In order to overcome the low shale inhibition property and poor compatibility of the present cationic shale inhibitors

a low molecular weight cationic poly (acrylamide) with hydrophobic modification structures

i. e.

BJX-1

was prepared by precipitation polymerization in ethanol/butyl acetate mixtures. Acrylamide

methacryloxyethyl trimethylammonium chloride

and octadecyl acrylate were selected as the monomers. The factors

such as solvent composition

temperature

initiator concentration

which influence the molecular weight of BJX-1 were studied; the results show that the molecular weight of BJX-1 is significantly influenced by solvent composition

thus the molecular weight of BJX-1 can be adjusted by changing solvent composition; the best shale inhibition result can be achieved by keeping the molecular weight of BJX-1 at 1. 45 × 10

5

g/mol~1. 87 × 10

5

g/mol

the rolling recovery of shale cuttings at 120℃ is about 78%. The rolling recovery of shale cuttings at 120 ℃ could be more than 90% when increases the content of hydrophobic units in BJX-1 to 2~4%. The optimum reaction conditions are:

V

ethanol

:

V

butylacetate

= 90: 10~100: 0

0. 1% of initiator

3% of monomer

reaction temperature is 80℃

reaction time is 7h. A comparative study on the performances of BJX-1 and the present cationic shale inhibitors in drilling fluids was conducted

the results show that when keep the shale inhibitor addition at 1 %

the rolling recovery of shale cuttings at 120℃ of BJX-1 is 27. 85% and 50. 06% more than the most commonly used cationic compound JA-1 and cationic polymer DY-1. The results indicate that BJX-1 can improve the rheological properties of drilling fluid and make the rheological properties of drilling fluid more stable; BJX-1 can also show good HTHP fluid loss control capability.