Study On Rock Permeability And Thermal Properties Of Deep Geothermal Reservoirs

Pore type reservoir and bedrock fissure reservoir are the main reservoirs for the exploitation and utilization of deep geothermal resources in north China.In this paper,the permeability and thermophysical properties of typical rock samples above are tested and studied,and the main work and conclusions are as follows:For the porosity reservoir,taking typical sandstones from Minghuazhen formation and Guantao formation of Neogene in southern North China Basin and Bohai Bay Basin as an example,and their pore characteristics are tested including XRD,specific surface area,micro CT scanning and geotechnical analysis.Then the actual permeability of sandstones is tested.Results show that as the clay content increases,the specific surface area and apparent porosity tend to increase and decrease,respectively.Complex sedimentary cycles may cause non-uniform pore distribution of sandstones,thereby forming narrow local throats and reducing the permeability.For air-dried sandstones with high clay contents,soaking swelling,dissolution and disintegration of clay minerals are inclined to occur during the test,thereby expand the inner pore paths and enlarge the actual permeability.For the above pore-type sandstones,conventional empirical model do not give satisfied prediction accuracy.During the practical exploitation and reinjection of geothermal wells,it should be careful to choose the permeability prediction model and evaluate the corresponding calculation results.For bedrock fracture reservoirs,taking the mesoproterozoic dolomite samples in north China as an example.The thermal conductivity of dolomite samples at room temperature and high temperatures are measured by SEM,XRD and geotechnical tests.The results show that the order degree and degree of dolomitization of the tested samples are higher overall.The samples are mainly developed in the evaporative tidal flat sedimentary environment,and the pore structures are dominated by fractures and dissolution pores.The crystal structure of dolomites under scanning electron microscope includes euhedral crystal-allotrophic crystal and allotrophic crystal structure.The thermal conductivity decreases with the increase of porosity,and decreases first and then increases with the increase of quartz content.The high temperature thermal conductivity of dolomite tends to decrease with the increase of temperature.After high temperature action,the porosity of dolomite increases with the increase of temperature,and the thermal conductivity decreases with the increase of temperature.After heated to 400 ?,dolomite internal appears more micro cracks,the porosity of dolomite increases obviously and the thermal conductivity decreases rapidly.