Solid Earth Cycles and Geodynamics

1
Solid Earth Cycles and Geodynamics

• Downhole Measurement Scientific Priorities
• DHT Workshop Day 1

2
Solid Earth

• Rifting
• Seafloor Spreading
• Mid-plate Processes
• Subduction Collision

3
Scientific Themes and Initiatives

• Theme Areas
• Rifted Continental Margins
• Oceanic Lithosphere
• LIPs
• Recycling of Oceanic Lithosphere (Subduction
  Factory)
• Earthquake and Tsunami Processes
• Formation of Continental Crust

• Initiatives
• Continental breakup and sed. basin formation
• Large Igneous Provinces
• Seismogenic Zone
• 21st Century MoHole

4
Passive Margins

• Margin Architecture Processes
• Rifting processes
• Sedimentary architecture and history
• Slope failure and mass transport mechanisms
• Drilling Environment
• Ultra-shallow to intermediate water depth
• Overpressure, hydrocarbon potential
• Downhole Priorities
• Pore pressure
• Fluid sampling
• BSE (borehole seismic experiments) for
  borehole-surface integration

5
Rift Processes

• Continental break-up and transition to seafloor
  spreading
• Mechanics of low-angle normal faulting
• Exposure of mantle at NVRM

Woodlark Basin active low-angle normal faulting
6
Oceanic Plateaus and LIPs

• Fluid circulation processes in and around
  plateaus, ridges, oceanic flood basalts,
  seamounts
• Architecture, seismic properties, and composition
  of volcanic and intrusive rocks

7
Ridge Processes

• Processes of formation of oceanic crust
• Hydrothermal circulation
• 21st Century MoHole concept
• This idea from the dawn of DSDP has renewed
  currency (but still is kind of remote)
• Will continue to depend on proxies
• Fluids and associated chemical and thermal
  signatures
• Seismic interrogation

8
Recycling at Convergent Margins (Subduction
Factory)
9
Recycling at Convergent Margins (Subduction
Factory)

• Cycling and mass balance of solids and volatiles
  in oceanic crust, sediments, and fluids as plates
  subduct and interact with the mantle and the
  overriding plate.
• Quantify heat, fluid inputs and partitioning in
  the system
• Downhole Priorities
• Temperature
• Fluid sampling

10
Seismogenic Zone Initiative

• What controls the updip and downdip limits of the
  seismogenic zone? Why does the coupling on the
  seismogenic fault change laterally, and what is
  the nature of seismic asperities?
• What fundamental mechanisms control the
  earthquake cycle of elastic strain buildup and
  its sudden release through fault rupture?
• Are there temporal changes of stress, pore
  pressure, chemistry, and other parameters that
  define the times of increasing probability of
  great earthquakes?
• What is the nature of the tsunamigenic earthquake
  zone?

11
Seismogenic Zone

• Investigation of fields of stress, strain, and
  fluid pressure to address processes involved in
  seismogenesis
• Borehole environment
• Shallow to deep, sediments to hard rock, low to
  high P-T conditions
• Downhole priorities
• Temperature, pressure (sed. and rock to high T)
• Active packer tests for pore pressure,
  permeability, principal stresses
• Borehole seismic experiments

12
Downhole Measurements/Samples in Common

• BSE (VSP, offset time-lapse VSP, cross-well)
• Stress and pore fluid pressure
• Temperature
• In-situ fluid sampling
• Borehole Environment
• Sediment vs. rock measurements
• High temperature, high pressure, chemically
  hostile environments (hydrothermal fluids,
  hydrocarbons)
• Unstable formations

13
Borehole Seismic Experiments

• Science Drivers
• Ground-truth surface seismic
• Large-scale structure
• Petrophysical properties of zones of interest
  (e.g., fault zones)
• Extending borehole information into surrounding
  volume
• Vp and Vs, anisotropy, attenuation, reflectivity,
  AVO/AVA response
• Time-varying properties

14
BSE examples
15
Downhole Fluid Pressure and Stress Measurement

• Pore Fluid Pressure
• DVTP-P or Piezoprobe style
• Wireline Formation Testers (RFT)
• Openhole Drill Stem Tests (DST/MDT)
• Formation Stress
• Lateral stress tools?
• Extended leak-off test (XLOT) or hydrofrac
• Measures formation breakdown pressure (s3 C0)

16
Fluid Sampling

• Geochemical proxies for tectonic processes
• Hard to squeeze water out of low-porosity cores
• Sampling at in-situ pressure desirable

17
Summary and Critical Needs

• Downhole measurements are critical for ongoing
  emphasis on tectonic processes
• Fluid pressure
• one or more principal stresses
• hydrologic properties
• seismic structure
• fluid chemistry
• Technological challenges
• High temperature robustness
• Multi-platform portability

18
Points to Ponder

• Drill ship vs. wireline re-entry
• Time-of-drilling vs. time-dependent properties
• Keeping abreast of rapid developments in industry
• New built tools
• New fundamental sensor technology (fiber optic
  sensors, MEMs, high-T electronics)

19
Sampling Through Casing?

• Cased Hole Dynamics Tester (CHDT) (new
  Schlumberger tool)
• Lowered into borehole to drill up multiple holes
  through casing, acquire formation pressure and
  fluid sample, then plug hole.