Impact of silica diagenesis on the porosity of fine‐grained strata: An analysis of Cenozoic mudstones from the North Sea

Abstract

AbstractSilica diagenesis has the potential to drastically change the physical and fluid flow properties of its host strata and therefore plays a key role in the development of sedimentary basins. The specific processes involved in silica diagenesis are, however, still poorly explained by existing models. This knowledge gap is addressed by investigating the effect of silica diagenesis on the porosity of Cenozoic mudstones of the North Viking Graben, northern North Sea through a multiple linear regression analysis. First, we identify and quantify the mineralogy of these rocks by scanning electron microscopy and X‐ray diffraction, respectively. Mineral contents and host rock porosity data inferred from wireline data of two exploration wells are then analyzed by multiple linear regressions. This robust statistical analysis reveals that biogenic opal‐A is a significant control and authigenic opal‐CT is a minor influence on the porosity of these rocks. These results suggest that the initial porosity of siliceous mudstones increases with biogenic opal‐A production during deposition and that the porosity reduction during opal‐A/CT transformation results from opal‐A dissolution. These findings advance our understanding of compaction, dewatering, and lithification of siliceous sediments and rocks. Moreover, this study provides a recipe for the derivation of the key controls (e.g., composition) on a rock property (e.g., porosity) that can be applied to a variety of problems in rock physics.