Preparation and Evaluation of New Borehole Wall Strengthening Agent

Thief zones frequently encountered in offshore drilling often negatively affect drilling speed and do harm to reservoirs.A bore hole strengthening agent,ENPRES-Seal has been developed to enhance the strengths to bear higher pressures that the formationscannot stand before strengthened by ENPRES-Seal.ENPRES-Seal is made of rigid particles,soft particles and deformable particles.Experiments on visual sand bed demonstrated that the mass ratio of the three particles is 2:1:2.Evaluation of ENPRES-Seal shows that the optimum concentration in drilling fluid is 2%-3%,and at this concentration it poses very small effect on the rheology of drilling fluid.ENPRES-Seal can be used at high temperatures as high as 200℃,and it does not blind shale shaker screen;85% of ENPRES-Seal passes 0.180 mm screen.ENPRES-Seal also renders drilling fluid good lubricity.The adsorption of ENPRES-Seal renders formation high compressive strength,as high as 17 MPa,and it also improves the quality of mud cake.ENPRES-Seal has been used on a HTHP well in Block Pinghunear Shanghai,where bottom hole temperature has been as high as 180℃,and mud density at well completion 1.90 g/cm³,and the strength of the borehole wall has been greatly enhanced.