澳大利亚鲍恩盆地冲断带煤层气构造控气特征研究

Study on gas control features of coalbed methane structure in thrust belt of Bowen Basin in Australia

为了明确前陆盆地山前冲断带构造对煤层气富集的控制作用,以澳大利亚鲍恩盆地为例,利用地震资料解释结果和煤层气试验分析数据,对构造控气模式进行了精细研究和量化表述,探讨不同构造下煤层含气性差异的原因,并阐明富集模式机理。研究结果表明:经过多阶段演化形成的构造特征是前陆盆地冲断带煤层气富集的主控因素,叠瓦构造煤层含气量随埋深增加而增大,该构造低洼区是最常见的煤层气富集区;断后向斜和冲起-三角构造的埋深大,挤压应力强,含气量高,为15~20m^3/t;蛇头构造与断弯背斜受构造受抬升影响严重,局部拉张使得应力得到释放,气体散失,含气量小于10 m^3/t。得出了构造对煤层气富集的控制作用方式,提出前陆盆地冲断带的叠瓦斜坡富集区、断后向斜富集区、对冲-三角富集区为今后煤层气勘探关键区域。

In order to have a clear definition on the thrust belt structure at the piedmont area of the foreland basin affected to the control role of the coalbed methane enrichment,taking Bowen Basin in Australia as the example,the seismic information were applied to interpret the results and analysis data of the coalbed methane test. A fine study and quantitative expression were conducted on the structure gas control mode. The causes of the coalbed methane differences under the different structures were discussed. The mechanism of the enrichment mode was stated. The study showed that the tectonic features formed by the multi stage evolutions would be the major control factor of the coalbed methane enrichment in the thrust belt of the foreland basin,the gas content of the imbricate structure seam would be increased with the depth increased and the imbricate structure low-lying area would be the most common coalbed methane enrichment area. The final syncline and washed up-triangle structure would have a deep depth,strength squeezing stress and high gas content ranging from 15 ~ 20m^3/t. The snake structure and fault anticline structure were seriously affected by the uplift,the stress was released by the local tension,the gas was dissipated and the gas content was less than 10 m^3/t. A control role mode of the structure to the coalbed methane enrichment was obtained. The paper proposed that the imbricate slope enrichment area,faulted syncline enrichment area and washed up-triangle structure of the thrust belt in the foreland basin would be the key areas of the late coalbed methane exploration.