Coalbed Methane-bearing Characteristics and Reservoir Physical Properties of Principal Target Areas in North China

The coalbed methane (CBM) resources in North China amounts up to 60% of total resources in China. North China is the most important CBM accumulation area in China. The coal beds of the Upper Paleozoic Taiyuan and Shanxi formations have a stable distribution. The coal reservoir of target areas such as Jincheng, Yanquan-Shouyang, Hancheng, Liulin, etc. have good CBM-bearing characteristics, high permeability and appropriate reservoir pressure, and these areas are the preferred target areas of CBM developing in China. The coal reservoirs of Wupu, Sanjiaobei, Lu'an, Xinmi, Anyang-Hebi, Jiaozuo, Xinggong and Huainan also have as good CBM-bearing characteristics, but the physical properties of coal reservoirs vary observably. So, further work should be taken to search for districts with high pressure, high permeability and good CBM-bearing characteristics. Crustal stresses have severe influence on the permeability of coal reservoirs in North China. From west to east, the crustal stress gradient increases, while the coal reservoirs permeability decreases.

A Comprehensive Appraisal on the Characteristics of Coal-Bed Methane Reservoir in Turpan-Hami Basin

The rich coal-bed methane resources in the Turpan-Hami Basin are mainly located in the Shisanjianfang,Hami,Shanshan,Sha'erhu,Kekeya,Kerjian,Aidinghu inclines and the Dananhu coal-bed methane reservoirs. The big-ger coal-bed reservoirs are sitting at a depth of less than 1500 m. The coalbed methane generation,storage and confin-ing conditions of the Turpan-Hami basin can be indicated by eight key parameters. They are coal-bed thickness,coal rank,missing period,permeability,Langmuir volume,rock covering ability,structural confinement and hydrodynamic sealing environment. These parameters constitute a comprehensive appraisal index system of the coal-bed methane res-ervoir characteristics of the Turpan-Hami basin. In these parameters,the missing period of coal-bed methane is indi-cated by a stratum missing intensity factor. It reflects the relative exposure period of coal series. The results of a fuzzy comprehensive judgment showed that the Shisanjianfang coal-bed methane reservoir has the best prospects for exploita-tion and the Sha'erhu,Shanshan,Hami coal-bed methane reservoirs are next in line.

Physical simulation of hydrodynamic conditions in high rank coalbed methane reservoir formation

In order to select highly productive and enriched areas of high rank coalbed methane reservoirs,based on hydrologic geology as one of the main factors controlling coalbed methane(CBM) reservoir formations,the effect of hydrodynamic forces controlling CBM reservoir formations was studied by a physical simulation experiment in which we used CBM reservoir simulation facilities.The hydrodynamic conditions of high coal rank reservoirs in the Qinshui basin were analyzed.Our experiment shows the following results:under strong hydrodynamic alternating action,δC1 of coalbed methane reservoir changed from the start at -2.95%～-3.66%,and the lightening process occurred in phases;the CH4 volume reduced from 96.35% to 12.42%;the CO2 volume decreased from 0.75% in sample 1 to 0.68% in sample 2,then rose to 1.13% in sample 3;the N2 volume changed from 2.9% in sample 1 to 86.45% in sample 3.On one hand,these changes show the complexity of CBM reservoir formation;on the other hand,they indicate that strong hydrodynamic actions have an unfavorable impact on CBM reservoir formation.It was found that the gas volume and hydrodynamic intensity were negatively correlated and low hydrodynamic flow conditions might result in highly productive and enriched areas of high rank CBM.

Characteristics of Coalbed Methane Resources of China

The paper deals with the coalbed methane gas-bearing characteristics such as the gas content, theoretical gas saturation, gas concentration and abundance, as well as coal reservoir characteristics such as the adsorption, desorption and permeability of China's coal reservoirs. The paper also introduces the resources of coalbed methane with a gas content ≥ 4 m3/t and their distribution in China.

