Analysis of the corrosion failure causes of shale gas surface pipelines

A shale gas gathering and transportation pipeline in a good block in Sichuan Province started leaking after less than a year of operation. To investigate the causes of corrosion of the sulfate-reducing bacteria (SRB), optical microscopy, scanning electron microscopy, and X-ray diffraction were used to analyze the corrosion and perforation of the shale gas surface pipeline in conjunction with bacterial corrosion simulation experiments. The results showed that the pipeline material (L360N) conformed to the requirements of the American Petroleum Institute 5 L standard and that extracellular polymeric substances were present in the corrosion pits. The corrosion products mainly included FeCO₃, FeS, CaCO₃, MgCO₃, and Fe mineralization. At 40°C, the uniform corrosion rate of L360N in the simulation experiment was 0.234 mm/a, and the local corrosion rate was 0.458 mm/a. SRB, saprophytes, and iron bacteria were detected in the on-site water medium and corrosion products, indicating that the main causes of shale gas pipeline corrosion are bacterial and CO₂ corrosion.     

页岩气开采对环境的影响分析及对策建议

我国页岩气资源非常丰富,但勘探开发难度巨大。分析了页岩气资源大规模开发对水资源、大气环境、地质环境及周边环境产生的影响。提出了需要健全的页岩气开发的环境监管法规规范,只有制定好产业政策,加强对技术和开采原料的研究等,才能促进页岩气产业健康、快速发展,更好地服务于中国和谐社会的建设与发展。     

Biomarker geochemistry of Eq34-10 cyclothem shale in Qianjiang Depression of the Jianghan salt lake facies Basin

The objective of this study is to provide biomarker geochemistry information on shale between sheet-like salts from Qianjiang Depression of the Jianghan salt lake facies Basin, and illustrate the depositional conditions, source organic matter input and maturation. 7 shale samples from Eq3⁴-10 rhythmic were analysed with gas chromatography-mass spectrometry. The investigated biomarkers show that the shale oil are charactertized by an apperent odd-even preference of n-alkane, low Pr/Ph values and a high content of gammacerane and C₃₀+ hopanes, maderate C_21-/C₂₁₊ ratios, the high relative content of C₂₇ 5α(H), 14α(H), 17α(H)- steranes (20R), and an anomaly high C₂₉ sterane ββ/(ββ + αα) value. These biomarker geochemistry characterizations suggested that the shale oils were derived from mixed aquatic organisms and land plants, and deposited in an anoxic and saline-hypersaline depositional environment.     

Effect of mineralogical composition and kerogen content on oil shale natural floatability

Mineralogical composition is one of the important factors that affect the performance of separation processes. In the current study, two oil shale samples, from El-Nakhil and El-Bieda localities, differ in their mineralogical composition, were subjected to flotation tests. Chemical analysis, differential thermal analysis (DTA), thermo-gravimetric analysis (TGA), and microscopic examination are among the used characterization techniques. In addition, their responses for upgrading by flotation were conducted as a function of pH, solid-liquid ratio, stirring speed and different particle sizes. The characterization results indicated that the kerogen content in El-Nakhil sample was 30% while in El-Beida sample was 10%. On the other hand, the flotation results indicated that El-Bieda responses better than that of El-Nakhil in terms of the difference in kerogen % between the original sample and the concentrated ones. The difference in flotation results of two samples can be explained by the difference in kerogen morphology as well as its interaction with surrounding matrix. In El-Bieda the kerogen has a laminated structure but in El-Nakhil it appears as laminated liptinitic component, in addition to the higher carbonate content in El-Nakhil sample in comparison to higher clay content in El-Bieda sample.     

