Jin Zhang

Date of Award

January 2020

Document Type


Degree Name

Doctor of Philosophy (PhD)


Geological Engineering

First Advisor

Dongmei D. Wang


The techniques of horizontal wells and hydraulic fracturing enable oil production from low-permeable shale, sandstone and carbonate rock formations. However, the extremely low permeability and porosity properties lead a sharp declination of oil production and a low oil recovery factor (typically, 5-15% of original oil in place) as reservoir pressures dropping. Surfactant EOR (enhanced oil recovery) has been considered as one of the best options for geological challenging formations. In our previous studies, we developed a method using surfactant formulation spontaneous imbibition to stimulate the oil recovery from tight formations through wettability alteration and the interfacial tension (IFT) reduction. However, the slow oil extraction rate and the limited penetrating area into the rock matrix in laboratory experiments may prove impractical for real-time extraction. To address this problem for the carbonate-rich formations, such as Bakken, Eagle Ford and Niobrara, this research attempted to investigate whether an approach – using a forced surfactant imbibition process coupled with enhanced contact area stimulation (acidizing, for instance) could speed up the oil extraction rate and also force the surfactant formulation deep into the carbonate–rich matrix through acidification, thereby improving oil recoveries. In the first stage of this study, experiments were performed to evaluate the oil extraction by forced surfactant imbibition process (core flooding process) from three paired core plugs of the Middle Bakken. The effects of initial water saturation, surfactant concentration, and brine salinity were also investigated during the flooding process. In the second stage, a series of experiments were conducted to evaluate the feasibility of studied chemical formulations (CF) to the target rock formation by forced imbibition process. Although the methods of core flooding and acidizing have been used for conventional rock type oil production stimulation for decades, no literatures reported yet using above comprehensive studies for oil recovery improvement onto tight Bakken Formation prior to this thesis research. Based on the laboratory studies, we conclude: (1) Forced surfactant imbibition EOR for tight rocks with low permeability (10-3 md) has good potential for oil recovery enhancement at various conditions in this study. (2) The ultimate oil recovery is dominated by permeability, heterogeneity or lithology differences. (3) Fractures apparently played an important role in oil recovery, especially in flooding process. (4) Positive oil extraction rate was observed compared to the spontaneous imbibition. (5) The aqueous imbibition process coupled with acidizing treatment was capable to recover oil in Bakken cores from 27.4% to 81.1%. (6) The contact area enhancement method – acidification was determined by the rock homogeneity (permeability distribution and mineral composition distribution). (7) The chemical formulation penetrated in and interacted with carbonate minerals in rock matrix resulted in the asperities on the fracture surface and adjacent matrix led petrophysical properties (porosity and permeability) improvements, thereby extracting more oil. The laboratory study result may serve as a possible approach for a field application to improve the hydrocarbon recovery using aqueous forcible imbibition process from well to well besides of huff-n-puff method.