Pore fluid evolution, distribution and water-rock interactions of carbonate cements in red-bed sandstone reservoirs in the Dongying Depression, China

Prediction of diagenetic facies using well logs – A case study from the upper Triassic Yanchang Formation, Ordos Basin, China

“…As a consequence of regional collisional tectonism and related intra-plate deformation in the Late Triassic (Vermeesch, 2012), the Ordos Basin evolved into a foreland basin, characterized in its asymmetric cross-section by low-gradient north-eastern and high-gradient south-western flanks, and dominated by fluvial and lacustrine depositional systems during much of the Late Triassic (Figs 1 & 2; (Henares et al, 2014;Wang et al, 2016). Six tectonic units in the Ordos Basin have been identified, i.e., the Yimeng Uplift in the north, the Western Trust Belt on the west margin, the Tianhuan Depression in the west, the Yishan Slope in the center, the Weibei Uplift in the south, and the Jinxi Fault-Fold Belt in the east (Fig.…”

Origin and Distribution of Carbonate Cement in Tight Sandstones: The Upper Triassic Yanchang Formation Chang 8 Oil Layer in West Ordos Basin, China

“…Petrography and CL analysis show that calcite is often replaced by ferroan calcite, indicating that the formation timing of the Fe-calcite is after that of calcite (Figures 7(e)-7(h)). Isolated Fe-calcite also occurs in intragranular feldspar dissolution pores (Figure 7(g)), which indicates that the reservoirs experienced dissolution before the precipitation of Fe-calcite [12]. Type II carbonates can be distinguished from Type I carbonate cement since they display weak dull red/orange colors and blotchy luminescence patterns due to the presence of Fe and Mn ions (Figures 7(i and 7(j)).…”

“…Areas that have high percentages of carbonate cemented sandstones often occur along the margins of the sandstone bodies, where sandstone pinches out into mudstone [9,53]. Since sandstone reservoirs interbedded with mudstones are readily influenced by a variety of sources of fluids, the sandstone-mudstone interface is the area with strong water-rock interactions [11,12]. Diagenetic mineral assemblages from ECS logging data show that carbonate cement has a highly zonal distribution, confined to thin beds or concretions in general, and the carbonate cement is much more commonly observed in sand bodies which are adjacent with the Chang 7 source rocks (Figures 10 and 11).…”

“…Carbonate cementation is an important diagenetic alteration that has profound impact on sandstone reservoir quality and heterogeneity [9][10][11][12]. Precipitation of carbonate cement is an important agent of lithification [11], and it often contributes to the poor reservoir property.…”

The role played by carbonate cementation in controlling reservoir quality of the Triassic Skagerrak Formation, Norway

“…(Asquith, 1979;Chowdhury and Noble, 1996;Dutton and Flanders, 2004;Irwin et al, 1977;Purvis and Wright, 1991;Salomons et al, 1978) and more recently effects on reservoir quality (e.g. (Dutton, 2008;Taylor, 1990;Wang et al, 2016;Xiong et al, 2016). Earlyprecipitation of pore-filling carbonates could increase the pressure-resistance of reservoir sandstones and provide a chance for subsequent dissolution (Chi et al, 2003;Morad et al, 2010), whereas late-precipitation of carbonate cements filling residual pores could reduce the final porosity.…”