蜀南地区富有机质页岩孔隙结构及超临界甲烷吸附能力

以蜀南地区龙马溪组下部富有机质页岩为研究对象，通过场发射扫描电镜（FE-SEM）、低压氩气吸附实验和重力法高压甲烷吸附实验，研究页岩孔隙结构特征及超临界状态下页岩储层的甲烷吸附能力，并讨论了页岩孔隙结构对甲烷吸附能力的影响。研究表明，蜀南地区龙马溪组富有机质页岩主要发育有机质孔隙，页岩孔隙结构非均质性强，比表面积为16.846~63.738 m²/g，孔体积为0.050~0.092 cm³/g，微孔和介孔贡献页岩90%以上的比表面积，介孔和宏孔贡献页岩90%以上的孔体积。甲烷在地层条件下处于超临界状态，过剩吸附曲线在约12 MPa时出现极大值，随后开始下降。使用修正过的四元Langmuir-Freundlich （L-F）方程拟合高温甲烷过剩吸附曲线，拟合效果较好，相关系数大于0.997。页岩饱和吸附量为0.067 0~0.220 2 mmol/g，不同页岩样品吸附能力差异明显。海相富有机质页岩中，随着有机质含量的增大，有机质孔隙数量增多，且页岩中微孔比例增大，微孔的吸附能力远大于介孔和宏孔，故页岩吸附能力增强。有机质含量是影响蜀南地区海相富有机质页岩孔隙结构和甲烷吸附能力的主要因素。     

页岩各向异性对被动源微地震波场的影响

页岩储层具有较强的各向异性特征，忽略页岩各向异性对被动源微地震波（水力压裂产生）传播的影响，可能会降低储层表征结果的可信度。为此，提出一种定量评估地震波场旅行时和振幅偏差的方法，并基于理论数值算例，研究页岩各向异性对被动源微地震波场的影响。首先，利用矩张量模型描述爆炸型和剪切型微地震震源，并基于三维各向异性介质弹性波动方程和交错网格有限差分算法，正演模拟被动源的微地震波场；然后，对比不同震源、不同程度各向异性介质的理论波场，计算其P波和S波相对于各向同性介质波场的旅行时及振幅偏差，定性分析和定量评估不同震源机制下页岩各向异性对微地震波场特征的具体影响。数值算例的结果表明：对于所采用的地面微地震监测系统和平层VTI介质模型，页岩各向异性对微地震波场旅行时和振幅的影响均较为显著，旅行时偏差可达子波周期的30%，振幅相对偏差则高达60%，且旅行时偏差随炮检距增加而增大。此外，不同震源机制下，微地震波场特征受页岩各向异性影响的规律相似。     

重庆下古生界页岩顺层滑脱变形域的形成及其地质意义

在野外露头和岩心观察基础上，通过力学分析，对重庆下古生界页岩中顺层滑脱变形域的类型、特征及其形成进行了研究，并结合页岩气勘探实践，对其地质意义进行了探讨。顺层滑脱变形域包括挤压型和重力型两类。挤压型顺层滑脱变形域形成时水平挤压构造应力占主导地位，岩层发生“逆断层”运动；重力型顺层滑脱变形域形成时上覆地层压力占主导地位，岩层发生"正断层"运动。挤压型顺层滑脱变形域地层变形相对较强，影响范围相对较大。埋藏深度和岩层倾角是控制同一地区同一页岩层中顺层滑脱变形域形成的关键地质要素。页岩埋深越大，形成挤压型顺层滑脱变形域时的临界岩层倾角越大，而形成重力型顺层滑脱变形域的临界岩层倾角则越小。重力型顺层滑脱变形域破坏页岩气保存条件。背斜构造部位挤压型顺层滑脱变形域所形成的顺层破碎带和网状裂缝系统是页岩气重要的运移通道和储集空间，向斜构造部位挤压型顺层滑脱变形域所形成的顺层破碎带和网状裂缝系统成为页岩气向临近背斜构造部位运移或向地表散失的重要通道。     

A numerical simulation study of CO 2 injection for enhancing hydrocarbon recovery and sequestration in liquid-rich shales

Less than 10% of oil is usually recovered from liquid-rich shales and this leaves much room for improvement, while water injection into shale formation is virtually impossible because of the extremely low permeability of the formation matrix. Injecting carbon dioxide (CO₂) into oil shale formations can potentially improve oil recovery. Furthermore, the large surface area in organicrich shale could permanently store CO₂ without jeopardizing the formation integrity. This work is a mechanism study of evaluating the effectiveness of CO₂-enhanced oil shale recovery and shale formation CO₂ sequestration capacity using numerical simulation. Petrophysical and fluid properties similar to the Bakken Formation are used to set up the base model for simulation. Result shows that the CO₂ injection could increase the oil recovery factor from 7.4% to 53%. In addition, petrophysical characteristics such as in situ stress changes and presence of a natural fracture network in the shale formation are proven to have impacts on subsurface CO₂ flow. A response surface modeling approach was applied to investigate the interaction between parameters and generate a proxy model for optimizing oil recovery and CO₂ injectivity.