苏里格气田低阻气层分布特征及识别方法研究

RESEARCH ON THE DISTRIBUTION CHARACTERISTICS AND IDENTIFYING METHOD OF LOW RESISTIVITY GAS RESERVOIRS IN SULIGE GAS FIELD

苏里格气田苏6区块存在大量的低阻气层,这些气层的电阻率接近于水层的电阻率,有的甚至比水层的电阻率还小,仅依靠传统的阿尔奇公式计算含气饱和度或根据电阻率的幅度差很难将这些气层识别出来。文章首先统计了低阻气层电阻率的分布规律低阻气层主要分布在盒8段,其次是山西组山1段,山2段很少,其峰值电阻率小于25Ω·m;然后从储层微观孔隙结构和粘土矿物含量等方面分析了低阻气层的成因;在此基础上提出了孔隙度重叠法来识别气层。由于这个方法并不是根据含气饱和度的大小判断流体性质,所以判别结果不受电阻率的影响,对低阻气层和正常气层都适用。研究结果表明,无论是低阻气层,还是正常气层,DDT参数存在明显的正异常。含气层和气水层正异常较小,水层的异常接近于0,而干层为明显的负异常。根据这一规律能够有效地识别低阻气层,经现场试气资料证实该方法是可行的。

There exist many low-resistivity gas reservoirs in Su-6 block of Sulige gas field. The resistivities of these gas reservoirs are close to, even smaller than those of water-bearing layers, so that it is difficult to identify these gas reservoirs through calculating gas saturation only according to conventional Archie formula, or in light of the difference in resistivity amplitude. In the paper, the distribution of the low-resistivity gas reservoirs is counted up and the results show that they are mainly distributed in the 8th member of Shihezi Formation, Permian, then the 1st member of Shanxi Formation, Lower Permian and there exist a few in the 2nd member of Shanxi Formation, the peak resistivity being less than 25Ω &middot m; the genesis of the low-resistivity gas reservoirs is analyzed in consideration of the microscopic pore structure and clay mineral content in the reservoirs; then a porosity overlapped method of identifying gas reservoirs is put forward on the basis of the investigation. Because the method isn't based on identifying the nature of fluid by the magnitude of gas saturation, the results identified wouldn't be affected by resistivity so that it is suitable for both low-resistivity and normal-resisitivity gas reservoirs. Through investigation, it was indicated that the DDT parameter of either low-resistivity or normal resistivity reservoirs showed an obviously positive anomaly; that of gas-bearing layer/ags-water layer showed a smaller positive anomaly; that of water-bearing layer was close to zero; and that of dry layer showed an obviously negative anomaly. The low-resistivity gas reservoir can be effectively identified according to such a law. It was proved by the in-situ testing data that this method is feasible.