Experiment Of Natural Gas Dissolution And Degassing With Oil-Based Drilling Fluid

Under downhole temperature and pressure due to different properties of base oil,such as type,content and viscosity of base oil,it is of great academic and engineering significance to study and analyze the dissolution characteristics of oil-based drilling fluid to natural gas under the condition of drilling temperature and pressure.This provides theoretical basis for gas logging total hydrocarbon value,hydrocarbon group correction and degassing efficiency correction.It also lays a foundation for quantitative evaluation of gas logging data.The indoor experiment methods are used to simulate the downhole temperature and pressure conditions,test the solubility of natural gas in oil-based drilling fluid,test the degassing efficiency of oil-based drilling fluid and test the cracking situation of oil-based drilling fluid.Then,the influence law of temperature,pressure,base oil content and drilling fluid viscosity on the test target is analyzed by using multiple experimental data processing method and the corresponding relationship model is established.The design temperature range is 40 ℃ to160 ℃,and the pressure range is 2MPa to 68 MPa.2 type gas samples are field gas samples and high-purity C1-C3 respectively,2 type drilling fluid are field collected drilling fluid and indoor drilling fluid.The solubility of methane,ethane,propane and natural gas decreases with the increase in temperature and increases with the increase in pressure.The methane degassing efficiency of high viscosity oil-based drilling fluid is lower than that of low viscosity drilling fluid,while the ethane degassing efficiency of high viscosity oil-based drilling fluid is higher than that of low viscosity drilling fluid,the higher the temperature the higher the degassing efficiency,the degassing efficiency of natural gas is between 10% and 60%.The downhole temperature and pressure do not meet the conditions of hydrocarbon gas cracking as no gas is produced.Basic models for natural gas solubility have been presented using screening procedures and the general predictive model for solubility in oil-based fluids measured under downhole conditions is developed using linear interpolation method.