• Energy Research

Abstract The energy efficiency (EE) is a key parameter to evaluate the performance of methane hydrate (MH) dissociation by thermal stimulation. Experiments of MH formation and dissociation have been performed in a 2D reactor to analyze the EE of hot brine injection, and different influencing factors of EE including geological parameters (MH saturation, intrinsic permeability and initial temperature of the reservoir) as well as thermal stimulation parameters (brine temperature, brine injection rate, brine concentration and the amount of injected heat) have been studied. It is shown that the EE grows with the increasing initial temperature of MH reservoir (−1∼5 °C), intrinsic permeability (100~1200 × 10−3 μm2) and brine concentration (2%∼20%), and the corresponding maximum EE is 5.7, 5.3 and 8.4, respectively. While the EE reaches a peak and then declines when the total amount of injected heat increases from 100 kJ to 1240 kJ (480 kJ for the maximum EE of 6.4), the temperature of injected brine from 30 °C to 50 °C (40 °C for the maximum EE of 5.2), the brine injection rate from 10 cm3/min to 25 cm3/min (20 cm3/min for the maximum EE of 5.1), and the MH saturation from 16% to 64% (48% for the maximum EE of 7.2).

A new one-dimensional experimental system for natural gas hydrate (NGH) exploitation is designed, which is used to study the formation and dissociation processes of NGH. NGH is formed in the sand-packing tube, and then hot-brine is injected into the tube to study the thermal dissociation characteristics. The injection parameters that influence gas production rate and energy efficiency are analyzed. The results show that the higher the injection temperature and injection rate are, the higher the gas production rate is. In addition, the most sensitive parameter, which influences the energy efficiency of thermal stimulation is the hot-brine temperature, followed by the hot-brine injection rate and injection time. This study provides an experimental basis for further study on NGH exploitation in the future.

Natural gas hydrate(NGH) is a clean resource with huge reserves. The depressurization method is an economical and effective exploitation method. In the process of depressurization, reservoir absolute permeability has an important influence on production results. Based on the data of Shenhu hydrate reservoirs, this paper established a depressurization production numerical simulation model. Then, the production performances such as pressure, temperature, gas production rate, cumulative gas production, and hydrate dissociation effect are all studied under different permeability conditions.study the change of reservoir pressure, gas production rate, cumulative gas production, reservoir temperature change and hydrate dissociation effect under different permeability conditions. Results show that higher permeability is conducive to the depressurization of hydrate reservoirs.

Gas production from an offshore hydrate-bearing sediment (HBS) by depressurization will reduce the strength of cementation and increase the effective stress of hydrate reservoirs, which can result ...

Abstract As a new energy source with abundant resources, clean combustion, and high calorific value, gas hydrates have received much attention in recent years. However, the sampling cost is relatively high because the gas hydrates exist in deep seas and frozen soils. Digital core technology can reconstruct hydrate cores without destroying rock samples. In this paper, the advanced image processing technology is used to process the gas hydrate computed tomography (CT) scan image, and a three-dimensional hydrate digital core model is constructed, which can depict the sample's pore structure features. avizo software is used for filtering and image segmentation; the porosity is calculated as 35.90%, the hydrate saturation is 36.92%, and the pore network model is established. The pore radius is mostly distributed in 0–1 × 102 µm, and the average pore radius is 168.131 µm; the throat radius is mostly distributed in 0.5–1×102 µm. The seepage simulation on the pore scale is carried out, and the absolute permeability is calculated to be 76.8 µm2. Compared with conventional physical experiments, the digital core technology can obtain the true distribution of the pores inside the hydrate core, which is very helpful for analyzing the physical parameters of the hydrate core. The digital core technology is of great significance in the study of hydrate reservoirs.

Abstract Experimental simulation is an important approach to study the gas hydrate dissociation mechanism, and similarity theory is an effective tool for the design of experimental model. Based on hydrate kinetic reaction model in HydrateResSim, seventy-three similarity numbers are derived by means of inspectional analysis and dimensionless analysis. Gas production from the natural gas hydrate reservoir is controlled by two mechanisms, namely dissociation-controlled mechanism and flow-controlled mechanism. Two groups of schemes are put forward for the design of experimental model of natural gas hydrate according to these two mechanisms respectively: for flow-controlled hydrate reservoir the scale of injection rate of heat and water, and parameters associated with size is the same with that of length, the scale of time is the square of length scale; for dissociation-controlled hydrate reservoir, the scale of parameters associated with size is the same with that of length, the scale of absolute permeability is 4/3 times square of length scale, the scale of time is 2/3 times square of length scale, the scale of injection rate of heat and water is 7/3 times square of length scale.

Abstract A 3D numerical model for gas production from hydrate reservoirs is developed, which considers kinetics of dissociation, heat and multiphase fluid flow. Three components (gas, water and hydrate) and three phases (gas, water and hydrate) are considered in the model. The equations are spatially discretized by a finite difference method. IMPES method is used to solve the mass balance equations and temperature is solved implicitly. Based on the model, gas production from Class I hydrate reservoir (with underlying free gas) under constant bottom-hole pressure was simulated. The sensitivity analysis of the factors including development parameters and reservoir parameters were performed. Results show that hydrate dissociation rate increases with the increases of initial reservoir temperature. The larger the absolute permeability is, the higher the hydrate dissociation rate is. Hydrate dissociation rate is significantly improved, when dissociation rate constant increases. However, higher initial reservoir pressure and bottom-hole pressure will lead to lower hydrate dissociation rate. Research results provide theoretical support for hydrate production.