•Abundance of active organic matter constrained diagenetic stages.•Sediments with lean OM remain in stages of aerobic respiration, sulfate reduction.•Methanogenesis may happen only with high OM contents survived from BSR.•The gray mudstone was insignificant to biogenic gas generation in the Qaidam Basin.

Mesozoic marine black shales are mainly distributed in the Qiangtang Basin,Qinghai-Tibet plateau,in the Upper Triassic Xiaochaka Formation(T3x),the Jurassic Buqu Formation(J2b) and the Suowa Formation(J3x).They are formed in the reducing sedimentary environment which is abundant in organics that are easily preserved.The sedimentary facies are mainly platform facies,followed by basinal facies and delta facies.The thickness is 41-474 m;TOC is 0.25%-8.34%;organic matter is typeⅡ;the average value of Ro is 1.21%-3.0%,showing in the gas stage of high-over mature.The brittle minerals are mainly quartz and feldspar,total contents are 65%-70%,and the shale porosity is about 2%.Compared with each index of gas shales in the main basins of American,we can consider that the Mesozoic marine black shales in Qiangtang Basin have the features of large deposition thickness,low organic abundance,high maturity of thermal evolution,numerous species of brittle minerals,low content of quartz,high content of feldspar and clay minerals,and low porosity.It means that the shales have the condition of producing shale gas and the basin is one of the sedimentary basins,in which the marine shale gas could be explored.From the comprehensive evaluation of the shale gas prospective areas,it can be predicted that in the Upper Triassic Xiaochaka Formation shale gas is widely distributed,followed by the Buqu Formation and the Suowa Formation.

针对我国南方旅游景区植物造景存在的问题,提出了应用科学发展观理论、节约型园林理论、生态经济理论、景观生态学理论,适地适树理论、生态位理论、美学理论、植物群落顶极理论等理论来指导旅游景区植物造景,因地制宜,精心设计,营造出高水平、高档次、高效益的旅游景观等对策,指明了我国南方旅游景区植物造景的发展方向.

Qiangtang Basin is an important exploration target in Tibetan area that was conducted little exploration and research before this study. Xiaochaka Formation is major source rocks in Upper Triassic, Mesozoic in the basin. According to the evaluation standard of source rocks established specially in this basin, the occurrence features of this formation in different structural units was analyzed comprehensively and then the favorable source kitchens were predicted on the aspects of its sedimentary environment, thickness and organic geochemical characteristics. The work was conducted on the samples from many geological profiles in field survey routes and the analytical data on organic carbon, maceral, rock pyrolysis, vitrinite and bitumen reflectance, and carbon isotopes, etc. The conclusions are as follows: firstly, the organic matter abundance of limestone and mudstone in Xiaochaka Formation is high so that they belong to medium-good source rocks; however, the actual areal division of their distribution shows by the fact that the values are variable in different areas; this formation mainly distributes in the middle part of Southern Qiangtang Basin with mainly II B organic matter type and high maturity; limestone is slightly better than mudstone in organic matter type, but smaller in the favorable source kitchens. All the above-mentioned research has an important reference meaning for the further determination of major source rocks, resource evaluation and exploration prospect on oil and gas.

Based on MAPGIS software,the suitability for reclamation of temporary-using land of freeway was evaluated.The information inquiring was realized through spatial summation analysis,buffer zone analysis and establishing attribute database.This supplied scientific basis for reasonable reclamation and available utilization of land resources.

