Sand Production Prediction of Depleted-Reservoir Underground Gas Storage – An Experimental Study

Abstract

ABSTRACT: Depleted-reservoirs underground gas storage are playing an increasingly important role in seasonal demanding of natural gas, ensuring stable gas supply and strategic reserves. However, due to the physical properties of the reservoir, the problem of sand production in the wellbore cannot be ignored. This research is based on the high-pressure sand production experiment simulation device system. Using the in-situ core, through experiments to simulate the sand production of the high-pressure gas storage reservoir, the sand production is systematically and quantitatively studied. The experimental results show that there are two key pressures for sand production caused by the destruction of the inner wall of the wellbore, namely, the equivalent initial sand production pressure (critical confining pressure) and the strength of the thick-walled barrel (collapse pressure). After the confining pressure exceeds the equivalent initial sand production pressure, the core begins to produce sand, and the sand has a relatively smaller particle size. The sand production is found to increases linearly with the equivalent confining pressure. After the confining pressure exceeds the strength of the thick-walled barrel, the core body is damaged and a large amount of sand is produced. The sand body has a relatively large particle size. The particle size distribution indicates the increase of sand particle size during the sand production of the gas storage well. This experiment provides guidance for the operation and completion of gas storage in depleted oil reservoirs, and also provides a quantitatively experimental method for the study of wellbore sand production. 1. INTRODUCTION In recent years, with the increasing demand for natural gas, the stable supply of natural gas has attracted more and more attention. Therefore, gas storage as a means of peak regulation has developed rapidly in a short period of time in China. As a safe, efficient and convenient gas storage place, the stable operation of gas storage needs a higher technical level as a support (Wei et al., 2015;Dong et al., 2020). Compared with regular gas production wells, there are two main reasons why gas storage wells are more prone to sand production: • The service life of gas storage wellbore is longer than that of production wells, generally about 30 to 50 years. The long-term stress alternation will weaken the cementation and connection between rock particles, resulting in instability of wellbore wall and the damage of the formation. • When the supply and demand are unbalanced due to seasonal changes, the gas storage needs to meet the operating conditions of high throughput and large discharge. Under the action of the highspeed fluid dragging force, the wellbore has a higher probability of sand production. (Wei et al., 2019; Li et al., 2005; Liu et al., 2021)