Quantifying the Uncertainty of the Ultimate Recoverable Oil Reserves Using the Monte Carlo Simulation Techniques From ‘OWA’ Marginal Field, Onshore Niger Delta, Nigeria

Abstract

A review on the development of marginal oil fields in Nigeria has now become an important strategic issue if she must remain amongst the top producers in the global market, and these fields are vast available all over the Niger Delta. Four (4) deviated wells and 3D seismic volume (362 inlines and 401 traces) were interpreted for the evaluation of the field. The petrophysical evaluations were interpreted using the Power Log software and the seismic, Geographix and Petrel software. Stochastic reserves estimation were done using Monte Carlo sampling techniques and subjected to uncertainty quantification using the Crystal Ball software. Production profile was predicted based on some assumptions and history matching which resulted in the overall Expected Ultimate Recovery (EUR). The development of the field was further considered by running the cashflow analysis and establishing the economic indications. Nine (9) hydrocarbon sands were identified but only three (3), (B1, D and E), representing shallow, mid and deep reservoirs were further evaluated. 1P and 2P reserve estimates were 4.8MMBO and 5.7MMBO for B1; 15.2MMMscf and 16.4MMMscf for D; 8.4MMMscf and 8.8MMMscf for E respectively. The Monte Carlo Simulation of 1,000,000 trials with mainly triangular distribution assumption generated P10, P50, P90 were 6.5MMBO, 5.6MMBO and 4.4MMBO for B1; 17.5MMMscf, 13.7MMMscf and 10.8MMMscf for D; 10.4MMMscf, 8MMMscf and 6.1MMMscf for E respectively. The sensitivity analysis and coefficient of variability of about 15%, 19% and 20% for B1, D and E respectively indicated that there is a very low level uncertainty of reserve estimation based on the distributions of input parameters. The two-well scenario gave up to 80% EUR (4.7bbls) before abandonment rate for a field life of about 15 years. The cashflow analysis showed an attractive marginal project with positive Net Present Value (NPV) for the $50/bbl base oil price scenario and the contractor’s take was estimated to be about 22% of the total share. The greatest effect on the NPV was seen from the Petroleum Profit Tax and the oil price in the sensitivity analysis which is negative and positive respectively. OWA marginal field reflects a typical low reserve development category and with effective cost management even at extreme low crude oil prices, a marginal profit can be ascertained and eventually fostering the Nigeria economy.

AAPG Datapages/Search and Discovery Article #90332 © 2018 AAPG International Conference and Exhibition, Cape Town, South Africa, November 4-11, 2018