海洋细粒砂质水合物储层渗透率预测模型研究

Research on permeability prediction model of marine fine-grained sandy hydrate reservoirs

海洋细粒砂质沉积层中的天然气水合物分布最广、储量最大,建立合理的渗透率预测模型,进而制定科学的储层渗透率改造措施与增产制度,有助于推进水合物产业化开发。利用特制的含水合物沉积物渗透率测试系统,对级配参照中国南海北部陆坡实际水合物储层沉积物的试样,开展了渗透率测试、CT扫描试验;通过归一化渗透率处理,将实验测试结果与已有渗透率理论模型计算结果进行了对比,在此基础上建立了仅用饱和度就可快速预测渗透率的计算模型。结果表明:水合物饱和度小于37.8%的Ⅰ型水合物倾向于生长在孔隙孔壁上;而水合物饱和度小于35%的Ⅱ型水合物以孔隙填充为主;它们分别对应水合物分布理想模型中的毛细管模型和颗粒模型。同时,水合物饱和度与细粒砂质水合物储层渗透率密切相关,本文建立的渗透率模型K_(r)=(1-S_(h))^(2.85)/(1+S_(h))^(3.67)与“KC方程修正模型”吻合度最高,可适用于海洋细粒砂质水合物储层,能应用于中国南海神狐水合物储层渗透率预测。

The natural gas hydrate in the marine fine-grained sandy sedimentary layer has the most extensive distribution and the largest reserves.Establishing a reasonable permeability prediction model,and then formulating scientific reservoir permeability modification measures and production stimulation systems are helpful to promote the industrialization of hydrates development.Using a special permeability test system for hydrate-bearing sediments,permeability tests and CT scan tests were carried out on specimen whose gradation was based on the actual hydrate reservoir sediments on the northern slope of the South China Sea.The experimental test results were compared with the calculation results of the existing theoretical permeability models,and on this basis,a calculation model that could quickly predict permeability only with saturation was established.The results show that type Ⅰ hydrates with a hydrate saturation of less than37.8%tend to grow on the pore walls;while type Ⅱ hydrates with a hydrate saturation of less than35%center on filling pores;they correspond to capillary model and particle model in the ideal hydrate distribution model respectively.At the same time,the hydrate saturation is closely related to the permeability of fine-grained sandy hydrate reservoirs.The permeability model K_(r)=(1-S_(h))^(2.85)/(1+S_(h))^(3.67) established in this paper has the best coincidence with the“KC equation revised model”,which is suitable for marine fine-grained sandy hydrate reservoirs and applicable for predicting the permeability of Shenhu hydrate reservoirs in the South China Sea.