宁明盆地超浅层气地质赋存特征及其工程危害  

GEOLOGICAL OCCURRENCE CHARACTERISTICS AND ENGINEERING HAZARDS OF ULTRA SHALLOW-BURIED GASES IN NINGMING BASIN

作　　者：张帆[1] 贾鹏飞[1] 王勇[2] 陈楷文 ZHANG Fan;JIA Pengfei;WANG Yong;CHEN Kaiwen(State Key Laboratory of Continental Dynamics,Department of Geology,Northwest University,Xi'an 710069,China;State Key Laboratory of Geomechanics and Geotechnical Engineering,Institute of Rock and Soil Mechanics,Chinese Academy of Sciences,Wuhan 430071,China;School of Civil and Architectural Engineering,Guilin University of Technology,Guilin 541004,China)

机构地区：[1]西北大学地质学系大陆动力学国家重点实验室,西安710069 [2]中国科学院武汉岩土力学研究所,岩土力学与工程国家重点实验室,武汉430071 [3]桂林理工大学土木与建筑工程学院,桂林541004

出　　处：《工程地质学报》2023年第3期1105-1115,共11页Journal of Engineering Geology

基　　金：国家自然科学基金(资助号:51979269)。

摘　　要：浅层气是一种自然资源,同时也是一种地质灾害,在工程卸荷扰动下,浅层气在地层压力作用下逸出,进而诱发工程危害和事故。以广西宁明盆地内纳利大桥建设中遭遇到浅层气地质灾害为研究背景,通过地质钻孔取样和地球化学实验相结合的研究手段,对研究区超浅层天然气的赋存特征及其工程危害进行研究。结果表明:(1)区域构造活动频繁,裂缝发育,泥岩所夹的薄层粉砂、粉砂岩和粉砂质泥岩厚度2~200 mm不等,实测孔隙度约25.6%,渗透率约37.2~46.8μm^(2),浅层气以相控、缝控、壳控以及它们之间的过渡等形态赋存于各类储层中,呈独立、不连续、交错分布特征;(2)区域内泥岩层深厚,有机碳含量(TOC)为0.61%~1.24%,有机质丰度较高,产气能力良好,是浅层气的烃源岩,泥岩盖层实测孔隙度22.8%~34%,渗透率(2.4~22.2)×10^(-3)μm^(2),封闭能力一般;(3)区域内超浅层天然气的地质赋存特征使得在工程勘探和施工深度(10~100 m)范围内难以形成异常压力,桥梁钻孔灌注桩成桩过程中虽不会出现强烈的井喷事故,但会对桩基混凝土造成气侵危害,影响桩身完整性,建议采用超前排气和改善施工工艺等处置措施。Shallow gas is a natural resource and also can bring about geological hazard.The disturbance of engineering unloading and the effect of formation pressure cause shallow gas evolution,resulting in damages to engineering works and accidents.This paper examines the shallow gas geological disasters occurred during the construction of Nali Bridge in Ningming Basin in Guangxi.In this context,the occurrence characteristics of ultra-shallow gas in the research area and its damage to engineering works are studied using geological drilling sampling method combined with geochemical experiments.Results show that:(1)Due to the frequent regional tectonic activities and fracture development,the thin silt,siltstone and silty mudstone sandwiched by the mudstone had a thickness of varying from^(2)mm to 200mm,with a measured porosity of about 25.6%,and the permeability of about 37.2~46.8μm^(2).Shallow gas occurs in all kinds of reservoirs in the form of facies control,fracture control,shell control and their transition,showing the characteristics of independent,discontinuous and staggered distribution.(2)The deep and thick mudstone layer in the region with an organic carbon content(TOC)of 0.61%to 1.24%and abundant organic matter and high gas production capacity belongs to the source rock of shallow gas.The measured porosity of mudstone cap rock is 22.8%to 34%,with a permeability of(2.4~22.2)×10^(-3)μm^(2)and ordinary sealing capacity.(3)Due to the geological occurrence characteristics of ultra-shallow natural gas in the area,it was hard to generate abnormal pressure within the range of engineering exploration and construction depth(10~100m).Despite no occurrence of strong blowout accident during the construction of bridge cast-in-situ bored piles,it would cause gas invasion damage to the pile foundation concrete and affect pile body completeness.It is recommended to adopt advanced exhaust gas measures and to improve relevant technologies.

关 键 词：宁明盆地 泥岩 浅层气 分布特征 组分特征 烃源岩特征 储集特征 气侵 

分 类 号：P694[天文地球—地质学]