In-situ stress of coal reservoirs in the Zhengzhuang area of the southern Qinshui Basin and its effects on coalbed methane development

In-situ stress is a critical factor influencing the permeability of coal reservoirs and the production capacity of coalbed methane(CBM)wells.Accurate prediction of in-situ stress and investigation of its influence on coal reservoir permeability and production capacity are significant for CBM development.This study investigated the CBM development zone in the Zhengzhuang area of the Qinshui Basin.According to the low mechanical strength of coal reservoirs,this study derived a calculation model of the in-situ stress of coal reservoirs based on the multi-loop hydraulic fracturing method and analyzed the impacts of initial fractures on the calculated results.Moreover,by combining the data such as the in-situ stress,permeability,and drainage and recovery data of CBM wells,this study revealed the spatial distribution patterns of the current in-situ stress of the coal reservoirs and discussed the impacts of the insitu stress on the permeability and production capacity.The results are as follows.(1)Under given fracturing pressure,longer initial fractures are associated with higher calculated maximum horizontal principal stress values.Therefore,ignoring the effects of the initial fractures will cause the calculated values of the in-situ stress to be less than the actual values.(2)As the burial depth increases,the fracturing pressure,closure pressure,and the maximum and minimum horizontal principal stress of the coal reservoirs in the Zhengzhuang area constantly increase.The average gradients of the maximum and minimum horizontal principal stress are 3.17 MPa/100 m and 2.05 MPa/100 m,respectively.(3)Coal reservoir permeability is significantly controlled by the magnitude and state of the current in-situ stress.The coal reservoir permeability decreases exponentially with an increase in the effective principal stress.Moreover,a low lateral pressure coefficient(less than 1)is associated with minor horizontal compressive effects and high coal reservoir permeability.(4)Under similar conditions,such as resource endowments,CBM well capacity is higher in primary structural coal regions with moderate paleotectonic stress modification,low current in-situ stress,and lateral pressure coefficient of less than 1.

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, 6C~ of coalbed methane reservoir changed from the start at -2.95% ~ -3.66%, and the lightening process occurred in phases; the CI-I4 volume reduced from 96.35% to 12.42%; the CO2 vo- lume 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.

CBM geology conditions study of Gemudi syncline,Western Guizhou Province

Through the analysis of the surrounding rock, coal seam burial depth, coal quality and hydrologic geological condition, the methane-bearing property characteristics of the coal reservoir in the Gemudi syncline were elucidated. Most of the wall rock of the coal reservoir is mudstone and silt, which is a favourable enclosing terrane. Burial depth of the main excavating coat seam is moderate. The groundwater activity is thin, and there are absolute groundwater systems between each coal seam, which make poor intercon- nections to accelerate CBM enrichment. In our research, the area coal reservoir meta- morphosis is high, CBM content is high, hole-cranny system development degree is high, and permeability of the great mass of the main coal seam exceeds 0.1×10^-3 μm2, The result demonstrates that the southeast of the Gemudi syncline has the best conditions for prospecting and exploiting CBM.

