How does Cement Bond Log Work?

CBL is a special logging operation carried out to determine the bond integrity between casing-to-cement and cement-to-formation. CBL is usually carried out after cementing the annulus of the well having probably a 7 inch or 9-5/8 inch casing. Cementing however, is done for isolation purpose to avoid the inflow of water into the perforated zones in the reservoir and for durability of the resevoir. It is worthy to note that the CBL represented pictorially above, was ran in hole using GR + CCL + PACE tool assembly. Where GR is Gamma Ray Log, CCL is Casing Coller Locator and PACE is Pulsed Acoustic Cement Evaluation. The tool assembly is what helps to generate and interpret the CBL data.

GR Log helps to identify various lithologies across the wellbore. It also helps for correlations between 2 different GR Logs in terms of depth matching log signatures. CCL is used to locate the position of each casing callers along the wellbore while the PACE is used to generate and interpret the log signatures of amplitude, VDL - Variable Density Log as well as tension log signature. The 3 tool assembly combined are connected together and ran in hole with the help of a wireline conveyed unit.

Nevertheless, there are three basic conditions to determine if a cement job in a well is carried out successfully or very poorly. For a cement job to be good and successful, then it mus meet 3 conditions which include: Low Amplitude, High Attenuation and Weak VDL. From the above CBL data, there are six columns each on both logs. The 3rd column and 5th column of the 1st log, has a low amplitude and a weak VDL - indicating a very good and successful cement job. On the other hand, the 3rd column and 5th column of the 2nd log, has a high amplitude and strong VDL - indicating a very poor cementing job.

With this interpretation, it can be deduced that the cement job as recorded by the CBL on the first log meets the conditions of a good cement job. While the second log failed the conditions of a good cement job. Therefore, it is highly recommended that for every cement job carried out, a CBL should be ran to determine the bond integrity of cement in the annulus of the well. With that, the company can determine how best to proceed with the operations ahead.

Vigor's Memory Cement Bond Tool assesses cement bond integrity by measuring the Cement Bond Amplitude (CBL) with near receivers at 2-ft and 3-ft intervals and using a far receiver at 5-ft for Variable Density Log (VDL) measurements. It provides a thorough 360° evaluation by dividing the analysis into 8 angular segments, each covering 45°. We also offer a customizable compensated sonic Cement Bond Tool with a compact design, ideal for memory logging applications.

If you are interested in Memory Cement Bond Tool from Vigor or other drilling and completion logging tools for oil & gas industry, please do not hesitate to contact us for the most professional products and best quality service.

For more information, you can write to our mailbox info@vigorpetroleum.com & marketing@vigordrilling.com