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.
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.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe BP Holstein and Mad Dog oilfields in the Gulf of Mexico are high-profile deepwater projects with high production and high costs. Wellbore construction for both fields includes a completion packer to manage tubing loads and reliably isolate production fluid and pressures from the casing, tiebacks, and risers.Several drivers influenced the packer selection and development process. The magnitude of the packer loading pointed toward high-performance permanent packers. Life-ofwell and life-of-field requirements for planned and unplanned workovers pointed toward the operational flexibility of retrievable packers. High rig costs, a desire for accelerated production, and difficult wireline access "S" curve wells indicated the value derivable from interventionless completions. And the high cost of failure pointed toward high performance and quality standards to reduce risk of failure and potential malfunctions. Together, these drivers pointed toward a new packer solution. Ultimately a high-performance, modular, removeable, "V0 rated," interventionless production packer was developed which met all of these criteria. This paper describes the Holstein and Mad Dog completion environment, and details the selection, development, deployment, and lessons learned with the hydrostatic set, interventionless, removeable packer solution.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractThe BP Holstein and Mad Dog oilfields in the Gulf of Mexico are high-profile deepwater projects with high production and high costs. Wellbore construction for both fields includes a completion packer to manage tubing loads and reliably isolate production fluid and pressures from the casing, tiebacks, and risers.Several drivers influenced the packer selection and development process. The magnitude of the packer loading pointed toward high-performance permanent packers. Life-ofwell and life-of-field requirements for planned and unplanned workovers pointed toward the operational flexibility of retrievable packers. High rig costs, a desire for accelerated production, and difficult wireline access "S" curve wells indicated the value derivable from interventionless completions. And the high cost of failure pointed toward high performance and quality standards to reduce risk of failure and potential malfunctions. Together, these drivers pointed toward a new packer solution. Ultimately a high-performance, modular, removeable, "V0 rated," interventionless production packer was developed which met all of these criteria. This paper describes the Holstein and Mad Dog completion environment, and details the selection, development, deployment, and lessons learned with the hydrostatic set, interventionless, removeable packer solution.
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