南海北部无明显BSR地区天然气水合物识别研究

Gas hydrate identification in non-BSR region, northern South China Sea

似海底反射(BSR)作为海域天然气水合物的重要地震识别标志之一,已得到广泛认同.然而,科学钻探证实,天然气水合物和BSR之间并不具有严格对应关系,即存在水合物的地区却并不一定存在BSR.本文在分析BSR与天然气水合物非充分必要对应关系及其原因的基础上,着重对无明显BSR地区天然气水合物的地震识别方法和应用进行研究.对经钻探证实的存在天然气水合物的神狐海域地震资料进行处理分析后发现,含水合物沉积层具有层速度相对较高、高波阻抗、瞬时高频等特征,且层速度反演、波阻抗反演和瞬时属性分析等方法能有效识别无明显BSR区域的天然气水合物.最后,综合利用这些识别方法,应用于琼东南盆地无明显BSR地区的天然气水合物地震识别,取得了较好的效果.

Abstract A distinctive reflection known as the Bottom Simulating Reflection （BSR） has been widely recognized as one of the main geophysical indicator for marine gas hydrate geological system all over the world. However, the scientific drilling has showed that there is not a strict one-to-one correspondence relation between gas hydrate and BSR. The presence of a BSR may be not a strong indicator that at least a small amount of gas hydrate is present and gas hydrate has been documented where no BSR is observed, and the lack of a BSR does not imply that gas hydrate is absent. Based on the analysis of the non-sufficient and necessary relation and its reasons between gas hydrate and BSR, the seismic recognition methods and their impttcatton the present paper. Focused on Shenhu area, northern South China Sea where the gas hydrate is documented by drilling, the seismic data processing and reversion showed that the gas hydrate layer is of the high layer velocity, high P-impedance, high instantaneous frequency, and the layer velocity reversion, p-impedance inversion and instantaneous feature analysis may be the effective methods for recognition of gas hydrate in the non-BSR region. Combination of these methods may effectively improve the recognition accuracy of gas hydrate layer especially in the non-BSR region. The gas hydrate recognition was reached a good result by using the layer velocity reversion, Pimpedance inversion and instantaneous feature analysis in the non-BSR region of Southeast Hainan Basin.