An Excellent Calcium- and Salt-Resistant Adsorptive Retarder for Acid Job

An adsorptive retarder for acid job has been developed aimed at enhancing the stimulation effect of acid job. The retarder is synthesized using monomers such as monomeric sulfonate (MS), acrylamide (AM), allyl polyoxyethylene glycol (APEG-2400) and octadecyl dimethyl allyl ammonium chloride (DMAAC-18) in a concentration ratio of n(AM)∶n(MS)∶n(DMAAC-18)∶n(APEG-2400) = 90∶5∶1∶4. The concentration of the monomers is 35%, the concentration of the initiator is 1.0%, the reaction temperature is 50 ℃ and the reaction time is 5 h. These reaction conditions were determined through single-factor experiment. The characterization of the molecular structure of the retarder with FT-IR shows that the reaction product is what was expected. The retarding efficiency of the retarder at a concentration of 1.3% is 81.56%, and the system has its apparent viscosity stabilized at 3 mPa∙s, an excellent low viscosity property. At 110 ℃, the retarding efficiency of the retarder exceeds 83%, indicating that the retarder has good high temperature performance. This retarder has good compatibility with cleanup additives, iron ion stabilizers and corrosion inhibitors; no flocculation and precipitation exist when the retarder is used with other additives. This retarder is able to resist the contamination by 70,000 mg/L CaCl₂. It also has good thermal stability; at 350 ℃, the rate of mass loss of the retarder is only 17.59%. Observation of the retarder under SEM shows that the retarder is adsorbed on the surfaces of the rocks and forms a dense layer of adsorption membrane.