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Assessment of Transport Properties Using High Previous HitResolutionNext Hit CT and NMR: An Example from the Central Tengiz Platform Reservoir, Pricaspian Basin, Kazakhstan*

By

Jeroen A.M. Kenter1, Olga Vizika2, Elisabeth Rosenberg2, P.M. (Mitch) Harris3, Mark Skalinski4, and Matthew Buoniconti3

 

Search and Discovery Article #20049 (2008)

Posted May 20, 2008

 

*Adapted from oral presentation at AAPG Annual Convention, Long Beach, California, April 1-4, 2007.

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 Chevron Energy Technology Company, Voorburg, Netherlands ([email protected])

2 Institut Français du Pétrole, 1 et 4, avenue de Bois-Préau, 92852 Rueil-Malmaison Cedex, France

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

4 TengizChevroil, Atyrau, Kazakhstan

 

Abstract

The central platform in the Tengiz buildup contains a succession of cyclic shallow water deposits ranging from Famennian to Bashkirian in age. The upper Visean, Serpukhovian, and Bashkirian form the main hydrocarbon-bearing interval and contain cyclic, depositional cycles ranging from dm- to m-scale to 10’s of meters in thickness. The distribution of reservoir rock types in the central platform is determined by a combination of primary depositional and burial diagenetic modification and includes spatial variations of both porosity enhancing (corrosion) as well as porosity filling (reducing) effects.

A pilot study using a combination of pore network modeling of the petrophysical properties from high Previous HitresolutionNext Hit (~1 micron) CT microscanner imagery of several selected plug samples resulted in spatial pore and pore-throat size distributions, level and type of pore interconnectivity as expressed by the aspect ratio as well as the coordination numbers (number of pore throats per pore). Porosity, permeability, capillary pressure, and formation factors were estimated from CT and NMR analyses and show a close match with those derived from analytical measurements. Most strikingly, the CT imagery allowed the extraction of the 3D distribution of pore type and connectivity as well as cement types, information essential to reservoir quality assessment but very difficult to reconstruct using the classic petrographic approach.

High Previous HitresolutionNext Hit CT and NMR imagery of key reservoir intervals provide reliable data on rock properties and, more importantly, they fill the essential link between petrophysics and geology at the scale of even small pore types (~1-3 microns) and pore filling cements.

 

uAbstract

uFigures

uRationale

uRock types and cyclicity

uPNM & CMT

uNMR & pore size

uSummary

uReference

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

uAbstract

uFigures

uRationale

uRock types and cyclicity

uPNM & CMT

uNMR & pore size

uSummary

uReference

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

uAbstract

uFigures

uRationale

uRock types and cyclicity

uPNM & CMT

uNMR & pore size

uSummary

uReference

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

uAbstract

uFigures

uRationale

uRock types and cyclicity

uPNM & CMT

uNMR & pore size

uSummary

uReference

 

 

Rationale

  • Tengiz platform reservoir quality is controlled by diagenetic modification of a cyclic depositional system.
  • Complex and multiple stages of diagenetic modification.
  • Reservoir quality = primary depositional texture + “mostly”diagenesis.
  • Pore typing difficult and non-quantitative using classic petrographic methods.
  • Identification and mapping of diagenetic events and their genesis allows spatial modeling.
  • Pore Network Modeling (PNM) links spatial diagenetic overprint, petrophysics and effective transport properties.

 

Depositional Rock Types and Cyclicity

 

Late Visean and Serpukhovian

  • Highly cyclic arrangement of complete grainy porous shoaling cycles with basal thin and tight lagoonal intervals.
  • Significant diagenetic overprint.
  • Predictable facies and reservoir quality.

Bashkirian

  • High energy facies with thin lagoonal/ash intervals.
  • Significant early diagenetic overprint (compaction and corrosion).
  • Relatively predictable Previous HitlateralTop facies BUT poorly predictable reservoir quality.

 

Pore Network Modeling (PNM) Using CT imagery (CMT)

  • X-Ray Microtomography (CMT): characterization of the pore space at the micron scale.
  • Extraction of pore image in order to fit realistic and representative structures of pore networks.
  • Calculation of transport properties by Pore Network Modeling satisfying comparison between experiments (dual Phi/K).

 

Nuclear Magnetic Resonance (NMR) for Effective Pore Size Distributions

  • T2 curves show effective porosity at different scale pores; here microporosity and connected larger pores.
  • CT and NMR imagery fill the essential link between petrophysics and geology at the scale of even small pore types (~1-3 microns) and pore filling cements.

 

Summary and Conclusions

  • Tengiz platform Unit I reservoir quality controlled by multiple diagenetic phases overprinting a primary cyclic system.
  • Each of the diagenetic phases has specific spatially differential impact (porosity creation and occlusion).
  • CTM/NMR imaging and PNM modeling produces reliable data on effective transport properties as well as quantitative pore type (and connection) distributions.
  • No outcrop or literature information on diagenetic analogs; RTM models available.
  • Spatial prediction of distribution of multiple diagenetic phases through focusing PNM, petrophysics and diagenetic studies(CL, stable isotopes) on one or more end member cycles across platform.
  • Issues are representative volumes, scaling, calibration, etc.
  • Project in progress……

 

Reference

Jones, Gareth D., and Yitian Xiao, 2006, Geothermal convection in the Tengiz carbonate platform, Kazakhstan: Reactive transport models of diagenesis and reservoir quality: AAPG Bulletin, v. 90, p. 1251-1272.

 

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