Anisotropy of crack initiation strength and damage strength of coal reservoirs

The crack volume strain method and acoustic emission(AE)method are used to analyze the anisotropy of the crack initiation strength,damage strength,the failure mode and the AE characteristics of coal reservoir.The results show that coal reservoirs show obvious anisotropic characteristics in compressive strength,cracking initiation strength and damage strength.The compressive strength of coal reservoirs decreases with the increase of bedding angle,but the reservoirs with bedding angles of 450 and 900 differ little in compressive strength.The crack initiation strength and damage strength decrease first and then increase with the increase of bedding angle.The crack initiation strength and damage strength are the highest,at the bedding angle of 0°,moderate at the bedding angle of 90°,and lowest at the bedding angle of 45°.When the bedding angle is 0°,the failure of the coal reservoirs is mainly steady propagation of large-scale fractures.When the bedding angle is 45°,one type of failure is caused by steady propagation of small-scale fractures,and the other type of failure is due to a sudden instability of large-scale fractures.When the bedding angle is 90°,the failure is mainly demonstrated by a sudden-instability of small-scale fractures.Compared with the cumulative count method of the AE,the cumulative energy method is more suitable for determining crack initiation strength and damage strength of coal reservoirs.

Physical characteristics of high-rank coal reservoirs in different coal-body structures and the mechanism of coalbed methane production

The physical characteristics of coal reservoirs are important for evaluating the potential for gas desorption,diffusion,and seepage during coalbed methane(CBM)production,and influence the performance of CBM wells.Based on data from mercury injection experiments,low-temperature liquid nitrogen adsorption,isothermal adsorption,initial velocity tests of methane diffusion,and gas natural desorption data from a CBM field,herein the physical characteristics of reservoirs of high-rank coals with different coal-body structures are described,including porosity,adsorption/desorption,diffusion,and seepage.Geometric models are constructed for these reservoirs.The modes of diffusion are discussed and a comprehensive diffusion-seepage model is constructed.The following conclusions were obtained.First,the pore distribution of tectonically deformed coal is different from that of normal coal.Compared to normal coal,all types of pore,including micropores(<10 nm),transitional pores(10-100run),mesopores(100-1000 nm),and macropores(>1000 nm),are more abundant in tectonically deformed coal,especially mesopores and macropores.The increase in pore abundance is greater with increasing tectonic deformation of coal;in addition,the pore connectivity is altered.These are the key factors causing differences in other reservoir physical characteristics,such as adsorption/desorption and diffusion in coals with different coal-body structures.Second,normal and cataclastic coals mainly contain micropores.The lack of macropores and its bad connectivity limit gas desorption and diffusion during the early stage of CBM production.However,the good connectivity of micropores is favorable for gas desorption and diffusion in later gas production stage.Thus,because of the slow decline in the rate of gas desorption,long-term gas production can easily be obtained from these reservoirs.Third,under natural conditions the adsorption/desorption properties of granulated and mylonitized coal are good,and the diffusion ability is also enhanced.However,for in situ reservoir conditions,the high dependence of reservoir permeability on stress results in a weak seepage of gas;thus,desorption and diffusion is limited.Fourth,during gas production,the pore range in which transitional diffusion takes place always increases,but that for Fick diffusion decreases.This is a reason for the reduction in diffusion capacity,in which micropores and transitional pores are the primary factors limiting gas diffusion.Finally,the proposed comprehensive model of CBM production under in situ reservoir conditions elucidates the key factors limiting gas production,which is helpful for selection of reservoir stimulation methods.

Impact of Reservoir Properties on the Production of the Mannville Coal Measures, South Central Alberta from a Numerical Modelling Parametric Analysis

Numerical simulations are used to investigate the impact of intrinsic and extrinsic reservoir properties on the production from coal and organic rich lithologies in the Lower Cretaceous Mannville coal measures of the Western Canadian Sedimentary Basin. The coal measures are complex reservoirs in which production is from horizontal wells drilled and completed in the thickest coal seam in the succession (1 m versus 3 m), which has production and pressure support from thinner coals in the adjacent stratigraphy and from organic-rich shales interbedded and over and underlying the coal seams. Numerical models provide insight as to the relative importance of the myriad of parameters that may impact production that are not self-evident or intuitive in complex coal measures.

