Computer modeling and simulation of coalbed methane resources

Coal seam gas reservoirs are complex both geologically and in the mechanism of gas production. Understanding these naturally fractured reservoirs for two-phase (gas–water) flow conditions is often limited by a lack of data. This paper illustrates that reservoir simulation is a powerful tool which can be used to determine key data requirements, and how variability in reservoir properties and operating practices affect performance at the field level. The paper presents examples of how reservoir simulation can be used to assess the efficiency of well completions (fracturing or cavitation), identify candidate wells for remedial treatment, examine methane drainage in advance of mining, and assess the impact of errors in measured data on long-term gas production forecasts.     

焦作矿区煤层气开发地质综合评价

应用层次分析法,从影响煤层气开发的各种地质条件出发,对矿区进行了综合地质评价,寻找出有利于煤层气开发的区域。     

The Multiple Sources and Patterns of Methane inNorth Sea Waters

The methane concentration in the atmosphere andsurface water was surveyed along 58° N acrossthe North Sea. In addition, the vertical methanedistribution in the water column was determined at sixstations along the transect. The methane contents ofthe surface water as well as in the water column wereextremely inhomogeneous. Input by freshwater fromriver discharge and injection of methane from thesediment were both observed. The survey continued fromthe western side of the North Sea to the Elbe Riverestuary. The Elbe River appears to have low methaneconcentrations compared to other European rivers, itsaverage input into the North Sea is estimated to be70 nmol s-1 of methane. Near 58° N,1°40' E, an abandoned drill site releases about 25 % ofthe North Sea's emission of methane to the atmosphere.The advective methane transport induced by watercirculation was assessed for May 16, 1994, using a 3-DNorth Sea circulation model. For the period of thissurvey, the North Sea's source strength foratmospheric methane is estimated using in situwind velocities. In comparison to the advectivetransport by the water circulation, the gas flux tothe atmosphere appears to be the dominant sink ofNorth Sea methane. This flux is estimated to bebetween 1500 · 106 mol a-1 and 3100 ·106mol a-1, depending on the relationbetween wind speed and gas transfer velocity.     

Effect of atmospheric pressure and temperature on entrapped gas content in peat

Entrapped biogenic gas in peat can greatly affect peatland biogeochemical and hydrological processes by altering volumetric water content, peat buoyancy, and ‘saturated’ hydraulic conductivity, and by generating over‐pressure zones. These over‐pressure zones further affect hydraulic gradients which influence water and nutrient flow direction and rate. The dynamics of entrapped gas are of global interest because the loss of this gas to the atmosphere via ebullition (bubbling) is likely the dominant transport mechanism of methane (CH₄) to the atmosphere from peatlands, which are the largest natural terrestrial source per annum of atmospheric CH₄. We investigated the relationship between atmospheric pressure and temperature on volumetric gas content (VGC) and CH₄ ebullition using a laboratory peat core incubation experiment. Peat cores were incubated at three temperatures (one core at 4 °C, three cores at 11 °C, and one core at 20 °C) in sealed PVC cylinders, instrumented to measure VGC, pore‐water CH₄ concentrations, and ebullition (volume and CH₄ concentrations). Ebullition events primarily occurred (71% of the time) during periods of falling atmospheric pressure. The duration of the drop in atmospheric pressure had a larger control on ebullition volume than the magnitude of the drop. VGC in the 20 °C core increased from the onset of the experiment and reached a fluctuating but time‐averaged constant level between experiment day 30 and 115. The change in VGC was low for the 11 °C cores for the initial period of the experiment but showed large increases when the growth chamber temperature increased to 20 °C due to a malfunction. The core maintained at 4 °C showed only a small increase in entrapped gas content throughout the experiment. The 20 °C core showed the largest increase in VGC. The increases in VGC occurred despite pore‐water concentrations of CH₄ being below the equilibrium solubility level. Copyright © 2009 John Wiley & Sons, Ltd.     

西沙海域天然气水合物地震资料高密度双谱速度分析技术探讨

基于南海西沙海域天然气水合物二维高分辨率多道地震数据资料,使用Geovation地震资料处理系统的高密度双谱速度分析方法进行处理。在叠前时间偏移处理后的道集基础上,进行高密度双谱非双曲线型NMO自动拾取,最终获得解决各向异性问题后的叠前时间偏移剖面。分析结果表明,高密度双谱速度分析技术实现了速度逐道逐点的自动拾取,提高了时间方向的分辨能力、空间方向的分析密度,可以充分挖掘水合物地震数据的潜力。高密度双谱速度分析方法在提高处理质量的同时,可以帮助判定水合物的富集层位,研究似海底反射层附近的详细速度结构,为西沙海域水合物地震资料综合解释提供依据。     

