Shale gas wastewater from hydraulic fracturing poses significant environmental risks due to its high salinity and complex inorganic composition. This study investigates the behavior of major and trace inorganic constituents across a full-scale treatment train in the Sichuan Basin, China. Despite multi-stage processes including equalization, flocculation, flotation, biological reactors, membrane filtration, and clarification, key inorganic species such as Cl, Na, Br, Sr, Li, and B remained largely persistent in the final effluent with values of 13,760, 8811, 70, 95.9, 26.6, and 60.2 mg/L, respectively. Geochemical tracers including Br/Cl (average: 0.0022 mM/mM), Na/Br (average: 125 mg/mg), and Sr/Ca (average: 0.15 mM/mM) ratios, combined with halide endmember mixing models, revealed that salinity primarily originated from highly evaporated formation brines, with limited evidence for halite dissolution or external contamination. Elevated Sr (average: 89.3 mg/L) and Ca (average: 274 mg/L) levels relative to Mg (average: 32 mg/L) suggest significant water–rock interaction. Environmental risk assessments showed that concentrations of several elements in treated effluent greatly exceeded national and international discharge or reuse standards. These findings underscore the limitations of conventional treatment technologies and highlight the urgent need for advanced processes and regulatory frameworks that address the unique challenges of high-TDS (total dissolved solids) unconventional wastewater.

Guizhou Province of China is rich in shale gas resources. In recent years, important progress has been made in the exploration and development of shale gas in the Upper Ordovician Wufeng Formation-Lower Silurian Longmaxi Formation in Zheng'an block in northern Guizhou, adjacent to Sichuan Basin. Due to the complex geological conditions and fragile ecological environment in the shale gas distribution area, serious environmental pollution risks may exist in shale gas exploitation. Therefore, this paper conducted element, hydrogen and oxygen isotope analyses for shale gas fracturing flowback/produced water of Well AY7-4 in Zheng'an block. The results showed that the contents of K, Na, Ca, Mg and NH+4 in the flowback/produced water of Well AY7-4 were very high, with an average of 118 mg/L, 7616 mg/L, 266 mg/L, 47 mg/L and 76 mg/L, respectively. The content of Na, Ca and Mg is similar to that of shale gas flowback/produced water in Weiyuan, but lower than that in Changning and Fuling. NH+4 content was similar to that in Changning, but much higher than that in Weiyuan. The average Cl content was 11605 mg/L, which was similar to that in Weiyuan, but lower than that in Changning and Fuling. The average Br content is 48 mg/L, slightly lower than that of Weiyuan, and about half of that of Changning and Fuling. Correspondingly, the Br/Cl value of Well AY7-4 is the lowest, reflecting its relatively low Br content. The average content of Li, B and Sr is 17 mg/L, 10 mg/L and 45 mg/L, respectively, which is similar to that of the Weiyuan, Changning and Fuling shale gas fields. The distribution model of Li and Sr is similar to that of Cl, Br and Na, but the B content and B/Cl value of Well AY7-4 are the lowest. The linear relationship between Br and Cl contents and between delta D and delta 18O of flowback/produced water of Well AY7-4, freshwater used for hydraulic fracturing and hydraulic fracturing injected fluid indicates that flowback/produced water of Well AY7-4 is mainly the mixed product between low salinity injected fracturing fluid and high salinity brine retained in shale formation. The hydrogen and oxygen isotopic compositions gradually become heavier over time, indicating that the proportion of high salt end formation brine in flowback/ produced water is increasing. The contents of Cl, Br, Na and NH+4 in the flowback/produced water of Well AY7-4 are far higher than the allowable discharge value, which is a potential environmental pollution risk and cannot be discharged directly. (c) 2024 Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences AND Research Institute of Petroleum Exploration and Development, PetroChina. Publishing services by Elsevier B.V. on behalf of KEAI Communications Co. Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Sichuan Basin is important commercial shale gas producing basin in China, where shale gas explorations were mainly targeted at the Upper Ordovician Wufeng-Lower Silurian Longmaxi formations with burial depth mostly of 2000 similar to 3500 m. This study performed a detailed investigation about the delta H-2 features of shale gases from the Wufeng-Longmaxi shale with burial depth of <2250 m (Taiyang), 2250 similar to 3500 m (Jiaoshiba) and >3500 m (Weirong). The average delta H-2(1) and delta H-2(2) values are of -135 parts per thousand and -146 parts per thousand, -137 parts per thousand and -157 parts per thousand, -137 parts per thousand and -124 parts per thousand, respectively in Taiyang, Jiaoshiba and Weirong shale gas fields. The average delta H-2(1) values are nearly the same in the three gas fields, while average delta C-13(1) values increase from -35.2 parts per thousand to -28.5 parts per thousand as from Weirong to Taiyang. When wetness >8%, delta H-2(1) values increase with decreasing wetness rapidly implying dominant influences from maturity, when wetness <8%, the delta H-2(1) variation is small and mainly in the range of (-140 +/- 15)parts per thousand, indicating a strong influence from cogenetic water. All gases are characterized by a trend of delta C-13(1) > delta C-13(2) > delta C-13(3), and gases in Taiyang and Jiaoshiba are characterized by delta H-2(1) > delta H-2(2), while gases in Weirong are dominated by delta H-2(1) < delta H-2(2). Generally, with decreasing gas wetness, ethane first become more enriched in D and C-13, then become more depleted in D and C-13, and finally become more enriched in D and C-13 again. The turning point of wetness from rollover to post-rollover zones is 1.2% for the delta C-13(2) while 0.8% for the delta H-2(2). Such delay in delta H-2(2) also indicates the strong influences from the cogenetic water medium.

