An Effective Way to Find Formation Brittleness

Contributors: Ritesh Sharma

The discrimination of fluid content and lithology in a reservoir is an important characterization that has a bearing on reservoir development and its management.

For the unconventional reservoirs, such as shale gas formations, besides other favorable considerations that are expected of them, it is vital that reservoir zones are brittle. Brittle zones frac better, and fracing of shale gas reservoirs is required for their production.

Among the different physical parameters that characterize the rocks, Young’s modulus (E) is a measure of their brittleness. Attempts are usually made to determine this physical constant from well log data, but such measurements are localized over a small area. For studying lateral variation of brittleness in an area, 3-D seismic data needs to be used, because computation of Young’s modulus from seismic data requires the availability of density (ρ).

The computation of density, in turn, requires long offset data, which usually is not available.

In this study, we propose a new attribute (Eρ) in the form of a product of Young’s modulus and density, which can be determined from seismic data without the requirement for long-offsets.

For a brittle rock, both Young’s modulus and density are expected to be high, and so the Eρ attribute would exhibit a high value and serve as a brittleness indicator.

The determination of lithology and fluid content distribution in a reservoir is a desirable objective for its characterization and subsequent management.

Physical properties such as porosity and permeability make it possible to evaluate a hydrocarbon reservoir – however, the properties that have a direct impact on the relevant elastic constants, among others, are bulk modulus, shear modulus and Young’s modulus.

  • Bulk modulus is a measure of a material’s resistance to change in volume and is known as incompressibility. It is treated as a porosity indicator.
  • Shear modulus is measure of rigidity of a rock or resistance to deformation taken in a shear direction and is treated as a lithology indicator.
  • Young’s modulus (E), also known as stiffness modulus is a measure of the stiffness of the material of the rock.

Historically, geoscientists have attempted to delineate the fluid and lithology content of a reservoir on the basis of these physical properties.

An estimation of the physical properties described above requires P- impedance, S-impedance and density. For computing these prerequisites, prestack inversion of surface seismic data is usually performed. Extraction of density from seismic data needs far-offset information – but it also is true that the quality and amplitude fidelity deteriorate significantly at large angles of incidence. So, the computation of density is considered an arduous task.

In the absence of density, efforts have been made for characterization of a reservoir in terms of lithology and fluid content. For this purpose, P-impedance and S-impedance are used for litho-fluid discrimination, as the former is sensitive to fluid, whereas the latter is not.

The determination of rock physics parameters such as Lame’s constants λ (sensitive to pore fluid) and μ (sensitive to the rigidity of the rock matrix) may be difficult to isolate from seismic data, and so their product with density are usually sought – i.e. λρ and μρ can easily be determined from P-impedance and S-impedance.

The stiffness of a rock is an important property – especially for shale gas reservoirs where fracing is employed for stimulation. Stiffer shales frac much better than ductile ones and enhance the permeability of those zones. Young’s modulus can characterize such stiffer pockets in shales.

Considering the importance of a lithology indicator as well as an attribute that could yield information on the brittleness of a reservoir, we propose a new attribute, Eρ, which is the product of Young’s modulus and density. It can be derived from the P-impedance and S-impedance and can be shown to be a scaled version of μρ.

For a brittle rock, Young’s modulus would be high – and density would be high, too –therefore the product of Young’s modulus and density would be high as well and would accentuate the brittleness of the rock.


In figure 1 we show a comparison of the μρ and Eρ curves for a well in northern Alberta.

Notice, the Eρ curve emphasizes the variation corresponding to lithology change more than in the μρ curve.

For ease in interpretation, we segment the input log curves – and the results shown in figure 2 stand out nice and clear.

For implementation of this analysis on seismic data we considered a gas-impregnated Nordegg member of the Jurassic Fernie formation of the Western Canadian Sedimentary Basin.

The Nordegg member of the Fernie formation varies throughout the WCSB. It consists of predominantly brownish, greyish and black shales, which vary from siliceous rich cherts and dolomites to carbonate rich shale.

Due to the complex geology of the reservoir in the Nordegg, differentiating the lithology and fluid content is a challenge.

The Nordegg-Montney interface is a regional unconformity that separates the Jurassic and Triassic strata in the area. The Montney formation is composed of fine-grained siltstone grading to fine-grained sandstones, with limited shale content. There is a diagenetic dolomitic overprinting on the siltstones and sandstones. In local areas of the Montney there is a coquina facies made up of bivalves.

As the first step, simultaneous impedance inversion was run on the pre-conditioned 3-D seismic data to obtain P-impedance and S-impedance volumes. Next, these impedance volumes were transformed into μρ and Eρ volumes.

In figures 3a and b, we show segments of vertical sections from the μρ and Eρ volumes, respectively.

Apparently, we notice Eρ has a higher level of detail than the μρ attribute. The upper parts of the figures exhibit lower values of the attributes as they correspond to the sandstone presence, whereas the higher values are seen in the lower part, verifying the availability of dolomitic siltstone in this zone.


We have proposed a new attribute (Eρ) in the form of a product of Young’s modulus and density, which is a good lithology indicator. We describe it as a scaled version of the μρ attribute and illustrate that it intensifies the variation in lithology.

This attribute can be derived seismically, and we have shown that with it we can determine the brittleness of a formation.

We thank Athabasca Oil Corporation for giving us permission for presentation of the results shown in this study. We also thank Arcis Seismic Solutions for permission to present this work.

