Reactive transport modelling of reflux dolomitization in the Arab‐D reservoir, Ghawar field, Saudi Arabia

Abstract

It has long been recognized that the Arab-D reservoir in Ghawar field has been significantly dolomitized and that the distribution of dolomites is highly heterogeneous across this reservoir. Previous studies indicated that dolomite occurs with either a stratigraphic or non-stratigraphic distribution; when mapped, dolomite tends to form several parallel linear trends across the field. Although stratigraphic dolomite was suggested to be formed early from highly evaporated pore fluids sourced from overlying evaporite deposits, non-stratigraphic dolomite was thought to be generated primarily from hydrothermal fluids sourced from below. This study focuses primarily on these non-stratigraphic dolomites, and proposes that: (i) these dolomites initially formed via seepage reflux, but were reinforced by late stage hydrothermal dolomitization; and (ii) reflux is also responsible for the formation of parallel, linear trends of dolomite. The reflux model hypothesizes that an evaporative lagoon (which is the source of dolomitizing fluids) formed during the falling stage systems tract of a depositional sequence, and that with continuing sea-level fall this lagoon migrated progressively towards deeper parts of an intrashelf basin adjacent to the Ghawar field, leaving behind lines of dolomite bodies along a series of temporary coastlines. Two-dimensional reactive transport models have been built to test this hypothesis, and have resulted in a predicted pattern of dolomite bodies that agrees with both the observed vertical distribution of non-stratigraphic dolomite, as well as the mapped lateral distribution of the dolomite trends. In addition, the major ion compositions of Late Jurassic seawater are calculated based on fluid inclusion data in the literature. Using Jurassic seawater in current models leads to the absence of anhydrite cements and less potential of over-dolomitization than using modern seawater.

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

“…RTM has already been extensively applied to study the formation of dolomites in low-temperature shallow reflux systems (Jones and Xiao, 2005;Garcia-Fresca et al, 2009;Al-Helal et al, 2012;Xiao et al, 2013;Lu and Cantrell, 2016), as well as during burial diagenesis by fluids circulating due to geothermal convection (Wilson et al, 2001;Whitaker and Xiao, 2010) and sedimentary compaction (Consonni et al, 2010;Frazer et al, 2014).…”

Bed‐scale spatial patterns in dolomite abundance: Part II. Effect of varied fluid chemistry, flow rate, precursor mineralogy, temperature, textural heterogeneity, nucleation density and bed geometry

“…Streamlines are dominantly horizontal for tens of kilometres with geothermal circulation in stratified carbonates (Caspard et al ., ; Whitaker & Xiao, ). Models of compaction‐driven flow or hot fluids injected from faults into layered limestones all exhibit horizontal flow due to permeability differences between layers (Consonni et al ., ; Xiao et al ., ; Corbella et al ., ; Lu & Cantrell, ). Vertical flow is concentrated below brine pools in reflux models (Xiao & Jones, ; Xiao et al ., ), but there is also a dominance of horizontal flow with distance from the brine pool due to high vertical anisotropy in the permeability of layered carbonates (Jones et al ., ; Al‐Helal et al ., ; Gabellone et al ., ; Lu & Cantrell, ).…”

“…Models of compaction‐driven flow or hot fluids injected from faults into layered limestones all exhibit horizontal flow due to permeability differences between layers (Consonni et al ., ; Xiao et al ., ; Corbella et al ., ; Lu & Cantrell, ). Vertical flow is concentrated below brine pools in reflux models (Xiao & Jones, ; Xiao et al ., ), but there is also a dominance of horizontal flow with distance from the brine pool due to high vertical anisotropy in the permeability of layered carbonates (Jones et al ., ; Al‐Helal et al ., ; Gabellone et al ., ; Lu & Cantrell, ). For example, Lu & Cantrell () modelled a 1·5 km brine pool on a 20 km long profile of vertically stratified sediments, and their results indicate that the lateral distance dominated by vertical flow is only about 10% of the lateral distance dominated by horizontal flow.…”

“…However, prior RTM studies of regional‐scale dolomitization (reviewed in Xiao & Jones, ) indicate that multiple factors can impact the dolomitization process. These factors include: chemistry and salinity of the dolomitizing fluid, temperature and/or fluid flow rates (Jones & Xiao, ; Al‐Helal et al ., ; Corbella et al ., ; Gabellone & Whitaker, ; Lu & Cantrell, ; Araújo & Leite, ); precursor mineralogy (Gabellone & Whitaker, ; Araújo & Leite, ); and precursor texture (Whitaker & Xiao, ; Al‐Helal et al ., ; Xiao et al ., ; Gabellone et al ., ; Lu & Cantrell, ).…”

Effect of Micrite Content on Calcite Cementation in an Upper Jurassic Carbonate Reservoir, Eastern Saudi Arabia

“…Numerous studies have been focused on the structure, stratigraphy, depositional environment, lithofacies and diagenesis of the reservoir (e.g. Mitchell et al, 1988;Meyer and Price, 1993;Handford et al, 2002;Cantrell and Hagerty, 2003;Cantrell et al, 2004;Swart et al, 2005Swart et al, , 2016Lindsay et al, 2006;Lu and Cantrell, 2016). Zhang et al (2018) used micrite content as a quantitative texture descriptor in multivariable regression and neural network models to predict permeability from porosity in the same reservoir.…”