Title

NMR integrated subsurface characterization and wettability alteration detection for enhanced oil recovery

Author Identifiers

Chamini Karunarathne

https://orcid.org/0000-0001-9939-3083

Date of Award

2022

Degree Type

Thesis

Degree Name

Master of Engineering Science

School

School of Engineering

First Advisor

Stefan Iglauer

Second Advisor

Alireza Keshavarz

Third Advisor

Ahmed Zarzor Al-Yaseri

Abstract

The global demand for energy is continuously soaring, where the oil and gas industry is relentlessly striving to meet the energy requirements of growing populations. Accordingly, there is an increasing interest towards economically feasible enhanced oil recovery techniques that can be applied to existing reservoirs. However, the successful application of such technology is yet to be achieved. In recent years, improved oil recovery through low salinity waterflooding has received attention within industry due to its simplicity and low costs. Rock wettability alteration, which remains poorly understood, could be regarded as a leading mechanism that is driving the low salinity effect. Hence, one objective of this study is to further investigate the effects of low salinity brine injection (0.6 M and 0.2 M NaCl) as a non-wetting fluid, where Soltrol-130 features as the wetting fluid on outcrop limestone samples (chalk) considering steady-state as well as unsteady-state flow for both imbibition and drainage processes in core-flooding experiments. The results indicate that ionic interactions during low salinity waterflooding change the surface charge of chalk samples towards more negative values, which in turn causes wettability alteration of sedimentary rock from mixed-wet to more water-wet conditions; hence, improving oil recovery rates. The results reveal a clear drop in irreducible water saturation when switching to low salinity flooding.

In spite of rock surface charge being a significant factor in forecasting oil recovery, much uncertainty still exists about the effects of acidic subsurface characteristics in predicting reservoir behavior. A significant proportion of sandstone reservoir oxides consists of silica that creates surface charges on rock in the presence of aqueous acids by undergoing numerous chemical reactions. Analysis of these rock chemical mechanisms could be beneficial in determining information on reservoir characteristics, including rock wettability, which is a crucial parameter for a reservoir in many aspects of reservoir simulation. However, standard methods to estimate these parameters are expensive, time consuming and laboratory based; thus, the successful application of a low cost and fast technique that can be measured downhole, is necessary for reservoir characterization. As a solution, application of Nuclear Magnetic Resonance (NMR) technology has become increasingly recognized, since its parameters are highly responsive to fluid-rock interactions. Nonetheless, there is still a need for the development of a reliable model for corelating NMR measurements with wettability modifications.

Therefore, this study focuses on the effect of hydrochloric acid concentrations in altering surface charge, rock chemistry and wettability of Bentheimer sandstone rock cores, and the application of NMR in detecting these characteristics. The results indicate that much shorter relaxation times are yielded for higher acidic concentrations, which can be attributed to the protonation and deprotonation reactions of silanol groups that exist on quartz surfaces.

Similarly, the later section of this study provides details of experiments conducted on Berea sandstone, treated with a different range of chemicals including trialkoxysilanes, hydrochloric acid and crude oil, incorporating NMR technology. The results show the application of NMR techniques to provide unique insight for in-situ determination of wettability alteration and pore size distribution.

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