SEM (Scanning Electron Microscopy)

SEM (Scanning Electron Microscopy)

SEM is a powerful tool for visualising reservoir pore and grain framework systems. It is particularly useful combined with XRD for understanding the impact of clay mineral occurrence and habit on reservoir behaviour, which is often dramatically disproportionate to mineral volume.

Magnification Range: 10x ->30,000x

Sample Types: Outcrop, core, SWC, ditch cuttings

Key applications in petroleum geology include the determination of:

  • pore geometry, size & interconnectivity

  • rock texture (grain size, sorting, grain contacts, compaction, etc)

  • framework grain : cement / interstitial clay relationships

  • clay mineral morphology, location and habit

  • formation damage assessment

  • resolving factors effecting Sw & unexpectedly tight horizons

  • microfossil identification

  • diagenetic sequencing and phase relationships

Related services include:

  • EDX (Energy-Dispersive X-Ray) analysis provides elemental signatures used in mineral phase identification
  • BSE (Back-scattered electron) analysis can be used to discriminate and quantify mineral compositions
  • TEM (Transmission electron microscopy) can produce even higher magnification views of wafers, but is typically used for research applications
  • Pore Casts can be made using resin impregnation and dissolution of host rock, revealing the pore connectivity;  this is particularly useful in conjunction with MICP (mercury injection capillary pressure) analysis.

A multi-Darcy sweet zone at 3.5kms burial depth preserved by early diagenetic chlorite pellicles.

This diagenetic phase has stabilized grain framework from grain slippage and compaction and inhibited quartz overgrowth, preserving high levels of macroporosity

Sample from a zone of high log porosity but with anomalously low permeability.

Here, syndepositional clay floccules have migrated to pore throats and then been cemented in-situ by pore-lining diagenetic chlorite.

Rosettes of Fe-chlorite platelets line pores having seeded on clay floccules.  This has greatly increased surface area resulting in high Sw and low permeability.

CPI interpretations are often incorrect due to the disproportionately large effect that chlorite has on Sw values.

Note also later passive overgrowth by a rhombic carbonate phase..

Diagenetic illite can have a devastating effect on reservoir performance, especially where 'hairy' filamentous habits bridge pores / pore throats.  Permeability: porosity relationships can plunge by several orders of magnitude.

Critical point freeze drying of samples may be required to properly appreciate these delicate structures, which can collapse during conventional drying, making the pores system look erroneously open.