Abstract:

During the process of drilling operation，the penetrated formation rocks are firstly exposed to drilling fluids，if the fluids which can ensure borehole stability can effectively decreases rock strength instantaneously，the rate of penetration will be considerably increased.The natural cores with different permeability are soaked in KSZJ fluids with different concentration for different duration，the changes of instantaneous rock strength and final strength shows KSZJ can penetrate into the cracks of the rocks at higher permeable rate and larger permeable volume，so as to enhance the stress off crack tip and make the cracks quickly extend，the strength of rocks in broken up instantaneously，so the stress of crack tip is enhanced，the cracks are forced to quickly extend as to the stress is broken up instantaneously，the rockbreaking efficiency is improved and rate of penetration increased.As the increase of the soaking duration，the core stress increases quickly and tends to stability，which is favorable for borehole stability and well bore regularity.The KSZJ technology was used to test device of jetting drilling simulator to penetrate the rocks with different hardness and the insitu test in well 12688，Hailar Basin，results show KSZJ fluid technology effectively solves the problem of borehole instability and the mean rate of penetration is considerably increased.

Key words: fast penetration drilling fluid (KSZJ), rock strength, rate of penetration（ROP）, borehole stability, mechanism