Importance of Well Spacing and Orientation for Multi-Lateral Pads on Production: Learnings from Production Analysis and Numerical Modelling of the Mannville Coal Measures, South Central Alberta

The modelling results from numerical simulations of the Early Cretaceous, Mannville coal measures with anisotropic permeability provide insights into development strategies not readily visualized or otherwise intuitive. The complex relationships between water and gas production, the contribution from multiple coal seams as well as from organic rich shales, and the impact of well interference combined with anisotropic fracture permeability are investigated through a series of numerical simulations of four well-pads (on the corners of a square mile of land with decreasing well spacing from 1, 3, to 4 laterals per pad). After 25 years of production, the two pads with optimally-oriented laterals with respect to the fracture permeability anisotropy produce 61% of the recovered gas for the 1 lateral/pad model, 52% for the 3 laterals/pad model, and 50% for the 4 laterals/pad model. Downspacing has a greater impact on increasing the gas production from pads with the poorly-oriented main laterals than from the pads with the optimally-oriented main laterals. The cumulative gas production at the end of the 25 year history is 4.2% higher for an optimally-oriented pad (pad1) and 1.1× higher for a poorly-oriented pad (pad3) for a model with 4 laterals/pad than 3 laterals/pad and an optimally-oriented pad is 1.1% higher for an optimally-oriented pad and 1.5× higher for a poorly-oriented pad for a model with 3 laterals/pad than 1 lateral/pad. Although downspacing from 3 to 4 laterals/pad has a greater impact on increasing the cumulative gas production from optimally-oriented pads than downspacing from 1 to 3 laterals/pad, the lower impact on poorly-oriented pads results in a lower total increase the cumulative gas production from the four pads. At the end of the 25-year production history, 9.0% more gas is recovered for the 4 lateral/pad model than the 3 lateral/pad model, which predicts 1.2× more gas than the 1 lateral/pad model. The recovered shale gas exceeds the recovered coal gas after ~7 years of production. The higher contribution of produced coal gas predicted due to downspacing results from a higher contribution of recovered gas from the main coal seam, while the contribution from the minor coal seams is lower. Downspacing has a minimal impact on the cumulative water production;after 25 years of production a difference of 1.0% is predicted between models with 4 and 3 laterals/pad and 1.7% between models with 1 and 3 laterals/pad. While downspacing increases the cumulative water production for the poorly-oriented pads (1.1× for 3 to 4 laterals/pad and 1.3× for 3 to 1 lateral/pad after 25 years), the cumulative water production for the optimally-oriented pads is lower over the majority of the production history (after ~4 years and 3.2% lower after 25 years for 3 to 4 laterals/pad and after ~6 months and 1.1× lower after 25 years for 1 to 3 laterals/pad).

海孜煤矿深部勘查区中组煤层气储层物性特征分析

【目的】煤层气储层的物性特征是进行煤层气开发研究的关键因子。【方法】重点对海孜煤矿深部勘探区域中组煤储层的物性参数进行调查,以对井田内中组煤储层物性特征进行研究。【结果】研究表明,煤层的物性特征适宜开采,其中有机显微组分占优,无机显微组分次之。该煤层含气量多,虽然煤层渗透率相对较小,但符合煤层气开采条件。煤层开采时的吸附作用一般,但有利于煤层气储集和缩短煤层气的开发周期。【结论】研究结果可为该研究区煤层气抽采提供可靠的技术参考。

