Geomechanical Modeling of In-Situ Stresses Around a Borehole

In this paper, we present a modelling of the in-situ stress state associated with the severe hole enlargement of a wellbore. Geomechanical information is relevant to assure wellbore stability, i.e., to prevent damages in the formation and later on, the casing. Many of the drilling parameters, as mud weight or the optimal orientation of the borehole, require some knowledge of the mechanical behaviour of the rock. The lack of these kind of data in exploratory areas, where there are usually insufficient constraints for the geological model, increases even more the risk, hence the costs. The present model uses the concepts of poroelasticity theory to compute the stationary 2D, brittle response of the formation around a borehole that is submitted to effective compressive horizontal stresses. The numerical solution is obtained using a finite element approximation. The initial stress state at the far field was estimated combining a frictional-failure theory with the observations of dipmeter caliper in a particular borehole that presents elongations in a preferential direction. The direction and relative extension of the observed breakouts at a particular depth are modelled successfully using formation realistic parameters and dimensions, although the exact shape of the borehole (at all angles) was unknown. For the particular case study, the orientation of the breakout is NE-SW, at about 82 degrees azimuth. Therefore, the maximum horizontal stress lies at approximately 350 degrees azimuth. The ratios of horizontal principal stresses to vertical stress that best honor the observations are SHmax = 2.3Sv and Shmin = 1.7Sv. The compressive strength necessary for the rock to fail, as indicated by the caliper data under this stress field, is about 140 MPa.Massachusetts Institute of Technology. Borehole Acoustics and Logging ConsortiumMassachusetts Institute of Technology. Earth Resources Laborator

Multiscale determination of in situ stress and fracture properties in reservoirs

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2008.Includes bibliographical references (p. 287-299).In this thesis we address the problem of determining in situ stress and fracture properties in reservoirs using borehole logs and surface seismic reflection data. The dissertation covers four subtopics. The first is the determination of horizontal stress magnitudes from measurements in a borehole. Two types of data used are stress-induced rock failures in the borehole, known as "breakouts," and the dispersions of polarized flexural waves which propagate along the borehole. Traditionally these data are analyzed to derive stress orientations but not magnitudes. To determine the magnitude of stresses directly from breakouts, we use an iterative elastic modeling of stresses around the borehole and Mohr-Coulomb failure criterion to match the borehole deformation. As a second method we use dispersion curves of the two polarized flexural waves and their crossover points. These methods are applied to data from a well in northeastern Venezuela. The combination of these two techniques provides a complete profile of stress as a function of depth since the first method is applied at the breakout depths and the second is applied everywhere else in the borehole. Both borehole methods agree in the estimation of stress orientation and magnitude. The maximum horizontal stress is in the NNW-SSE direction, in agreement with a regional stress model calculated from the relative motions of the Caribbean and South America plates. The magnitudes of principal stresses are on average, SHmax 1.1Sv (Sv: vertical stress) and Shmin 0.9Sv (Shmin: minimum horizontal stress). This suggests strike-slip faulting, consistent with earthquake mechanisms in the region. The in situ stresses play an important role on determining the properties of fractured formation. The azimuth of SHmax determines the preferred orientation of open fractures. Surface seismic reflection data provide the means for detecting the fractures.(cont.) The second contribution of this thesis is developing a method to detect discrete fractures, and to determine their orientation and average spacing. We developed a novel and practical technique, called the F-K method, based on the frequency wavenumber (f-k) domain analysis of seismic coda. The fractured medium targeted in this study is a network of rather regularly spaced, parallel, sub-vertical fractures, with dimensions similar to seismic wavelength. The seismic response of a fractured medium is studied by finite difference numerical models for a variety of situations where orientation, spacing, height, and fracture compliance are varied. In the direction normal to fractures, scattered waves propagate with slower apparent velocities than waves propagating along the fractures. The orientation of fractures is well constrained from the azimuthal dependence of scattering. The spectral characteristics (frequency, wavenumber and amplitude) of the backscattered waves are related to fracture properties like spacing, compliance, and height. The dominant wavenumber is very sensitive to fracture spacing. We use the F-K method to analyze a data set from the Lynx Field in Canada. Characterization of fracture properties in this field is important for development plans to maximize the gas production. In the field data, the acquisition geometry results in irregular fold, with under sampling of certain azimuths and offsets. We address the acquisition footprint issue by controlling the azimuth binning of the data and neglecting the low/irregular fold gathers in the fracture analysis. We also apply the Scattering Index (SI) method (Willis et al., 2006) to the same data from the Lynx Field. The SI method is a robust method to detect fractures and to provide fracture orientations using multi-azimuth/multi-offset pre-stack data. In the realm of existing 3D seismic surveys, data with such acquisition characteristics are few.(cont) The fourth contribution of this thesis is therefore the conception of a post-stack version of the SI method that extends the scope of this method to practically every 3D seismic surface data set. In this version, a scattering index is computed for a fully stacked trace per CMP gather. As long as the bin contains traces parallel to the fracture strike, the stacking process of all azimuths and offsets preserves the reverberating character introduced by the fractures. The post-stack SI at a fractured location has a large value in comparison to a non-fractured location. The variations of post-stack SI values across the field reveal the distribution of highly fractured areas. Fracture strike cannot be determined in this case because it does not include the azimuthal behavior of the scattering. However, the results from the post-stack SI are helpful to identify areas of interest to focus the more specialized scattering analysis methods. We apply the F-K and SI methods to the Lynx Field seismic data and compare the results. Since spatial resolution of the two methods are different we upscale the SI maps to match the resolution of the F-K method. The combined analysis of the Lynx Field indicates that the preferred fracture orientation is N400E, which agrees with the regional stress field. The distribution of highly fractured regions appears to be associated to the geological features, such as folds and faults. The average fracture spacing, obtained by the F-K method shows that, in the Lynx Field, fracture spacing decreases in the west side of the field where the structural dips are higher.by Samantha Grandi-Karam.Ph.D

