Analytical and numerical modelling of elastic properties of isotropic and anisotropic rocks and their stress dependencies

The research is focused on analytical and numerical modelling of elastic properties of rocks and their stress dependencies. A number of approaches to model and simulate stress dependencies of elastic properties of rocks were tested. Proposed models were, at first, tested on isotropic rocks and then further developed to anisotropic case and applied to shales. The study was supported by the numerical simulations using Finite Element Method on realistic 3D models reconstructed from computer tomography images

An Open Source Web Service For Registering And Managing Environmental Samples

Records of environmental samples, such as minerals, soil, rocks, water, air and plants, are distributed across legacy databases, spreadsheets or other proprietary data systems. Sharing and integration of the sample records across the Web requires globally unique identifiers. These identifiers are essential in order to locate samples unambiguously and to manage their associated metadata and data systematically. The International Geo Sample Number (IGSN) is a persistent, globally unique label for identifying environmental samples. IGSN can be resolved to a digital representation of the sample through the Handle system. IGSN names are registered by end-users through allocating agents, which are the institutions acting on behalf of the IGSN registration agency. As an IGSN allocating agent, our goal is to implement a web service based on existing open source tools to streamline the processes of registering IGSNs and for managing and disseminating sample metadata. In this paper, we present our ongoing work on the design and development of the web service, and its data schema and database model for capturing key aspects of environmental samples. We show how existing controlled vocabularies can be incorporated into the service development to support the metadata registration of different types of samples. The proposed sample registration and curating approach has been trialed in the context of the Capricorn Distal Footprints project on a range of different sample types, varying from water to hard rock samples. The initial results demonstrate the effectiveness of the service while maintaining the flexibility to adapt to various media types, which is critical in the context of a multi-disciplinary project

Parameterization of elastic stress sensitivity in shales

Stress dependency and anisotropy of dynamic elastic properties of shales is important for a number of geophysical applications, including seismic interpretation, fluid identification, and 4D seismic monitoring. Using Sayers-Kachanov formalism, we developed a new model for transversely isotropic (TI) media that describes stress sensitivity behavior of all five elastic coefficients using four physically meaningful parameters. The model is used to parameterize elastic properties of about 20 shales obtained from laboratory measurements and the literature. The four fitting parameters, namely, specific tangential compliance of a single crack, ratio of normal to tangential compliances, characteristic pressure, and crack orientation anisotropy parameter, show moderate to good correlations with the depth from which the shale was extracted. With increasing depth, the tangential compliance exponentially decreases. The crack orientation anisotropy parameter broadly increases with depth for most of the shales, indicating that cracks are getting more aligned in the bedding plane. The ratio of normal to shear compliance and characteristic pressure decreases with depth to 2500 m and then increases below this to 3600 m.This may allow the reconstruction of the stress dependency of all five elastic compliances of a shale from log data, for example

Stress dependency of elastic properties of shales: the effect of uniaxial stress

Understanding seismic anisotropy in shales is important for quantitative interpretation of seismic data, 4D monitoring and pore pressure prediction. Along with intrinsic anisotropy caused by preferred mineral orientation that is common in shales, anisotropic stress is an important factor that affects shale elastic response. While variations of elastic coefficients with anisotropic stress have been the subject of experimental studies, theoretical insight is still largely lacking. Here we suggest a new model that allows parameterization of the stress dependency of elastic coefficients of shales under anisotropic stress conditions. We show that the parameterization requires four parameters, namely, specific tangential compliance of a single crack, the ratio of normal to tangential compliances, characteristic pressure and a crack orientation anisotropy parameter. These parameters can be estimated from experimentally measured stress sensitivity of elastic coefficients in shales to isotropic stress

