Category Archives: News and Events

Latest CRGC-related News and Events.

Seminar: Application of 3D VSP acquired with DAS and 3C geophones for site characterisation and monitoring program design: preliminary results from Stage 3 of the CO2CRC Otway project

Ms. Julia Correa, PhD Candidate, Exploration Geophysics, Curtin University

Title: Application of 3D VSP acquired with DAS and 3C geophones for site characterisation and monitoring program design: preliminary results from Stage 3 of the CO2CRC Otway project

Held: Tuesday 9 October 2018, 11AM–12PM


Distributed Acoustic Sensing (DAS) is a relatively novel technology that is gaining increasing popularity in the seismic industry, particularly as a tool for permanent reservoir monitoring and time-lapse imaging. Recent studies show that DAS can deliver promising results for such applications, presenting satisfactory levels of repeatability and signal-to-noise ratio. However, issues such as high angle dependent sensitivity and high levels of noise still limit certain applications of the method.

In this work, we present the preliminary results from a 3D VSP survey acquired using a cemented single-mode fiber-optic cable as a part of the seismic monitoring and characterisation effort within CO2CRC Otway Project. We investigate the imaging limitations of a 3D VSP acquired with DAS by analysing the quality of DAS datasets in relation to offset and angle, as well as assess a migrated line from the DAS VSP datasets.

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Seminar: Solid substitution: Modeling elastic properties of porous and cracked rocks saturated with liquid and solid octodecane

Mr. Yongyang Sun, PhD Candidate, Exploration Geophysics, Curtin University

Title: Solid substitution: Modeling elastic properties of porous and cracked rocks saturated with liquid and solid octodecane

Held: Monday 8 October, 10AM–11AM

ABSTRACT: Quantifying the impact of pore fill on elastic properties of porous rocks, especially cracked rocks, is of ongoing interest in geophysics. Different from fluids, the finite rigidity of high viscoelastic or solid pore fill prevents the pressure equilibration within the pore space due to the coexistence of stiff and soft pores. Indeed, the variation of the shear modulus of the pore fill can produce larger change in the effective elastic properties than one may expect from the change of the shear modulus of inclusions.

Our analysis shows that the pressure dependency of elastic properties of cracked rocks is controlled by the squirt flow between stiff, compliant, and so-called intermediate pores (with an aspect ratio larger than that of compliant pores but much less than that of stiff pores). In this paper, we present a triple porosity recipe for solid substitution. Compared to ultrasonic measurements on an octodecane saturated sandstone, the model predictions reveal a reasonable fit for both bulk and shear modulus with the aspect ratio of stiff pores set to 0.22, which is much smaller than the previously assumed value 1 for spherical pores.

Computation of liner elastic properties directly from the digitised tomographic images using numerical simulation based on the finite element method (FEM) shows excellent fit to the predictions of our model, which confirms the validity and applicability of this theory.

Seminar: Extended imaging conditions for shot migration

Dr. Ian Jones, Senior Geophysical Adviser, ION GX Technology, London

Title: Extended imaging conditions for shot migration

Held: Thursday 4 October 2018, 11AM–12PM


Wavefield extrapolation migration of shot records involves downward continuing a synthetic source wavefield down into the earth, and at the same time, backward (upward) continuing the actual real recorded wavefield back into the earth.

At each propagation time-step, these two 3D wavefields are multiplied together, and at the end of the extrapolation process (when we’ve exhausted all the useful propagation time) all these hundreds of 3D product volumes are summed together to form the image contribution resulting from this particular shot record.

This summation of wavefield products is referred to as the convolutional imaging condition in shot migration: the image is being formed by what is essentially a correlation of downgoing and upcoming wavefields.

This process is repeated for all available shots, and all these overlapping 3D shot-contribution volumes are summed to form the full migrated image of the study area.

However, each of the elemental sub-images resulting from the migration of an individual shot-record only contains a zero-offset trace: there is no inherent pre-stack gather resulting from this process. The convolutional imaging condition only produces the image, and not gathers. Hence, to create a gather (say for use in subsequent velocity analysis of AVA study) we need to invoke some additional computational tricks.