甲烷水合物在人工毛细管沉积物柱中的形成和分解

天然气水合物在海底的形成与沉积物性质密切相关,沉积物的粒度、孔隙度、矿物组成等都可以影响到水合物的成核生长。通过拉曼测试和显微镜下观察人工毛细管模拟沉积物中CH4水合物的形成和分解过程,实验发现无论是在气液界面还是在溶有过饱和CH4的流体内,水合物都能够成核形成,但水合物更容易在气液和固液界面成核,并迅速生长;水合物在较大粒径石英砂(39~53μm)形成的孔隙内的成核机会比在粘土粒级的砂粒孔隙中的机会更大;水合物晶体主要呈发丝状附着于沉积物颗粒表面。     

多步分解法初步研究石英砂中甲烷水合物p-T稳定条件

设计加工了一套研究海底沉积物水合物稳定条件实验装置,采用多步加热分解的方法对不同孔隙度的石英砂沉积物甲烷水合物相态平衡点(p-T稳定条件)进行了初步研究。为校验实验装置和实验方法,首先对甲烷水合物在十二烷基硫酸钠(SDS)溶液中的生成和分解过程进行了研究,获得的实验数据与文献数据吻合得很好。在此基础上,以4种不同粒径(96~180μm、180~380μm、212~380μm和380~830μm)的石英砂为介质,分别研究了甲烷水合物的p-T稳定条件。结果表明,实验测得的数据与纯水溶液中的结果基本一致,说明在实验所用的不同粒径石英砂构成的孔隙尺度内,毛细管作用对水合物相态点的影响可以忽略。     

孔隙压力对煤岩基质解吸变形影响的试验研究

煤层气开采过程中,伴随着煤层气不断地吸附、解吸和渗流,煤体产生变形,极易导致煤和瓦斯突出事故。以晋城天地王坡煤矿为例,通过实验室内试验,模拟煤层气在复杂地层漫长的形成和逐渐开采过程,得到了孔隙压力与解吸量、应变的变化关系,并拟合得出其相应关系表达式,揭示了一些新的规律:(1)初期解吸速度较快,解吸量随时间的增长而不断增加,后期解吸速度减缓,解吸量逐渐趋于稳定;(2)孔隙压力与解吸量、应变呈现抛物线曲线关系,随孔隙压力的升高,吸附和膨胀变形占主导,其值均在增大;(3)存在最小孔隙压力值,随孔隙压力的增大,解吸时间增长,孔隙压力越小,吸附解吸规律越不明显,对于晋城天地王坡煤矿3#煤样,该值在1.0MPa左右;(4)不同加载方式对解吸量和变形量影响较大,先部分加载吸附后全部载荷解吸结果同比加全部载荷吸附解吸结果高13%～77%。试验结果可为煤层气(CBM)抽放安全和煤与瓦斯突出防治提供理论依据。     

内蒙古西部额济纳旗地区X井油气显示特征与油气源探讨

根据内蒙古额济纳旗地区X井白垩系额济纳旗组、侏罗系麻木乌苏组、古生界顶面风化壳等不同层段的油气显示特征和钻井泥浆烃类气体组分、甲烷C同位素的分析结果,认为侏罗系和白垩系油气显示特征相同,为油与气显示,气体样品的干燥系数(C1/C总)为0.80~0.87,甲烷C同位素δ13C1为-48.19‰~-50.87‰,表现了低成熟热解气的特征;古生界风化壳为气显示,天然气干燥系数(C1/C总)为0.91~0.92,甲烷C同位素δ13C1为-21.56‰~-30.91‰,表现了高成熟热解气的特征。该井及邻区的中生界、古生界烃源岩干酪根类型及其演化程度具有显著的差别,中生界烃源岩以低成熟混合型干酪根为主,古生界烃源岩为成熟—高成熟(或过成熟)的混合型-腐泥型干酪根。表明该区存在以中生界侏罗系—白垩系低成熟烃源岩为油气源的油气系统和古生界高成熟(或过成熟)烃源岩为气源的油气系统,指示了古生界油气资源前景。     

Methane hydrate formation comparisons in media with and without a water source supply

Water is a necessary element during gas hydrate formations. Therefore, by analyzing water depletion changes in media, the reaction characteristics of methane hydrate in media can be studied. In this study, two water sources supplying some liquid water which may be consumed by the methane hydrate formation reactions were designed and assembled. Using them, the full formation processes of methane hydrate was studied. Experimental results show the following： If heat released from nucleation reaction of methane hydrate is diffused rapidly, the nucleation ratios will be enhanced discernibly. While the hydrate is formed, a force is generated that sucks fresh water from the source into the vicinity of the hydrate, slowing down the cementation process and causing some hydrate grain dissociation. As a result of cementation differences, the hydrate reaction processes with different water sources present linear or quadratic equation characteristics. After a few repeated dissociation and formation processes of some hydrate grains caused by the fresh water, the gas amounts contained in hydrate will be significantly enhanced.