Transformation And Heat Transfer Study On Utilizing Abandoned Oil Well For Extracting Deep Geothermal Energy

With the development of society,the shortage of energy and the pollution of environment have become the major problems we are facing,especially the heating problem in our country,so the development and utilization of renewable energy has become imminent.Geothermal energy is a relatively reliable renewable energy,which has been paid more and more attention by people.Due to the rich and deep geothermal energy resources in the middle and deep layers,it has the characteristics of wide distribution,large storage capacity,reliable and stable,environmentally friendly and clean,etc.Therefore,it is being used more and more,but the deep well bored tube heat exchanger also has the problems of high drilling difficulty and high cost.In the later stages of oilfield development,many oil reservoirs were depleted and oil wells were abandoned.In fact,approximately 2.03 billion abandoned wells have been produced globally,for example,improper plugging may lead to safety hazards or leakage and damage the environment.Generally,the geothermal resources in the oil and gas basin where the abandoned well is located are relatively rich,and the geothermal gradient and geothermal flow value are high.If the abandoned well can be transformed into a abandoned well heat exchanger,Pass the circulating water into the well,and the middle and deep geothermal energy can be collected by casing with the rock and soil layer,the circulating liquid will not contact with the rock directly,which can solve the problems of reinjection,corrosion and scaling.At the same time,it can well alleviate the current energy shortage and the high cost of the middle and deep heat pump well drilling,improve the environment and promote economic development.This paper makes full use of the existing abandoned well resources,and carries out the simulation research on the transformation of abandoned well and the operation of heatextraction.In this paper,the in-depth coaxial heat exchanger is summarized,and the well forming process of abandoned oil well,the existing structure of typical abandoned well and its structural optimization are introduced in detail.This paper introduces the selection of numerical calculation method,puts forward the finite difference method to solve the calculation method,and explains the mathematical model of heat transfer analysis,the mathematical model of the heat transfer analysis of the mid-deep coaxial buried tube heat exchanger,the discretization of the region and the establishment and solution of the difference equation are explained.This paper introduces the calculation software "geothermal Star II" and its application method as well as the calculation of nominal heat intake.Finally,the performance parameters of the heat exchanger after the well abandonment and reconstruction are analyzed,including:the nominal heat intake of the heat exchanger increases with the increase of the annual average temperature of the local atmosphere,the heat flow of the earth,the flow rate,the thermal conductivity of the outer pipe and the thermal conductivity of the backfill material;decreases with the increase of the thermal conductivity of the central pipe and the diameter of the pipe;increases with the depth of the borehole thermal insulation section and the thermal conductivity of the thermal insulation section Decrease and decrease.The existence of the heat insulation section has a negative impact on the nominal heat intake of the heat exchanger.It is very necessary to backfill the annulus part for the reconstruction of abandoned oil wells.This paper introduces the simulation calculation of the heat transfer operation of the heat exchanger of the third and fourth abandoned wells,including the calculation parameter setting of the abandoned wells,the selection of the inner tube and the simulation of the heat transfer operation of the reformed heat exchanger,including the operation simulation for many years under the condition of single heat transfer.It is analyzed that the heat exchanger of the third abandoned wells can operate well under the second and third working conditions,but the overall design is as follows The heat is not large;the heat exchanger of four open abandoned wells can operate well under the setting conditions in the paper,and the overall heat intake is much larger than that of three open abandoned wells;then,the influence radius of the four open abandoned wells heat exchanger under the above conditions is calculated,and theoperation simulation situation after the setting of the reinjection load data in the paper is analyzed.It is found that after the reinjection load is added,the length of the heat exchanger is much longer The operation of time is more favorable;Finally,it analyzes the application of heat extraction of the heat exchanger in the abandoned well,including the addition of heat pump,well spacing,pipeline insulation,long-distance heat transfer and economy.