土壤水分特征曲线在天然气水合物开采数值模拟中的应用探讨

在使用TOUGH+HYDRATE程序进行水合物开采数值模拟时常用van Genuchten模型计算毛管力,而毛管力大小直接影响水合物开采过程中的产气和产水,因此在数值模拟过程中正确选用模型参数尤为必要。我国某海域天然气水合物储层为未胶结泥质粉砂储层,常规的毛管力测定方法如压汞法、离心法等对该类岩心并不适用,如何测定该类岩心的毛管力并将其应用于van Genuchten模型参数选取具有重要意义。本文探讨了如何应用土壤水分特征曲线测定实验间接获取该类岩心的毛管力数据,为验证该方法的可行性,本文对参考文献[7]中公开的粉砂土壤水分特征曲线测定实验数据进行换算和拟合后得到T+H程序所需的van Genuchten模型参数,结果可为泥质粉砂储层水合物产能研究工作提供参考。     

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。     

Numerical modeling of methane gas production from hydrate reservoir of Krishna Godhavari basin by depressurization

Natural gas hydrates are considered as a strategic unconventional clean hydrocarbon resource in the energy sector. This paper analyzes the spatiotemporal effectiveness of the depressurization technique for producing methane gas from an unconfined Class 4 clayey setting in the Krishna Godavari (KG) basin, east coast of India. The production potential of a well by depressurization based on the borehole-based pumping technique is modeled using the newly developed spatiotemporal numerical tool, IndHyd 1.0, built using MATLAB for a constant borehole ΔP. The model is aided by TOUGH+HYDRATE reservoir production simulation software. From the IndHyd 1.0 simulation results, it is identified that a vertical well in the location NGHP-01-10D could have a lateral well reach, longevity, and a cumulative methane gas production potential of 145?m, 1.2 years, and ～0.6 billion m³, respectively. For the formation with a postdissociation permeability of 200 mD, a possible scenario in the fractured settings, the well reach, longevity, and gas production potential could be 340?m, 3.6 years, and ～9 billion m³, respectively.