Study on the properties of urea-formaldehyde resin in repairing microcracks of cement stone in oil well under CO2 acid environment

Abstract

To solve the problem of microcracks caused by CO2 erosion in the cementing ring, an environmental responsive polymer (LJIY) was prepared to repair microcracks. LJIY was synthesized from formaldehyde and urea, and its structure and properties were analyzed by FTIR, SEM, laser particle size analyzer and environmental responsiveness test etc. The results showed that LJIY was microsphere with an average particle size of 5.33 μm. LJIY was responsive to environmental pH, structurally stable in alkaline environments, and crosslinkable in acidic environments. LJIY had obvious repair effect on the microcracks of cement stone. After 28 days of repair in CO2 solution, the compressive strength recovery rate of cement stone mixed with 5% LJIY was 87.2%, the permeability was reduced to 0.001 μm2, and the microcracks were basically healed. The healing mechanism of LJIY on cement microcracks was that when the microcracks in the cement stone were formed, CO2 penetrates into the cement stone, and the pH of the solution environment was reduced to acid. Under acidic conditions, LJIY crosslinked to form a polymer film that adhered or filled the microcracks, thereby healing the microcracks.