Bakken Crude Oil Research Articles

Spontaneous Imbibition and Core Flooding Experiments of Enhanced Oil Recovery in Tight Reservoirs with Surfactants

Despite the implementation of hydraulic fracturing technologies, the oil recovery in tight oil reservoirs is still poor. In this study, cationic, anionic, and nonionic surfactants of various sorts were investigated to improve oil recovery in tight carbonate cores from the Middle Bakken Formation in the Williston Basin. Petrophysical investigations were performed on the samples prior to the imbibition and core-flooding experiments. The composition of the minerals was examined using the XRD technique. To investigate the pore-size distribution and microstructures, nitrogen adsorption and SEM techniques were applied. The next step involved brine and surfactant imbibition for six Bakken cores and two Berea sandstone cores. The core samples were completely saturated with Bakken crude oil prior to the experiments. The core plugs were then submerged into the brine and surfactant solutions. The volume of recovered oil was measured using imbibition cells as part of experiments involving brine and surfactant ingestion into oil-filled cores. According to the findings, oil recovery from brine imbibition ranges from 4.3% to 15%, whereas oil recovery from surfactant imbibition can range from 9% to 28%. According to the findings, core samples with more clay and larger pore diameters produce higher levels of oil recovery. Additionally, two tight Bakken core samples were used in core-flooding tests. Brine and a separate surfactant solution were the injected fluids. The primary oil recovery from brine flooding on core samples is between 23% and 25%, according to the results. The maximum oil recovery by second-stage surfactant flooding is approximately 33% and 35%. The anionic surfactants appear to yield a better oil recovery in tight Bakken rocks, possibly due to their higher carbonate mineral concentrations, especially clays, according to both the core-scale imbibition and flooding experiments. For studied samples with larger pore sizes, the oil recovery is higher. The knowledge of the impacts of mineral composition, pore size, and surfactant types on oil recovery in tight carbonate rocks is improved by this study.

Volumetric Swelling of Bakken Crude Oil with Carbon Dioxide and Hydrocarbon Gases at 110 °C and Pressures of up to 34.5 Megapascals

Volumetric Swelling of Bakken Crude Oil with Carbon Dioxide and Hydrocarbon Gases at 110 °C and Pressures of up to 34.5 Megapascals

Hedging and machine learning driven crude oil data analysis using a refined Barndorff-Nielsen and Shephard model

In this paper, a refined Barndorff-Nielsen and Shephard (BN-S) model is implemented to find an optimal hedging strategy for commodity markets. The refinement of the BN-S model is obtained with various machine and deep learning algorithms. The refinement leads to the extraction of a deterministic parameter from the empirical data set. The problem is transformed to an appropriate classification problem with a couple of different approaches — the volatility approach and the duration approach. The analysis is implemented to the Bakken crude oil data and the aforementioned deterministic parameter is obtained for a wide range of data sets. With the implementation of this parameter in the refined model, the resulting model performs much better than the classical BN-S model.

Comparison of CO2 and Produced Gas Hydrocarbons to Dissolve and Mobilize Bakken Crude Oil at 10.3, 20.7, and 34.5 MPa and 110 °C

ABSTRACT: The ability of an injected gas to dissolve crude oil hydrocarbons may be a major factor controlling the success of enhanced oil recovery (EOR) projects in unconventional reservoirs. Multi...

Chemical composition of Bakken crude oil burn residue: Environmental relevance following train derailment fires

Shipments of Bakken crude oil by rail have increased in concert with the production of unconventional crude oil in the Williston Basin over the past 10 years, during which time multiple fiery train derailments resulted in tragic loss of life and/or environmental impacts. In this study the compositions of Bakken oil burn residues from a derailment fire(s) are compared to fresh and laboratory-evaporated Bakken crude oil. The absolute and hopane-normalized concentrations of n-alkanes, unsubstituted and substituted PAHs, and petroleum biomarkers and their percent depletions and enrichments (relative to hopane) are reported. Bakken oil burn residues lost 67–78% of their total chromatographable mass (C5 to C44) and exhibit chemical trends distinct from naturally-evaporated oil, including (1) the shape of their UCM profiles, (2) depletion of n-alkanes up to (at least) n-C30, (3) enrichment of priority pollutant (pyrogenic) PAHs, specifically favoring PAH isomers containing three or more linear aromatic rings (anthracene or benz[a]anthracene) or 5-member rings (fluoranthene or indeno[1,2,3-c,d]pyrene), and (4) depletion of some lower boiling petroleum biomarkers (C23-C25 tricyclic terpanes). Despite relative enrichment of most priority pollutant PAHs the absolute concentrations of both total PAH (TPAH50) and priority pollutant PAH (PPAH16) in the burn residues were depleted 69–78% and 41–48%, respectively, compared to fresh Bakken oil. These results demonstrate the changes and range of compositions among fresh, evaporated, and variably-combusted residues of Bakken crude oil, the latter of which are important in assessing the potential effect(s) of burn residues on the environment proximal to train derailment fires.

