Edinburgh Anisotropy Project

The Edinburgh Anisotropy Project (EAP) is a research team based at the British Geological Survey and University of Edinburgh, working on all aspects of Applied Seismic Anisotropy. EAP is supported by a consortium of major software, service and oil companies. The consortium operates in three-year phases, and is now entering the twentieth year and the first year of 9th phase programme.

Current Programme

The programme proposed for the 9th Phase (2012-2015) is a natural continuation of the 8th Phase. On one hand, we will keep focussing on geophysical issues about converted-wave processing and imaging, and fracture characterization using AVD technology, arising from discussions with sponsors. On the other hand, we will continue studying rock physics model-based inversion for fluid properties to consolidate our understanding of the resultant seismic FAVO effect. In addition, with the globally increasing importance of unconventionals and shale gas reservoir, we will also study shale gas reservoir from geophysical point of view encompassing elastic modelling, seismic modelling and inversion issues, and relevant software development. The programme has four components:

An important aspect of EAP research is that the development of theory, methodology and algorithms is combined with application to real data, supplied by the sponsors, to demonstrate the value of the technology produced.


History

8th Phase (2009 - 2012) Achievements

Three topics have been highlighted for incorporation into this 8th phase of the project. The new programme as a whole is continuing to tackle the most important hurdles in the application of seismic anisotropy for reservoir characterization, these being: (1) the marine environment - through the use of 4C and time-lapse seismic data; (2) seismic characterization of fractures - through the use of AVD and frequency-dependent effects; (3) links with fuid flow - through the study of rock physics models and time-lapse seismic. A frequency-dependent AVO inversion scheme was proposed to estimate seismic dispersin from prestack data. The three main topics are:

  • Fracture characterization
    Extension of traditional AVD (attributes versus direction) methods to exploit frequency-dependent anisotropy for robust fracture density information together with fluid saturation and dominant scale length.
  • Converted-wave analysis for improved imaging of reservoir structure
    Development of new GUI tools for PP and PS joint velocity analysis,PP and PS events registration and joint PP,PS wave inversion.
  • Anisotropic rock physics for analysing frequency-dependent anisotropy
    Progress towards gaining more insights into the information content of frequency-dependent anisotropy through experimental studies, calibrated theoretical developments and analysis of surface data,
    frequency-dependent AVO inversion scheme.

 

7th Phase (2006 - 2009) Achievements

During the 7th Phase (2006-2009), we have continued our effort to consolidate our ideas on frequency-dependent anisotropy and its links to fluid mobility, and have carried out a number of calibrated case studies to narrow the gaps in the application of seismic anisotropy for lithology and fluid detection. One of the key findings is the sensitivity of the slow shear-wave to fluid viscosity and its implication for oil-water discrimination. Highlights of the 7th phase include:

  • Anisotropy rock physics
    -Improved understanding of the effects of viscosity and saturation on the slow shear-wave in a multi-scale fractured media and their experimental verification
    - Theory for frequency-dependent AVO inversion
    - Nonlinear rock physics theory for rocks saturation with multiple fluids.
  • Converted-wave analysis
    Extension of current converted-wave imaging tools (e.g. CXtools) to account for diodic converted-wave effects and further development of depth-imaging tools for building a common anisotropic earth model.
  • AVD technology for Fracture characterization
    - Quantitative SVD inversion procedure for fracture density using P-wave attributes
    - Estimation of attenuation anisotropy in VSPs and crosswell seismic data
    - A number of successful integrated case studies(e.g. Xingchang and Shengli 3D 4C data)

These developments have been well received by all sponsors. As a result, EAP has also attracted a record number of sponsors, which encourages us to continue developing our work through real data applications during the next phase from 2009 to 2012, with a primary focus on the integration of rock physics with the interpretation and inversion of PP and PS multicomponent data.

 

6th Phase (2003 - 2006) Achievements

During the 6th Phase (2003-2006), we have focused on consolidating our ideas and findings for technology transfer. This led to the release of three software packages, i.e. CXtools for convertedwave imaging, RU for rock physics and fracture modelling, and GeoLab for depth model building and imaging. Major progress has been made in the following areas in the past five years:

  • Converted-waves analysis - New theories and algorithms for converted-wave imaging are consolidated into CXtools, which makes it possible to perform anisotropic imaging with high accuracy but low cost - A number of successful case studies (e.g. Lomond 2D 4C data, Afflect 3D 4C data) - Ideas for decoupled migration to perform multiwave type prestack depth imaging.
  • Fracture characterization - Frequency-dependent P- and S-wave attributes to characterize fluid saturation and dominant scale length - A number of successful case studies (e.g. Clair and Emilio 3D 4C data).
  • Time-lapse seismic data analysis - Improved dynamic rock physical model with multi-scale fluid flow - Ideas of frequency-dependent time-lapse anisotropy for discriminating the effects of pore pressure and saturation.

     

    5th Phase (2000 - 2003) Achievements

    Four topics have been highlighted for incorporation into this 5th phase of the project, each being a natural extension of the activities in the past three phases, and capitalizing upon past EAP achievements. The new programme as a whole is aimed at tackling the most important hurdles in the application of seismic anisotropy for reservoir characterization, these being: (1) the marine environment - through the use of AVD and converted wave imaging; (2) links with fluid flow; (3) the importance of geological architecture in the reservoir.

