One of the main challenges in deep-water drilling is gas-hydrate plugs,which make the drilling unsafe.Some oil-based drilling fluids(OBDF) that would be used for deep-water drilling in the South China Sea were tested to investigate the characteristics of gas-hydrate formation,agglomeration and inhibition by an experimental system under the temperature of 4 ?C and pressure of 20 MPa,which would be similar to the case of 2000 m water depth.The results validate the hydrate shell formation model and show that the water cut can greatly influence hydrate formation and agglomeration behaviors in the OBDF.The oleophobic effect enhanced by hydrate shell formation which weakens or destroys the interfacial films effect and the hydrophilic effect are the dominant agglomeration mechanism of hydrate particles.The formation of gas hydrates in OBDF is easier and quicker than in water-based drilling fluids in deep-water conditions of low temperature and high pressure because the former is a W/O dispersive emulsion which means much more gas-water interfaces and nucleation sites than the later.Higher ethylene glycol concentrations can inhibit the formation of gas hydrates and to some extent also act as an anti-agglomerant to inhibit hydrates agglomeration in the OBDF.
Fulong NingLing ZhangYunzhongTuGuosheng JiangMaoyong Shi
目前,天然气水合物物性认识和资源评价研究都受到了天然岩心来源的极大限制。因此,开发出一套贴近于水合物地层的人造岩心技术特别是基础骨架制备思路显得尤为必要。从实际水合物地层特性出发,选取地质资料丰富、水合物成藏条件良好的美国阿拉斯加北部斜坡冻土区Mount Elbert Unit C-GH1井段地层作为模拟对象,选用石英砂环氧树脂压制胶结岩心方法,通过全面实验分析了影响人造岩心渗透率的主要因素,然后以渗透率和孔隙度为实验指标设计正交实验研究各因素对指标的影响,确定了与目标地层渗透率和孔隙度最为接近的2个配方,并通过力学单轴抗压强度值的比较进一步明确了较优配方。实验研究结果表明,设计的较优配方与目标地层的粒径配比、渗透率、单轴抗压强度和密度基本相同,孔隙度则较为接近,采用这种技术流程可以制备出贴近原位的水合物沉积物骨架。
