Chronological Study of Coal-seam Water and its Implication on Gas Production in the South Qinshui Basin

The knowledge of the residence time of formation water is fundamental to understanding the subsurface flow and hydrological setting.To better identify the origin and evolution of coal seam water and its impact on gas storage and production,this study collected coalbed methane co-produced water in the southeast Qinshui Basin and detected chemical and isotopic compositions,especially 36Cl and 129I concentrations.The calculated tracer ages of 129I(5.2–50.6 Ma)and 36Cl(0.13–0.76 Ma)are significantly younger than the age of coal-bearing formation(Pennsylvanian-Cisuralian),indicating freshwater recharge after coal deposition.The model that utilises 129I/I and 36Cl/Cl ratios to constrain the timing of recharge and the proportion of recharge water reveals that over 60%of pre-anthropogenic meteoric water entered coal seams since 10 Ma and mixed with residue initial deposition water,corresponding to the basin inversion in Cenozoic.The spatial distribution of major ion concentrations reveals the primary recharge pathway for meteoric water from coal outcrops at the eastern margin to the basin center.This study demonstrates the occurrence of higher gas production rates from wells that accept water recharge in recent times and suggests the possible potential of the non-stagnant zones for high gas production.

Geochemical Characteristics and Development Significances of Constant and Trace Elements from Coalbed Methane Co-Produced Water:A Case Study of the Shizhuangnan Block,the Southern Qinshui Basin

As an unconventional natural gas resource,coalbed methane(CBM)development releases a large amount of CBM wells co-produced water.Geochemical characteristics of the co-produced water provide an essential foundation for the production dynamics of CBM reservoirs if the impacts of fracturing fluids and other aquifers can be ignored.In the Shizhuangnan Block of the southern Qinshui Basin,constant and trace elements in CBM co-produced water from the wellheads were collected and determined,which is applied to assess water source,fracturing fluid effect,and CBM production.Based on principle component analysis and hierarchical clustering analysis,the water samples are divided into four categories.It suggests that different characteristics affected by water-rock interaction,reservoir environment,aquifer recharge,and hydraulic fracturing result in the various ratios of Na^(+)/Cl^(-),alkalinity(HCO_(3)^(-)+CO_(3)^(2-))/Cl^(-)and other specific rules.Moreover,Cl^(-)is selected as a dividing line for complete fracturing fluid flow back,associated with organic-bound chlorine complexes in the original coal seam water.Compared to constant elements,there is a significant correlation between Li and Sr concentrations and CBM productivity,so templates regarding trace elements can be used to distinguish various sources of the co-produced water.

Characteristics of dissolved inorganic carbon in produced water from coalbed methane wells and its geological significance

Based on long-term dynamic tracing of dissolved inorganic carbon(DIC)and stable carbon isotope(δ13CDIC)in produced water from 20 coalbed methane(CBM)wells in western Guizhou,the spatial-temporal dynamic variations ofδ13CDIC of the GP well group produced in multi-layer commingled manner were analyzed,and the relationship between the value ofδ13CDIC and CBM productivity was examined.The produced water samples of typical wells in the GP well group were amplified and sequenced using 16S rDNA,and a geological response model ofδ13CDIC in produced water from CBM wells with multi-coal seams was put forward.The research shows that:δ13CDIC in produced water from medium-rank coal seams commonly show positive anomalies,the produced water contains more than 15 species of methanogens,and Methanobacterium is the dominant genus.The dominant methanogens sequence numbers in the produced water are positively correlated withδ13CDIC,and the positive anomaly of v is caused by reduction of methanogens,and especially hydrogenotrophic methanogens.Vertical segmentation of sedimentary facies and lithology in stratum with multi-coal seams will result in permeability and water cut segmentation,which will lead to the segmentation ofδ13CDIC and archaea community in produced water,so in the strata with better permeability and high water cut,theδ13CDIC of the produced water is abnormally enriched,and the dominant archaea is mainly Methanobacterium.In the strata with weak permeability and low water cut,theδ13CDIC of the produced water is small,and the microbial action is weak.The shallow layer close to the coal seam outcrop is likely to be affected by meteoric precipitation,so theδ13CDIC of the produced water is smaller.The geological response model ofδ13CDIC in produced water from multi-coal seams CBM wells in the medium-rank coal reveals the geological mechanism and microbial action mechanism of theδ13CDIC difference in the produced water from the multi-coal seams CBM wells.It also provides effective geochemical evidence for the superimposed fluid system controlled by sedimentary facies,and can also be used for the contribution analysis of the produced gas and water by the multi-layer CBM wells.

