7,434 research outputs found
Seismic Ray Impedance Inversion
This thesis investigates a prestack seismic inversion scheme implemented in the ray
parameter domain. Conventionally, most prestack seismic inversion methods are
performed in the incidence angle domain. However, inversion using the concept of
ray impedance, as it honours ray path variation following the elastic parameter
variation according to Snellâs law, shows the capacity to discriminate different
lithologies if compared to conventional elastic impedance inversion.
The procedure starts with data transformation into the ray-parameter domain and then
implements the ray impedance inversion along constant ray-parameter profiles. With
different constant-ray-parameter profiles, mixed-phase wavelets are initially estimated
based on the high-order statistics of the data and further refined after a proper well-to-seismic
tie. With the estimated wavelets ready, a Cauchy inversion method is used to
invert for seismic reflectivity sequences, aiming at recovering seismic reflectivity
sequences for blocky impedance inversion. The impedance inversion from reflectivity
sequences adopts a standard generalised linear inversion scheme, whose results are
utilised to identify rock properties and facilitate quantitative interpretation. It has also
been demonstrated that we can further invert elastic parameters from ray impedance
values, without eliminating an extra density term or introducing a Gardnerâs relation
to absorb this term.
Ray impedance inversion is extended to P-S converted waves by introducing the
definition of converted-wave ray impedance. This quantity shows some advantages in
connecting prestack converted wave data with well logs, if compared with the shearwave
elastic impedance derived from the Aki and Richards approximation to the
Zoeppritz equations. An analysis of P-P and P-S wave data under the framework of
ray impedance is conducted through a real multicomponent dataset, which can reduce
the uncertainty in lithology identification.Inversion is the key method in generating those examples throughout the entire thesis
as we believe it can render robust solutions to geophysical problems. Apart from the
reflectivity sequence, ray impedance and elastic parameter inversion mentioned above,
inversion methods are also adopted in transforming the prestack data from the offset
domain to the ray-parameter domain, mixed-phase wavelet estimation, as well as the
registration of P-P and P-S waves for the joint analysis.
The ray impedance inversion methods are successfully applied to different types of
datasets. In each individual step to achieving the ray impedance inversion, advantages,
disadvantages as well as limitations of the algorithms adopted are detailed. As a
conclusion, the ray impedance related analyses demonstrated in this thesis are highly
competent compared with the classical elastic impedance methods and the author
would like to recommend it for a wider application
Bifurcations and dynamics emergent from lattice and continuum models of bioactive porous media
We study dynamics emergent from a two-dimensional reaction--diffusion process
modelled via a finite lattice dynamical system, as well as an analogous PDE
system, involving spatially nonlocal interactions. These models govern the
evolution of cells in a bioactive porous medium, with evolution of the local
cell density depending on a coupled quasi--static fluid flow problem. We
demonstrate differences emergent from the choice of a discrete lattice or a
continuum for the spatial domain of such a process. We find long--time
oscillations and steady states in cell density in both lattice and continuum
models, but that the continuum model only exhibits solutions with vertical
symmetry, independent of initial data, whereas the finite lattice admits
asymmetric oscillations and steady states arising from symmetry-breaking
bifurcations. We conjecture that it is the structure of the finite lattice
which allows for more complicated asymmetric dynamics. Our analysis suggests
that the origin of both types of oscillations is a nonlocal reaction-diffusion
mechanism mediated by quasi-static fluid flow.Comment: 30 pages, 21 figure
A study of underbalanced drilling application for granite basements in Vietnam
Underbalanced drilling (UBD) has gained popularity during the recent years as it
provides a method to prevent formation damage, minimize lost circulation risks, and
increase the rate of penetration. However, drilling with a bottomhole pressure less than
the formation pore pressure will often increase the risk of borehole instability due to the
shear or compression failure of the rock adjacent to the wellbore. The extent of rock
failure is related directly to the pressure in the annulus between the drillpipe, collars and
the wellbore which can only be calculated through modelling multiphase flow in the
drilling system. The relationship between rock failure and wellbore hydraulics becomes
more complex due to the appearance of the influx formation fluid in UBD. Therefore,
the aim of this research is to describe methods to solve the complex interaction of
wellbore stability, rock yielding, collapse, wellbore hydraulics, and production capacity
during UBD operations.
To achieve the aim, analytical and numerical solutions have been codified into
two programs WELLST, and UBDRILL. Commercial software packages such as
ABAQUS, PERFORM, HYMOD were also used to model the process. Field data from
granite basement reservoirs of Basin X, Vietnam were used as the parameters input into
the model to calculate. This research includes:
⢠An analysis of the influences of time dependence, thermal and hydraulic
diffusivity, wellbore pressure changes, inclination and azimuth variation,
poroelastic and thermo-poroelastic deformation, cooling and heating effects
on wellbore stability in UBD.
⢠An analysis of pressure, temperature, fluid properties distribution in the
annulus and inside the drillpipe while UBD.
⢠An analysis of the suggested liquid gas rate window (LGRW) which gives
field engineers flexibility in the selection of liquid and gas injection rates on
the drilling site when UBD is applied.
⢠An estimation of production capacity in UBD operations.
