塔里木盆地顺北5号断裂带北段奥陶系油气成藏期次及其控制因素

Hydrocarbon accumulation stages and their controlling factors in the northern Ordovician Shunbei 5 fault zone,Tarim Basin

在塔里木盆地顺北地区,顺北走滑断裂对断溶体油气藏具有重要的控制作用。对顺北5号断裂带北段奥陶系储层方解石脉的期次进行识别和划分,通过流体包裹体技术厘定油气成藏期,结合断裂活动性分析揭示走滑断裂对油气成藏期的控制作用。研究表明顺北5号断裂带北段奥陶系储层中发育3期方解石脉体,其中第2期方解石脉形成于志留纪末期。储层中沥青和流体包裹体发育特征揭示研究区存在两期油充注。第1期油充注发生于第2期方解石形成之前,推测是加里东晚期,后在海西早期遭到破坏。第2期充注时间为海西晚期—印支期,距今约260~230 Ma,为奥陶系断溶体油藏的主成藏期。顺北5号断裂带活动性研究结果,指示油气充注和破坏时间与顺北5号断裂活动时期具有很好的对应关系,说明顺北地区走滑断裂活动史是控制油气成藏时期的主要因素。

The characterization of faulted-karst reservoirs in the Shunbei area demonstrates well the important role played by strike slip faults in hydrocarbon accumulation.Based on the identification and division of the crystallization stages of the calcite veins in the Ordovician reservoirs at the north section of the Shunbei 5 fault belt,the hydrocarbon accumulation stages are determined through fluid inclusion analyses and the effect of strike-slip faults on hydrocarbon accumulation stages is revealed by fault zone activity analyses.The results show that there are three phases of calcite vein generation in the Ordovician reservoirs,of which the second phase was formed during the late Silurian.The development characteristics of bitumen and fluid inclusions in the reservoirs reveal two stages of oil charge,with the first stage presumably occurring(before the second phase of the calcite generation) in the late Caledonian and being destroyed later in the early Hercynian.The second stage from the late Hercynian to Indosinian(ca.260-230 Ma) is the main stage for hydrocarbon accumulation in the Ordovician faulted-karst.Fault zone activity analyses of the Shunbei 5 fault belt show a good correspondence between the activity times and the hydrocarbon charge and destruction stages,indicating that the strike-slip fault activities in the Shunbei area is the main factor controlling the hydrocarbon accumulation.