煤层气原位注热开采的数值模拟研究及工程实践

煤层的低渗透性和甲烷的强吸附特征是制约煤层气开采的关键性问题,如何快速高效开采煤层气是目前煤层气开采研究中的重要课题。首先基于构建的水-气-热-固耦合数学模型,建立了煤层气注热开采的物理模型并验证了模型的正确性,然后从水气运移角度分析了注热方法的产气规律,最后在煤矿井下进行了现场注热试验。数值模拟结果表明:煤层气注热开采过程中水气运移遵循“前期排水,后期采气”的变化规律。煤层中的水对甲烷的解吸和运移产生了重要的影响。注热过程中水占据了甲烷的运移通道,水对甲烷的抑制作用大于温度的促进作用;注热后的抽采过程中,高温促进了甲烷的解吸,解除了水对甲烷的抑制作用,使煤层气的产量大幅度提高。通过现场注热试验,已经形成了2种成熟的井下注热强化煤层气开采方法,即间歇注热方法和交替注热方法。2种注热方法具有相似的产气规律,即注热阶段的日产气量和甲烷体积分数一般比较低,而注热后抽采阶段的日产气量和甲烷体积分数均大幅度提高。现场注热试验结果表明,与传统的负压抽采方法相比,间歇注热方法可以使甲烷的体积分数和日产气量分别提高10倍和100倍以上,交替注热方法可以使甲烷的体积分数和日产气量分别提高10倍和50倍以上。现场注热试验结果与数值模拟结果共同表明,注热强化煤层气抽采的效果显著,注热后抽采阶段是煤层气的高产时间段。

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。

煤系天然气电潜螺杆泵举升管柱水粉两相流动态特性

分析油管柱煤粉颗粒群体随水流运移特性对提高电潜螺杆泵的可靠性和保障煤系天然气井连续稳定排采具有重要意义。综合大浓度、低流速和低黏度等多因素影响,把管柱内流固耦合作用和煤粉颗粒运移动力学统一起来,建立适用于电潜螺杆泵油管柱水粉两相双流体运移数学模型及其求解方程,从而更全面和准确地分析煤粉粒径、两相流速和油管内径对水流携煤粉运移特性的影响。结果表明:电潜螺杆泵油管柱煤粉颗粒群体随水流沿径向整体呈现抛物线运移特征,且煤粉固相运移速度要小于井液流动速度,煤粉随水流朝上运移主要分布于管柱中心区域,随两相流量的增大,煤粉固相运移速度不断提升且排出量先是显著增加而后两相流量升至一定阈值后排出量增加趋势逐渐减弱,合理选取筛缝控制煤粉粒径同时采用衬管减小管柱内径可有效提高煤粉排出量。

Characteristics of microbial communities in water from CBM wells and biogas production potential in eastern Yunnan and western Guizhou, China

