Analytical model of cold water front advancement applied to geothermal reservoir 'I' + 'K' in Croatian exploitation field Ivanic

摘要

Jedan od važnijih čimbenika prilikom donošenja odluke o investiranju u neki geotermalni projekt je pouzdana procjena vremena obnovljivosti toplinske energije u ležištu. U današnje se vrijeme radi očuvanja okoliša i podržavanja ležišnog tlaka projekti s geotermalnim procesima izvode uz vraćanje vode u ležište nakon predaje topline. Predstavlja li neki geotermalni projekt dobru investiciju ovisi o različitim čimbenicima, posebice o uspješnu održavanju nepromjenjivima dva fizikalna parametra u što dužem periodu, a to su proizvodno-utisni kapacitet i temperatura proizvedene vode. Naime, povećanje količina utiskivane i proizvedene geotermalne vode može tijekom vremena utjecati na postupno smanjenje temperature vode na ušću proizvodne bušotine. To u konačnici može izazvati nedostatak energetskog potencijala za ciljani projekt. Poglavito je to važno u slučaju kada se vruća voda i/ili vodena para koriste u geotermalnim elektranama. U radu je izložen analitički model pomicanja fronte pothlađene vode kroz geotermalno ležište od utisne prema proizvodnoj bušotini, i to u ovisnosti o vremenu i utisnutim količinama. Rezultat proračuna daje podatak o vremenu nakon kojega će pothladena voda prodrijeti u proizvodnu bušotinu.%One of the major factors, when deciding upon investing into a certain geothermal project, is the reliable evaluation of the time of heat energy reproducibility in a reservoir. Nowadays, to protect the environment and maintain reservoir pressure, projects that include geothermal processes are performed with return of water in the same reservoir after delivery of thermal energy. The question whether a certain geothermal project is profitable depends on various factors, especially on maintaining two reservoir parameters temporally invariable as long as possible: production/injection capacity and temperature of produced water. Namely, after a time the increase of injected and produced quantities may cause a premature and faster temperature decrease of produced water. In the end, it may provoke energy deficiency for the aimed project. It is particularly important when hot water and/or steam are used in geothermal power plants for production of electricity. This article introduces the analytical model of cold-water front advancement through geothermal reservoir from injection to production well, and its dependence upon time and injection/production quantities. The result of calculations shows the time when cold-water breakthrough will occur in the production well. Calculations are made for geothermal reservoir „I"+„K" of the exploitation field Ivani6 - a promising geothermal source due to its good reservoir temperature and permeability characteristics. Attention is focused on the influence of different pore space geometry sorts within various reservoir rocks on the advance of the cold-water front. Heterogeneity and certain types of porosity, especially fractured, are emphasized, where the disadvantageous circumstance of premature cold-water breakthrough may be expected.