裂缝填充型天然气水合物识别及饱和度预测

Recognition and saturation prediction of gas hydrates with fracture fill characteristics

天然气水合物通常以孔隙和裂缝两种充填形态存在于自然界中,不同赋存形态的水合物具有不同的岩石物理性质,判别天然气水合物赋存形态对资源评价和开发具有重要意义。速度、密度和电阻率是反映水合物物理特征最常用的三个参数,本文基于岩石物理模型构建了含天然气水合物沉积物纵横波速度、密度、电阻率随水合物体积分数变化的数值模型,发现在相同水合物含量的背景下,含裂隙填充型水合物沉积层的纵波速度比孔隙型的稍低,密度明显小于孔隙型,但其电阻率却高得多。由此构建了水合物赋存类型的判别图版,并以南海典型水合物为例进行了验证,实际数据与理论图版吻合良好,成功识别了天然气水合物赋存形态并计算了裂缝填充型水合物的饱和度,证明此方法可以用于南海裂缝填充型天然气水合物的判别及资源量计算。

Gas hydrates typically exist in two filling forms within natural environments:pore-filling and fracturefilling.Different hydrate occurrence forms exhibit distinct rock physics properties,making their accurate discrimination crucial for a resource assessment and development.Velocity,density,and resistivity are commonly used parameters reflecting hydrate physics characteristics.This study utilizes a rock physicsbased numerical model to simulate the influence of hydrate volume fraction on P-wave and S-wave velocities,density,and resistivity in hydrate-bearing sediment.It was observed that,at equivalent hydrate content,fracture-filling hydrate sediments exhibit slightly lower P-wave velocities,significantly reduced densities,and markedly higher resistivity compared to pore-filling sediments.This study constructed a discrimination chart based on these distinct geophysical signatures.Applying this chart to a case study of gas hydrates in the South China Sea demonstrated strong matching between actual data and theoretical predictions.The chart successfully identified hydrate occurrence forms and calculated the saturation of fracture-filling hydrates,proving effective for discriminating and estimating the resource quantity of fracture-filling gas hydrates in the South China Sea.