Interfacial interactions between Bakken crude oil and injected gases at reservoir temperature: A molecular dynamics simulation study

Due to large amounts of oil remain in the Bakken Formation, an effective enhanced oil recovery (EOR) method is crucially important. Cyclic gas injection, like CO2, methane, and ethane, can mobilize the residual oil and enhance oil recovery. In this study, the gas solubility, volume swelling factor, oil diffusion coefficient, and minimum miscibility pressure (MMP) were studied to compare the efficiency of different gases in the EOR process. Based on the Bakken oil components, a molecular model of the crude oil containing different types of alkanes was built. A series of molecular dynamics (MD) simulations were carried out to study the interfacial interactions between Bakken crude oil and the injected gases. At various pressures and reservoir temperature, density profiles were plotted to show the distribution of different components, and the solubility of gases in crude oil was calculated. The swelling factor was obtained by comparing the density of gas-saturated crude oil and that of the pure crude oil. The vanishing interfacial tension (VIT) method was used to determine the MMPs. The simulation results show that all three gases hold great potential in further improving oil recovery. As the pressure increases, the gas solubility increases, and the interfacial width becomes wider. At constant temperature and pressure, ethane holds the highest solubility in crude oil and can induce the most pronounced oil swelling. Meanwhile, ethane can achieve the lowest MMP and the most significant oil diffusion coefficient, which means ethane is most effective in mobilizing and producing crude oil from the reservoir.

Polymer nanoparticles based nano-fluid for enhanced oil recovery at harsh formation conditions

The application of nano-fluids for enhanced oil recovery (EOR) has attracted noticeable attention and has formed a new research area in recent years. Currently the great challenge for this area is to formulate a stable nano-fluid for oil reservoirs with high-temperature and high-salinity, in particular, when divalent ions are present. In this paper, a novel nano-fluid was developed by using nano-composite formed with polymer nanoparticles (PolyNPs) and a betaine-type zwitterionic surfactant. The developed nano-composite was characterized using electron microscopies (TEM and SEM), Fourier transform infrared (FTIR) spectrometry, dynamic light scattering (DLS), etc. The nano-fluid showed noticeable stability at relatively high salinity (15 wt% simulated brine) and high temperature (80 °C) for more than 30 days. The potential of the nano-fluid in recovering oil was evaluated by investigating the interfacial tension with Bakken oil and the oil contact angle in the nano-fluid. The results showed that the water–oil interfacial tension of the Bakken crude oil decreased by 99.49% and the contact angle increased by 125.73% compared to the original values. Then, the EOR efficiency of the nano-fluid was tested using Berea rocks saturated with Bakken crude oil through core flooding experiments. The results showed that the total oil recovery by nano-fluid is 9.32% higher than that of the control. Finally, the possible mechanism of the nano-fluid for EOR was proposed based on the investigation of dynamic displacing processes. The results demonstrated that the developed nano-fluid is a highly promising oil displacement agent for enhanced oil recovery.

Surfactant-Augmented Functional Silica Nanoparticle Based Nanofluid for Enhanced Oil Recovery at High Temperature and Salinity.

