水合物储层颗粒间微力测试与分析

Measurement and analysis of interparticle microforce in synthetic hydrate reservoir

海域天然气水合物储层具有离散特征,从颗粒角度研究水合物与储层泥砂之间的力学行为,有助于揭示水合物储层力学和出砂行为的微观机理,为离散元数值模拟提供参数。本文基于自行搭建的颗粒间微力测试装置,分析了模拟水合物储层中水滴与砂团的吸附行为,测试了水合物颗粒与砂板在干燥和润湿条件下的黏附力,以及不同法向力、接触时间和温度条件下的水合物颗粒与砂团间的切向力,并模拟观测了水合物储层在加热分解过程中的介观剪切滑移。研究结果表明:干燥砂团对水滴产生了强烈的吸附;在干燥条件下,砂板与水合物颗粒无明显黏附行为,润湿条件下黏附力急剧增大;水合物颗粒与砂团的接触切向力与法向力符合摩尔-库仑准则,短接触时间(120 s)内接触切向力增大趋势不明显,在相平衡温度附近出现微弱峰值。在温度稳定条件下,水合物储层介观滑移中未观测到明显的砂团破坏和砂粒剥离;在加热分解条件下,分解水迅速进入砂团中,造成砂团局部砂粒剥离,随着分解水增多,剪切滑移过程中砂团整体被破坏,可能诱发储层出砂和沉降。

Natural gas hydrate reservoir in ocean has discrete characteristics.To study the mechanical behavior between hydrate and reservoir silt and sand from the perspective of particles is helpful to reveal the microscopic mechanism of mechanical behavior and sand production of hydrate reservoir and provide parameters for discrete element numerical simulations.Based on the self-built micro-force testing device,the adsorption behavior of water droplets and sand groups in hydrate reservoir was analyzed.The adhesion between hydrate particles and sand plate was tested under dry and wet conditions.The tangential forces between hydrate particles and sand clusters under different conditions of normal forces,contact time and temperatures were measured directly.Mesoscopic shear slip of hydrate reservoir during heating decomposition was simulated.The results show that the dry sand cluster has strong adsorption on water droplets.There is no obvious adhesion between hydrate particles and sand plate under dry condition,but the adhesion increases sharply under wet condition.The tangential and normal forces in contact between hydrate particles and sand cluster are in accord with Mohr-Coulomb strength criterion,the increase trend is not obvious in short contact time(120 s)and a weak peak appears near the phase equilibrium temperature.The mesoscopic slip of synthetic hydrate reservoir under the condition of stable temperature is observed without obvious sand cluster damage and sand decohesion.Under the condition of heating,the decomposed water from hydrate quickly enters into the sand cluster,resulting in partial sand decohesion of the sand cluster.As the water increases,the sand cluster can be destroyed as a whole in the process of shear slip,which may induce reservior sand production and subsidence reservoir subsidence.