Evaluation of Foam Cementing the Reservoir Liner in Deviated Wells on the Ekofisk M Platform
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Foam cementing the reservoir liner has proven to be a good solution for achieving zonal isolation due to its low permeability and high compressive strength. However, out of the 32 reservoir liners cemented on the Ekofisk M platform only 16 were defined as 100 % successful. In this thesis foam cement and liner string components are introduced before evaluating the outcome of the different jobs. A success criterion for the outcome is established, incorporating liner centralization, zonal isolation and liner movement. The criterion regards the outcome a success if liner manipulation is maintained throughout the job and no remedial job is needed, a semi-success if manipulation is maintained for most of the job and no remedial job is needed, and a failure if none of the previously mentioned. Data from all the reservoir liner cementing operations are gathered and the outcome of each is evaluated based on the above criterion. 16 of the liners were cemented successfully, 6 were semi-successfully, and the last 10 were failures. Failing to reestablish rotation after setting the liner hanger is the most common reason for failure, 7 out of 10 failures can be related to this. Wellbore inclination and liner length are both parameters which seems to contribute to the outcome of foam cementing the reservoir liner. 13 of the 32 wells have an inclination above 80 º at the liner shoe. Out of these 13 wells only 4 are regarded as successful, the rest are either semi-successful, 4, or failures, 5. Even though failures are observed for all inclinations, this happens more frequently at higher inclination. The success rate also seems to be influenced be the length of the liner. For shorter liners, i.e. with a length below 2000 ft, nearly 78 % of the cement jobs were successful, whereas the same percentage for liners with a length between 5000 ft and 6000 ft is 25 %. In fact, a near linear trend is observed for the success rate as the length increases.
Master's thesis in Petroleum engineering