A serious and complex problem in hydrocarbon recovery is the asphaltene precipitation since it affects all aspects of petroleum production, processing, and consequently transportation. It is very desireable to predict and simulate the asphaltene precipitation during upstream recovery processes from oil and gas reservoirs. Many models have been developed to predict the precipitation behavior of asphaltenes.

We present implementation of an asphaltene precipitation model into a fully implicit, 3D, parallel, multiphase, multicomponent, EOS compositional simulator called GPAS developed at the Center for Petroleum and Geosystems Engineering to model the phase behavior and simulate the dynamic aspects of the asphaltene precipitation problem that occurs in oil and gas reservoirs.

After studying many models for asphaltene precipitation available in the petroleum engineering literature, testing and utilizing various simulators (e.g. ECLIPSE, CMG, VIP) to simulate the problem under primary depletion, CO2 and water flooding scenarios, a particular thermodynamic approach was chosen to be implemented in the GPAS simulator. This model treats the precipitating asphaltene as a single component residing in a pure solid phase, while hydrocarbon phases are modeled with an EOS.

The primary goal of GPAS, currently under development, is to support realistic, high-resolution reservoir studies using millions of gridcells on massively parallel computers. Key features for this simulator include the ability to handle multiple physical models, multiple fault blocks, and flexible gridding.

With the incorporation of asphaltene simulation into GPAS, many equations in the original code were modified, added, and implemented including the phase equilibrium, volume constraint, and mass conservation equations. Multiphase flash calculations were developed to predict the onset point and the amount of asphaltene precipitation throughout the life of a reservoir. Since this phenomenon severely damages the physical properties of formation, models were also implemented to estimate the effects on porosity, relative permeability, and wettability. The fully implicit formulations of GPAS added a great deal to the complexity of the formulations.

Simulation results indicate that asphaltene precipitation reduces oil production. A key conclusion of the achivements is the capability to predict the detrimental effects of asphaltenes in reservoirs without the need for data generation from expensive downhole samples. This research also led to a more powerful reservoir simulator that can be used by E&P companies to predict asphaltene precipitation in reservoirs and help with the design of primary and secondary recovery processes on their desktops or clusters of computers to solve E&P challenges of the future.

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