煤层气流压回升型不正常井储层伤害机理与治理

合理控制套压和井底流压、合理排水降压采气是提高煤层气井开发效果的关键技术。井底流压回升可抑制煤层气解吸产出,造成储层伤害,降低煤层气井产量,影响煤层气井开发效果。通过沁水盆地樊庄区块生产实践动态分析、理论研究和室内实验,提出了煤层气流压回升型不正常井起因,通过理论研究和现场数据分析,明确煤层气井流压回升对储层伤害机理,提出流压回升对储层伤害程度评价方法及治理对策。研究结果表明:煤层气井煤没度增加导致套压降低,套压下降速率越快,则井底流压下降越快;煤没度增加速率过快的煤层气井,其井底流压回升对储层伤害严重,导致气体产出阻力增加,部分气体被毛细管压力封堵在孔隙中,难以产出。流压回升伤害指数可以表征流压回升导致储层伤害程度,抽油泵凡尔漏失和气锁导致煤层气井排水量小于煤层向井筒供水量是井底流压回升的主要原因,其治理措施可通过液压冲洗清除固定凡尔煤粉,通过机械振动清除游动凡尔煤粉,通过恒沉没防气锁工艺与煤层气井间断抽水工艺相结合措施治理气锁。      

An improved permeability model of coal for coalbed methane recovery and CO2 geosequestration

An alternative approach is proposed to develop an improved permeability model for coalbed methane (CBM) and CO₂-enhanced CBM (ECBM) recovery, and CO₂ geosequestration in coal. This approach integrates the textural and mechanical properties to describe the anisotropy of gas permeability in coal reservoirs. The model accounts for the stress dependent deformation using a stress–strain correlation, which allows determination of directional permeability for coals. The stress–strain correlation was developed by combining mechanical strain with sorption-induced strain for any given direction. The mechanical strain of coal is described by the general thermo-poro-elastic constitutive equations for solid materials under isothermal conditions and the sorption-induced strain is approximated by treating the swelling/shrinkage of coal matrix equivalent to the thermal contraction/expansion of materials. With directional strains, the permeability of coal in any given direction can be modeled based on the theory of rock hydraulics. In this study, the proposed model was tested with both literature data and experiments. The experiments were carried out using a specially designed true tri-axial stress coal permeameter (TTSCP). The results show that the proposed model provides better predictions for the literature data compared with other conventional coal permeability models. The model also gives reasonable agreement between the predicted and measured stress–strains and directional permeabilities under laboratory conditions.     

Distribution rule of the in situ stress state and its influence on the permeability of a coal reservoir in the southern Qinshui Basin,China

The recent development of the coalbed methane (CBM) industry has a significant role in advancing hydraulic fracturing theory and technology. However, further development requires a better understanding of how fractures influence reservoir permeability. In situ stress data from 54 CBM wells in the southern Qinshui Basin, China, were obtained by the injection/falloff test method to analyse the effect of in situ stress on the permeability of the CBM reservoir. The types of in situ stress states were classified, and the coal reservoir permeability under different in situ stress states was analysed. The results indicate that the maximum horizontal principal stress (σ_H), minimum horizontal principal stress (σ_h) and vertical principal stress (σ_v) all have positive linear relationships with the coal seam burial depth. Three in situ stress states were observed from the shallow to deep regions of the CBM reservoir in the study area: σ_H?>?σ_h?>?σ_v, σ_H?>?σ_v?>?σ_h and σ_v?>?σ_H?>?σ_h, which account for 9, 76 and 15% of the test wells, respectively. Coal reservoir permeability decreases with increasing horizontal principal stress, whereas it first decreases with increasing σ_v, then increases and finally decreases. The variation in permeability with σ_v is due to the conversion of the in situ stress states. Coal reservoir permeability has obvious differences under different in situ stress states. The permeability is the largest when σ_v?>?σ_H?>?σ_h, followed by σ_H?>?σ_h?>?σ_v and smallest when σ_H?>?σ_v?>?σ_h. The permeability differences are caused by the fracture propagation shape of the rock strata under different in situ stress states.     

