Cement evaluation at early hours of cement setting

An operator in Alaska was experiencing issues with depleted sands, equivalent circulating densities, and a narrow fracture pressure window, which resulted in a small allowance in density among the drilling mud, MUDPUSH spacer family for cementing, and LiteCRETE lightweight cement slurry. The densities of the different fluids were 10.4, 11.0, and 11.5 lbm/galUS, respectively, with an acoustic impedance difference of approximately 0.3 Mrayl after 10 hours. State regulations require an operator to confirm TOC and circumferential coverage before continuing operations. Based on the close range of the impedance values, the operator would have needed to wait at least 3 days.

Optimizing wait on cement time

The operator consulted with Schlumberger and, due to the challenges of the job, elected to use Invizion Evaluation service's workflow to predict fluid placement at the end of the cement job and to determine any possible contamination and the expected top of fluids at the end of the job. Due to the well deviation, it was critical to account for possible contamination on the narrow side of the annular space. An ultrasonic cement analyzer (UCA) laboratory test conducted at the most probable contamination percentage and the WELLCLEAN II numerical cement placement simulator was used to indicate the expected acoustic properties of the cement top. The operator and Schlumberger analyzed the UCA tests and log to determine that the cement would require at least 3 days to be visible to a conventional ultrasonic imager. Schlumberger recommended logging with Isolation Scanner service to take advantage of the sensitivity of the tool's flexural attenuation measurement for identifying the solids and fluid interfaces.

Invizion Evaluation service brings higher degree of confidence

Logging the well with Isolation Scanner service 25–27 hours after the cement job confirmed that the cement had set to significantly save rig costs for WOC, which typically requires from 42 to 72+ hours. The flexural attenuation measurement, which is highly sensitive to the material behind the casing, was used to determine the quality of the cement bond, even with a relatively short wait for the cement to set. The TIEs were used to determine the pipe centralization and velocity of the material behind the casing, from which the presence or absence of cement was inferred. The Isolation Scanner service's measurement of acoustic impedance, flexural attenuation, and TIE quantitatively evaluated the cement job and casing condition where conventional ultrasonic technologies could not provide the best answers. The TOC, which was predicted by the WELLCLEAN II simulator, was correlated with the Isolation Scanner services' measurement at the same depth resulting in an interpretation with a high degree of confidence for the operator.