The comprehensive geochemical cross section in the main structures of the Qiangtang basin was established to evaluate the source rock and predict the favorable hydrocarbon generation areas, based on the data of organic abundance, type and maturity from a large number of outcrop samples in the Mesozoic marine mudstone and carbonate source. The results show that relation between TOC and hydrocarbon potential (S1+S2), chloroform bitumen "A" and total hydrocarbon content (HC) has good correlation, generally in positive liner, of which in carbonate and oil shale is higher than that in the mudstone and coal, dependent on their lithology to some extent. Subaerial weathering has small impact on organic abundance, but has significant impact on hydrocarbon potential, chloroform bitumen "A" and total hydrocarbon content (HC). The Mesozoic marine source rocks development varies in different structural unit, for example, carbonate rocks in the Suowa Formation and Delta mudstone in the Xiaochaka Formation of Dirangbicuo-Tumen sag are of good quality source rock. Oil shale and shale in the Xiaochaka Formation of Paducuo-Najiangcuo sag are of extreme good quality source rock, deep water shelf and platform carbonate rock are middle class source rocks. And platform carbonate rock in the Buqu Formation and Suowa Formation buried deep in the Dongcuo-Huluhu and platform carbonate in the Buqu Formation and upper carbonate in Xiaochaka Formation buried deep in the Tupocuo-Baitanhu are middle class quality source rock. Organic matter,is mainly Ⅱ type, with maturity various in different areas, ranging from mature to over-mature, most mature-high mature and increasing from top to bottom in a single cross section. Sedimentary environment is the main controlling factor of source rocks quality. Middle deep marine black shale or mudstone in Upper Triassic Xiaochaka, with wide hydrocarbon generation area, are the most important source rocks. While the still water mud-carbonate rocks in water closed carbonate plateform in the Jurassic Buqu Formation (J2b) and Suowa Formation (J3s) are important source rocks, with wide carbonate hydrocarbon-generation. Further study on the source rock characteristics and major source rock has significance for future oil and gas exploration.

There is a large lake and original primitive mountain in Tianchi Hill in Nanning of Guangxi Province,its design and planning are according to the original topography,and the landscape design is harmonized with natural eco-environment.There are five greening landscape groups equipped with stilt floor greenbelt,garden greenbelt,offshore water greenbelt,and water system,which enable the general planning to embody the characteristics of restoration nature,unanimity of heaven and men,fusion of modern and classical.

Large quantities of biogenic gas were accumulated in the Quaternary section of the Qaidam Basin, NW China, with proven gas reserves of 7.9 Tcf. The gases are dominated by methane (>95%), with δ13C1 values in the range from -65 to -68‰. Major source rocks are lean lacustrine shales with average TOCs of around 0.5%. Gas reservoirs, with burial depths generally less than 1900m, are Lower Pleistocene unconsolidated siltstones and muddy siltstones which form carrier beds within the petroleum system. Formation water circulation and early formed syn-depositional anticlines play an important role in the maintenance of the dynamic charge-leak biogenic gas accumulations. Although considerable work has been done, little is understood about the biogenic gas origin and accumulations. Gas compositions, microorganism community, source rock geochemistry, and petrophysical mudstone permeability assessments were thoroughly investigated to identify source rocks and to assess the rate of gas charge and leaking.

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.

There existed a large area of lakes and original ecological mountain in "Tianchi Hill" in Nanning of Guangxi Province due to geographic advantage. Its design and planning should be in accordance with original topography, and landscape design was in harmonious integration with original ecological environment. There were five greening landscape groups in the residential area, which were equipped with stilt space greenbelt, garden feature greenbelt, water-front greenbelt and waterscape system, lending the whole planning the characteristics of "restoration of nature, unity of heaven and human, integration of modernity and classics".

Sanhu depression of Qaidam Basin is the largest biogenic gas production region in China. Headspace samples were collected from two wells in this region, and hydrogen and propylene compounds were detected in these samples with a certain concentration. The stable hydrogen isotope ratio of H2 is relatively light (−700‰− −820‰). The stable carbon isotope ratio of propylene ranges from −27‰ to −40‰, which coincides with the rule of change of the stable carbon isotope of kerogen at the corresponding horizon. The characteristic analysis of sediments, structures, and Ar and He components in the region indicates that these microelement compounds are the product of degradation of organic substances by microorganisms, rather than from the mantle source, inorganic reaction or other sources. Detection of these components provides solid evidence for the strong ongoing methanogenesis in this region.

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.

The Sebei gasfield is the largest biogas accumulation found in China and many reservoirs and seal rocks superposed on a syndepositional anticline in Quaternary. The biogas charging and dissipating process and its distribution have been a research focus for many years. The authors suggest a diffusing and accumulating model for the biogas, as they find that the shallower the gas producer, the more methane in the biogas, and the lighter stable carbon isotope composition of methane. Based on the diffusing model, diffused biogas is quantitatively estimated for each potential sandy reservoir in the gasfield, and the gas charging quantity for the sandy reservoir is also calculated by the diffused gas quantity plus gas reserve in-place. A ratio of diffusing quantity to charging quantity is postulated to describe biogas accumulating state in a sandy reservoir, if the ratio is less than 0.6, the reservoir forms a good gas-pool and high-production layer in the gasfield, which often occurs in the reservoirs deeper than 900 m; if the ratio is greater than 0.6, a few gas accumulated in the reservoir, which frequently exists in the reservoirs shallower than 900 m. Therefore, a biogas accumulation model is built up as lateral direct charging from gas source for the sands deeper than 900 m and indirect charging from lower gas-bearing sands by diffusion at depth shallower than 900 m. With this charging and diffusion quantitative model, the authors conducted re-evaluation on each wildcat in the central area of the Qaidam Basin, and found many commercial biogas layers.

