Quick, Easy, and Economic Mineralogical Studies of Flooded Chalk for EOR Experiments Using Raman Spectroscopy

Abstract

Understanding the chalk-fluid interactions and the associated mineralogical and mechanical alterations on a sub-micron scale are major goals in Enhanced Oil Recovery. Mechanical strength, porosity, and permeability of chalk are linked to mineral dissolution that occurs during brine injections, and affect the reservoir potential. This paper presents a novel "single grain" methodology to recognize the varieties of carbonates in rocks and loose sediments: Raman spectroscopy is a non-destructive, quick, and user-friendly technique representing a powerful tool to identify minerals down to 1 µm. An innovative working technique for oil exploration is proposed, as the mineralogy of micron-sized crystals grown in two flooded chalk samples (Liége, Belgium) was successfully investigated by Raman spectroscopy. The drilled chalk cores were flooded with MgCl 2 for ca. 1.5 (Long Term Test) and 3 years (Ultra Long Term Test) under North Sea reservoir conditions (Long Term Test: 130 • C, 1 PV/day, 9.3 MPa effective stress; Ultra Long Term Test: 130 • C, varying between 1-3 PV/day, 10.4 MPa effective stress). Raman spectroscopy was able to identify the presence of recrystallized magnesite along the core of the Long Term Test up to 4 cm from the injection surface, down to the crystal size of 1-2 µm. In the Ultra Long Term Test core, the growth of MgCO 3 affected nearly the entire core (7 cm). In both samples, no dolomite or high-magnesium calcite secondary growth could be detected when analysing 557 and 90 Raman spectra on the Long and Ultra Long Term Test, respectively. This study can offer Raman spectroscopy as a breakthrough tool in petroleum exploration of unconventional reservoirs, due to its quickness, spatial resolution, and non-destructive acquisition of data. These characteristics would encourage its use coupled with electron microscopes and energy dispersive systems or even electron microprobe studies.

Chalk Surface Area Evolution during Flow of Reactive Brines: Does Oil Play a Role?

“…During the subsequent injection of MgCl 2 , we observe a decrease in the magnesium concentration and an increase in calcium concentration. These trends are in line with previous observations as nonequilibrium between the calcite surface and MgCl 2 brine leads to dissolution of calcite and precipitation of magnesium-bearing minerals. ,− ,,− The magnesium-ion concentration stabilized around 0.19–0.20 mol/L, and the calcium-ion concentration varied between 0.02 and 0.04 mol/L.…”

When conventional methods fall short: identification of invasive cryptic Golden Apple Snails (Pomacea canaliculata; P. maculata) using environmental DNA

“…Two types of stretching (symmetric-600-1,200 cm −1 and asymmetric-1,200-1,700 cm −1 ) of carbonate group (CO 3 ) 2− are observed. The band present at 1,081 cm −1 due to the υ1 symmetric mode of carbonate ions, and other bands such as 155-210 cm −1 are the lattice mode, 701/703 cm −1 are the υ4 mode of carbonate ions (Harris et al, 2015;Borromeo et al, 2018). The existence of two bands at 1,119/1,123 and 11,509/1,512 cm −1 was observed due to single and double carbon-carbon bonds in the shell, signifying the presence of polyenes in the snail shell (Kupka et al, 2016;Komura et al, 2018).…”

Provenance of Bengal Shelf Sediments: 1. Mineralogy and Geochemistry of Silt

“…Although Raman spectroscopy is proven to be an effective method to identify and count mineral grains down to the size of 1-2 µm only [105][106][107], this technique could not be applied to the <5-µm class of our samples. The finest sediment fraction mostly consists of clay minerals and very-fine-silt grains that display low Raman scattering, mainly because of the thin lamellar habit of phyllosilicates and, consequently, insufficient volume analyzed by the spectrometer.…”