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PSReservoir Characterization of the Korolev Field, North Caspian Basin, Kazakhstan*

By

Kevin. L. Putney1, Joel. F. Collins1, Paul. M. Harris2, Akmaral Zhumagulova3, and Dennis J. Fischer3

 

Search and Discovery Article #20055 (2008)

Posted June 10, 2008

 

*Adapted from poster presentation at AAPG Annual Convention, Calgary, Alberta, June 19-22, 2005.

Click to view list of articles adapted from presentations by P.M. (Mitch) Harris or by his co-workers and him at AAPG meetings from 2000 to 2008.

 

1 ExxonMobil Development Company, Houston, Texas, U.S.A. ([email protected])

2 ChevronTexaco Energy Technology Company, San Ramon, California, U.S.A. ([email protected])

3 TengizChevroil, Atyrau, Kazakhstan

 

Abstract

Korolev field is an isolated carbonate platform located 15 km. from the better known Tengiz field. It was discovered in 1986 and had been characterized as a smaller version of the 1979 Tengiz discovery due to similarities in stratigraphic age, reservoir thickness and oil properties. However, new drilling at Korolev has identified key differences between the two fields that impact assumptions about hydrocarbon distribution and producibility. Further insights on reservoir performance have also been gained since Korolev began producing in 2001.

Differences in Korolev and Tengiz reservoir properties were apparent during drilling. Unlike Tengiz, where drilling circulation losses are prevalent only in slope facies surrounding the platform, lost circulation occurs in both the platform and slope at Korolev. Lost circulation is commonly associated with relatively thin zones of high permeability that greatly enhance well productivity and reservoir connectivity. Pressure vs. depth measurements obtained in new wells and pressure transient tests between producing wells provide supporting evidence for pressure communication throughout Korolev field.

Pyrobitumen is present as a pore-filling cement at Korolev and Tengiz, but its distribution varies between the two fields. Tengiz slope facies contain elevated volumes, commonly near lost circulation zones, while Tengiz platform facies have much lower volumes. In contrast, Korolev platform and slope facies both contain high pyrobitumen volumes thought to be associated with increased frequency of high permeability zones. The high degree of connectivity in the Korolev platform is thought to result from dissolution and diagenesis associated with multiple pore volumes of fluids spilling from Tengiz into this much smaller field.

 

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Korolev Field Summary

  • Korolev discovered in 1986 with K-10 well (Tengiz 1979).
  • Both fields are located below thick Kungurian salt.
  • TengizChevroil (TCO) operates Korolev & Tengiz.
  • 50% Chevron, 25% ExxonMobil, 20% Kazmunaigas, 5% Lukarco.
  • Highly undersaturated oil, properties similar to Tengiz.
  • 47° API gravity, 15% H2S (both are similar to Tengiz).
  • High reservoir pressure (11,000-12,000 ps, similar to Tengiz).
  • 17 wells control field area.
  • 5 wells drilled by TCO (K-3882, K-3483, K-3682ST, K-3185ST, K-3880).
  • 3 deepenings by TCO (K-11ST, K-18, K-19).
  • 3 full penetrations of Korolev platform (K-3483, K-3682ST, K-18).
  • 1281m core: Various Russian wells=356m, K-3882=119m, K-3483=395m, K-3682st= 108m, K-19=109m, K-3880=194m).
  • Production began Nov. 2001 (K-10 & K-3882 wells).
  • K-3882 capable of 16+ kbd, K-10 tested 11 kbp, K-3483 tested 9 kbd.
  • Vertical connectivity seen in platform and slope.
  • MDT pressure data indicates excellent connectivity throughout field.

 

Conclusions

Prior assumptions that Korolev was perfectly analogous to Tengiz were inaccurate. Several aspects of this can be attributed directly to Korolev’s smaller areal extent:

  1. Deeper platform facies form the dominant depositional environment.
  2. Later diagenesis has a greater effect on reservoir quality.
  3. LCZ’s and fractures play a larger role in field connectivity and depletion.
  4. Pyrobitumen volumes are elevated, greatly reducing the oil storage capacity of the Korolev platform.

MDT data reveal extensive pressure continuity throughout Korolev that is associated with a network of thin, high permeability zones where lost circulation zones of probable late diagenetic origin are common. The net result is a field with excellent connectivity and wells with high flow rates. The prevalence of pyrobitumen at Korolev is thought to be a function of multiple pore volumes of hydrocarbons spilling from Tengiz and distributed throughout Korolev via this high permeability network.

Excellent pressure continuity at Korolev due to extensive high permeability network was created in part by diagenetic fluids.

Multiple hydrocarbon pore volumes spilling from Tengiz to Korolev created conditions favorable for pyrobitumen formation.

 

Acknowledgements

This study was a team effort. We thank consultants Jeroen Kenter for his core descriptions and Paul Brenckle for bio-stratigraphic analyses. We also recognize the contributions and support of others from ExxonMobil (Peter Hillock petrophysical support, Tom Frantes, supervisor). We thank TengizChevroil and its shareholder companies Chevron, ExxonMobil, Kazmunaigaz, and BPLukArco) for support of our studies.

 

References

Weber, L.J. et al, 2003, Stratigraphy, lithofacies and reservoir distribution, Tengiz Field, Kazakhstan: SEPM Special Publication 78 and AAPG Memoir 83, p. 351-394.

Della Porta, G. et al, 2003, Microbial boundstone dominated carbonate slope (Upper Carboniferous, N. Spain), in Microfacies, Lithofacies Distribution and Stratal Geometry. Facies 49, p. 175-208.

Lucia, F.J., 1995: Rock fabric / petrophysical classification of carbonate pore space for reservoir characterization: AAPG Bulletin, v. 79, p.1275-1300.

 

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