The study of microbial communities in the produced water of coalbed methane(CBM)wells is an important aspect of microbial-enhanced methane production.Water produced from 15 CBM wells in four synclines in eastern Yunnan and western Guizhou was collected.Through the use of 16S ribosomal RNA(16S rRNA)amplicon sequencing and realtime fluorescence quantitative polymerase chain reaction(PCR),the characteristics of bacterial and archaeal communities before and after enrichment culture were studied.The methanogenic pathways of secondary biogas were discussed,and potential microbial-enhanced methane production was preliminarily evaluated.The results showed that the bacterial DNA content in uncultured produced water was low,so it is difficult to detect.After enrichment,the dominant bacteria phyla were Proteobacteria,Bacteroidetes,and Firmicutes.A total of seven phyla were detected in the uncultured produced water,and the dominant archaeal phylum was Euyarchaeota.Methanogens were the main component of archaea.The dominant archaeal genera were Methanobacterium,Methanoculleus and Methanobrevibacter.The community structure of the archaea changed noticeably after four days of enrichment culture.The relative abundance of Euryarchaeota increased to 99%in most samples after enrichment culture.It was found that there was a transition from Methanoregula to Methanobacterium within genera.The relative abundance of Methanobacterium increased,which can produce hydrogenotrophic methane.Combined with the isotopic composition of the produced water and gas,it is considered that the CBM in the Tucheng and Enhong synlines consists of a mixture of thermogenic gas and biogas.The proportion of secondary biogas in the Tucheng and Enhong synlines are estimated to range from 10.89% to 49.62%.There are mainly hydrogentrophic methanogens in the study area,and CO_(2) reduction is the main way of microbial gas production.After enrichment culture of produced water in the study area,the hydrogenotrophic methanogens were enriched.These two areas have strong potential for microbial-enhanced methane production.

煤层气高产水井原因分析及水源识别——以沁水盆地柿庄南区块3号煤井为例

高产水、低产气是煤层气生产过程中常见的一种现象,查明煤层气井高产水原因、确定产水来源一直是行业性难题。为此,以柿庄南区块3号煤层高产水井为例,根据测井、录井、微地震监测及生产数据,运用排除法找到了该区高产水井产水高的原因,通过同位素示踪、产水量和含水层发育特征相关性分析等技术手段,弄清了高产水井的产水来源。分析结果表明:①断层和压裂缝沟通含水层是该区煤层气井高产水的主要原因;②断层沟通含水层型高产水井产出水主要为来自于上石炭统太原组及奥陶系的石灰岩岩溶水;③压裂缝沟通含水层型高产水井产出水主要来源于下二叠统山西组底部的K_(7)砂岩。

樊庄区块煤层气井产能差异的关键地质影响因素及其控制机理

以樊庄区块16口煤层气井地质资料、排采资料为依据,分析了该区块煤层气井之间产水量和产气量差异的地质影响因素,并进一步探讨了这种差异的地质控制机理。研究结果表明:产水阶段,地下水流体势通过影响煤层水的流向和煤储层含水量控制煤层气井产水量,渗透率通过影响煤层水在储层中的流动能力控制煤层气井的产水量,煤储层渗透率与地下水流体势的负相关性促进了煤层气井之间产水量的差异;产气阶段,排水降压效果通过影响煤层气的解吸量及气、水两相的饱和度和相对渗透率控制煤层气井之间的产水量和产气量差异;另外,煤层气井连通后出现的气水分异现象,进一步促进了煤层气井之间产水量、产气量的差异。

美国煤层气地面集输工艺技术

随着常规天然气资源不断减少,能源需求不断增加,特别是对环境保护要求的日趋严格,煤层气作为巨大的潜在资源在能源消费中的地位也逐步提高。美国在研究、勘探、开发利用煤层气方面处于世界领先地位,尤其是圣胡安和黑勇士两个煤田的集输系统已经相当成熟。为此,从井场工艺、集输系统、集中处理站工艺、水处理系统、腐蚀防护以及现场操作经验几个方面介绍了美国圣胡安盆地煤层气的集输工艺技术,可为我国煤层气集输工艺发展的思路提供参考。

