巴中地区须四段致密砂岩钙质夹层识别及成因

Features and Genesis of Calcareous Interbeds in Tight Sandstone, Xujiahe 4 Member, Bazhong Area

综合利用岩心观察、X衍射、普通薄片、铸体薄片、常规测井和成像测井等资料,对川东北巴中地区须四段砂岩钙质夹层特征和成因进行分析。研究表明:巴中地区须四段砂岩钙质夹层在测井曲线上表现为低自然伽马、低声波时差、高密度、低中子和高电阻率值的特征。在成像测井上表现为呈亮带状分布的影像特征。钙质夹层主要分布在三角洲前缘水下分流河道砂体的下部或裂缝发育部位。钙质夹层主要形成于深埋中—晚成岩时期,钙质夹层对储层性质和油气分布有负面影响,其分布受沉积微相和断层的控制,射孔应避开钙质夹层段。

Based on core observation, X-ray diffraction analysis, identification of thin section and casting thin section, and conventional and imaging well-logging data, we studied both features and genesis of calcareous interbeds in tight sandstone, Xujiahe 4Member, Bazhong area, northeastern Sichuan Basin. Results show that, the interbeds appear some natures from well-logging curves,containing low natural gamma-ray value, low acoustic travel time,high density, low neutron value, and high resistivity, whereas from imaging well-logging curves, representing a feature of light bandshaped distribution; they are mainly distributed in the lower part or fractured- developed regions of underwater distributary channel sandbody in deltaic front; dominantly formed in a period from middle to later diagensis, they have a negative effect on reservoir property and hydrocarbon distribution, and their distribution is affected by sedimentary microfacies and fault; and to carry out a perforation should avoid these calcareous interbeds.