Study and Application of a Novel Thixotropic Additive for Oil Well Cement

Conventional thixotropic additives used in oil well cement have some shortages such as weak thixotropy and poor overall performance which negatively affecting operation safety. A new thixotropic additive BCJ-200S has been developed to overcome these shortages. BCJ-200S is made of a synthetic polymer and an ultra-fine inorganic powder in a ratio of 2:3. Studies on the performance of BCJ-200S showed that it remarkably improves the thixotropy of oil well cement. A cement slurry treated with 1.5% BCJ-200S had 10 min gel strength increased from 2.3 Pa to 61.0 Pa after standing 10 min. The φ₃₀₀ readings of the cement slurry before and after standing were 206 and 210, respectively. The gel strength of the cement slurry became 61.3 Pa after standing 10 min more. These data indicate that the cement slurry treated with BCJ-200S had good reversible thixotropy, and BCJ-200S did not negatively affect the thickening, filtration and strength performances of the cement slurry. Laboratory studies also showed that BCJ-200S helps improve the mechanical performance of set cement and enhance the resistance of set cement to breaking. BCJ-200S is also well compatible with other commonly used oil well cement additives. BCJ-200S was first used on the well Guan38-22 in Dagang oilfield. The Ng2 water section in the wellbore was sealed off with 12 m³ thixotropic cement slurry successfully on the first try. The maximum squeezing pressure used to pump cement slurry was 16 MPa. After drilling out the cement plug, the wellbore section sealed was pressure tested with 8 MPa, with no leaking. With the use of BCJ-200S, water cut was finally suppressed.