MPP Simulation of Complex Water Encroachment in a Large Carbonate Reservoir in Saudi Arabia

Abstract

Reservoir simulation has entered a new era with the advent of massively parallel processing and its ability to handle millions of cells. In this study a simulation model was constructed from the geologic model without scale up, the resulting model having 1.38 million cells. The majority of effort was spent on reviewing geologic and engineering data. History match changes were made at the well level and interpolated in Kh and Kv arrays using a deterministic mapping routine. Despite the complexity and model size, a successful history match was achieved in 40 runs. The model has been very successful in identifying well locations for bypassed oil recovery. Introduction Reservoir simulation projects are often a balance between complexity to (presumably) produce more accurate results and reasonable computer turn-around time. Because of constraints in computer resources conventional simulation technology usually requires upscaling of high-resolution geology. Recent developments in massively parallel processing (MPP) computer technology have dramatically increased computer horsepower giving us the choice of either enhancing geologic and/or engineering complexity or enjoying faster turn-around.1,2,3 Is more complexity worth it? Will a high-resolution model better replicate the physics in the reservoir? Will we be able to make better decisions with a high-resolution model? In this case study, the Hadriya reservoir in Berri field was chosen as a test case for Saudi Aramco's new POWERS MPP simulator.4 This large carbonate reservoir has been on production since 1970 and peripheral waterflood since 1975. Water encroachment into the reservoir is complex with extensive water-over-oil bypassed areas. The decision was made to simulate this reservoir at the scale of the geologic model. Background Berri Hadriya has been on production since 1970 and peripheral waterflood since 1975. Remaining development options are mainly in bypassed areas behind the floodfront or in dry areas of lower rock quality. The overall objective of this project was to guide development drilling especially in the bypassed oil areas. The Berri Hadriya reservoir is characterized by highly permeable intervals separated by thin tight streaks that influence water encroachment. To maintain reservoir character and capture the complex water encroachment, the decision was made to simulate the reservoir at the scale of the geologic model. The resulting simulation model has 1.38 million cells. During the history match only permeability was changed. Structure, cell thickness, porosity and facies from the geologic model were unchanged. The overall strategy was to make changes only at well locations and use a mapping program to rebuild the model for each run. Where available, core data, pressure buildups and flowmeters would be honored.