Abstract
Effective production of oil from carbonate reservoirs often requires the application of improved oil recovery technologies such as waterflooding. However, conventional waterflooding in carbonates usually results in low hydrocarbon recovery as most of these formations exhibit a complex pore throats structure and are mostly oil-wet. Therefore, improved insight into the causes of hydrophobic wetting behavior of such reservoirs is important for understanding the fluid distribution, displacement and enhancing recovery processes. The characterization of fluid-rock interactions is, however, challenging with existing laboratory methods, which are typically based on macroscale (mm) observations. In this experimental study, an advanced imaging technique, namely environmental scanning electron microscope, was applied for the comprehensive investigation of microscale (µm) wettability variations in carbonate rocks covered with organic layers. For the first time, the presence of organic layers on the sample was proved using energy dispersive X-ray mapping. Furthermore, the chemical bond of this layer and carbonate rock surfaces was determined using the transmission electron microscopy and electron energy-loss spectroscopy. The thickness of layer was estimated by using image processing software. These findings show that the application of combined microscopic techniques reveals important details about the reason of hydrophobic wetting properties of real carbonate rocks.
Highlights
Carbonate reservoirs, limestones and dolomites, represent more than half of the world’s oil resources[1]
This is achieved using cryo-focused ion beam (Cryo-FIB) sample preparation approach followed by the implementation of scanning/transmission electron microscopy (S/TEM) and electron energy loss spectroscopy (EELS)
The current work based on the latest advances in ESEM28,30,32–35 and Cryo-FIB36,37 focuses on identification and characterization of organic layers adsorbed on real carbonate surfaces on micro - and nanoscales
Summary
Limestones and dolomites, represent more than half of the world’s oil resources[1]. The key element of our work is the investigation of the nature of the layers adsorbed onto real carbonate surfaces and their influence on wetting properties This is achieved using cryo-focused ion beam (Cryo-FIB) sample preparation approach followed by the implementation of scanning/transmission electron microscopy (S/TEM) and electron energy loss spectroscopy (EELS). Deglint et al.[30] carried out the micro-wettability (μm) measurements using ESEM with the middle Bakken samples and inferred that these results could be used for more accurate estimation of multi-phase flow parameters (e.g. relative permeability, capillary pressure), which in turn would improve primary and secondary oil recovery processes. The current work based on the latest advances in ESEM28,30,32–35 and Cryo-FIB36,37 focuses on identification and characterization of organic layers adsorbed on real carbonate surfaces on micro (μm) - and nanoscales (nm)
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