A New Cement Logging Panorama to Improve Evaluation and Assist with Cement Repair Decisions

Zonal isolation has recently come into the forefront of concerns in well construction after the tragic Gulf of Mexico incident in 2010. Proper cementing is a primary factor in complying with the zonal isolation objective and the subsequent cement evaluation plays a critical part in the overall assurance process.

Cement evaluation logs are intended to assist in determining the level of zonal isolation and the need for cement repair operations to achieve this isolation if it does not exist in critical areas of the well. Various techniques exist for cement evaluation but very often they lack proper definition of the material behind the casing to fully assist in deciding on a repair operation especially in these times of deeper and more deviated wells, and the more common usage of low impedance, nitrogenated and elastomeric cements.

This work introduces a new method to look at and interpret the materials in the casing annulus that will assist in gauging the probability of success with a cement repair operation. The process is based on combining in a single log presentation, the existing Acoustic Impedance map, from conventional ultrasonic cement evaluation tools, and its impedance variations, with a new measurement, Flexural Attenuation, to provide a more complete determination of the materials behind the casing.

A number of examples from Mexico are presented to highlight the simple technique used in this study. This diagnostic method is useful for almost any type of cement but it is especially important for cases of lighter cements or neat cements where there is a high probability of cement contamination, environments where the conventional cement logs provide poor diagnostics. Hopefully innovative techniques like this one can help reduce the risks that arise from poor zonal isolation in the future.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California