Nanofluids in recent years have shown great potential as a chemical enhanced oil recovery (EOR) technology, thanks to their excellent performance in altering interfacial properties. However, because of the great challenge in preparing stable systems suitable for an elevated temperature and a high salinity environment, expanding the application of nanofluids has been greatly restrained. In this work, a novel nanofluid was prepared by integrating positively charged amino-terminated silica nanoparticles (SiNP-NH2) with negatively charged anionic surfactant (Soloterra 964) via electrostatic force. The resulted nanofluid could be stored at relatively high salinity (15 wt % NaCl solution) and high temperature (65 °C) for more than 30 days without aggregation. Successful coating of the surfactant on target SiNPs was verified by Fourier transform infrared spectrometry and the surface charge and size distribution. In addition, the potential of the nanofluid in recovering oil was investigated by analyzing the nanofluid/Bakken oil interfacial tension and the variation trend of the oil contact angle when brine was replaced by nanofluids. Experimental results showed that the water-oil interfacial tension of the Bakken crude oil decreased by 99.85% and the contact angle increased by 237.8% compared to the original value of 13.78 mN/m and 43.4°, respectively, indicating strong oil displacement efficiency and obvious wetting transition from oil-wet toward water-wet. Spontaneous imbibition tests conducted on Berea rocks showed that the nanofluid yielded a high oil recovery rate of 46.61%, compared to that of 11.30, 16.58, and 22.89% for brine, pure SiNP-NH2, and pure surfactant (Soloterra 964), respectively. In addition, when core flooding was applied, a total of 60.88% of the original oil in place could be recovered and an additional oil recovery of 17.23% was achieved in the chemical flooding stage. Moreover, a possible mechanism of the EOR using the nanofluid was proposed. Overall, the developed nanofluid is a promising new material for EOR.

Natural degradation of low-level petroleum hydrocarbon contamination under crop management

Natural degradation of petroleum hydrocarbons (PHC) is a crucial process to consider when managing contaminated soils. However, the degradation rate is dictated by site-specific environmental factors and contaminant characteristics, so it is highly variable. Thus, region-specific research is required to determine the capacity of natural degradation processes to reach cleanup goals. This study describes the natural degradation of low levels of Bakken crude oil contamination in the Northern Great Plains, USA. Soils contaminated by PHC from an accidental release of Bakken crude oil in western North Dakota, USA, were used to construct research plots adjacent to an active remediation site. The plots had four different initial PHC concentrations, 1400, 700, 220, and 100 mg kg−1, and they were monitored over two growing seasons under crop production. The wheat (Triticum aestivum L.) and field pea (Pisum sativum L.) grown in the plots were assessed for uptake of polycyclic aromatic hydrocarbons (PAH). After two growing seasons under crop management, PHC concentrations were reduced between 46 and 53%. Neither the incorporation of composted manure nor the depth of sampling had any effect of PHC reduction, indicating that initial concentration is the driving factor in determining how long it will take to meet a given threshold. Half-life values ranged from 455 to 573 days, which is critical information for land managers determining the best remediation approach. Notably, crops grown in these contaminated soils did not show increased risk of plant uptake of PAHs. Overall, these findings indicate that soil PHC concentrations decrease while producing common agricultural crops in this region, and the crops grown in these contaminated soils show no increased risk to crop safety. Thus, depending on specific project goals, continuing a normal crop rotation may be a viable management strategy for low-level soil contamination in this region.

Full‐Scale Drinking Water System Decontamination at the Water Security Test Bed

The EPA's Water Security Test Bed (WSTB) facility is a full-scale representation of a drinking water distribution system. In collaboration with the Idaho National Laboratory (INL), EPA designed the WSTB facility to support full-scale evaluations of water infrastructure decontamination, real-time sensors, mobile water treatment systems, and decontamination of premise plumbing and appliances. The EPA research focused on decontamination of 1) Bacillus globigii (BG) spores, a non-pathogenic surrogate for Bacillus anthracis and 2) Bakken crude oil. Flushing and chlorination effectively removed most BG spores from the bulk water but BG spores still remained on the pipe wall coupons. Soluble oil components of Bakken crude oil were removed by flushing although oil components persisted in the dishwasher and refrigerator water dispenser. Using this full-scale distribution system allows EPA to 1) test contaminants without any human health or ecological risk and 2) inform water systems on effective methodologies responding to possible contamination incidents.

Tesoro oil refinery to co-process renewable feedstock and Bakken crude oil

High Temperature Hydrogen Attack (HTHA) of steels plagues higher temperature industrial applications, especially in the petrochemical industry, due to the lack of a mechanistic understanding of the phenomenon and the use of empirically established design criteria, such as the Nelson curves. By using advanced microscopy techniques to explore the microstructure immediately ahead of crack tips and along cavitated grain boundaries, we gained a better understanding of the physical processes occurring early during the HTHA damage process, which can guide the development of models for the degradation process accounting for methane formation and creep cavitation. The results confirm the fundamentals of previously proposed models, but also provide finer details than have been previously known. Based on the underlying deformation and grain boundary fracture, we propose a model for material failure underlying HTHA.