高阶煤煤层气井稳产时间预测方法及应用

煤层气井稳产时间预测对煤层气井合理稳产气量预测与排采制度优化具有重要意义。基于沁水盆地南部樊庄?郑庄区块不同井型的大量生产数据,明确煤层气井稳产阶段及稳产时间的基本概念,提出稳产时间预测经验公式并分析其影响因素。结果表明,煤层气井依靠持续降低井底流压保持稳产,稳产时间为开始稳产时刻的井底流压降至集气管线压力所用的时间。提出能够有效表征直井、L型筛管水平井、L型套管压裂水平井稳产阶段累积稳产时间与井底流压关系的经验公式,基于经验公式得到的最终稳产时间计算公式能够准确预测各井型的稳产时间,误差仅为?8.30%~8.03%。稳产时间的影响因素较多,第一,稳产流压损耗系数越大稳产时间越短,稳产流压损耗系数与解吸压力成反比,与提产流压损耗系数成正比,提产流压损耗系数控制在0.006 5 d?1以下利于长期稳产;第二,开始稳产时刻,井底流压越高、稳产时间越长,应该高压提产、高压稳产;第三,对不同的煤层气井,稳产气量高,稳产时间不一定短,需确定合理的稳产气量。提出的稳产时间计算方法可实现不同稳产气量下稳产段累积产气量的预测,进而可确定合理的稳产气量。      

不同煤阶煤应力敏感特征及其控制机理

煤储层应力敏感降低储层渗透率,进而影响煤层气井产能,如何降低排采中的应力敏感性影响值得深入研究。为了弄清不同煤阶煤储层的应力敏感性特征及差异性,分别采集樊庄高煤阶煤、保德中煤阶煤和二连低煤阶褐煤的样品,系统开展加载和卸载过程中不同煤阶煤的应力敏感性实验,并对应力敏感的产生机理进行分析。结果表明,随煤阶的升高,煤样的应力敏感性逐渐增强,含明显裂缝的样品敏感性更强。加载有效应力10 MPa条件下,相比初始渗透率,二连低煤阶褐煤样品渗透率下降79.26%,卸载后不可逆渗透率损害率平均33.4%;保德中煤阶煤样渗透率下降79.4%,卸载后不可逆渗透率损害率平均51.4%;樊庄高煤阶煤样加载后渗透率下降92.33%,卸载后渗透率只能恢复30%左右。产生这种差异的机理主要是由于不同煤阶煤的物质组成、孔裂隙结构以及渗流通道不同造成的。低煤阶煤变质程度低,主要发育大、中孔隙,割理–裂隙不发育,为基质孔隙–喉道渗流,渗透率主要受连通喉道控制,应力加载时主要是大、中孔压缩变形严重,而尺度较小的喉道受压缩变形小,因而其应力敏感性相对弱;而高煤阶煤孔隙以微、小孔为主,镜质组含量高,割理–裂隙发育,控制其渗透性,应力加载时微、小孔难以被压缩,而裂隙抗变形能力弱,易发生韧性变形破坏或闭合,卸载后也难以恢复,表现出强应力敏感特征。考虑到高煤阶煤储层埋深更大、应力更高,因此其应力敏感性对产能伤害大,排采初期宜以较小强度进行,降低不可逆渗透率伤害,扩大压降范围;而低煤阶煤储层本身应力低、渗透率较高,应力敏感对产能影响相对较小,排水期可适当加快速度,提高排水效率。      

