UNVEILING RESERVOIR UNCERTAINTIES: A 3D GEOLOGICAL MODEL ANALYSIS OF FIELD X IN THE ONSHORE NIGER DA, NIGERIA

Field 'X 'in which this study is undertaken is located southeast of Port Harcourt, Nigeria.The field is contained in a relatively simple anticlinal structure.The 3D geological model interpretation is a stacked model consisting of horizons A, B, C and respectively.However, the 3D model was built with the mentioned four (4) horizons and eighteen (18) faults interpreted from seismic.The fluid contacts were interpreted mostly from the well logs.The study aimed at evaluating the uncertainties that is associated with the volumes in-place.To achieve these objectives, fluid contacts (oil water contact and gas water contact) synthesis, facies and Petrophysical data evaluation and incorporation into a 3D static model was carried out.The five facies interpreted are Shales, Channel Heterolithics, Channel, Upper Shoreface and Lower Shoreface.The facies interpretations were constrained to the seismic amplitude maps so as to respect the different depositional environments.Petrophysical uncertainty in this study is limited to the uncertainty within the petrophysical variables which comprises effective porosity (PHIE), water saturation (Sw) and net-to-gross reservoir definition (NTG).The petrophysical properties (PHIE, NTG, and Sw) were therefore constrained to the associated facies (AFs) model and modelled with the sequential Gaussian simulation (SGS) while the facies model was distributed using the sequential indicator simulation (SIS).This showed that zones or areas of optimistic NTG as related to facies distribution in this study exhibited good porosities and permeabilities while zones with degraded facies showed poor petrophysical properties.An uncertainty analysis was carried out using Petrel Software to assess the impacts of the uncertain parameters on the volumes of fluids-in-place.However, the fluid contact uncertainties carried out on the four reservoir horizons in this study have direct effect on the gross rock volume (GRV) thereby directly affecting the in-place volumes.The deeper contact (representing the high case) will have higher volumes while the shallower fluid contacts will have lower volumes in place.The gas-oil contact is also a factor that has an effect on the volume in place; a deeper gas oil contact (GOC) reduces the oil in place and vice versa.The results showed that the fluid contact variation, facies proportions and NTG have the most significant impact on the base case STOIIP volume computation.