ABSTRACT

On an artificial island in the United Arab Emirates, a local operator planned to drill and complete 45 wells. Among these wells, the plan was to drill a dual gas-injector well that was expected to be under an alternating surface pressure of 5,500 psi. The operator was targeting to inject produced hydrocarbons into two narrow reservoirs, forcing the perforations to have an interval of only 47 ft. between them. The 9 5/8-in intermediate liner was over pulled 1,200 ft above its targeted depth; jeopardizing the whole well integrity. These factors caused the cementation and zonal isolation of the 7-in production liner to be extremely challenging.

A new generation of cementing system with optimized mechanical properties and self-repairing capabilities was implemented for this operation and discussed over the paper. Formerly, the operator has never been able to pump cement systems with both characteristics (ductility and self-sealing property) thus facing logistical and operational constraints when it came to cement the production liners. To achieve the required mechanical properties and self-repairing capabilities in a single cement system, comprehensive lab test study was carried out. The cement system's elastic constants and its expansion properties were tested over several days, and the sealing capability was established using a novel HPHT multi-function test cell simulating the well's downhole conditions.

The larger-than-planned hole created after the production liner was over-pulled resulted in poor centralization across the interval, and the industry-recommended turbulent fluid flow was not achievable. To ensure good hole cleaning, a novel fluid displacement software model was used to assess effective laminar flow. The self-sealing feature of the cementing system in the presence of hydrocarbons flow through a crack or micro micro-annuli was validated and its ability to seal repeatedly was confirmed. Furthermore, linear expansion of the set cement was targeted to compensate for the shrinkage of the cement and to ensure better bonding to the pipe and formation. The cementing pumping operation was carried out successfully. A CBL log was run after 48 hours, verifying good zonal isolation over the entire interval followed by a successful 5,500 psi casing pressure test. An injectivity test was performed on the two perforated zones. No fluids communication was observed, eliminating the need of any remedial cementation.

This paper describes the successful implementation of the resilient and self-sealing cementing system from the slurry design and lab testing through the cement placement. Modelling simulation of the ECD, centralization, and fluid displacement will be also shared. The review of this case history will provide useful lessons-learned for successful cementing of critical injector wells.

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