126 research outputs found
On the importance of the heterogeneity assumption in the characterization of reservoir geomechanical properties
The geomechanical analysis of a highly compartmentalized reservoir is performed to simulate
the seafloor subsidence due to gas production. The available observations over the hydrocarbon
reservoir consist of bathymetric surveys carried out before and at the end of a 10-yr
production life. The main goal is the calibration of the reservoir compressibility cM, that is,
the main geomechanical parameter controlling the surface response. Two conceptual models
are considered: in one (i) cM varies only with the depth and the vertical effective stress
(heterogeneity due to lithostratigraphic variability); in another (ii) cM varies also in the horizontal
plane, that is, it is spatially distributed within the reservoir stratigraphic units. The latter
hypothesis accounts for a possible partitioning of the reservoir due to the presence of sealing
faults and thrusts that suggests the idea of a block heterogeneous system with the number of
reservoir blocks equal to the number of uncertain parameters. The method applied here relies
on an ensemble-based data assimilation (DA) algorithm (i.e. the ensemble smoother, ES),
which incorporates the information from the bathymetric measurements into the geomechanical
model response to infer and reduce the uncertainty of the parameter cM. The outcome from
conceptual model (i) indicates that DA is effective in reducing the cM uncertainty. However,
the maximum settlement still remains underestimated, while the areal extent of the subsidence
bowl is overestimated. We demonstrate that the selection of the heterogeneous conceptual
model (ii) allows to reproduce much better the observations thus removing a clear bias of
the model structure. DA allows significantly reducing the cM uncertainty in the five blocks
(out of the seven) characterized by large volume and large pressure decline. Conversely, the
assimilation of land displacements only partially constrains the prior cM uncertainty in the
reservoir blocks marginally contributing to the cumulative seafloor subsidence, that is, blocks
with low pressure
Estimate of a spatially variable reservoir compressibility by assimilation of ground surface displacement data
Abstract.
Fluid extraction from producing hydrocarbon reservoirs can cause anthropogenic land subsidence. In
this work, a 3-D finite-element (FE) geomechanical model is used to predict the land surface displacements above
a gas field where displacement observations are available. An ensemble-based data assimilation (DA) algorithm
is implemented that incorporates these observations into the response of the FE geomechanical model, thus re-
ducing the uncertainty on the geomechanical parameters of the sedimentary basin embedding the reservoir. The
calibration focuses on the uniaxial vertical compressibility
c
M
, which is often the geomechanical parameter to
which the model response is most sensitive. The partition of the reservoir into blocks delimited by faults moti-
vates the assumption of a heterogeneous spatial distribution of
c
M
within the reservoir. A preliminary synthetic
test case is here used to evaluate the effectiveness of the DA algorithm in reducing the parameter uncertainty
associated with a heterogeneous
c
M
distribution. A significant improvement in matching the observed data is
obtained with respect to the case in which a homogeneous
c
M
is hypothesized. These preliminary results are
quite encouraging and call for the application of the procedure to real gas fields
Very low noise AC/DC power supply systems for large detector arrays
In this work, we present the first part of the power supply system for the CUORE and LUCIFER arrays of bolometric detectors. For CUORE, it consists of AC/DC commercial power supplies (0–60 V output) followed by custom DC/DC modules (48 V input, ±5 V to ±13.5 V outputs). Each module has 3 floating and independently configurable output voltages. In LUCIFER, the AC/DC + DC/DC stages are combined into a commercial medium-power AC/DC source. At the outputs of both setups, we introduced filters with the aim of lowering the noise and to protect the following stages from high voltage spikes that can be generated by the energy stored in the cables after the release of accidental short circuits. Output noise is very low, as required: in the 100 MHz bandwidth the RMS level is about 37 μVRMS (CUORE setup) and 90 μVRMS (LUCIFER setup) at a load of 7 A, with a negligible dependence on the load current. Even more importantly, high frequency switching disturbances are almost completely suppressed. The efficiency of both systems is above 85%. Both systems are completely programmable and monitored via CAN bus (optically coupled)
Accurate analytical approximation of asteroid deflection with constant tangential thrust
We present analytical formulas to estimate the variation of achieved deflection for an Earth-impacting asteroid following a continuous tangential low-thrust deflection strategy. Relatively simple analytical expressions are obtained with the aid of asymptotic theory and the use of Peláez orbital elements set, an approach that is particularly suitable to the asteroid deflection problem and is not limited to small eccentricities. The accuracy of the proposed formulas is evaluated numerically showing negligible error for both early and late deflection campaigns. The results will be of aid in planning future low-thrust asteroid deflection mission
Targeted delivery of photosensitizers: efficacy and selectivity issues revealed by multifunctional ORMOSIL nanovectors in cellular systems
PEGylated and non-PEGylated ORMOSIL nanoparticles prepared by microemulsion condensation of vinyltriethoxy-silane (VTES) were investigated in detail for their micro-structure and ability to deliver photoactive agents. With respect to pure silica nanoparticles, organic modification substantially changes the microstructure and the surface properties. This in turn leads to a modulation of both the photophysical properties of embedded photosensitizers and the interaction of the nanoparticles with biological entities such as serum proteins. The flexibility of the synthetic procedure allows the rapid preparation and screening of multifunctional nanosystems for photodynamic therapy (PDT). Selective targeting of model cancer cells was tested by using folate, an integrin specific RGD peptide and anti-EGFR antibodies. Data suggest the interference of the stealth-conferring layer (PEG) with small targeting agents, but not with bulky antibodies. Moreover, we showed that selective photokilling of tumour cells may be limited even in the case of efficient targeting because of intrinsic transport limitations of active cellular uptake mechanisms or suboptimum localization
A coherent polarimeter array for the Large Scale Polarization Explorer balloon experiment
We discuss the design and expected performance of STRIP (STRatospheric
Italian Polarimeter), an array of coherent receivers designed to fly on board
the LSPE (Large Scale Polarization Explorer) balloon experiment. The STRIP
focal plane array comprises 49 elements in Q band and 7 elements in W-band
using cryogenic HEMT low noise amplifiers and high performance waveguide
components. In operation, the array will be cooled to 20 K and placed in the
focal plane of a meter telescope providing an angular resolution of
degrees. The LSPE experiment aims at large scale, high sensitivity
measurements of CMB polarization, with multi-frequency deep measurements to
optimize component separation. The STRIP Q-band channel is crucial to
accurately measure and remove the synchrotron polarized component, while the
W-band channel, together with a bolometric channel at the same frequency,
provides a crucial cross-check for systematic effects.Comment: In press on the Proceedings of the SPIE Conference Astronomical
Telescopes + instrumentation 2012, Amsterdam, paper 8446-27
QUBIC: the Q&U Bolometric Interferometer for Cosmology
The primordial B-mode polarisation of the Cosmic Microwave Background is the imprints of the gravitational wave background generated by inflation. Observing the B-mode is up to now the most direct way to constrain the physics of the primordial Universe, especially inflation. To detect these B-modes, high sensitivity is required as well as an exquisite control of systematics effects. To comply with these requirements, we propose a new instrument called QUBIC (Q and U Bolometric Interferometer for Cosmology) based on bolometric interferometry. The control of systematics is obtained with a close-packed interferometer while bolometers cooled to very low temperature allow for high sensitivity. We present the architecture of this new instrument, the status of the project and the self-calibration technique which allows accurate measurement of the instrumental systematic effects
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