The hydraulic isolation of the wellbore casing and cement is critical for the completion of production and injection wells. Zonal isolation prevents the production of fluids from non-completion intervals, contamination of ground water by fluids in the wellbore, and allows conformance control of injected fluids. Current acoustic evaluation techniques may be limited by the acoustic properties of the material behind casing and by the inability to see beyond the cemented region near the casing. A new ultrasonic imaging tool has been developed to address these limitations. The new imager tool combines the classical pulse-echo technique with a new ultrasonic technique that provides temporally compact echoes arising from propagation along the casing and also reflections at the cement-formation interface. Processing these signals yields unprecedented characterization of the cased-hole environment in terms of the nature and acoustic velocity of the material immediately behind casing, the position of the casing within the borehole, and the geometrical shape of the borehole.5 In order to provide answers to the casing/cement evaluation questions, a field study was performed to evaluate the results provided by both sonic and this new ultrasonic tool in the different cement materials, drilling fluids, and casing sizes. Field examples are presented to illustrate the actual response of the new ultrasonic tool to these various completion environments including wells cemented with conventional and lightweight cement. The results demonstrate enhanced cement evaluation for all cement types and a significant reduction in the uncertainty in making a squeeze or no-squeeze decision. The new cement evaluation tool implements both the traditional pulse-echo technique and the new flexural wave concept. The flexural mode enables deep imaging of the cement sheath up to the cement-formation interface. In addition, the measurement of the borehole geometrical shape makes it possible to evaluation double casing string conditions for potential damage. Introduction Sonic logging tools have been used since the 1960's to evaluate the placement of cement for hydraulic isolation of formations. There have been several advancements in the logging tools that improved the ability to evaluate the cement sheath since that time. During the same period of time there has been little change in the types of cement. In the past few years, however, there has been an emphasis on optimizing the cementing operation and reducing the overall cost of the completion. To the cementing operation, this meant developing lightweight and specialized cements that would allow setting casing strings deeper without worrying about lost returns. Other gains in efficiency were also achieved using lighter cements while drilling and completing weak formations. Changes in these cements, and their properties, have also brought about the need for re-evaluating the techniques and tools used for the evaluation of these cements with the sonic logging tools currently available. The Cement Bond Log (CBL) type tools, which include all tools that measure amplitude or attenuation, have a common theory of measurement, interpretation principles, strengths, and weaknesses. The principle of measurement of these tools is to measure the amplitude of a sonic signal, produced by a transmitter emitting a 20 kHz acoustic wave, after it has traveled through a section of the casing as an extensional mode. This amplitude is then converted into attenuation by either using a ratio of multiple transmitter and receiver amplitudes, or using chart book conversions. At this point the interpreter has to select a value for the attenuation of a 100% bonded interval. This can be done based on the CBL data collected in the well or it can come from the predicted cement properties. The value for the attenuation in a 100% bonded interval is the key to the interpretation of this type of log. Zonal isolation is estimated from an empirical data base. These tools also provide a qualitative indication of bond to the formation through the use of a Variable Density Log (VDL) waveform.

This paper was selected for presentatmn by an SPE Program COmmltteO fo{lowmg revfew of Informal!on ccmtamed LOen abstract sutm !tted by tfw author(s) Ccmtents of the pap+r, as presented, have not b%en rewewed by IM %cmty of Petroleum Engineers and are subject lo Correchan by (he au!hor(s) The mater$al as presented, does not necessarily reflect any poslban of the %cmty of Petroleum Engineers ,ts offbeers,or members Papers presented al SPE meellngs are subject to publlcalon rev$ew by Edllorlal Comm,ltees of me Society of Petroleum Engmews Permtsslon to copy IS restncled to an abstracl of not mwe than 300 words Illustrations may not be Copied The abstract should Con!am conspicuous acknowledgment of where and by whom the paper was presented Write Lrbrar$ an, SPE P O Box B32J3M, Richardson, TX 75093 .383S U S A fax 01.214.952-9435 Abstract The primary cement job is critical to the success of a well completion. In many instances, the use of present spacer technology has resulted in mud contaminated cement. This paper discusses how the ARCO designed spacer system exhibits exceptional performance to clean out the wellbore and improve the quality of the cement job. Field examples from Offshore Gulf of Mexico show that this cleanout technology, together with pipe centralization and proper job execution, has resulted in good downhole placement of the cement slurry with minimal mud contamination.This success not only has drastically reduced the need for remedial cement work, but also has made the cement bond evaluation straight forward.This spacer technology has been successfully applied in water-based, oil-based and synthetic-based mud systems.Furthermore, the use of this spacer technology is now being expanded to other ARCO operations aro~nd the world.

