Synthesis And Research Of Thermal-resistant Retarder For Oil Well Cement

Well cementing is an important part of well drilling and completion, which includes two steps: casing and cementing. And the cement additive plays a vital role in cementing. With development of hydrocarbon exploration, deep layers have become key target and popular field for hydrocarbon exploration. However, the temperature and pressure in the bottom hole increase quickly with well depth increment. Thus the high-demand to the performance of additive has been put forward. At present, the commonly used retarder in China has the following problems: strong dispersive ability, poor compatibility with other additives, two phenomena ?false set? and ?abnormal gel? appear in the thickening experiments under high temperature and so on. All these problems will bring great risk to the cementing operation.To solve these problems, the tetrapolymer retarder AMPS/NVP/AA/MAH was synthesized by using 2-acrylamide-2-methyl propane sulfonic acid(AMPS), N-vinyl-2-pyrrolidone(NVP), Acrylic Acid(AA) and Maleic Anhydride(MAH) as monomers. Through the orthogonal experiment, the optimum reaction conditions of copolymerization can be obtained with the AMPS/NVP/AA/MAH mass ratios of 7: 0.75: 1.25: 1, ammonium persulfate(APS) dosage of 1%(based on the weight of monomers), while the reaction carries out at p H 6 under 45°C. And the tetrapolymer retarder under the optimum reaction conditions was named PANAM.The retarder PANAM was characterized by IR and 1H NMR. And the PANAM was stable when the temperature was below 365°C, which was proved by DSC analysis.The evaluation results of application performance show that the PANAM has low dispersive ability, excellent high temperature retardation property, salt tolerant ability, good compatibility with other additives and little negative effect on the compressive strength of the cement stone. The copolymer PANAM is expected to be an excellent thermal-resistant retarder for oil well cement and can be applied in different salt concentration and different density cement slurries.Moreover, the retarding mechanism of PANAM was analyzed and discussed by SEM. It was found that either a nucleation poisoning or surface adsorption mechanism may potentially explain the inhibition of hydration of PANAM.