Oil-based drill-in fluids for horizontal gravel-packed South African wells

Drilling and completing long horizontal openhole gravel-packed intervals in a subsea west African field using oil-based drilling fluid has resulted in significant cost savings and increased well productivity. Before, the upper nonpay portions of the wells were drilled with oil-based drilling fluids while the horizontal reservoir sections were drilled with a sized calcium carbonate (CaCO3)/polymer drill-in fluid. Acidization of the entire horizontal interval was required to remove filter-cake damage after gravel packing. New drilling and completion procedures have resulted in improved drilling, considerable cost savings, and productivity indexes two to three times higher than similar wells drilled with water-based drill-in fluids.