The analyses of the whole and the monomer paraffin hydrocarbons carbon isotope of 20 oil samples from the Lunnan and Hadexun oilfields in combination with the research of oil source, regional structural evolution and reservoir forming process show that the whole carbon isotope of the oil samples from the Lunnan area is more than -32‰, and that of the oil samples from the Hadexun area is less than -32‰, the carbon isotope of monomer paraffin hydrocarbons of the oil samples from the Lunnan area is also heavier than that of the oil samples from the Hadexun area. This feature is caused by the difference between the oil pools formation in the two areas. The main factor that caused the carbon isotope of oil samples from the Lunnan area heavier than that of oil samples from the Hadexun area is the mixture of the Cambrian degraded oil in the Lunnan area, not because that they have different source rocks.

A method for the analysis of saturated hydrocarbons in crude oil was established by comprehensive two-dimensional gas chromatography coupled to time-of-flight mass spectrometer(GC×GC/TOFMS).All compounds were identified according to their family characteristics and each spectrum.Alkanes,cyclic alkanes,bicyclic alkanes,adamantanes,diamantanes,terpanes,steranes and hopanes are separated into easily recognizable bands in the GC×GC chromatogram.The characteristics of terpanes,hopanes and adamantanes' contour chromatogram are defined.C31—C35 tricyclic terpanes were often neglected in the past.Provide petroleum geological experiment workers reference to carry out their work on GC×GC/TOFMS.Compare with the GC/MS,GC×GC/TOFMS has higher sensitivity and bigger peak capacity,which is more suitable for the analysis of complex mixture systems.It will be a helpful tool in the petroleum geological experiment.

全二维气相色谱/飞行时间质谱是20世纪90年代商品化的仪器,具有峰容量大、分辨率及灵敏度高等特点,但利用该仪器解决石油地质方面的问题国内外才刚刚起步.通过对柱系统的选择以及对升温程序、调制周期、热吹时间、载气流速、采集频率、数据处理等实验参数的优化,建立了全二维气相色谱/飞行时间质谱对石油样品中芳烃组分的分析方法.芳烃组分中极性不同的化合物在二维谱图上呈区带分布,每一区带中同系物根据取代基个数的不同呈瓦片状排列,根据其二维图谱特征和各化合物的质谱谱图,对各化合物进行了定性鉴定,化合物依据极性大小和环数多少在同一谱图上的不同空间展布,直观反映芳烃中各化合物的分布特征.一些在普通色谱-质谱图谱上重叠的化合物峰在二维谱图上被完全分开,有利于化合物的定量分析.一些含量很低的杂环原子芳香族化合物由于其极性的差异可以与干扰的芳烃化合物分开,利用该方法可以很清晰地被识别和鉴定.该方法的建立和图谱识别为石油地质实验工作者提供了利用全二维气相色谱/飞行时间质谱开展工作的参考依据.

