Evolution of Hydrate Dissociation by Warm Brine Stimulation Combined Depressurization in the South China Sea

Abstract

Abstract:To evaluate the gas production performance of the hydrate accumulations in the South China Sea, a numerical simulation with warm brine stimulation combined depressurization has been conducted. A dual horizontal well system is considered as the well configuration in this work. In order to reduce energy input and improve energy utilization, warm brine (<30 °C) instead of hot brine (>50 °C) is injected into the reservoir for hydrate dissociation. The effect of the intrinsic permeability of the hydrate reservoir, the salinity and the temperature of the injected brine to gas hydrate exploitation have been investigated. The numerical simulation results indicate that the average gas production rate Q avg is about 1.23 × 10 5 ST m 3 /day for the entire hydrate deposit, which has the same order of magnitude compared with the commercially viable production rate. The injected brine can be pumped out from the upper production well directly after the hydrate between the two wells is dissociated completely. Thus, the effective region of heat and inhibitor stimulation is limited. The sensitivity analyses indicate that the dissociation rate of hydrate can be enhanced by increasing the temperature of the injected brine and raising the salinity of the injected brine. The parametric study of permeability shows that the hydrate of the reservoir with the larger permeability has a higher dissociation rate. OPEN ACCESS

Numerical Investigation of Hydrate Dissociation Performance in the South China Sea with Different Horizontal Well Configurations

“…Moreover, Li et al [10] showed that the increase of injection temperature had a limited effect on hydrate dissociation. Feng et al [26] further indicated that warm brine injection had a higher energy ratio than the high-temperature brine injection. In this work, warm brine stimulation combined with depressurization is employed for gas production from the hydrate reservoir.…”

“…Meanwhile, gas and water are pumped out from the right horizontal well (RW) which is conducted under constant-P production. The driving force of depressurization is the same as the previous work [26], in which ΔP W (ΔP W = P W0 − P W ) is 0.44 P W0 . P W = 9.73 MPa is the constant well pressure, and P B = 17.47 MPa is the initial pressure of the HBL at the location of the horizontal well.…”

“…Figure 11 shows the evolution of energy ratio during 30-year production. Energy ratio is the ratio of the recovered energy to the total input energy, which can be calculated [26] as:…”

“…As each single unit represents the same region of hydrate reservoir, each pair of injection well and production well stands for the same region of the hydrate reservoir in Pattern i and Pattern ii. Feng et al [26] carried out a numerical simulation with Pattern i of gas production in the South China Sea by the depressurization combined with warm brine stimulation method. In their work, the injected warm brine can be pumped out directly from the upper well at the 118th day when the hydrate between the two wells is completely dissociated, then the effect of warm brine stimulation on gas production is weakened.…”

“…First a model of a gas hydrate reservoir in the South China Sea is established according to the available data. Based on a previous study [26], a new dual horizontal well system (Pattern ii shown in Figure 2b) is constructed. In this work, the method of depressurization combined with warm brine stimulation is employed.…”