Abstract: At present, shallow gases have received much attention due to low cost in exploration and production. Low‐mature gases, as one significant origin to shallow gas, turns to be an important research topic. The present understanding of low‐mature gases is confined within some geological cases, and few laboratory studies have been reported. Therefore, the potential and characters of low‐mature gases are not clear up to now. Here, two premature samples (one coal and the other shale) were pyrolyzed in a gold confined system. The gaseous components including hydrocarbon gases and non‐hydrocarbon gases were analyzed. Based on kinetic modeling, the formation of low‐mature gases was modeled. The results showed that during low mature stage, about 178 mL/gTOC gas was generated from the shale and 100 mL/gTOC from the coal. Two third to three fourth of the generated gases are non‐hydrocarbon gases such as H2S and CO2. The total yields of C1–5 for the two samples are almost the same, 30–40 mL/gTOC, but individual gaseous hydrocarbon is different. The shale has much lower C1 but higher C2–5, whereas the coal has higher C1 but lower C2–5. Hydrocarbon gases formed during low‐mature stage are very wet. The stable carbon isotope ratios of methane range from −40% to −50% (PDB), in good consistence with empiric criterion for low‐mature gases summed up by the previous researchers. The generation characters suggest that the low‐mature gases could be accumulated to form an economic gas reservoir, but most of them occur only as associated gases.

Sanhu area in eastern part of the Qaidam Basin is rich of biogas, but its distribution in the area is hetero-equilibrium not only in different tectonic locations but also in different reservoir-cap combinations of same biogas field. In order to find the controlling effect of reservoir-cap combination quality on distribution feature and rich grade of biogas in the area, displacement pressure differences and biogas diffusion ratios of all reservoir-cap combinations of biogas fields found there were calculated out, and then relationships of displacement pressure differences, biogas diffusion ratios, biogas reserves and unit reserves coefficient were investigated. According to the results, only the reservoir-cap combinations which had great displacement pressure differences were rich in biogas, and correspondingly, those with small displacement pressure differences could not be rich in biogas. On the other hand, reservoir-cap combinations with great diffusion ratios had small reserves and lower unit reserves coefficients, and those with small diffusion ratios always were high rich in biogas. Because the displacement pressure difference and biogas diffusion ratio represented quality of reservoir-cap combination, the relationships between the both parameters and biogas richment grades reflected controlling effect of reservoir-cap combination quality on distribution features and richment grades of biogas in Sanhu area.

Several giant biogenic gas fields (with proven gas reserves greater than 25 billion cubic meters) have been discovered in recent years in the Sanhu area of eastern Qaidam Basin. This area has an average surface altitude of around 2800m, and forms the northern segment of the Qinghai-Tibet Plateau. The biogenic gas fields occur mostly within or adjacent to the depocenter of approximately 3400m of Quaternary sediments. The gas reservoirs, with burial depth generally less than 1900m, are unconsolidated sandstones with approximately 24–40% porosity, and are interbedded with mudstones containing on average 0.3% TOC. The occurrence of methanogens in the shallow Quaternary sediments appears to depend on both the sedimentary facies and burial depths, thus most of the biogenic gases in the Sanhu area appears to have derived from the source kitchens in the central sag above a biogenic gas floor at the depth around 1800m. The key gas system elements for the formation of the giant biogenic gas accumulations include (1) secular low surface temperatures and lake water hypersalinity favor the preservation of suitable organic substrates for biogenic methane generation, (2) well-developed sand and mud interbeds, (3) sufficient cumulative thickness of water-saturated mudstones as caprocks, (4) presence of syndepositional anticlines of Pleistocene and later age, (5) a regional hydrogeological system favoring northeastward gas migration, and (6) ongoing dynamic gas migration and accumulation with abundant gas supply.

