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. Introduction The subject field is located on the Eastern flank of South Oman basin (Fig. 1). The reservoir is a fine-medium sandstone formation. The formation is divided into upper and lower zones each consisting of several layers. These zones are separated by a shale marker. The lower zones have a moderate bottom aquifer and the upper zones have a weak aquifer which provides some edge drive support. This resulted in a pressure differential between upper and lower zones. The reservoir crude characteristics are moderate to low API, i.e. 22 deg API oil and 90 cp viscosities. Whereas the original reservoir pressure was 9300 kPa and bubble point pressure is 7670 kPa. Currently the pressure has depleted to 4000 - 8000 kPa. The reservoir has been on production since 1980 and currently has around 78 active wells which consist of 15 water injectors and 63 oil producers.

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fax 01-972-952-9435. AbstractThe case reservoir is a field in South

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