Online Journal for E&P Geoscientists

Al Shemsi, Abdullah H.¹; Khemissa, Hocine ^*1; Fathalla, Magdy ¹; Walia, Samir ²
(1) ADMA-OPCO, Abu Dhabi, United Arab Emirates. (2) Roxar, Abu Dhabi, United Arab Emirates.

Upscaling is required to build reservoir simulation grids model guided by the criteria’s, the design has to retain the structure and the heterogeneity of the detailed geological model, it has to be able to meet reservoir management needs in defining new drilling well locations, sidetracks and workovers, the simulation layers have to be detailed enough to define any vertical barriers, high permeability streaks and to handle any changes in flow or storage capacity.

The reservoir corresponds to an alternate of high heterogeneous porous and dense layers, with lithology limestone and dolomite, vugs and high permeability streaks.

To maintain our reservoir heterogeneity during Upscaling, a difficulty was faced which is simulation “CPU” capability. Therefore, a new method called ‘optimal simulation grid design’ provided by IRAP/RMS (SPE 95759 King , et al.) has been applied to upscale a large geological model with objectives to capture maximum heterogeneity in simulation grid keeping in mind “CPU” limitation (computing speed and time and create the irregular 3D grid in all I, J and K direction.

In the present case study, challenge was to upscale the 20 million cell size fine geological grid up to 2.5 million cell size simulation grid. The “optimal simulation grid design” is a recursive algorithm works by merging two adjacent layers with the minimum variation change, until a single layer model is generated. This algorithm is using the model properties such as bulk volume, porosity, permeability and rock type as input to quantify the heterogeneity.

The lateral and vertical heterogeneities were calculated for each zone. The heterogeneity versus model layers was plotted and the number of irregular Column, Row and Layer versus the heterogeneity was optimized. Later on the facies and properties were up scaled to the simulation grid. Various methods such as histograms, scatter plots and streamline simulation have been used to compare properties between geological and simulation grid. The high quality of simulation grid and Geological heterogeneity are also confirmed by reservoir engineer.