INTEGRATING ROCK PHYSICS AND SEQUENCE STRATIGRAPHY FOR CHARACTERIZATION OF TURBIDITE SAND SYSTEM IN “NOJA” FIELD, OFFSHORE NIGER-DELTA

Abstract

Integration of rock physics and sequence stratigraphy analysis was utilised in the characterization of turbidite sand systems in deep-offshore Niger Delta. Seismic sequence analysis using reflection termination patterns which are erosional truncation, toplap, onlap, and downlap were used for the mapping of depositional sequences. Rock physics concepts were utilised to evaluate reservoir continuity, diagenetic and environment of deposition effects influencing reservoir properties. Two reservoirs (R1 and R2) of interest occurred at a depth interval of 7868 to 8075 ft. Reservoir (R1) has average volume of shale of 22%, effective porosity 20%, hydrocarbon saturation 53% and permeability 556 mD. Reservoir (R2) has average volume of shale of 10%, effective porosity 26%, hydrocarbon saturation 79% and permeability 1044 mD. Seismic structural maps gave insight into rock deformation and hydrocarbon potential of the field. The probable structure responsible for the trapping of oil and gas is a faulted anticlinal structure. Four depositional sequences exist in the field. Amplitude maps of the two stratigraphic surfaces gave insight into sand and shale distribution and possible environment of sediment deposition. Environment of sediment deposition of the reservoirs is weakly confined and distributary channel complexes. Reservoir (R1) has low degree of connectivity (loosely amalgamated turbidite sand system) and reservoir (R2) possesses high degree of connectivity (highly amalgamated turbidite sand system). Compaction studies revealed that at depth of 3.2 km, quartz cementation of sands and velocity of sandstones became higher than that of shales or uncemented sands. Rock physics templates of constant, contact and friable showed that the reservoir sands are poorly cemented to unconsolidated. These models indicate that the reservoir sands are both influenced by depositional and depth related diagenetic effects.