Evaluating Uncertainty in the Volumes of Fluids in Place in an Offshore Niger Delta Field

Evaluating Uncertainty in the Volumes of Fluids in Place in an Offshore Niger Delta Field.

ABSTRACT 

The purpose of this work is to evaluate the uncertainty in the volumes of fluids in place in Fault Block A (Segment 3) of the G-1 Sands in the OND field located offshore Niger Delta. The evaluation was performed in three parts: (1) building of the static model and division into three hydrocarbon zones with reference to the oil-water-contact (OWC).

Stimating the distribution of petrophysical properties such as porosity, water saturation and net-to-gross ratio in the reservoir and; (3) generation of various realizations of the volumes of fluids in place (STOOIP) and evaluation of uncertainty of STOOIP in the OND field.

The first part was executed by building a grid-based model of the reservoir using eclipse and Petrel. A 100 x 60 x 4 grid was built and the faults were created in the model to delineate the reservoir into six segments. The second part of the study involved the calculation of the petrophysical properties that affect the volumes of fluids in place and distributing them in the geologic model.

This was done by assigning various probability distribution functions to porosity, water saturation and net-to-gross; and calculating STOOIP for the three hydrocarbon zones using the method of Monte Carlo simulation. One hundred realizations of STOOIP were generated for each zone in the reservoir.

In the third part of the study the estimates of STOOIP for each zone were plotted as histograms to determine the P10, P50 and P90 values of STOOIP and these yardsticks were used to evaluate the uncertainty of the volumes of fluids in place (STOOIP) in the Fault Block A of the G-1 Sands in the OND field.

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 INTRODUCTION

Reservoir Characterization is a process of integrating various qualities and quantities of data in a consistent manner to describe reservoir properties of interest in inter well locations (Ezekwe and Filler, 2005). The main purpose of reservoir characterization is to generate a more representative geologic model of the reservoir properties.

More so, the goal of any reservoir characterization or reservoir modeling is to understand the reservoir connectivity in static and dynamic conditions by integrating data from different sources (Mondal, 2010). Thus, in building a Geologic representation of what a reservoir is most likely to be, it is necessary to adequately capture the uncertainty associated with not knowing its exact picture (Odai and Ogbe, 2010).

The success of any hydrocarbon exploration and exploitation program depends on the building of a reliable reservoir model. Furthermore, a reservoir’s commercial life begins with exploration that leads to discovery, followed by characterization of the reservoir.

However, the main challenge in reservoir development is the availability of limited data and huge uncertainty. Thus, this makes the evaluation of reservoir uncertainty very important in achieving a good understanding of reservoir management risks. Hence, the use of a practical method for estimating uncertainty without compromising accuracy is therefore clearly needed.

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REFERENCES 

Akinwumi, F. V., Arochukwu, E. C., and Abdul-Kareem, A. S.: “Managing Uncertainties in Hydrocarbon-in-place Volumes in a Northern Depobelt Field, Niger Delta, Nigeria” paper SPE 88880, presented at the 28th Annual SPE International Technical Conference and Exhibition in Abuja, Nigeria, August 2-4, 2004.
Allen, J.R.L.: “Late Quaternary Niger Delta, and Adjacent Areas-Sedimentary Environments and Lithofacies,” AAPG Bulletin, 1965, v.49, p.547-600.
Aprilia, A.W., Li, Z., McVay D.A., and Lee, W.J.: “Quantifying Uncertainty in Original-Gas-in- Place Estimates With Bayesian Integration of Volumetric and Material Balance Analyses,” paper SPE 100575 presented at the 2006 SPE Gas Technology Symposium, Calgary, Alberta, Canada, May 15-17.
Baldwin, D.E.: “A Monte Carlo Model for Pressure Transient Analysis,” paper SPE 2568 presented at 1969 SPE Annual Meeting, Denver, 28 September – 1 October.
Burke, K., 1972, Longshore drift, submarine canyons and submarine fans in development of Niger delta: AAPG Bulletin, v. 56:1975-1983.

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