Fracture Characterization from Scattered Energy: A Case Study

We use 3D surface seismic data to determine the presence and the preferred orientation of fracture corridors in a field. The Scattering Index method is proving to be a robust tool for detecting and mapping fracture corridors. Fracture corridors largely control permeability and fluid flow in some fractured reservoirs. To apply the Scattering Index method, we compute the scattering transfer functions from the reservoir interval using prestack migrated data collected in four azimuth sectors. By measuring the azimuthal differences in the amount of scattering, we obtain maps of density of fracture corridors and their orientation across the survey area. We use geostatistical filtering to improve the spatial correlation of scattering index maps. The distribution and orientation of the final fracture corridors are interpreted considering the structure, fault network, and stress information. In the field, we observe several regions of high fracturing near the anticline’s crest and on its steepest slopes, on the southwest flank. Around well locations, fractures are oriented to the NW and NNW, which agrees with estimates of maximum stress direction from well data.Massachusetts Institute of Technology. Earth Resources Laborator

Analysis of Scattered Signal to Estimate Reservoir Fracture Parameters

We detect fracture corridors and determine their orientation and average spacing based on an analysis of seismic coda in the frequency-wave number (f-k ) domain. Fracture corridors have dimensions similar to seismic wavelengths which causes scattering. The distribution of energy in shot records in the f-k domain depends upon the orientation of the records relative to the fracture strike. In the direction normal to fractures, scattered waves propagate with slower apparent velocities than waves propagating along the fracture channels. The associated f-k spectral differences allow the identification of the preferred fracture orientation and spacing. We apply our technique to a fractured reservoir in the Lynx field, in the Canadian foothills. The estimated preferential fracture orientation is about N40 E, which agrees with regional stress measurements. The average fracture spacing is 75 m on the West side of the survey, while fractures are more sparse on the East side. We also apply the Scattering Index methodology (Willis et al., 2006) to the same data, post-stack and pre-stack. This technique has higher resolution to map fracture distribution, intensity and orientation, and therefore complements the spectral method in providing an integrated description of reservoir fractures.United States. Dept. of Energy (award number DE-FC26-06NT42956)Massachusetts Institute of Technology. Earth Resources Laborator

