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    再论无机生油假说及中国找油前景

    A further discussion on the abiogenetic petroleum origin hypothesis and the prospect of oil prospecting in China

    • 摘要: 新中国成立后石油勘探的第一个成功范例是1958年大庆油田的发现和开发。相应的概念上的创新是颠覆了只有海相地层才能找到大油田,确立陆相地层中同样可以找到大油田。普查勘探方法上的革新是采用了先进的地球物理方法开展战略性大面积普查,不再局限于几个地表有油苗的山前盆地进行工作。寻找石油资源急需开辟一个新的领域。其特点是普查勘探的对象不局限于地壳,还要拓宽到研究岩石圈。思想上的创新是要摒弃海相生油和陆相生油等陈旧生油理论,确立地幔生油的新思维。根据物理学热力学理论,甲烷是唯一一种在标准温压条件下稳定的碳氢化合物,直链烷属烃只有在压力> 3 MPa温度> 700℃时(相当于地下深度约100 km)才有可能形成。因此,海相生油理论和陆相生油理论都不靠谱,在地表赋存的不论是海相地层还是陆相地层内都不能生油,油气是地幔内(软流圈)无机生成,然后运移到海相盆地或陆相盆地中聚集成藏的。海相油田或陆相油田是储存的条件不同,但不是生成油田的机制不同。地球物理对寻找幔内生油区有独特的作用,许多石油地质学家认为,地球物理揭示的岩石圈内的低速低阻层与深藏油层有密切的关联。并且我们发现,在已开发的油田下方往往有软流圈物质的积聚。这些软流圈物质常常富有强烈的活动性,它们可以穿透覆盖在它们上面的地幔物质来到壳幔边界,在地幔中形成一个蘑菇云状的构造。这为开辟找石油的深层源头找到了捷径。根据中国地震层析资料探测得到的地幔内存在的低速带,以及区域地质背景条件,笔者提出中国3片找油最有远景的地区,即东亚西太平洋裂谷区、东特提斯地幔隆升区以及新疆深断裂分布地区:(1)东亚西太平洋低速带是在中新生代时,东亚大陆边缘岩石圈裂变所形成。它包括深浅、范围、形态各不相同的3个带。从西向东依次为:松辽-华北-东南沿海陆内裂谷带;日本海-黄海-东海-南海东亚边缘海裂谷带,以及四国海盆-帕里西维拉海盆-巴布亚新几内亚洋内裂谷带(2)东特提斯隆升区是指中国西南的兰坪盆地、思茅盆地、楚雄盆地为中心的一个地区,它们原本与当今最富油气的中东地区同属一个构造带,约在5 Ma时由于印度板块的向北挺进,青藏高原隆升,在这一地区的构造受到前所未有的破坏,但仍有残余下来可能含油气地区。(3)新疆地区由于受到印度地块的挤压,形成一系列背型和向型构造。深藏油气只能从切割它们的深大断裂中溢流到地表。笔者根据卫星重力资料,提出巴彦敖包-西宁不连续带;淖毛湖-茫崖不连续带;于田-克里雅河不连续带和阿拉木图-塔什库尔干不连续带等4条不连续带。它们都可能是深层石油上升的通道,希望能引起找油专家们关注。

       

      Abstract: The first successful case for exploration oil in New China was the discovery of the Daqing oil field in 1958. The discovery of the Daqing oil field subverted the concept that oil can only be formed in marine strata, and proved that oil field could also be formed in continental strata. Besides, in the exploration of Daqing oil field advanced geophysical methods were adopted to carry out strategic regional investigation, and the geophysical work was no longer confined to front basins with oil seepage.In the upcoming oil exploration, we should create a common perspective that oil is generated in the mantle, and hence the work should expand to the whole lithosphere.According to thermodynamics, methane is the sole hydrocarbon which can be stably living under the standard temperature and pressure condition; straight-chain alkanes hydrocarbons can be formed only under the condition pressure > 30 kbar and temperature > 700℃ (corresponding to a depth about 100 km). Therefore, both marine oil generation theory or terrestrial oil generation theory cannot hold the water. In fact, oil is generated in the mantle, and then migrate to marine basins or terrestrial basins for accumulation of petroleum.Geophysical methods play an important role in prospecting for deep oil reservoir. Many petroleum geologists have considered that the low velocity-low resistivity layer is closely related to oil reservoir. Besiders, researchers have found that, under the known oil fields, there frequently exists asthenospheric matter. Asthanosphric matter is active and can penetrate mantle matter to form a mushroom cloud in the mantle.Based on seismic tomography and regional geological environtal condition, the authors put forward three perspective regions for oil exploration:(1) The East Asia-West Pacific Oceanic low-velocity region. There are three zones which were formed in MesozoicCenozoic period and are different in depth, extent and shape. From west to east, they are Songliao-North China -SE China coastal continental rift zone; Japan Sea-Yellow Sea-East Sea-South China Sea marginal sea rift zone, and Shikoku Sea basin-Parece Vela Sea basin -Papua New Guinea marine rift zone(2) East Tetisi mantle uprifting region:The East Tetisi mantle uprifting region consists of Lanping basin, Simao basin and Chuqiong basin in Southwest China. This region originally had the richest oil and gas reservoirs in the world, but its structures were severely destroyed under the extrusion of the Indian block(3) The deep faults in Xinjiang region:The Xinjiang region formed a series of synformal and antiformal structures under the extrusion of the Indian block, and hence deep oil may migrate upward to the surface through deep faults. According to satellite gravity, the authors hold that Bayan-Ovoo-Xining discontinuous zone, Naomaohu-Mangnai discontinuous zone, Yutian-Keriya Hu discontinuous zone, and Alma-Ata-Taxkorgan discontinuous zone are favorable areas for oil exploration.

       

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