Suggestions on Application of Non-Foam Ultra-Low-Density Cement Slurries

Many oil and gas wells in China are cemented with ultra-low-density cement slurries because these wells penetrated lowpressure and easy-to-leak formations. Design criteria, test methods and slurry mixing procedure for cement slurries of normal density can not be used in operation with ultra-low-density cement slurries because of the low density of the light-weight materials, difference in breaking resistance of different materials and low density ratio of the solid phase and liquid phase in the ultra-low-density cement slurry. All these factors negatively affect the property stability of the cement slurry. Thus, improvement should be made to the program of field testing the ultra-low-density cement slurry and the program of mixing cement slurry based on the physical properties of the light-weight materials and the designed density of the cement slurry. To investigate the problems encountered in using ultra-lowdensity cement slurry, laboratory studies were conducted from several aspects, such as light-weight material, ratio of liquid to solid, downhole condition, compressive strength experiment, quality of cement slurry, cement mixing and field mixing of cement slurry etc. Suggestions have been provided regarding the selection of microspheres, optimum window of liquid-solid ratio, correction of downhole environment, selection of strength experiment method, control of cement slurry properties, quality assurance of the dry cement and LVF dynamic slurry mixing system etc. These suggestions are of instructive significance for the increase of the success rate of cementing wells with ultra-low-density cement slurries.