鄂尔多斯盆地致密砂岩气层测井评价新技术

NEW METHODS OF LOG EVALUATION OF THE TIGHT SANDSTONE GAS RESERVOIRS IN E’ERDUOSI BASIN

鄂尔多斯盆地上古生界以陆相、海陆交互相碎屑岩为主,属于低孔、低渗的致密砂岩储集层。由于其低孔、低渗、非均质性强等原因,使利用常规测井资料正确识别气层的难度增大。文章分析认为,上古生界气田测井特征受岩性物性作用比较明显,石英砂岩和岩屑砂岩的测井特征与含气特征不同,电性上高低电阻率气层共存。在综合利用成象测井新技术提供的新方法及多信息、高精度参数,在分析储层特征的基础上,结合实验数据确定了核磁共振变等待时间的测井参数,提出了对致密气层识别有效的气层识别新方法,主要为基于核磁共振测井的差谱法、移谱法,基于交叉偶极声波测井纵波差值法。通过实例分析,证明了方法的有效性,较好地解决了低孔、低渗致密气层和低阻砂岩储层的气层识别问题,提高了测井识别的准确率,解释符合率达85%以上。

The Upper Paleozoic in E'erduosi Basin is mainly composed of the elastic rocks of continental and transitional facies, and its reservoir belongs in low-porosity and-permeability tight sandstone. Therefore it was difficult to identify correctly the gas reservoir by applyin conventional log data because of its low porosity, low permeability and strong heterogeneity. Through analyzing, it was considered that the influence of lithology and petrophysical property on log response was relatively evident; and the log features of quartzose sandstones and lithic sandstones were nonidentical with the gas potential, the gas reservoir showing both high and low resistivities. By use of the new method, multiple information and high-accuracy parameter supplied by imaging logging technique and on the basis of analyzing reservoir characteristics, the log parameter of the variable-waiting time of nuclear magnetic resonance was determined in combination with experimental data; and the effective identification methods of tight gas reservoir was proposed, they including the difference spectrum and migrating spectrum methods based on nuclear magnetic resonance log and the compression wave differential value method based on cross-dipole acoustic logging. Through analyzing an example, it was proved that these methods are effective. Therefore the problem of identifying the low-porosity and-permeability tight gas reservoir and the low resistivity sandstone gas reservoir was well solved and the accuracy of log identification was greatly raised with an interpretation coincidence rate of more than 80%.