Understanding the wettability of rock using Atomic Force Microscope

  • Omar Bashir Wani

Student thesis: Master's Thesis

Abstract

Understanding the wettability of porous surfaces at the reservoir rocks is an important factor for the success of water flood techniques in EOR processes. Till date a conclusive study about the fundamental chemical understanding of all the factors affecting the wettability of a reservoir remains elusive. This is due to the absence of techniques with high spatial resolution to observe the wettability at pore scale and also due to the complex nature of intrinsic properties of the rock. In this thesis we have employed macroscopic, microscopic and nanoscopic analytical techniques on an idealized flat surface of a mineral which is representative of a carbonate reservoir, i.e., atomically flat idealized calcite crystal. This study was conducted to provide a baseline for further studies about the mechanisms involved in altering the wettability. We have shown that the wettability of calcite in ambient conditions depends on the intrinsic characteristics, i.e., crystallographic planes and on extrinsic factors which include wetting history. Freshly cleaved calcite undergoes wettability transition from super hydrophilic to hydrophobic nature after being exposed to ambient for 120 hours. In ambient, when calcite is cleaved the dangling bonds of calcite are balanced by hydrolyzed water. The wettability transition occurs from the growth of these hydrate layers which are confirmed by Atomic Force Microscope (AFM) imaging and FTIR spectrum. When exposed to water, calcite undergoes wettability change from being super hydrophilic to slight hydrophilic nature. The calcite crystal undergoes dissolution with time which was observed with AFM imaging and FTIR spectrum. The macroscopic experiments were carried out by drying the sample with nitrogen, however at the Nanoscopic level when observed under an AFM probe there is always a layer of water present on top of the sample surface. The layer of water will affect the contact angle measurements and therefore puts the wettability results of Macroscopic level into question. We have demonstrated that macroscopic measurements alone are not sufficient to understand the wettability of calcite varying with time and the causes of wettability transition. In this thesis we have also correlated the macroscopic results with Nanoscopic results on exposure to ambient conditions which allowed us to understand the surface properties with finer spatial resolution. We believe that the work presented in this thesis has established a baseline for the investigation of calcite wettability and the results can be applied for further studies on water flooding EOR. Establishing a baseline with study on an idealized reservoir representing mineral is the first step towards the application of smart water flooding in the carbonate reservoirs of UAE.
Date of AwardDec 2016
Original languageAmerican English
SupervisorSaeed Al Hassan (Supervisor)

Keywords

  • Applied sciences
  • Atomic force microscopy (afm)
  • Calcite
  • Low salinity eor
  • Wettability
  • Chemical engineering
  • 0542:Chemical engineering

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