TOUGH+HYDRATE 水合物模型参数敏感性分析

运用国际上较为先进的水合物开采模拟软件TOUGH+HYDRATE(T+H)对我国南海水合物藏竖井降压开采假设进行数值模拟,采用LH-OAT全局敏感性分析方法,对模型中19个普遍应用的水合物层参数进行了敏感性分析,并对参数敏感性从重到轻进行了极敏感、敏感、一般敏感和不敏感4个水平的等级划分。研究表明:T+H的参数敏感性随评价目标、时间和空间位置的不同而不同。对CH4气体累积产量有显著影响的参数有:Stone指数(n)、固相渗透率缩减指数(PRE)、绝对渗透率(Permeabilities)、流体临界饱和度(CMPS)。随着模拟时间的增加,参数对水合物饱和度的整体敏感度提高。在空间分布上,随着与井壁水平距离的增加,所有参数对水合物饱和度的敏感度降低。敏感参数的确定对提高模型的准确性有重大意义。在实际应用中要有针对性地调节参数,以获得最优效果。

Parameters sensitivity analysis of TOUGH+HYDRATE model

TOUGH+HYDRATE(T+H) is one of advanced softwares widely used in the simulation of the hydrate production. In this paper, T+H is employed to simulate the hydrate dissociation and gas production process in the South China Sea with the vertical well depressurization. Based on the simulation, the LH-OAT method is used to analysis the sensitivity values of 19 parameters used in the model, and the parameterswere ranked to 4 levels including extremely sensitive, sensitive, general sensitive and non-sensitive under different conditions. The results indicate that the parameter sensitivity is not immutable. It can be influenced by different evaluation objects, simulation time, and different space positions. The stone equation index(n), permeability reduction exponent for solid phase bearing system(PRE), absolute permeabilities along the three principal axes(Permeabilities) and critical mobile phase saturation(CMPS) were key parameters which affected the CH₄ gas cumulative production. The general trend of parameter sensivity for the hydrate saturation enhanced over simulation time, and the sensivity decreased along with the increase of distance from the wellbore. The determination of sensitive parameters is very important to improve the accuracy of the model. In practical application, the parameters should be adjusted under different conditions in order to obtain optimal effect.