Abstract
The main purpose of this study is to investigate the production behaviors of gas hydrate at site DK-2 in the Qilian Mountain permafrost using the novel five-spot well (5S) system by means of numerical simulation. The whole system is composed of several identical units, and each single unit consists of one injection well and four production wells. All the wells are placed horizontally in the hydrate deposit. The combination method of depressurization and thermal stimulation is employed for hydrate dissociation in the system. Simulation results show that favorable gas production and hydrate dissociation rates, gas-to-water ratio, and energy ratio can be acquired using this kind of multi-well system under suitable heat injection and depressurization driving forces, and the water production rate is manageable in the entire production process under current technology. In addition, another two kinds of two-spot well (2S) systems have also been employed for comparison. It is found that the 5S system will be more commercially profitable than the 2S configurations for gas production under the same operation conditions. Sensitivity analysis indicates that the gas production performance is dependent on the heat injection rate and the well spacing of the 5S system.
Highlights
Natural gas hydrates (NGH) are crystalline compounds formed by water and small gas molecules under suitable thermodynamic conditions
Simulated the gas production from the Mount Elbert gas hydrate deposit by depressurization using both vertical and horizontal wells, and the results showed that the horizontal wells could increase the production rates by almost two orders of magnitude when comparing with the vertical wells
The novel five-spot horizontal well system is employed for the gas production from the hydrate reservoirs of DK-2 drilling well in the Qilian Mountain permafrost
Summary
Natural gas hydrates (NGH) are crystalline compounds formed by water and small gas molecules under suitable thermodynamic conditions (low temperature and high pressure). A lot of scientific drilling and exploration projects have been implemented for the verification of gas hydrate occurrence, the evaluation of its resource potential, and the field testing of the production strategies [2]. Natural gas was successfully extracted from gas hydrate in the seafloor in Pacific waters off Japan during the hydrate exploitation research program in 2013, which provided direct evidence for the possibility of gas production from natural oceanic hydrate deposits. Because of the ever increasing energy demand in China, natural gas hydrates have been studied as a kind of potential and challenging energy resource in this country. After the gas hydrate samples were obtained in the Shenhu area of the northern South China Sea in May 2007, core samples containing gas hydrate were successfully collected from the scientific drilling wells in 2008–2009 in the Qilian
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