Cement behind casing, as the critical component of well integrity is a real challenge all over the world. Despite the efforts drilling operators and service providers dedicate to this phase of well construction in the South Pars gas field, final set cement quality does not establish zonal isolation in 9 5/8" casing and 12 1/4" openhole section.

In order to study this issue, twenty-four wells have been analyzed based on theoretical analysis, close hands-on operations and track record of cementing in the field. Data were acquired from the daily drilling reports, data acquisition system of cement units, mud logging records, daily mud reports, cement slurry laboratory test sheets and wireline log records.

The main effective factors on cement quality have been studied in four groups namely: well preparation, slurry design, mud removal and post-cementing practices. Good and poor quality cement in all wells have been compared with actual field parameters using a cementing displacement simulator software. Structural stress model has also performed for one of the wells whose cement was prone to be impacted by post cementing practices.

Results have been obtained over one year of parallel laboratory testing, field experience, simulation and evaluation. The simulations results illustrate turbulent flow is not practical for cementing of this section and effective laminar flow technique shows an efficient alternative, however all criteria of this technique could not have been fully met due to some well restriction. The results reveal mud removal parameters in terms of casing centralization have significant effects on the final cement quality in this field. Cement quality devastation persisted even in cases where the cement slurry properties were modified and used in four wells in order to evaluate slurry design impact degree on final set cement quality. The stress model results illustrate that imposed stress on the well exceeds the compressive and tensile strength of the cement sheath. These results reinforce the idea that mud removal and post cementing practices govern the cement quality in the field.

This paper is a comprehensive study of all effective parameters on cement quality in 9 5/8" casing cementing and highlight the main sources of cement quality devastation in the field and it can be used as a guideline for cementing similar cases around the world.

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