Study On Potassium Formate Fuzzy Ball Drilling Fluid In Jintan Salt Cavern Gas Storage

Jintan Salt Cavern Gas Storage is drilled into Sanduo Formation,Dainan Formation hard brittle mudstone and Funing Formation mud,salt and gypsum interbeds.The lithological changes are complex,and borehole wall collapse and sticking are easy to occur.In order to ensure wellbore stability and increase drilling speed,the mechanism of wellbore instability in Jintan salt cavern gas storage is explained through the analysis of lithologic mineral composition,physical and chemical properties and the performance of drilling fluid in use.It is proposed that a solid-free drilling fluid with inhibition and plugging can be prepared by adding appropriate amount of potassium formate as an inhibitor on the basis of the fuzzy ball with plugging function.Laboratory experiments show that the fluid density of potassium formate fuzzy ball is 0.95-1.34g/cm~3,the plastic viscosity is 13-17m Pa·s,and the dynamic shear force is4-14.5Pa.The density and rheological properties are easy to adjust.The specific surface area of clay particles decreased from 0.46 m~2/g to 0.07 m~2/g by adding potassium formate step by step,which indicated that the system had good inhibition.The permeability meter is used to measure the core whose fracture width is 2 mm and the pressure at the injection end is over 20 MPa,which shows that the drilling fluid system has a good plugging performance.In the field application of MX1 well,the drilling fluid has stable performance,no leakage,collapse and other phenomena occur,the drilling cycle is 28.57%lower than that of adjacent wells,the average enlargement rate of borehole diameter is 5.2%,and the success rate of electric logging is 100%.The results show that the combination of fuzzy ball and potassium formate can reduce the formation collapse pressure of Jintan salt cavern gas storage to ensure the wellbore stability and meet the field requirements.