塔里木盆地北部地区超深断控油藏关键成藏期

Key oil accumulation periods of ultra-deep fault-controlled oil reservoir in northern Tarim Basin,NW China

塔里木盆地北部地区奥陶系碳酸盐岩发现了埋深大于6000 m的断控型特大油田,关键成藏期厘定对油气成藏研究与勘探开发具有重要意义。在岩相学精细分析基础上,开展12口井断裂充填方解石的流体包裹体组合(FIA)测试分析,并结合烃源岩及其生油期、断裂与圈闭形成期研究断控油藏成藏期。结果表明,①FIA类型多样,主要存在坳陷区黄色荧光与隆起区黄绿色荧光2类不同成熟度油包裹体,指示2期石油充注;②FIA中盐水包裹体均一温度多遭受升温作用的影响,与油包裹体共生的盐水包裹体最小温度值更接近成藏期温度;③黄色荧光的FIA都检测到低于50℃的均一温度,黄绿色荧光的FIA均检测到70~90℃的温度数据,揭示中晚加里东期与晚海西期的2期石油成藏期;④中晚奥陶世为走滑断裂、奥陶系碳酸盐岩缝洞体储集层与圈闭的关键形成期;⑤下寒武统主力烃源岩的生油高峰期为晚奥陶世,坳陷区以晚奥陶世成藏为主,隆起区以早二叠世成藏为主。研究认为,塔里木盆地北部地区超深断控油藏关键成藏期为加里东晚期,坳陷区保存了加里东期的原生古油藏,隆起区发育晚海西期从坳陷区调整过来的次生油藏;保存条件是该区走滑断裂带石油富集的关键,阿满过渡带坳陷区油气更富集、勘探开发潜力更大。

A giant fault-controlled oilfield has been found in the ultra-deep(greater than 6000 m)Ordovician carbonate strata in the northern Tarim Basin.It is of great significance for hydrocarbon accumulation study and oil exploitation to determine the key oil accumulation periods.Based on detailed petrographic analysis,fluid inclusion association(FIA)in calcite samples filling in fractures from 12 wells were analyzed,and key accumulation periods of the strike-slip fault-controlled oilfield was studied by combining oil generation periods of the source rocks,formation periods of the fault and traps,and the fluid inclusion data.(1)There are multiple types of FIA,among them,two types of oil inclusions,the type with yellow fluorescence from the depression area and the type with yellow-green fluorescence from the uplift area with different maturities indicate two oil charging stages.(2)The homogenization temperature of the brine inclusions in FIA is mostly affected by temperature rises,and the minimum temperature of brine inclusions symbiotic with oil inclusions is closer to the reservoir temperature during its forming period.(3)FIA with yellow fluorescence all have homogenization temperatures below 50℃,while the FIA with yellow-green fluorescence have homogenization temperatures of 70–90℃tested,suggesting two oil accumulation stages in Middle-Late Caledonian and Late Hercynian.(4)The Middle-Late Ordovician is the key formation period of the strike-slip fault,fracture-cave reservoir and trap there.(5)The oil generation peak of the main source rock of the Lower Cambrian is in the Late Ordovician,and the oil accumulation stage is mainly the Late Ordovician in the depression area,but is mainly the Early Permian in the uplift area.The key oil accumulation period of the strike-slip fault-controlled reservoirs is the Late Caledonian,the depression area has preserved the primary oil reservoirs formed in the Caledonian,while the uplift area has secondary oil reservoirs adjusted from the depression area during the Late Hercynian.Oil reservoir preservation conditions are the key factor for oil enrichment in the strike-slip fault zone of northern Tarim,and the Aman transition zone in the depression is richer in oil and gas and has greater potential for exploration and development.