The Preliminary Study On Methods Of Improving The CO₂ Injection Ability In Low Permeability And Porosity Region

In the process of using CCS technology, we will face a problem inevitably that the supposed reservoirs may have low porosity and low permeability. It is known that petrol industry tends to employ artificial fracturing to improve the permeability and the porosity of a low-productivity oilfield. This technology could be used in CCS, but undoubtedly it will dramatically increase the cost of CO₂ emission reduction.Therefore, the thesis chose the subject that improves the injectivity of a reservoir with both low permeability and porosity through varying injection scenarios ,not by changing intrinsic nature of the reservoirs. With the help of the numerical simulation technology, this paper designed four normal scenarios （the constant pressure 20Mpa and 18Mpa, constant 100000 tons/year and 50000tons/year） and an exploration plan （variable speed 60000tons/year）. An comprehensive evaluation of the sealed layer and effect was conducted by calculating the changes of system maximum pressure and at one moment the state and quality of CO₂ in each layer of the system.This paper used the TOUGH2-MP/ECO₂N to simulate the large-scale perfusion process. By the calculation of seven aspects（ the amount of perfusion, change of hole pressure, mass fraction of gas phase CO₂, reservoir and cap layer charcateristics, the system pressure, the saturation of gas phase CO₂, mass fraction of water solution phase）, the sealed layer and effect was evaluated comprehensively.In the process of five simulations, the paper compared the differences of each scheme, and made the quantitative analysis of the sealed system in general. On the perfusion amount side, the scheme of the constant pressure 20Mpa was the best. Of the two quantitative schemes, the hole pressure changed severely at the beginning, and tended to be stable at a later time. When the perfusion terminated, the mass fraction of CO₂ decreased gradually, which showed that the system tended to be stable. However, the scheme of constant pressure could not give the conclusion.Through the calculation of the five schemes, the CO₂ levels kept low in the sealed layers all the time, which demonstrated that the system owned a good characteristic and could seal CO₂ long and safety. At the end of it, the system pressure also restored to initial condition gradually. The gas phase CO₂ and water soluble phase CO₂ had the same characteristic in the distribution. In the horizontal level, they showed no difference, while they expanded vertically in some degree.But they were all kept in their position, which meaned that the closure of the whole system was good.