Study on degradable drilling fluid system for coalbed methane horizontal drilling
Abstract：To mitigate drilling fluid damage on coalbed methane（CBM）reservoir as much as possible,synthetically evaluated the performances of degradable drilling fluid for CBM horizontal drilling.The series experiments included formulation test,solid size distribution test,mud cake elimination experiment,high temperature high pressure（HTHP）swelling capacity test,gas permeability test of coal sample,etc.It shows that liquid bio-enzyme has faster gel breaking speed and higher gel breaking efficiency in degradable drilling fluid.The gel breaking ratio is greater than 85% in 2 hours and the apparent viscosity after gel breaking is less than 2.5 mPa·s.Employing the double gel breaking technology,which includes bio-enzyme degradation plus hydrochloric acid acidification,damage of degradable drilling fluid on CBM reservoir can be effectively eliminated.It can recover and even increase gas permeability of coal samples and the range varies between 15.47% and 38.92%.Degradable drilling fluid contains the excellent features of maintaining wellbore stability and protecting reservoir and is suitable for coalbed（especially soft coalbed）horizontal drilling.
Keywords：coalbed methane horizontal welldrilling fluidbio-enzymegel breakingacidificationgas permeability
Publication Date：2011-01-01
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)