Comments (0)


Geophysical Corner

Geophysical Corner - Satinder Chopra
Satinder Chopra, award-winning chief geophysicist (reservoir), at Arcis Seismic Solutions, Calgary, Canada, and a past AAPG-SEG Joint Distinguished Lecturer began serving as the editor of the Geophysical Corner column in 2012.

Geophysical Corner - Ritesh Kumar Sharma

Ritesh Kumar Sharma is with Arcis Seismic Solutions, Calgary, Canada.

Geophysical Corner

The Geophysical Corner is a regular column in the EXPLORER that features geophysical case studies, techniques and application to the petroleum industry.


See Also: Book

Desktop /Portals/0/images/_site/AAPG-newlogo-vertical-morepadding.jpg?width=50&h=50&mode=crop&anchor=middlecenter&quality=90amp;encoder=freeimage&progressive=true 4483 Book
Alternative Resources, Structure, Geochemistry and Basin Modeling, Sedimentology and Stratigraphy, Geophysics, Business and Economics, Engineering, Petrophysics and Well Logs, Environmental, Geomechanics and Fracture Analysis, Compressional Systems, Salt Tectonics, Tectonics (General), Extensional Systems, Fold and Thrust Belts, Structural Analysis (Other), Basin Modeling, Source Rock, Migration, Petroleum Systems, Thermal History, Oil Seeps, Oil and Gas Analysis, Maturation, Sequence Stratigraphy, Clastics, Carbonates, Evaporites, Seismic, Gravity, Magnetic, Direct Hydrocarbon Indicators, Resource Estimates, Reserve Estimation, Risk Analysis, Economics, Reservoir Characterization, Development and Operations, Production, Structural Traps, Oil Sands, Oil Shale, Shale Gas, Coalbed Methane, Deep Basin Gas, Diagenetic Traps, Fractured Carbonate Reservoirs, Stratigraphic Traps, Subsalt Traps, Tight Gas Sands, Gas Hydrates, Coal, Uranium (Nuclear), Geothermal, Renewable Energy, Eolian Sandstones, Sheet Sand Deposits, Estuarine Deposits, Fluvial Deltaic Systems, Deep Sea / Deepwater, Lacustrine Deposits, Marine, Regressive Deposits, Transgressive Deposits, Shelf Sand Deposits, Slope, High Stand Deposits, Incised Valley Deposits, Low Stand Deposits, Conventional Sandstones, Deepwater Turbidites, Dolostones, Carbonate Reefs, (Carbonate) Shelf Sand Deposits, Carbonate Platforms, Sebkha, Lacustrine Deposits, Salt, Conventional Drilling, Directional Drilling, Infill Drilling, Coring, Hydraulic Fracturing, Primary Recovery, Secondary Recovery, Water Flooding, Gas Injection, Tertiary Recovery, Chemical Flooding Processes, Thermal Recovery Processes, Miscible Recovery, Microbial Recovery, Drive Mechanisms, Depletion Drive, Water Drive, Ground Water, Hydrology, Reclamation, Remediation, Remote Sensing, Water Resources, Monitoring, Pollution, Natural Resources, Wind Energy, Solar Energy, Hydroelectric Energy, Bioenergy, Hydrogen Energy
Desktop /Portals/0/PackFlashItemImages/WebReady/book-s65-Application-of-Structural-Methods-to-Rocky-Mountain.jpg?width=50&h=50&mode=crop&anchor=middlecenter&quality=90amp;encoder=freeimage&progressive=true 5826 Book

See Also: DL Abstract

In overcoming the technical challenges of oil production in the Arctic, are we making the most of a strategic resource or heading for an environmental and political minefield? The vast Arctic region is probably the last remaining unexplored source of hydrocarbons on the planet. Ultimate resources are estimated at 114 billion barrels of undiscovered oil and 2000 trillion cubic feet of natural gas. This great prize, in a world of diminishing resources, has stimulated both governmental and industry interest. Harnessing the considerable resources of the ‘Final Frontier’ is going to be fraught with many technical, political and environmental challenges that will engage many minds, both scientific and political over the next half century.

Desktop /Portals/0/images/_site/AAPG-newlogo-vertical-morepadding.jpg?width=50&h=50&mode=crop&anchor=middlecenter&quality=90amp;encoder=freeimage&progressive=true 838 DL Abstract

See Also: Field Seminar

The field trip will visit sites where evidence of this volcanic history can be examined as well as the petrified forest and new visitor center and paleontology lab at Florissant Fossil Beds National Monument.
Desktop /Portals/0/PackFlashItemImages/WebReady/ace2015-ft-02-hero.jpg?width=50&h=50&mode=crop&anchor=middlecenter&quality=90amp;encoder=freeimage&progressive=true 14183 Field Seminar

See Also: Short Course

This course will address integration of source rock, produced oil and gas, and mud gas data to better understand and exploit 3-dimensional details of petroleum systems. Carbon isotope and oil biomarker geochemistry will be stressed as a way to determine quantity and type of generated hydrocarbons and migration distance and direction within source rock and tight oil plays.

Desktop /Portals/0/PackFlashItemImages/WebReady/Practical-Aspects-Of-Petroleum-Geochemistry-For-Resource-Plays-hero.jpg?width=50&h=50&mode=crop&anchor=middlecenter&quality=90amp;encoder=freeimage&progressive=true 13514 Short Course