郯庐断裂南段糜棱岩波速变化及油气地质意义

The Wave Veloity Change Through the Mylonite in Southern Section of the Tancheng-Lujiang Fault and Its Geological Implicatilns for Oil and Gas

为探索深部无机成因天然气 (CO2 等 )的封盖条件 ,特选定构造滑脱带韧性断层岩 (糜棱岩 )作为对象 ,采用超声波方法 ,对糜棱岩的波速进行了测试和计算。结果表明 ,糜棱岩波速与岩石组构、构造应力及成藏条件之间有着密切的关系。波速与孔隙度呈反相关 (VPZ=5 .96～ 0 .89Ф) ,波速与其密闭性之间有着很好的相关性。岩石表现出明显的各向异性 ,最小波速方向为油气的封闭方向 。

For the inorganic origin natural gas, especially the carbon dioxide gas, its accumulation in the deep seated part of basin and inside mountain chain is related to cap rocks, which the tectonic decollement rifted rock (mylonite) is an ideal rock type. The ultrasonic method is optimum for detecting the sealing effect of cap rock because it is effective, economic and convenient. The ultrasonic wave refers to the elastic wave propagating in continunm with its frequency over the hearing threshold value of human beings. The method is tenable theoretically and is useful in study the anisotropy of rock's wave velocity by means of ultrasonic wave,analyzing the wave velocity anisotropic body that shows oil and gas bearing bed and sealing cover,and judging the migration direction of oil and gas. However, the study of wave velocity related to sealing cover based on mylonite has not been reported so far. In this paper, the wave velocity of mylonite is detected and calculated. The result indicates that the wave velocity of mylonote is closely related to rock fabrics, tectonic stress field and accumulation forming conditions. The wave velocity is negatively related to porosity( V pz=5.96-0.98Ф) and postively to sealing performance. The rock shows evident anisotropy,the minimum wave velocity direction indicating the sealing trend while the maxmum the favourable direction for migration of oil and gas.