Analysis of Drilling Fluid Properties and Lost Circulation Problems in the Cretaceous Sequences of the Bida Basin, Niger State, North Central Nigeria

The Bida Basin in Niger State, North Central Nigeria, represents a frontier onshore sedimentary province with ongoing exploration activities targeting Cretaceous clastic sequences. Drilling operations in this basin have encountered persistent lost circulation events related to naturally fractured formations and unconsolidated shallow sections. This study analyses drilling fluid property optimisation requirements and evaluates lost circulation material effectiveness for Cretaceous sequence drilling in the Bida Basin. Well completion reports and drilling incident logs from three exploration wells drilled in the basin between 2015 and 2022 were reviewed to characterise lost circulation zones by depth, formation type, and severity of mud loss. Drilling fluid formulations used in each well were evaluated against the American Petroleum Institute RP 13B standard for water-based muds. Particle size distribution analysis of candidate lost circulation materials including calcium carbonate, mica flakes, and walnut shell granules was performed to match pore throat and fracture aperture distributions estimated from image log data. Bridging quality calculations using the Abrams criterion were applied to identify optimal particle size blends for each loss zone category. The study finds that a blend of coarse calcium carbonate and medium-sized mica flakes achieves sealing in fracture apertures between 0.3 and 1.5 millimetres, which covers the dominant loss zone character in the Cretaceous section. Recommendations are provided for proactive pre-treatment mud programmes in future Bida Basin wells. Keywords: lost circulation, drilling fluid, Bida Basin, Niger State, Cretaceous sequence.