鄂尔多斯盆地上古生界煤岩气成藏地质条件及勘探方向

为了进一步提高鄂尔多斯盆地煤岩气勘探开发效益,综合钻井、录井和分析测试等资料,从盆地尺度上系统地研究了上古生界煤系地层聚煤环境、煤质特征、储层物性和含气性,分析了盆地煤岩气成藏条件,总结了煤岩气勘探开发关键技术,评估了盆地煤岩气资源,并指出了煤岩气的勘探方向。研究结果表明:①盆地石炭纪本溪期海陆交互相沉积与二叠纪山西期陆相三角洲沉积发育形成广泛分布的煤岩,热演化程度较高,镜质组含量高,生烃规模大。②盆地深层煤质优良,以光亮煤和半亮煤为主,煤体结构良好,以原生结构煤为主,固定碳含量高,挥发分和灰分产率低。③煤岩储层发育储集空间包括气孔、植物组织孔和无机矿物质孔,割理和裂隙发育,平均孔隙度为4.80%,平均渗透率为2.35 mD,属于致密储层;煤岩平均含气量为22.53 m^(3)/t,其中游离气平均含量为5.65 m^(3)/t,占总含气量的25.08%。④煤岩与上覆不同岩性形成了煤岩-泥岩、煤岩-石灰岩和煤岩-砂岩3种储盖组合,控制了游离气富集分布,提出了“源储一体、持续生烃、盖层封堵”的煤岩气成藏模式。⑤在煤岩气勘探实践中形成了地震地质综合建模、水平井钻完井、压裂改造和限压排采等一系列配套工程技术。⑥盆地本溪组8号煤岩和山西组5号煤岩埋深1500 m以深煤岩叠合总面积16.70×104 km^(2),估算煤岩气总资源量23.47×10^(12) m^(3)。其中8号煤岩分布面积10.63×104 km^(2),煤岩气资源量17.43×10^(12) m^(3);5号煤岩分布面积6.06×104 km^(2),煤岩气资源量6.04×10^(12) m^(3)。结论认为:①鄂尔多斯盆地煤岩气地质条件优越,资源潜力巨大,勘探配套技术已基本形成,煤岩气勘探开发前景良好;②神木周边、榆林周边、乌审旗周边、米脂北、佳县、绥德、吴堡、大宁-吉县等区带8号煤岩,神木-伊金霍洛旗、榆林-佳县、乌审旗北、横山-子洲等区带5号煤岩是近期煤岩气的重点勘探方向。

Laboratory study of fluid viscosity induced ultrasonic velocity dispersion in reservoir sandstones

Ultrasonic velocities of a set of saturated sandstone samples were measured at simulated in-situ pressures in the laboratory.The samples were obtained from the W formation of the WXS Depression and covered low to nearly high porosity and permeability ranges.The brine and four different density oils were used as pore fluids,which provided a good chance to investigate fluid viscosity-induced velocity dispersion.The analysis of experimental observations of velocity dispersion indicates that（1）the Biot model can explain most of the small discrepancy（about 2–3%）between ultrasonic measurements and zero frequency Gassmann predictions for high porosity and permeability samples saturated by all the fluids used in this experiment and is also valid for medium porosity and permeability samples saturated with low viscosity fluids（less than approximately 3 mP·S）and（2）the squirt flow mechanism dominates the low to medium porosity and permeability samples when fluid viscosity increases and produces large velocity dispersions as high as about 8%. The microfracture aspect ratios were also estimated for the reservoir sandstones and applied to calculate the characteristic frequency of the squirt flow model,above which the Gassmann’ s assumptions are violated and the measured high frequency velocities cannot be directly used for Gassmann’s fluid replacement at the exploration seismic frequency band for W formation sandstones.

Geophysical criterion of pre-outburst coal outsqueezing from the face space into the working

The initial process of coal and gas sudden outburst is studied in the article when under the influence of rock and gas pressure the part of a coal seam layer(a coal section)is squeezed out from the mouth of the future outburst cavity in a jump-like manner into the working.Geo-mechanical criterion for a part of a coal seam layer outsqueezing in the form of the relation of active(squeezing out)and passive(preventing the outsqueezing)forces is defined in the article.Based on it,the geophysical criterion is defined by expressing basic physical parameters through geo-physical ones:the current stress is defined by spectral-acoustic method through the ratio of high frequency and low-frequency components of an acoustic signal,which is generated into a face working space by the mining equipment operating in the face;in-situ gas pressure is defined by gas analytical method by the concentration of methane in the atmosphere of the working;the strength of the most broken coal layer is defined by a strength measuring device(a device for measuring the depth of a steal cone punched into the coal by a spring mechanism).This paper studies the influence of acoustic,strength and filtrating and collecting properties of a face working space on the limit value of an obtained geophysical criterion of pre-outburst squeezing of a coal‘‘plug”out of the mouth of the future outburst cavity into the working.

