Lightweight Cement Evaluation Using Ultrasonic Measurements

Abstract

Abstract Hydraulic isolation of wellbore casing and cement is critical for the completion of petroleum wells. Zonal isolation prevents contamination of groundwater by fluids in the wellbore and allows conformance control of 1,2the injected fluids. New lightweight cement formulations have been developed to allow more efficient completion operations especially in low-strength formations. These cements, although less dense (<13 lbm/gal) than conventional cements, actually provide higher acoustic impedance, lower porosity, and lower permeability material properties. Cement evaluation is routinely performed in wells using sonic and ultrasonic tools. The latest generation of ultrasonic cement evaluation tools can provide high quality measurements of casing dimensions and cement acoustic impedance properties. To investigate the ultrasonic tool response to lightweight cement compositions, experiments were run in 5 ½-in. casing sections to measure the acoustic characteristics of many of the new cement compositions. Depending on the density of the composition, the measured acoustic impedance values ranged from 3 to 7 MRayls. For completeness, other cement compositions tested in this project included standard neat cements, foam cements, and high-density cement mixtures. Additional experiments confirmed the importance of the preflush fluid in removing drilling mud from the casing surface (especially for oil-base mud systems). The results from this project are compared to the sonic and ultrasonic data acquired from actual wellbore completions using the new lightweight cements. Although lightweight and foam cements have generally lower acoustic impedance properties, they can be evaluated with current logging tools.