Importance of vertical effective stress for reservoir quality in the Skagerrak Formation, Central Graben, North Sea

Abstract

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

“…If two conditions, including correct assumed initial porosity P i , negligible internally derived cement and grain dissolution, are met, the calculated COPL and CEPL are accurate (Lundegard, 1992). In this study, the initial porosity in Skagerrak Formation sandstones is assumed to be 45% (Lundegard, 1992;Paxton et al, 2002;Stricker et al, 2016a). The plot of COPL vs. CEPL shows that porosity loss is mainly due to compaction (av.…”

“…Previous studies attribute the exceptional reservoir porosities to chlorite coats (Stricker et al, 2016a;Stricker et al, 2016b;Taylor et al, 2015), overpressure (Grant et al, 2014;Nguyen et al, 2013;Stricker et al, 2016a;Stricker et al, 2016b), halite dissolution (Nguyen et al, 2013) and limiting time for quartz cement due to rapid burial (Maast, 2016). However, the occurrence of various carbonate cements within fluvial channel facies has been neglected.…”

“…(Bishop, 1996;Matthews et al, 2007;McKie, 2014;Smith et al, 1993). The Smith Bank Formation,6 representing the basal part of the pod fills, was deposited in lacustrine and playa settings (Stricker et al, 2016a). The Smith Bank Formation shows highly variable thicknesses and mini-basin geometries, i.e.…”

“…9-11, 13 and 15). Burial history model (well 7/11-7R) shows that the Skagerrak Formation in the Norwegian sector experienced an early shallow burial phase over a long period of time, and then went rapidly into deep burial phase until present day (Stricker et al, 2016a). Macroquartz cementation starts generally at temperature between 70 °C and 80 °C (McBride, 1989;Walderhaug, 1994;Walderhaug, 1996).…”

“…Chlorite has been widely reported as an important grain coating clay mineral inhibiting quartz overgrowth and help preserve porosity (Bloch et al, 2002;Ehrenberg, 1993;Stricker and Jones, 2016;Taylor et al, 2010). Bloch et al (2002) and Ajdukiewicz and Lander (2010) (Stricker et al, 2016a). Hence overpressure and importantly low vertical effective stress has less impact upon porosity maintenance in the Norwegian sector, which explains the poorer reservoir quality and higher degree of compaction.…”