The drilling fluid in a vertical well may only be in the pay zone for few hours while in a horizontal well the time can be measured in weeks.This can cause a significant formation damage problem that has the potential for reducing productivity in horizontal wells during drilling operations.A common practice following drilling operations involove filter cake removal operation followed by displacement of wellbore fluids by completion fluid in order to prepare the well for production operations.Presence of drilling fluids in horizontal wells for several weeks is not considered in the design for cleaning fluid recipies targeting drill-in fluid damage.The filter cake buildup time affect its physical characteristics and thus,on the removal process.This study focused on the characterization and the cleanout of the filter cake during the different buildup stages that may occur in the horizontal section.The focus of this study is to highlight the effects of not promptly removing the filter cake.Filter press instrument was used to simulate filter cake formation on the wellbore wall at 500 psi and 300°F.The filter cake formation process was performed using oil-based drilling fluid at different buildup times(i.e.,3 hours,3 days and 3 weeks),under 500 psi and 300°F.The comparison of the different scenarios showed that a thicker filter cake was formed with buildup time(up to 2.5 inch after 21 days).The CT scan results showed that the heterogeneity increased up to 4 layers and the solubility of in the cleanout fluid decreased to 4% by weight.
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