山西阳泉矿区煤层气分层排采分析

煤层气开发过程中,由于各煤层及其顶底板之间物性特征等方面的差异,易导致层间干扰,影响煤层气产能。阳泉矿区煤层气资源储量丰富,主要可采煤层有3#、8#、9#、15#煤层,其中3#煤层为局部可采煤层。以该区YQ-191和YQ-359井为例,通过分析8#、9#、15#煤层在渗透率、储层压力、煤层厚度、含气量、埋藏深度、水文地质条件的差异,发现,YQ-191井8#、9#的各项参数较为接近,层间干扰小,适宜合层开采;YQ-359井8#、15#煤层渗透率与储层压力相差较大,层间干扰严重,合层开采严重影响15#煤层的产能,该井8#、15#煤层不适宜合层开采。     

Determination of in-situ stress direction from cleat orientation mapping for coal bed methane exploration in south-eastern part of Jharia coalfield, India

Accurate prediction of in-situ stress directions plays a key role in any Coal Bed Methane (CBM) exploration and exploitation project in order to estimate the production potential of the CBM reservoirs. Permeability is one of the most important factors for determination of CBM productivity. The coal seams in Jharia coalfield generally show low permeability in the range of 0.5 md to 3 md. To estimate the in-situ stress direction in the study area, an attempt has been made to undertake the cleat orientation mapping of four regional coal seams of two underground coal mines located at south-eastern part of Jharia coalfield, India. Cleat orientation mapping is critical to determine the maximum principal compressive horizontal stress (S_H) direction for CBM exploration and exploitation, which in turn controls the direction of maximum gas or water flow though coal beds. From the field study it is found that the average face and butt cleat azimuths are towards N15°W and N75°E respectively. Average permeability of the four above-mentioned major coal seams has been calculated from well logs of nine CBM wells distributing over an area of 7.5 km², adjacent to the underground mines. The cleat orientations are congruous with the regional lineament pattern and fits well with the average permeability contour map of the study area to infer the orientation of in-situ maximum horizontal stress. Goodness of fit for the exponential regressions between vertical stress and permeability for individual coal seams varies between 0.6 and 0.84. The cleat orientation is further validated from the previous fracture analysis using FMI well log in Parbatpur area located southern part of the Jharia coalfield. The major coal seams under the study area exhibit directional permeability, with the maximum permeability, oriented parallel to the direction of face cleat orientation.     

河北省煤层气资源及其勘探开发建议

河北省煤层气资源分布总体呈现南高北低、东高西低的趋势,煤层气集中在邯峰矿区-开平煤田的NE向带状区域。通过对省内4个重点区及5个一般地区煤层资源评价,底板标高-2000m以浅的煤层气资源总量为6046．32亿m^3,可采资源量为2523亿m^3,主要分布在底板标高为-1500m～-2000m的煤层中。根据煤层气资源和煤储层物性特征,认为峰峰矿区是河北省煤层气勘查开发的有利地区。在大淑村、小屯矿等无烟煤、贫煤发育区,可实施短半径水平分支井;在煤层气富集、渗透率适当的中煤级煤地区,可以实施垂直井或井组;在高瓦斯的煤矿开拓区,可以采用三维立体的煤层气（瓦斯）抽采模式。     

我国煤层气高效开发关键技术研究进展与发展方向

"十三五"期间,围绕"突破煤层气单井产量低"这一制约我国煤层气高效开发的重大难题,借助国家科技重大专项和其他技术攻关研究,煤层气勘探开发理论认识和工程技术都取得明显进展,表现在4个方面:(1)勘探理念从寻找富集甜点区向高产甜点区转变,开发部署由平铺式到精细化调整转变.(2)围绕高效增产技术方面,在实现由二维地震向三维地...     

