Study on Calculation Method of Low and Medium Temperature Geothermal Well Bottom Pressure

Abstract

Low-Medium temperature geothermal field is widely distributed in China, and geothermal resources are abundant. Well test is an important means of determining geothermal reservoir reserve and geothermal well productivity. However, in well test process, dynamic water level is often higher than static water level, and the abnormal water level difference cannot be used to calculate geothermal well productivity. In order to solve this problem, the paper firstly derives equation for calculating well bottom pressure by integral method. Taking measured geothermal well temperature and water level data as an example, dynamic water pressure and hydrostatic pressure of a geothermal well bottom are calculated by integral method. In addition, the calculation results were compared with those obtained by average density method and segmentation method. The comparison results showed that whether static water level is higher than dynamic water level or dynamic water level is higher than static water level, dynamic water pressure at bottom of the geothermal well is less than hydrostatic pressure. Therefore, when calculating geothermal well productivity, pressure difference of geothermal well bottom is more reasonable and more accurate than water level difference. The results showed that integral method objectively reflects continuous characteristics of downhole temperature distribution, and is more accurate than average density method and segmentation method to calculate geothermal well bottom pressure.