These results were obtained by analyzing the field data of granite basement
formations and clastic formations of Basin X, Vietnam which is under compression in a
strike-slip environment
The Mechanical Behavior of Salt X
Rock salt formations have long been recognized as a valuable resource - not only for salt mining but for construction of oil and gas storage caverns and for isolation of radioactive and other hazardous wastes. Current interest is fast expanding towards construction and re-use of solution-mined caverns for storage of renewable energy in the form of hydrogen, compressed air and other gases. Evaluating the long term performance and safety of such systems demands an understanding of the coupled mechanical behavior and transport properties of salt. This volume presents a collection of 60 research papers defining the state-of-the-art in the field. Topics range from fundamental work on deformation mechanisms and damage of rock salt to compaction of engineered salt backfill. The latest constitutive models are applied in computational studies addressing the evolution and integrity of storage caverns, repositories, salt mines and entire salt formations, while field studies document ground truth at multiple scales. The volume is structured into seven themes: Microphysical processes and creep models Laboratory testing Geological isolation systems and geotechnical barriers Analytical and numerical modelling Monitoring and site-specific studies Cavern and borehole abandonment and integrity Energy storage in salt caverns The Mechanical Behavior of Salt X will appeal to graduate students, academics, engineers and professionals working in the fields of salt mechanics, salt mining and geological storage of energy and wastes, but also to researchers in rock physics in general
A fully coupled 3D wave-current interaction model on unstructured grids
We present a new modeling system for wave-current interaction based on unstructured grids and thus suitable for very large-scale high-resolution multiscale studies. The coupling between the 3D current model (SELFE) and the 3rd generation spectral wave model (WWM-II) is done at the source code level and the two models share same sub-domains in the parallel MPI implementation in order to ensure parallel efficiency and avoid interpolation. We demonstrate the accuracy, efficiency, stability and robustness of the coupled SELFE-WWM-II model with a suite of progressively challenging benchmarks with analytical solution, laboratory data, and field data. The coupled model is shown to be able to capture important physics of the wave-current interaction under very different scales and environmental conditions with excellent convergence properties even in complicated test cases. The challenges in simulating the 3D wave-induced effects are highlighted as well, where more research is warranted
Modelling of hydraulic fracturing in unconventional reservoirs
Hydraulic fracturing (HF) is a process of fluid injection into the well in order to create tensile stresses in the rock to overcome the tensile strength of the formation. In this study, the development and application of a fuzzy model to predict the efficiency of hydraulic fracturing is presented with application in a coal mine as an unconventional reservoir. The most important parameters affecting the HF process of a coal seam are: dip, thickness, seam uniformity, roof and floor conditions, reserve of coal seam and coal strength. In the developed model, the efficiency of hydraulic fracturing of coal seams is calculated as a dimensionless numerical index within the range 0-100. The suggested numerical scale categorizes the efficiency of HF of seams to very low, low, medium, high and very high, each one being specified by a numerical range as a subset of the above range (0-100). HF in the coal bed in PARVADEH 4 Tabas mine in Iran is investigated as a case study. The results show that the developed model can be used to identify seams that have high potential for HF Moreover, a three-phase hydro-mechanical model is developed for simulating hydraulic fracturing. The three phases include: porous solid, fracturing fluid and reservoir fluid. Two numerical simulators (ANSYS Fluent for fluid flow and ANSYS Mechanical for geomechanical analysis) are coupled together to model multiphase fluid flow in hydraulically fractured rock undergoing deformations, ranging from linear elastic to large, nonlinear inelastic deformations. The two solvers are coupled, using system coupling in ANSYS Workbench. The coupled problem of fluid flow and fracture propagation is solved numerically. The fluid flow model involves solving the Navier-Stokes equations using the finite volume method. The flow model is coupled with the geomechanics model to simulate the interaction between fluid flow inside the fracture with rock deformations. For any time step, the pore pressures from the flow model are used as input for the geomechanics model for the determination of stresses, strains, and displacements. The strains derived from the gomechanics model are in turn used to calculate changes to the reservoir parameters that are fed as input to the flow model. This iterative process continues until both (fluid and solid) models are converged. The laboratory-scale study of hydraulic fracturing in the Second White Specks (SWS) shale was simulated using the developed model. The numerical and experimental results were compared. Comprison of the results shows that the numerical model can predict the behaviour of the shale under hydraulic fracturing with a good accuracy
Market-based Options for Security of Energy Supply
Energy market liberalization and international economic interdependence have affected governmentsâ ability to react to security of supply challenges. On the other side, whereas in the past security of supply was largely seen as a national responsibility, the frame of reference has increasingly become the EU in which liberation increases security of supply mainly by increasing the number of markets participants and improving the flexibility of energy systems. In this logic, security of supply becomes a risk management strategy with a strong inclination towards cost effectiveness, involving both the supply and the demand side. Security of supply has two major components that interrelate: cost and risk. This paper focus the attention on costs in the attempt to develop a market compatible approach geared towards security of supply.Energy supply, Market-based options
Simulation Studies For Relative Importance Of Unconventional Reservoir Subgrid Scale Physics Parameters
In this endeavor we attempt to better understand gas transport in shale gas reservoirs, specifically the impact and effects of different physical phenomena. We start by documenting the nature of the reservoirs and the need for accurate modeling of various physical phenomena in multiple interconnected continua. The physical phenomena of interest include non-linear Forchheimer flow, Knudsen diffusion in the form of slip Klinkenberg flow and adsorption/desorption. The numerical methods used in the reservoir simulator are also introduced, along with a derivation of the main equations used. Various verification and validation results are compared against manufactured and analytical solutions and finally advanced features including mesh adaptivity and multi-block support are showcased. Several detailed parameter survey studies are conducted with realistic and exaggerated field values to identify the need for advanced physics models based on deviation from Darcy models. Recommendations as to the applicability of each model are presented along with suggested best practices of when to apply these models in real simulations. A redefinition of the SRV is proposed, based on the need to apply a non-Darcy flow model. This new definition would highlight the need for advanced (and costly) non-linear flow ow models near the wells and hydraulic fractures. The judicious application of computationally intensive physical models in the SRV and lower fidelity models further away is presented as an efficient alternative to large scale high fidelity simulations
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