黔西小屯井田煤层气多层合采产层组合优化

贵州小屯井田龙潭组煤系具有煤层数量多、煤层间距小、煤层厚度薄等特点,煤层气开发需以多层合采为主要方式;与单一厚层状煤层相比,多煤层合采易发生层间干扰,影响合采效果及资源动用程度。基于小屯井田钻孔岩性与含气性分析,识别出有利、较有利与不利3种煤岩层组合类型,考查各煤层厚度、埋深、含气量等特征,对比各煤层的煤层气资源条件,综合考虑储盖组合、含气性、渗透性、储层压力、地应力等因素,划分出Ⅰ(6上煤+6中煤+6下煤)、Ⅱ(7煤)、Ⅲ(33煤+34煤)共3套叠置煤层气系统;在此基础上,优化合采产层组合,并确定有序开发模式为优先开发上部产层组合(6上煤+6中煤+6下煤),其次为下部组合(33煤+34煤),最后考虑经济与时间成本确定是否单独开发7煤;确立了资源条件分析-含气系统划分-产层组合优化的多-薄煤层发育区煤层气合采层位优选思路。

鄂尔多斯盆地中东部本溪组深部煤岩分形特征与成储机理

对鄂尔多斯盆地石炭系本溪组8^(#)深部煤岩的代表性样品的煤岩工业组分、物性特征、孔隙特征进行实验分析,进而结合分形维数的方法对煤孔隙的非均质性展开研究,明确了煤岩工业组分对储层的影响机理。研究结果表明:(1)鄂尔多斯盆地中东部本溪组8^(#)煤岩的渗透性能和孔隙连通性较好,中上部煤岩的煤岩工业组分和储层物性优于下部;(2)研究区分形维数较高,孔隙结构复杂,储层非均质性较强,当灰分<20%时,少量矿物填充孔隙和裂隙,使得孔隙结构复杂程度减弱,储层逐渐均一,当灰分>20%时,大量的杂质矿物胶结和填充孔隙和裂隙,导致储层的非均质性增强;(3)煤岩的孔隙度受到灰分和热演化程度的影响,当灰分含量较低时,由于高热演化程度的煤发育大量的微孔,孔隙度升高,但会导致孔隙结构复杂,非均质性增强;(4)结合实验结果和工业组分对深部煤层气体扩散、运移影响进行研究,建议以低灰分低水分(A_(d)<20%,M_(ad)<2%)的中上部煤岩层段为优质深部煤层气开采层段。

鲁班山北矿15采区瓦斯赋存特征及地面预抽采部署

瓦斯地面预抽采能够提高煤炭的高效安全开采及实现瓦斯资源的有效利用,依据采区的瓦斯赋存特征可部署瓦斯地面预抽采井,从而助力区域煤与瓦斯高效协调开发。结合川南地区合鲁班山北矿15采区煤层展布情况、储层物性特征和瓦斯测试结果,从保存条件和资源条件2个方面分析瓦斯赋存的影响因素,采用体积法估算15采区主力煤层的瓦斯资源量,并根据15采区煤炭开采规划,结合矿井瓦斯地质特征和地形地貌特点以划分接替抽采区域且进行地面抽采井井位优选。优选结果显示:以15采区1518、1538工作面为先期试验区,以2和3号煤层(组)、7和8号煤层(组)为主,优选直井+定向井组合模式,形成不规则的丛式井组井网,矩形井网的长边方向与裂隙方向平行,井间距取值200~250 m。

煤储层含水性及其对煤层气产出的控制机理

煤储层的含水性不仅决定了煤层气吸附成藏理论的应用,影响储层改造措施的选取,也决定了对煤层气产出过程的认识。针对煤层的含水性,煤层气地质学认为煤储层基本饱和水,而瓦斯地质学在瓦斯含量计算和瓦斯渗流中基本没考虑水的影响,相当于认为煤储层饱和气。从煤层水来源、煤储层埋藏及热演化史的角度阐述了煤储层含水性的变化,分析现今煤储层可能存在饱和水、超低饱和含水、不饱和含水和不含水4种状态。煤储层热演化生烃及其造成的储层润湿性的改变,先存气体对后期水侵作用的影响是影响储层现今含水性的关键因素。由于我国构造运动复杂,多发生后期水侵,“大孔裂隙饱和水、小微孔饱和气”可能为多数煤储层气、水赋存状态。这种气、水赋存状态,可以有效回应煤层气地质理论中“煤储层饱和水,兰氏吸附理论不适用”的论点,同时也决定了在煤储层含气性分析中应该考虑毛管力的影响。此外,煤储层为低孔、低渗储层,早期的排采阶段一般为单相水流,煤层气的排采过程需要确定并考虑启动压力梯度的影响。综上所述,开展煤-水-甲烷条件下的煤储层润湿性研究,生烃作用及先存气体对储层含水性的影响研究,重新认识煤储层的含水性,并基于此进一步刻画煤层气的赋存和产出过程,可能是解决我国煤层气,特别是中、高煤阶煤层气低产问题的一把钥匙。

