## 2 Optimization of Sand Control Methods in Hydrate Reservoirs
### Analysis of Sand Production and Plugging Mechanisms
Referring to the above mechanism analysis, five groups of argillaceous fine silt gas hydrate reservoirs samples are selected for the experiment, and the sand size distribution of argillaceous fine silt hydrate reservoir is analyzed by laser particle size test method, as shown in the following Table 1. The median grain size (D\({}_{50}\)) of the five groups of rock samples is between 10 and 30 um, and the rock sand particles are extremely fine, the homogeneity coefficient is greater than 5, and the heterogeneity is large. The X-ray diffractometer is used to measure the argillaceous content of rock samples and the relative content of illite, montmorillonite, kaolinite and chlorite. The measured argillaceous content is between 25% and 30%. In view of the argillaceous fine silt hydrate reservoirs with high clay content and small sand grain diameter, the sand control operations are required to achieve effective sand control without blocking the productivity release. Through further research on the causes and mechanisms of sand production in the argillaceous fine silt gas hydrate reservoirs, the following understandings have been obtained:  
The first one, due to the small sand grain diameter of the argillaceous fine silt gas hydrate reservoirs and the unconsolidated and loose state of the formation, under a certain production system, such as the effect of different pressure reduction, sand production happens extremely easily. Meanwhile, under the flow of fluids such as gas and water, the argillaceous fine silt can easily pass through the seepage channels and gradually accumulate near the wellbore or enter the wellbore, resulting in sand production in the wellbore or plugging of the sand screen. In addition, there are numerous clay particles in the argillaceous fine silt gas hydrate reservoirs. These particles will migrate along with the produced fluid, causing a reduction in permeability around the wellbore. This, in turn, increases the drag force of the produced fluids in a variable direction, and leads to sand production. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{**D\({}_{10}\) (μm)**} & \multirow{2}{*}{**D\({}_{40}\) (μm)**} & \multirow{2}{*}{**D\({}_{50}\) (μm)**} & \multirow{2}{*}{**D\({}_{90}\) (μm)**} & \multirow{2}{*}{**D\({}_{95}\) (μm)**} & **UC** & **SC** \\  & & & & & & **(Unevenness Coefficient)** & **(Sorting Coefficient)** \\ \hline
1 & 54.519 & 26.246 & 20.786 & 3.480 & 2.245 & 7.543 & 24.287 \\
2 & 50.723 & 27.304 & 21.913 & 3.663 & 2.340 & 7.454 & 21.681 \\
3 & 54.435 & 25.792 & 19.833 & 2.469 & 1.384 & 10.448 & 39.334 \\
4 & 47.730 & 21.334 & 16.156 & 2.812 & 1.929 & 7.587 & 24.744 \\
5 & 65.167 & 31.054 & 25.162 & 4.087 & 2.353 & 7.598 & 27.701 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Test data of hydrate reservoir sand particle size. Thirdly, it is caused by the special physical and chemical properties of the gas hydrate reservoirs themselves. When the hydrate has not decomposed, it exists in a solid form, either cemented to the sediment framework or in the form of a skeleton. When the hydrates are decomposed and produced, particles such as mud and sand will lose their supporting or cementing reliance and migrate under the action of fluid flow, resulting in sand production. We called this theory The Sand Production Mechanism of Argillaceous fine silt, as shown in Figure 1.  
Under a certain range of fluid flow velocities in the argillaceous fine silt hydrate reservoirs, the main influencing factors of sand production are the decomposition of the hydrate reservoirs themselves and the destruction of in situ stress. Meanwhile, it is affected by the particle size distribution of the reservoirs. When the particle sizes are evenly distributed, the amount of sand production will decrease. In addition, the structure and size of the screen tube will significantly affect the amount of sand production in the hydrate reservoirs.