Time-Lapse Analyses of Geomechanical Parameters in a Tertiary Reservoir, Niger-Delta, P - Field

Abstract Time-lapse analyses of geomechanical parameter of a tertiary reservoir in Niger Delta, P-field was carried out. The aim of the study was to carry out 4D model-based seismic inversion to extract geomechanical properties from 4D impedance volumes and carry out time-lapse analyses for possible compaction, subsidence, and sanding. Suite of well logs from three wells (well 001, well 025 and well 029) were used alongside 4-D seismic data acquired at different epochs in time (11 years apart). Edited and quality checked well data were used to run petrophysical analysis and also generate pseudo logs. Well to well correlation along with mapped faults and a time structure map was able to reveal and distinguish the varying depths of the well. Root-Mean-Square (RMS) amplitude was extracted from the seismic volume along the mapped horizon (Hor-2b-intrp). This revealed bright amplitudes around the well locations in the base slice but the amplitude was observed to be reduced in the monitor, which suggests changes in the reservoir, induced by production. Model-based seismic inversion was done on both the base and monitor seismic volumes to produce an acoustic impedance (AI) volume from which properties/attributes were extracted. The geomechanical parameters extracted from the AI volumes along the horizon of interest and their range of values are: Bulk modulus[K] (18.1x106GPa -23.4x106GPa), Lambda[λ] (9.85GPa – 12.01GPa), Mu[μ] (5.66GPa – 32.05GPa), Mu-rho[μρ] (7.24GPa-32.65GPa) and Poisson's ratio (0.29 – 0.38). RMS amplitude, Bulk modulus, lambda, Poisson's ratio and mu showed clear reduction in porosity from base to monitor data. This reduction in porosity is a clear indication of compaction in the reservoir which could ultimately leads to subsidence. Mu-rho showed a possibility of brittle-ductile transition (BDT) in well 001 and 029 resulting from porosity loss and possible increase in temperature due to compaction.