中、上扬子地区常压页岩气勘探前景——以湘中坳陷下寒武统为例

doi:10.11743/ogg20190601

摘要/Abstract

摘要： 中、上扬子地区常压页岩气领域是一个备受关注的新热点，湘中坳陷下寒武统属于盆外常压页岩气领域的典型例子。基于2条野外露头实测剖面，8条观察剖面，1口浅钻井和地震等第一手资料，开展了湘中坳陷下寒武统页岩气地质特征研究。该坳陷下寒武统具有优越的页岩气形成条件，其中，黑色炭质页岩、硅质页岩形成于有利的大陆斜坡-盆地相深水环境，连续厚度超过150 m，优质页岩厚度为50~90 m；黑色页岩TOC值介于1.12%~22.07%，平均为4.64%，R_o平均为2.78%。页岩储集空间包括有机质纳米孔、溶蚀孔、黄铁矿晶间孔、粘土矿物晶间孔、岩心尺度高角度裂缝以及层理缝等，以有机质孔为主；有机质纳米孔因泄压后暴露于地表而呈现为长条、不规则多边形，孔径大小为21.8~328.4 nm；地表样品见到大量的淡水成因的次生溶蚀孔和构造成因的裂缝，孔隙度介于2.22%~8.7%，平均为6.05%；矿物主要以石英为主，平均含量为61.2%，其次为粘土矿物，平均含量为23.5%，脆性矿物含量平均为73.38%。等温吸附实验测试表明页岩平均吸附能力为5.95 m³/t。通过综合地质方法，预测了下寒武统新层系Ⅰ类页岩气有利区面积为8 766.1 km²；在龙山凸起两侧，下寒武统埋深多在3 000~4 000 m，保存条件较好，具有良好的页岩气勘探前景。

关键词: 深水硅质页岩, 常压页岩气, 下寒武统, 湘中坳陷, 中上扬子

Abstract: The domain of normal pressure shale gas in the Middle and Upper Yangtze region is a new focus of attention,with a typical case of the Lower Cambrian shale gas in the Xiangzhong Depression.Based on two measured outcrop sections,eight observation outcrop sections,one shallow-drilling and seismic data,we studied the geological characteristics of the Lower Cambrian shale gas in the Xiangzhong Depression.The study area is favorable for the generation of shale gas.The Lower Cambrian black-carbonaceous and siliceous shales were deposited under deep-water environments for favorable slope and basinal facies,with a continuous thicknesses of more than 150 m and a high-quality shale thickness of 50-90 m.The TOC of the black shales ranges between 1.12% and 22.07%,averaging at 4.64%;and the reflectance of vitrinite (R_o) averages 2.78%.The shale reservoir space consists of organic-matter nanopores,dissolved pores,intergranular pores of pyrites and clay minerals,high-angle fractures,bedding-parallel fractures,and so on,but the organic-matter nanopores are dominant.The organic-matter nanopores occur in strips or irregular polygons due to pressure relief and exposure to the surface,with aperture size ranging from 21.8 nm to 328.4 nm.Samples from the surface are observed to be filled with many secondary dissolved pores of meteoric water origin,and cracks due to tectonic stress.The porosity ranges between 2.0% and 8.7%,averaging at 6.05%.Quartz predominates the mineral composition of shales,averaging at 61.2%.Clay minerals rank second,averaging at 23.5%.Brittle mineral content averages 73.38%.Large number of isothermal adsorption experiments have indicated that its average adsorption capacity is 5.95 m³/t.Favorable zones of Type I shale gas in the new interval of Lower Cambrian were predicted to distribute in an area of 8 766.1 km²,by comprehensive geological methods.It is proven that the exploration potential of shale gas is significant in the both sides of the Longshan uplift,where the burial depth of the Lower Cambrian is mostly between 3 000 m and 4 000 m,a favorable condition for preservation.

Key words: deep-water siliceous shale, normal-pressure shale gas, Lower Cambrian, Xiangzhong Depression, Middle and Upper Yangtze regions

中图分类号:

TE132.2

郑和荣,彭勇民,唐建信,等. 中、上扬子地区常压页岩气勘探前景——以湘中坳陷下寒武统为例[J]. 石油与天然气地质, 2019, 40(6): 1155-1167. doi: 10.11743/ogg20190601 Zheng Herong,Peng Yongmin,Tang Jianxin,et al. Exploration prospect of normal-pressure shale gas in Middle and Upper Yangtze regions: A case study of the Lower Cambrian shale in Xiangzhong Depression[J]. Oil & Gas Geology, 2019, 40(6): 1155-1167. doi: 10.11743/ogg20190601

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