“Exploring petroleum inside source kitchen”: Connotation and prospects of source rock oil and gas

Based on the transitional background of the global energy structure, exploration and development of unconventional oil and gas, and investigation of key basins, the unconventional oil and gas resources are divided into three types: source rock oil and gas, tight oil and gas, and retention and accumulated oil and gas. Source rock oil and gas resources are the global strategic supplies of oil and gas, the key resource components in the second 150-year life cycle of the future petroleum industry, and the primary targets for "exploring petroleum inside source kitchen". The geological connotation of source rock oil and gas was proposed, and the models of source rock oil and gas generation, expulsion and accumulation were built, and five source rock oil and gas generation sections were identified, which may determine the actual resource potential under available technical conditions. The formation mechanism of the "sweet sections" was investigated, that is, shale oil is mainly accumulated in the shale section that is close to the oil generation section and has higher porosity and permeability, while the "sweet sections" of coal-bed methane(CBM) and shale gas have self-contained source and reservoir and they are absorbed in coal seams or retained in the organic-rich black shale section, so evaluation and selection of good "sweet areas(sections)" is the key to "exploring petroleum inside source kitchen". Source rock oil and gas resources have a great potential and will experience a substantial growth for over ten world-class large "coexistence basins" of conventional-unconventional oil and gas in the future following North America, and also will be the primary contributor to oil stable development and the growth point of natural gas production in China, with expected contribution of 15% and 30% to oil and gas, respectively, in 2030. Challenges in source rock oil and gas development should be paid more attention to, theoretical innovation is strongly recommended, and a development pilot zone can be established to strengthen technology and promote national support. The source rock oil and gas geology is the latest progress of the "source control theory" at the stage of unconventional oil and gas. It will provide a new theoretical basis for the new journey of the upstream business in the post-industry age.

工作面覆岩采动裂隙演化规律物理及数值模拟研究

了解工作面推进过程中采动裂隙的演化规律对于煤层气抽采及瓦斯控制至关重要。采用相似模拟和数值模拟的方法研究了工作面推进过程中采空区覆岩采动裂隙的演化规律,研究结果表明:采空区中部和采空区边界处靠近巷道的区域上覆岩层的采动裂隙存在截然不同的变化规律。采空区中部区域,上覆岩层的采动裂隙随着工作面的移进及越过呈现“迅速增加—逐步减低—稳定”的变化规律;采空区边界靠近巷道的区域,呈现“迅速增加—稳定”的变化规律。远离开切眼、靠近巷道的采空区上覆岩层采动裂隙发育最为充分;工作面走向平行于最大水平主应力时的各区域采动裂隙发育,显著高于工作面走向垂直于最大水平主应力时的;较硬直接顶对于提高采动裂隙渗透率有积极作用。

西北煤层气资源特征及开发潜力评价

通过对中国西部低阶煤储层煤层气资源分布及赋存特征的研究,认为西北地区煤储层含气量较低,但因煤层巨厚特征导致它含有巨大的煤层气资源量,占中国低阶煤层气总资源量的53.1%。另外,煤层气资源分布极不均匀,主要分布在新疆地区的准噶尔盆地和吐哈盆地。当前的开发实践显示,西北地区具有巨大的开发前景,但勘探开发主要集中在准噶尔盆地和吐哈盆地局部地区,仍需要加大勘探开发力度,加强煤层气战略选区评价。