临汾-运城盆地氦气富集要素及成藏条件

为认识临汾-运城盆地氦气资源前景,促进氦气勘查工作,笔者根据地球物理资料、元素地球化学实验及构造资料,分析了临汾-运城盆地氦源岩分布和氦气运移通道条件;在收集和整理临汾-运城盆地前新生界地热、气测录井及物探资料的基础上,开展了以地热和煤系气为主的氦载体特征研究。研究发现:①临汾-运城盆地具备地幔物质上涌和本溪组铝土岩系2种氦源条件。②控制盆地和凹陷的深大断裂贯通了深部氦源与前新生代地层,盆地内发育的正断层在很大程度上可提高前新生界各地层间的连通性,有良好的运移通道。③临汾-洪洞地区石炭系—二叠系具有优越的煤系气成藏条件。综合氦源岩分布、氦气运移通道、氦载体和保存等氦气成藏条件,认为临汾-运城盆地中奥陶统马家沟组为主要富氦地热储层,且临汾-洪洞地区太原组和山西组具备富氦煤系气的找矿前景。

三交区块8+9号煤层气储层水文地质条件及水源判识研究

【目的】三交区块8+9号煤层气井受外来水侵入影响导致产能较差,因此厘清三交区块水文地质特征、查明其对煤层气井开发的影响成为煤层气产能突破的关键。【方法】基于实际地质和生产资料,收集水化学数据,采用Fisher判别方法进行水源判识,进一步利用测井解释对太原组各含水层分布及其含水性进行识别,最终实现了8+9号煤储层水文地质条件的精细化研究。【结果】研究结果表明,煤层气井主要生产太原组灰岩水,局部由于受到张性走滑断层的控制,水化学特征显示为太原组灰岩和二叠系砂岩混合水;太原组8号顶板发育L1-L5共5套灰岩层,灰岩发育总体比较稳定,局部存在分叉合并现象,北部明显减薄;5套灰岩的富水性在垂向上和平面上都存在明显的非均质性。【结论】针对灰岩不同发育程度和富水性强弱的区域,应采用相对应的开发策略,以保证煤层气井的高效开发。本次研究对厘清三交区块水文地质特征、指导后续开发部署等都具有非常重要的意义。

滨海沼泽相煤系气地质与成藏——以湖南郴州地区龙潭组为例

煤系岩性组合复杂多样,沉积相带亦因所处构造环境的不同而具有多样性,如何评价不同沉积相带的煤系气成藏地质条件,是目前煤系气勘探急需解决的一个重大问题。湖南郴州地区上二叠统龙潭组煤系具有明显的滨海沼泽沉积特征,以其为目的层的煤系气成藏地质条件、资源潜力评价和有利区带优选,对该地区非常规天然气勘探本身及煤系气成藏地质评价方法研究具有重要的实用价值和理论指导意义。在野外地质调查、单井分析并结合有机碳、扫描电镜、X射线衍射分析等测试成果所作的烃源岩地质、地球化学特征与储层矿物组分、物性、脆性、微观孔隙特征研究的基础上,进行煤系气成藏地质条件分析和资源潜力预测。结果表明:龙潭组为滨海沼泽相沉积,下段含煤线少,上段含煤线多,煤层累计厚度0.25~18.98 m,泥页岩累计厚度50~222.5 m,有机碳为1.55%~4.16%,镜质体反射率为1.54%~3.51%,有机质类型以Ⅱ、Ⅲ型为主,存在两期生气高峰;晶间孔、溶蚀孔发育,含气性较好;体积法计算煤系气资源量为52850.2×10^(8)m^(3)。结论认为,研究地区存在P2l-P2l含气系统,两期成藏,具备煤系气勘探前景,常宁-耒阳、灵武-宜章地区是有利勘探区带。

中国低煤阶煤层气地质特征

低煤阶煤层气是中国煤层气勘探开发一个相当重要的潜在接替领域。中国含煤盆地的地质构造背景复杂,多数煤田经历了不同期次、不同性质构造及其组合以及应力-应变对煤储集层的改造,煤层气的富集成藏有自身的特点:厚度大、层数多、含气量低、渗透性较好、煤层气资源量和资源丰度大,厚度大而分布广泛的煤层及巨大的煤炭资源弥补了含气量小的缺点,使得低煤阶煤层气具有良好的勘探开发前景。低煤阶煤层气藏开发过程中解吸引起的基质收缩效应造成储集层渗透率增大,从而有利于低煤阶煤层气的开发,易形成工业性气流。低煤阶煤层气成藏过程简单,多为一次沉降,一次调整,如果构造、成煤环境及水文地质等主控因素能够有利匹配,有可能形成煤层气高产富集区。