Biogenic gas is the product of methanogen in anaoxic environment. Its formation and occurrence is controlled by the distribution of methanogen. The present method in studying the distribution of methanogen is MPN (numbers of methanogen). Because methanogen is strict with its environment, especially with the occurrence of oxygen, trivial change should disturb the bacterial collects and make the number different from the reality. Otherwise, collection of the fresh groundwater is difficult for us. All those make MPN turn to be hard to be dealed with. The concentration of some special biomarkers of methanogen, especially its core membrane components, could reflect the distribution of methanogen for a time. This method is simple and easy to operate, could make up the deficiency. In this paper, the distribution of archaeol, the core membrane structure components, is analyzed in the sediment from two wells in the Sanhu depression Qaidam basin. The results showed a good relationship between methanogen and salinity. In high salt area, the activity of methanogens was depressed in the shallow (above 1000m), and then turned to active up to 2000m. While in the surrounding area like Sebei 1 area, the salinity of sediment is much lower, the depression of methanogen in the shallow is slight that make methanogen mainly concentrate above 1000m and is low below 1000m. In the final, combined with the sediment palaeoenvironment and salinity of the sediment, the activation of methanogen in Sanhu depression is characterized.

生物气主要有两种生成途径:乙酸发酵和二氧化碳还原.一般,海相环境以二氧化碳还原型为主,而陆相淡水—微咸水沉积环境主要以乙酸发酵型为主,随着深度增加,二氧化碳还原所占比例提高.通过对中国柴达木盆地三湖地区涩北一号构造区新涩3-4井系列取样分析认为,生物甲烷的两种产生途径并不严格按照深度分布.乙酸发酵成因类型分布在浅层(160～400m)及井底部位(1650～1700m);近地表(50～160m)及中深部是二氧化碳还原型.浅层乙酸发酵型甲烷明显偏重的稳定碳同位素值与相对封闭的泥岩环境及相对有限的母质来源有关;而井底部位(1650～1700m)正常乙酸发酵型生物甲烷与粉砂岩为主的相对开放的环境有关,该层段水中极高的乙酸含量说明充分的营养供给不会造成甲烷碳同位素明显变化,同时也意味着本层段地下水活动强烈,从外界携带大量营养底物进入.分析结果同时表明一定浓度的烯类气体暗示着该区细菌活动性强的事实.商业性的聚集以CO2还原成因类型为主,乙酸发酵所占比例较少.

柴达木盆地东部涩北气田是我国发现的最大生物气田, 为了揭示其充注-散失过程与生物气富集规律, 利用不同深度生物气组成和稳定碳同位素分馏现象, 结合成藏地质模式分析, 用扩散模型计算了其成藏以来的生物气散失量, 并与现存储量相加得到充注量. 涩北生物气田为多储盖组合叠置的背斜气田, 其深部储层为气源直接充注、浅部储层接收下伏气层扩散来的生物气为间接充注. 提出的某一储层相对散失量(散失量与充注量的比值)可以表征生物气富集程度, 当相对散失量 0.6则不利于生物气聚集、或者形成低效气藏.

The distribution of two formation pathways of biogenic methane, acetate fermentation and reduction of CO2, has been extensively studied. In general, CO2 reduction is the dominate pathway in marine environment where acetate is relatively depleted because of SRB consuming. While in terrestrial freshwater or brackish environment, acetate fermentation is initially significant, but decreases with increasing buried depth. In this paper, character of biogenic gases is profiled in the XS3-4 well of the Sebei 1 gas field in the Sanhu depression, Qaidam Basin. It indicates that those two pathways do not change strictly with increasing buried depth. CO2 reduction is important near the surface (between 50 m and 160 m), and at the mesozone (between 400 and 1650 m). While acetate fermentation is the primary pathway at two zones, from 160 to 400 m and from 1650 to 1700 m. δ 13C of methane generated in those two acetate fermentation zones varies greatly, owing to different sediment circumstances. At the second zone (160–400 m), δ 13C1 ranges from −65‰ to −30‰ (PDB), because the main deposit is mudstone and makes the circumstance confined. At the fourth zone of the well bottom (1650–1700 m), δ 13C1 is lighter than −65‰ (PDB). Because the deposit is mainly composed of siltstone, it well connects with outer fertile groundwater and abundant nutrition has supplied into this open system. The high concentration of acetate is a forceful proof. δ 13C of methane would not turn heavier during fermentation, owing to enough nutrition supply. In spite of multi-occurrence of acetate fermentation, the commercial gas accumulation is dominated by methane of CO2-reduction pathway. A certain content of alkene gases in the biogenic gases suggests that methanogensis is still active at present.