Distributed Persistent Identifiers System Design

The need to identify both digital and physical objects is ubiquitous in our society. Past and present persistent identifier (PID) systems, of which there is a great variety in terms of technical and social implementation, have evolved with the advent of the Internet, which has allowed for globally unique and globally resolvable identifiers. PID systems have, by in large, catered for identifier uniqueness, integrity, and persistence, regardless of the identifier’s application domain. Trustworthiness of these systems has been measured by the criteria first defined by Bütikofer (2009) and further elaborated by Golodoniuc 'et al'. (2016) and Car 'et al'. (2017). Since many PID systems have been largely conceived and developed by a single organisation they faced challenges for widespread adoption and, most importantly, the ability to survive change of technology. We believe that a cause of PID systems that were once successful fading away is the centralisation of support infrastructure – both organisational and computing and data storage systems. In this paper, we propose a PID system design that implements the pillars of a trustworthy system – ensuring identifiers’ independence of any particular technology or organisation, implementation of core PID system functions, separation from data delivery, and enabling the system to adapt for future change. We propose decentralisation at all levels — persistent identifiers and information objects registration, resolution, and data delivery — using Distributed Hash Tables and traditional peer-to-peer networks with information replication and caching mechanisms, thus eliminating the need for a central PID data store. This will increase overall system fault tolerance thus ensuring its trustworthiness. We also discuss important aspects of the distributed system’s governance, such as the notion of the authoritative source and data integrit

An estimation of sonic velocities in shale using clay and silt fractions from the elemental capture spectroscopy log

Anisotropic differential effective medium approach is used to simulate elastic properties of shales from elastic properties and volume fractions of clay and silt constituents. Anisotropic elastic coefficients of the wet clay pack are assumed to be independent of mineralogy and to be linearly dependent on clay packing density (CPD), a fraction of clay in an individual wet clay pack. Simulated compressional and shear velocities normal to the bedding plane and are shown to be in a good agreement with measured sonic velocities. Further, elastic coefficients of shales, and, calculated from the log sonic velocities, calibrated porosity and clay fraction obtained from the mineralogy tool are used to invert for elastic constants of clays, C33 and C44. The obtained elastic coefficients of clays show lower scatter than the original elastic coefficients of shales. The noticeable increase of the clay elastic coefficients with the depth increase is shown to result from the positive trend of the CPD with depth. Being interpolated to the same CPD = 0.8, elastic coefficients of clays show no depth dependency. Our findings show that the CPD and silt fraction are the key parameters that can be used for successful modelling of elastic properties of shales

The Challenge of Ensuring Persistency of Identifier Systems in the World of Ever-Changing Technology

The identification of information objects has always been important with library collections with indexes having been created in the most ancient times. Since the digital age, many specialised and generic persistent identifier (PID) systems have been used to identify digital objects. Just as many ancient indexes have died over time, so too PID systems have had a lifecycle from inception to active phase to paralysis, and eventually a fall into oblivion. Where the indexes within the Great Library at Alexandria finally succumbed to fire, technology change has been the destroyer of more recent digital indexes. We distil four PID system design principles from observations over the years that we think should be implemented by PID system architects to ensure that their systems survive change. The principles: describe how to ensure identifiers’ system and organisation independence; codify the delivery of essential PID system functions; mandate a separation of PID functions from data delivery mechanisms; and require generation of policies detailing how change is handled. In addition to suggesting specific items for each principle, we propose that a platform-independent model (PIM) be established for persistent identifiers – of any sort and with any resolver technology – in order to enable transition between present and future systems and the preservation of the identifiers’ functioning. We detail our PID system—the PID Service—that implements the proposed principles and a data model to some extent and we describe an implementation case study of an organisation’s implementation of PID systems that implement the Pillars further but still not completely. Penultimately, we describe in a Future Work section, an opportunity for the use of both the Pillars and the PIM; that of the World Wide Web Consortium’s Permanent Identifier Community Group who is seeking to “set up and maintain a secure permanent, URL re-direction service for the web”

Rock Physics Analysis of Shale Reservoirs

This chapter reviews major developments in rock physics of organic-rich shales (ORSs). First, it brings together available published laboratory measurements on shales including those shales whose total organic carbon (TOC) content is unknown. Next, the chapter reviews experimental and theoretical studies of anisotropic elastic properties of ORSs in connection with their TOC fraction, partial saturation, and maturity. It focuses on the effects of microstructure and maturity on elastic parameters of ORSs. Recent seismic surveys are used to assess the application of the findings of rock physics modeling for predicting the seismic response of ORSs. The chapter discusses an attempt to estimate orientation of vertical fracture sets permeating Bakken Shale from amplitude versus offset and azimuth (AVOAz) data. It presents a study in which the investigated naturally matured samples of the Bakken Shale showed huge differences in mineralogy. These mineralogical differences affect elastic properties and can obscure the effects of maturity