Constraining fluid flow processes and the physical properties of sediments relevant to CCS Jonathan M. Bull University of Southampton National Oceanography Centre Southampton Acknowledgements: Ben Callow, Melis Cevatoglu, Mark Vardy, Christian Berndt (GEOMAR), Benoit Berges, Paul White, Jerry Blackford (PML), Henrik Stahl, Doug Connelly, Rachael James, Tim Leighton, Tom Gernon, Ian Wright and whole QICS and STEMM CCS consortia. Funding from EU Horizon 2020 and NERC.
Motivations Carbon Capture and Storage marine QICS experiment creating CO 2 chimneys/pipes in the sub surface. Observations of pipe structures in sedimentary basins offshore Smaller scale features onshore Underway experiments/future work Conclusions Outline
Motivations Understanding mechanisms for vertical/subvertical fluid flow in the sub surface that do not involve large faults. Seal Bypass Systems. Understand the commonly observed seismic chimneys/pipes found in offshore sedimentary basins. What are they and how do they form? Constrain sub surface permeability Increase knowledge on understanding likely impacts of (marine) Carbon Capture and Storage
CCS Projects on shore < > off shore Sleipner since 1996 K12 B since 2004 Snøhvit since 2008 Tomakomai since 2016 Longest operated site (since 1996) 1 Mt CO 2 a 1 Sleipner K12 B Snøhvit Tomakomai off shore CCS projects
Carbon Capture and Storage (CCS) Implementation Limited experience with the monitoring, verification and reporting of actual physical leakage rates and associated uncertainties Leakage Assurance Capture + Transport + Storage + Impact + Monitoring = CCS Implementation
QICS experiment and stratigraphy Blackford, Stahl, Bull et al., 2014 Nature Climate Change
Seismic data acquisition
Time lapse seismic reflection profiles and cartoon illustrating gas pathways above the site of CO 2 release at the QICS experiment (Cevatoglu et al, 2015 and unpub) with propagation of the gas and generation of seismic chimneys during the release. The position of the CO 2 injection site 11m beneath the seabed is indicated (red dots). Note that two years postrelease the seismic chimneys disappear, but there is still enhanced reflectivity on Horizon 2.
Below H2 : mud Above H2 : sand Jain and Juanes, 2009
Chimney / Pipe structures in Offshore sedimentary basins Natural fluid pathways Chimneys: diffuse seismic image Pipe structures: sharp vertical boundaries Karstens, 2015
Seismc Chimneys/Pipes German North Sea Norwegian North Sea S. Viking Graben (Karstens and Berndt, 2015).
Chimney / Pipe structures distribution Ubiquitous in sedimentary basins Linked to overpressured fluid sources Termination in pockmarks with authigenic carbonates and/or hydrates Widths up to 800 m, vertical extent can be 2 km Karstens and Berndt, 2015 Karstens, 2015
Conceptual flow system for an injectionsite Partial breach of the lower seal allows communication with a distant gas chimney. The red arrows indicate potential leakage paths. The purple arrows indicate approximate horizontal and vertical permeability in md ( log scale). Very poor control on permeability. Primary and secondary CO 2 accumulations are shown as solid red areas.
Seismic reflection section illustrating a chimney structure in the German sector of the North Sea (Schlesinger, 2006). The chimney (boxed) cross cuts the top c. 3 seconds two way time (TWT) of the sedimentary overburden (c. 3 km).
Seal Bypass Systems Seal Bypass Systems are defined as features that are embedded within sealing sequences allowing for cross stratal fluid flow migration, which bypasses the pore network of the sealing Sequence. (Cartwright et al., 2007). Typically within 2 km of the surface, representing metre to kilometre scale vertical or sub vertical upward fluid flow from underlying reservoirs, through overwise impermeable overlying sealing sequences in the sub surface
Onshore Field Study Area South Yellowbank Beach near Santa Cruz, California Thanks to Andrew Hurst, University of Aberdeen
Main observations at South Yellowbank Beach 1. Erosive margins 2. Included mudstone clasts Photo and interpretation, Ben Callow
Main observations at South Yellowbank Beach 3. Conjugate fractures 4. Layers dipping towards intrusion centre Photo and interpretation, Ben Callow
Interpretation Sand injectite formation Model of formation: 1. Transport of fluid 2. Critical overpressure 3. Hydrofracture propagation 4. Fluid pressure drops Loseth et al., (2009)
Interpretation Origin of the fluids Boehm and Moore, 2002 Hard to find convincing examples onshore of scale of features seen offshore. Prior interpretion of onshore examples as being driven by fluid migration and supralithostatic fluid overpressure, which generate fluidized flow and hydrofracture propagation
Hypotheses Bull et al. unpub. Conceptual model for a seismic chimney structure which extends close to the seabed. We hypothesize that North Sea sediments are pervasively faulted. Where seal rupture occurs (A) pore fluids drive fracture propagation and linkage (B) allowing fluids to rise due to buoyancy and elevated fluid pressure. In the near surface fluids will migrate along impermeable stratigraphic interfaces (C). In rare situations fractures may propagate to the very near surface (D) or even rupture the seabed.
Underway/Future Work STEMM CCS and CHIMNEY Comprehensive geophysical experiment of a pipe structure 4D seismic experiment of active pipes Broadband seismic anisotropy experiment Drilling of a pipe structure Field analogues onshore Laboratory measurements for geophysical ground trothing Permeability Numerical modeling to understand and quantify the processes BGS RockDrill
Status Update 1. May 2017 successful acquisition of Controlled Source Electromagnetic data 2. May 2017 Some seismic reflection data collected 3. September 2017 Anisotropy experiment using ocean bottom seismometers and a suite of seismic sources (surface and deep tow sparker, GI guns, large airguns). 4. Coring with BGS rockdrill will be rescheduled due to ship issues (May 2017). Late 2017 or 2018.
Conclusions Free gas was successfully imaged on time lapse seismic reflection data and its migration pathway determined. Gas injection likely caused fracturing in silty muddy sediments, and capillary invasion and fluidisation in sandy sediments during active gas release. Seismic chimneys disappeared post release, while CO2 migrated up dip along a stratigraphic interface. The disappearance of chimneys has implications for structures seen in the North Sea. Seismic chimneys/pipes imaged on seismic reflection data in sedimentary basins worldwide can be 2 km in vertical extent and 800 m in width, and are linked to fluid escape features at the surface. Their origin and internal structure are not well understood Seal bypass systems imaged onshore tend to be relatively small in scale, and their relevance to seismically imaged chimneys is ambiguous. There is no evidence that CO 2 release at the seabed is harmful to biota.