Natural Gas Industry B (Dec 2022)
Evaluation of the heat extraction performance of an abandoned well pattern in multilayer commingled production oil reservoirs
Abstract
Oilfield geothermal energy is one important part of geothermal resources, and it can be developed and used for power generation and heating. The geothermal reserves and production of multi-layer sandstone oil reservoirs account for 50% of the total geothermal reserves and production in China, respectively, but due to the influence of interlayer heterogeneity, interlayer interference is common in the process of geothermal development by water injection. Therefore, it is in an urgent need to evaluate the heat extraction performance of oil-bearing geothermal reservoirs in multi-layer commingled production. Taking a depleted oil reservoir (and even a high- or an extra-high water-saturation oil reservoir) as the research object, this paper establishes a numerical model of coupled oil–water two-phase heat flow in a multi-layer commingled production oil reservoir. Then, interlayer interference characteristics and temperature and pressure distribution situations under different porosity, permeability and initial oil saturation are compared. Finally, the influence of interlayer interference on heat extraction performance is analyzed. And the following research results are obtained. First, under the research conditions and model settings of this paper, the injection–production pressure difference and production temperature difference between low-permeability layers and high-permeability layers of the reservoir with different permeability after 20 years' production are up to 3.27 MPa and 24.5 K, respectively, which are much higher than the corresponding differences of oil-bearing homogeneous reservoirs. Second, the lower the initial oil saturation, the smaller the reservoir production temperature and injection–production pressure difference. And after 20 years, the maximum difference is 1.32 MPa. Third, interlayer interference is sensitive to permeability. The fluid in the high-permeability layers comes from the injection well of the same layer and low-permeability layers. The production temperature of the reservoirs with different permeability can rise by 5.33 K at most. In conclusion, permeability is the key parameter influencing production temperature and injection–production pressure difference of oil-bearing reservoirs while porosity has less influence on production behaviors. In addition, injection–production pressure difference is more sensitive to the change of initial oil saturation and the existence of oil phase can increase the injection pressure significantly. Furthermore, if there is a boundary geothermal source, the reservoirs with strong interlayer interference can obtain high heat extraction more easily, so this type of reservoirs can be given priority in the heat extraction of abandoned wells.
