Search

Subaerial marine sedimentary basins in China have undergone three phases of important tectonic changes at the end of the Early Paleozoic, Late Paleozoic-Early Mesozoic and Late Cenozoic. These tectonic changes have exerted strong impacts on hydrocarbon generation, migration and accumulation as well as on the occurrence and distribution of hydrocarbon reservoirs. The Tarim Basin is a typical example of multiphase hydrocarbon accumulations in a marine basin of China. The Early Paleozoic tectonic framework laid a geological basis for the marine setting of hydrocarbon formation in the Tarim Basin, but most accumulations were destroyed later due to frequent tectonic movements so that only bitumen is left at present. In the Late Paleozoic, the Ordovician source rock located in the western Manjar Sag entered peak generation stage and hydrocarbons successively accumulated at its southern and northern uplifted positions. Tectonic compressional deformation developed in the Early Mesozoic and the subsequent uplift and denudation allowed hydrocarbons accumulated at this phase to suffer from bacterial degradation. In the Late Cenozoic, the superimposition of basinal margin reconstruction and terrestrial molasse formation accelerated the formation of secondary cracking of hydrocarbons to gases in the platform of the basin, the influx of deeper natural gases dissolved in crude oils accumulated early and a unique large-scale condensate pool was then formed. The three tectonic changes controlled not only the formation of the marine basin, the sedimentation and evolution of source rocks, and the formation of reservoirs, but also the accumulation process and alteration of hydrocarbons in the marine sedimentary basin. Key words: important tectonic change phase, marine sedimentary basin, hydrocarbon accumulation history, hydrocarbon accumulation composite effect, multiple hydrocarbon reservoir, Tarim Basin

Exploiting and using sour natural gas safely, effectively and economically is very important for improving China's self-sufficient rate of sulfur, getting rid of the high dependence on import, and ensuring the market independence and environmental safety. The proved reserves of sour natural gas in China are about 1×1012 m3, and the economically recoverable reserves are above 3 700×108 m3. By statistics of the abundance of sulfur and geological reserves, we calculate that the proved reserves of sulfur are 14 946.04×104 t in China, of which the economically recoverable reserves are 9 001.69×104 t. However, the high sour natural gas being developed mainly in dolomite reservoirs, the imbalance distribution of geological reserves, the gas reservoirs' deep burial and the high concentration of sulfur, determine the sulfur reserves, recovery cost, supply, and regional price imbalance, and finally affect the industry chain trend of sulfur-chemical fertilizer-biological energy-petroleum price in the Chinese market. The sulfur market development situation in China and abroad indicates that seeking the stable, traditional market of Southeast Asia and preempting the market of high concentration phosphate fertilizers in South America are the inevitable choice to achieve stable exploitation of Chinese sour natural gas and to resolve the contradiction between market supply and demand. 摘 要: 安全、有效、经济地开发和利用含硫天然气，对于提高中国硫磺自给率，摆脱高度依赖进口的窘境，保障市场自主性以及环境安全十分重要。中国的含硫天然气探明储量近万亿立方米，含硫天然气经济可采储量逾3 700×108 m3，通过统计含硫天然气田含硫丰度和地质储量，计算出中国含硫气田中硫磺资源的探明数量为14 946.04×104 t，经济可采量9 001.69×104 t。中国高含硫天然气多发育在白云岩储集层中并且地质储量分布不均衡，气藏埋深大、含硫浓度高，这些地质特征直接决定了硫磺资源量、回收成本、供应量和地区价格不均衡，最终影响中国市场硫磺-化肥-生物能源-原油的产业链走势。分析国内外硫磺市场的发展形势表明，寻求稳定传统的东南亚市场，抢占南美洲的高浓度磷肥市场以及开拓硫磺应用领域，是平稳开发中国高含硫气田和解决市场供求矛盾的必然选择。 Key words: high sulfur gas field, sulfur reserves, formation condition, market strategy