低渗煤层压裂机理及应用

构造煤由于煤层渗透性低,地面煤层气开发进程迟缓。通过研究低渗煤层的地质模型,结合以往工程实践经验分析,探讨了低渗煤层中采用水力压裂技术进行储层改造增产的机理,并在淮北矿区芦岭煤矿地面煤层气井中进行了应用。研究表明,采用高强度水力压裂技术工艺可在低渗煤层中产生比较长的裂缝,取得比较理想的产气效果。研究结果对我国碎软低渗煤层开展地面煤层气开发具有一定的推动作用。      

煤层气井排采动态主控地质因素分析

沁水盆地寿阳区块和柿庄区块煤层气(CBM)井的排采动态在整体上表现出明显差异,而单一区块内部煤层气井的排采动态也存在较大差异。本文就两个区块的煤系地层沉积相、煤层渗透率、断裂构造、地应力类型和构造应力强度以及顶底板岩性组合类型等因素对排采动态的影响开展对比分析。基于静态地质条件和排采动态资料的综合研究表明:煤系地层沉积相、煤层渗透率、地应力类型和构造应力强度的差异是两个区块煤层气井排采动态差异的主要原因;单一区块内煤层气井的排采动态差异受控于局部断裂构造、地应力类型以及煤层顶底板岩性组合类型等局部因素;在煤层气开发选区和开发井位部署时,应综合考虑资源量、渗透率和多种局部地质因素的共同影响。     

煤储层应力敏感性试验及其评价新方法

煤储层应力敏感性是影响煤层气井产能的关键地质因素,在煤层气井排采过程中如何降低或避免煤储层应力敏感性对渗透性的影响是值得考虑的问题。通过不同应力下煤储层渗透性试验,研究了有效应力作用下煤储层渗透率的变化规律;在对已有应力敏感性评价参数分析的基础上,提出了新的应力敏感性系数S₁与S₂,揭示了有效应力对煤储层渗透性的影响规律。研究结果表明:煤储层渗透率随有效应力的增加按负指数函数规律降低,在煤层气开发中煤储层表现出明显的应力敏感性;试验煤样应力敏感回归系数a为0.099~0.115 MPa-1,平均为0.108 MPa-1,应力敏感性系数S₁为0.383~0.436,平均为0.414,应力敏感性系数S₂为0.572~0.666,平均0.625;应力敏感性系数S₁与S₂具有整体性与唯一性,可以结合应力敏感回归系数a进行煤储层渗透率应力敏感性评价。      

高阶煤煤层气井产量递减规律及影响因素

为揭示高阶煤煤层气井产量递减规律，基于沁水盆地南部樊庄区块10余年的开发数据，通过数值模拟、统计分析等方法，对现有开发技术条件下高阶煤煤层气井产量递减点（即煤层气井产量开始递减时的煤层气采出程度）、递减类型及影响因素进行分析。结果表明:樊庄区块煤层气井产量递减点平均为25%，单井平均递减点为21%，大部分井在排采4 a后开始递减；煤层气井递减点由基质渗透率和裂缝半长决定，基质渗透率和裂缝半长越大，单井有效控制半径越大、有效控制储量越多，递减点越大；基质渗透率越高，裂缝半长增加引起的递减点增幅越大。由此可知，渗透率是煤层气井递减类型的主控因素，渗透率越高，递减指数越小，递减速度越慢。随着渗透率增加，递减类型依次为线性递减、指数递减和双曲递减。综合分析认为，储层平均孔隙半径越大，煤的应力敏感性越弱，煤基质收缩对渗透率的改善程度越大，导致储层动态渗透率越高，递减速度越慢。该研究为合理控制高阶煤煤层气井产量递减具有指导意义。移动阅读      

柳林地区煤层气开采动态及单井产量主控因素分析

柳林地区是我国煤层气勘探开发的热点地区之一,初步实现了煤层气商业化开发。根据柳林地区煤层气井生产数据,对气井产气动态进行了分析,按产量大小进行了气井统计,中产气井比例较高,为42.9%,高产气井占28.6%,低和极低产气井比例为28.5%。分析煤层气井排采曲线特征,总结归纳气井的产气模式有单峰式、高峰-稳定式和低峰-高峰-稳定式三类。从影响煤层气产能的构造、气含量、渗透率、煤层厚度、煤层埋深、水文地质条件等地质因素入手,分析了各地质因素对气井产能的影响,并建立各类因素与煤层气井产能的关系。研究认为:柳林地区煤层气井的高产条件并非受单一因素的控制,而是主要取决于多种有利地质主控因素的有机匹配、共同作用的结果。      

