Encapsulated ATMP Microspheres with Slow-Release Scale Inhibition Function

Synthesis of solid scale inhibitors with a sustained-release function has become one of the most promising scaling control methods in the oil and gas industry. It is still a challenge to synthesize a low-cost, high-efficiency, and long release period solid scale inhibitor. In this study, diatomaceous earth (DE) was used to adsorb amino trimethylene phosphonic acid (ATMP) to get ATMP-DE solids, which were then double-coated with aluminum cement (AC) and poly(vinyl alcohol)-glutaraldehyde (PVA-glut) step by step to synthesize ADAP microspheres (ATMP-DE/AC@PVA-glut). Scanning electron microscopy (SEM) was used to verify the adsorption of ATMP onto DE, and the double-coating structure of the ADAP microspheres. The optimized mass ratio of AC/ATMP-DE (first coating) was determined to be 2:1. At this mass ratio, the ATMP release lifetime starts to level off, indicating that a nearly complete encapsulation was achieved. The optimized mass percentage of PVA-glut (second coating) was determined to be 1.5% when the release lifetime stops increasing and a complete secondary coating of ATMP-DE/AC was achieved. The controlled-release property of the ADAP microsphere has been tested under laminar and turbulent flow conditions using static and dynamic sampling methods from 20 to 80 °C, to simulate different working conditions during oil and gas production. Under laminar flow conditions, the release time ranges from 300 to 200 h and from 220 to 140 h from 20 to 80 °C using static and dynamic sampling methods, respectively. Under turbulent flow conditions and 60 °C, the release time decreases to 120 and 70 h using static and dynamic sampling methods, respectively, showing the acceleration release kinetics with more agitation. Under the most severe conditions (dynamic sampling under turbulent flow conditions), the scale inhibition efficiency of released ATMP has been tested. Within 60 h, the scale inhibition efficiency of the released sample solution is over 90%, and from 60 to 80 h, it drops to 90 to 70%. Such good scaling efficiency shows great potential of the newly synthesized ADAP microspheres in the oil and gas industry.