From Static Design to Dynamic Safety: Well Control–Based Casing Depth Optimization in Niger Delta Wells

Well design in oil and gas drilling is traditionally performed under static pore–fracture pressure constraints, often neglecting dynamic well control behavior during kick circulation. This limitation is particularly critical in narrow pore–fracture margin environments, where small influxes can rapidly escalate into underground blowouts. This study develops a pressure-balance-based well control model that integrates maximum allowable annular surface pressure (MAASP) and maximum allowable kick volume (MAAKV) into casing depth optimization. The methodology is demonstrated using real subsurface pressure profiles, gas kick properties, and well configuration data from two offshore Niger Delta wells. Base-case casing programs were re-evaluated under dynamic circulation conditions and compared with optimized designs incorporating under-reaming in critical narrow-margin sections. Results show that MAAKV decreases sharply with depth, reaching critically low values (< 12 bbl in Well A and 26 bbl in Well B) in deep intervals, indicating that small kicks may escape detection and cannot be safely circulated without fracturing the formation at the casing shoe. Introducing under-reaming increased kick tolerance by up to 342% in Well A and 96% in Well B, substantially expanding the safe operating envelope. The proposed approach enhances well control safety, reduces underground blowout risk, and offers economic benefits through optimized casing placement.