Monte Carlo (MC) Assessment of Structurally-Controlled Shallow Offshore “Teldomi” Reservoirs, Niger Delta, Nigeria - Inferences from 3D Seismic and Wireline Log Data

Abstract

Monte Carlo Simulation (MCS) was used to assess the properties of three structurally controlled reservoirs namely, Reservoir A, Reservoir B, and Reservoir C in the study area. Geologically plausible ranges specified by the mean and standard deviation values of the initial petrophysical parameters of gross pay volume (GPV), net-to-gross (NTG), porosity (POR), and hydrocarbon saturation (S_h) were estimated from six wells and 3D seismic data. The MC simulation consisted of the generation of independent random values, representing the uncertainties constrained by a random probability distribution. For each randomly simulated combination of these parameters, original-oil-in-place (OOIP) was simulated. This process was repeated ten thousand (10000) times for each parameter after which the cumulative distribution functions (CDFs) for the simulated parameters were constructed from which summary statistics, risks and uncertainties were determined at P10 (downside), P25, P50, P75 and P90 (upside). Between the downside and upside probabilities, the GPV would be more than 13000 acre feet but less than 141000 acre-feet; the NTG would be more than 0.43 but less than 0.84; the porosity could be as low as 6% but not more than 29%; the hydrocarbon saturation would be more than 36% but less than 100%. At any given percentile, Reservoir C contains more hydrocarbon than the other two reservoirs but has the highest uncertainty. The three reservoirs would have more than 16 million barrels at P10, but not more than 111.5 million barrels combined in-place oil volume at P90. The results obtained can guide optimal future development decision on the reservoirs in the study area and thus confirmed MC simulation as veritable uncertainty modelling tool.

Keywords: Monte Carlo, Structural, 3D Seismic, Wireline Log, Reservoir