南方古生界典型区块页岩气勘探潜力评价研究进展报告

A Study on Exploration Potential of Paleozoic Shale Gas in the Typical Block,Southern China

为评价皖南芜湖区块古生界页岩气勘探潜力、优选勘探层系,根据钻井岩心、露头岩样地化、岩石学分析数据及野外调查等资料,对该地区古生界3套富有机质层系的页岩气形成地质-地球化学条件进行初步研究,厘定了下扬子芜湖地区三套页岩的厚度和埋深,对比研究了三套烃源岩的地球化学特征,揭示了页岩脆性、孔隙类型及其发育的控制因素,进而对页岩气储层及勘探潜力进行了初步评价。从最近钻探的4口参数井中采集了365个页岩样品进行TOC和RockEval分析,采用低温N2吸附和场发射扫描电镜(FE-SEM)方法对其中的57个样品进行了研究。结果表明,古生界上奥陶统五峰组-下志留统高家边组、二叠系(孤峰组+龙潭组+大隆组)富有机质泥页岩层系在区内分布广、厚度较大、有机质丰富(TOC普遍>2%),且以偏腐殖型为主、热演化程度较高(Ro=1.3%~3.0%),具有形成页岩气的良好物质基础。它们的矿物基质孔和有机质空隙发育,大小从几个纳米-上百纳米,56柱心样品总孔隙度主体在2.03%~6.5%之间,其中以介孔和微孔为主;总比表面积为7.19~20.84 m^2/g,这些特征与四川盆地志留系龙马溪组页岩储层特征相似。同时,其埋深适中且泥页岩与硅质岩相伴生,利于人工压裂和勘探开发,有较大勘探潜力。另一方面,古生界寒武统黄柏岭组富有机质页岩有机质丰度高且以腐泥型为主,也有良好的成气潜力,但因其普遍深埋、成熟度偏高,该区后期发生的多期强烈构造运动等因素对早期形成页岩气的富集及保存可能有一定影响,其勘探潜力有待进一步深究。

In order to investigate the exploration potential of the Paleozoic shale gases in the South Anhui, geochemical and reservoir petrologic analysis were made on the representative core samples from the study area. A preliminary study was performed on the geological-geochemical conditions of Paleozoic shale gas formation, by the combination of the data with geological information and outcrop data. it can be found that three sets of organic-rich shale strata, including the lower Cambrian Huangpaling Formation（∈1h）, the upper Ordovician Wufeng Formation（O3w） to the lower Silurian Gaojiabian Formation（S1g）,and the Permian Formation（Gufeng Formation（P1g）, Longtan Formation （P2l）,Dalong Formation （P2d） are developed within Paleozoic. The 365 black shale core samples from 4 wells drilled recently were obtained for TOC and Rock Eval analysis, and the geochemistry and pore structures of about 57samples were investigated using low pressure N2 adsorption analysis, field emission scanning electron microscopy （FE-SEM） observations. The results show that the O3w- S1g and P1g＋P2l＋P2d shales with a wide distribution in the studied area have relatively big thickness, high TOC（＆gt;2%）, type IIb-III kerogens,high thermal maturity （Ro=1.3%~3.0%）, and high quartz contents. Both mineral matrix and organic matter pores are well developed with pore sizes ranging from several to several hundred nanometers. The total porosity for the 56 samples ranges mainly from 2.03% to 6.5% with majorities of mesoporous and microporous. The total surface area ranges from 7.19~20.84 m2/g.These characteristic are similar to those of Lower Silurian Longmaxi Formation shales in Southern Sichuan Province.Therefore, they could have favorable geological conditions for forming shale gas and relatively big exploration potentia1. On the other hand,∈1h organic-rich shale with type I kerogens should also have relatively great gas generation potential, but its deep burial and over- maturity, especially late multiphase tectonic movement may have some influence on the generation, accumulation and preservation of shale gases within the strata, so its exploration potential of shale gases need further study.