Evaluation And Utilization Of The Geothermal Resources Of The Middle-Shallow Layers In The Dagang Oilfield,Tianjin

The geothermal resources in the Dagang oilfield（Tianjin）is abundant.The potential prediction research of the geothermal resources in the middle-shallow layers is helpful to promote the sustainable and efficient development of the geothermal energy and stimulate significant social and economic benefits to the Dagang Oilfield.Based on the basic data including the geological structure,drilling data,hydrochemistry data and thermophysical data,this paper analyzes the distribution characteristics and formation condition of the geothermal resources in Dagang Oilfield,determines the resource amount of each thermal reservoir and formulates the development and utilization scheme of the geothermal resources in the middle-shallow layers.The thermal conductivity of the shallow rock and soil in the Dagang Oilfield ranges from1.46W/（m·K）to 1.60W/（m·K）.The present-day geothermal gradient in the Dagang Oilfield range from 2.5℃/100m to 3.5℃/100m.The southern Dagang Oilfield show the relatively high geothermal gradient with a peak of～4.0℃/100m.Due to the differerential thermal conductivity,the geothermal gradient in the sandstone layers is lower than that in the mudstone layers.The average heat flow in the Dagang Oilfield is 55.69m W/m².The ratio of the crust heat flow and mantle heat flow is 0.64,indicating that the lithosphere thermal structure is a“cold crust and hot mantle”type.In addition,the thickness of present-day thermal lithosphere in the Dagang Oilfield is 112～123 km.The formation of the geothermal resources in the Dagang Oilfield is related to the heat source,fluid channel,thermal reservoir and cap rock.The total amount of the geothermal resources in the research institute of exploration and economic research institute,Dagang Oilfield,is calculated to be 2.65×10¹⁹J with the heating storage method.According to the geothermal geological condition in the Dagang Oilfield,this study provides the design scheme of the ground source heat pump for the shallow geothermal energy and the design scheme of exploitation Wells and recharge Wells for the middle-layer geothermal energy.The one-dimensional linear heat flow model was adopted to calculate the system heat exchange for the shallow geothermal resources.According to the on-site thermal response tests of the four holes,the heat transfer per unit of depth for one-hole ranges from29.03W/m to 50.94W/m.The supply and recovery of the heat storage in the Middle Guantao Formation were predicted by the mining wells and recharge wells.When the recharge amount of the heat pump unit is 50 m³/h,the heat supply capacity reaches to 1699 k W.This paper clarified the present-day geothermal field and favorable formation condition of the geothermal resources in the Dagang Oilfield and evaluated the amount of the geothermal resources and the exploitation and utilization feasibility,which has important guiding significance for the further geothermal resource exploration and development.