北部湾盆地迈陈凹陷断裂差异发育特征及对油气成藏控制作用

DIFFERENCE IN FAULT DEVELOPMENT AND ITS CONTROLLING ON OIL AND GAS ACCUMULATION IN MAICHEN SAG,BEIBUWAN BASIN

利用地震、钻井等资料对迈陈凹陷东部断裂系统的发育演化及成因机制进行了分析,同时探讨了断裂对油气成藏的影响。研究结果表明,迈陈凹陷不同区域断裂的组合和活动特征存在明显差异,发育6种构造样式:多米诺式、阶梯式、复式"Y"形(塌陷构造)、铲式扇、牵引式、叠加式;4种断裂活动类型:持续活动型、早期活动型、中期活动型、晚期活动型。迈陈凹陷断裂系统是在先存构造条件下,两期不同方向的裂陷作用(E1ch—E2l时期为北西—南东方向伸展,E3w时期为南北向伸展)叠加形成,不同区域构造样式和断裂活动的差异主要是由先存构造分布和活动的差异性造成。断裂系统一方面控制了迈陈凹陷主力烃源岩的沉积厚度与分布范围,另一方面对油气运移有控制作用,进而控制了油气成藏模式,造成了迈陈凹陷油气的差异分布特征。

Using the seismic and drilling data,the development,evolution and origin of the fault system in the east of Maichen Sag were analyzed,and the influence of fault on oil and gas accumulation were discussed in this paper. The results show that the fault combinations and activity characteristics have obvious differences in different regions of Maichen Sag; There are six types of tectonic styles developed,including domino structure,stepped fault,complicated ＂Y ＂ shaped structure（ collapse structure）,listric-fan structure,drag structure,and superposed fault; And there are four types of fault activities,including continuous activity,early-activity,midterm-activity and late-activity. The fault system in Maichen Sag are developed in the superposition of multi-periodic rifting with different extension directions（ NW-SE extension during E1ch-E2 l,NS extension during E3w） under the pre-existing tectonic conditions. The differences of structural styles and fault activities are caused by different distribution and activity of pre-existing structures. The fault system control not only the thickness and distribution of source rock but also the oil and gas migration which impact the oil-gas accumulation model and lead to different oil and gas distribution in Maichen Sag.