In recent years specialized cements have been developed for use in the oilfield. These cements have ranged from very lightweight to very heavy cements. They have included additives such as glass or ceramic beads to alter their properties. With an increased use of these cements, concerns have risen about the cement evaluation. Quite often the question is asked, "Can we evaluate these cements?" rather than, "How do we evaluate these cements?" This paper will discuss some logging techniques that can be used to evaluate these new cements. The desire to cement longer casing intervals without exceeding the formation fracture gradient has led to the use of very light weight cements. These cements have low acoustic impedance values that are not much higher than the acoustic impedance values of drilling fluids. The compressive strength of these cements can also vary significantly. Acoustic impedance and compressive strength are the properties that cement evaluation tools use to differentiate between the fluids and the solids in the casing formation annulus. To identify these differences it is critical that the proper logging techniques and input parameters are selected for the sonic and ultrasonic tools. A statistical analysis of acoustic impedance measurements from the ultrasonic tools has also proven to be valuable for the evaluation of these special cements. Examples from Alaska, and other areas where these types of cements are being used to solve difficult completion problems, will be shown to demonstrate the use of these cement evaluation techniques. Introduction Since the 1960s sonic logging tools have been used to evaluate the placement of cement for hydraulic isolation of formations in both production wells and injection wells. Since this time, there have been several advancements in the logging tools that improved the ability to evaluate the cement sheath. During the same period of time the cements being used changed little. During the past few years however, there has been an emphasis on optimizing the cementing operation and reducing the overall cost of the completion. To the cementing operation, this meant developing lightweight and specialized cements that would allow setting casing strings deeper without worrying about lost returns. Other gains in efficiency were also achieved using lighter cements while drilling and completing weak formations. Changes in these cements, and their properties, have also brought about the need for re-evaluating the techniques and tools used for the evaluation of these cements with the sonic logging tools currently available. The Cement Bond Log (CBL), while still in existence in the same form it was originally developed, has also evolved into several other cement logging tools using the same physics of measurements with improved measurement outputs. The first tool of this type uses two transmitters and three receivers to make a direct measurement of attenuation that compensates for many of the problems observed in the basic CBL measurement of amplitude. This measurement was then put into another tool that could measure the attenuation in six sectors around the circumference of the casing. Since the use of the Cement Bond Log first began, there have been several different versions of the standard CBL tool to measure the amplitude in different sectors around the casing.

fax 01-972-952-9435. AbstractOn 20Apr05, while bringing Mad Dog Slot W1 back on production after a brief shut-in, pressure developed on the A annulus and persisted despite repeated bleeds. Diagnostic pressure tests and logs eliminated a number of possible sources of the annulus pressure, eventually leading to the conclusion that the 9-7/8 in. production tieback had been breached. Further investigative logs led to the observation of ovalization of the production tubing.This study summarizes the efforts of the team assigned to investigate the causes of the production tubing and casing deformation. The outcome of the analysis suggests a subtle failure mode, ultimately related to attempts at annular pressure build-up mitigation. The subtlety emphasizes the importance of (a) design considerations in uncemented annuli opposite salt, (b) the importance of creating a complete cement sheath and (c) the inherent difficulties in converting an appraisal well into a producing well.The study concludes with a brief review of the changes implemented in the replacement well intended to eliminate a repeat of the identified failure mechanism(s).

TX 75083-3836 U.S.A., fax 1.972.952.9435. AbstractThe hydraulic isolation of the wellbore casing and cement is critical for the completion of production and injection wells. Zonal isolation prevents the production of fluids from noncompletion intervals, contamination of ground water by fluids in the wellbore, and allows conformance control of injected fluids. Current acoustic evaluation techniques may be limited by the acoustic properties of the material behind casing and by the inability to see beyond the cemented region near the casing. A new ultrasonic imaging tool has been developed to address these limitations.The new imager tool combines the classical pulse-echo technique with a new ultrasonic technique that provides temporally compact echoes arising from propagation along the casing and also reflections at the cement-formation interface. Processing these signals yields unprecedented characterization of the cased-hole environment in terms of the nature and acoustic velocity of the material immediately behind casing, the position of the casing within the borehole, and the geometrical shape of the borehole. 5 In order to provide answers to the casing/cement evaluation questions, a field study was performed to evaluate the results provided by both sonic and this new ultrasonic tool in the different cement materials, drilling fluids, and casing sizes. Field examples are presented to illustrate the actual response of the new ultrasonic tool to these various completion environments including wells cemented with conventional and lightweight cement. The results demonstrate enhanced cement evaluation for all cement types and a significant reduction in the uncertainty in making a squeeze or no-squeeze decision.The new cement evaluation tool implements both the traditional pulse-echo technique and the new flexural wave concept. The flexural mode enables deep imaging of the cement sheath up to the cement-formation interface. In addition, the measurement of the borehole geometrical shape makes it possible to evaluation double casing string conditions for potential damage.