Search

In view of the technical problems of poor wellbore stability, high friction torque of drilling tools and bad borehole cleaning when using water-based drilling fluid in the horizontal wells in shale reservoir, an environmental friendly water-based drilling fluid used multiple silicon treatment agents was formed, which is consist of multiple silicon treatment agents such as potassium sodium silicate, organosilicon modified potassium humate, and polysilsesquioxane. The ECso of the agents used in this system is more than 3 X 104 mg/L, reaching the non-toxic level. The temperature resistance of the system reaches 180 t, the rheological property is stable, and it has good inhibition, plugging and lubricity. The shale rolling recovery is more than 98. 53%, the shale expansion rate is below 0.26%, the HTHP is less than 2.8 mL, the extreme pressure lubrication coefficient is 0. 081 and the viscosity coefficient of mud cake is 0.042. The heavy metal content of the new water-based drilling fluid meets the requirement of secondary discharge national standard, and the BOD/COD is up to 31.7%, which is easy to be biodegraded, showing an excellent environmental friendliness. The drilling fluid has been successfully applied in the shale horizontal section of Dongping-1 well, effectively ensuring the stability of the shale horizontal section. The dynamic/plastic ratio maintains at 0. 41— 0.48, and the average wellbore diameter expansion rate of the horizontal section is only 3.85%. During drilling, the friction resistance of drilling tool is 6-8 t, and the average ROP is 10.28 m/h. It is the first application of water-based drilling fluid in shale horizontal section in China. [ABSTRACT FROM AUTHOR]