AVO探测煤层瓦斯富集的理论探讨和初步实践——以淮南煤田为例

以煤层瓦斯富集地质理论为基础，根据煤层瓦斯与常规砂岩储层天然气赋存机理的对比，提出了以煤层割理裂隙为探测目标的煤层瓦斯富集AVO技术预测理论. 根据AVO理论模拟，煤层顶面反射振幅通常是随着炮检距的增大而减小；不同结构煤体在AVO响应上存在明显的差异，随着煤层割理裂隙发育程度的增强，煤层顶面AVO的截距和梯度都会增大；煤层厚度的调谐作用对其AVO特征有明显的影响. 通过对淮南煤田实际地震资料的处理和分析，探讨了煤田地震资料AVO的处理和解释方法，认为AVO梯度和伪泊松比反射系数是对煤层割理裂隙发育程度最为敏感的属性，获得了研究区内有工程使用价值的瓦斯突出区预测成果，初步证实了应用AVO技术检测煤层割理裂隙、预测煤层瓦斯富集部位的可行性.

Theory and application of AVO for detection of coalbed methane --A case from the Huainan coalfield

Based on the geological theory of coalbed methane accumulation and contrast between the preserving mechanism of methane in coalbeds and that of natural gas in sandstone reservoirs,we propose a theory for detecting methane accumulation targeting at cleats and fractures in coalbed with the AVO technique.According to AVO modeling,amplitudes of the coalbed top interface decrease with the offset increasing.The AVO responses of coal of different structures are considerably different.Both intercept and gradient on the coalbed top interface increase with the density of cleats and fractures increasing.It also shows that the tuning effect of coalbed thickness can impair its AVO response.Then the AVO technique is practiced in the Huainan coalfield,and methods for seismic data AVO procession and interpretation are studied.The result shows that AVO attributes such as gradient and pseudo Poisson's ratio reflectirity are sensitive to gas accumulation and density of cleats and fractures in coalbeds.Dangerous zones with methane accumulation in the study area have been predicted according AVO anomalies.And the result is of engineering value for methane prevention and control.Furthermore,the AVO technique has been confirmed practicable in detection of cleat and fracture density and gas accumulation in coalbeds.