Heat Extraction Performance and Optimization for a Doublet-well Geothermal System in Dezhou, China

Tianfu Xu,Shuai Liu,Bo Feng,Jichu Zhao,Zhitao Liu,Yue’An Zhao,Lanxin Zhang,Gaofan Yue,Guanhong Feng

doi:10.1177/01445987211043578

Abstract

Dezhou City is located in northwestern Shandong Province, China, and is rich in geothermal resources. Approximately 30% of the geothermal wells and geothermal heating areas of Shandong Province are located in Dezhou. A doublet-well layout geothermal system was completed by the Lubei Geo-engineering Exploration Institute for local winter heating, which has been in operation for 4 years. The wellbores penetrated the Guantao Formation with a well spacing of 180 m. This study aims to assess the heat extraction performance of the current well layout and predict the temperature evolution and lifespan. Furthermore, larger well spacing schemes were used in a simulation to test the heat supply potential and sustainability. In this study, the thermal conductivity and permeability were calibrated using in situ measured data from a field production test. A relatively high permeability layer was found between the depths of 1468 and 1536 m. The temperature remained stable in the first 6 years and then started to decrease. The recharging (injection) water tended to concentrate along the bottom highly permeable layer and accounted for over 64% of the outflow in the 100th year of the simulation test. The outflow temperature decreased from 53.9°C to 50°C in the 32nd year, making it less viable for subsequent sustainable exploitation. Hence, a larger well spacing is required for long-term operation based on the same geothermal reservoir. It was found that a spacing of 400 m could guarantee an outflow temperature above 50°C over a 100-year lifespan with an 80 m3/h pumping (production) rate. Moreover, the sustainability of the 600-m spacing was almost 2.5 times that of the 400 m case. The modeling and analysis method can be useful for the development and optimization of a doublet-well geothermal system under similar conditions.

Highlights

BackgroundTraditional power generation based on fossil fuels is generally considered unsustainable in the long term
Geothermal energy has the advantage of a wide distribution, huge reserves, and features that are not affected by weather and seasonal changes (Pang et al, 2017; Pellizzone et al, 2017)
Based on the modeling results and analyses, the following conclusions can be drawn: 1. A relatively high permeability layer is found at a depth of 1468–1536 m, which could explain why the pumping rate and drawdown exhibit an approximately parabolic relationship rather than a linear relationship

Summary

Introduction

BackgroundTraditional power generation based on fossil fuels is generally considered unsustainable in the long term. Many efforts have been made worldwide to introduce more renewable energy sources (Ellabban et al, 2014; Majorowicz and Grasby, 2019; Sowizdzal, 2018; Zarrouk and Moon, 2014). Geothermal energy has the advantage of a wide distribution, huge reserves, and features that are not affected by weather and seasonal changes (Pang et al, 2017; Pellizzone et al, 2017). As a result, it is widely promoted and has become one of the most competitive and strategic renewable resources. According to the utilization styles, it can be categorized into indirect use (electrical power generation and combined heat and power in cogeneration applications) and direct use of heat (district heating, heat pump applications, bathing, fish farming, etc.) (Fridleifsson, 2001; Hepbasli, 2008)

Objectives

Results

Conclusion