低压低渗煤层气多分支水平井开发关键技术研究——以沁水盆地郑庄区块15号煤层为例

沁水盆地太原组15号煤层总体低压低渗低饱和,煤储层相对较薄,地质条件复杂,煤层气井产量普遍偏低。以沁水盆地郑庄区块为研究对象,依据本区15号煤层LDP-22H多分支水平井的成功开发经验,全面论述低压低渗煤储层煤层气钻完井工艺、标志层判定、井眼轨迹控制等关键技术。结果表明:采用钻井-录井-测井一体化地质导向技术可以有效卡准目的煤层,同时实时修正钻头轨迹,煤层平均钻遇率在97%以上,极大地提升了煤层有效进尺。865 d的排采实践表明,LDP-22H多分支水平井日产气量突破15万m^(3),日产气量稳定在8万m^(3)左右,全程累计产气量为2091.5469.3万m^(3),实现了超高产和稳产,标志着多分支水平井在低压低渗煤储层煤层气高效开发上有较好的适用性。另一方面,多分支水平井要优化井位,加强水平井底部位排采能力,稳定压降速率,减小对煤储层渗透率敏感性伤害,提高排采的连续性,减少停泵和检修作业频次,保证产能的延续性。

Coalbed methane reservoir boundaries and sealing mechanism

It is important to investigate the coalbed methane reservoir boundaries for the classification, exploration, and development of the coalbed methane reservoir. Based on the investigation of the typical coalbed methane reservoirs in the world, the boundaries can be divided into four types: hydrodynamic boundary, air altered boundary, permeability boundary, and fault boundary. Hydrodynamic and air altered boundaries are ubiquitous boundaries for every coalbed methane reservoir. The four types of the fault sealing mechanism in the petroleum geological investigation (diagen- esis, clay smear, juxtaposition and cataclasis) are applied to the fault boundary of the coalbed methane reservoir. The sealing mechanism of the open fault boundary is the same with that of the hydrodynamic sealing boundary. The sealing mechanism of the permeability boundary is firstly classified into capillary pressure sealing and hydrocarbon concentration sealing. There are different controlling boundaries in coalbed methane reservoirs that are in different geological backgrounds. Therefore, the coalbed methane reservoir is diversiform.

河东煤田谭坪勘查区煤层气成藏地质特征

研究区位于鄂尔多斯含煤盆地东缘河东煤田南段,是稳定的克拉通内的大型含煤盆地。通过分析研究以往地质成果资料,从地质构造特征、沉积环境、煤层分布、储层特征、含气性、烃源岩因素、封盖层条件、水文地质条件等方面分析了研究区煤层气成藏地质特征。研究结果显示,研究区地质构造简单,储层分布稳定,埋深适中,含气饱和度较低,盖层封闭条件好,具有良好的煤层气勘探开发前景,煤层弱径流区和含气量较高地区是该区煤层气勘查的主要目标区。

山西沁水盆地广志区煤层气藏地质特征研究

沁水盆地煤层气田是中国第一个开展煤层气开发的热点地区,广志区位于沁水盆地复向斜东翼中段,盆地构造演化的主导作用导致煤层气成藏过程复杂。为揭示广志区中—高煤阶煤层气成藏富集规律及地质特征,依据该区以往测试实验成果资料和勘探成果资料,采用定量和定性分析分析相结合的方法,对该区主力煤层15号煤的煤层厚度、埋藏深度、煤岩煤质、储层物性、含气性、等温吸附特征、煤岩热演化程度等条件进行分析,建立煤层气成藏模式。结果表明:广志区煤层气成藏条件较好,主力煤层为15号煤层全区发育,厚度4.7 m,煤层含气量14.20 m~3/t;煤岩热演化程度较高,保存条件完好,具备良好煤层气成藏基础;煤层气成藏主要受构造特征、沉积特征及煤变质作用控制,次级背斜构造高部位为富集高产区。