the quantitative index of CBM development unit is adopted to outline the grade I, II, III coal reservoir distribution areas, and thus to pick out the favorable development areas. The practical application in the Yuwang block of Laochang in Yunnan proved that the favorable area evaluation process proposed can effectively overcome the defects of selecting favorable development areas only relying on evaluation results of a major coal seam pay, and enhance the accuracy of the evaluation results, meeting the requirements of selecting favorable areas for multi-coal seam commingled CBM production.

Developments of coalbed methane development in the U.S.

After decades of development and technology advancement, coalbed methane has become an important source for U S. energy consumption. Especial in recent year, U S. coalbed methane production continues its healthy growth rate of about 10% per year. The paper takes emphasis on the technology developments and the engineering approaches of coalbed methane in the U S.

Fuzzy pattern recognition model of geological sweetspot for coalbed methane development

From the perspective of geological zone selection for coalbed methane(CBM) development, the evaluation parameters(covering geological conditions and production conditions) of geological sweetspot for CBM development are determined, and the evaluation index system of geological sweetspot for CBM development is established. On this basis, the fuzzy pattern recognition(FPR) model of geological sweetspot for CBM development is built. The model is applied to evaluate four units of No.3 Coal Seam in the Fanzhuang Block, southern Qinshui Basin, China. The evaluation results are consistent with the actual development effect and the existing research results, which verifies the rationality and reliability of the FPR model. The research shows that the proposed FPR model of geological sweetspot for CBM development does not involve parameter weighting which leads to uncertainties in the results of the conventional models such as analytic hierarchy process and multi-level fuzzy synthesis judgment, and features a simple computation without the construction of multi-level judgment matrix. The FPR model provides reliable results to support the efficient development of CBM.

China's Development of Coalbed Methane Attracting World Attention

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沁水盆地南部中深部煤层气储层特征及开发技术对策

为了实现沁水盆地南部中深部煤层气高效开发,以郑庄北-沁南西区块为研究对象,基于参数井取心分析测试、注入/压降测试、地应力循环测试结果和大量动静态数据,通过与浅部对比,阐述了中深部煤储层特征,分析了从浅部到中深部煤层直井压裂和水平井分段压裂两种开发技术的改进,进而提出了中深部煤层气主体开发技术。结果表明,郑庄北-沁南西区块3号煤平均埋深1200 m左右,为中深部煤层气储层。随着埋深增加,研究区含气量和吸附时间均先增加后降低,含气量和吸附时间峰值分别位于埋深1100~1200 m和800~1000 m;随着埋深增加,研究区地应力场类型发生了2次转换,埋深小于600 m时,为逆断层型地应力场类型,水力压裂易形成水平缝,利于造长缝;埋深大于1000 m时为走滑断层型地应力场类型,水力压裂易形成垂直缝,裂缝延伸较短;埋深为600~1000 m时,地应力场由逆断层型向走滑断层型转换阶段,水力压裂形成的裂缝系统较为复杂。与浅层相比,中深部储层含气量、解吸效率和应力场发生明显转变。随着埋深增加,无论是直井(定向井)还是水平井,均应采用更大的压裂规模才能获得较好的效果。对于直井,埋深大于800 m后,压裂液量达到1500 m^(3)以上、排量12~15 m^(3)/min以上、砂比10%~14%以上,单井日产气量可以达到1000 m^(3)以上;对于水平井,埋深大于800 m后,压裂段间距控制在70~90 m以下,单段液量、砂量分别达到2000、150 m^(3)以上,排量达到15 m^(3)/min以上开发效果较好,单井产量突破18000 m^(3)。随着埋深增加,水平井开发方式明显优于直井,以二开全通径水平井井型结构、优质层段识别技术和大规模、大排量缝网压裂为核心的水平井开发方式是适用于沁水盆地南部中深部煤层气高效开发的主体工艺技术。

