Preventing Asphaltene Deposition in Oil Reservoirs by Early Water Injection

Abstract

Abstract A comprehensive modeling and simulation of asphaltene precipitation and deposition in petroleum reservoirs is carried out. The effects of the asphaltene deposition on reservoir properties, and the productivity of the vertical and horizontal wells during primary oil recovery are demonstrated. An early water-injection development scheme for suppressing asphaltene deposition is proposed and its feasibility is investigated by means of simulation. The performance of the early water-injection development scheme is compared with the direct depletion development scheme. The results indicate that the early water-injection not only increases the oil recovery significantly but also extends the economic production life of the reservoir considerably. Introduction Asphaltene is the heaviest component in crude oil. It is dissolved in the crude oil under the initial reservoir fluid conditions. However, the changes in reservoir pressure, temperature, and composition may cause asphaltene to precipitate from the crude oil. Therefore, asphaltene can precipitate during primary oil recovery (pressure change), stimulation (temperature and composition change), CO2 flooding (composition change), and hydrocarbon miscible flooding (composition change). Consequently, the asphaltene precipitates separating from the oil may deposit over the pore surfaces and/or plug the pore throats. This causes a decrease in the pore space and/or reduction of the ability of fluid to flow in the formation. Therefore, the deposition of asphaltene in petroleum reservoirs during production can induce significant formation damage and decline of productivity of the wells [1–7]. The asphaltene precipitation process is reversible with pressure decrease across the bubble point 8–9 during the primary oil recovery. Therefore, the modeling and simulation of asphaltene precipitation and deposition in reservoirs during primary oil recovery is different from those in stimulation, CO2 flooding, and hydrocarbon miscible flooding. Most previous modeling efforts focused on the asphaltene precipitation caused by composition change (i.e. with additional components). Only a limited number of studies have dealt with a few aspects of asphaltene precipitation and deposition in reservoirs during primary oil recovery. In this paper, a comprehensive model is presented for prediction of the effects of asphaltene precipitation and deposition on reservoir properties and performance of vertical and horizontal wells during primary oil recovery. A polymer solution model with improved computational features is applied to describe the asphaltene precipitation due to pressure decline during primary oil recovery. A bi-variate asphaltene deposition envelope model is also presented. The asphaltene deposition in porous media is described by means of three deposition mechanisms: surface deposition, pore throat plugging, and re-entrainment of asphaltene deposits into oil. The porosity reduction and permeability impairment caused by asphaltene deposition in pore space are described by an empirical correlation. The modeling approaches are verified by analyzing a series of experimental data obtained by laboratory core tests. Then, a simulator for asphaltene deposition in petroleum reservoirs is developed by incorporating asphaltene precipitation and deposition models, porosity and permeability reduction models, and an asphaltene mass balance equation into a three-dimensional and three-phase black-oil simulator. The simulator is applied to investigate the formation damage and productivity decline of vertical and horizontal wells in multiple-well reservoirs due to asphaltene deposition during primary oil recovery. The effect of asphaltene deposition on reservoir porosity, permeability, and well productivity is investigated. An early water-injection development scheme is suggested and investigated for preventing asphaltene deposition and compared with the direct depletion development scheme.