折射方法在南海北部潮汕坳陷中生界地层研究中的应用

Application of refraction velocity in studing Mesozoic strata in Chaoshan Depression on northern margin of South China Sea

潮汕坳陷是中生界地层为主的沉积坳陷,被认为是南海油气勘探的重要勘探领域。潮汕坳陷已有丰富的多道反射地震资料,但是由于多次波干扰严重,获取的反射波速度精度低。潮汕坳陷多道反射地震资料中包含丰富的折射波数据,但是很少人重视多道地震记录中的折射波信息并利用他。在此我们通过编写处理程序拾取了折射层的地震速度。试验测线所在海区的水深在600—800m,测线的最大偏移距为6 250m。测线所测的第三系地震折射波速度为2.0—2.5km.s-1,与潮汕坳陷其他地方的第三系地震波速度基本相等。但是潮汕坳陷西南部中生界的地震折射波速度在3.5—4.2km.s-1,低于潮汕坳陷中东部中生界的地震波速度(4.0—5.0km.s-1),预示潮汕坳陷西南部油气储集物性可能较好。

As a deposition depression mainly with the Mesozoic strata, the Chaoshan Depression is an important area for gas and oil exploration in the South China Sea. Plenty of multi-channel seismic data has been obtained in this area, but it is hard to get reflection wave velocity with enough fidelity from the stac- king velocity spectrum due to strong multiple interference. Since remarkable information of refraction wave velocity could be obtained from the multi-channel seismic data of top interface of the Mesozoic strata, a program package is provided in this paper to pick up refraction seismic velocity from the multi-channel seismic data. In the experiment area, the water depth is 600--800m, and the maximum offset of the survey line is 6 250m. The obtained refraction velocity of the Tertiary is 2.0-2.5km·s^-1 , which is similar to the velocity of the Tertiary in the other areas of the Chaoshan Depression. The refraction velocity of the Mesozoic in the southwestern part of the Chaoshan Depression is about 3.5-4.5km·s^-1 , generally lower than that of 4.0-5.0 km·s^-1 in the middle and eastern parts of the Chaoshan Depression, which may imply that the reservoir property for oil and gas in the southwestern part is better.