塔里木盆地奥陶系生物礁露头的地球物理特征

Geophysical Characteristics of Ordovician Reef Outcrops in Tarim B asin

奥陶系生物礁为塔里木盆地重要的储集层 ,明确露头上生物礁的内部结构及发育规模 ,探索露头和井下生物礁对比研究的新手段有重要意义。应用探地雷达及自然伽马能谱仪对塔里木盆地巴楚达吾孜塔格奥陶系露头进行了探测。研究表明 ,探地雷达剖面上多数生物礁为扁平透镜状或层状 ,这与露头上观察的结果有所差别 ;高分辨率雷达剖面揭示出较出露生物礁发育程度更大、个体更小的疙瘩状礁体或礁团块 ;礁体内部的分层性及礁体内部水道充填体的斜层理在雷达剖面上反映明显 ,雷达分辨率可达到分米级别。礁灰岩的自然伽马值高于亮晶砂、砾屑灰岩 ,而低于泥晶灰岩、棘屑灰岩、泥晶生屑灰岩、泥灰岩的放射性。生物礁在自然伽马曲线上表现为漏斗形、钟形或箱形 ;自然伽马曲线也反映出礁体内部的分层性。露头和轮南井下奥陶系生物礁的自然伽马放射性特征有一定的相似性 。

The Ordovician reefs are important hydrocarbon reservoirs in Tarim Basin. It is significant to explore new methods for the comparative study between outcrop r eefs and those found in wells to understand their size and internal architectu re. Ground penetrating radar (GPR) and gamma-ray spectrometer h av e been used to detect Dawuzitage Hills Ordovician outcrops in Bachu area, Tarim Basin. GPR data indicate that most reefs are flat and lenticular or layered, whi c h is different from what have been found in outcrop surfaces by naked eyes. Smal l patches of reefs or reef bioherms have been widely revealed by high-resolu ti on GPR profiles. The layering character and slant bedding of channel-filled in tr aclasts of reefs are obvious in GPR profiles with the decimeter resolution. The gamma ray value of reef bafflestone is higher than those of sparrenite and sparr udit e, and lower than those of micritic limestone, wackstone, echinoderm grainstone and marlstone. In outcrop gamma-ray curves, reefs are of funneled, bell-shaped or box-shaped and layering feature of reef can also be reflected. The gamma radi oa ctivity of reefs in outcrop and in wells of Lunnan area has similar characterist ics.It provide good method for the comparative study between outcrop r eefs and those found in wells.