The case reservoir is a field in South Oman and produces high viscous oil from well sorted unconsolidated formation sand with a small average grain size (40 microns). Initially the wells were completed with downhole sand control but suffered from extreme plugging due to very fine nature of formation sand.
After performing some trials it was proved that, it is better to produce the wells without downhole sand control. A pre-drilled liner is used for downhole completion and Progressive Cavity Pump is for artificial lift as it is the most sand tolerable available pump.
Sand co-production (i.e. sand removal at surface) is the optimal development for this field. Sand fill up in the well bore however became an issue in the high producers that are impacted by nearby water injection wells. This phenomenon caused a reduction in well productivity. Few methods were trialed to remedy this issue. Sand clean out with a wash string by reverse circulating didn't work because the reservoir is sub-hydrostatic.
Coiled Tubing clean out with foam was trialed but somehow the result was not effective to bring the well back to previous productivity especially on long horizontal wells. The annular velocity was probably not high enough to lift up sand from the well bore.
Concentric Coil Tubing was trialed also which does not require foam or nitrogen for sand clean out. This unit and its special tool (i.e. jet pump) uses water to create a vacuum in the well bore to have fluid return while lifting loose sand or debris to surface. This method bring the well back to its actual productivity when no hard obstruction is encountered during clean out.
This paper presents WRM team experiences in dealing with sand clean out and sand co-production issues.