Abstract

Asphaltene precipitation and deposition models were established and verified by typical experimental data. These models, the porosity and permeability reduction models, and the asphaltene mass balance equation were incorporated into a three-dimensional, three-phase black-oil simulator. Two typical cases involving asphaltene deposition in petroleum reservoirs associated with vertical and horizontal wells were investigated using the simulator. During the three-year period of production, the productivity index declined more than 50 % for both the vertical and horizontal wells. The pattern of asphaltene deposition in the reservoir with a horizontal well was found to be different from that in the reservoir with a vertical well.

Introduction

The existence state of asphaltene in crude oil is different than in solvent [1]. The crude oil containing asphaltene is a real solution, but asphaltene forms aggregation in solvent [1]. The process of asphaltene precipitation in hydrocarbon miscible flooding is also different from that due to pressure depletion during primary oil recovery [1]. The detailed review of the existence state of asphaltene in crude oil, and the precipitation and deposition of asphaltene in petroleum reservoirs is given in Table 1–7 by Wang [1].

In this paper, an asphaltene precipitation model is developed and verified by a typical experimental data. Then, a porous media deposition model for asphaltene is established and applied to six sets of experimental data. Finally, the precipitation and deposition models for asphaltene as well as other auxiliary models are incorporated into a three-dimensional, three-phase black-oil simulator. Two typical cases are evaluated with the simulator and representative results are reported.

Asphaltene Precipitation Model

The polymer solution theory represents the existence state of asphaltene in crude oil more accurately than the colloidal theory [1]. Hirschberg et al. [11] first applied the polymer solution theory to simulate the asphaltene precipitation problem. By combining the Flory-Huggins theory for polymer solution and Hildebrand solubility concept, Hirschberg et al. [11] obtained the following equation:

  • Equation (1)

where, fA is the volume fraction of asphaltene dissolved in the crude oil. VA is the molar volume of asphaltene, assumed constant. VL is the molar volume of liquid phase, calculated with the modified Benedict-Webb-Rubin state equation in the Hirschberg et al. model. R is the universal gas constant and T is the absolute temperature. dL is the solubility parameter of asphaltene, given as :

  • Equation (2)

where h is a specific constant for each oil and dL is the solubility parameter of the liquid phase defined by [49]:

  • Equation (3)

where ?Uvaporization is the internal energy change during the vaporization of a unit mole liquid.

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