Technology Trends in Evaluating Cement Jobs Using Logging Tools
Authors: Wilson Adam 
Published: May 2018

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 188274, “Technology Trends in Cement-Job Evaluation Using Logging Tools,” by Mahmoud Khalifeh, SPE, University of Stavanger/IRIS; Dave Gardner, SPE, IRIS; and Muhammad Yasser Haddad, University of Stavanger, prepared for the 2017 Abu Dhabi International Petroleum Exhibition and Conference, Abu Dhabi, 13–16 November. The paper has not been peer reviewed.

Cement-job evaluation is a process that identifies whether the objectives of a cement-job operation have been achieved after cement placement. This paper reviews the technology trends in cement-job evaluation using logging tools and considers the main advantages and concerns associated with each technology. The technologies covered are acoustic tools, temperature logging, noise logging, resistivity logs, oxygen-activation logs, X-ray measurements, gamma/gamma density measurements, neutron/neutron logging, and fiber-optic measurements.

Introduction

After a cementing operation has been performed and the cement has set, cement evaluation is conducted either through hydraulic testing or by using various well-logging methods. Verification of casing-cement quality by logging tools has been a contentious subject for the past few decades. On one hand, some experts claim that current technologies are not sufficient to show the sealing capacity and quality of casing cement. On the other hand, others claim that data processing and misinterpretation of the obtained data from cement-job evaluations are the crucial challenges, not the logging technologies. However, another critical element must be considered as a limiting factor—downhole condition. The downhole condition, which includes well parameters and well design, has a major influence on technology development and data interpretation. The well parameters include downhole temperature, downhole pressure, wellbore-fluid properties, casing size and thickness, cement thickness and type, fast formation, slow formation, and unconsolidated formation. Fig. 1 shows the most-likely well design and the worst-case scenarios that need to be considered when developing technology with an assumption that there is no formation washout.

As shown in Fig. 1, cement sheaths may be relatively thin but they are very long, especially in the case of surface and intermediate casings. This means that extensive vertical defects along the bore-hole axis would be necessary to create a leakage pathway. Cement defects that can cause leakage include low top of cement (TOC), mud channels, chimneys, and microannuli.

Acoustic and ultrasonic logging tools are the standard tools used for indirect cement-quality measurement and for finding TOC. However, limitations exist concerning the measurement and interpretation accuracy that can be achieved using standard cement-bond logs. In addition, logs do not provide continuous, real-time, long-term monitoring of cement-barrier quality. Therefore, different technologies have been proposed that might have the potential to address the limitations of acoustic and ultrasonic logging tools.