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Joint inversion of 4D AVO and time-shifts for geomechanical evaluation
Get PDFThe research outlined in this thesis discusses the significance of geomechanical
deformation within and around producing reservoirs worldwide and its implications for
reservoir behaviour during production. It emphasizes the role of geomechanical
monitoring in understanding the changes in subsurface stress and strain caused by pore
pressure decline due to reservoir production. The resulting deformation can lead to
various issues such as compaction, fluid flow performance changes, and extension or
subsidence in the overburden or seafloor.
In this thesis, I begin with highlighting the use of travel timeshifts as valuable indicators
of geomechanical deformation in reservoirs and overburden. These timeshifts, caused by
changes in pore pressure, saturation, and physical displacements in rocks, can provide
insights into reservoir pressure models, areas for infill drilling, and overburden behaviour.
Overburden timeshifts can also indicate casing failures, making monitoring crucial to
mitigate wellbore instability risks. I then discuss the use of time-lapse amplitude variation-with-offset (AVO) analysis and timeshifts to distinguish between changes in
fluid saturation and reservoir pressure, facilitating reservoir characterization.
Geomechanical modelling is emphasized as an important component in the inversion
process for accurate estimation of reservoir pore pressure changes, with considerations
for density, overburden strains, and anisotropy. The study also introduces new analytic
approximations for time-lapse reflectivity, shedding light on the effects of geomechanics
on time-lapse AVO. The results from field-realistic synthetic modelling highlight the
potential of overburden amplitudes to estimate geomechanical contrasts across interfaces,
particularly in cases of localized reservoir depletion or steeply dipping reservoirs. This
information is valuable for mapping drilling hazards in the extending overburden. The
intercept term in time-lapse AVO can directly estimate vertical strain in the reservoir,
complementing time-shift information. The approach is applicable to compacting fields
with large overburden strains, where the AVO signature is defined at a discrete interface
determined by rock properties. I then highlight the importance of using field values
instead of laboratory values for accurate results, given the limitations of using laboratory
values in real field depletion scenarios. Neglecting density, overburden strains, and anisotropy in 4D AVO inversion can lead to significant errors in estimating reservoir pore
pressure changes.
Field-realistic synthetic modelling demonstrates that overburden amplitudes can be used
to estimate geomechanical contrasts, particularly in localized depletion or steeply dipping
reservoirs. Extracting vertical and lateral strains from time-lapse AVO attributes and
calibrating the difference between gradient and intercept may provide additional
attributes to monitor well deformation and assess risk.
A joint inversion scheme is presented, linking time-lapse P-wave AVO to geomechanical
strains. It is applied to both synthetic seismic data and field data from clastic and
carbonate fields in the North Sea. The time-lapse intercept attribute proves useful in
estimating vertical strain in the reservoir, while horizontal strains can be extracted from
the gradient term of time-lapse AVO. The distribution of horizontal strains may serve as
an additional attribute for monitoring overburden and reservoir deformation.
Incorporating time-lapse amplitude changes in 4D seismic response modelling is
highlighted as crucial for robust interpretation
A geomechanical correction for time-lapse amplitude variation with offset
No full textAccurate inversion of time-lapse amplitude variation with offset (AVO) to reservoir pressure change requires knowledge of strain/stress changes in the reservoir and overburden. These geomechanical effects have not been taken into account in previous studies. We have determined that there are three contributions of importance that must be included in the AVO equations: A density term in the reservoir, the seismic anisotropy generated by the reservoir deformations, and the impact of the changing overburden properties. To calculate the error in neglecting these contributions, we derived analytic expressions for the 4D intercept and gradient as functions of the strains developed in the reservoir and overburden during production. The 4D AVO behavior is found to be controlled by three R-factors that relate to time-lapse variations in P- A nd S-wave velocities. These factors can be estimated from rock-physics measurements in the laboratory or calibrated to field data measurements of time shifts via the well-known Hatchell-Bourne-Røste R-factor. Numerical computation indicates that the error in not accounting for the anisotropic contribution to the P-P reflectivity is 50%-300% for the 4D zero-offset intercept and 62%-155% for the 4D gradient. Thus, in most applications, the time-lapse anisotropy in the reservoir and the overburden cannot be neglected when estimating pressure changes using 4D AVO.</p
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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