Research and Application of the Fluid Loss Additive with Temperature Resistance of up to 240 °C for Oil Well Cement Slurry

Deep and ultradeep layers are important areas for increasing oil and gas storage and production. Cementing in complex environments, such as ultradeep and ultrahigh temperatures, poses serious challenges for key cementing materials. To solve the problems of conventional polymeric fluid loss additives, such as insufficient resistance to ultrahigh temperature, low-temperature thickening, and high-temperature dilution, an ultrahigh-temperature resistant fluid loss additive, DRF-3L, with low molecular weight was developed. It was synthesized through molecular structure optimization, introduction of temperature- and salt-resistant groups, and synergistic effect of poly(carboxylic acid)s, and its comprehensive performance was evaluated. Results show that the average molecular weight of DRF-3L is 29 534 Da, which is 92% lower than that of conventional products. It has the characteristics of no viscosity increase at low temperatures and a weak dispersion at high temperatures. An obvious thermogravimetric loss occurred above 330 °C, indicating that its molecular structure has strong thermal stability. DRF-3L is suitable for temperatures ranging from 10 to 240 °C and is resistant to saturated sodium chloride. The API fluid loss of saturated brine cement slurry with 5% DRF-3L was 42 mL at 240 °C. Meanwhile, DRF-3L had no adverse effect on the initial consistency, rheological properties, and mechanical strength development of the cement slurry. DRF-3L and its supporting cement slurry have been applied to more than 30 wells in Sichuan-Chongqing, Tarim, Bohai Bay, and other areas, and have been successfully used in the highest temperature well, Qiantan 1 (213 °C), in the Dagang Oilfield. The cementing quality is high, which provides engineering technical support for deep and ultradeep oil and gas exploration and development and has broad application prospects.