Petroleum Development Oman operates a large number of heavy oil fields in the south of Oman.One of the fields is being developed with horizontal wells completed with sand exclusion screens and beam-pumps to produce the heavy crude oil to surface. Development drilling is in progress as per the field development plan requiring more than 10 wells to be drilled each year.The integrated asset team carried out a post production evaluation of the 2007 newly drilled wells. The evaluation identified five underperforming wells requiring further examination to establish cause of performance impediment and to devise ways to remedy the problem.The well performance modelling of the underperforming 2007 wells indicates very high skin values. This suggests the wells are severely damaged (e.g., reduced permeability) and/or only a fraction of the sand face is open to flow, suspect due to presence of mud filter cake. The high skin values are significantly impacting the gross fluid production consequently affecting net oil production from these wells.A wellbore clean up and stimulation treatment was designed and well interventions scheduled to remove the suspected mud filter cake, consequently improving well productivities. This paper reviews the production performance following wellbore clean up and stimulation of five underperforming wells. Covering well performance analysis, treatment design, execution methodology and post treatment results including the way forward to advance the current wellbore clean up process to deliver higher productivity wells in the upcoming 2009 and future drilling campaigns.

A cluster area "H" consists of 4 carbonate gas fields producing dry gas from N-A reservoir in the Northern area of Oman. These fields are producing with different maturity levels since 1968. An FDP study was done in 2006 which proposed drilling of 7 additional vertical wells beside the already existing 5 wells to develop the reserves and enhance gas production from the fields. The FDP well planning was based on a seismic amplitude "QI" study that recommended drilling the areas with high amplitudes as an indication for gas presence, and it ignored the low amplitude areas even if it is structurally high. A follow up study was conducted in 2010 for "H" area fields using the same seismic data and the well data drilled post FDP. The new static and dynamic work revealed the wrong aspect of the 2006 QI study, and proved with evidence from well logs and production data that low seismic amplitudes in high structural areas have sweet spots of good reservoir quality rock. This has led to changing the old appraisal strategy and planning more wells in low amplitude areas with high structure and hence discovering new blocks that increased the reserves of the fields.Furthermore, water production in these fields started much earlier than FDP expectation. The subsurface team have integrated deeply with the operation team and started a project to find new solutions to handle the water production and enhance the gas rate. The subsurface team also started drilling horizontal wells in the fields to increase the UR, delay the water production and also reduce the wells total CAPEX by drilling less horizontal wells compared to many vertical as they have higher production and recovery. These subsurface and surface activities have successfully helped to stabilize and increase the production of "H" area cluster by developing more reserves and handling the water production.