33 research outputs found
Measuring hydraulic fracture apertures: A comparison of methods
Hydraulic fracture apertures predominantly control fluid transport in fractured rock masses. Hence, the objective of the current study is to investigate and compare three different laboratory-scale methods to determine hydraulic apertures in fractured (Fontainebleau and Flechtinger) sandstone samples with negligible matrix permeability. Direct measurements were performed by using a flow-through apparatus and a transient-airflow permeameter. In addition, a microscope camera permitted measuring the mechanical fracture apertures from which the corresponding hydraulic apertures were indirectly derived by applying various empirical correlations. Single fractures in the sample cores were generated artificially either by axial splitting or by a saw cut resulting in hydraulic apertures that ranged between 8 and 66 µm. Hydraulic apertures, accurately determined by the flow-through apparatus, are used to compare results obtained by the other methods. The transient-airflow permeameter delivers accurate values, particularly when repeated measurements along the full fracture width are performed. In this case, the derived mean hydraulic fracture apertures are in excellent quantitative agreement. When hydraulic apertures are calculated indirectly from optically determined mechanical apertures using empirical equations, they show larger variations that are difficult to compare with the flow-through-derived results. Variations in hydraulic apertures as observed between methods are almost certainly related to differences in sampled fracture volume. Overall, using direct flow-through measurements as a reference, this study demonstrates the applicability of portable methods to determine hydraulic fracture apertures at both the laboratory and outcrop scales
Interpretation of permeability change due to effective stress with special focus on pore space geometry
see Abstract Volum
Outcrop analogue study to determine reservoir properties of the Los Humeros and Acoculco geothermal fields, Mexico
The Los Humeros geothermal system is steam dominated and currently under exploration with 65 wells (23 producing). Having temperatures above 380 ∘C, the system is characterized as a super hot geothermal system (SHGS). The development of such systems is still challenging due to the high temperatures and aggressive reservoir fluids which lead to corrosion and scaling problems. The geothermal system in Acoculco (Puebla, Mexico; so far only explored via two exploration wells) is characterized by temperatures of approximately 300 ∘C at a depth of about 2 km. In both wells no geothermal fluids were found, even though a well-developed fracture network exists. Therefore, it is planned to develop an enhanced geothermal system (EGS).
For better reservoir understanding and prospective modeling, extensive geological, geochemical, geophysical and technical investigations are performed within the scope of the GEMex project. Outcrop analogue studies have been carried out in order to identify the main fracture pattern, geometry and distribution of geological units in the area and to characterize all key units from the basement to the cap rock regarding petro- and thermo-physical rock properties and mineralogy. Ongoing investigations aim to identify geological and structural heterogeneities on different scales to enable a more reliable prediction of reservoir properties. Beside geological investigations, physical properties of the reservoir fluids are determined to improve the understanding of the hydrochemical processes in the reservoir and the fluid-rock interactions, which affect the reservoir rock properties
Permeability of matrix-fracture systems under mechanical loading – constraints from laboratory experiments and 3-D numerical modelling
The permeability of single fractures is commonly
approximated by the cubic law assumption, which is however
only valid under the condition of a single phase laminar flow
between parallel plates. Departure from cubic law are related
to many features like aperture fluctuations due to fracture
surface roughness, relative shear displacement, the amount
of flow exchange between the matrix and the fracture itself,
etc. In order to quantify constitutive relationships among the
aforementioned aspects, we have conducted a flow-through
experiment with a porous rock sample (Flechtinger sandstone)
containing a single macroscopic fracture. Based on
this experiment, we obtained range of variations of intrinsic
rock parameters, permeability and stress-strain relationships
of the combined matrix-fracture system under hydrostatic
loading. From the measured deformation of the matrixfracture
system, we derived the evolution in the mechanical
aperture of the fracture. In order to quantify the processes
behind the laboratory observations, we carried out coupled
hydro-mechanical simulations of the matrix-fracture system.
Navier–Stokes flow was solved in the 3-dimensional open
rough fracture domain, and back-coupled to the Darcy flow
and the poroelastic behaviour of the rock matrix. The results
demonstrate that the elastic behaviour and the related permeability
alteration of the fracture domain could be captured by
the numerical simulation. Furthermore, the stress-strain values
obtained in the vicinity of the fracture asperities suggest
that inelastic deformation develops at low mechanical load.
An attempt was made to quantify the inelastic deformation
by using the failure envelope obtained by laboratory experiments
(whether tensile, shear, compaction, or a combination
of those). However, change in permeability observed in the
experiments are significantly larger than that in the simulation
showing the importance of plastic deformation during
opening and closure of the fracture and its impact on the cubic
law approximation
Well path design and stimulation treatments at the geothermal research well GtGrSk4/05 in Groß Schönebeck
see Abstract Volum
A 4D view on the evolution of metamorphic dehydration reactions
Metamorphic reactions influence the evolution of the Earth's crust in a range of tectonic settings. For example hydrous mineral dehydration in a subducting slab can produce fluid overpressures which may trigger seismicity. During reaction the mechanisms of chemical transport, including water expulsion, will dictate the rate of transformation and hence the evolution of physical properties such as fluid pressure. Despite the importance of such processes, direct observation of mineral changes due to chemical transport during metamorphism has been previously impossible both in nature and in experiment. Using time-resolved (4D) synchrotron X-ray microtomography we have imaged a complete metamorphic reaction and show how chemical transport evolves during reaction. We analyse the dehydration of gypsum to form bassanite and H2O which, like most dehydration reactions, produces a solid volume reduction leading to the formation of pore space. This porosity surrounds new bassanite grains producing fluid-filled moats, across which transport of dissolved ions to the growing grains occurs via diffusion. As moats grow in width, diffusion and hence reaction rate slow down. Our results demonstrate how, with new insights into the chemical transport mechanisms, we can move towards a more fundamental understanding of the hydraulic and chemical evolution of natural dehydrating systems
Evaluation of an IBAD thin-film process as an alternative method for surface incorporation of bioceramics on dental implants: a study in dogs
Experimentelle Untersuchung des Einflusses von Dekarbonatisierungsreaktionen auf die Transporteigenschaften von Gesteinen
Available from TIB Hannover: RR 6134(2000,14) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman
Coupling of hydraulic and electrical transport properties in sandstones
see Abstract VolumeIstituto Nazionale di Geofisica e Vulcanologia, Italy (INGV)
Centre National de la Recherche Scientifique (CNRS)
ExxonMobil Upstream Research CompanyUnpublishedErice, Italyope