塔里木盆地塔中地区奥陶系油气成藏主控因素及勘探选区

Key Factors of Oil-gas Reservoir-forming and Exploration Targets in Ordovician in Tazhong Area,Tarim Basin

通过对塔中地区钻遇奥陶系的60余口探井油气成藏及失利原因的综合分析,提出该区奥陶系油气成藏的主控因素为:①中、上奥陶统(相当于黑土凹组—萨尔干组的层位)主力烃源岩控制了塔中地区的油气分布,其主要分布于塔中凸起北部斜坡区;②4套碳酸盐岩储层(志留纪—泥盆纪古潜山岩溶储层、中奥陶世晚期—晚奥陶世早期古潜山岩溶储层、上奥陶统良里塔格组棚缘礁滩体埋藏溶蚀储层及下奥陶统内幕白云岩储层)的分布及其非均质性对成岩—岩性圈闭油气藏的形成起到了至关重要的作用;③二叠纪—早三叠世是塔中地区现今工业性油藏的主要成藏期;④圈闭及其封盖—保存条件决定了油气藏的规模。针对塔中地区奥陶系油气勘探选区及勘探步骤,提出具体的勘探工作可分3个层次进行:①近期主攻塔中I号断裂带南侧良里塔格组棚缘礁滩体成岩圈闭特大型岩性油气藏,兼探中央断垒带东段(塔中401—塔中9井区)下奥陶统古潜山岩溶储层油气藏;②对塔中10号构造带及其与中央断垒带之间的中奥陶世晚期—晚奥陶世早期形成的下奥陶统鹰山组中上部古潜山岩溶储层油气藏及塔中1—塔中7—塔中48井区下奥陶统古潜山岩溶储层油气藏进行勘探;③在存在沟通油源断裂的前提下,对满加尔凹陷区上奥陶统浊积砂岩—陆棚—三角洲—滨岸潮坪砂岩的构造及岩性圈闭油气藏进行勘探。

Synthetically analyzing on the oil-gas pools formation and losing reasons of over 60 drilling wells in Ordovician in Tazhong area, Tarim basin, the key factors to form Ordovician oil-gas reservoirs in this area are as below: (1)the important source rocks, which are corresponding to Heituwa Formation and Sha'ergan Formation in Middle-Upper Ordovician, control the distribution of oil and gas in northern slope of Tazhong uplift; (2)the distribution and heterogenesis of four sets of carbonate reservoirs, such as paleo-burial hill karst reservoir generated from Silurian to Devonian (EKR-1), paleo-burial hill karst reservoir formed from later Middle Ordovician to early Late Ordovician (Liandeilo to early Caradoc) (EKR-2), shelf marginal reef-shoal burial karst reservoir in Upper Ordovician Lianglitage Formation and Lower Ordovician interlayer dolomite reservoir , play a very important role in forming diagenetic-lithologic oil-gas traps; (3)the main reservoir-forming stage of commercial oil reservoirs at present would be from Permian to Early Triassic in Tazhong area; (4) the conditions of traps, cap rocks and oil-gas conservation controlled the scale of oil-gas pools. As to oil-gas exploration targets and steps of Ordovician in Tazhong area, it is suggested that three stages should be conducted, including in the near term, the ultra-large lithologic oil-gas reservoirs of Lianglitage Formation distributed in shelf marginal reef-shoal in the southern side of Tazhong-I fault belt should be firstly explored, at the same time, the Lower Ordovician oil-gas pools distributed in eastern part of central fault-horst belt from Tazhong- 401 to Tazhong-9 well block should also be explored; secondly, the paleo-burial hill oil-gas pools in the middle and upper part of Yingshan Formation in Lower Ordovician distributed in Tazhong-10 structural belt and the area between it and central fault-horst belt, and Lower Ordovician in the area of Tazhong-1-Tazhong-7-Tazhong-48 well blocks should be explored; if existing the fault to link source rocks, the structural and stratigraphy traps with turbidite sandstones, shelf-delta, and shore-tidal sandstones in Upper Ordovician in Manjia'er sag can be explored.