The Study Of Evaluation Methods For Geothermal Energy In Hydrocarbon Reservoir

Evaluating the geothermal reserve of one geothermal system or reservoir is the basis for designing exploitation plan.There are various data and documents about geothermal system and evaluation method for geothermal energy in public literatures,which includes volumetric method,terrestrial heat flux method and geothermometer method.These methods have their own origins and concentrate on different characteristics of geothermal system.It is important to select proper method to finish the evaluation for geothermal energy.Heat flux is one of factors that influence the geothermal field and also an indicator for the geothermal energy in one area.Therefore,calculating the thermal conductivity with formation temperature gradient can get the heat flux within formation.Boxing Sag of Jiyang Depression,WSW depression of Beibuwan basin and Tabamiao area in the Ordos basin are the interested areas for geothermal evaluation with the four classical evaluation methods in the thesis.After the comparison between the four methods,volumetric method is used to calculate the geothermal reserves of the hydrocarbon reservoirs in the Tabamiao and Boxing,while terrestrial heat flux method is utilized for the oil reservoir in the WSW depression.Previous works always concentrates on geothermal reserves for a whole basin,whereas all the three targets are specific hydrocarbon reservoirs in the thesis,which can get more valuable results for design of geothermal exploitation.It is also significant to characterize the difference of geothermal resources from craton basin and rift basin.Jiyang and WSW have a higher formation temperature gradient that is usually more than 3.5 ?/100 m,while the temperature gradient varies from 1.6 to 2.7 ?/100 m in Ordos basin.After contrastive analysis,it is found that there are abundant data and materials from hydrocarbon exploration and exploitation in Jiyang depression and Ordos basin,which are also available for geothermal evaluation.However,WSW depression has been put into exploitation for a short time,there are not much available information for geothermal evaluation,and the hydrocarbon reservoir distributes loosely in the depression.Therefore,the method for geothermal energy in WSW depression is different to Jiyang depression and Ordos basin.Volumetric method is appropriate for reservoir with geometric shape is easy obtained and distributing stably.With volumetric method,the 1^st,2^nd and 3^rd section of Lower Shihezi group in Tabamiao have geothermal reserves of 9.7×10¹⁸J,3.5×10¹⁸J and 2.5×10¹⁸J respectively,15.7×10¹⁸J in total.The recovery geothermal energy for Lower Shihezi group is 3.93×10¹⁸J,which equals about 130 million ton standard coal;the same reserve for the 3rd section of Shahejie group is 3.6×10¹⁹J with recovery one of 8.95×10¹⁸J that is equivalent to 310 million standard coal.The parameter of abundance of geothermal energy can indicates the level of geothermal enrichment for one area.The abundances of geothermal energy for Lower Shihezi group and 3^rd section of Shahejie group are equal 310000 ton standard coal/km² and 920000 ton standard coal/km² respectively.It investigate and sum different heat flows from ground,spring,river and natural heat hole to know the geothermal anomaly in the investigated area.Volumetric method is not available for WSW depression due to the reservoir in the depression distributes scatteredly and lack of relevant fundamental data.Thus,it requires to utilize another way to finish the evaluation work for geothermal energy in WSW depression.It calculates the recovery heat from produced liquid during the testing mining period from all the 4 production wells in WSW area using a similar thinking way as Terrestrial heat flux method.Based on the specific heats of oil and water,A1 H,A2H,and A5H wells produce 3.9×10¹²J,3.4×10¹²J and 1.2×10¹²J heat from their accumulated oil production respectively,while the heat from the accumulated water production of A4 H well is 1.3×10¹²J that is more than 9.4×10¹¹J of heat from its oil production.Furthermore,the total thermal power of the 4 wells is 300.5 KW.Consequently,it shows that volumetric method is good to calculate the heat reserve in hydrocarbon reservoir with nice geometric shape and abundant exploration documents,while it is also reasonable to study the recovery heat in the produced liquid from hydrocarbon wells in a given period,which is considered as the basic data for geothermal energy developing design.Specific heat and thermal conductivity of rock is both key parameters for studying geothermal reserve and formation thermal flow.Rock is composite of mineral and porous liquid.Currently,there is no logging technology that can directly detect the two thermodynamic parameters of underground formation.In addition,it is hard to collect data about the two parameters of the objects in the thesis.Therefore,the volumetric specific heats of rock matrix in the 1^st,2^nd,3^rd sections of Lower Shihezi and 3^rd section of Shahejie are 2129438.6J/m³·K,2182849.4J/m³·K,2094933.4J/m³·K and 1959008.2J/m³·K respectively by arithmetic mean model with their mineral composition data.Accordingly,the thermal conductivities of the four sections' rock matrix are 6.27W/m·K,7.22W/m·K,6.09W/m·K and 4.53W/m·K respectively with geometric mean model.There is a good linear relationship between geometric mean model,series model and parallel model based on the calculated thermal conductivities by them.Additionally,higher crystallized mineral content in the rock matric mean higher thermal conductivity,whereas clay is not good for thermal conductivity of rock.The basic theory of geothermometer is dissolution balance between water and rock,this balance is related to the temperature of environment.The advantage of geothermometer is that it can appropriately estimate the temperature of underground rock storing geothermal water by analyzing water sample collected on surface.This method has been widely used in spring or boiling spring study.The point of geothermometer is that choosing a proper dissolution balance based on ion composition of geothermal water.It is the first time to use such method for formation water from hydrocarbon reservoir to confirm whether or not geothemometer method is good enough to estimate the reservoir temperature.However,Na-K geothermometer,Na-K-Ca geothermometer and K-Mg geothermometer mostly produce error results with large deviation to actual formation temperature based on formation water composition of Lower Shihezi and 3rd section of Shahejie,whereas only the Truesdell equation of Na-K geothermometer gives two results close to Lower Shihezi temperature in Da39 well and Da47 well.Thus,geothermometer method is hard to generate a reliable result for formation temperature of hydrocarbon reservoir.