Influence of asphaltene precipitation on development effect of typical heavy oil reservoirs in eastern South China Sea

During the development of heavy oil reservoirs in the eastern South China Sea， asphaltene precipitation can cause blockages in reservoir throats， wellbores， and pipelines， leading to a decrease in the productivity of oil wells. This article took nine typical heavy oil reservoirs in PY Oilfield as an example， selected nine natural core samples with high， medium， and low content of asphaltene， and conducted critical pressure experiments for asphaltene precipitation by using viscosity and light transmission methods. The quantitative relationships between different samples and permeability loss of reservoirs were analyzed， and numerical simulation methods were used to simulate and calculate the influence of different reservoir permeability models and asphaltene damage conditions on the production of oil wells. The research results show that thicker heavy oil in PY Oilfield indicates a higher asphaltene content and a smaller precipitation pressure difference. During the production process， asphaltene is more easily precipitated and deposited. The differences between the reservoir formation pressures and the precipitation pressures of asphaltene （precipitation pressure difference） are 1.55-6.25 MPa. The asphaltene molecules in crude oil precipitate through the cores if the formation pressures drop below the precipitation pressures of asphaltene. They first block small pores and throats and then block large throats and medium-large pores. A higher asphaltene content indicates a greater reservoir permeability loss. The permeability loss of 3 000 mD samples ranges from 20% to 60%， and that of 5 000 mD samples ranges from 20% to 40%. When the formation permeability is higher， asphaltene would quickly pass through large throats and pores after precipitation， and most of them would not precipitate in throats and pores， causing less damage to the reservoir permeability under the same conditions. The precipitation pressures of asphaltene should be kept lower than the formation pressures during the process of heavy oil production， which can effectively avoid the occurrence of asphaltene precipitation damage to the reservoir near the wellbore due to pressure drop and reduce the impact on the production capacity of oil wells.