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Utilizing Reactive Transport Modeling to Inverse Model the Origin and Evolution of Stratiform Dolomite Geobodies and Mvt Deposits, Maestrat Basin, Iberian Chain, Spain

Stafford, Sherry L.1; Whitaker, Fiona F.2; Xiao, Yitian 1; Gomez-Rivas, Enrique 3; Martín-Martín, Juan Diego 4
1 ExxonMobil Upstream Research Company, Houston, TX.
2 University of Bristol, Bristol, United Kingdom.
3 Universitat Autònoma de Barcelona, Barcelona, Spain.
4 Universitat de Barcelona, Barcelona, Spain.

In the Benicàssim-Orpesa area of the Maestrat Basin, Iberian Chain, Spain, Aptian Age, synrift limestone beds of shallow marine origin are partially replaced by stratiform-to-sub-stratiform dolomite bodies. The dolomite bodies are in close proximity to normal faults related to Lower Cretaceous rifting. Mississippi Valley Type (MVT) mineralization also occurs in the area. Understanding the primary controls on early and/or burial carbonate diagenesis in the Iberian Chain has implications for prediction of enhanced or degraded reservoir quality distribution. This field area is a potential analog for partly dolomitized reservoirs in the Middle East and N. America.

Two main hypotheses have been suggested for the origin of the stratiform dolomite and/or MVT deposits: (1) Michel (1974) suggested dolomitization as a result of reflux of evaporated seawater with concomitant sulfide precipitation resulting from concentration of metals in the refluxing residual brines; (2) Salas et al. (1986) suggested a spatial relationship between dolomite geobodies and normal faults and invoked circulation of fluids through Triassic Age evaporites as a source for Mg and trace metals with subsequent circulation through extensional fault networks to produce dolomitization and related MVT deposits.

In this study, we use Reactive Transport Modeling (RTM) to test these two hypotheses by inverse modeling the origin of the dolomite bodies and/or MVT deposits observed in outcrop. RTM is an emerging technology capable of predicting spatial and temporal evolution in reservoir quality by coupling fluid flow, thermodynamics, kinetics, and porosity/permeability feedbacks for fluid-rock interaction studies. RTM is useful for testing diagenetic sensitivities and conceptual models, especially when uncertainties are somewhat constrained. Specifically, we test the sensitivities of dolomitization processes and MVT formation to the definition of structural domains, fluid flow histories, host limestone characteristics, and fluid chemistry using outcrop data to constrain RTM input variables. Outcrop data used to constrain the model include the geologic framework, carbonate facies, petrography, rock property data, geochemical data, and fault analysis.

Preliminary results suggest that dolomitization and/or MVT alteration of the Aptian Age limestones was primarily controlled by the structural domain and the original characteristics of the limestone host.


AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009