Evaluation of the reservoir permeability of anthracite coals by geophysical logging data

Permeability is one of the most significant reservoir parameters. It is commonly obtained by experiment, history simulation, injection/falloff well test and geophysical logging. Among these, geophysical logging remains as the most economic and efficient technique in evaluating coal permeability in the vicinity of an open-hole. In this paper, geophysical logging data are used to evaluate the coal reservoir permeability for the No. 3 coal seam in the southern Qinshui Basin (Fanzhuang and Zhengzhuang coal zones). Ideally coal reservoirs consist of coal matrix and fracture networks that can be represented by a model called a collection of sheets. Based on the model, coal reservoir permeability can be quantitatively calculated using the theoretical formula of k_f = 8.50 × 10^− 4 w²φ_f, in which fracture width (w) and fracture porosity (φ_f) were obtained by dual laterolog and density logging data, respectively. Calculative results show that coal reservoir permeability ranged from 0.017 mD to 0.617 mD for the Fanzhuang coal zone and from 0.047 mD to 1.337 mD for the Zhengzhuang coal zone. The permeability decreases with coal burial depth, reflecting variations in penetration capability of coal reservoirs at varying depths. Comparing results with those from injection/falloff well tests, however, shows that the model-calculated permeability is slightly higher. This is expected because the model did not include the influence from coal anisotropy.     

基于煤矿“先抽后建”及资源开发的煤层气地面井位抽采部署及应用

针对目前煤矿"先抽后建"提出的安全指标及贵州黔北矿区多煤层的资源特征,同时弥补目前地面抽采部署缺乏系统性、盲区大的问题,以贵州对江南煤矿为例,进行了煤层气地面抽采井位部署研究。综合该区复杂的地形条件、煤层发育特征（层数多、厚度薄、成群分布）、煤体结构及开发部署要求,优选出分段压裂水平井为主、丛式井为辅的开发方式。沿着1、2号采掘工作面分别部署了4个水平井组和16个垂直井（丛式井）,占地7个井场。通过精细化地质模型建立、网格划分,利用CBM-SIM数值模拟软件模拟了20口井（井组）5 a地面抽采效果平均日气量可达26 036.54 m3,地面抽采5 a后1、2号工作面内M78煤层气含量降幅超过30%。模拟结果显示,对江南煤矿的精细化井位抽采部署,有效降低了采掘工作面瓦斯含量,兼顾煤矿安全生产和煤层气资源利用的双重目的。该方法可为煤层气地面抽采及煤矿井下采掘安全协同发展,提供新思路、新方法。      

沁水盆地南部煤层气直井合层排采产气效果数值模拟

随着煤层气勘探开发的深入,多煤层合层排采受到广泛关注。合层排采管控工艺是确保煤层气合采井高产稳产的关键,而多煤层组合条件下复杂的地质条件增加了合层排采管控的难度。数值模拟技术是研究煤层气井合层排采管控工艺的有效手段,科学、可靠的模拟结果可为合采井排采管控提供依据。考虑温度效应、煤基质收缩效应、有效应力作用对煤层流体运移规律以及渗透率等煤层物性参数的影响,建立煤层气直井合层排采生产动态过程多物理场耦合数学模型,并进行有限元法的多物理场耦合求解。通过对沁水盆地南部郑庄区块煤层气合采井组的模拟,探讨不同排采速率下煤层气直井合层排采产气效果及渗透率等煤层物性参数动态演化特征,提出煤层气直井合层排采工程建议。模拟结果显示,郑庄区块3号、15号煤层整体含气量较高,煤层气合采井组具有较大增产潜力,提高排采速率对提高煤层气采收率的效果不显著;排采过程中,煤基质收缩效应对渗透率的影响强于有效应力作用,是提高煤层气井排采速率的保障,在确保排采速率不超过煤层渗流能力上限的基础上,适当提高排采速率可实现煤层气井增产。基于模拟结果,建议排采速率的调整以控制动液面或液柱压力为主;以3号、15号煤层气合采井增产为目标,产水阶段和憋压阶段,郑庄区块煤层气直井合层排采速率以液柱压力降幅0.12~0.20 MPa/d或动液面降幅12~20 m/d为宜,既可实现煤层气增产,又可避免储层伤害。      

