Giant reservoirs of Middle East contain substantial portion of the world's total hydrocarbons. Accurate simulation of these reservoirs requires as many as billion cells. A billion-cell parallel reservoir simulator was first presented in 2009. This paper discusses the progress in the past two years and future projections. In addition to black oil models, paper presents a large full field compositional model involving over billion unknowns. Throughout the paper grid size effects, computational work distribution and parallel scalability are discussed and illustrated. Paper also presents futuristic technologies for building and analyzing large simulation models.
This paper describes an application of a Massively Parallel Reservoir Simulator for a Giant Carbonate Reservoir with faults, fracture and Super-K zones. It is shown that by using a multi million cell description, premature water breakthrough and complex reservoir behavior is captured with minimum up scaling of the original geological description. The new technology used in this work provides significant reduction in simulation model construction and history matching time. Super-K is a well-known phenomenon in parts of Ghawar where it provides extremely large conductivity to fluid flow. These formations are comprised of vugs, faults, fractures and stratiform dolomite rocks. They form effective flow conduits for water and impact the overall sweep. For the proper accounting of complex heterogeneities, a portion of the reservoir was simulated using a 2.5 million-cell reservoir simulation model. The fault map from the 3-D seismic was incorporated; a thin layer described stratiform Super-K layers with 70 Darcy permeability. A dual porosity type grid was imposed to handle the high permeability conduits. The fine grid in the area of interest was gradually coarsened for the proper accounting of boundary fluxes. This model with over 50 years of history and about 800 wells, was run using Saudi Aramco's parallel simulator, POWERS1. The total execution time was 4 hours. Premature water breakthrough in the middle of the reservoir was matched closely. The phenomenon of water movement in the vertical direction was duplicated as observed in the field. This study has shown that the ability to handle extreme heterogeneities leads to a more realistic history match. State of the Art technologies enable engineers to build, execute and complete the history match in a few months. Introduction The Ghawar field is the world's largest oil reservoir. Oil production from this field is sustained by peripheral water injection. This giant carbonate field contains faults, fracture and Super-K zones2. The Super-K zones behave like high velocity flow conduits. These heterogeneities have lead to premature water breakthroughs in certain parts of the reservoir. The objective of this work is to capture the complex geological features described above using a relatively fine grid multi million-cell simulation model so that the resulting model could be used to forecast future reservoir behavior. Another objective of this work is to construct the simulation model and obtain a history match in a reasonable period of time (a few months and not years as is normal for a giant oil reservoir). New technology in processing huge amounts of data fast and state of the art parallel reservoir simulation coupled with efficient visualization tools to view the results have been used in this work. The focus of this paper will be limited to the two main objectives of this work. Discussions of the efficient visualization capabilities for multi million-cell models and next generation technologies are presented in a companion paper3. Saudi Aramco's proprietary simulator, POWERS1 was used to simulate the Super-K behavior. POWERS was built from scratch to run on parallel supercomputers to model the giant oil reservoirs in Saudi Arabia. To adequately simulate the performance of these fields, multi million-cell model simulation capabilities are essential. State of the art parallel processing technology was used in developing POWERS to ensure that these simulations can be performed in a reasonable amount of computer time (usually a few hours).
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