Laboratory Study and Field Application of High Temperature Resistant and Permeable Flooding Nanofluid for Enhanced Spontaneous Imbibition Oil Recovery

Abstract Microemulsion with excellent properties has shown significant potential in enhancing oil recovery from tight formations by spontaneous imbibition. High temperature resistant and permeable flooding nanofluid (HTPF-NF) was prepared through microemulsion dilution method. Firstly, an evaluation process of HTPF-NF properties was evaluated through the particle size and high temperature resistant experiments, interfacial tension (IFT) and wettability measurements, as well as the static adsorption experiment. Meanwhile, Transmission Electron Microscope (TEM) was utilized to characterize the particle size and morphology of HTPF-NF before and after solubilization of the crude oil. Optical Microscope (OM) was also used to observe the morphological characteristics of emulsified oil droplets. Then, the spontaneous imbibition oil recovery (SIOR) mechanisms of- HTPF-NF were proposed ulteriorly by adopting imbibition tests and CT scanning technology. Moreover, the field application effects of HTPF-NF micro-fracture huff and puff in Shengli Oilfield were also analyzed. The results show that the optimum concentration of HTPF-NF is 0.2wt% with excellent comprehensive performances. Under this concentration, the particle size is 7.5 nm, the IFT value reaches ultra-low IFT, the wettability alteration ability is remarkable and the adsorption loss is minimized. Afterwards, adhesion work reduction factor (AWRF), solubilization coefficient (SC) and the self-driving force (SDF) are defined and calculated based on the IFT and contact angle for quantitatively analyzing the SIOR mechanisms. Furthermore, the data and images of spontaneous imbibition and CT scanning present that the longer the imbibition distance, the higher SIOR of HTPF-NF. In conclusion, the SIOR mechanisms of HTPF-NF are summarized as follows: remarkable property of solubilizing crude oil, brilliant ability of reducing oil/solid adhesion work by synergistic effect of IFT reduction and wettability alteration, and excellent capability of increasing imbibition distance by larger self-driving force. After soaking for two months, YB well was produced with the dramatic increase of the liquid production from 9.55 bbl/d to 34.5 bbl/d, the oil production from 5.15 bbl/d to 19.1 bbl/d and the water cut from 27.3% to 40.8%.