Gas Permeability and Production Potential of Marine Hydrate Deposits in South China Sea

Abstract

The permeability of marine sediments is critical to the gas production assessment of hydrate reservoirs. In this work, the sample of natural marine sediments was obtained from Shenhu Area of South China Sea at the depth of 1600 m, and the gas permeability of the sample was measured in the laboratory under various confining pressures. The porosity of the sample decreased from 41.82% to 29.54%, and the effective gas permeability of the sample decreased from 2.638 × 10−16 m2 to 0.872 × 10−16 m2 as the confining pressure increased from 0 to 23 MPa. The gas permeability of the natural sediments was determined to be 1.535 × 10−16 m2 with confining pressure of 15 MPa and porosity of 32%. The deformation of sample in longitudinal direction was sensitive to the confining pressure, and the compressibility in the radial direction was limited. On the basis of the experimental results, the particle size term in the classical Kozeny–Carman equation was revised by correction factor N, and the experimental results fitted well with the curves with N = 2.40. Moreover, the gas production potential at the site of W–17 in the Shenhu Area was numerically studied based on the measured gas permeability. The simulation results showed that the cumulative volume of produced gas was approximately 1.46 × 106 ST m3 after 30 years. A new enlarged permeable well wall method was proposed to improve the poor gas production caused by low permeability. The cumulative gas production increased by 2.7 times as the permeable well wall radius increased from 0 to 5 m. Regarding the gas and water production rates, water production increased with the increase of permeable well wall radius. Spatial distributions of hydrate and gas saturations, pressure, and temperature were investigated as well.

Increasing Gas Production of Continuous Freeze-Thaw Hydrate Deposits Based on Local Reservoir Reconstruction

“…(3) The maximum value of R GW in the original case is close to 94, but the maximum value of R GW in the reference case exceeds 143; especially when r F = 5:0 m, the maximum value of R GW exceeds 173, which has achieved a huge breakthrough in the technical bottleneck for hydrate production in lowpermeability reservoirs (4) The value of R GW in the case of k F = 1000 mD was close to that of the reference case, which indicates there is an ideal value of k F between 100 and 1000 mD. The thickness of OB and UB is sufficient to prevent the free gas and fluid from flowing to the hydrate HBL at the end of the simulation (5) The sensitivity analysis between the fracturing radius and the spacing between two horizontal wells optimizes the well layout and gas production parameters for hydrate production in permafrost regions…”

“…At present, NGH deposits mainly include marine hydrate deposits and permafrost hydrate deposits. The principle of recovering natural gas from NGH deposits in two different environments is to destroy the stable occurrence state of hydrate reservoirs [4,5]. For example, when the stability of hydrate is damaged due to the pressure drop or temperature rise in the sediments, the hydrate will be decomposed into methane gas and water.…”

Recent Advances on Natural Gas Hydrate Exploration and Development in the South China Sea

“…Shen et al used sediment samples recovered from the Shenhu area and measured the permeability in the laboratory under various confining pressures. 99 The experiment device for gas permeability measurements is presented in Figure 11. As the confining pressure increased from 2 MPa to 23 MPa, the effective gas permeability of the samples decreased from 2.6 × 10 −4 μm 2 to 0.9 × 10 −4 μm 2 .…”

“…They also formulated an empirical equation that described the relationship between relative permeability and hydrate saturation of GHBS in the Shenhu area. Shen et al used sediment samples recovered from the Shenhu area and measured the permeability in the laboratory under various confining pressures . The experiment device for gas permeability measurements is presented in Figure .…”

Numerical Investigation of Hydrate Production Characteristics in a Fractured Reservoir via Depressurization: Assessing the Influence of Fractures

“…The main method of exploiting hydrates is to reduce the pressure, raise the temperature, or change the phase equilibrium condition. There are three traditional exploitation methods: the depressurization method, − the heat injection method, , and the injection inhibitor method. − Among them, the depressurization method has a lower cost and a better effect. , However, in low permeability reservoirs, the low pressure has little effect on the distant part of the reservoir. In addition, the temperature in deep water is low, and the process of hydrate dissociation is endothermic.…”