The Reservoir Temperature-Pressure Modeling Study Of Gas Hydrate Exploitation By Heat Injection And Depressurization

Hydrate has certain temperature and pressure, when temperature and pressure change, the hydrates will break down. As a result, not only the stress but also the temperature will change during exploitation. By simulating the heat injection and depressurization mining model, this paper studied the change laws of temperature and pressure during hydrates exploitation.Firstly, various models of hydrates expoitation are summarized in this paper. Simulated from the hydrates depressurization mining model, the changes of temperature and pressure in reservior are analyzed: as hydrates decomposition, the reservior temperature from wellbore to decompose frontier rises over time, the temperature gradient declines; Pressure from the wellbore to the decompose frontier increases over time, the pressure gradient declines too.By considering the the heat injection and the depressurization mining model comprehensively, this paper put forward the heat injection and depressurization mining physical model. In this model, a quality and energy conservation equation and its dynamic equation are analyed, the hydrate physical parameters are caculated, the pressure and the saturation are obtained through the difference computation of quality equation, the temperature distribution in formations are obtained through the difference computation of enegy equation.Thus lay the foundation for the next simulation.In the heat injection and depressurization model, the changes in temperature, pressure and saturation during the first and the second cycles are simulated, and the relation of the hydrates decomposition versus time is analyzed. Research showed that the temperature, pressure and saturation have a inflection point when the depressurization completes or the heat injection starts, the inflection point represents depressurization has been completed, and then the heat injection process begins; Meanwhile, the gas production rate changed in a curve, and it can be divided into three stages: drop, rise, drop again. Finally, this paper made the sensitivity analysis of factors such as the permeability and the temperature, the results showed that the permeability affect the decomposition rate by changing the spread rate of the pressure drop, and the temperature influence the decomposition rate by changing the balance pressure of hydrates. The higher the absolute permeability and the temperature are, the faster is the hydrates decomposition and the gas procuction rate.