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Sand production has become a common phenomenon in the exploitation of unconsolidated natural gas hydrate reservoirs, which will hinder the long-term production of natural gas hydrate reservoirs. However, there are few literatures reported on the influences in reservoir physical properties such as permeability and porosity, and production laws caused by sand production. This paper provides a numerical model, coupled with reservoir sand-gas-water multiphase flow processes, which is capable to simulate the process of sand production in natural gas hydrate reservoirs. The simulation results indicate that sand settlement is mainly concentrated near the wellbore due to the high concentration of migrated sand. The decrease in reservoir porosity and permeability caused by sand settlement has a significant impact on production. The impact of sand production on reservoir fluid fluidity shows that fluid flow is inhibited near the wellbore, while fluid flow performance increases far away from the wellbore. The numerical model and analysis presented here could provide useful insight into changes in reservoir physical properties and production laws caused by sand production in the natural gas hydrate-bearing marine sediments using depressurization method. [ABSTRACT FROM AUTHOR]

The formation sands of natural gas hydrate (NGH) reservoirs in the South China Sea are fine silty sands with a high content of clay, and it is difficult to be controlled effectively. We carried out a series of experiments to investigate the microcosmic retaining and plugging behavior of screen media with highly argillaceous fine sand samples, with median size of 10.13 μm. The screen sand-retention media and joint involved four types with slot width or accuracy of 20–60 μm. The screen media/joint sample was placed in the linear/radial flowing apparatus, and then the mixture of gas, water and sand were displaced flowing into the media to simulate the sand retaining process. The Microscopic imaging system was used to visually observe the dynamics of sand particle deposition and plugging inside the media as well as on its surface. The plugging permeability and the amount of the passed sand were also analyzed. According to the result, three microcosmic mechanisms of sand retaining and plugging were proposed, concerning fine sand invading and coarse sand bridge, partial sand block, and integrated sand bridge. The plugging permeability performance of screen media generally shows three stages of slow decreasing, rapid increasing and balance. At the balance stage of displacement, the plugging permeability of media sample mostly decreases more than 90%. During the whole test, the sand passing rate tends to slow down gradually, and the final retained sand ratio were more than 85%. Different configurations of sand retraining test show a little difference in plugging performance, depending on the factors of medium type, accuracy, sand characteristics, and flow conditions. Based on the effect of sand retaining and final flow ability observed in these experiments, the sand control in NGH reservoirs with highly argillaceous fine sands is practicable. • Microcosmic retaining and plugging of screen medias by highly argillaceous fine sand in NGH reservoir. • Plugging permeability of screen and the amount of sand production were quantified. • Three microcosmic mechanisms of sand retaining and plugging of screen medias with fine sand from NGH reservoir. [ABSTRACT FROM AUTHOR]

The existence of solid hydrate in porous media always greatly reduces the relative permeability, which limits the development of hydrate reservoirs. Therefore, to recover the gas, it is necessary to carry out reservoir reconstruction measures that induce fractures around the production wells to increase the gas production of hydrate reservoirs. At present, there is limited quantitative research on the promotion of gas production by induced fractures in hydrate reservoirs. In this paper, numerical models of Class Ⅲ hydrate reservoirs with induced fractures are established. By comparing the gas production with and without induced fractures, the effectiveness of induced fractures in promoting the depressurization production of natural gas hydrates is verified. An index of improved efficiency is established and calculated to measure the promotion effect of induced fractures during the fracture promotion stage. The multiple regression calculation formulas of improved efficiency with reservoir geological parameters are obtained by integrating nonlinear regression and linear regression. The calculation model is helpful to quickly and directly measure the rationality and economy of the induced fracture depressurization method to promote hydrate development. • Numerical models of Class Ⅲ hydrate reservoirs with induced fractures are established. • An index of Improved Efficiency is established to measure the promotion effect of induced fractures. • The improved efficiency of induced fractures under different geological parameters is calculated and compared. • The multiple calculation formulas of improved efficiency with geological parameters are obtained by stepwise regression. [ABSTRACT FROM AUTHOR]

Sand screens act as the key downhole equipment for sand control in weakly consolidated oil and gas reservoir, but always face the risk of erosion failure in sanding wells with high productivity. To develop an effective methodology to predict erosion performance in actual wells is a pressing demand of high reliability sand control. In this work, we conducted series of erosion experiments to investigate the failure mechanism and influencing factors of typical premium mesh screen with gas and liquid carrying sand. The results show that the protective shroud and the metal mesh medium show similar erosion laws under various sensitive factors. The erosion rate increases nonlinearly with fluid velocity, but increases linearly with sand particle size and concentration, and decreases linearly with erosion distance. In addition, erosion angles within 30°∼60° can result in higher erosion rates than other angles. With new proposed screen structure function and eroding condition function, an integrated model for erosion rate prediction of protective shroud and metal mesh medium was developed for gas and liquid carrying sand respectively by experiment data fitting. To make it easy to use the new model to predict the erosion performance of actual wells, an index of partial inflow factor (PIF) was furtherly put forward to describe the highest inflowing velocity in the heterogeneous inflow profile caused by the heterogeneity of reservoir properties. Considering the erosion of sand particles and the protection of the screen by sand accumulation, a systematic method was proposed to simulate the erosion performance of wells with sand control screen. Using this method, the final result of whether screen erosion failure can take place at the end of early stage the well production can be predicted, which depends on the relative speeds of screen erosion and sand accumulation in the wellbore annulus. The proposed methodology of erosion performance simulation takes into account not only the characteristics of screen itself, but also the actual inflow condition of well bottom hole. The models and methods are really very easy for practical application and offer a reliable access for sand control and well completion design, and integrity evaluation of completion string in weakly consolidated reservoirs. • This paper revealed the frontal gnawing and lateral cutting mechanism of the screen tube erosion machine. • In general, the time until erosion failure of the protective shroud is 5 to 10 times that of the sand retaining structure (metal mesh medium). • It was found that the local accumulation of sand particles on the surface of the screen had a protective effect on erosion. • The erosion rate increases with fluid velocity. An erosion angle within 30°~60° can lead to higher erosion rates than other angles. • Based on the experimental data, two functions considering the screen structure and erosion conditions were proposed. [ABSTRACT FROM AUTHOR]