The influence of uncertain parameters on Stock Tank Oil Initially in Place (STOIIP) during reservoir modeling was quantified and ranked using "OA-Field" in coastal swamp of Niger Delta. The data set available for this study include: base map of the area, 250km2 3D migrated seismic section (inline and cross lines), composite well logs (Gamma ray logs, caliper logs, resistivity logs, sonic, neutron and density logs) and checkshot data. This study was to interpret the available seismic data, correlate the different sequence boundaries across the entire field using the log data, identify and analyze the uncertain parameters observed when building the geological models; and subsequently rank the uncertainties and generate P10, P50 and P90 volumetrics.

The methods involved lithologic correlation and identification of reservoir units, fault interpretation, seismic to well tie, horizon mapping, time map generation, velocity modeling, depth map generation, fault modeling and 3D geo-cellular grid construction. Thereafter, property logs otherwise known as computer process logs (PHIT, PHIE, SW and Vshale) were generated and subsequently up-scaled to the grid resolution using arithmetic weighting approach to capture observed heterogeneity present in logs effectively. Volumetrics was estimated using base case scenario and Monte Carlo simulation.

Results of volumetric estimates obtained for the tested reservoir is 433mmbbl of STOIIP. In addition, volumetric estimates from Monte Carlo simulation using a Latin hypercube algorithm to obtain probabilistic values of P10, P50 and P90 for the reservoir are 407.03, 430.38 and 444.10 mmbbl respectively. The regression analysis result using the Tornado chart obtained reveals that PHIE and Fluid contacts have a positive influence and are useful in reservoir modeling, with respect to quantification and ranking of STOIIP.

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