A comparison of LWD and wireline dipole sonic data

Data measured by both wireline and LWD tools in the same borehole are compared. Discrepancies in shear velocities as calculated from the data are on average around 5% and discrepancies between compressional velocities are less than 3%. The consistency of the bias between logs suggest it is related to the calculation of velocity. Comparison of industry and ERL velocity processing show excellent agreement and give an example of possible spread of velocity data due to processing chain. A short section of data in an unconsolidated zone shows velocity differences of just over 10% with an opposite trend to the over all bias. Dispersion analysis of the waveforms show this is consistent with a damaged zone surrounding the borehole wall caused by drilling.Massachusetts Institute of Technology. Earth Resources LaboratoryMassachusetts Institute of Technology. Borehole Acoustics and Logging Consortiu

Participatory Planning for the Creation of a Coastal Protected Area: Middle Basin from Arroyo Solís Grande, Canelones – Uruguay

Se presentan resultados de un caso de estudio perteneciente a un proyecto de investigación internacional, que estudia la gestión de procesos deliberativos que incorporan conocimientos locales y tradicionales, articulan diversos intereses y valoraciones asociadas a servicios ecosistémicos y la biodiversidad. El caso de estudio se centra en el proceso de creación de la primera área en integrar el SDAPA (Sistema Departamental de Áreas de Protección Ambiental) de Canelones: “Cuenca Media del Arroyo Solís Grande”. El estudio se realizó con un enfoque de Manejo Costero Integrado, y se centró en la realización de entrevistas semiestructuradas a integrantes de la Comisión Administradora del área que fueron prota- gonistas del proceso de planificación. Se presenta una sistematización del proceso deliberativo que condujo a la creación del área y su Comisión Administradora, identificando las razones que motivaron el proceso y el método empleado para ello. Los principales resultados se centran en la identificación de barreras y facilitadores del proceso de implementación que el área tiene por delante. Por tratarse de un proceso pionero, se sistematizaron lecciones aprendidas que fueran rele- vantes también para futuros procesos de creación de áreas dentro del SDAPA u otros procesos en áreas costeras similares. A partir de este caso de estudio, se proponen ideas y alternativas en torno a importantes desafíos del Manejo Costero Integrado: la integración de diferentes cuerpos de conocimiento, la participación efectiva de actores clave, la facilitación o mediación ante conflictos de intereses y el involucramiento de privados en iniciativas de conservación.This work displays the results of a case study included in an international research project, which studies delibera- tive processes of management that incorporate local and traditional knowledge, and articulate diverse interests and values associated with ecosystem services and biodiversity. The case study focuses on the creation process of the first area to integrate the SDAPA (Departmental System of Environmental Protection Areas) of Canelones: “Cuenca Media del Arroyo Solís Grande”. The study was carried out with an Integrated Coastal Management approach. Data collection was done through semi-structured inter- views with members of the administrative commission of the area who were protagonists of the planning process. This work displays a systematization of the deliberative processes that led to the creation of the area and its ad- ministrative commission, identifying the reasons that motivated the process and the methods used to achieve this goal. The results show the barriers and facilitators of the imple- mentation process that may shape upcoming developments in the area. Since this was a pioneering process, this work systematized the lessons learned that are relevant for future SDAPA area creation processes or similar processes in other coastal areas. Based on this case study, ideas and alternatives are proposed regarding important challenges of Integrated Coastal Management: the integration of different bodies of knowledge, the effective participation of key stakeholders, the facilitation or mediation of conflicts of interest, and the involvement of the private sector in conservation initiatives

Different paths, same destination: divergent action potential responses produce conserved cardiac fight-or-flight response in mouse and rabbit hearts