贵州松河及织金煤层气产出水的地球化学对比及其地质意义

基于松河和织金区块16口煤层气井产出水样品的常规离子,微量元素,氢氧同位素测试,结合其地质背景、产能特征,对比分析了两区块产出水地球化学特征及其对产能的指示意义。研究表明:松河产出水Cl-,Na+质量浓度高度异常,水质为Na-Cl型,表明地层水受压裂液污染;织金产出水来自煤层,Na+和HCO-3富集,水质为Na-HCO3型,反映出较封闭的地下水环境。松河和织金产出水均表现出明显的D漂移特征,且松河区块煤中氢氧同位素组成较重。除Li元素外,松河产出水中大部分微量元素溶出量均大于织金。提出了更具普适意义的反映地层水环境的封闭性指数。封闭性指数和日产气量、累计产水量相关关系显著,中等封闭指数更有利于实现高产,可提取作为评价产能潜力的地化指标,并初步建立了基于HCO-3和Cl-质量浓度的产出水来源判识模板,划分出两个区域:低产井产出压裂液区和高产井产出煤层水区。

基于氢、氧同位素的煤层气合排井产出水源判识——以黔西地区比德—三塘盆地上二叠统为例

有效的排采水源识别是煤层气多层合排诊断的重要举措,而水中稳定同位素是水源信息的指示计。黔西上二叠统发育多煤层,煤层气开发以直井多层合排为主,不同产层组合下产能效果差异显著,产出水来源得不到有效判识。为此,基于黔西比德—三塘盆地11口煤层气井产出水样品的定期采集,对产出水样、矿井水样和地表水样共计38个样品开展同位素地球化学测试,结合煤层气井生产数据,揭示了研究区产出水氢、氧同位素组成特征及其排采水源判识意义:基于研究区大气降水线方程,煤层气井产出水氢、氧同位素组成普遍显现D漂移特点,封闭型水中氢、氧同位素偏重,水-岩作用反应强烈;区分了典型高产井和典型低产井,低产井受制于表层水干扰,产出水表现为氢、氧同位素组成较轻且D漂移不明显,而高产井产出水以同位素组成较重、D漂移明显为特点。建立了反映产出水D漂移程度的参数,其数值与平均日产气量正相关而与平均日产水量负相关。结合Cl^-、Na^+离子浓度,建立了基于产出水地球化学特征的排采水源判识模板,区分出表层水、煤层水和压裂水3类水源,气井只有产出煤层水才能获得较高的产能。黔西地区比德—三塘盆地上二叠统上部含气系统由于容易受表层水干扰,排采条件欠佳且与中、下部含气系统兼容性差,建议优先开发中部和下部含气系统。

沁水盆地南部煤层气井产出水源解析及合层排采可行性判识

长期以来,沁水盆地南部丰富的太原组煤层气资源无法规模性动用,煤层气单井产量难以进一步提高,合层排采产出水来源得不到有效判识,合排难易程度无法客观评价。面对这些生产技术难题,基于28口单层及合层排采井产出水样品的微量元素测试分析,建立了产出水来源判识及合层排采可行性评价方法,进而以7口合层排采井为例进行了初步判识。分析表明,煤层气井产出水微量元素中蕴含着丰富的产出水来源信息,基于水岩作用原理可合理提取产出水源解析的特征微量元素。在甄别煤储层返排清污程度基础上,初步建立了由提取产出水特征微量元素、建立单煤层产出水特征微量元素标准模板、产出水来源与合排可行性判识3个步骤构成的评价流程。应用这一方法,在7口合层排采井中识别出产出水来源和层间干扰程度的3种情况。

潘河煤层气试验区产能影响因素分析

煤层气生产过程中,为了掌握其生产动态,提高煤层气井的产能,有必要对煤层气产出特征进行综合分析,总结其变化规律,确定影响产能的主要因素。以潘河煤层气生产试验区的实际排采资料为基础,从煤层气的运移机理以及产出特征出发,利用对比、统计方法,综合分析了生产各阶段气、水产量变化趋势及其主要控制因素,把区内煤层气产出曲线划分为3种特征类型:高产—低产—高产、中高产—高产、高产—低产,其中高产—低产—高产曲线类型为主要特征类型。研究结果表明:煤层含气量、构造、煤层埋深、储层裂隙发育特征等是影响煤层气产能的重要因素,含气量、煤层埋深则影响生产曲线的阶段特征,裂隙发育的地区往往是高产井分布区,向斜部位的井对于井网的整体排水降压具有重要的意义。

