Preparation and stabilization mechanism of carbon dots nanofluids for drag reduction
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ORIGINAL PAPER
Preparation and stabilization mechanism of carbon dots nanofluids for drag reduction Yi‑Ning Wu1 · Yuan Li1 · Meng‑Jiao Cao1 · Cai‑Li Dai1 · Long He2 · Yu‑Ping Yang3 Received: 27 May 2020 © The Author(s) 2020
Abstract During the development of low or ultra-low permeability oil resources, the alternative energy supply becomes a prominent issue. In recent years, carbon dots (CDs) have drawn much attention owing to their application potential in oil fields for reducing injection pressure and augmenting oil recovery. However, carbon dots characterized of small size, high surface energy are faced with several challenges, such as self-aggregation and settling. The preparation of stably dispersed carbon dots nanofluids is the key factor to guarantee its application performance in formation. In this work, we investigated the stability of hydrophilic carbon dots (HICDs) and hydrophobic carbon dots–Tween 80 (HOCDs) nanofluids. The influences of carbon dots concentration, sorts and concentration of salt ions as well as temperature on the stability of CDs were studied. The results showed that HICDs are more sensitive to sort and concentration of salt ions, while HOCDs are more sensitive to temperature. In addition, the core flooding experiments demonstrated that the pressure reduction rate of HICDs and HOCDs nanofluids can be as high as 17.88% and 26.14%, respectively. Hence, the HICDs and HOCDs nanofluids show a good application potential in the reduction of injection pressure during the development of low and ultra-low permeability oil resources. Keywords Carbon dots · Nanofluids · Drag reduction · Stabilization mechanism · Salt tolerance
1 Introduction With the continuous growth in crude oil demand, unconventional oil and gas resources become increasingly significant (Liu et al. 2017, 2019). Due to the low or ultra-low permeability of the formation, the water-injection pressure is extremely high, increasing the difficulties in the subsequent energy supply and exploitation. Recently, nanofluids with Handling Editor: Zhen-Hua Rui Edited by Xiu-Qiu Peng * Yi‑Ning Wu [email protected] * Cai‑Li Dai [email protected] 1
Shandong Key Laboratory of Oilfield Chemistry, School of Petroleum Engineering, China University of Petroleum (East China), Qingdao 266580, China
2
Petroleum Engineering Institute, Northwest Branch of Sinopec, Urumchi 830000, China
3
CNPC Engineering Technology R&D Company Limited, Beijing 100007, China
high thermostability and interfacial activity attract more and more attention (Noreen et al. 2016; Lu et al. 2017). Previous studies have also indicated that nanofluids have shown the application potential in drag reduction, chemical flooding, filtration reducer and so on (Zhao et al. 2018a, b; Ramesh and Prabhu 2011; Soltanipour et al. 2016; Zhong et al. 2011; Mu et al. 2010; Zhao et al.2018a, b; Hwang et al. 2008; Dai et al. 2020; Li et al. 2020; Zhao et al. 2019). However, for further field application, the instability of nanofluids is an essential problem. The relatively low resis
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