含气煤层纵波反射波AVO响应特征研究
Research status and exploration enlightenment on over-pressure and enrichment shale gas in North America
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摘要: 为研究不同含气饱和度对煤层物性参数和纵波反射波(称PP波)AVO响应特征的影响,根据流体替换原理,建立初始煤层模型,计算了不同水、气相对饱和度情况下煤层的物性参数值,并依据反射系数谱理论,对不同含气量煤层的PP波振幅和相位随入射角变化曲线进行了数值模拟。结果表明:即使煤层基质孔隙中含有少量气体(体积分数为5%),也可使煤层纵波速度、纵横波速度比、泊松比及纵波阻抗明显降低,各参数降幅分别可达323 m/s、0.397、0.062、620 g·m/(s·cm~3),而PP波振幅在纵波垂直入射时的降幅可达0.2。因此,纵波速度、纵横波速度比、泊松比和纵波阻抗可作为检测煤层气存在与否的敏感因子,证明利用PP波AVO信息寻找煤层气富集区在理论上是可行的。Abstract: ln order to acutely seek a rich and high production target of the shale gas in China.the analysis on the exploration and developmentfeatures of the shale gas in North America would have high benefts. Based on the discussion on the distribution and features of the overpressureshale gas in North America,the paper had a study on the overpressure formation mechanism of the shale gas and the evaluation techmnology of the favorable enrichment zone.The results showed that the overpressure features of the emerging North America shale gas zone were obvious andthe gas reservoirs of the Marcellus shale and Haynesville shale were typical. The organic matter content of the overpressure shale was high generally and would have a high thermal evolution degree,a relative high porosity and a good preservation condition.The fre-gas volume had a highpercentage in the overpressure shale gas zone and the gas reservoir productivity would be relatively high generation and the pressure increased to make the micro fractures and could highly enhance the seepage performances of the reservoir. Meanw hile,the pressure increased could improve the shale gas content and could be favorable to improve the sealing of the shale oil and gas.As for each exploration block in China,the core zone determined would be important to the pressure relationshio of the strata. The certain enrichment evauation should enhance the pressure analysis on the fuid of the strata and should emphasize to seek the over-pressure sweet zones in the shalegas reservoir.