非成岩弱胶结天然气水合物沉积物弹性力学参数的实验分析

An experimental analysis on the elastic mechanical parameters of weakly-consolidated nondiagenetic gas hydrate sediments

海洋环境中的大部分天然气水合物(以下简称水合物)都存在于弱胶结沉积物中,原状取心难度大、成本高,因而不得不通过室内试验来了解水合物声学性质与弹性力学性质之间的关系。为此,通过室内制备水合物沉积物样品,并对其进行岩石物理实验,通过实验测得了水合物沉积物的岩电、声波参数,根据弹性理论计算出3种不同三轴压力、3种不同粒径骨架、3种不同泥质含量情况下的动态弹性力学参数,分析不同条件对水合物沉积物动态弹性力学参数的影响规律。研究结果表明:(1)在一定的水合物饱和度范围内,水合物的饱和度和沉积物的弹性参数呈现出一定的正比关系;(2)当水合物饱和度一定时,随着粒径(0.125～1.180mm)的变大、泥质含量的减少、轴压的增大,水合物沉积物的动态杨氏模量增大,而泊松比与轴压的关系则不大;(3)建立了弹性参数与泥质含量、轴压的关系模型。结论认为,利用声波测井方法分析水合物的动态弹性力学参数,可以解决水合物取心难、造价高、无法获取连续数据的问题;该研究成果为利用测井资料计算水合物沉积物的力学性质提供了借鉴和参考。

Gas hydrate(hereinafter,"hydrate"for short)in the marine environment mostly lies in weakly consolidated sediments,so its undisturbed coring is difficult and costly.In view of this,it is necessary to understand the relationship between acoustic properties and elastic mechanical properties of hydrates through laboratory experiments.In this paper,samples of hydrate sediments were prepared indoors.Then,petrophysical experiments were carried out on these samples to measure the electric parameters and acoustic parameters of hydrate sediments.Finally,according to the theory of elasticity,the dynamic elastic mechanical parameters under three axial compressions,three particle sizes and three shale contents were calculated to analyze their effects on the dynamic elastic mechanical parameters of hydrate sediments under different conditions.And the following research results were obtained.First,when the hydrate saturation is in a certain range,it is in a proportional relationship with the elastic parameters of sediments.Second,when the hydrate saturation is constant,the dynamic Young's modulus of hydrate sediments increases,but the Poisson's ratio has little to do with the axial compression as particle sizes(0.125–1.180mm)and axial compression increase and shale content decreases.Third,a model of the relationship between the elastic parameters and the shale content and axial compression is established.In conclusion,the dynamic elastic mechanical indexes of gas hydrate obtained from the acoustic logging methodology will solve the above difficulties and the research results provide a reference for calculating the mechanical properties of hydrate sediments by use of logging data.