Formulation of the Re-Development Scheme: Reservoir Modeling for the Highly Heterogeneous Reservoir to Assess IOR
Authors: Doi M. , Suzuki S. 
Published: December 2007

Qualified asset management requires optimum re-development scheme to the matured fields applying IOR options. The keys for successful re-development planning are to evaluate the uncertainty of the reservoir properties and how to integrate technology available in the reservoir simulation study targeting realistic flow modeling.

A reservoir re-development scheme was formulated for a highly heterogeneous limestone reservoir which has production history for more than 35 years. Systematic approach was made to improve the accuracy of the reservoir simulation model when water or associated gas injection was considered. The uncertainty range of the reservoir rock properties was first investigated to assess the past reservoir practice. Then, the evaluation of the gas injection was performed with high resolution reservoir simulation. After examining PVT properties, discussions were made to preserve the fluid flow characteristics in the heterogeneous reservoir on the coarse gridded flow simulation model, which was up-scaled from the fine scale model realized by the geostatistical approach. The grid block size was carefully selected by a number of numerical experiments to simulate the heterogeneous nature. The impact of the up-scaled vertical permeability on the gas injection performance was also evaluated. The 3D-flow based up-scaling technique for near-well region was examined in order to simulate the horizontal well performance in the reservoir scale simulation model.

It was concluded thatthe rigid IOR assessment was achieved presenting superior performance of gas injection than that of water injection through high resolution reservoir simulation, thatthe application of streamline method for evaluating vertical permeability of up-scaled grid made well-preserved heterogeneity in the fine scale model and thatThe 3D well model for horizontal well is required only when the duration of the displacement front advancement in near well region significantly exceeds the time step size.

Introduction

The Khafji Oil Field is situated in the offshore neutral zone between the Kingdom of Saudi Arabia and the State of Kuwait. The studied limestone reservoir in the field has been producing heavy crude oil for more than 35 years. Since the reservoir has little natural support of driving energy noticed by the sharp decline of its pressure, IOR application is essential for efficient reservoir development. This paper describes the systematic approach to improve the reliability of numerical reservoir simulation for the IOR assessment.

Recently, intensive geological and reservoir engineering studies were carried out to clarify the reservoir nature, and the results were integrated into a fine scale geostatistical model and a coarse grid flow simulation model. The geostatistical model satisfactorily described the spatial distribution of the petrophysical characteristics, and the up-scaled flow simulation model adequately reproduced the past reservoir performances. 1 However, when the reservoir development scheme with IOR is adopted, the reservoir is going to encounter at the extreme pressure / saturation conditions which have never happened in the past production history. Modeled reservoir elements which may affect the simulation results should be examined and re-evaluated to assure the reliability of prediction.