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Shagapov V.Sh., Davletshina M.R. On the theory of hydrate formation decomposition under thermal influence. Multiphase Systems. 14 (2019) 4. 243–252 (in Russian).
2019. Vol. 14. Issue 4, Pp. 243–252
URL: http://mfs.uimech.org/mfs2019.4.031,en
DOI: 10.21662/mfs2019.4.031
On the theory of hydrate formation decomposition under thermal influence
Shagapov V.Sh., Davletshina M.R.∗∗
Mavlyutov Institute of Mechanics UFRC RAS, Ufa
∗∗Ufa State Petroleum Techologial University, Ufa

Abstract

A mathematical model of the process of decomposition of gas hydrate during heat exposure is proposed and developed. Based on the proposed technological scheme and the corresponding theoretical model, the problem of the action of a heat source on a porous layer of finite length, initially saturated with methane hydrate, is considered. The task describes the heating and simultaneous extraction of gas into a combined well. According to the adopted scheme, a coolant in the form of hot water is supplied to the annular channel, and the internal well communicates with the formation and gas is produced there, which was formed during the hydrate decomposition as a result of thermal exposure. The influence of the temperature of the heat source on the evolution of thermal fields around the well, on the nature of the motion of the phase transition boundary, is studied, and the law of its motion is obtained. The heat consumption for heating the formation and the evolution of gas output over the considered time interval at various values of the heating temperature and pressure drop are analyzed. The dynamics of the gas mass flow rate and the energy efficiency of methane production at various values of the temperature difference between the reservoir and the fluid injected into the heat pipe are revealed. A quasistationary solution is obtained that corresponds to the case when a pressure is maintained in the well equal to the equilibrium value for the initial temperature of the gas hydrate formation. The dependence of the energy efficiency of the proposed method of gas production on the porosity of the formation is analyzed. It was established that with a twofold increase in the hydrate content of the formation, this value grows by about ten percent. The obtained solutions make it possible to determine the most favorable heat exposure regimes. Moreover, this solution is in good agreement with the numerical results obtained by a more general theoretical model.

Keywords

gas filtration,
gas hydrate,
phase transition,
quasi-stationary solution,
heat-transfer

Article outline

The purpose of this study is to build a theoretical model that describes the processes of decomposition of hydrate in the reservoir under thermal influence and the selection of the formed gas.

A homogeneous porous layer of finite length is considered, containing in the initial state only methane hydrate. Let a well be drilled in the formation through which hot water is pumped, the temperature of which is kept constant during the entire decomposition process. The gas formed during the decomposition of the hydrate will enter the inner well. As a result of the thermal effect of the well - reservoir system, two regions are formed in the reservoir: the near one, saturated with hydrate decomposition products (gas and water) and the distant one, containing only hydrate in its composition. Therefore, it is assumed that the decomposition of the hydrate into water and gas occurs at the front boundary between these areas.

Methods of solution: The numerical solution of the original system of partial differential equations is carried out according to an explicit scheme by the method of catching the front in a node of the spatial grid.

Results: The problem of the possibility of decomposition of a gas hydrate reservoir under thermal influence was solved. For a radial problem with a frontal boundary of phase transitions, solutions are constructed that describe the temperature fields, as well as the dynamics of the motion of the boundary of hydrate decomposition and the mass flow rate of gas. Comparison of numerical solutions with analytical ones is given, which agree for small times. In addition, an analytical solution is obtained, assuming that the decomposition of the gas hydrate includes quasi-stationary processes.

Conclusion: The solutions obtained will make it possible to analyze various modes of thermal impact from the point of view of energy efficiency of methane production and the feasibility of developing such deposits.

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