UKCCSRC Bristol, 23 October 2014

UKCCSRC Bristol 23rd October 2014 Monitoring of the deep subsurface: leakage pathways –

understanding and monitoring the mechanics of CO2 storage

Physics of Rocks for CO2 reservoir characterisation and monitoring

Angus Best

Acknowledgements: Ismael Falcon, Laurence North, Jeremy Sothcott & Clive McCann

National Oceanography Centre, University of Southampton Waterfront Campus, European Way, Southampton, SO14 3ZH, United Kingdom, angus.best@noc.ac.uk

UKCCSRC Bristol, 23 October 2014

• Physics of rocks • DiSECCS study • Fractured rock/seismic anisotropy

– Pore fluid viscosity – Sw

• New CO2 rig • New acoustic pulse tube

Outline

UKCCSRC Bristol, 23 October 2014

• 58 papers • Seismic attenuation /velocity dispersion • Seismic anisotropy • Geomechanics • Microstructural models • Digital rock physics • Elastic properties • Joint elastic-electrical properties • Fluids and carbonates • Reservoir characterisation and monitoring

Physics of Rocks

UKCCSRC Bristol, 23 October 2014

• Contrast reservoir styles – Sleipner (sand) – Snøhvit (sandstone) – In Salah (tight sandstone)

DiSECCS Study & Geomechanics • Diagnostic Seismic toolbox for

Efficient Control of CO2 Storage • BGS, NOC, Leeds, Edinburgh,

Manchester • Statoil, BP

UKCCSRC Bristol, 23 October 2014

• Scale dependent • Grain alignment • Bedding fabric • Aligned fractures

Images from Armstrong et al. 1994

Transverse Isotropy

Seismic Anisotropy (In Salah example)

UKCCSRC Bristol, 23 October 2014

• NOC – lab experiments • BGS – theoretical models

Pore fluid viscosity & anisotropy in fractured rocks

Shear wave splitting (SWS)

UKCCSRC Bristol, 23 October 2014

Frequency dependent seismic anisotropy (Chapman Theory)

Wave propagation at 30° to the fracture normal.

Meso-scale fractures

Meso-scale fractures Microcracks

Microcracks

P-waves

S-waves

(Chapman 2003)

• Poro-visco-elastic model • Squirt flow • Attenuation • Velocity dispersion

• Vertically fractured reservoirs

• Multi-component seismics

• Azimuthal VSPs • Fracture

characterisation • Pore fluid detection

UKCCSRC Bristol, 23 October 2014

Chapman Model

Chapman (2003), Geophysical Prospecting, 51, 369-379.

UKCCSRC Bristol, 23 October 2014

• P- & S-wave velocity and attenuation • Very accurate (± 0.3%, ± 0.1 dB/cm) • 400 – 900 kHz • Effective pressure up to 65 MPa • Rotating S-wave transducer

Ultrasonic pulse-echo system

Best, Sothcott & McCann (2007)

UKCCSRC Bristol, 23 October 2014

Synthetic sandstones with aligned cracks

Leach out aluminium disks with acid

Silica-cemented sand blocks

UKCCSRC Bristol, 23 October 2014

Rock property Value Grain size 120 μm

Porosity 30 %

Permeability 21 mDarcy

Fracture density 0.0314 ± 0.0059

Ave fracture radius 2.91 ± 0.06 mm

Ave fracture aspect ratio

0.0429 ± 0.0008

Octagonal sandstone samples

UKCCSRC Bristol, 23 October 2014

Model predictions Blank sample (no fractures) Anisotropic background Fractured sample

Minimise errors in Thomsen weak anisotropy parameters: epsilon, gamma & delta

SWS = 1.45% CD = 3.14%

Tillotson et al (2014), Geophysical Prospecting, 62, 1238-1252.

UKCCSRC Bristol, 23 October 2014

Results - pore fluid viscosity

SWS = 4.59% (1.45% + 3.14%)

Tillotson et al (2014), Geophysical Prospecting, 62, 1238-1252.

UKCCSRC Bristol, 23 October 2014

Results – attenuation & Sw Blank Fractured

Amalokwu et al (2014), Geophysical Journal International, 197, 943-947.

UKCCSRC Bristol, 23 October 2014

New CO2 rig (Falcon, North, Best)

• THMC (Thermal-Hydro-Mechanical-Chemical)

UKCCSRC Bristol, 23 October 2014

New CO2 rig (Falcon, North, Best)

1

Ultrasonicpulse-echo

Bufferroad-top

Bufferroad-bottom

Electrodes

Sample

σ3

σ1

Lateral strain gage

Axial strain gage

Static moduli vs

Dynamic moduli

UKCCSRC Bristol, 23 October 2014

New CO2 rig (example data)

1

UKCCSRC Bristol, 23 October 2014

• Geophysics • Seabed gas quantification • CH4 & CO2 • Hydrates • P-waves 500 Hz – 10 kHz • Frequency-dependence • Samples 7 cm diameter,

50 cm long • 60 MPa fluid/confining • 4 to 100 degC • S-waves ~ 1 kHz • ERT • Sands, muds

Greenhouse Gas Pulse Tube Sat. 5th July 2014

UKCCSRC Bristol, 23 October 2014

Greenhouse Gas Pulse Tube

a) b)

c) d)

McCann et al (2014), Geophysical Prospecting, 62, 97-116.

1 – 10 kHz

UKCCSRC Bristol, 23 October 2014

Acoustic Bubble Resonance Anderson & Hampton (1980a, b)

Recent theoretical developments: Leighton (2007)

Kuhs et al (2004)

Velocity

Attenuation

Bubble size distributions

UKCCSRC Bristol, 23 October 2014

• Need controlled lab studies to understand: – Seismic anisotropy in fractured porous rocks – Pore fluid viscosity effects – Gas saturation effects – Geomechanical response to CO2 injection – Validate theoretical models for application to reservoir

characterisation & monitoring

• Acoustic pulse tube studies – Seabed greenhouse gas quantification – Gas bubble resonance phenomena

Conclusions