    • AVD extends our post-stack shear wave work into the marine environment, where the ability to consider pre-stack P-wave sections and converted waves is now being combined with sea-bottom acquisition and vertical cable technology to form a highly appropriate system for anisotropy estimation and possible time-lapse analysis.

    • The project on sub-basaltic imaging is a byproduct of converted wave studies in dolomites, where the properties of shear waves in high velocity layers were analysed. Use is made of the anisotropic nature of the basalts in the imaging analyses.

    • The requirement to understand and improve the current range of rock physics models and their scaling between different geophysical measurements is driving the repeat VSP and up-scaling projects to help to isolate those contributions and scales important to fluid flow.

    • The desire to place a value on the practical observation of seismic anisotropy is the motivating factor for performing case studies of reservoir characterization. Here, integration of larger scale components in the heterogeneous reservoir architecture is achieved through collaboration with various experts within BGS.

    • We have now developed a comprehensive rock physics model to model wave propagation in media with multi-scale fractures. One of the implications of this model is the prediction of frequency-dependent seismic anisotropy. A case study from a multi-component VSP has been analysed and successfully modelled. We are currently investigating the effects of multi-scale fractures on P-wave AVO response and also examine the fluid effects on wave attenuation and related low frequency gas shadow.

     

    4th Phase (1997 - 2000) Achievements

    Four topics have been highlighted for incorporation into this 4th phase of the project, each being a natural extension of the activities in the past three phases, and capitalizing upon past EAP achievements. The new programme as a whole is aimed at tackling the most important hurdles in the application of seismic anisotropy for reservoir characterization, these being: (1) the marine environment - through the use of AVD and converted wave imaging; (2) links with fluid flow; (3) the importance of geological architecture in the reservoir.

    • AVD extends our post-stack shear wave work into the marine environment, where the ability to consider pre-stack P-wave sections and converted waves is now being combined with sea-bottom acquisition and vertical cable technology to form a highly appropriate system for anisotropy estimation and possible time-lapse analysis.

    • The project on sub-basaltic imaging is a byproduct of converted wave studies in dolomites, where the properties of shear waves in high velocity layers were analysed. Use is made of the anisotropic nature of the basalts in the imaging analyses.

    • The requirement to understand and improve the current range of rock physics models and their scaling between different geophysical measurements is driving the repeat VSP and up-scaling projects to help to isolate those contributions and scales important to fluid flow.

    • The desire to place a value on the practical observation of seismic anisotropy is the motivating factor for performing case studies of reservoir characterization. Here, integration of larger scale components in the heterogeneous reservoir architecture is achieved through collaboration with various experts within BGS.

     

    3rd Phase (1994 - 1997) Achievements

    In the 3rd phase, a series of case studies in fractured chalks, dolomites and sandstones led to a subsequent improvement in our understanding of the relationships or potential links between seismic anisotropy and the reservoir. Attributes such as polarizations, polarisation change, time-delay were correlated with fracture strike, fracture intensity, and zones of productivity and fluid flow. At this stage, the project became more applied, and the advances in inversion, design of optimum geometries, and interpretation now enabled us to actively pursue our main focus of reservoir characterisation. Thus, the EAP team began to interface with oil and service companies to discuss the design of seismic acquisitions. The programme became more specific to target only certain reservoirs where seismic anisotropy was known to be of value. This combined with an integration of other geophysical and geological information to support the findings from the seismic anisotropy. The start of our development of techniques for use in marine data also began during this phase. The developed routines were inserted into PROMAX software for more routine use by all sponsors.

    • case studies detailing correlations between seismic anisotropy and reservoir parameters

    • integrated studies for multicomponent land and marine surface and VSP seismics

    • pre-acquisition modelling for survey design of specific reservoirs

    • insertion of SWAP into the PROMAX environment

     

    2nd Phase (1991 - 1994) Achievements

    In the 2nd (1991-1994) phase of the project, the group developed processing techniques for identifying, estimating, and inverting shear-wave anisotropy in seismic data, to yield information about crack and fracture properties of the subsurface. This work blended seismic processing, modelling and interpretation, under-pinned by a solid foundation of theoretical expertise. The various techniques employed were subsequently coordinated into a shear-wave analysis package (SWAP), which today still remains the generic name for much of our code. The research then concentrated on extracting this information from multicomponent VSP and surface seismics. These studies were typified by three conditions: shear-waves; post-stack/near-offset analyses; horizontal layering.

    • development of SWAP software for processing and analysis of seismic data;

    • application of early rock model and SWAP to multicomponent data;

    • further development of processing specifically for multicomponent seismics;

     

    1st Phase (1988 - 1991) Achievements

    The basic objective of the EAP consortium is to understand the internal architecture of the hydrocarbon reservoir using the phenomenon of seismic anisotropy. This phase is the feasibility stage of EAP. Early work focussed on carrying out a feasibility study, to determine whether anisotropic behaviour observed in earthquake records could also be observed in exploration data. In the first three years (1988-1991) this objective was tackled by a generally broad fronted approach. All datasets were considered whether they were earthquake, mining, cross-well, VSP or surface seismics. EAP also started theoretical developments to build a reservoir model which could adequately match the observations.

    • prove that seismic anisotropy effects exist in exploration data;

    • ascertain the feasibility of estimating seismic anisotropy effects in exploration data;

    • initial development of a rock model to interpret the findings.