ABSTRACT

This paper investigates the sand production issue in the process of natural gas hydrate depressurization production and employs the T-H-M-C coupled model to describe the complex behavior of hydrate decomposition and fluid-solid coupling. A homogeneous geological model was constructed using Comsol software for the simulation of hydrate extraction, analyzing the changes in reservoir parameters during the extraction process and the impact of sand production on formation settlement. This paper also examines the mechanism of sand production and its effect on well productivity, to explore methods of enhancing the productivity of hydrate reservoirs

INTRODUCTION

Natural gas hydrate is a kind of white solid crystalline material formed by gas and water under certain temperature and pressure conditions. It is widely found in shallow sediments and polar permafrost (Sloan, 2003). Under standard conditions, 1 m3 hydrate can be decomposed to produce 164 m3 methane gas and 0.8 m3 water (J. Li et al., 2022). At the same time, the reserves are huge, and the global total is estimated to be 1015-1018 m3, equivalent to 2 × 105 billion tons of oil equivalent, which is twice the carbon reserves of conventional fossil energy in the world (Zhu et al., 2020). Because of its wide distribution, low pollution, and high combustion efficiency, hydrate has been widely considered an ideal alternative energy source in the future.

At present, natural gas hydrate mining methods mainly include the depressurization method, thermal excitation method, chemical reagent method, gas displacement method, solid fluidization method, and combined mining of these methods (X. Li et al., 2024). A large number of tests and field tests show that the depressurization method is the most economical and effective mining method. However, the depressurization method may lead to serious reservoir sand production. During the hydrate production test at the Mallik mine in Canada, depressurization was forced to suspend after only about 30 hours due to the blockage of the electric submersible pump (ESP) caused by sand mining (Collett et al., 2005). Sand production was observed during the first two stages of the hydrate production test at the Ignik Sikumi mine in the United States and affected gas production rates (Hauge et al., 2014). In Japan, two tests were carried out in the Nankai Trough, and the production was forced to stop due to the large amount of sand production (Chen et al., 2018). In summary, the problem of sand production in hydrate exploitation is a key bottleneck restricting the safe and efficient exploitation of hydrate. Many scholars have also conducted a series of studies on the problem of sand production in the mining process.

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