A novel retarder for ultra-high temperature cementing slurry

Deep and ultra-deep formation has become an important field for increasing oil and gas reserves and production in China, but its oil and gas exploration and development is of high difficulty, and especially the cementing safety and cementing quality of deep and ultra-deep wells under the complicated working conditions of ultra-high temperature could not be guaranteed, which brings severe challenges to ultra-high temperature cementing slurry technology. Retarder is the key material to ensure the cementing safety of deep and ultra-deep wells and directly determines the success or failure of cementing operation. At present, however, domestic polymer retarder fails to meet the cementing needs of bottom hole circulation temperature over 200℃ for it is intolerant of the temperature over 200℃, so ultra-high temperature retarder is still mainly dependent on import. To provide technical support for the exploration and development of deep and ultra-deep oil and gas, a retarder DRH-3L was prepared for ultra-high temperature cementing slurry by means of free radical aqueous solution polymerization, through the optimized design of molecular structure and the effective introduction of temperature-tolerance and salt-resistance groups. Its comprehensive performance was evaluated. DRH-3L had wide applicable temperature range (70℃-220℃) and excellent retarding performance, and after its introduction, the thickening time of cement slurry at 220℃ is more than 500 min. A good linear relationship between the thickening time of cement slurry and the dosage and temperature of retarder was observed. DRH-3L is well compatible with the commonly used fluid loss additives. Under large temperature difference of 50℃-120℃, the strength of set cement developed rapidly and no adverse effect on the development of the mechanical strength of high-temperature set cement was observed.