Engineered Oilwell-cement-based Systems for Optimum Validation of Cased-hole Ultrasonic Tools

Cement evaluation is commonly thought of as running a cement bond log (CBL) and attempting to interpret the results to determine if there is isolation in the wellbore. Oftentimes that interpretation is made in isolation with little or no information on what occurred during the drilling and cementing of the well, or the cement systems used. Evaluating cement in older wells where the drilling report states, "ran casing, cemented same" can be particularly challenging. Cement evaluation is much more than a CBL. Understanding the objectives of the cement job, the design limitations imposed by those objectives and the resulting slurry and job designs are all integral parts of cement evaluation. Oftentimes the selection of a specialty cement system to meet specific well requirements can dictate how the cement can be evaluated. To properly evaluate a cement sheath, knowledge of the cement job, slurry designs and the limitations of the evaluation technique must be understood. To attempt to perform a cement evaluation based solely on the log output from a CBL, or any log, invites considerable error and bias into the resulting interpretation. This paper reviews various methods of cement evaluation, from job data, casing and formation pressure testing through sonic and ultrasonic logging. The assumptions associated with each technique are outlined and the discussion includes the limitations of the various techniques along with cautions on how misinterpretation of the results can lead to assumptions of cement integrity that may not be appropriate. The impact of new boutique cement designs, which incorporate high concentrations of inert materials to give the set cement unique properties, is discussed. The ability of specific logging techniques to evaluate the presence of these slurries is presented. Data on selected boutique cement systems where conventional UCA strength data is not representative of the crush strength of the cement due to the incorporation of specialty materials is included. An overview of cement evaluation, and a risk based discussion of what technique may be most appropriate based on the cementing objectives is presented. Methods of reducing risk uncertainty in cement evaluation are discussed along with the "validity" of the various data sets available to the engineer to perform a proper cement evaluation on the well. Understanding the objectives of the cement job sets the boundary conditions for the designs, and from those designs the ability to evaluate the resulting cement placement and well isolation can be determined. Setting the evaluation methodology and understanding the type of information required to apply that methodology can improve the quality of the evaluation.

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Improving Wellbore Economics and Long Term Integrity by Optimizing the Design and Evaluation of Annular Sealants for Hydraulically Fractured Wells: A Case Study

Jimenez

Pereira

Matzar

2017

Day 3 Wed, April 26, 2017

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The rapid increase in oil and gas shale exploration has shifted industry dynamics by generating substantial unconventional resources. Advances in horizontal drilling and hydraulic fracturing have played important roles in enabling unconventional developments. However, high-pressure cycles from fracturing and stimulation operations can result in cement failure, which compromises well integrity because cement acts as the annular barricade, protecting and supporting the casing while preventing unwanted fluid communication. To address the relationship between cement performance during fracturing and wellbore integrity, this paper proposes a comprehensive methodology for designing and evaluating cement systems for improved integrity during stimulation and production cycles. A life-of-the-well design approach, comprised of computational modeling of both cement placement and its capacity to withstand long-term temperature/pressure cycles, is coupled with frequent cement-evaluation techniques (e.g., sonic/ultrasonic tools) to help ensure an optimum seal behind casing throughout the well's life. The methodology was tested and/validated in field applications. The proposed methodology includes identifying the purpose of the cement operation, the cement system to accomplish that purpose, the type of evaluation technique(s) to be used, and the recommended evaluation frequency. The field test was performed in a horizontal well, where 23 fracturing stages were planned with a maximum pressure of 7,000 psi; production was intended to last 10 years, with maximum pressure differentials of 500 psi. These operational loads and others experienced during the wellbore construction were also considered to determine which cement system had sufficient capacity to withstand the predefined loads and provide long-term wellbore integrity. Results indicated that elastic cements are more suitable for cyclic loads attained during fracturing and production operations because of their higher strength-to-elastic modulus ratio. Finally, ultrasonic tools were used to diagnose the cement integrity after cementing was completed and before fracturing and production operations, and annually after production began, particularly if additional fracturing stages were considered. Initial integrity diagnostics indicated that ultrasonic logs showed optimum performance of the cement sheath before and after stimulation/production operations. This methodology helps reduce the operational risks associated with poor sealant design and inadequate cement evaluation, which can result in performing unnecessary repair work, production of unwanted fluids, and premature well abandonment. Moreover, as a result of the cement's enhanced integrity and capability to withstand fracturing loads, it was determined that not using a fracturing string could result in significant economic gains to the operator.

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Engineered Oilwell-cement-based Systems for Optimum Validation of Cased-hole Ultrasonic Tools

Cited by 3 publications

References 15 publications

Evaluation of Epoxy Resin Thermal Degradation and its Effect on Preventing Sustained Casing Pressure in Oil and Gas Wells

Evaluation of Epoxy Resin Thermal Degradation and its Effect on Preventing Sustained Casing Pressure in Oil and Gas Wells

Cement Evaluation - A Risky Business

Improving Wellbore Economics and Long Term Integrity by Optimizing the Design and Evaluation of Annular Sealants for Hydraulically Fractured Wells: A Case Study

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