Research on Coaxial Casing Closed Cycle Heat Extraction Technology for Middle Deep Geothermal Wells in Beijing, Tianjin, and Hebei in 2025

1. Technical principles and regional adaptability‌

• ‌Closed loop design: Closed circulation of working medium (water or supercritical CO ₂) is realized through coaxial casing (inner pipe DN100 steel pipe/outer pipe DN200 HDPE) to avoid groundwater exploitation, which conforms to the hydrological protection policy of the North China Plain.

• ‌Heat extraction mechanismA deep well of 2500-3000 meters can obtain a heat source of 80-110 ℃, which can achieve a single well heat extraction power of 1.5-2MW through a countercurrent heat exchange process of 'downward flow of inner tube and upward flow of annular gap'.

‌2. Breakthrough points in core technologies‌

(1) Geological targeted exploration technology

• Application of 3D seismic+microseismic monitoring to locate thermal reservoirs (mainly composed of dolomite in the Wumishan Formation of the Jixian System)

• Core thermal property testing (priority drilling in areas with thermal conductivity>2.8W/(m · K))

(2) High temperature resistant casing material

• The inner pipe adopts P110 grade sulfur resistant steel pipe (temperature resistance of 150 ℃/pressure resistance of 30MPa)

• Modified HDPE for annular gap pipe (adding carbon fiber to enhance creep resistance at 120 ℃)

(3) Intelligent control system

• Underground fiber optic temperature measurement (accuracy ± 0.5 ℃) linked with variable frequency pump

• Dynamic flow regulation based on load forecasting (AI algorithm optimization)

‌3. Beijing Tianjin Hebei characteristic application scenarios‌

• ‌Beijing Municipal Administrative CenterDevelop a cluster of 20 3000 meter wells in a contiguous manner to replace gas boilers for heating 3 million square meters

• ‌Xiong'an New AreaMulti energy complementary system of geothermal and energy storage, meeting 24-hour stable heating needs

• ‌Tianjin Binhai Industrial Zone90 ℃ tail water is used for preheating in petrochemical processes, resulting in a 40% increase in comprehensive energy efficiency

‌4. Economic and environmental benefits‌

• ‌Return on InvestmentThe cost of a single well is about 6-8 million yuan, with a payback period of 5-8 years (saving over 2 million yuan in annual operating costs compared to coal-fired power)

• ‌Emission reduction dataReduce carbon emissions by 18000 tons per well annually, contributing to the goal of carbon neutrality in the Beijing Tianjin Hebei region

‌5. Policy support and challenges‌

• ‌Special subsidiesIncorporate into the High Quality Development Plan for Geothermal Energy in North China, with a 30% subsidy for drilling costs

• ‌technical riskTo prevent karst collapse of Ordovician limestone layers, drilling and plugging technology should be adopted

This technology will promote the construction of a large-scale demonstration zone for clean heating in the Beijing Tianjin Hebei region, and relevant results can be obtained through the Geothermal Energy Innovation Center of the China Geological Survey.