Evaluation Of The Fluid Connectivity And Heat Exchange In A Fractured Reservoir Of Enhanced Geothermal System Based On The Tracer Technique

Geothermal resources cover a wide range of Earth’s heat source, including notonly the hydrothermal resources which easy to accessed, but also the worldwide hotdry resources in the deep crust. Hot Dry Rock, which as a kind of geothermalresources, is considered to be the most potential resources in the21st centurybecause of its wide distribution, cleaning and huge thermal reserves. The EnhancedGeothermal Systems (EGS) is a artificial geothermal systems which economicecploits quite a number of thermal energy from the low-permeability rock of thedeep underground though the method of artificial geothermal reservoir formation,that is, exploited thermal energy from hot dry rock. But we need to creat theconnection between injection wells and production wells though the technique ofartificial fracturing in Hot Dry Rock reservoirs to enhancing the connectivity offracture systems and improving the heat production of reservoirs. In order to makeartificial fracturing optimize, we need to assessment two key parameters——connectivity and fracture-matrix heat exchange area which could measure the effectof reservoir reconstruction by the method of tracer technology though the period ofreservoir reconstruction or after the that. Geothermal tracer numerical simulationtechnology as an essential step tracer tests could fully perfect the result analysis offield tracer tests.Songliao Basin is the study area of this study which is one of China’s five majorgeothermal resource distribution areas, and the object of this study is theYINGCHENG rhyolite fractured reservoir. First, quantitative evaluate theconnectivity and fracture-matrix heat exchange area of the core-scale singlefracture by the method combining tracer experiment and numerical simulation. Second, numerical simulate a tracer test of field-scale fracture reservoir to analyzingthe transport of water and thermal in the reservoirs between different wells and thetracer breakthrough curves, then qualitative analyze the connectivity and fracture-matrix heat exchange area of different injection wells and production wells. Third,select the optimal injection well and production well in the field and analyze thesensitivity of important parameters which used in this study.Through this research we mainly obtain the following conclusions:(1) The permeability of the core-scale single fracture could be accuratelymeasured by the tracer experiment. It could get a credible result of the quantitativeevaluation of the connectivity of core fracture by the parameter of the void volumewhich fluid flow though. It also could get a credible result of the quantitativeevaluation of the fracture-matrix heat exchange area in core-scale by the methodwhich fitting the simulation results and experimental datas of tracer breakthroughcurves.(2) From the results of TOUGHREACT EOS1software numerical simulationof field interwell tracer tests of different injection wells or production wells we canknow that, the high permeability fracture which nearby the injection wells orproduction wells will preferred transport the interwell flow and enhance the reservoirconnectivity between injection wells or production wells, but also may lead topremature thermal breakthrough of production wells. Comprehensive analysis, theoptimal combination solutions of injection wells and production wells in SongliaoBasin Yingshen area are Yingshen2well-Shuang33well, Shuang44well-Yingshen4well and Yingshen4well-Yingshen2well.(3) There is a positive correlation of reservoir fracture permeability and theconnectivity of fractured reservoir, while a smaller reservoir fracture permeability, alarger degree of influence on reservoir connectivity though increasing the fracturepermeability, in other words, a higher sensitivity. But the change of the reservoirpermeability has no effect on thermal conductivity of the reservoir. There is nocorrelation of fracture aperture and thermal conductivity of fractured reservoirs.There is a negative correlation of the unit volume of fractured reservoir space and thermal conductivity of fractured reservoirs, and the impaction is large. When thefracture space is small (less than100m), the greater the change in the thermalconductivity of the reservoir due to differences in fracture spacing, namelysensitivity higher.In summary, usually use both conservative and reactive tracers in EGSgeothermal tracer tests, and evaluate fractured reservoir connectivity and fracture-matrix heat exchange area by the method of combining numerical simulation andfield tests. While studying the abroad experience of EGS field tracer tests, this studyalso lay the foundation to carry out our deep geothermal field tracer tests andaccelerate the development of domestic deep geothermal tracer technology, but alsoprovide a theoretical basis for the design of EGS engineering and evaluation ofreservoir artificial fracturing effect.