新疆煤层气大规模高效勘探开发关键技术领域研究进展与突破方向

新疆煤层气资源量7.5万亿m^(3)(2000 m以浅),已施工煤层气井450口,年产气量达到0.8亿m^(3),新疆维吾尔自治区提出了2025年实现煤层气产量25亿m^(3)的目标,煤层气大规模高效开发成为紧迫的重大需求。从煤层气富集模式与选区技术、“甜点”预测探测技术、加速滚动开发与快速增储上产策略、地质适配性开发技术、煤层气与煤炭、油气协同开发技术5个关键技术领域,系统梳理了新疆煤层气勘探开发已取得的主要研究进展,分析提出了可能突破方向。研究表明:新疆煤储层具有多-厚煤层普遍、低阶煤发育、急倾斜煤层多见、煤体变形与构造控制显著、水文条件和露头条件复杂,和三“低”(含气量低、甲烷体积分数低、含气饱和度低)五“高”(高含气强度、高孔隙度、高地应力变化、高储层压力变化、高渗透率变化)的含气性及物性等煤层气地质独特性;煤层气成因与富集模式具有多样性,包括生物成因气、热成因气或生物-热复合成因及其相应富集模式,生物成因气藏或生物成因气贡献普遍;煤层气分布赋存规律呈现前陆盆地、山间盆地显著差异性;创新形成基于“两”分开(浅部与深部,低阶煤与中高阶煤)“两”结合(地质评价与工程评价,多元数据)的科学评价与基于“机器学习+三维地质建模”的精准选区技术是第1个突破方向。深部煤层气/煤系气“甜点”发育区域主要为盆内坳陷的凸起、盆内隆起的凹陷、盆缘斜坡,高产井位多为构造高点,发育层位为割理裂隙发育的原生结构煤层或孔裂隙发育的煤系砂砾岩储层;基于“地球物理+岩石物理+岩石力学地层新方法”和“地质甜点+工程甜点新理念”的深部煤层气/煤系气“甜点”预测探测技术是第2个突破方向。低风险、短周期、高效率、多批次工程部署是加速滚动开发的基本原则;中浅部煤层气快速增储上产技术策略是在优选新区块布井建井、对老区块煤层气井进行增产改造;深部煤层气快速增储上产技术策略是在大型盆地缓坡深部和盆内凸起“甜点”区优先部署开发;科学加速滚动开发与高效快速增储上产的工程部署方法与技术策略是第3个突破方向。在井网井型差异性优化部署、低储层伤害钻井固井、高可靠性录井测井试井、多井型高效分段压裂、低套压-控压排采管控等工程技术取得重要进展;发展构建新疆煤层气大规模高效勘探开发地质适配性技术体系是第4个突破方向。开展先采气后采煤、煤层气与煤共采、煤层气与原位富油煤共采,推动中浅部煤层气与煤炭协同勘探开发;开展煤系叠合型气藏开发、煤层气与煤系气共探共采、煤系全油气系统勘探开发,推动深部煤层气与油气协同勘探开发,已有关注和探索;煤层气与煤、油气共探共采是第5个突破方向。成果试图为新疆煤层气大规模高效勘探开发提供技术支持和工程决策参考。

新疆准噶尔盆地白家海凸起深部煤层气勘探开发进展及启示

白家海凸起侏罗系煤是国内深部煤层气直井产量很早取得突破的地方,为准噶尔盆地的重要靶区。煤储层为特低灰、低水分、中高挥发性煤,孔渗系统较好。具有“古生新储”和“自生自储”两种成藏模式,煤层含气量高、游离气占比高、含气饱和度高,为优质煤层气储层。历经多年的勘探开发证明:多数直井试采无需排水降压即可快速见气(2~5 d),排采初期日产气量较高(2100~9890 m^(3)),日产水量少甚至不产水(<5 m^(3)),可自喷生产,返排率低,长期试采压力均衡下降,且具有一定的稳产期(25~60 d);煤层射孔层厚度、压裂液体系、压裂加砂比均可影响煤层气试气效果,其中冻胶、胍胶体系优于活性水-清洁压裂液体系。最新施工的彩探1H水平井试采表现出压裂开井后即高产,试采最高日产气量5.7万m^(3),日产水量少(0.5~3.0 m^(3)),表现出常规天然气特征,随后衰减稳定,表现为吸附气与游离气共同产出;与直井对比,水平井产量高、稳产时间长、压降速率小。基于研究区储层特征和含气性特征,及勘探开发历程,得到3方面启示。一是深部多类型气藏富集规律再认识:需重视油气运聚圈闭的成藏演化研究,重视深部位气水空间分配和富集规律的研究。二是深部中低阶煤储层可压性评价:针对凸起高部位孔渗系统好的中低煤阶储层,需形成适合的压裂工艺体系。三是深部多类型气藏开发方式优化:针对游离气占比高的气藏,实现游离气-吸附气的接续产出,保持降压面积稳定扩展,排采控制尤为关键。

