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Understanding and Predicting Fractures at Tengiz – A Giant, Naturally Fractured Previous HitReservoirNext Hit in the Caspian Basin of Kazakhstan*

By

Wayne Narr1, Dennis J. Fischer2, Paul M. (Mitch) Harris1, Thomas Heidrick2, Ben T. Robertson2, and Karen Payrazyan1

 

Search and Discovery Article #20057 (2008)

Posted June 25, 2008

 

*Adapted from oral presentation at AAPG Hedberg Conference, "Carbonate Previous HitReservoirNext Hit Previous HitCharacterizationNext Hit and Simulation: From Facies to Previous HitFlowNext Hit Previous HitUnitsNext Hit," El Paso, Texas, March 14-18, 2004.

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

3 Tengizchevroil, Atyrau, Kazakhstan

 

Abstract

Tengiz oil field in Kazakhstan produces from an isolated carbonate platform (areal extent of 160 km2) of Devonian and Carboniferous age, consisting almost exclusively of limestone. Seismic and well data clearly show two principal regions within the buildup, platform and slope (or flank) that directly relate to Previous HitreservoirNext Hit quality and production characteristics. Natural fractures significantly impact producibility of the flank portion of the Previous HitreservoirNext Hit.

Previous HitCharacterizationNext Hit of fractures in the Tengiz Previous HitreservoirNext Hit has two primary objectives:

  • To advance a consistent, qualitative, geological conceptual model that allows us to understand the fracture distribution.
  • To build a quantitative model for use as the basis for fluid-Previous HitflowNext Hit simulation.

Most Tengiz fractures formed syndepositionally due to gravitational collapse of the laterally expanding Tengiz carbonate platform. Many Previous HitreservoirNext Hit fractures are equivalent to neptunian dikes, which originate as syndepositional extension fractures. Syndepositional faults may also be present, but in smaller abundance. The Tengiz fractures strike parallel to the depositional margin and are in greatest abundance in the vicinity of the paleo-shelf-margin (rim) and slope. Facies showing the highest lateral growth-rate have the greatest fracture density. The Permian Capitan shelf margin of the Guadalupe Mountains of New Mexico presents a genetic analog for this style of fracturing.

Constructing a model for Previous HitflowNext Hit simulation involves progressing from discrete fractures to computation of effective medium Previous HitflowNext Hit properties for model cells. Fracture data for our Previous HitreservoirNext Hit model come primarily from image logs and core. These discrete fractures are converted to fracture density logs (fracture surface area/m3). We use a neural-net approach for spatial distribution of fracture properties throughout the model. This allows various distributed properties (matrix porosity, facies, seismic attenuation, etc.) to determine the spatial distribution of fracture density. The approach is similar to non-linear multiple regression; the input parameters predict the output distribution. The choice of distributed properties (input parameters) is where geologic knowledge and intuition come into play.

The final step combines fracture density, fracture geometry, and matrix permeability to compute permeability tensors for each grid cell. This step uses a boundary-element model that combines the interacting effects of fracture-Previous HitflowNext Hit and matrix-Previous HitflowNext Hit.

 

uAbstract

uFigures

uComparison with analog

uFracture prediction

uConclusions

uAcknowledgements

uReference

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

uAbstract

uFigures

uComparison with analog

uFracture prediction

uConclusions

uAcknowledgements

uReference

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

uAbstract

uFigures

uComparison with analog

uFracture prediction

uConclusions

uAcknowledgements

uReference

 

 

Comparison of Tengiz and Capitan Margin Fractures

  • Mechanically equivalent fractures in Tengiz and Capitan margin:
    • Orientation
    • Location/facies of occurrence
    • Density of occurrence
  • Outcrops show that syndeposition fractures are long, significant features of the margin.
  • A significant difference: solution-enhancement at Tengiz.

 

Prediction of fractures

  • Fractures do not generally behave according to conventional geostatistical expectations.
  • Use other distributed properties as predictors of fracture density.
    • Facies
    • Porosity
    • Formation
    • Shape factor
    • Seismic P.C. anomaly

 

Conclusions

Fractures at Tengiz are mainly syndepositional extensional fractures that developed during lateral growth of the carbonate platform.

We use an NFR workflow that involves:

  • ID and confidence ranking of effective fractures.
  • Neural-net –based interpolation of fracture density.
  • Tensor K input for simulator.

 

Acknowledgements

We thank Tengizchevroil and its partners for allowing us to share information about the Tengiz oil field—ChevronTexaco, ExxonMobil, KazMunaiGas, LukArco, and Republic of Kazakhstan.

 

Reference

Playford, P.E., 1984, Platform-margin and marginal slope relationships in Devonian reef complexes of the Canning basin, in P. G. Purcell, ed., The Canning basin, W.A.: Proceedings of the Geological Society of Australia/Petroleum Exploration Society of Australia Symposium, p. 189-214.

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