针对下扬子宣城地区复杂地质条件下二叠系页岩气勘查难度大的问题,基于岩石物性测试,运用高精度重力、高精度磁法、复电阻率法(CR法)进行联合勘查,探讨复杂地质条件下有效的页岩气勘查方法。研究表明:宣城地区孤峰组页岩具有“弱磁、低密度、中低阻、高极化”特征,含炭硅质页岩具有明显的低电阻率、高极化率特征,主要影响孤峰组的侵入岩体(花岗斑岩)具有“弱磁、低密度、低阻、低极化”特征。在宣城地区魏墩一带孤峰组页岩气勘查过程中,应用高精度重力、高精度磁法寻找弱磁、低重力地区,推断岩体分布情况;然后在岩浆岩不发育区布设CR法剖面,选择低电阻率(小于1 000.00 Ω·m)、高极化率(大于4.00%)的位置来布设钻井进行验证,共钻遇视厚度达50.89 m孤峰组含炭硅质页岩、硅质泥岩,取得了良好的应用效果。研究内容对宣城地区乃至下扬子复杂地质条件区富有机质页岩层段识别和页岩气“甜点”区优选具有重要的指导意义。
In view of great difficulties in the exploration of Permian shale gas under complex geological conditions in Xuancheng Area, Lower Yangtze Block, an effective shale gas exploration method under complex geological conditions is explored by applying a joint exploration with high-accuracy gravity prospecting, high-precision magnetic method and complex resistivity method (CR method) based on rock property testing. The study shows that The shale of Gufeng Formation in Xuancheng Area is characterized by "low magnetic intensity, low density, medium low resistivity and high polarization", the carbonaceous siliceous shale characterized by low resistivity and high polarization, and the intrusive rock (granite porphyry) that mainly affects Gufeng Formation characterized by "low magnetic intensity, low density, low resistivity and low polarization". In the shale gas exploration at Gufeng Formation, Weidun Belt, Xuancheng Area, high-accuracy gravity prospecting and high-precision magnetic method are applied to identify the areas with low magnetic intensity and low gravity and to deduce the distribution of rock mass. Then, CR profile is arranged in the area where magmatic rock is not developed, and wells are drilled for verification at the locations with low resistivity (less than 1 000.00 Ω·m) and high polarisation (more than 4.00%). A total of 50.89 m thick carbonaceous siliceous shale and siliceous mudstone of Gufeng Formation are drilled, achieving excellent application effect. This study provides an important guide to the identification of organic-rich shale formations and the selection of shale gas "sweet spot" in Xuancheng Area and even in the area with complex geological conditions in Lower Yangtze Block.
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