To understand the biogas formation in geological basins, the present work investigated the reactive organic matter in sediments of the Sanhu depression of Qaidam Basin, a prolific region of biogenic gases with a proved reserve of 300 bil steres. The ROC (reactive organic carbon) was obtained by ultrasonic extraction from sediment samples in the solution of 6 mol/L HCl and 5% K2SO4. To investigate the effect of early diagenesis, parts of the samples were heated at 80°C before extraction. The results showed that the ROC content at a constant temperature decreased with increasing burial depths, which should be attributed to the microbial consumption. For the same sample, the ROC content heated at 80°C was dramatically higher than the unheated. The increment of the ROC content for some samples was as high as 200% in the experiment. The dramatically increasing ROC by thermal action should be the major nutrient substrate for the deep biospheres in most geological basins. There is a positive correlation between the reactive organic carbon (ROC) and the traditional insoluble organic carbon (TOC), not only for its absolute content of the ROC, but also for the ‘ROC’ produced in thermal action, all of these are clearly related with TOC. These data showed that higher abundance of organic matter can contribute more to the reactive organic matter, and is more favorable to the formation of biogenic gases. In the Sanhu depression of Qaidam Basin, more than 85% of the biogenic gas reserves occur in the lower layers (K5-K13) with a relatively high abundance of organic matter. The exploration has provided further evidence that deposits with higher abundance of organic matter are effective biogas source rocks.

The Paleozoic carbonate stratum at the bottom of superimposed basins is very important for petroleum exploration in China.The evolution of pores,cracks and holes is responded to the formation and preservation of carbonate reservoirs.The strata unconformity and fault system are the important factors influencing the formation of carbonate reservoirs.Based on the different properties of fault system and control mechanism of the fault system to fracture evolution and induced karst of carbonate reservoir,the effects of four fault systems on carbonate reservoirs were researched,including the effect of fault overturning in the process of hydrocarbon accumulation and the formation of carbonate reservoirs,the effects of fault-related folds on the formation of different types of carbonate reservoirs,the lapping effects of multi-stages faults on the evolution of carbonate reservoirs and their characteristics of petroleum geology,the carbonate reservoir properties and hydrocarbon accumulation resulted from hydrothermal alteration induced by faults.The study result shows that the inversion faults are beneficial to the late accumulation of hydrocarbon under the ideal conditions of early extension and late burial as well as the fault-related folds beneficial to form the insider type of anticline reservoir.The fault-enrichment zone,multi-lapping faults and karst slope are favorable to the formation of effective strata and related hydrocarbon accumulation in the carbonate reservoirs.

There is a close relationship between seismic interpretation and basin modeling. The data which are needed by basin modeling which is based on the quantitative evolution can be obtained from the basic equations among geological parameters of different rocks, those equations depend on the characteristics and values of the rocks, as well as their distribution in the 3D space. In this aspect the 3D seismic interpretation which is based on growth structure and sequence stratigraphy could play a key role in predicting the geological parameters through seismic inversion and attribute analysis. In studies of oil&gas accumulation, 3 major factors control the accumulation and distribution of the oil and gas, the 3 factors are tectonic evolution, sequence stratigraphic framework, as well as migration and accumulation condition, as a result the main study contents for joint seismic interpretation and basin modeling including the following: (1)The integration of 3D seismic structure interpretation and tectono-evolution history modeling, representation of deformation process for the growth strata, and revelation of time-space matching relation of geological effect factors and hydrocarbon accumulation factors which control formation of effective reservoirs. (2)Based on seismic interpretation and lithology prediction for the sequence strata, constraining reconstruction of sedimentary history, analyzing source reservoir cap assemblage, and providing solid and favorable evidence, (3)Integration of porosity and permeability which were inverted from impedance inversion with reservoir evolution and oil&gas accumulation. The results from the basin modeling depend on the quality of the rock's properties which were inverted from well data and seismic data, at the same time the flow direction, saturation, crushing and other information from the numerical simulation provide excellent quality control method for testing capillary pressure and connectivity hypothesis, and they also lead to better seismic inversion results. In this paper raising the reliability of quantitatively studying the oil & gas accumulation in petroleum geology was tried, aiming at applying integration of multi-disciplines in the studies of oil & gas accumulation and distribution laws, and at last scientifically guiding the oil & gas exploration.

