Abstract

Some of the land fields in Middle East contain important potential gas reserves, but zonal isolation of long drilling and production liners have been a challenge. Cementing these long liners along formations with low fracture gradients risks formation breakdowns when exceeding the maximum allowable equivalent circulation densities. Consequences include severe losses, formation damage, and insufficient placement necessitating costly remedial cementing, or even loss of the well.

Many wells in one field were abandoned and not completed because of the tight pore-fracture pressure window, which induced severe losses while drilling the intermediate and production sections. Operators have struggled to mitigate those drilling challenges, and one of the last approaches was to use an ultra-slim hole design; however, this design exacerbated the cementing challenges for the long 7-in. liner. We review this case history and outline the corresponding planning (spacer/cement fluid designs, placement simulations, and lab test results), pre-job practices, and job execution with evaluation.

In this particular well, the 8 3/8-in. open hole section was drilled to the casing point with no losses. However, while running the 7-in. liner (at > 10,000 ft) total losses occurred. A new design approach was developed and applied to mitigate the problems associated with cementing this section. This approach centered on the careful selection and engineering design of a spacer to cure and mitigate induced losses, and the use of high-performance cement slurries. Desirable properties of the latter include very low fluid loss and exceptional fluidity (low rheology) without development of free fluid or sedimentation. Finally the 7-in. liner was successfully cemented, and cement was found on top of the liner after reversing out.

A comprehensive approach on how to cure or reduce lost-circulation problems during cementing operations for critical sections (such as very long liners along fragile formations) are presented and discussed in this study. Case histories from several wells in the area are used to demonstrate the success of this approach with guidelines and lessons learned for similar upcoming projects.

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