Conference Paper, 2024

Investigating Rock Material Impact on Low Salinity Water Flooding: Experimental Study with Chalk Samples of a Danish North Sea Oil Reservoir

Day 2 Thu, June 27, 2024, 10.2118/220089-ms

Contributors

Mokhtari, Rasoul 0000-0003-1387-1633 [1] Afrough, Armin 0000-0001-9923-2378 [1] Talaei, A [1] Feilberg, Karen Louise 0000-0001-7417-2380 [1]

Affiliations

  1. [1] Technical University of Denmark
  2. [NORA names: DTU Technical University of Denmark; University; Denmark; Europe, EU; Nordic; OECD]

Abstract

Abstract The low salinity water-flooding technique, an enhanced oil recovery (EOR) method, alters the initial crude oil/brine/rock (COBR) equilibrium, enhancing oil mobilization and potentially reducing CO2 footprint of oil production. Uncertainties arise with natural crude oils and reactive rock surfaces, such as chalk. A study on low salinity waterflooding in Danish Chalk reservoirs yielded results differing from existing literature. To further investigate these results, core flooding experiments were conducted using diverse chalk samples, including outcrop material, dry-stored reservoir core plugs, and preserved reservoir core samples. It's crucial to highlight that existing literature data predominantly relies on outcrop sample experiments, potentially limiting their relevance to reservoir conditions. Computed tomography (CT) images were captured before the experiments to assess rock integrity. Nuclear Magnetic Resonance (NMR) measurements post-experiments gauged the average wettability of the core plug. Contact angle measurements assessed wettability alteration, and ion chromatography analyzed the effluent brine samples. Coreflooding outcomes revealed that preserved core samples initially exhibited an oil-wet state, reflective of reservoir conditions, but underwent changes post-waterflooding and cleaning. This renders direct comparisons challenging, making these cores non-reusable. Conversely, dry-stored reservoir core plugs maintained consistent wetting states across multiple experiments, ensuring reusability and facilitating repeatable, comparable results. However, outcrop samples yielded fundamentally dissimilar results from reservoir samples, proving inadequate analogs. Contact angle measurements highlighted significant differences in wetting conditions and wettability alteration between outcrop and reservoir samples. This discrepancy explains why the negative impact of sulfate ions was evident only in reservoir samples. Ion chromatography results revealed calcite dissolution and concurrent magnesium precipitation during low salinity water injection. While extensively demonstrated in sandstones and some carbonates, the application of low salinity water flooding faces significant challenges in carbonate reservoirs, especially chalk formations. Moreover, the current reported findings regarding chalk samples rely on experiments conducted using outcrop samples. Consequently, there is a lack of experimental data on real reservoir material in existing literature. The conflicting outcomes compared to the literature underscore the significance of conducting experiments on actual reservoir material.

Keywords

CO2 footprint, Chalk Formation, Danish, NMR, North Sea oil reservoir, alterations, analogs, angle measurements, applications, average wettability, brine samples, calcite, calcite dissolution, carbon, carbonate reservoirs, chalk, chalk reservoirs, chalk samples, challenges, changes, chromatography, chromatography results, cleaning, comparison, computed tomography, conditions, contact, contact angle measurements, core, core flooding experiments, core plugs, core samples, crude, crude oil, crude oil/brine/rock, data, discrepancy, dissolution, effluent, enhance oil mobilization, enhanced oil recovery, equilibrium, experimental data, experimental study, experimentation, experiments, findings, flood, flooding experiments, footprint, formation, images, impact, injection, integration, ion chromatography, ion chromatography results, ions, lack, lack of experimental data, literature, literature data, low salinity water flooding, low salinity water injection, low salinity waterflooding, magnesium precipitation, magnetic resonance (NMR, material impact, materials, measurements, mobility, multiple experiments, natural crude oils, negative impact, non-reusable, nuclear magnetic resonance (NMR, oil, oil mobility, oil production, oil recovery, oil reservoirs, oil-wet state, outcomes, outcrop material, outcrop samples, outcrops, plug, post-experiment, post-waterflooding, precipitation, production, recovery, reduced CO2 footprint, relevance, reservoir, reservoir conditions, reservoir core samples, reservoir material, reservoir samples, results, reusability, rock integrity, rock surface, salinity water flooding, salinity water injection, salinity waterflooding, samples, sampling experiments, sandstone, significance, significant challenges, state, study, sulfate ions, surface, technique, tomography, uncertainty, water flooding, water flooding techniques, water injection, waterflooding, wet conditions, wet state, wettability, wettability alteration, wetting

Data Provider: Digital Science