Article outline

The purpose of this paper is to simulate the process of substituting methane in a hydrate reservoir by injecting liquid carbon dioxide into it, because this can solve two problems - the extraction of natural gas and the utilization of carbon dioxide.

Methodology. The first stage is solved by the method of finite differences using the explicit-implicit scheme. To do this, a uniform spatial and non-uniform time grid is constructed, the time step is selected so that in the time interval the boundary of the moving front is shifted exactly by one step of the spatial grid. The system of equations of the second stage is solved by the method of finite differences using the explicit scheme. The stability condition was determined from the Courant condition.

Findings. It is shown that in the first stage (piston displacement) for 4 minutes, the carbon dioxide consumption and methane gas output remain constant, since free gas is expelled from the pores. At the second stage, carbon dioxide begins to be consumed and the amount of methane gas released increases from zero, the highest value of which is achieved 6 minutes after the start of hydrate formation, which corresponds to the time when the front of the filtered gas filter reaches the right boundary. The next stage (from 10 to 40 minutes) is characterized by a decrease in the methane gas output due to a decrease in the concentration of dissolved gas in the formation, the carbon dioxide intake and output flow begins to approach the same value. After the completion of hydrate formation (after 40 minutes), the remaining gas is washed out of the formation.

Value. It is shown that the process of methane replacement in a hydrate reservoir by injecting liquid carbon dioxide into it can consist of the following steps: piston displacement of free gas from the pores; replacement of methane with liquid carbon dioxide, its dissolution and leaching from the formation; completion of hydrate formation and leaching of the remaining methane gas from the hydrate reservoir.