A Wellbore-Reservoir Coupled Model and its Application in Sand Production Prediction During Sandstone Geothermal Exploitation
Authors: Zeng Hao , An Youkeren , Liu Jinjian , Zhang Yiqun , Hasan Khanjar , Jin Yan 
Published: August 2024

ABSTRACT:
Hydrothermal sandstone is an important form of geothermal energy, which is usually distributed in areas with shallow formation water and obvious geothermal activities, and has great potential for exploitation. However, the exploitation of hydrothermal sandstone reservoirs is often accompanied by severe sand production, which reduces the heat exchange efficiency and the service life of the devices. This paper presents the prediction method of sand production in hydrothermal sandstone reservoirs. Firstly, we conducted mechanical tests on hydrothermal sandstone cores. Secondly, the criteria for judging hydrothermal reservoir stability were proposed and the wellbore-reservoir coupling model was established. Finally, the influence of different reservoir and perforation parameters on sand production was analyzed. The results show that: 1) the interface between the borehole wall and perforation is the weakest place in the well, and the risk of sand production is the maximum; 2) the reservoir parameters (cohesion, friction angle, Poisson's ratio) and perforation parameters (phase angle, length, diameter, density) affect sand production; 3) the perforation phase angle of 60° is the best for sand control. This paper provides valuable insights and guidance for sand production and sand control in the development of sandstone geothermal reservoirs.

1. INTRODUCTION
Geothermal energy is a renewable resource obtained from the Earth's internal heat (Fridleifsson, 2001). Hydrothermal sandstone, primarily consisting of sandstone and carbonate rock, constitutes a significant geothermal reservoir, containing enormous amounts of energy (Gallup, 2009; Zhang et al., 2019). However, the high sand content presents a considerable challenge during reservoir exploitation, causing adverse impacts on exploitation efficiency, equipment longevity, and production safety (Ahad et al., 2020; Song et al., 2021). Managing sand production is critical for successful geothermal resource development, making reliable prediction studies essential (Sun et al., 2023).
At present, research on sand production prediction mainly focuses on laboratory experimental and numerical simulation. Through research, it has been observed that reservoir parameters (Shahsavari et al., 2021) and perforation parameters (Shabdirova et al., 2019) significantly impact sand production. Nouri (Nouri et al., 2006) investigated the influence of perforation and reservoir conditions on sand production, proposing specific criteria to ascertain sand production occurrence and extent. Bai (Bai et al., 2011) introduced equivalent plastic strain to enhance the accuracy of sand production prediction. Some scholars have developed erosion models or employed techniques such as ALE and FEM to account for rock erosion effects in sand production issues (Gravanis et al., 2015; Li et al., 2018). Zamani (Zamani&Knez, 2021) introduced a novel Safety Factor Index specifically designed to assess the influence of mechanical stresses and hydrodynamic forces on sand production in sandstone reservoirs. Khamitov (Khamitov et al., 2022) employed a CFD-DEM coupled model to examine the sand production mechanisms in the perforation zone. These studies have provided crucial references and theoretical foundations for dealing with sand production prediction issues in sandstone reservoir exploitation.