含天然气水合物沉积物三维孔隙结构数值重建

三维孔隙结构重建是揭示沉积物内天然气水合物(以下简称水合物)形成机理及分布规律的基础和前提。在现有的数值重建方法中,模拟退火法被广泛应用。为使该方法的重建结构更加接近于实际,对该方法进行了改进,所构建的数值重建模型能够纳入沉积物颗粒形状(包括圆球状、椭球状、扁球状、长扁球状、片状和针状)、尺寸分布(如正态分布)以及水合物分布模式(如胶结状、悬浮状或颗粒状)等重要结构与统计信息,并利用改进后的模型对含水合物沉积物的三维孔隙结构进行了数值重建。最后,对重建的沉积物(不含水合物)孔隙结构进行特征化分析,可获得沉积物内孔隙率和孔径分布等信息;对重建的含水合物沉积物孔隙结构进行特征化分析,可获得各组分体积分布及其截面平均体积分数沿x轴方向的分布曲线等信息。结论认为:所开发的数值重建模型能够重建出与实际情况较为接近的含水合物沉积物三维孔隙结构,且能揭示水合物分布模式对沉积物孔隙内水(或冰)和天然气空间分布的影响。

Numerical reconstruction of 3D pore structure for gas hydrate bearing sediments

Reconstruction of 3D pore structures is the basis and prerequisite for revealing the formation mechanisms and distribution laws of gas hydrate in sediments (hereinafter referred to as gas hydrate). Among the existing numerical reconstruction methods, the simulated annealing method is widely used. In this paper, the simulated annealing method was improved so that the actual situations could be presented better by the reconstructed structures. Important structural and statistical information could be introduced into the improved numerical reconstruction model, including the shapes of sediment particles (e.g. spherical, ellipsoidal, oblate spheroid, prolate spheroid, flakey and acicular), size distribution of sediment particles (e.g. normal distribution), and morphology of gas hydrate (e.g. cementing, floating and particle). Then, the 3D pore structures of gas hydrate bearing sediments (hereinafter referred to as sediments) were numerically reconstructed by using the improved model. Conclusions in two aspects were obtained. First, through characterization analysis on the pore structures of sediments, certain key information can be revealed, including the porosity and pore size distribution in sediments, the volume fractions of specific components and the distribution of sectional average volume fraction along x axis. Second, with the proposed numerical reconstruction model, the 3D pore structures of sediments closer to the actual situations can be reconstructed, so that the effect of gas hydrate morphology on the spatial distribution of water (or ice) and gas in the pores of sediments can be revealed.