The combination of ultrasonic pulse-echo and flexural-attenuation measurements was adopted in this project in the South China Sea for cement-integrity evaluation. This new method aids in understanding why integrity losses occur in certain sections, by analyzing third-interface information uniquely provided by flexural-wave imaging, and in formulating improvement actions for future cementing jobs. This method achieves a more-explicit cement-integrity-evaluation result with detailed graphical annulus information compared with the limited output from conventional acoustic measurements.
Introduction
In the Weizhou field in the South China Sea, most of the development wells are drilled as long extended-reach wells with a deviation greater than 70°. The wells are designed to reach more than 70° deviation at a very shallow depth (approximately 900 m) compared with the total depth of the well (approximately 4500 m). In a typical well, surface casing (13.375 in.) runs beyond the kick-off point and reaches maximum deviation of the well at a shallow depth (approximately 900 m). Intermediate casing (9.625 in.) runs from surface to more than 4000 m, with three different fluids/slurries pumped in the annulus: regular-weight tail cement (1.90 g/cm3), freshwater displacement cement, and lightweight lead cement (1.58 g/cm3). The completion liner (7 in.) hangs on the intermediate casing, with 1.90-g/cm3 cement pumped in the annulus.
A campaign was planned to perform cement-integrity evaluation in five wells (A9, A10, A1, A2, and A3). The basic information about these five wells is listed in Table 1 of the complete paper. The objective for Well A9 was to evaluate the 7-in.
