塔中奥陶系碳酸盐岩油气成藏机理

在塔里木盆地塔中Ⅰ号构造带发现了目前中国最大的奥陶系生物礁型碳酸盐岩凝析气田，为没有明显边底水、油气水分布复杂的非常规油气藏。研究了其油气成藏地质条件和油气成藏机理。结果认为：目前发现的油气主要分布在上奥陶统良里塔格组大型镶边台地边缘礁滩相中，礁滩体储层纵向叠置、横向连片，沿台地边缘大面积分布，低孔低渗储层的储集空间以次生溶蚀孔洞为主；塔中Ⅰ号构造带历经多期油气充注与调整，油气成藏系统生储盖组合配置优越，储层是油气富集的主控因素；低孔低渗碳酸盐岩储层的非均质性是油气赋存差异的基础，多期油气充注是油气水分布复杂化的重要原因，晚期气侵则是形成非常规凝析气藏的重要机制，多期油气充注与储层非均质性造成了油气产出的复杂性。

MECHANISM OF HYDROCARBON POOLING IN THE ORDOVICIAN CARBONATE RESERVOIRS IN TAZHONG AREA OF THE TARIM BASIN

An Ordovician condensate gas field of bioherm type has been discovered in the structural zone Tazhong Ⅰ of the Tarim basin. It is the largest unconventional hydrocarbon reservoir discovered in China by now, with complicated distribution of oil, gas and water but no obvious edge or bottom water. The following understandings are obtained through study of its geologic conditions and mechanism of hydrocarbon pooling. The current discovered oil and gas are mainly distributed in the Ordovician Lianglitage Fm reef and bank reservoirs on a large platform margin. These reef and bank reservoirs are widely distributed along the platform margin with vertically superimposed and laterally connected, and are dominated by low porosity and low permeability reservoirs of secondary dissolution pore cavity type. The structural zone TazhongⅠ is characterized by multistage hydrocarbon charging and adjustment and favorable combination of source reservoir cap rocks, with reservoir as the major controlling factor of hydrocarbon enrichment. The heterogeneous carbonate reservoirs with low porosity and low permeability are the basis of differential hydrocarbon occurrence, and multistage charging is the main cause of the complicated distribution of oil, gas and water, while late gas invasion is the main mechanism of formation of unconventional condensate reservoirs. The multistage charging and reservoir heterogeneity jointly causes the complexity of oil and gas occurrence.