Numerical modelling in research on geothermal systems

Nowadays, numerical modelling is a common tool for support research of geothermal systems. This is possible because of development of computer sciences and access to software dedicated to numerical modelling of hydrogeological processes. With computer applications researches can do scheme of hydrogeological conditions and simulate work of geothermal systems and thermal water intakes. Researches create numerical models of geothermal systems in regional and local scale, for simulating work of specific thermal water formation and intakes and their particular elements - well active zone for example.In parallel with the economic development of the use of thermal water in Poland there are a lot of research projects where numerical modelling occurs as a primary or supporting tool. This paper provides an overview of research issues where the solution of the problem was found with using computer application and numerical simulators

Numerical Modelling and Simulation Optimization of Geothermal Reservoirs Using the Tough2 Family of Codes

In order to improve the reservoir engineering activities and, in particular, to optimize numerical modelling and simulation of geothermal reservoirs using the TOUGH family of codes, it has been decided to use the software T2Well for the interpretation of well-tests, coupling T2Well with the equation of state module EWASG, which describes the typical thermodynamic condition in high enthalpy geothermal reservoirs. T2Well-EWASG has been coupled and tested through the typical process of verification and validation. The application of T2Well-EWASG for the interpretation of well-tests related to the slim hole WW-01 drilled in the Wotten Waven Field (Commonwealth of Dominica) proves that it can be used as a tool for integrated interpretation of surface and downhole measurements collected during the performance of production tests in geothermal wells. The strength of this tool is that it allows to reduce the different possible solutions (in terms of reservoir characterization) within an acceptable error, by allowing the interpretation of surface and downhole measurements in conjunction, instead of separately. From this point of view T2Well-EWASG can effectively be used as a tool which allows an improvement of reservoir engineering activities. Finally, the huge amount of data managed during these activities has permitted to test and project the improvement of pre- and post- processing tools specific for TOUGH2 created by the geothermal research group of DICAM. In particular, the pre- and post-processing tools have been validated with a case study dealing with the migration of non-condensable gases in deep sedimentary formation

Numerical investigations of heat and mass transport in fractured porous rock masses

Fluid flow processes in the subsurface are accompanied by heat and mass transport with several important feedbacks including reactive flow, and precipitation/dissolution processes. Heat and mass transport through fractured rock masses occurs in many natural systems such as the plumbing of volcanic systems, mesothermal ore deposits, and post-seismic fluid flow. Anthropogenically-driven systems, such as fluid-injection in Enhanced Geothermal Systems (EGS), and the injection of waste-water from hydrocarbon extraction also involve heat and mass transport through porous or fractured rocks. Understanding in detail how mass and heat transfer interact in natural or in industrial applications requires numerical models in combination with field and laboratory experiments to determine the dominating factors. This thesis examines the impact of heat and mass transport on high pressure fluid propagation in the subsurface, as well as different numerical approaches of transient heat flow in fractured porous media and the heat exchange between flowing fluid and host rock. Many fluid-triggered seismic events show a tendency for upward migration of the seismic cloud, generally assumed to reflect a fluid-pressure dependent permeability. In a numerical investigation that combines pressure-dependent permeability with thermal and salinity effects, it is found that over short timescales pressure-dependent permeability does indeed have the strongest influence on asymmetric diffusion. However, it is also demonstrated that over longer timescales, for example the lifetime of a geothermal reservoir, temperature and salinity effects play an increasingly important role. Assessing the thermal field of a geothermal resource or in a CO2 sequestration project is essential for proper design and management. Typically, numerical simulations assume that the fluid and solid phases are in thermal equilibrium, an assumption that has to date not been investigated in detail. This assumption is examined in this work by simulating fluid and heat flow in a simple geometry to analyse the influence of site specific parameters on the simulation result. It is shown that the equilibrium model is not sensitive to porosity contrasts, while the non-equilibrium model shows a sensitivity to porosity contrasts, with simulation results diverging more strongly in less permeable zones. In a simulation of a hypothetical geothermal system, the equilibrium model shows higher production temperatures with a divergence of up to 7% between the approaches, which could impact the economic feasibility of a project. Finally, a new approach is introduced to determine the heat transfer coefficient h between rock walls and flowing fluid using the non-equilibrium model. Based on a numerical experimental setup with simple geometry and steady state scenario, a dynamic heat transfer coefficient is derived that depends on fracture aperture and flow velocity. This model is based on well-defined physical parameters, it is adaptable to complex geometries, and intrinsically adjusts to spatial heterogeneities and temporal changes in flow and temperature field. A possible extension of this dynamic approach is demonstrated in numerical simulations the reservoir scale

The conductive geothermal field as an energy and economic entity:Effects and implications for the province of Groningen, North-East Netherlands

Geothermische bronnen leveren hernieuwbare energie die direct als warmte kan worden toegepast, danwel gebruikt voor het opwekken van elektriciteit. Dit proefschrift richt zich op het identificeren en analyseren van mogelijke geothermische energie opwekking in noordoost Nederland. Dit potentieel wordt op twee manieren beschouwd: allereerst door de sterke warmtestroom door zoutlagen te onderzoeken en te benutten. De tweede casus is een gepland geothermisch systeem in de stad Groningen dat stap voor stap zowel technisch als economisch geëvalueerd wordt. De warmtegeleiding in zoutlagen is drie tot vier maal hoger in vergelijking met andere sedimenten. Dit heeft tot effect dat er direct boven een zoutkoepel een relatief hogere temperatuur wordt bereikt. Dit betekent dat een geothermisch project aldaar minder kosten hoeft te maken om toch interessante temperaturen te bereiken. Het temperatuurverschil tussen de top van een zoutkoepel en andere sedimenten op dezelfde diepte kan wel 25˚C bedragen, wat resulteert in een 40% hogere warmteopbrengst alsmede een belangrijke kostenbesparing omdat men minder diep hoeft te boren. In de analyse van het voorgenomen geothermische project van de stad Groningen worden de onzekerheden van de verschillende project elementen onder de loep genomen. Dit betreft ten eerste geologische en operationele onzekerheden en hun effect op het beschikbare thermisch vermogen. Vervolgens wordt gekeken naar het gedrag van het systeem in respons tot seizoensvariaties in de warmtevraag. Hierbij wordt ook onderzocht of dit tot geochemische veranderingen in de ondergrond leidt. Tenslotte wordt aan de hand van technische en economische modellering onderzocht wat de financiële opbrengst van het project kan zijn. Voor dit laatste aspect blijkt de seizoensafhankelijke warmtevraag een belangrijke succesfactor. De beschikbaarheid van warmteopslag capaciteit is hierbij essentieel. Verder wordt duidelijk gemaakt dat een juiste fasering van de projectonderdelen en een aanpassing van het subsidie kader de economische waarde van het project aanzienlijk zouden kunnen doen toenemen