CHARACERIZATION AND PERFORMANCE EVALUATION OF VARIOUS TYPES OF POLYMERS BASED LATEXES FOR CEMENTING APPLICATION

Gas migration through cemented casings may introduce a risk for wellbore integrity if cement formulations do not contain additives such as polymer latex. Polymer latex have been used to help reduce the fluid loss to minimize gas migration, improve wellbore integrity, and aid in the mixing ability of cement slurries. Many theories and mechanisms have been detailed to prevent annular gas flow through a cement column. Cement slurry loses its ability to transmit hydrostatic pressure during the transition from liquid phase to semi-solid phase until complete loss of hydrostatic pressure as cement slurry sets. In high pressure formation, gas or liquids can travel up through cement matrix due to lost hydrostatic pressure. This migration of liquid or gas can cause high surface pressure that may prevent us from fully utilization of these wells. Similar produced latex is employed as a binding agent in cement used primarily for construction applications. The construction cement is, however, exposed to ambient temperature and pressure conditions. Thus, it is proposed to study the performance of latex used in construction industry for cementing applications at elevated temperature and pressure conditions. Analytical techniques such as nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared analysis (FTIR), differential scanning calorimeter (DSC), and thermogravimetric analysis (TGA) were used to help in elucidating the structures and physical properties of different latexes. Tests such as thickening time test, fluid loss test, and rheology measurement test were conducted to compare the performance of different latexes in cement slurries. Different concentrations of polymer latex based on emulsion of polyvinyl acetate were used without success resulting in extreme fluid loss. So, we had to increase the concentration of polyvinyl alcohol in the local PVA by conducting in-situ hydrolysis. We have utilized lime or Ca (OH)2 to achieve this. The result was polyvinyl alcohol and calcium acetate. Treating styrene butadiene polymer-based latex with citric acid extended the thickening time of cement slurries beyond 6 hours which is enough to perform cementing operations for oil and gas wells. As the pH is reduced by the addition of citric acid, thickening time will be longer and fluid loss will be lower. The ability of forming a film to reduce filtration is improved by reducing the deprotonation of the latex in basic solution (less interaction with calcium ions).