Structural Discontinuities and Reservoir Fluid Flow Patterns in Yowi Field, Offshore Niger Delta, Nigeria

Abstract

Structural discontinuities, including faults and fractures, can influence reservoir connectivity, fluid mobility and production response. This study evaluates how structural discontinuities relate to reservoir fluid-flow behaviour in the N5.2 reservoir of the Yowi Field, offshore Niger Delta, Nigeria. The work integrates 3D seismic interpretation, ant-tracking attributes, well-log analysis, core observations, CT-scanned core plugs, petrophysical modelling and production-performance data. Structural interpretation shows that the field is characterised by a rollover anticline associated with east–west-trending growth faults and fault-assisted closures. The major growth faults appear to support hydrocarbon trapping rather than direct aquifer invasion. However, ant-tracking attributes and CT-scanned core plugs indicate short, disconnected and locally dense fracture networks within the reservoir interval, particularly around well areas and within the time interval corresponding to the N5.2 sand. The reservoir displays a blocky to cylindrical log motif, a sharp lower contact and a gradational upper contact, suggesting lateral continuity. Petrophysical and facies models indicate a sand-dominated reservoir with a net-to-gross ratio greater than 83%, negligible shale volume, and high porosity and permeability. The Dykstra–Parsons coefficient of 0.30 indicates relatively low permeability heterogeneity, while the Winland plot shows many samples with permeability above 1000 mD. Production data show early water breakthrough, increased water cut and declining oil rate after initial high production. The results suggest that fracture-enhanced vertical permeability, high reservoir quality and production-management conditions contributed to early water coning and reduced oil recovery. Structural discontinuities, including faults and fractures, can influence reservoir connectivity, fluid mobility and production response. This study evaluates how structural discontinuities relate to reservoir fluid-flow behaviour in the N5.2 reservoir of the Yowi Field, offshore Niger Delta, Nigeria. The work integrates 3D seismic interpretation, ant-tracking attributes, well-log analysis, core observations, CT-scanned core plugs, petrophysical modelling and production-performance data. Structural interpretation shows that the field is characterised by a rollover anticline associated with east–west-trending growth faults and fault-assisted closures. The major growth faults appear to support hydrocarbon trapping rather than direct aquifer invasion. However, ant-tracking attributes and CT-scanned core plugs indicate short, disconnected and locally dense fracture networks within the reservoir interval, particularly around well areas and within the time interval corresponding to the N5.2 sand. The reservoir displays a blocky to cylindrical log motif, a sharp lower contact and a gradational upper contact, suggesting lateral continuity. Petrophysical and facies models indicate a sand-dominated reservoir with a net-to-gross ratio greater than 83%, negligible shale volume, and high porosity and permeability. The Dykstra–Parsons coefficient of 0.30 indicates relatively low permeability heterogeneity, while the Winland plot shows many samples with permeability above 1000 mD. Production data show early water breakthrough, increased water cut and declining oil rate after initial high production. The results suggest that fracture-enhanced vertical permeability, high reservoir quality and production-management conditions contributed to early water coning and reduced oil recovery.