Abstract
Shales are mostly unexploited energy resources. However, the extraction and production of their hydrocarbons require innovative methods. Applications involving carbon dioxide in shales could combine its potential use in oil recovery with its storage in view of its impact on global climate. The success of these approaches highly depends on various mechanisms taking place in the rock pores simultaneously. In this work, properties governing these mechanisms are presented at technically relevant conditions. The pendant and sessile drop methods are utilized to measure interfacial tension and wettability, respectively. The gravimetric method is used to quantify CO2 adsorption capacity of shale and gas adsorption kinetics is evaluated to determine diffusion coefficients. It is found that interfacial properties are strongly affected by the operating pressure. The oil-CO2 interfacial tension shows a decrease from approx. 21 mN/m at 0.1 MPa to around 3 mN/m at 20 MPa. A similar trend is observed in brine-CO2 systems. The diffusion coefficient is observed to slightly increase with pressure at supercritical conditions. Finally, the contact angle is found to be directly related to the gas adsorption at the rock surface: Up to 3.8 wt% of CO2 is adsorbed on the shale surface at 20 MPa and 60 °C where a maximum in contact angle is also found. To the best of the author’s knowledge, the affinity of calcite-rich surfaces toward CO2 adsorption is linked experimentally to the wetting behavior for the first time. The results are discussed in terms of CO2 storage scenarios occurring optimally at 20 MPa.
Highlights
Concerns regarding anthropogenic CO2 emissions are strongly growing
The first aim of the current study is to investigate fluid–fluid and rock–fluid interactions at pressures up to 40 MPa through the measurement of interfacial tension (IFT) in C O2-brine systems at conditions that have not been investigated so far, the measurement of IFT in a system comprising C O2 and oil extracted from Jordanian shale, quantifying wettability alteration of the relevant system, as well as the assessment of C O2 adsorption and gas diffusion
Aside from the favorable consequences of C O2 dissolution into the oil such as oil swelling and viscosity reduction (Li et al 2013), its impact on interfacial tension (IFT) is relevant for mobilizing the oil and increasing its recovery
Summary
Concerns regarding anthropogenic CO2 emissions are strongly growing. Tackling the increasing atmospheric CO2 concentrations has become the top priority on political and environmental agendas worldwide. In unconventional organic-rich formations such as coalbeds, application of enhanced gas recovery takes advantage of the preferential adsorption of CO2 on organic matter relative to CH4, which leads to the desorption of C H4 and enhancing methane recovery (Prusty 2008). This mechanism has proven effective in gas shale formations (Godec et al 2014; Tao and Clarens 2013). As a result, coupling of carbon storage with enhanced oil and gas recovery could result in the double benefit of achieving higher hydrocarbon recovery factors and the reduction of greenhouse gases through storing C O2 geologically (Liu et al 2019)
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