Gjøa is an oil and gas field located off the Norwegian Coast that is due to be developed with subsea infrastructure tied back to a floating production facility. Nine horizontal oil producers and four S-shaped gas producers are planned and all will require some form of sand prevention. Extensive rock mechanical work using Statoil's finite element modeling method suggests that oriented perforations can prevent sand production in the horizontal wells. This was offered as an alternative to mechanical sand control in the long horizontal wells due to traverse several shale and sand bodies of varying quality.

Perforation tunnels with optimal "structural" stability for the given inherent material strength of the formation rock can be achieved by targeting perforations in the most stable direction with respect to the in-situ stress field. For high angle wells this normally equates to shooting in the vertical plane through the well path. Over a decade of production experience with this technique on the Norwegian Continental Shelf (NCS) confirms that oriented perforating can be a good sand prevention measure in suitable fields. Despite this track record and the rock mechanical analysis performed, the Gjøa project team wanted to conduct laboratory tests to confirm its applicability and also to optimize perforating parameters. An extensive laboratory test program was conducted on representative core and outcrop material. Five modified API RP 19B Section IV tests were performed to assess the influence of static and dynamic wellbore pressure conditions and wellbore fluid on perforation clean-up and PI. In addition, two tests were conducted on field core material in order to evaluate the sanding propensity of oriented perforations under conditions approximating those predicted during pressure depletion. The laboratory conditions required to induce sand production were quite extreme and vastly exceed the production scenario for the planned oil wells in the field. However, the cell geometry, boundary conditions and stress field in these experiments are not truly representative of the in-situ conditions around a true perforation in a well. In order to translate the sanding results into a conclusion relating to the validity of oriented perforating for the field, a finite element model was built to reproduce the lab conditions. This model correctly predicted the conditions required for sand failure as observed in the lab. This agreement provided validation of the operator's general sand prediction methodology and gave good confidence in the earlier rock mechanical predictions made for the field.

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