Removing mud from around the casing or liner and replacing it with drilling or cement fluid is fundamental to achieving zonal isolation. One significant parameter needed to achieve flow around the casing is proper casing centralization. Casing centralization is a function of many wellbore properties, such as fluid and centralizer data, which are obtained from the directional survey and caliper data. Computer simulations are used to optimize centralizer selection and placement prior to running the casing into the wellbore and the cementing operations. This paper presents the method and technology used to compare simulated vs. real centralization and the key lessons learned from a Kuwait project.

To complete the continuous improvement cycle, it is important to confirm the casing standoff in a postcement operation to determine if the prejob assumptions and the simulations were accurate. Using standard cement evaluation logs, it is not possible to directly measure the casing standoff. Therefore, conclusions have to be made indirectly, based on the cement evaluation data. The new-generation ultrasonic flexural measurement tools can be used to evaluate casing centralization directly by evaluating the time between the first casing reflection (mud to casing interface) and the third reflection (cement formation interface).

For a Kuwait project, a new one-piece slip-on centralizer was introduced for field operations. Prejob standoff simulations were performed to optimize the casing standoff to meet the operator and service company recommendations. All available well and fluid data were included in the simulations to accurately predict the casing standoff. The simulations used a state-of-the-art, stiff-string simulator to provide the most accurate simulations results.

To evaluate the standoff simulations and centralizer performance, the third-interface echo (TIE) measurements were used to determine actual standoff. The ultrasonic measurements were run on three different cemented intervals. These intervals ranged from a vertical 16-in open hole interval to a highly deviated 8½-in openhole section. By comparing the actual measurement with the simulations results, a direct standoff evaluation was made possible regarding the centralizer selection and placement and the assumptions made during the well planning phase. It also provides better understanding on the performance of the centralizers.

Using the advanced flexural ultrasonic logging tool and the TIE measurement provided the opportunity to compare actual casing standoff results vs. prejob casing centralization simulation. The results demonstrated the importance of having accurate well data available during the design phase and the impact particular assumptions have on the final casing standoff. By comparing the actual casing standoff results vs. prejob casing centralization simulation, important lessons can be learned about centralizer selection, placement, and how standoff simulations can be implemented during field development to improve casing standoff. Thus, the probability of effective mud removal and zonal isolation increases.

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