煤层气井产出水中氯离子变化规律回归分析模型

基于沁水盆地枣园区块大量煤层气井产出水分析化验数据,通过数学统计方法,研究总结了产出水中氯离子浓度与排采时间的变化规律。指出排采初期氯离子对环境影响最大,远超出国家Ⅱ类饮用水标准;同时利用SPSS软件进行了非线性回归分析,建立了氯离子浓度变化数学模型。通过模型可以合理预测氯离子浓度达到国家标准所需要的时间,为煤层气井产出水水质变化监测及地面水质处理提供了技术支持。

单相流驱替物理模拟实验的煤粉产出规律研究

为研究煤层气井排采过程中煤粉的产出机理及其影响因素,开展了单相流驱替状态下煤粉产出物理模拟实验。通过改变单相流驱替流速及煤砖样品上、下围压的大小,分析不同实验条件下煤粉产出量、煤粉粒度分布特征以及裂隙导流系统的渗透率变化等参数,归纳煤粉的动态产出规律。实验结果表明:在围压稳定的实验条件下,煤粉的产出具有一定的启动运移速率;煤粉的产出量与驱替液流速呈正相关、与围压呈负相关;煤粉在裂隙系统中的存在与运移会对其渗透率产生显著的影响;间断后重启单相流驱替作用会使煤粉产出量瞬间剧增。根据模拟实验结果可以认为,优化煤层气井的排采制度、控制井底流压降压速率的变化、稳定控制排水强度,将会有效地控制煤粉的产出量。

煤层气井煤粉产出规律及排采管控实践

为减少煤粉对储层的伤害,分析了煤层气井煤粉产出规律及其对排采的影响。基于煤层气井煤粉浓度、产气量、产水量等监测数据,总结了煤粉产出动态规律;研究了产气初期煤粉大量产出对采气设备及储层渗流通道的影响;提出了通过提高排采设备携粉能力,增加煤粉排出量的极限煤粉浓度管控方法。实践表明该方法能减少煤粉对储层的伤害,延长检泵周期,释放煤层气井产能。

高压注水对煤体瓦斯解吸特性影响的试验研究

为了研究高压水作用后的煤层瓦斯解吸特性,依据地面水力压裂煤层抽采煤层气的方案和工艺,设计一系列含瓦斯煤体注水后的解吸特性试验,说明实际状态下的含瓦斯煤体在受到高压水的长期作用后解吸能力及规律的变化。试验装置采用自主研制的吸附-注水-解吸成套设备,分阶段地进行吸附、高压注水和解吸试验,对于不同煤种同等吸附压力下、相同煤种不同吸附压力下的块状原煤进行自然解吸和不同压力下的高压注水解吸试验,以获得不同条件下试验煤体的瓦斯解吸规律。结果表明:(1)在相同吸附平衡压力下,试验用1-1#贫煤的自然解吸率为56.17%,略高于试验用2-1#无烟煤的51.50%,与矿井实际的条件相同;(2)水对含瓦斯煤体的解吸特性影响较大,等压注水后的1-1#,1-2#和2-1#煤体的瓦斯解吸率分别为40.15%,47.17%和27.09%,只有自然解吸时的50%～70%,无烟煤的影响最大,较高瓦斯吸附压力下的贫煤影响最小;(3)随着注水压力的增加,最终解吸率逐渐呈非线性的规律衰减,在注水压力达到一定极值后解吸率会保持稳定;(4)解吸的时间效应与注水有关,自然解吸在较快时间内可以达到平衡,而注水后的解吸达到平衡的时间有不同程度的增加。