Abstract

The deposition of asphaltene is considered to be one of the most difficult problems during oil production. The mechanism of Asphaltene precipitation and deposition is not fully understood until now. Asphaltene deposition in the reservoir is a complex problem and due to high depth of reservoir, it is impossible to do field experiments. Laboratory tests are expensive and time consuming. In order to study effects of asphaltene deposition, it is be necessary to rely on different models which are developed for Asphaltene adsorption and deposition. These models consist of several matching parameters. Iteration method was used to obtain an acceptable match for experimental data. Deposition equations are highly coupled therefore deposition parameters cannot be optimized independently. Due to dependency of parameters, ordinary optimization methods are not applicable for deposition.

In this paper we introduce a new model for asphaltene deposition in porous media and corresponding numerical method was developed using implicit scheme, then a procedure for matching the asphaltene deposition and adsorption parameters was described and a new optimization method was introduced. In this method genetic algorithm was applied and the result of it was used as input for direct search to obtain an acceptable match for experimental data.

Introduction

Asphaltene is the heaviest component of crude oil. Commonly asphaltene define a fraction that is soluble in toluene or benzene and insoluble in low boiling alkanes such as n-pentane or n-heptane. At initial reservoir condition asphaltene is dissolved in crude oil. Asphaltene can be precipitated due to change in specific reservoir condition such as pressure, temperature, and composition. In fact, Asphaltene can precipitate during primary oil recovery, flooding, and hydrocarbon miscible flooding. Asphaltene precipitates may deposit to the surface of pores or plug the pore throat causing permeability reduction, wettabillity alteration and formation damage.

The mechanism of Asphaltene precipitation and deposition is not fully understood until now. Asphaltene deposition in the reservoir is a complex problem and it is impossible to do field experiments. Laboratory tests are expensive and time consuming. In order to study effects of Asphaltene deposition, it is becomes necessary to rely on different models which are developed for asphaltene adsorption and deposition. The lack of information makes modeling and simulation of asphaltene deposition become difficult. No satisfactory model and simulator are available for asphaltene deposition in reservoirs during primary oil recovery. Therefore, it is necessary to obtain the better understanding of the problem and establish a better model to simulate the asphaltene precipitation and deposition in petroleum reservoirs during primary oil recovery.

Formulation

In order to develop a mathematical model for asphaltene deposition and adsorption in core test the following assumption are made:

  1. The effects of gravity are not included in the derivation of models, based on the assumption that the flow in core tests is usually one-dimensional and horizontal.

  2. Capillary pressure is also considered negligible because asphaltene precipitation and deposition involve only liquid phase.

  3. It is assumed that no connate water occurs in cores in asphaltene deposition tests.

  4. Oil, gas and asphaltene are at the same temperature and temperature is constant during the tests.

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