Characterization of chemical fingerprints of unconventional Bakken crude oil

The ability to characterize the composition of emerging unconventional Bakken tight oil is essential to better prepare for potential spills and to assess associated environmental concerns. The present work measured and compared the physical and chemical properties of Bakken crudes with conventional crude oils from various regions and different types of refined petroleum products. The physicochemical properties of Bakken crude are overall similar to those of conventional light crudes. The Bakken crude consists of high concentrations of monoaromatic hydrocarbons and alkylated PAHs with a clear dominance of the alkylated naphthalene homologues followed by the phenanthrene series. Its pyrogenic index (PI) values are considerably lower than typical conventional crude oils. The Bakken crude oils in this study exhibit a low abundance of petroleum biomarker such as terpanes, steranes and diamondoids and bicyclic sesquiterpanes. Since tight oil from the Bakken region is produced from low-permeability formations, variations in abundance and diagnostic ratios of common target petroleum hydrocarbons were found among these oils.

New York State's Inland Geographic Response Plans

Geographic Response Plans (GRPs) are location-specific plans developed to provide guidance for oil spill responses throughout the United States. Until recently, the majority of crude oil transportation in the United States has occurred via waterways on oil tankers and barges, therefore, most existing GRPs focus on the protection of sensitive biological resources and socio-economic features in near shore environments. The recent development of crude oil extraction from the Bakken formation has resulted in a significant increase in the volume of crude oil being transported via railroads and pipelines and has highlighted the need for inland response planning. Rail cars transporting the volatile and flammable Bakken crude oil now traverse more than 850 miles of New York State on two major Class 1 Railroads. In response, Executive Order 125 was issued by the governor directing state agencies to strengthen the state's preparedness for incidents involving crude oil transportation. New York State's (NYS) Department of Environmental Conservation (DEC), in collaboration with the Department of Homeland Security & Emergency Services and Department of Health, are leading a multi-stakeholder effort to develop Inland GRPs for the 21 NYS counties currently impacted by crude-by-rail transportation. County steering committees were established consisting primarily of local first response agencies, as well as their state and federal partners. Utilizing Sensitive Resource Maps developed by DEC, coupled with the local steering committee input, location-specific response plans were drafted, reviewed, and set as final working “evergreen” documents, which are open for update/refinement at any time in the future. The NYSDEC GRPs are similar to typical GRPs in that they are map-based, location-specific contingency plans that outline response strategies for the protection of sensitive resources. However, the NYSDEC GRPs differ from traditional GRPs in several ways. They extend contingency planning to cover spills on land, in addition to surface water-based spills. Due to the flammability of Bakken crude oil, much more emphasis is placed on the fire risks associated with a train derailment. This is done by mapping sensitive human receptors (e.g., schools, daycare centers, assisted living centers, etc.), critical infrastructure, and identifying fire (and vapor) suppression assets. The NYSDEC GRPs also place more emphasis on the initial response options available to local first responders, options that can be implemented before other response assets may arrive on-scene (State, Federal, and RP). This presentation will discuss the development, structure, proposed implementation, training and exercises associated with this ongoing program.

Complexities of Oil Spill Contingency Planning for Railroads – Lessons Learned In Washington State

Abstract 2017-405 With the energy renaissance in the United States and the lack of inland pipeline distribution systems, increasingly railroads are transporting crude oil to coastal ports for refining and for further distribution over the water. In Washington State, rapidly changing modes of crude oil transportation, shifting away from vessel and towards rail delivery, resulted in a regulatory requirement for rail operators to develop state approved oil spill contingency plans. Oil spill planning for railroads can be complex, for instance, planning for spills in all types of terrains, environments and habitats, as railroads cross both inland and marine waters. Washington State regulations for railroad contingency plans have been developed in response to changes in oil movement and this paper presents lessons learned from that endeavor. During the rule process, a unit train carrying Bakken crude oil derailed in the Columbia River Gorge, providing an opportunity to draw those lessons into the final rules as adopted. This paper describes the State’s approach to working with large and small rail operators and concerned citizens, and shares the lessons that address the obstacles and opportunities unique to complex railroad oil spill planning.

