Insights to controls on dolomitization by means of reactive transport models applied to the Benicàssim case study (Maestrat Basin, eastern Spain)

Abstract

Partially dolomitized carbonate rocks of the Middle East and North America host large hydrocarbon reserves. The origin of some of these dolomites has been attributed to a hydrothermal mechanism. The Benicàssim area (Maestrat Basin, eastern Spain) constitutes an excellent field analogue for fault-controlled stratabound hydrothermal dolomitization: dolostone geobodies are well exposed and extend over several kilometres away from seismic-scale faults. This work investigates the main controls on the formation of stratabound versus massive dolomitization in carbonate sequences by means of two-dimensional (2D) reactive transport models applied to the Benicàssim case study. Simulation results suggest that the dolomitization capacity of Mg-rich fluids reaches a maximum at temperatures around 100 °C and a minimum at 25 °C (studied temperature range: 25–150 °C). It takes of the order of hundreds of thousands to millions of years to completely dolomitize kilometre-long limestone sections, with solutions flowing laterally through strata at velocities of metres per year (m/a). Permeability differences of two orders of magnitude between layers are required to form stratabound dolomitization. The kilometre-long stratabound dolostone geobodies of Benicàssim must have formed under a regime of lateral flux greater than metres per year over about a million years. As long-term dolomitization tends to produce massive dolostone bodies not seen at Benicàssim, the dolomitizing process there must have been limited by the availability of fluid volume or the flow-driving mechanism. Reactive transport simulations have proven a useful tool to quantify aspects of the Benicàssim genetic model of hydrothermal dolomitization.

Reactive transport modelling of hydrothermal dolomitisation using the CSMP++GEM coupled code: Effects of temperature and geological heterogeneity

“…1 Thirdly, a layered model geometry bisected by a fault extending from the top to the bottom of the grid was adapted from Corbella et al (2014). It • and offsets the layers by 30 m. Two different meshes were created for this setup; a patch dependent mesh for the model with a vertical fault (4614 triangular elements and 2446 nodes, average element area 77 m 2 ) and a patch independent mesh for the model with a normal fault (6250 triangles and 3289 nodes, average element area 32 m 2 ) (see fig.…”

“…The paper ends with a discussion comparing HTD bodies predicted by our reactive transport simulations with those from Corbella et al (2014), and with natural examples from various outcrops. 4 2.…”

“…HTD bodies can have a patchy and localised distribution around sub-seismic scale faults (Machel, 2004;Wilson et al, 2007;Lopez-Horgue et al, 2010), but can also occur as stratabound bodies extending laterally for several tens of kilometres away from the faults proposed to have sourced the hydrothermal fluids (Davies and Smith, 2006;Corbella et al, 2014;Dewit et al, 2014). Important uncertainties remain as to the controls on the nature of hydrothermal alteration and the extent to which this process can form laterally extensive dolomites.…”

“…RTM simulations by Corbella et al (2014) explored major controlling parameters on the development of stratabound dolomite bodies associated with fault-controlled hydrothermal fluids in the Benicàssim area (Maestrat Basin, eastern Spain). They concluded that layers with differences in permeability of two orders of magnitude are needed in order to produce the observed kilometer long dolomite bodies within the more permeable packstone-grainstone beds.…”

“…For example, Corbella et al (2014) performed a sensitivity analysis on the influence of temperature on the rate of dolomitisation, but the RTM code RETRASO used in their study did not include the permeability update from changing porosity. Both CSMP++GEM (Yapparova et al, 2017) and TOUGHREACT (Xu et al, 2004) have this feature implemented.…”