鄂尔多斯盆地东缘临兴地区煤系气富集的构造-热作用控制

鄂尔多斯盆地东缘的临兴地区是我国煤系三气勘探开发的重点地区之一,从构造-热作用控制的角度,探讨临兴地区煤系气共生富集规律及其控制因素。受紫金山岩体侵入影响,区域单斜构造格局分划为中央隆起带、环形褶皱带和单斜构造带3个次级构造单元,各次级构造单元构造变形特征差异,决定了煤系气共生组合类型和煤系气富集规律。煤系地温梯度和储层压力梯度由中央隆起带向外逐渐降低,导致煤层气、页岩气等吸附气含气量依次降低,致密砂岩气则呈现出相反趋势。地下水矿化度分布特征表明环形褶皱带内水动力条件最弱,有利于吸附气保存。根据不同次级构造单元内煤系气富集主控因素特征,提出与中央隆起带、环形褶皱带、单斜构造带相对应的"岩浆侵入型→向斜与水力封堵型→缓倾单斜与岩性封堵型"的煤系气富集成藏模式。

煤层气聚集理论研究进展综述

煤层气是一种非常规天然气,其"自生自储"的特点与常规天然气的生、储、盖、运、聚、保等基本成藏地质条件不同,煤层气成藏富集的基本条件主要包括生成条件、储集条件和保存条件。通过对国内外大量文献的调研,分析了煤层厚度、煤变质程度、煤岩组分、煤岩孔隙-裂隙结构、封盖条件、水文地质条件、构造条件等7个因素对煤层气富集成藏的控制作用。对煤层气聚集成藏领域的新进展进行了综述,并指出了其未来的发展方向。

黄陇煤田永陇矿区煤层气成藏条件及主控因素研究

黄陇侏罗纪煤田属于典型的低阶煤含煤层气区带,煤炭勘查结果显示其西部具有一定的煤层气开发潜力,为了弄清该煤层气成藏条件,以黄陇煤田永陇矿区麟北区为例,从煤层气地质、煤储层特征、气藏保存条件3个方面研究了黄陇煤田西部地区的煤层气成藏条件及主控因素。研究结果表明:黄陇煤田西部地区延安组煤变质程度低,煤层厚度大,埋深适中,含气性较好,但煤储层渗透性较差;煤层气富集主要受水动力条件影响,埋深其次,构造和盖层影响较小,埋深500~700 m是该区煤层气成藏的最佳深度;因受成煤后期燕山运动等多期次构造运动的影响,原生生物气和热成因气大量逸散,新生代以来煤层接受浅部地表水和大气降水的补给,接受次生生物气的补充,是煤层气成藏的关键,属典型的盆缘缓坡晚期生物成藏模式。

低煤阶煤层气藏水动力条件的物理模拟实验

水动力条件是影响低煤阶煤层气成藏的重要因素之一。利用煤层气成藏模拟装置模拟了低煤阶煤层气藏水动力条件。研究表明,强烈的水动力交替作用使煤层气藏中的H2S含量降低、甲烷碳同位素变轻、甲烷含量降低、氮气和二氧化碳含量增大。这些变化对煤层气成藏造成不利影响。同时,对鄂尔多斯盆地东缘水动力条件进行了分析,对比了煤层气藏保存条件的差异。

沁水盆地郑庄区块煤储层水力压裂曲线类型及其地质影响因素

基于郑庄区块64口直井的压裂曲线分析,对水力压裂裂缝的扩展规律进行了总结,深入探讨了水力压裂曲线类型与煤体结构、天然裂缝发育、埋深和构造应力的关系。研究结果表明:最小水平主应力值较大、裂缝发育情况较差,不利于煤层起裂形成主缝,易形成上升型压裂曲线;最小水平主应力值较低、裂缝发育条件较好时,煤层容易起裂形成主缝,易形成下降型、稳定型和波动A型曲线;当垂向主应力与最小水平主应力相差不大时,易同时发育水平缝和垂直缝,形成波动B型曲线。大样煤岩压裂模拟实验表明该评价结果具有较好适用性。

