Reservoir Rock Typing Definitions

Using well log data to subdivide and group the subsurface into meaningful packages is a common task within geoscience and peterophysics. It allows log responses and rocks that exhibit similar responses and characteristics to be grouped together into what is known as facies. Once they are grouped together they can be used for further analysis, for example creating porosity-permeability transforms on a facies by facies basis.

Within the literature, many definitions exist for different methods of grouping the subsurface, and in some cases these have been used interchangeably.

The table below is an attempt to bring together multiple definitions from the literature into a single place. This list is by no means a definitive list.

References for each description is included at the bottom of the article.

TermDescription
BiofaciesA grouping of sedimentary deposits based on palaeontological attributes such as fossil assemblages that are restricted to a particular environment allowing differentiation of that unit from adjacent units.
ElectrofaciesGrouping of sedimentary deposits based on electrical well log properties allowing it to be distinguished from adjacent beds (Serra & Abbott, 1982).
FaciesThe term facies was introduced by Gressly (1838) to include both sedimentological and palaeontological characteristics. Since then it is used to describe a unit of rock classified based on specific physical properties, biological content and processes that reflect the environmental and depositional conditions in which it formed. It should be distinguishable from overlying and underlying rock units (Reading, 2001).
Flow UnitsHydraulic flow units/flow zones within a reservoir are defined by the physical properties (both geological and petrophysical) of the rock that have an impact on fluid flow and are used to identify pore geometry variations within different lithofacies (Gomes et al., 2008; Amaefule et al., 1993). The units show consistency and can be readily identified from adjacent intervals.
LithofaciesA grouping of sedimentary deposits based on similar lithological and chemical properties of the rock where biological properties are not considered important or are absent (Reading, 2001). The inclusion of sedimentary structures are optional (Gomes et al., 2008).
Lithofacies AssociationA grouping of individual facies that share common porosity-permeability relationships and are associated with a similar depositional environment (Gomes et al., 2008).
LithotypeThe definition of lithotype doesn’t seem to be as well defined with multiple authors having their own definition. Gluyas & Swarbrick, (2013) define a lithotype as “being based on the permeability characteristics of the rock rather than the full suite of physical and chemical properties” and “invented to enable characterisation of the reservoir in terms of how it is likely to perform under production.” Eschard et al., (2014) discuss the combining of lithofacies, with similar petrophysical properties into lithotypes. McCarthy & Curtis (1997) describe lithotypes as merged lithofacies (which includes log, VShale, porosity and permeability) to account for the scale of geostatistical simulations and reservoir model flow properties.
MicrofaciesInitially used to describe petrographic and palaeontological features that were observable under the microscope from thin sections. However, more recently it is used to describe “the total sedimentological and palaeontological data which can be described and classified from thin sections, peels, polished slabs or rock samples” (Flügel, 2004).
PetrofaciesThe dominant use of petrofacies is used for description of sandstones and conglomerates relating to the detrital composition and can be attributed to patterns of sedimentary provenance (De Ros & Goldberg, 2007). A smaller amount of studies relate the term to petrography of mudrocks, carbonates and evaporates. Porras, et al (1999) as cited in Rushing et al., (2008), describes petrofacies as rock units that have similar average pore throat radius, and consequently have similar fluid flow characteristics..
Petrofacies(Reservoir)Reservoir petrofacies are defined by the petrographic attributes (textures, mineralogy, diagenetic effects) of the rock bodies and rock units that impact both petrophysical and geophysical properties which in turn impact how they are defined during exploration and production. Diagenetic processes can be linked to specific ranges in values of porosity and permeability and distinctive log and seismic responses (De Ros & Goldberg, 2007).
Petrophysical GroupsA grouping of rock units characterised by porosity-permeability relationships, capillary pressure and pore throat size distribution obtained from RCA and MICP data. Petrophysical groups may be composed of multiple facies (Gomes et al., 2008).
Rock Types“Units of rock deposited under similar conditions which experienced similar diagenetic process resulting in a unique porosity-permeability relationship, capillary pressure profile and water saturation for a given height above free water in a reservoir.” (Archie, 1950).

References

Amaefule, J. O., Altunbay, M., Tiab, D., Kersey, D. G. and Keelan, D. K. (1993) ‘Enhanced reservoir description: using core and log data to identify hydraulic (flow) units and predict permeability in uncored intervals/wells’, In SPE Annual Technical Conference and Exhibition.

Archie, G. E. (1950) ‘Introduction to Petrophysics of Reservoir Rocks’, AAPG Bulletin, vol. 34, no. 5, pp. 943–961.

Curtis, A. A. (2015) ‘SPE-175560-MS Multi-scale Reservoir Characterisation from Pore Scale to Simulation Scale : Concepts and Workflows Scales Used in Reservoir Characterisation’, Society of Petroleum Engineers.

Eschard, R., Deschamps, R., Doligez, B., Lerat, O., Langlais, V. and Euzen, T. (2014) ‘Connectivity estimation between turbiditic channels and overbank deposits from the modelling of an outcrop analogue (Pab Formation, Maastrichtian, Pakistan)’, Geological Society, London, Special Publications, vol. 387, no. 1, pp. 203–231.

Flügel, E. (2004) Microfacies of Carbonate Rocks, Berlin, Heidelberg, Springer Berlin Heidelberg.

Gluyas, J. and Swarbrick, R. (2013) Petroleum Geoscience, John Wiley & Sons.

Gomes, J. S., Ribeiro, M. T., Strohmenger, C. J., Negahban, S. and Kalam, M. Z. (2008) ‘Carbonate Reservoir Rock Typing – The Link between Geology and SCAL’, Abu Dhabi International Petroleum Exhibition and Conference 2008, pp. 1–24.

McCarthy, J. . and Curtis, A. A. (1997) ‘The impact of upscaling techniques in the geostatistical characterisation of a heterogeneous petroleum reservoir’, Quantitative Geology and Geostatistics, vol. 8, no. 1, pp. 551–562.

Reading, H. G. (2001) ‘Clastic facies models, a personal perspective’, Bulletin of the Geological Society of Denmark, vol. 48, no. 2, pp. 101–115.

De Ros, L. . and Goldberg, K. (2007) ‘Reservoir Petrofacies: A Tool for Quality Characterization and Prediction’, Search and Discovery Article.

Rushing, J. A., Newsham, K. E. and Blasingame, T. A. (2008) ‘Rock Typing: Keys to Understanding Productivity in Tight Gas Sands’, SPE Unconventional Reservoirs Conference, pp. 72–102.

Serra, O. and Abbott, H. T. (1982) ‘The Contribution of Logging Data to Sedimentology and Stratigraphy’, Society of Petroleum Engineers Journal, vol. 22, no. 01, pp. 117–131.

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