Paluxy sandstone

• 10.1016/j.chemgeo.2019.06.004

Abstract — Imaging has emerged as a valuable means of geological sample characterization and parameterizing reactive transport simulations where image analysis can provide porosity, mineral composition and mineral accessible surface area data, for example. Images can be collected using a variety of techniques and at a range of resolu- tions, yet the impact of image resolution on measured properties is largely unknown. In this work, the impact of 2D image resolution on the calculated mineral abundances, accessibilities and effective surface areas are ex- amined for a sample from the Paluxy formation, Kemper County, Mississippi. Scanning electron microscopy (SEM) backscatter electron (BSE) images of thin sections were captured at resolutions ranging from 0.3 μm to 6 μm. Images were segmented into pores and discrete mineral phases using ImageJ and algorithms developed in MATLAB. Porosity, mineral abundances and mineral accessibilities were calculated by counting pore and mi- neral pixels in the segmented image where accessible minerals were deemed as those adjacent to the pore space. A 3D X-ray computed tomography (CT) image of a core sample was collected, segmented, and analyzed to evaluate the 3D connected porosity. Cuboids with the same total area as the 2D image were randomly sampled and used to calculate the 3D connected surface area. This was then multiplied by mineral accessibility to cal- culate accessible mineral surface areas for non-clay minerals. Minimum variations were observed for mineral abundances calculated from images with varying resolutions. For high resolution images, 0.3 μm to 1 μm, mi- neral accessibilities agreed relatively well. For images with resolutions from 1 μm to 6 μm, the calculated ac- cessibility of smectite/illite decreased with decreasing resolution while quartz accessibility increased. This in turn resulted in higher effective surface areas for quartz with decreasing resolution. No significant variations were observed for calcite, siderite and K-feldspar.

• https://doi.org/10.1029/2020GL087665

Abstract — Understanding the impacts of porous media properties on geochemical reactions is challenging due to the highly heterogeneous nature of natural samples. This work explores the use of 3‐D printing to create synthetic rock samples with reactive properties mimicking those of natural samples. Here, X‐ray Computed Tomography and 3‐D printing were used to recreate the pore network structure and reactive properties of a Paluxy sandstone. Novel, reactive filaments for 3‐D printing synthetic rock samples were constructed from mixtures of high impact polystyrene and calcite. The distribution and accessible calcite surface area of printed samples were evaluated and compared to values for the real rock sample. Only a small fraction of the total calcite was on the surface of the printed sample, but the accessible calcite surface area was comparable to real samples such that 3‐D printing may be a feasible means of fabricating reactive porous media samples.

• https://doi.org/10.1016/j.ijggc.2019.102887

Abstract — The Paluxy formation is being considered as a prospective CO2 reservoir at the Kemper County CO2 Storage Complex. Here, the pore and pore-throat size distributions and connectivity of the Paluxy formation is evaluated through analysis of 3D X-ray Computed Tomography images. In spite of resolution limitations that constrain the pore-throat sizes detectable by imaging, the permeability contributing pore-throats are successfully character- ized through 3D imaging analysis. Image-obtained pore and pore-throat size distributions and pore connectivity are then utilized to construct pore network models and simulate permeability. After CO2 is injected, it will dissolve into formation brine and create conditions favorable for dissolution of primary minerals and pre- cipitation of secondary minerals. These reactions will alter the porosity and permeability of the system to varying degrees depending on the spatial location of reactions. Here, the possible porosity-permeability evo- lution is simulated using pore network models considering mineral reactions occurring uniformly and non- uniformly throughout the network. For a given change in porosity, there is a large range of possible permeability outcomes. Depending on the extent and spatial location of mineral reactions, permeability may decrease by more than one order of magnitude as minerals precipitate. During dissolution, simulated permeability increases as much as 500%.