Risking CO 2 leakage along faults what do we know?

Transcription

1 TCCS talk, Risking CO 2 leakage along faults what do we know? Alvar Braathen, Elin Skurtveit, Kei Ogata, Kim Senger and Jan Tveranger, and with contributions from Gabrielsen, Olaussen, Osmundsen, Evans, Petrie, and many others 1) Why the concern around faults? 2) How is the industry handling faults? 3) What are faults actually made up of? 4) How and where are faults allowing fluid/co 2 mobility? 5) What do we need to know to move forward on fault risking? Water, hydrocarbons or CO 2. the future of Smeaheia?

2 1) Why the concern around faults? Faults, fracture corridors and sand injectites the steep route for fluids towards the surface Over-pressured storage fm may cause breaching of roof or faults Out-of-containment fluid flow Torabi et al ) Spill out of physical closure 1 2 CO2 plume 2) Breaking through the roof 3 4 3) Leaking up along fault 4) Leaking across fault Flow across and in faults: Capillary entry pressure Relative permeability Forces for Darcy flow fluid migration: Naturally driven by buoyancy of fluid Driven by pressure changes caused by production

3 NORCCS Smeaheia storage formations bound by faults From OED 2016 Faults may explain? 1) No HC in Smeaheia 2) Pressure depletion in Smeaheia from Troll production 3) Pockmarks (old seeps?) Main targets at 800 to 1300 m depth

4 2) How is the industry handling faults? => Key business decisions Fill-spill scenarios Juxtaposition Shale content in faults Færseth et al Water-HC contact Case X - leak Case Y partly leak 1 2 plume 1) Spill out of 3 physical closure 2) Breaking through the roof 4 3) Leaking up along fault 4) Leaking across fault Case Z underfilled; roof?

5 Clay content and fault rocks as fault-seals Along-fault layers Across-fault barrier Seal or baffle? Qualitative fault seal evaluation Combining fault architecture and juxtaposition Færseth et al Fossen and Gabrielsen 2010

6 3) What are faults actually made up of? Fossen & Gabrielsen 2005 Fossen et al. Faults => rock volume or envelope of - high-strain Core - low-strain Damage zone Zone/envelope saturated with deformation Offset of markers

7 Fault zone in outcrops Faults offer significant 3D challenges Can we learn more or even quantify their charactersitcs? Bartlet fault core with: 1) Sandstone lenses 2) Crush sand membranes 3) Along-fault fractures Slick Rock Mbr Morrison Fm Ceder Mnt Mbr Bartlet Fault Utah, USA Hanging wall shale and sandstone Footwall eolian sandstone Throw ~ 200 m (including c. 100 m drag)

8 Fault core which elements can baffle or transport fluids? Elements classified as facies Extensional fault Sinai, Egypt Footwall - Nubian Sst Hanging wall Raha Fm shale and sst Throw ~ 200 m Architecture of volumetric fault Shaley membrane Lenses in core and towards footwall damage zone Fractures Slip-surface Shale gouge layer (along fault) Membrane facies X Sand lens (tectonic contacts) Lens facies A ~10 M Sand-shale lens Lens facies C

9 Faults and fluid mobility Architecture of basement faults Joint swarms Fracture corridors Faults Three fundamental types of fracture systems in sedimentary rocks and basement that guide fluid flow Joint swarms Fracture corridors Faults Gabrielsen and Braathen 2014

10 4) How and where are faults allowing fluid/co 2 mobility? Utah, USA Dewey Bridge Mbr Navajo Sst Entrada Slick Rock Mbr Up-fault fluid migration causing footwall sweep by reducing fluids seen as bleaching by dissolution of FeO minerals in high Poro-Perm eolian sandstone Cache Valley, Outside Arches National Park, Utah, USA Fault core Faults Throw ~ 12 m J. Summerville Fm Throw ~ 30 m Navajo Sst Fault core Stacked reservoirsseals Up-fault flow of reducing fluids seen as bleaching by dissolution of FeO minerals in fractured damage zone in tidally deposited shale and mudstone East San Rafael Swell, Utah, USA

11 Fractures and fracture corridors Through-Going fracts Fracture Corridor ~ W ~ E Bed-Confined fracts Mostly joints Fracture corridors: roughly tabular to lenticular zones characterized by high fracture frequency, from tens of cm up to 4-6 m wide and m long Closely spaced TGs and interconnecting BCs

12 Conclusion: Faults and fracture corridors are seal-bypass systems (extensional systems) Large scale network of fault-parallel and perpendicular fluid flow conduits 1) Joint swarms: outer arc extensional regime of folds 2) Faults: flow barriers (e.g. clay membranes) in major faults 3) Faults: fluid flow along fractures in fault core and damage zones Ogata et al. 2014

13 6a) What do we need to know to move forward on fault risking? Learning from seeps, seismic chimneys and pockmarks 1. Onland seeps inform seismic chimney studies => they are the same 2. Seeps are mostly along faults or associated with faults 3. Seeps record upward fluid flow bypassing seals in < 10 m wide, < m long zones 4. Significant pressure gradients trigger and drive seeps 5. CO 2 seeps tend to be self-sealing by calcite precipitation (ca years?) 6. Only super-user modelling software capable of handling along-fault flow Fault-surface model Fault-volume grid-model Will over-pressure fracturing of top-seal causing leakage show similar flow patterns?

14 6b) What do we need to know to move forward on fault risking? Learning from fault studies 1. Faults make up rock volumes with distinct rock properties => predicting detailed fault architecture is challenging; but outcrop observations questions validity of SGR and SSF models (crude upscaling) 2. First order fault geometry can be identified in seismics => fault jogs and fault displacement gradients in 3D locate complex fault linkage zones; new learning with forecasting capability Fault surface map with contoured displacement

15 6c) What do we need to know to move forward on fault risking? Learning of significance for fault re-activation Application of re-shear criteria for fault reactivation is NAÏVE Fault strength is controlled by asperities/sticky spots, rock properties and healing (compaction, cement) 1. Faults make up rock volumes in which the prediction of rock properties is challenging => basically no fault-rock geomechanical data exists 2. Importance of asperities/sticky spots, rock properties and healing (compaction, cement) not tested => benchmark re-activation modelling needed on real geometries and rock properties 1 m Compaction healing 1 m Deformation band fault with quartz cement in porous sst

16 Faults are good fun thank you.