The Benefits of Enhanced Integration Capabilities in 3-D Reservoir Modelling and Simulation
Authors: O&apos;Rourke S.T. , Ikwumonu A. 
Published: December 2007

The use of proprietary, closely linked 3-D geological and reservoir simulation software has greatly enhanced the reservoir modelling process by enabling complete integration of geological and engineering data in a 3-D manner. The software were used to model and simulate a deltaic sandstone reservoir in the Nigerian Forcados Yokri field in order to describe the reservoir sweep pattern. A simple simulation of the reservoir was first carried out to identify the main controls on the reservoir performance, which in this case were the intra-reservoir shales. As they are the only baffles or barriers to flow, proper modelling of them was critical to achieving a history match. Well logs, 3-D seismic, limited core data and sequence stratigraphic concepts were used to define a three dimensional depositional model which was then used to guide the 3-D reservoir architecture modelling. The reservoir model was evaluated in the 3-D simulator and, when the initial model did not yield a proper match with the historical production data, alternative models were easily generated and simulated until an acceptable match was achieved. The result was a 10% increase in predicted ultimate recovery, a better understanding of the reservoir and an optimized reservoir depletion plan.

Introduction

With many of the world's hydrocarbon producing basins rapidly maturing, more and more staff time is being devoted to improving ultimate recovery from older producing fields. Increasingly, such studies are carried out using a completely three dimensional (3-D) approach. The field is mapped with 3-D seismic data, the reservoir architecture is modelled and visualized in 3-D, and the resultant geological model is then used as input to create a 3-D simulation of the reservoir's production. While this approach often results in a much better understanding of the producing reservoir, it is not without its difficulties. One of the major problems has been the inability to easily integrate the geologic and reservoir engineering data in the modelling and simulation process. Often, geologic models of the reservoir are constructed based only on well and seismic control without consideration of the reservoir production performance. This results in poor matches with the historical production data and an incorrect prediction of reservoir sweep patterns, efficiency, etc.

This paper describes how the data integration problem was overcome through the use of closely linked, Shell proprietary 3-D reservoir modelling and simulation software (GEOCAP 2 and MoReS, Refs. 1,2 & 3). These software were used to model and simulate a deltaic sandstone reservoir in the Nigerian Forcados Yokri Field (Fig. 1), Shell Petroleum Development Company's (SPDC) largest oil field. The study was carried out to describe the reservoir sweep pattern and identify by-passed oil in the northern fault block of the field (Fig. 2). The modelling and simulation results were so promising that the study was later expanded to model the entire D5.0 reservoir, which contains over 30% of the field's reserves.

Modelling and Simulation Methodology

The reservoir modelling and simulation were carried out in three steps. First, a simple "layer-cake" model of the reservoir was simulated to identify the main controls on reservoir fluid flow and production. Next, the information gained from the simple model was used to guide the geological modelling of the reservoir architecture. Thirdly, the reservoir model was upscaled and input into the simulator, where the results were used to refine the reservoir architecture until a satisfactory production history match was obtained. The reservoir production was then simulated until depletion, enabling estimates of ultimate recoveries, sweep patterns, etc.

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