Ultimate expellable potential


The Ultimate Expellable Potential (UEP) represents the cumulative mass of oil and gas that can be expelled from a source rock upon its complete maturation. UEP can be calculated in Zetaware’s KINEX software as a function of organofacies and source rock parameters (i.e. total organic carbon (TOC), hydrogen index (HI) gas/oil generation index (GOGI), and transformation index (TI)).

For use in resource estimation, these masses can be converted to volumes of oil and gas per unit area (mmstb/km2 and bscf/km2 or mmboe/km2, respectively). Like other regional elements, UEP varies across a basin or play and takes vertical stratigraphic heterogeneity and lateral stratigraphic variability of source rocks into account (Roller and Pepper, 2017).

UEP, together with migration loss, is one of the most important factors in charge risking (He, 2016). Volumetrically significant petroleum systems are supplied by source rocks with UEP of 10’s of mmboe/km2; with the world’s most prolific source rocks reaching 100 mmboe/km2 or more (Roller and Pepper, 2017; Pepper, 2019).

However, a modest UEP within closely coupled source rock/reservoir systems with few migration losses and a large focused fetch area (e.g. Eagleford-Woodbine, East Texas Basin) may be just as adequate as a high UEP in a widely separated source rock/reservoir system requiring much vertical migration and with more limited fetch areas (e.g. Jurassic-Miocene, GoM minibasins) (Roller and Pepper, 2017).

APT use Zetatware's Kinex software to gain a greater understanding of how source rocks behave. The Kinex outputs can be utilised in both 1D and 3D modelling to predict the expelled volumes within your region of interest.

Source rock UEPs

Ultimate expellable potential of various source rocks


Source RockTOC mean (%)HI mean (mg/gTOC)Organo-faciesThickness mean (m)ReferenceUEP mean (mmboe/km2)UEP/m


Arabian Basin Tuwaiq Mountain Fm 5.7 705 A 45 Roller and Pepper, 2017 30.4 0.68
West Siberian Basin Bazhenov Fm 15.5 650 A/B 24 Roller and Pepper, 2017 30.6 1.28
Williston Basin Bakken Fm 15 817 B 4 Roller and Pepper, 2017 7.6 1.90
Bohai Basin Shahejie Fm 2.9 380 C 102 Roller and Pepper, 2017 20.2 0.20
Generic Thick lean deltaic 2 160 D/E 500 Zetaware webpage 29.7 0.06
Generic Normal deltaic 3 250 D/E 200 Zetaware webpage 27.2 0.14
SE Asia Coals 65 350 D/E 30 Zetaware webpage 72.0 2.40
Europe North Sea KCF 5 600 B 100 Zetaware webpage 51.3 0.51
North America GoM Tithonian 7 650 B 100 Zetaware webpage 77.0 0.77
NE China Bohai Lacustrine 8 700 C 300 Zetaware webpage 281.5 0.94


He, Z., 2016. The Most Important Factors in Charge Risking and Best Practices. AAPG Hedberg Conference, The Future of Basin and Petroleum Systems Modeling, Santa Barbara, California, April 3-8, 2016.

Pepper, A.S., 2019. Source Rock Organofacies, Development and Preservation: The Basis for a Quantitative Description of Source Rock Expulsion Potential, Expelled Fluid Composition, and Properties – in Time and Space. AAPG Middle East Region GTW, Regional Variations in Charge Systems and the Impact on Hydrocarbon Fluid Properties in Exploration, Dubai, UAE, February 11-13, 2019.

Roller, E., Pepper, A.S., 2017. Estimating the ultimate expellable potential of source rocks: defining “world class” for aquatic organofacies with examples from the Arabian, West Siberian, Bohai and Williston basins. AAPG Annual Convention & Exhibition, Houston, Texas, April 2-5, 2017.