摘要:
根据X井钻遇的古近系和新近系有机质镜质体反射率分析,确定X井生烃门限深度在2 600 m以下,那么该井钻遇始新统流沙港组泥岩有机质丰度较高的井段(2 100~2 285 m)尚未达成熟门槛,而生烃门限以下的烃源岩有机质丰度较低,生烃潜力差,不能提供充足的烃源供给,故导致X井勘探失利。X井位于北部湾盆地迈陈凹陷东3洼南部边缘,钻遇流沙港组厚度达568.5 m,且泥岩厚度占该组地层的62.3%,其中单层泥岩最大厚度高达115 m,表明流沙港组沉积时期水体环境偏深,沉积可容空间大,可见X井钻探结果与前人"迈5号同生断裂始新世活动弱,沉积可容空间小,导致东3洼缺少油气形成的物质基础"的结论存在较大偏差。由于X井处在东3洼陷边缘,流沙港组顶部剥蚀强度较大,推测靠近东3洼沉降中心的始新统流沙港组湖相泥岩沉积厚,埋深亦加大,完全能够达到有机质成熟生烃门槛,故应具有较好的油气成藏地质条件和勘探潜力。
Abstract:
The vitrinite reflectance analysis of the samples from the Well X indicates that the threshold depth for oil generation is deeper than 2 600 meters, and the Eocene Liushagang mudstone with higher abundance of organic matter ranging in the depth of 2 100~2 285 m is above the threshold, while the organic matter of Liushagang mudstone below the threshold is too low to provide sufficient hydrocarbon supply for oil accumulation. As the result, the exploration of the Well X is failed. However, the Well X is located in southern edge of the East-3 Depression, where the Liushagang Formation is 568.5 m in thickness, of which 62.3% are mudstone and the maximum thickness of a single lager of mudstone is over 115 m. It means that water was rather deep during the deposition of the Liushagang Formation and the accommodation space was large. It is obviously different with the conclusion from previous studies, which believed that the Mai 5 growth faulting was weak then, that resulted in small accommodation space, so the East-3 Depression is lack of organic matters for oil and gas generation. Furthermore, as the Well X is located in the southern edge of the East-3 Depression, denudation of the Liushagang Formation might be quite intensive, so we speculated that the thickness of the Liushagang Formation must be larger and might exceed the threshold for hydrocarbon generation. The exploration potential in East-3 Depression remains lange and should not be ignored.
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