油气“穿断运移”模式、评价方法与应用——以珠江口盆地恩平凹陷为例

断层对油气藏的控制作用体现在油气藏的形成和演化过程中断层输导油气和封堵油气的双重作用。究竟起哪种作用主要取决于断层不同部位、不同层段封堵能力和输导能力的差异性。本文基于珠江口盆地恩平凹陷大量断层圈闭油藏的实际钻井资料,从断层活动速率、生长指数、泥岩涂抹因子(SSF)、断层泥比率(SGR)等角度建立了油气"穿断运移"模式和定量评价方法。指出对于恩平凹陷新近系圈闭而言,当控圈断层粤海组沉积期的活动速率<10m/Ma或生长指数<1.1、SSF>1.8~2.1或SGR<0.35~0.42时,油气能够横穿断层运移。基于这项研究,预测了恩平凹陷北部隆起带A1、A3、A4和南部隆起带A20等构造控圈断层的侧向开启部位和层段,推动了多个构造的钻探和3个商业油田的发现,证实了油气"穿断运移"模式和评价方法的准确性和适用性,对具有类似地质特征的地区具有良好的理论指导和实践价值。

Model of Oil-gas Cross-fault Migration,Evaluation and Application: A Case in the Enping Sag of Pearl River Mouth Basin

Fault controls on oil and gas reservoirs include transportation and sealing.The role of individual fault depends on the sealing and transportation abilities of the different segments of the fault and faulted stratigraphic layers as well.Based on a case study of the large number of faulted reservoirs in the Enping Sag of the Pearl River Mouth Basin,we established a cross-fault migration model of oil and gas and proposed a method of quantitative evaluation on the basis of fault activity rate,growth index,shale smear formula(SSF)and shale gouge ratio(SGR).It is likely that in the Neogene traps in the Enping Sag,oil and gas can migrate across the fault when the activity rate of controlling fault in the depositional period of the Yuehai Formation is less than 10 m/Ma or the growth index is less than 1.1,while SSF is more than 1.8–2.1 or SGR is less than 0.35–0.42.This study have successfully predicted the lateral opening position and intervals of Structures A1,A3 and A4 in the northern uplift belt and Structure A20 in the southern uplift belt of the Enping Sag,which promoted the drilling of the structures and led to the discovery of three commercial oilfields,thus,the accuracy and applicability of the oil-gas cross-fault migration model and evaluation method have been confirmed and may be useful for exploration in areas with similar geological background.