In a challenging well in a mature gas field offshore Germany, four different size liners with annular clearance of less than 1-in. with the open hole or previous casing were cemented. Successful cementing of these liners was critical in order to drill and complete the well before putting it into production.

To avoid lost circulation during cementing, we established loss-free mud circulation rates before the cementing operation and designed cement slurries with long thickening times for placement at low rates. Additionally, we used fibers in the cement slurry, and pumped treated micronized barite drilling fluid ahead of the cement slurry to lower friction pressures and optimize mud removal.

We validated cement slurry designs through a rigorous laboratory testing procedure, including go/no-go procedures in the high temperature/high pressure (HPHT) consistometer. Long thickening times were needed, especially on a 600 m long 6-in. expandable liner cement job. We tested the setting times of cement accurately with ultrasonic cement analysis and static gel strength analysis devices. Additives to reduce the risk of gas migration were included in all cement slurries.

In order to optimize mud removal and reduce the chance of cement slurry getting contaminated, custom made centralizers were strategically placed in highly critical areas. We optimized spacers through a full laboratory analysis of compatibility between spacer and the low-toxic oil based mud, as well as performing reverse emulsion and grid tests. We validated the mud removal design with 2-D simulations to predict the effectiveness of mud displacement from the wellbore.

Cement slurry was placed without losses on all liners. In all cases, we had positive indications that cement slurry reached up to the liner hanger by observing cement slurry in the returns back to surface. All formation integrity tests on the liner shoe were successful and allowed drilling of the consecutive section. The final production liner was logged using a radial bond tool and advanced cement evaluation processing was run on the data in order to better evaluate cement quality. Good cement bond quality was observed behind the production liner.

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