Ultrasonic Log Response Evaluates Barrier Cells for Cementing Applications
Authors: Carpenter Chris 
Published: April 2020

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 199578, “Validating Ultrasonic Log Response Against Reference Barrier Cells Simulating Downhole Well Conditions Encountered During Well Construction and Abandonment Operations,” by Amit Govil, SPE, Schlumberger; Dave Gardner, SPE, Norwegian Research Centre; and Guillermo Obando, Schlumberger, et al., prepared for the 2020 IADC/SPE International Drilling Conference, Galveston, Texas, 3–5 March. The paper has not been peer reviewed.

Borehole-cement-evaluation logs are used to verify the quality of the cement bond to the casing and formation and identify any defects that could compromise the quality of the annular seal. This study used ultrasonic logging to evaluate reference barrier cells constructed with known defects. The cell concept was developed with an emphasis on low cost and ease of use. Comparison of ultrasonic tool response against reference barrier cells validates the measurements, which are crucial in the decision-making process during well construction and abandonment.

Background: Barrier Verification

In 2013 and 2014, full-scale experiments were performed to investigate the sealing ability of annulus cement for a plug-and-abandonment design in which the tubing is left in hole (TLIH). The experimental configurations used 9⅝-in. casing with a 7-in. tubing, both with and without control lines clamped to the tubing surface. Experiments were run first using standard Class G cement. In a second phase, Class G cement with an expansion additive was used to compare the quality of the seal achieved. The barrier quality of the cement was evaluated by pressure-testing the casing cement sheath and the tubing plug. The test assemblies subsequently were cut into sections, enabling the cement displacement to be controlled visually. The results showed that good cement placement could be achieved with the tubing left in the well both with and without control lines. The pressure testing showed that the control lines did not have a detrimental effect on the barrier-seal quality compared with the test without control lines.

The choice of leaving the tubing in hole when abandoning a well is dependent on an assessment of the quality of the casing cement sheath. The barrier-verification project was initiated to build on the TLIH experiments by investigating the performance of annular-barrier evaluation technologies.

Materials and Fabrication

The project aim is to construct a barrier-verification reference facility with the objectives of

Evaluating technologies for logging through multiple tubulars

Investigating the performance of commercial logging technologies

Performing experiments with alternative barrier-verification techniques

In the first project phase, the TLIH sections were reused as much as possible to enable a starting point with known specifications and quality. The cement plug in the tubing was first removed carefully by hydrojetting. Thereafter, the desired defects, such as long holes of different sizes drilled through the cement immediately adjacent to the 7-in. tubing, were introduced.

Reference cells were constructed with the aim of mimicking a range of potential annular-leakage scenarios such as gas channels, mud channels, and micro annuli. A design requirement was to enable the required cells to be coupled easily using quick unions in the configuration required to meet the experimental objectives. The tubing-to-casing annulus was sealed such that both the tubing and annulus could be independently pressurized with the required fluid. The pressure rating for the tubing and annulus is 2,200 psi. Pressure ports machined into the annulus bulkheads allow controlled leakage rates to be applied using water or gas.