Formula Design And Numerical Simulation Of Low Temperature Drilling Fluid For Natural Gas Hydrate Permafrost

With the depletion of global conventional energy,finding new energy is imminent.Natural gas hydrate has huge resources,wide distribution and high energy density.Rational development and utilization can alleviate the shortage of oil and gas resources.During the exploration and drilling of natural gas hydrate,the intrusion of drilling fluid will cause hydration expansion and even collapse of the wellbore,the pollution of the reservoir and the decomposition of gas hydrate.In order to maintain well wall stability,reduce downhole accidents and avoid permafrost melting and natural gas hydrate decomposition,sodium silicate and potassium chloride are used to form film forming agent in accordance with 5:1 mass ratio,and NaCl as the main antifreeze agent,a new film drilling fluid formulation suitable for drilling in hydrate permafrost is selected by orthogonal test.Based on the conventional polyethylene glycol drilling fluid,a new formulation suitable for permafrost drilling is designed.The two kinds of formulations can meet the drilling requirements of conventional coal seam and cryogenic soil layer.The rheological properties and filtration characteristics of the optimized drilling fluid and polyethylene glycol drilling fluid were compared.The results show that the designed cryogenic drilling fluid is not frozen at low temperature,good mobility,moderate viscosity and dynamic shear force,and less filtration.The film forming drilling fluid formulation can form a layer of mud on the surface of the sample,which is superior to polyethylene glycol drilling fluid in preventing the wellbore hydration expansion and collapse.The two kinds of formula parameters are simulated in COMSOL software.The results show that the low temperature film drilling fluid and low temperature polyethylene glycol drilling fluid invade the reservoir,and the influence of the reservoir pressure and temperature is maintained within the equilibrium range of gas hydrate phase,and the natural gas hydrate reservoir is protected.