南方海相古生界沉积古地理特征研究及下扬子勘探潜力探讨

Sedimentary paleogeographic characteristics of marine Paleozoic in south china and exploration potential of the lower Yangtze

近几年来,我国南方海相古生界,特别是上扬子地区,在海相气、页岩气等领域取得多项勘探突破;下扬子古生界勘探层系多、潜力大,多个领域取得油气显示,但尚未取得显著进展。为明确下扬子地区勘探潜力,以我国南方地区作为一个整体开展地质特征对比分析和研究是十分必要的。在大量调研的基础上,开展了南方海相古生界沉积古地理特征研究,对比了上、下扬子地质特征差异性,提出了下扬子勘探思路和方向。研究认为:(1)南方海相古生界沉积期,整体表现为稳定沉降,接受广泛碳酸盐岩沉积,下扬子受加里东运动早幕、燕山至喜山期多次构造运动影响,在构造和沉积特征方面比上扬子更为复杂;(2)下扬子地区广泛发育下寒武统幕府山组、上奥陶统五峰组-下志留统高家边组和二叠系3套烃源岩,与上扬子不同,储层以海相碳酸盐岩为主,部分层系发育陆相碎屑岩,表现出混积岩的特征,成藏条件有利。根据“先易后难”的原则,建议首先开展二叠系致密碎屑岩勘探研究,其中甜点储层描述和工程改造对策是关键;然后由浅层至深层逐步开展二叠系、晚石炭、寒武系、震旦系海相碳酸盐岩勘探研究,其中沉积相带精细刻画和圈闭描述是关键;最后开展上志留-奥陶系、下寒武统、二叠系页岩气勘探研究,其中页岩品质评价、保存条件、甜点识别和工程改造对策是关键。

There are several Paleozoic strata series and great potential in the lower Yangtze being found in many fields,owing to oil and gas resources,but no significant progress has been made to extract these.To clarify the exploration potential of the lower Yangtze region,based on extensive research,this study assessed the sedimentary paleogeographic characteristics of the marine Paleozoic in the south,compared the differences between the geological characteristics of the upper and lower Yangtze,and proposed exploration ideas and directions for the lower Yangtze.The results revealed that①during the sedimentary period of the marine Paleozoic in South China,the overall performance was stable sedimentation,accepting extensive carbonate deposits.The lower Yangtze is more complex than the upper Yangtze in terms of structural and sedimentary characteristics because of the early Caledonian movement and multiple tectonic movements from Yanshan to Himalayan.②Three sets of hydrocarbon source rocks have widely developed in the lower Yangtze area,which are different from the upper Yangtze area.The reservoir is dominated by marine carbonate rocks,and some strata have developed with continental clastic rocks,exhibiting the characteristics of mixed rocks,which is favorable for reservoir formation.(3)According to the principle of“easy before difficult,”it is suggested that the exploration of Permian tight clastic rock should be carried out first,particularly to identify the sweet spot reservoir and engineering reconstruction measures.Then,the exploration of Permian,Late Carboniferous,Cambrian,and Sinian marine carbonate rocks can gradually be carried out from shallow to deep layers.Obtaining an intricate description of the sedimentary facies belts and the trap description are crucial steps.Finally,shale gas exploration of the Upper Silurian Ordovician,Lower Cambrian,and Permian should be carried out.The evaluation of shale quality,identification of preservation conditions,description of the desert,and identification of engineering reconstruction measures are of utmost importance.