Xiao Kun, Zou Changchun, Xiang Biao, Liu Jieqiong
School of Geophysics and Information Technology, China University of Geosciences, Beijing 10083, China.
ScientificWorldJournal. 2013 Jul 1;2013:101459. doi: 10.1155/2013/101459. Print 2013.
Gas hydrate model and free gas model are established, and two-phase theory (TPT) for numerical simulation of elastic wave velocity is adopted to investigate the unconsolidated deep-water sedimentary strata in Shenhu area, South China Sea. The relationships between compression wave (P wave) velocity and gas hydrate saturation, free gas saturation, and sediment porosity at site SH2 are studied, respectively, and gas hydrate saturation of research area is estimated by gas hydrate model. In depth of 50 to 245 m below seafloor (mbsf), as sediment porosity decreases, P wave velocity increases gradually; as gas hydrate saturation increases, P wave velocity increases gradually; as free gas saturation increases, P wave velocity decreases. This rule is almost consistent with the previous research result. In depth of 195 to 220 mbsf, the actual measurement of P wave velocity increases significantly relative to the P wave velocity of saturated water modeling, and this layer is determined to be rich in gas hydrate. The average value of gas hydrate saturation estimated from the TPT model is 23.2%, and the maximum saturation is 31.5%, which is basically in accordance with simplified three-phase equation (STPE), effective medium theory (EMT), resistivity log (Rt), and chloride anomaly method.
建立了天然气水合物模型和游离气模型，采用弹性波速度数值模拟的两相理论（TPT）对南海神狐海域未固结的深水沉积地层进行了研究。分别研究了SH2井处压缩波（P波）速度与天然气水合物饱和度、游离气饱和度和沉积物孔隙度之间的关系，并通过天然气水合物模型估算了研究区域的天然气水合物饱和度。在海底以下50至245米（mbsf）深度范围内，随着沉积物孔隙度减小，P波速度逐渐增大；随着天然气水合物饱和度增加，P波速度逐渐增大；随着游离气饱和度增加，P波速度减小。该规律与前人研究结果基本一致。在195至220米bsf深度范围内，P波速度实测值相对于饱和水模型的P波速度显著增加，确定该层富含天然气水合物。根据TPT模型估算的天然气水合物饱和度平均值为23.2%，最大饱和度为31.5%，与简化三相方程（STPE）、有效介质理论（EMT）、电阻率测井（Rt）和氯离子异常法基本吻合。
