Crude oil and natural gas are generated by organic matters in rocks in sedimentary basins. After incisive and systematic research on global petroliferous basins, it is realized that the distribution of oil and gas fields is highly heterogeneous, and most of oil and gas are enriched in a few sedimentary strata. Source rocks are the most significant factor that governs the distribution of crude oil and natural gas in sedimentary basins. The prerequisite to finding out a petroliferous basin is to search for source rocks. The abundance of organic matters determines the quality of source rocks and the quantity of generated hydrocarbons. In a sedimentary basin, the biological nutrients come from rivers. The biological nutrition is the key factor that controls the degree of reproduction and organic matter abundance in source rocks, which is a governing factor for the amount of oil and gas generated and the degree of petroleum resource enrichment in the sedimentary basin. Oil and gas are mainly distributed in three systems in the world: river-lake system, river-gulf system and river-delta system. The river-lake system is the main location of continental oil distribution. Lacustrine oil is mainly produced by organic matters originating from dead algae in lakes preserved in sedimentary rocks. Algae growth mainly depends on the nutrients that come from rivers, especially those with a long history, flowing through a wide area. The nutrients have a large amount of phosphorus, potassium and other minerals dissolved in water, providing a prerequisite to the growth of algae and a guarantee of the formation of high-quality source rocks. The river-gulf system is the main location of marine oil distribution. The gulf is the estuary of the river, which brings abundant minerals to promote the growth and proliferation of aquatic organisms such as algae. Gulfs are relatively closed and their exchange with the ocean is restricted, therefore the gulf is also conducive to the preservation of organic matters. The coaliferous gas has the world's most widely distributed and biggest reserves; many giant coaliferous gas fields are located in the river-delta system. The sediments brought by the river are fertile soil for the growth of higher plants, and the native higher plants on the river-delta plain are the solid material basis for the formation of coal-measure gas source rocks. Well-developed delta reservoirs with good reservoir-caprock configuration are beneficial for natural gas enrichment and accumulation.
针对现有压裂停泵压降模型不考虑支撑剂运移、无法解释支撑剂铺置效果的难题,提出适用于主加砂压裂的停泵压降模型,模型考虑了裂缝系统中携砂液-支撑剂靠黏度和速度耦合的水平运移与沉降运动,以及基质系统中压裂液靠黏性力和重力作用的三维流动,通过将裂缝系统与基质系统耦合求解,实现了主加砂压裂停泵过程的支撑剂运移模拟计算,获得的井底压降导数双对数曲线呈现出"厂"字型的形态特征,并按照停泵时间顺序划分为支撑剂沉降、支撑剂水平运移、支撑剂减速运移、支撑剂压实和支撑剂停止运移5个主控阶段.研究结果表明:支撑剂铺置越均匀(主次裂缝内砂量越接近),压降导数曲线越平缓,支撑剂沉降控制期越长,支撑剂减速运移期越短,支撑剂压实控制阶段会呈现出1/4斜率段;支撑剂充填比例越大(缝网总体积越小),压降导数曲线越陡,支撑剂水平运移控制期越短,支撑剂运移控制阶段的压降及导数会呈现重合趋势.选取涪陵页岩气田一口典型压裂水平井逐段开展停泵压降曲线拟合,反演获得各加砂压裂段的支撑裂缝体积与铺砂均匀程度,为定量评价水力压裂加砂效果、认识压后支撑剂运移规律提供了理论依据.
塔北地区奥陶系鹰山组上段斑状白云岩发育,为探究其成因机理及油气储集意义,基于岩心、岩石薄片和碳氧同位素、全岩及微区微量元素、稀土元素地球化学特征分析,系统讨论了鹰山组上段生物扰动选择性白云石化作用机理及其储层特征.斑状白云岩由白云质斑块和灰质基质构成,白云质斑块占比为30％～75％,沿Thalassinoides潜穴分布,主要由粉晶—细晶白云石组成.白云质斑块具有相对较高的Fe、Mn及Ni元素含量,δ13C值为-1.48‰～0.06‰,δ180值为-8.64‰～-6.95‰;灰质基质的δ13C值为-1.93‰～-0.61‰,δ18O值为-8.14‰～-7.08‰.白云质斑块和灰质基质的全岩稀土元素配分模式均为"平坦型",原位微区测试结果表明白云质斑块具有Eu正异常.鹰山组上段斑状白云岩的形成受生物扰动和微生物活动控制,生物扰动可改善潜穴部分的孔隙结构,为同期海水提供良好的运移通道;潜穴内部生物活动形成的有机质为其繁盛提供了充足的养料,微生物降解有机质生成NH3可提高潜穴微环境的pH值.在氧化环境中,蓝细菌通过光合作用和二氧化碳浓缩机制生成HCO3-和OH-;在还原环境中,硫酸盐还原作用和甲烷厌氧氧化作用消耗SO42-,释放Mg2+,并生成HCO3-,提高白云石化流体的碱度.整体上,微生物活动导致潜穴微环境中的Mg2+浓度和CO32-活性增加,有利于白云石化作用.白云质斑块发育连通性较好的白云石晶间孔,具有重要的储集意义.
泡沫排水采气(泡排)工艺因成本低、施工简单、见效快,在国内外各大气田中广泛应用,在众多排水采气工艺中扮演"主力军"作用.准确揭示泡排井井筒压降规律对于优化泡排工艺技术参数、提高泡沫排水采气工艺技术水平具有重要意义.由于漂移模型不划分流型,具有形式简单、便于工程计算的优点,是气液两相流发展的重要方向,而漂移模型的核心参数是漂移速度和分布系数.通过在30 mm内径的有机透明玻璃管中开展泡沫多相流实验,测试了不同倾斜角(0°～90°)液流速(0.01～0.20 m/s)、气流速(0～20m/s)及泡排剂浓度[(0～5000)×10-6]下的压降规律,利用实验数据对气液两相漂移模型的漂移速度和分布系数进行了改进,提出了泡沫流动条件下的含气率计算方法,以此建立预测泡沫排水采气井筒压降的新模型.利用现场数据对新建模型进行评价的结果表明,新建模型的预测能力优于采油气工程中常用的经验模型和机理模型.
天然气水合物被视为具有巨大潜力的清洁能源资源,90％以上的水合物分布在深海沉积物中.针对目前水合物开采技术现状,提出了注入常温海水强化海域水合物藏低频电场加热效率的新型开采方法,可发挥降压、电场原位生热、热对流以及海水就地取材等多重优势.通过数值模拟手段,分析了新方法提高海域水合物藏生产效率的可行性及生产机理,探讨了海水注入速率和电压对生产性能的影响.研究结果表明,在电场加热的基础上,注入常温海水进一步提升了产气速率、生产气水比及能效比,增产机理在于海水对流强化传热效率、提供气体流动驱动力以及增强储层导电性.随着注入速率的增加,对流传热效果进一步加强,产气峰值得到提高,但受产水量增加的影响,生产气水比不断减小,能效比先快速增加后趋于稳定.增加电压可显著提高产气量和生产气水比,但也加大了水合物储层内的热耗,导致能效比不断减小,建议在综合考虑气体产量与能效比的基础上对电加热制度进行优化.
