Construction of a Reference Well to Support the Qualification of Cement Evaluation Logging Tools and Data Processing

Abstract

Abstract Verification of annular well barriers is a critical process that can significantly affect the cost and complexity of plug and abandonment (P&A) operations, deep sidetracks, or any other drilled wells. Sonic, acoustic, and ultrasonic logging tools are nowadays used to evaluate the cement bond to the casing and infer information about the quality of the annular barrier seal. Nevertheless, as the comparison of the real annular condition and the log response can be uncertain or difficult to establish in a real well scenario, a well was drilled and completed with well-defined engineered defects introduced in the cement with the aim to establish a reference for assessing vertical and azimuthal sensitivity of the data delivered by logging tools. During the execution of this joint project between industry representatives and researchers, the first challenge was to select an appropriate material to simulate appropriate cement defects. Such material should have an acoustic response similar to water, be suitable for installation on the outside surface of a 9 5/8-in. casing, be robust enough to survive a trip downhole, and withstand the cement placement and curing process. After a screening process, four different synthetic rubber materials were selected as potential candidates worthy of further investigation. The characterization executed to select the material used included acoustic measurements and mechanical observations, as well as a detailed description of the well-designed and well construction procedure. The reference well has a 12 ¼-in. section drilled to 214 mRKB and was completed with 9 5/8-in. casing. The completion design comprises the shoe, the float collar, and 17 casing joints fully centralized. Ten casing joints were run into the well with defects installed on the outside wall of the pipe simulating defects in the annular cement. The defects mimicked water channels of 10°, 20°, 30°, and 45° width. After landing the casing, a cementing operation was executed utilizing Class G cement of 1.90 SG. The first logging run confirmed all engineered defects had survived the trip downhole and that the goal of creating defects with well-defined geometries had been achieved. The novel well facility was constructed with the aim of establishing a reference for the qualification of logging tools that can allow a direct comparison between log response and annular seal quality. This well provides the industry with the opportunity to compare different logging technologies to detect and evaluate cement defects and their performance to describe defects with specific lengths and sizes.