Investigation on the Preparation and Performance of a Novel Sustained-Release Type Fluid Loss Agent for High-Temperature Resistant Oil Well Cement

Fluid loss agents (FLA) can reduce the fluid loss of cement paste by adsorption on the surface of the cement particles during cementing and decreasing the permeability of the cement cake, ensuring the safety of the cementing. As the exploration of the use of cement is progressing toward deeper and ultra-deeper layers, the use of FLA at high temperatures is urgently necessary. Hence, in this article, we describe the preparation of FLA with an organic/inorganic intercalated microstructure to meet the requirements of cementing at 210 °C. The anionic polymer FLA (ASDA) consists of 2-acrylamido-2-methylpropane sulfonic acid, sodium p-styrenesulfonate, N, N-dimethylacrylamide, and sodium 3-allyloxy-1-hydroxy-1-propylene. Organic-inorganic hybrid FLA, magnesium/aluminum-ASDA-hydrotalcite (Mg/Al-ASDA-LDHs) was prepared by intercalating ASDA into the interlayers of magnesium/aluminum layered double hydroxides (Mg/Al-LDHs) via an anion-exchange reaction. The results of thermal stability analysis showed that Mg/Al-ASDA-LDHs had better thermal stability than ASDA, with a decomposition temperature of 416 °C. In addition, the structure effectively mitigated the decrease in compressive strength of the mud caused by the carboxyl groups in the polymer. The Mg/Al-LDHs structure avoids the problem of reduced compressive strength of hardened cements due to conventional polymer FLA. The compressive strength of the cement containing Mg/Al-ASDA-LDHs increased by 57.4% after 7 days of curing compared with the cement containing 3% bwoc ("% bwoc" is defined as "by the weight of cement") ASDA.