Digital rock physics approach to simulate hydraulic effects of anhydrite cement in Bentheim sandstone

Abstract

Abstract. Cementation of potential reservoir rocks is a geological risk, which may strongly reduce the productivity and injectivity of a reservoir, and hence prevent utilisation of the geologic subsurface, as it was the case for the geothermal well of Allermöhe, Germany. Several field, laboratory and numerical studies examined the observed anhydrite cementation to understand the underlying processes and permeability evolution of the sandstone. In the present study, a digital rock physics approach is used to calculate the permeability variation of a highly resolved three-dimensional model of a Bentheim sandstone. Porosity-permeability relations are determined for reaction- and transport-controlled precipitation regimes, whereby the experimentally observed strong decrease in permeability can be approximated by the transport-limited precipitation assuming mineral growth in regions of high flow velocities. It is characterised by a predominant clogging of pore throats, resulting in a drastic reduction in connectivity of the pore network and can be quantified by a power law with an exponent above ten. Since the location of precipitation within the pore space is crucial for the hydraulic rock properties at the macro scale, the determined porosity-permeability relations should be accounted for in large-scale numerical simulation models to improve their predictive capabilities.

Diagenetic Trends of Synthetic Reservoir Sandstone Properties Assessed by Digital Rock Physics

“…Hence, the presented approach allows to efficiently generate sandstone samples over a broad range of porosities with any desired size, sorting and shape of convex grains. In view of a virtual laboratory, these generated synthetic samples can be further altered to examine the impact of mineral dissolution [63,64] or precipitation [65,66] as well as synthetic fractures [67,68]. Hence, the understanding of various petrophysical correlations can be improved by this cost-effective digital approach.…”

Reactive transport model of kinetically controlled celestite to barite replacement

“…This approach considers interactions between individual particles, which are successively deposited under the influence of gravity. Combined with an additional grain cementation, this method enables to construct virtual sandstone samples with granulometric, hydraulic and elastic properties equivalent to those of the natural sample (Wetzel et al, 2020(Wetzel et al, , 2021. The geometry of the DEM is converted into a digital image comprising a rectangular uniform grid, in order to compute geometrical properties and perform additional grain pack alterations.…”

“…The dissolu-tion rate constant of celestite is calculated at each kinetic step following the approach of Palandri and Kharaka (2004), using data from Dove and Czank (1995). For calculating the precipitation rate constant of barite, a linear regression was used that accounts for temperature and ionic strength, which have been shown to have a significant impact (Tranter et al, 2021a;Zhen-Wu et al, 2016):…”

Permeability evolution of Bentheim Sandstone at simulated georeservoir conditions

“…In fact, BS is a suitable deep, warm aquifer for potential low-cost geothermal energy in the Netherlands ( de Groot et al, 2020), a case study rock for anhydrite cementi cation in georeservoirs (Wetzel et al, 2020) and one of the most important aquifers in the North German Basin (Kunkel & Agemar, 2019). The top of the BS formation is at a depth of about 1.5 km, but BS can be found at more than 2 km depth and has been buried as deep as 3.5 km (Parnell et al, 1996), so it is crucial to understand its properties at different depths.…”