珠江口盆地惠北地区煤系烃源岩新认识与勘探实践

New insights and exploration practices of coal-bearing source rocks in the Huibei area,Pearl River Mouth basin

珠江口盆地恩平组煤系烃源岩因分布主控因素认识不清、发育规模不明确,导致勘探潜力被忽视。以煤系烃源岩发育区惠北地区作为研究靶区,利用地震、钻井和地化等资料,系统分析了煤系烃源岩分布主控因素,据此确定煤系烃源岩发育规模和资源潜力,从而有效指导勘探。研究表明:①纵向上,从恩四段到恩一二段沉积期,惠北地区古气候温暖湿润,古水深逐渐变浅,古构造活动强度逐渐减弱,恩一二段和恩三段有利于煤层的发育和聚集,恩四段沉积期煤层不发育;②横向上,受古沉积条件的控制,煤系烃源岩主要分布于惠州14洼北部缓坡带辫状河三角洲河道间的河漫沼泽和洼陷带滨浅湖内的湖沼范围内。基于煤系烃源岩分布规律,预测惠北地区煤系烃源岩资源量约2亿方油当量,带动了惠北地区周边勘探,也展示了珠江口盆地煤系烃源岩勘探前景。

The exploration potential of the coal-bearing source rocks of the Enping Formation,located within Pearl River Mouth basin,has been overlooked due to a deficient comprehension of the main controlling factors in their distribution and the undefined scale of their development.Focusing on the developed coal-bearing source rocks in the Huibei area as a case study,this research utilized seismic,drilling,and geochemical data to systematically analyze the controlling factors influencing the distribution of these source rocks.Consequently,the development scale and resource potential of the coal-bearing source rocks were determined to guide exploration endeavors effectively.The study revealed that,①Vertically,during the depositional periods from the fourth Member to the first and second Members of the Enping Formation,the Huibei area experienced a warm and humid paleoclimate with progressively shallower paleo-water depths and decreasing paleo-tectonic activity intensity.The first,second,and third Members of the Enping Formation carry favorable conditions for the development and accumulation of coal beds,while the fourth Member exhibited very limited coal formation.②Horizontally,controlled by paleo-depositional environments,coal-bearing source rocks are primarily distributed in the inter-channel overbank swamps of braided river deltas within the northern gentle slope belt and in the lacustrine swamps within the shore-shallow lake areas of the Huibei depression.Based on the distribution law of coal-bearing source rocks,a resource volume of approximately 200 million cubic meters of oil equivalent in the Huibei area was estimated.This not only invigorated exploration in the adjacent regions of the Huibei area but also demonstrated the prospect of the exploration for favorable hydrocarbon-generating depressions with developed coal-bearing source rocks in the Pearl River Mouth basin.