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孔隙度是计算含天然气水合物地层速度和饱和度的重要参数,对其影响因素分析是准确计算孔隙度的关键.孔隙度在垂向上的变化受到一系列因素的影响,不同因素对孔隙度的整体和局部变化作用机制不同.针对水合物赋存的海底未固结成岩地层,基于ODP164,ODP204和IODP311航次实际钻探资料,根据孔隙度的整体变化和局部变化特点,将孔隙度划分为低频、中频、高频三个分量,然后对各分量的主要影响因素进行分析,同时讨论了各因素对孔隙度的影响程度.结果表明,未固结成岩地层孔隙度极高,低频分量随深度逐渐减小的变化趋势受到了沉积物压实作用的影响,初始孔隙度和变化斜率分别与细粒沉积物的含量和地温梯度有关;孔隙度中频分量能够反映沉积物中的岩性变化,受不同粒度沉积物组分变化和分布情况以及水合物的影响;孔隙度高频分量主要受沉积物粒度变化不均匀的影响,同时火山灰富集砂岩层的出现会使高频分量出现高值异常.
Porosity is an important parameter for calculating the velocity and saturation of gas hydrate-bearing formations, and the analysis of its influencing factors is the key to accurately calculating the porosity.The vertical variation of porosity is affected by a series of factors, and the influence of different factors on the porosity According to the actual drilling data of ODP164, ODP204 and IODP311 voyage, the porosity is divided into low-frequency, low-frequency, low-frequency, low-frequency and low- Middle frequency and high frequency.The main influencing factors of each component were analyzed and the influence degree of each factor on porosity was discussed.The results show that the porosity of the unconsolidated diagenesis is extremely high and the low frequency component decreases with the depth The small change trend is affected by the compaction of sediments. The initial porosity and change slope are respectively related to the content of fine-grained sediments and the geothermal gradient. The mid-frequency components of porosity can reflect the lithological changes in sediments and are affected by different grain sizes Changes in sediment composition and distribution as well as the impact of hydrates; high-frequency components of porosity are mainly affected by changes in sediment particle size Effect uniform, while the ash-rich layer will appear sandstone high-frequency component appears abnormal value.