Study of Near-Wellbore Damage Characterisation Using Pressure Transient Analysis in Sand-Prone Wells of OML 65, Bayelsa State

Near-wellbore damage in sand-prone reservoirs is a particularly complex diagnostic challenge because the skin effect measured from pressure transient tests reflects both formation damage and the pressure drop across the completion system, including perforation tunnels and gravel packs, making accurate damage quantification difficult. This study characterises near-wellbore damage conditions using integrated pressure transient analysis in gravel-packed sand-prone wells of OML 65, Bayelsa State, South South Nigeria. Production well test data from eight gravel-packed wells were processed using rate-normalised pressure analysis in IHS Harmony software. Wellbore storage effects were identified and removed using deconvolution. The composite skin factor was decomposed into its constituent components: formation damage skin, partial penetration skin, completion skin from gravel pack, and perforation skin, using published correlations for each component. Formation damage skin values ranged from plus 0.8 to plus 7.3 across the eight wells, with higher damage skins correlated with wells that experienced workover fluid losses to the formation during gravel pack installations. The study demonstrates that a modified selective acid wash programme targeting damage confined to the perforation tunnel region achieves skin reductions of 2 to 4 units without risking gravel pack destruction. Economic analysis confirms that the resulting production improvement justifies the cost of acid wash intervention in all candidate wells. Keywords: near-wellbore damage, pressure transient analysis, gravel pack, OML 65, Bayelsa State.