Field observations, along with experimental laboratory, exhibit evidence that enhancing production by CO₂ huff-n-puff process is a potential EOR technique that improves the, commonly low, ultimate oil recovery in unconventional liquid reservoirs (ULR). As pressure goes beyond the MMP, intermediate components of oil vaporize into the CO₂ and consequently condense at room pressure and temperature. In addition, Surfactant-Assisted Spontaneous Imbibition (SASI) process has been widely believed to enhance oil recovery in ULR, which has been investigated by several laboratory and numerical studies. During the hydraulic fracturing with surface active additives, surfactant molecules interact with rock surfaces to enhance oil recovery through wettability alteration and interfacial tension reduction. The wettability alteration leads to the expulsion of oil from the pore space as well as water being imbibed into the matrix spontaneously. However, the understanding of hybrid EOR technologies, combining both gas injection and surfactant imbibition, to enhance recovery in ULR is not well studied. In this manuscript, we assess the potential of combining both CO₂ huff-n-puff and surfactant imbibition techniques in optimizing oil recovery in ULR. Sidewall core samples retrieved from ULR were first cleaned utilizing the Dean-Stark methodology and then saturated by pressurizing them with their corresponding oil for three months. CO₂ huff-n-puff experiments were operated on shale core samples under different pressures in a set-up integrated into a CT-scanner. Those cores were then submerged in the surfactant solution, in a modified Amott cell, to observe whether any additional oil is produced through the process of SASI. Total production from these two different methods, which was done sequentially, will provide insight into the possibility of hybrid EOR technology. CO₂ huff-n-puff experiments were performed below and above the MMP which was previously determined by the slim-tube method. Contact angle (CA), interfacial tension (IFT) were also measured on the saturated shale core samples. CT-Scan technology was used to visualize the process of oil being expelled from the core plugs in both CO₂ huff-n-puff and spontaneous imbibition experiments. Experimental results provide a promising outcome on the application of hybrid EOR technology, CO₂ huff-n-puff and SASI, improving oil recovery from ULR. Oil recovery was observed to reach around 50% of measured OOIP from CO₂ huff-n-puff alone with an addition of 10% recovery from SASI after the CO₂ treatment. A detailed description of the correlated experimental workflows is presented to investigate the hybrid EOR technology in enhancing oil recovery in ULR. In addition, a discussion on the difference in mechanism of oil production from the huff-n-puff and SASI method is also included alongside several additional novel findings regarding the color shift of the produced oil. MMP data of CO₂ and oil measured as well as a change of contact angle (CA) and interfacial tension (IFT) when the surfactant is introduced into the system are also provided to support insight on the mechanism of the production improvement. All measured and compiled data deliver the required information for this study to demonstrate the possibility of combining both CO₂ EOR and SASI EOR, a hybrid EOR, as a practical method to produce a significant amount of oil from unconventional shale oil reservoirs.

Wellbore instability and formation collapse are crucial issues in the process of well excavation in the oil industry under extreme high temperature conditions. A novel zwitterionic quaternary copolymer (PDANV) of 4-vinylpyridine (VP), N, N-dimethylacrylamide (DMAA), 2-acrylamido-2-methylpropane sulfonic acid, N-vinylcaprolactam (NVCL) was synthesized in aqueous solution by free radical copolymerization reaction. The structure of PDANV was characterized by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance (1 H NMR), and the results indicated that ideal product are obtained. Thermal stability of PDANV was revealed by thermogravimetric analysis (TGA) and result showed that thermal degradation of PDANV mainly happened over 301°C. Simultaneously, PDANV was prepared to further evaluate its effect on rheological and filtration properties of water-based drilling fluids (WBDFs). The results showed that the fluid loss (FL_API) of PDANV/WBDFs was only 3.4 mL, 6.0 mL before and after hot rolling at 260°C for 16 h, respectively. Compared with the 19.2% and 57.9% reduction of traditional fluid-loss additives CMC and Driscal, the fluid-loss reduction rate of PDANV/WBDFs was 87.5% in ultra-high temperature environment. Additionally, PDANV performed satisfactorily with great properties in WBDFs even at high concentration of salts and calcium. Therefore, it can be used for applications where the PDANV is subjected to certain harsh environments, such as extreme salinity and ultra-high temperature conditions.