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。

基于层次分析灰色定权聚类的煤层气开发甜点预测方法——以柿庄北区块为例

随着煤层气产业的发展以及非常规油气勘探开发一体化的要求,当前煤层气的勘查评价工作逐渐由勘探选区向开发甜点选区推进。然而,受限于勘探开发阶段或资料占有程度,当前多数的选区评价体系对煤储层的可改性和煤层气的可采性考虑不足,在指导开发区井位优选或加密井方面效果不佳。基于沁水盆地柿庄北区块100余口煤层气参数井和开发井资料,分析区内3号煤层煤层气开发的资源条件、储层可改造性和煤层气可采性,采用层次分析和灰色定权聚类方法构建评价模型,评价了煤层气开发甜点区,为区内新井和加密井的部署提供依据。评价模型以煤层含气量、煤厚反映煤层气资源条件;综合考虑地应力环境和岩石力学性质,构建储层综合可改造性参数,评价储层可改造性;使用原始结构煤和碎裂煤占比、临储比和储层原始渗透率反映煤层气的可采性。每个参数采用word聚类方法分级,每个点位(每口井)计算出综合优度并排序,最终划分出煤层气开发甜点区。评价结果表明,研究区中部综合优度大于65的地区为进一步开展开发工作的甜点区。

安徽省两淮煤田废弃煤炭矿井剩余资源综合调查、开发利用现状及展望

随着去产能政策和能源供给侧改革的深入推进,安徽省两淮煤田先后关闭了大量资源枯竭、经济亏损、产能落后的煤炭矿井。本文在综合调查两淮煤田废弃煤炭矿井剩余资源潜力的基础上,梳理了两淮煤田废弃煤炭矿井资源开发利用现状,分析了当前面临的主要问题。研究结果表明:截至2023年底,两淮煤田63处废弃煤炭矿井剩余煤炭资源约24.33亿t、煤层气约102.83亿m^(3)、可利用地下空间约7383.80万m^(3)、天然焦约3.45亿t,此外还有丰富的矿井水、地热和土地等其他可利用资源,具有良好的资源开发利用潜力。虽然目前两淮煤田在废弃煤炭矿井煤层气、矿井水、土地和共伴生矿产等资源开发利用方面已取得了一定的经济效益与社会价值,但仍然面临基础资料缺失、管理体系不完善、资源开发利用模式单一和利用率低等一系列问题。针对上述主要问题,本文从信息化建设、基础理论研究和探索资源开发利用模式三个方面提出了建议与展望,以期加快开发利用两淮煤田废弃煤炭矿井资源,提高资源利用率。

鄂尔多斯盆地煤层(岩)气勘探开发进展及发展方向

鄂尔多斯盆地历经30余年的不断探索,已在盆地东缘形成了超千亿立方米探明储量规模的浅层煤层气产业基地,并于2019年后逐步实现了盆地深层煤岩气勘探开发重大突破。为了进一步推动盆地深层煤岩气规模效益开发,在系统梳理盆地煤层(岩)气勘探开发历程和开发地质特征的基础上,总结了盆地煤层(岩)气勘探开发取得的主要成果和形成的关键勘探开发技术,提出了煤层(岩)气勘探开发的理论与技术发展方向。研究结果表明:①盆地主体经历了勘探开发探索(1991-2002年)、典型区带勘探开发突破(2003-2008年)、浅-中层煤层气规模勘探开发(2009-2018年)和深层煤岩气规模勘探开发(2019年至今)4个阶段,煤层(岩)气产量和深度不断取得重大突破;②受控于沉积环境、埋深、构造、水文条件、应力场等地质因素,煤层(岩)气从浅层向深层形成孔渗物性变差、游离气含量增加、含水量降低等储层特征演化,生产特征由排水采气转变为开井见气;③深层煤岩气勘探思路由有利区向地质-工程一体化甜点区转变,形成了地下-地面一体化的大井丛井网设计技术,研发了“密切割+大排量+组合支撑剂+前置酸+变黏滑溜水”极限体积压裂技术体系,提出了全生命周期煤岩气排采理念和排采技术。结论认为:①浅层煤层气需要围绕“高产老区稳产、低产低效区盘活、未动用区效益建产、非主力层系接替”4个方面推动规模效益开发;②深层煤岩气继续强化“煤系组合-煤层结构-煤体结构-煤岩类型”4个层次差异,完善“地应力-天然裂缝-人工裂缝-井型与方位-井网井距”五位一体井网设计,攻关“立体勘探、有序开发、多气协同、效益产出”开发技术。