渝东南龙马溪组黑色页岩矿物组成及其页岩气意义

Mineral components of shales from Longmaxi Formation in southeastern Chongqing and their implications for shale gas

在野外露头和岩心观察描述的基础上,通过扫描电镜和X线衍射对矿物质量分数和毛管压力曲线进行分析,并分析渝东南地区下志留统龙马溪组页岩的矿物学、储层物性、孔喉分布和岩石脆性等特征。研究结果表明:研究区下志留统龙马溪组页岩矿物成分以黏土矿物和石英为主,其中黏土矿物平均质量分数为42.3%,石英平均质量分数为39.2%,其次为长石(平均质量分数为12.6%)、碳酸盐矿物(平均质量分数为5.6%)和黄铁矿(平均质量分数为0.8%),其中脆性矿物质量分数较高,平均质量分数可达58%,岩石脆度平均达45%。下志留统龙马溪组页岩有效孔隙度均值为3.18%,渗透率均值为11.8×10^(-5)μm2,属于低孔低渗的非常规致密储层;页岩中石英质量分数与储层有效孔隙度和渗透率呈正比例关系,而黏土矿物质量分数与有效孔隙度呈弱的正比例关系,与渗透率也呈较弱的反比例关系。

Based on the observation of field outcrops and cores selected from Silurian Longmaxi shale （SLS） in southeastern Chongqing, the mineralogical features, reservoir properties, pore throat characteristics and rock brittleness were analyzed by scanning electron microscopy and X-ray diffraction. The results show that clay mineral and quartz are dominant minerals in the SLS, with average mass fraction of 42.3% and 39.2%, respectively, followed by feldspar with average mass fraction of 12.6%, carbonate minerals with average mass fraction 5.6% and pyrite with average mass fraction of 0.8%. The mass fraction of brittle minerals is relatively high, with average mass fraction of 58%. The brittleness of the SLS is relatively high with average value 45%. The average effective porosity and permeability of Silurian Longmaxi Formation are 3.18% and 11.8 × 10 5 μn2, respectively, which belongs to the unconventional tight reservoir. The results also show a positive correlation between quartz mass fraction and effective porosity and permeability, and a slightly negative correlation between clay mineral and permeability.