采动煤岩渗透率演化模型及数值模拟

为描述采动煤岩渗透率演化过程,引入强度退化指数,基于Hoek-Brown强度准则,建立了考虑围压影响的煤岩应变软化力学本构模型。给出了体积应变和渗透率的关系方程,结合应变软化模型建立了采动煤岩渗透率演化模型,并在FLAC下予以实现。通过数值模拟研究了不同围压下圆柱岩样的峰后应变软化力学行为和某煤矿工作面开采过程中煤岩的渗透率演化过程,结果表明：（1）该模型能较好地反映围压对煤岩峰后应变软化行为的影响;（2）随着工作面推进,越来越多的煤岩单元破坏,渗透率也不断增长,逐渐成为瓦斯等流体运移的主要通道。（3）模型能再现采动煤岩渗透率演化的动态过程,从而为煤与瓦斯共采、煤层瓦斯抽放和瓦斯灾害防治提供指导。     

Evaluation of the damages of permeability and effective porosity of tectonically deformed coals

A high rank coal was tested in terms of loading and unloading to characterize changes in the permeability and effective porosity of tectonically deformed coals. The coal sample, an anthracite, is subdivided into four types according to its structure, namely, the primary structure coal, cataclastic coal (the weakest deformation coal), granulated coal (the moderate deformation coal), and mylonitic coal (the intensest deformation coal); the latter three types are considered to be tectonic deformation coals. Permeability of tectonically deformed coals shows a negative exponential relation to stress. The intenser the structural deformation in coal is, the lower the permeability. Two evaluation parameters, namely, loss rate m (0.8318–0.9476) and damage rate n (0.447–0.6556), which are related to changes in permeability, increase with increasing structural deformation in coal. The cleat compressibility factor declines with increasing difference in effective stress and increases with increasing structural deformation in coal. This study proposes a calculation method for evaluating the porosity damage. Similar to the loss ratio and damage rate, this parameter (η) increases with increasing structural deformation in coal and reveals the relationship between the porosity damage and the structural deformation in coal.     

洞穴完井工艺在寿阳地区煤层气钻井中的应用

洞穴完井工艺包括钻井、完井、排水采气等工序,为提高煤层渗透率,最大限度的保证煤层气解析与运移,洞穴完井一般要求有效井径3-4m,及一定范围的破碎带。远东能源公司为开采寿阳地区15#煤层中的煤层气,部署了4口生产井．其井身设计为三开结构。钻井主要设备为T685WS顶驱车载钻机及多台不同型号的空压机,采用潜孔锤冲击钻进．以空气、空气泡沫为冲洗介质,钻进至15#目标煤层底板以下46m处完钻,然后利用可伸缩式扩孔器进行扩孔。在扩孔至距三开井底8～10m时．开始采用空气和清水憋压,通过瞬间释放压力,使煤层坍塌,如此反复,至造穴直径达到要求。由于严格按照技术标准及操作流程作业,采取的技术措施合理,4口井均已顺利投入生产,增产效果显著。可见该种洞穴完井技术的应用,不仅可以保护煤层原生结构及环境,并且还能减少煤层气射孔、压裂等环节的费用．对于煤层气井施工具有重要的经济意义。