Displacement to a dedicated screen running fluid (e.g. low-solids mud) is a common method to lower the solids loading of the fluid prior running the completion screens in order to minimize the risk of blockages. However, some advanced drill-in fluids exhibit excellent long-term stabilities under downhole conditions which allow for a dual use also as screen running fluid. A systematic selection of such a fluid for a horizontal well in an oilfield offshore Norway is presented.

Samples of different 1.2 SG oil-based drilling fluids and screen running fluid candidates were statically aged at 200 bar and 87 °C for 1 and 2 months. Complementarily characterization was performed by running viscometer sag shoe tests and laser particle size analysis of the samples. Actual core plugs of the reservoir section were selected for core flooding/formation damage tests covering different drill-in fluids and sequences including screen insertion with and without prior displacement to an actual screen running fluid. The return permeability and a detailed required draw-down analysis was performed.

Experiments have shown that the downhole stability is commonly underestimated when the surrounding pressure is lower than in the field like in a conventional aging cell. One of the drill-in fluids showed superior long-term stability with maintaining mobility even after 2 months of aging and no phase separation of significant settling. In contrast, the low-solids oil-based mud showed significant phase separation and some settling. Laboratory results were implemented to the flied by strict specification of the mud properties and verification by a comprehensive post-operational QA/QC of field samples in the laboratory.

The success was proven by no negative impact on productivity of the well compared to previously drilled and completed wells in the field. However, running the completion in DIF resulted in significant de-risking of drilling operations, cost savings and eliminated logistical challenges from previous wells.

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