徐州煤矿采空区地下水库建库可行性研究

徐州城市规划区内煤炭资源开采已经形成了约140 km2的采空区,采空区破断垮落岩体间的自由空间及巷道构成地下水储存场所。据初步估算,14个关闭煤矿采空区储水总量可达7 583×104m3,但矿井水资源的有效利用程度相对较低。文章通过对徐州城市规划区内各关闭煤矿采空区储水空间、矿井水水质保障和可调储能力等地下水库建库条件和运行安全的综合分析,探讨了建设采空区地下水库的可行性,遴选出7个煤矿采空区地下水库,评价其可利用等级,结果表明:新河、卧牛山、大黄山等为I级采空区地下水库,韩桥、庞庄、权台和青山泉矿等为II级采空区地下水库,可为徐州城市应急供水提供新水源。

鹤岗矿区煤层气成藏控气因素分析

鹤岗盆地煤层厚度大、埋藏适中、含气量较高,显示出较好的生气能力,但尚未获得工业气流。依据煤矿井、实验分析及地震等现有资料,综合分析了煤层的厚度、埋深、演化程度、渗透性、含气性以及气保存条件等5个成藏控气要素。研究认为:新一矿部分地区煤层曾受过岩浆作用,煤阶大幅提升,生气能力变好;南一、新一矿区煤层厚度大、分布面积广、埋深适宜、保存条件好,是下步勘探的最有利区;断层发育程度以及顶、底板封盖条件是制约煤层气成藏规模的关键因素。

二连盆地霍林河地区低煤阶煤层气成藏条件及主控因素

我国越来越重视对低煤阶煤层气的勘探,但已有的资料表明,目前对低煤阶煤层气藏的认识还不够深入。为此,以我国典型的低煤阶煤层气区——二连盆地霍林河地区为例,对该区煤层气地质特征和煤岩煤质及煤岩演化程度、煤储层渗透性、煤层含气性等煤储层特征进行了分析,从构造条件、封盖条件及水文地质条件3个方面研究了煤层气藏主控因素及保存条件。结论认为:霍林河地区煤层气成藏条件有利,具有煤层厚度大、煤层埋深较浅、煤储层渗透性好、含气量较高、封闭保存条件好等特点;保存条件是该区煤层气成藏的主控因素,且封闭条件好的浅部是煤层气富集的有利区。

鄂尔多斯盆地古生界煤成气勘探进展

基于鄂尔多斯盆地天然气勘探实践,根据煤成气勘探现状,分析煤成气成藏控制因素,总结煤成气勘探进展。鄂尔多斯盆地已探明煤成气地质储量5.24×1012 m3,发现煤成气气田12个,主要分布于上古生界石炭-二叠系碎屑岩和下古生界奥陶系碳酸盐岩储集层中。上古生界形成致密砂岩气藏,广覆式生烃的煤系烃源岩和大面积分布的砂岩储集层相互叠置,储集层先致密后成藏,天然气近距离运移、大面积成藏,发现了苏里格气田,探明地质储量3.49×1012m3,落实了盆地东部和陇东地区两大储量接替区。下古生界形成海相碳酸盐岩气藏,上覆煤系烃源岩生成的天然气向下运移聚集成藏,奥陶系风化壳岩溶和白云岩储集层为天然气富集主要场所,发现了靖边气田,探明地质储量7 000×108 m3,同时发现多个含气富集区。

活跃地下水对煤层气藏的破坏及其物理模拟

水文地质条件是影响煤层气富集成藏的重要因素之一,但是目前与之相关的研究却比较薄弱。为此,通过研究活跃的地下水不仅使煤层含气性降低,同时也导致煤层甲烷碳同位素值变轻的现象,应用FY-Ⅱ型煤层气成藏模拟系统,探讨了活跃的地下水对煤层气藏的破坏作用。结果显示,活跃的地下水会破坏煤层气富集成藏,对煤层气的保存不利,而地下水滞留区才是煤层气勘探的有利区域。