The most widely used of these methods is called an extended imaging condition. The idea in an extended imaging condition is to shift the downgoing and upcoming 3D wavefield volumes with respect to each other just before they are multiplied together. These shifted product volumes are then summed as before to form the imagine contribution from this particular shot record. This shifting procedure is repeated several times, so that we end-up with many 3D imaged volumes for each shot, rather than a single image volume for the shot.

If we re-sort these shift-volumes into gathers, then we now have a pre-stack gather that can be used to velocity analysis and further post-processing prior to stack. The shifting can be done in four different ways: laterally in inline, laterally in crossline, vertically in depth, or vertically in propagation time. It could also be done in depth with respect to the reflector normal, but that is a bit too demanding. These shifting methods are referred to as extended imaging conditions. Alternatively, the 3D source and receiver wavefields can be preconditioned at each propagation time step prior to multiplication by filtering with respect to propagation direction (Poynting vector filtering: Poon & Marfurt, 2006). The history of these techniques dates back to focussing analysis in 2D preSDM (Faye &Jeannot, 1986; Audebert & Diet, 1990, MacKay & Abma, 1992) through to the more recent works of Sava & Fomel, 2003, 2006, and Biondo & Symes 2004, and others).

The basic shift-gather is not very intuitively useful, but they can be converted into subsurface ‘true’ angle gathers via various transforms. However, all this shifting and transforming suffers from aliasing of the underlying data due to poor sampling (primarily in the crossline direction). Hence we tend to work with angle gathers as a projection on the inline, rather than trying to extract both incident angle and azimuth). If we use a lateral inline or crossline shift, then the extended imaging condition gathers are called sub-surface-offset gathers, and if we shift vertically in propagation time, they’re called time-shift gathers. Either can be converted to angle gathers, ready for RMO picking and velocity update, or post-processing, etc. In the GXT RTM software, as can output most of these extended imaging condition gathers, but currently prefer to use the vertical propagation time delay gathers, as these are thought to be less error prone. These time shift gathers are then converted to angle gathers via a tau-p transform and a velocity scaling procedure.

Seminar: The Effect of Hydration on Elastic Properties of Shales

Mr. Alexey Yurikov, PhD Candidate, Exploration Geophysics Curtin University

Title: The Effect of Hydration on Elastic Properties of Shales

Thursday 27 September 2018, 11AM–12PM 


Shales play an important role in many engineering applications such as nuclear waste, CO2 storage and oil or gas production. Shales are often utilised as an impermeable seal or an unconventional reservoir. For both situations, shales are often studied using seismic waves. For example, 4D seismic is well established for monitoring of conventional oil and gas reservoirs. This technique is successfully used during production to track changes in rock formations such as variation in fluid saturation.

While the seismic response on changing fluid saturation in most sedimentary rocks like sandstones and carbonates is thoroughly studied, the effect of change of saturation on elastic properties of shales is still poorly understood. It has been shown that variation in saturation in shales leads to substantial structural changes and strongly affects the elastic properties of the rock. However, there is no agreement between reported dependencies of the elastic properties on hydration in different shales. In this work, we investigate structural changes in shales with variations in hydration using laboratory measurements and X-ray micro-computed tomography.

We observe deformation and decrease of porosity in shales with drying. Additionally, we study the elastic properties of the shale at different hydration states using low frequency and ultrasonic velocities measurements. The elastic moduli of the shale show substantial changes with variations in hydration, which cannot be explained with a single driving mechanism.

We suggest that changes of the elastic moduli with variations in hydration are driven by multiple competing factors:

  1. Variations in total porosity
  2. Substitution of pore-filling fluid
  3. Change in stiffness of contacts between clay particles
  4. Chemical hardening/softening of clay particles.

We qualitatively and quantitatively analyse and discuss the influence of each of these factors on the elastic moduli. We conclude that depending on the microstructure and composition of a particular shale, some of the factors dominate over the others, resulting in different dependencies of the elastic moduli on hydration.

Visiting Researcher Mr. Yubing Liu arrives at Curtin Geophsyics

Visitor Arrival: Visiting Researcher Mr. Yubing Liu.

Yubing is currently undertaking his Doctor of Philosophy in Mining Engineering at the University of Chongqing, China and will be carrying out research at Curtin under the Supervision of Prof. Maxim Lebedev.

Yubing’ s research interests include Rock mechanics and rock engineering; Rock-fluid interaction and unconventional natural gas exploitation.