Sympathetic activation of the heart results in positive chronotropy and inotropy, which together rapidly increase cardiac output. The precise mechanisms that produce the electrophysiological and Ca2+ handling changes underlying chronotropic and inotropic responses have been studied in detail in isolated cardiac myocytes. However, few studies have examined the dynamic effects of physiological sympathetic nerve activation on cardiac action potentials (APs) and intracellular Ca2+ transients (CaTs) in the intact heart. Here, we performed bilateral sympathetic nerve stimulation (SNS) in fully innervated, Langendorff‐perfused rabbit and mouse hearts. Dual optical mapping with voltage‐ and Ca2+‐sensitive dyes allowed for analysis of spatio‐temporal AP and CaT dynamics. The rabbit heart responded to SNS with a monotonic increase in heart rate (HR), monotonic decreases in AP and CaT duration (APD, CaTD), and a monotonic increase in CaT amplitude. The mouse heart had similar HR and CaT responses; however, a pronounced biphasic APD response occurred, with initial prolongation (50.9 ± 5.1 ms at t = 0 s vs. 60.6 ± 4.1 ms at t = 15 s, P < 0.05) followed by shortening (46.5 ± 9.1 ms at t = 60 s, P = NS vs. t = 0). We determined the biphasic APD response in mouse was partly due to dynamic changes in HR during SNS and was exacerbated by β‐adrenergic activation. Simulations with species‐specific cardiac models revealed that transient APD prolongation in mouse allowed for greater and more rapid CaT responses, suggesting more rapid increases in contractility; conversely, the rabbit heart requires APD shortening to produce optimal inotropic responses. Thus, while the cardiac fight‐or‐flight response is highly conserved between species, the underlying mechanisms orchestrating these effects differ significantly

Differential cross section measurements for the production of a W boson in association with jets in proton–proton collisions at √s = 7 TeV

Measurements are reported of differential cross sections for the production of a W boson, which decays into a muon and a neutrino, in association with jets, as a function of several variables, including the transverse momenta (pT) and pseudorapidities of the four leading jets, the scalar sum of jet transverse momenta (HT), and the difference in azimuthal angle between the directions of each jet and the muon. The data sample of pp collisions at a centre-of-mass energy of 7 TeV was collected with the CMS detector at the LHC and corresponds to an integrated luminosity of 5.0 fb[superscript −1]. The measured cross sections are compared to predictions from Monte Carlo generators, MadGraph + pythia and sherpa, and to next-to-leading-order calculations from BlackHat + sherpa. The differential cross sections are found to be in agreement with the predictions, apart from the pT distributions of the leading jets at high pT values, the distributions of the HT at high-HT and low jet multiplicity, and the distribution of the difference in azimuthal angle between the leading jet and the muon at low values.United States. Dept. of EnergyNational Science Foundation (U.S.)Alfred P. Sloan Foundatio

Penilaian Kinerja Keuangan Koperasi di Kabupaten Pelalawan

This paper describe development and financial performance of cooperative in District Pelalawan among 2007 - 2008. Studies on primary and secondary cooperative in 12 sub-districts. Method in this stady use performance measuring of productivity, efficiency, growth, liquidity, and solvability of cooperative. Productivity of cooperative in Pelalawan was highly but efficiency still low. Profit and income were highly, even liquidity of cooperative very high, and solvability was good

Juxtaposing BTE and ATE – on the role of the European insurance industry in funding civil litigation

One of the ways in which legal services are financed, and indeed shaped, is through private insurance arrangement. Two contrasting types of legal expenses insurance contracts (LEI) seem to dominate in Europe: before the event (BTE) and after the event (ATE) legal expenses insurance. Notwithstanding institutional differences between different legal systems, BTE and ATE insurance arrangements may be instrumental if government policy is geared towards strengthening a market-oriented system of financing access to justice for individuals and business. At the same time, emphasizing the role of a private industry as a keeper of the gates to justice raises issues of accountability and transparency, not readily reconcilable with demands of competition. Moreover, multiple actors (clients, lawyers, courts, insurers) are involved, causing behavioural dynamics which are not easily predicted or influenced. Against this background, this paper looks into BTE and ATE arrangements by analysing the particularities of BTE and ATE arrangements currently available in some European jurisdictions and by painting a picture of their respective markets and legal contexts. This allows for some reflection on the performance of BTE and ATE providers as both financiers and keepers. Two issues emerge from the analysis that are worthy of some further reflection. Firstly, there is the problematic long-term sustainability of some ATE products. Secondly, the challenges faced by policymakers that would like to nudge consumers into voluntarily taking out BTE LEI