大洋钻探天然气水合物储层测井评价研究进展

国际科学大洋钻探计划自1970年首次在布莱克海脊钻遇天然气水合物（以下简称水合物）以来，迄今已在全球三大洋（太平洋、大西洋、印度洋）的大陆边缘总共53个站位钻遇了水合物，采集了大量的地球物理测井资料，为理解水合物及其宿主沉积物原位特性提供了关键信息。水合物所具有的不导电、低密度、高声波速度、高含氢量等特性，为根据测井资料识别水合物并预测其分布提供了重要的依据。目前已提出的一系列根据测井资料估算水合物饱和度的方法，主要包括阿尔奇公式、密度—核磁共振测井联合、各种形式的三相声波方程以及基于不同岩石物理模型的弹性波速度模拟等方法。海底水合物具有明显的非均质分布特性，主要表现在水合物分布对宿主沉积物岩性的选择性以及在相同岩性宿主沉积物内部对成核部位的选择性上。尽管测井资料在评价水合物分布的非均质性、推断水合物生长习性方面已经得到了初步应用，但仍然存在着一些不足：①大洋钻探水合物测井解释中所依赖的地层模型还是过于简单，大多数都是两组分或三组分模型；②高分辨率随钻测井资料的应用还很有限；③测井解释与岩心地质研究的结合还不够紧密。结论认为，将水合物与宿主沉积物视为一个整体，基于更为复杂的地层模型，在岩心标定的基础上，依据多种高分辨率随钻测井资料，联合反演地层的岩性组分、孔隙度和水合物饱和度，或许是未来水合物储层测井评价发展的一个重要方向。

Current states of well-logging evaluation of deep-sea gas hydrate-bearing sediments by international scientific ocean drilling (DSDP/ODP/IODP) programs

Since deep-sea gas hydrate-bearing sediments were drilled for the first time in the Blake Ridge in 1970, gas hydrates have been discovered at 53 drill sites in the continental margins of global oceans with the International Scientific Ocean Drilling Programs (DSDP/ODP/IODP). As a result, massive amounts of geophysical well-logging data have been accumulated, which provide critical information for understanding the in-situ properties of gas hydrates and their host sediments. Gas hydrates have such physical and chemical properties as nonconductivity, low density, high acoustic velocity, and high hydrogen content, which form the basis of identifying gas hydrate-bearing sediments and predicting the distribution of gas hydrates using various well-logging data. A series of well-logging evaluation methods have been proposed to estimate gas hydrate saturation of sediments, including the Archie formula, combined methods of density and nuclear magnetic resonance well logging, various forms of three-phase acoustic wave equations, and elastic wave velocity simulations based on different rock physical models. The distribution of gas hydrates is highly heterogeneous, which is mainly manifested in the selectivity of hydrate distribution to the lithology of host sediments and to the nucleation sites within a host sediment of the same lithology. The scientific-ocean-drilling well logging data have also been preliminarily used for evaluating the heterogeneity of gas hydrate distribution and inferring the growth habit of gas hydrates in host sediments. Nevertheless, there still exist some deficiencies. (1) The formation models used are highly simplified, in which only two or three stratal components are involved. (2) The application of high-resolution logging while-drilling (LWD) data remains limited. (3) Log interpretation is not closely integrated with core geology. Therefore, joint inversion of formation lithologic components, porosity and gas hydrate saturation, which regards gas hydrates and their host sediments as an integrated system and is built on more complex formation models, together with the applications of high-resolution LWD logging data and core calibration, may represent an important direction in the well-logging evaluation of gas hydrate reservoirs in future scientific ocean drilling.