生物气作为一类特殊的天然气资源,具有完全异于常规油气的形成机制.尽管其形成的生物化学过程早已为人所知,但是,时至今日,人们对地质盆地内其形成的主控因素、源岩的特征和分布规律,以及何以有些盆地形成了巨大的聚集等问题仍然困惑不解.考虑到生物气是由产甲烷菌消耗为数不多的几类小分子物质而成,而这些小分子物质归根结底来源于沉积物中的可以为微生物消耗利用的活性有机质部分,考察和了解活性有机质的分布规律将是揭开地质盆地内生物气形成之谜的可能途径.通过对柴达木盆地三湖地区第四纪沉积物中有机质含量和类型的分析,发现:1)活性有机碳(ROC)含量随着埋深增加而逐渐降低,同时与酸解温度有关,随着温度的增加(20-80℃),ROC明显提高;这表明弱成岩过程中有机质在低温热力作用下可新产生一些易于为微生物降解利用的"活性有机质",说明生物气形成过程中的低温热力作用与生物化学作用一样不容忽视.2)活性有机碳(ROC)与传统不溶有机碳(TOC)具有较好正相关关系,不但表现在其绝对含量整体上随着TOC增加而增加,而且也表现在受热力作用新出现的"ROC"与TOC关系更为明确.这些数据表明有机质丰度越高所能贡献的活性有机质越多,对生物气形成越有利.柴达木盆地三湖地区85%以上的生物气储量分布在有机质丰度相对较高的下部层位(K5-K13)的事实进一步提供了高丰度有机质层是有效生物气源岩的佐证.

Kerogen in source rock at the high mature stage usually has a very low hydrogen index (HI),and its Ro value is often more than 2.0% or above,suggesting that it belongs to type I or type II organic matter,which usually contain less than 20 mg/g TOC,even 0 mg/g TOC. Therefore,kerogen of this kind is often regarded as sterile for gas-generating. This paper analyzes kerogens from various mature stages of kerogens by using elemental analysis and pyrolysis simulation test,finding that gas-generating potential is multiple of HI. For example,the sample with TOC of 12 mg/g and H/C atomic ratio of 0.46 still has a gas generating of 65 mg/gTOC,which accounts for 15% of total gas generation in a close system. This fact indicates that the HI of mature or over-matured orangic matters can not be used to evaluate gas-generating potential. Meanwhile,gas generation of kerogen has a good correlation to H/C atomic ratio,with a correlation factor up to 0.96. Calculation by the regression function shows that the minimum H/C atomic ratio for a gas-generating kerogen is 0.26.

The analytical results of the whole and the monomer paraffin hydrocarbons carbon isotope of the 20 oils from Lunnan and Hadexun oil fields show that the whole carbon isotope of the oils from Lunnan area is more than -32‰, and that of the oils from Hadexun area is less than -32‰, the carbon isotope of monomer paraffin hydrocarbons of the oils from Lunnan area is also heavier than that of the oils from Hadexun area. That the carbon isotope of oils from Lunnan area heavier than that of oils from Lunnan area caused the difference between the oil pools formation in the two areas. The main factor resulted in the carbon isotope of oils from Lunnan area heavier than that of oils from Hadexun area is the mixture between the degraded oil from the Cambrian source rock and the oils from Middle-Upper Ordovician source rock, instead of the different source rocks of the oils.