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PSGeothermal Convection at Tengiz: Reactive Transport Models of Predictive Diagenesis and Evidence from the Rocks*
By
G.D. Jones1, J.F. Collins2, Y. Xiao1, J.A.M. Kenter3, P.M. Harris3, and G. Kuanysheva4
Search and Discovery Article #20050 (2008)
Posted May 20, 2008
*Adapted from poster presentation at AAPG Annual Convention, Long Beach, California, April 1-4, 2007.
1 ExxonMobil Upstream Research Company, Houston, Texas, U.S.A.
2 ExxonMobil Development Company, Houston Texas, U.S.A.
3 Chevron Energy Technology Company, San Ramon, California, U.S.A. ([email protected]) ([email protected])
4 TengizChevroil, Atyrau, Kazakhstan
Reactive Transport Models that couple fluid flow and chemical reactions were used to test the viability of pre and post burial geothermal convection in the Tengiz carbonate platform reservoir
. Simulations demonstrate that geothermal convection can
drive
diagenetic reactions capable of modifying
reservoir
quality. Specific model predictions include: 1) Concurrent dissolution and cementation in a mixed-convective system prior to burial in the platform rim, 2) Dissolution by forced convection prior to burial towards the platform center, 3) Perpetuation of early diagenetic patterns, but at lower rates after burial, 4) Dissolution beneath salt-withdrawal basins and cementation in the platform interior due to free convective flow modified by halokinetics and 5) Minor to no dolomite.
Ongoing Tengiz reservoir
characterization studies were used to evaluate model predictions. Core and petrographic data support or at least do not rule out model predictions 2), 3) and 5). Enhanced porosity that is stratigraphically discordant, vertically oriented and platform-centric supports model predictions 2) and 3). Dolomite is present in the Carboniferous section but is generally volumetrically insignificant supporting prediction 5). Model prediction 1) is possible, but has been overprinted by later cementation and dissolution. A zone of enhanced porosity beneath a salt dome and not the adjacent withdrawal basin suggests model prediction 4) is either invalid or has been overprinted by later diagenesis.
This case study demonstrates the potential of Reactive Transport Models to develop viable and testable hypotheses that if integrated with observations from the rock record results in improved process-based predictions of carbonate reservoir
quality.
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‘Geothermal convection describes groundwater flow in response to temperature derived variations in fluid density’
Reactive Transport Models (RTMs)
We thank ExxonMobil, Chevron, TengizChevroil, and our Tengiz field business partners for permission to share the results of this study. Many colleagues have improved our understanding of Tengiz and helped provide the information necessary to constrain this reactive transport study and comparison to the rocks.
Collins, J.F., J.A.M. Kenter, P.M. Harris, G. Kuanysheva, D. J. Fischer, and K. L. Steffen, 2006, Facies and Heydari, Ezat, 2000, Porosity loss, fluid flow, and mass transfer in limestone reservoirs: Application to the Upper Jurassic Smackover Formation, Mississippi: AAPG Bulletin, v. 84, p. 100-118.
Jones, G.D., and Y. Xiao, 2006, Geothermal convection in the Tengiz carbonate platform Kazakhstan: Reactive transport models of diagenesis and
Kenter, J.A.M., P.M. Harris, J.F. Collins, L.J. Weber, G. Kuanysheva, and D.J. Fischer, 2006, Late Visean to Bashkirian platform cyclicity in the central Tengiz buildup, Precaspian Basin, Kazakhstan: Depositional evolution and Kohout, F.A., 1967, Ground-water flow and the geothermal regime of the Floridian Plateau (1): GCAGS Transactions, v. 17, p. 339-354. Machel, Hans G., and James H. Anderson, 1989, Pervasive subsurface dolomitization of the Nisku Formation in Central Alberta: Journal of Sedimentary Petrology, v. 59, p. 891-911. Saller, Arthur H., 1986, Radiaxial calcite in lower Miocene strata, subsurface Enewetak Atoll: Journal of Sedimentary Petrology, v. 56, p. 743-762. Sanford, W.E., F.F. Whitaker, P.L. Smart, and G.D. Jones, 1998, Numerical analysis of seawater circulation in carbonate platforms: I. Geothermal circulation: American Journal of Science, v. 298, p. 801-828.
Weber, L.J., B.P. Francis, P.M. Harris, and M. Clark, 2003, Stratigraphy, lithofacies and
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