The matrix volume of coal swells when CO2 / CH4 adsorb on the coal structure. In coalbed gas reservoirs, matrix swelling could cause the fracture aperture width to decrease, causing a considerable reduction in permeability. On a unit concentration basis, CO2 causes greater degree of coal matrix swelling compared to CH4. Much of this difference is attributable to the differing sorption capacity that coal has towards carbon dioxide and methane. This condition in a coal reservoir would lead to differential swelling. Differential swelling will have consequences in terms of porosity / permeability loss, with serious implication for the performance and implementation of carbon sequestration projects. Coal can be understood as a macromolecular cross-linked polymeric structure. An experimental effort has been made to measure the differential swelling effect of CO2 / CH4 on this macromolecular structure and to theoretically translate that effect in terms of porosity and permeability. A unique feature of this work is that, real time permeability measurements were done to see the true effect of differential strain from CH4 saturated coal core flooding experiments. IntroductionCoal matrix is heterogeneous and is characterized by three different porosity systems -micropore, mesopore and macropore. The macropores are the cleats, which are sub-vertically oriented to the bedding plane in coal.The cleat system consists of the face cleats, continuous throughout the reservoir, and butt cleats, which are discontinuous and terminate against the face cleat.Permeability of coal is recognized as the most important parameter for fluid transport through the seam. Being normal to the bedding plane and orthogonal to each other, the face and the butt cleats in coal seams are usually sub-vertically oriented. Thus changes in the cleat permeability can be considered to be primarily controlled by the prevailing effective horizontal stresses that act across the cleats, rather than the effective vertical stress, defined as the difference between the overburden stress and the pore pressure. During primary methane production, two distinct phenomenons are associated with reservoir pressure depletion, with opposing effects on coal permeability. The first is an increase in the effective horizontal stress under uniaxial strain conditions (Jaeger and
Many countries and companies are developing geothermal systems as a sustainable, secure, and domestic energy source. However, in the Netherlands, with a low thermal gradient, there are no governmental incentives for such developments, making geothermal heat and electricity production at best marginally economic. Therefore smart solutions are needed as to economize geothermal systems, such as integration into existing infrastructure, exploitation of synergies with fossil-fuel based systems, and innovation on well-construction technology.The Delft Geothermal Project was launched to provide for a demonstration of solutions to these needs. Initiated by students, staff and alumni of the Applied Geotechnology department of TU Delft, it evolved into a broad consortium of commercial, governmental and industrial parties aiming to develop an innovative geothermal system at the TU Delft campus. This system 1) is designed for commercial heat production for a grid heating network, 2) will be constructed with innovative drilling technology, and 3) will as well serve as an in-situ laboratory for geothermal measurements and experiments. As such, it provides for an energy production facility, a technology demonstration case, and a research facility.However, only assessing the system as described above would not honor the most valuable synergies that can be achieved. In the presence of existing gridheating networks, produced geothermal heat can be included in the gross energy mix. As such, a multi-source feeding of the network is achieved improving delivery reliability. By combing geothermal sources with power/heat cogeneration, a peak shaving effect on heat demand can be achieved. By colocating the geothermal system with carbon-based energy systems (such as cogeneration), CO 2 can be captured and dissolved in the return water as 'sparkling water' for co-injection, providing a safe and durable CO 2 sequestration option. When the geothermal source provides heat of sufficient quality (i.e. sufficient flux and high enough temperature), the heat can be used for electricity production, or can be cascaded through high-and low-temperature grid heating networks.As such, effective systems and network integration is achieved with a very high degree of flexibility. For this, the Zero-Emission Power Hub concept is proposed: a hub of energy networks and production systems which optimally exploits synergies, provides for back-up production, while minimizing CO 2 exhaust into the atmosphere. This way, we believe it is possible to create an economically feasible, environmentally sustainable multipurpose energy system. Enabling technologies for this are being identified and developed: To enable drilling deep geothermal
The high energy prices in the past year and the political and public demand for CO 2 reduction show that geothermal energy can compete with conventional (i.e. carbon-based) energy sources in North-western Europe. The accelerated transformation of glasshouses in the Netherlands, from conventional to geothermal heating, shows that the economics are positive. In addition, mining geothermal water for city heating (Heerlen, the Hague) and the combination of geothermal with co-generation of heat and electricity are being implemented. More conventional geothermal applications are planned for the near future. However, this also means that conflicts of interests are to be expected. In a country with about seventeen million people living on only 34000 km 2 land, the infrastructure is rather dense. Hence, the presence of geothermal constructions in densely populated areas requires effective development strategies and asset management concepts. At the same time, the availability of infrastructure also creates opportunities.Conventional exploration in the Dutch sub-surface was aimed at hydrocarbons. Besides the giant Groningen Gasfield, many small oil and gas fields have been discovered and are being, or have been produced. Because of that, geophysical exploration data and appraisal wells cover a major part of the Netherlands. Most of the discovered fields are at depths over 1.5 km and by that in the depth range of geothermal interest, i.e. they provide data on geo-temperatures, aquifers and their sedimentological and reservoir characteristics. Evaluation of the well data resulted in a low resolution geothermal map of the country. However, for successful implementation, the subsurface needs systematic characterization in terms of reservoir existence, quality and flow, as well as geothermal gradients. Deliverability of the reservoir in terms of production/injection-flow and temperature are two major critical parameters for the economics of any geothermal project. Considering the dense infrastructure, both space at the surface and in the subsurface are relevant parameters that must be considered.The new concepts for composite drilling of relatively shallow wells (< 2 km) and novel ideas of (economically) combining hydrocarbon and geothermal exploration/exploitation at greater depths gives more opportunities; respectively smaller footprints and higher production temperatures. For the common shallow doublets, existing technology as already used over the last decades in France and Germany, are available. However, the combination of higher temperatures and pressures of deeper reservoirs needs the expertise of oil exploration combined with high temperature geothermal projects such as performed in Iceland and Italy.New asset concepts include geothermal combined with electricity/heat cogeneration systems. When they are linked with CO 2 co-injection, innovative applications of Enhanced and Unconventional Geothermal Systems can lead to zero-emission energy production. Feasibility studies and demonstration projects on combined co-injecti...
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