To control sand production in a dry gas unconsolidated sandstone reservoir, cased-hole gravel packs were installed in several newly drilled wells. Routine flow-after-flow and build-up tests were carried-out in all the wells after completion and unexpectedly high Darcy skins were estimated from the test data for all of the wells. In order to prepare a remediation plan, it was crucial to understand the source of the skin. As the estimated Darcy well skins according to the tests conducted right after drilling and prior to the well completion were negligible it was concluded that the positive skins were created during the completion process. The accumulation of liquid in the formation around the wellbore during the completion process and nearwellbore damage of the formation were considered to be the two main causes of the observed well skins.
A remediation plan would not be required if the presence of the completion liquid had generated the skin as much of the liquid would be recovered at the surface in the course of production. The gas mobility reduction and blockage to the gas movement would be a consequence of completion fluid accumulated near the wellbore. In order to estimate the contribution of this completion fluid on the total skin, radial grid single-well models representing flow into the wells were constructed. The single-well model results indicated that the blockage to gas movement due to the presence of the completion liquid manifests itself as a low gas mobility area in the build-up well test data. The maximum skin arising from this low gas mobility around the well was significantly less than observed. Near-wellbore damage was therefore recognized as the main source of the high skin. A Hydrofluoric (HF) acid job was recommended based on this conclusion and a reasonable well skin was achieved after performing these acid jobs.