The distribution of coal gas pools is controlled by many geological factors in China. The accumulation and pool-forming process of coal measures gas is studied from aspects of structure, source rock evolution, reservoir, pool-forming history, etc. The comparison results show that there are many similarities in geology between the Upper Paleozoic gas pools in Ordos Basin and the Upper Triassic Xujiahe Formation gas pools in Sichuan Basin, and the difference of the gas pools features in the two basins is caused by different structural evolutions and pool-forming processes. In Ordos Basin, water shoved by gas migrated from lower to higher positions in the formation process of the gas pools, and the abnormality of low gas reservoir pressure was caused by the water and gas reversal. In Sichuan Basin, structural traps controlled the gas pools distribution in Xujiahe Formation, lithologic gas pools was found locally, and the main factors for the abnormally high pressure are the undercompaction due to quick deposition, the hydrocarbon generation of source rocks and the structural compression during the Himalayan period. Key words: coal-formed gas, Ordos Basin, Sichuan Basin, Upper Paleozoic, Xujiahe Formation, pool-forming history

The formation mechanism of deep effective reservoirs is elaborated based on the analysis of the conditions for forming natural gas accumulations in deep Kuqa Depression. Natural gas charging is closely related to the formation of effective sandstone reservoirs in the deep zone: reservoirs which capture oil and gas in the early period are of better quality during the long burial period; reservoirs which do not capture oil and gas in the early period is compact after deep burial because of compaction. Oil and gas charging before the reservoir is deeply buried significantly inhibits mechanical compaction and fracture closure as well as densification, so the effective pores and fractures will be preserved. The formation conditions of large gas fields in Kuqa Depression are as follows: sufficient coal gas source; great gas generation potential of high-evolution Jurassic source rocks; secondary pores and micro-fissures developed in deep sandstone reservoirs; wide distribution of gypsum-salt cap rock with large thickness; good association of source-reservoir-cap in space; well developed hydrocarbon migration pathways of dominantly faults; high expulsion efficiency; big migration and accumulation coefficient and deep or ultra-deep traps developed below salt structures. Key words: deep zone, low porosity and low permeability reservoir, coal-formed gas, fault transportation system, oil and gas charging, Kuqa Depression

Multiply isotopically substituted molecules (‘clumped’ isotopologues) can be used as geothermometers because their proportions at isotopic equilibrium relative to a random distribution of isotopes amongst all isotopologues are functions of temperature. This has allowed measurements of clumped-isotope abundances to be used to constrain formation temperatures of several natural materials. However, kinetic processes during generation, modification, or transport of natural materials can also affect their clumped-isotope compositions. Herein, we show that methane generated experimentally by closed-system hydrous pyrolysis of shale or nonhydrous pyrolysis of coal yields clumped-isotope compositions consistent with an equilibrium distribution of isotopologues under some experimental conditions (temperature–time conditions corresponding to ‘low,’ ‘mature,’ and ‘over-mature’ stages of catagenesis), but can have non-equilibrium (i.e., kinetically controlled) distributions under other experimental conditions (‘high’ to ‘over-mature’ stages), particularly for pyrolysis of coal. Non-equilibrium compositions, when present, lead the measured proportions of clumped species to be lower than expected for equilibrium at the experimental temperature, and in some cases to be lower than a random distribution of isotopes (i.e., negative Δ18 values). We propose that the consistency with equilibrium for methane formed by relatively low temperature pyrolysis reflects local reversibility of isotope exchange reactions involving a reactant or transition state species during demethylation of one or more components of kerogen. Non-equilibrium clumped-isotope compositions occur under conditions where 'secondary’ cracking of retained oil in shale or wet gas hydrocarbons (C2-5, especially ethane) in coal is prominent. We suggest these non-equilibrium isotopic compositions are the result of the expression of kinetic isotope effects during the irreversible generation of methane from an alkyl precursor. Other interpretations are also explored. These findings provide new insights into the chemistry of thermogenic methane generation, and may provide an explanation of the elevated apparent temperatures recorded by the methane clumped-isotope thermometer in some natural gases. However, it remains unknown if the laboratory experiments capture the processes that occur at the longer time and lower temperatures of natural gas formation.