Journal article
Elasticity and electrical resistivity of chalk and greensand during water flooding with selective ions
Department of Civil Engineering, Technical University of Denmark1
Department of Chemical and Biochemical Engineering, Technical University of Denmark2
CERE – Center for Energy Ressources Engineering, Department of Chemical and Biochemical Engineering, Technical University of Denmark3
Université Savoie Mont Blanc4
Department of Chemistry, Technical University of Denmark5
Polytechnic University of Turin6
Section for Geotechnics and Geology, Department of Civil Engineering, Technical University of Denmark7
Water flooding with selective ions has in some cases lead to increased oil recovery. We investigate the physical processes on a pore scale that are responsible for changes in petrophysical and mechanical properties of four oil-bearing chalk and four oil-bearing greensand samples caused by flooding with brines containing varying amounts of dissolved NaCl, Na2SO4, MgCl2 and MgSO4.
Ultrasonic P-wave velocity and AC resistivity measurements were performed prior to, during and after flow through experiments in order to identify and quantify the processes related to water flooding with selective ions. Low field Nuclear Magnetic Resonance (NMR) spectrometry measurements were performed at full water saturation, at irreducible water saturation, after aging and after flooding.
CT-scanning, X-ray diffraction (XRD), backscatter electron microscopy images (BSEM), mercury injection capillary pressure (MICP) curves and specific surface analysis (BET) reveal the mineralogy and texture of the rock samples before and after the injection. Low field NMR data indicates changes in the pore fluid distribution and wettability of chalk after aging of one of the samples.
NMR data for other samples indicate that chalk is water-wet after flooding. Greensand remained mixed wet throughout the experiments. Electrical resistivity data are in agreement with this interpretation. The electrical resistivity data during flooding revealed that the formation brine is not fully replaced by the injected water in both chalk and greensand.
Changes in the elasticity of chalk during flooding illustrate the softening effect of magnesium bearing brines as compared to the sodium bearing brines. The stiffness of greensand was not affected by water flooding with selective ions as determined from the elastic wave measurements. Precipitation of fines during flooding of chalk samples is indicated by an increase in specific surface area and a shift in the MICP to lower values but no fines were detected by NMR.
No changes were observed for greensand samples.
| Language: | English |
|---|---|
| Year: | 2018 |
| Pages: | 204-218 |
| ISSN: | 18734715 and 09204105 |
| Types: | Journal article |
| DOI: | 10.1016/j.petrol.2017.11.045 |
| ORCIDs: | Fosbøl, P. L. , Stenby, Erling Halfdan and Fabricius, Ida Lykke |
