Analysis of Well Test Interpretation Methods for Tight Gas Reservoirs Encountered in Exploration Wells in the Lower Benue Trough, Kogi State, North Central Nigeria

Tight gas reservoirs in the Lower Benue Trough of Kogi State, North Central Nigeria, present distinctive well test interpretation challenges compared to conventional reservoirs, owing to ultra-low matrix permeability, natural fracture contributions to flow, and stress-sensitive formation properties. This study analyses well test interpretation methods appropriate for tight gas reservoirs encountered in exploration wells in the Lower Benue Trough. Pressure transient data from two exploration wells encountering low-permeability gas-bearing sandstones were processed and interpreted using rate-normalised pressure analysis and pressure derivative methods. The presence of natural fractures was confirmed by the characteristic half-slope derivative response observed in both wells during early radial flow periods. Dual porosity and dual permeability reservoir models were fitted to the derivative data using non-linear regression. Estimated matrix permeabilities range from 0.05 to 0.18 millidarcy, while effective fracture permeabilities are one to two orders of magnitude higher, confirming that natural fractures dominate early-time productivity. Extended pressure build-up periods of 72 to 96 hours were required to achieve stabilised radial flow responses suitable for reliable permeability estimation. The study recommends a minimum 96-hour build-up protocol for future tight reservoir appraisal wells in the Benue Trough and evaluates the applicability of rate transient analysis as a lower-cost alternative to extended build-up testing in extended production test contexts. Keywords: well test interpretation, tight gas, Lower Benue Trough, Kogi State, dual porosity.