实验尺度下钻井液在含水合物地层流动数值模拟

钻井实践表明,钻井液侵入会改变井壁围岩特性,例如岩石强度、孔隙压力等。在非常规的含水合物地层,钻井液侵入还可能诱发地层中水合物分解和再形成,从而对井壁稳定和测井解释产生影响。因此,研究钻井液在含水合物地层中侵入流动特性有非常重要的理论和实际应用价值。基于野外水合物储层的相关数据和室内实验模拟系统,采用数值模拟方法研究了实验尺度下钻井液在含水合物地层中的侵入流动规律及其对储层物性的影响。模拟结果可为后续实验模拟方案设计以及热开采研究提供一定的指导作用。 

Numerical Simulation on the Drilling Fluid Flowing in Gas Hydrate-Bearing Sediment at the Laboratory Scale

The invasion of drilling fluid into sediments around borehole will influence their physical properties,for example,strength and pore pressure.In the gas hydrate-bearing sediments(GHBS),the invasion process may couple with the dissociation and reformation of gas hydrates around the borehole,and then affect wellbore stability and log interpretation in GHBS.Thus,the investigation on the invasion dynamics of drilling fluid into GHBS is important for drilling and logging.Here,we used a numerical simulation method to analyze the dynamic behaviors of drilling mud invasion and flowing in GHBS at the laboratory scale according to field data and an experimental simulation system.The results show that the hydrate layer is obviously influenced by the mud invasion,and the density,temperature and salt content of the drilling mud all have great effects on the process of the invasion,especially the density which controls the heat and salt transfer efficiency to some content.Also,it is found that hydrate might decompose in the process of the fluid migration because of reducing the dissolved methane in the pore water and destroying the dynamic balance between natural gas hydrate,water and dissolved gas although the phase equilibrium state of gas hydrate was not broken.