A Quantitative Evaluation of Trajectory, Fate, and Effects from Crude By Rail Releases: A case study using the Proposed Shell Puget Sound Refinery Anacortes Rail Unloading Facility

The proposed Shell Puget Sound Refinery Anacortes Rail Unloading Facility in Washington State is expected to receive six unit trains per week, each containing 60,000–70,000 barrels of conditioned Bakken crude oil. Oil spill trajectory, fate, and effects modeling was performed to evaluate risks from hypothetical releases of crude oil from crude-by-rail unit trains. The oil spill modeling predicted where released oil would move over land and in water, how it would behave within the environment, and how it may impact resources within the area. Hypothetical releases from train derailments were modeled using the OILMAP Land and SIMAP models, two state-of-the-art computational oil spill models that are routinely used internationally by industry, government, and academia. OILMAP Land was used to predict the overland and down slope trajectory and fate of released crude oil on land and within storm water drainage systems. SIMAP was used to characterize the trajectory, fate, and acute biological effects of oil within the water column. Releases were modeled at three representative locations along the rail corridor, including the Swing Bridge over the Swinomish Channel, the Skagit River crossing, and the Edmonds Ferry Terminal. Two environmental conditions were modeled at each location to capture the seasonal and environmental variability in tides, river flow rate, and winds. Two discharge volumes of conditioned Bakken crude oil were modeled. An overlay analysis was used to determine the potentially affected resources located within the oil spill footprint for each respective scenario. A biological effects assessment was conducted to estimate the potential short-term (acute) exposure of organisms to floating oil and subsurface oil contamination to estimate the resulting equivalent area of 100% predicted mortality. To bound the range of potential effects, biological impacts were assessed using two biological sensitivities. In total, 12 physical fates scenarios were modeled (3 locations × 2 environmental conditions × 2 release volumes) with 24 biological scenarios (2 sensitivities). Approximately 50% of the conditioned Bakken crude was predicted to evaporate within 48 hours, while the remaining oil formed surface slicks, oiled shorelines, and entrained within the water column, potentially interacting with SPM and oiling sediments. This assessment was used to quantitatively discuss the consequence side of risk associated with crude by rail releases from unit trains for the proposed Shell Puget Sound Refinery Anacortes Rail Unloading Facility. Results were included in Chapter 5 of the Environmental Impact Statement (EIS) addressing Environmental Health and Risk, as well as a technical report.

A flammability (risk) index for use in transportation of flammable liquids

Recent accidents involving trains carrying flammable liquids (crude oil, ethanol, etc.) and consequent release of these flammable liquids have resulted in the formation of large fires. These fires have caused significant property damage and, in some cases, fatalities.The focus of reducing such accidents has been on implementing train operational controls, improving tank car puncture resistance, and providing thermal protection systems on tank cars to reduce the rate of heat input from an external fire to the liquid in the tank. In addition, one of the current regulatory approaches for reducing the post-accident fire and explosion risk is to require the reduction in the product vapor pressure at the time of loading of the product into tank cars. This is based on the assumption vapor pressure is the sole metric of volatility and flammability.This paper demonstrates that vapor pressure alone cannot be a metric to evaluate the hazard potential of a flammable liquid. Other vapor properties, including the flammability range concentrations in air and the minimum ignition energy, must be considered. A Flammability Index (FI) is developed and applied to example flammable liquids. FI for a specific Bakken crude oil sample is 1.25 and for ethanol 11.3, making ethanol a more “flammable risk” material than crude oil, at normal temperatures. This result is completely opposite to what one would conclude based purely on vapor pressure (ethanol vapor pressure at 77 °F is 1.2 psia vs. 8.7 psia for crude oil at the same temperature).

Experimental and analytical methods to determine minimum miscibility pressure (MMP) for Bakken formation crude oil

The Bakken is one of the shale reservoirs that has been discovered to hold a vast amount of resource and is contributing to the production boom in the US. This unconventional reservoir, like most others, displays favorable initial production rates due to stimulation by hydraulic fracturing, but production rates quickly decline after few months. Due to the extremely low permeability and low recoveries, miscible gas injection is considered for improving the recovery of oil in the Bakken formation. Feasibility of miscible gas injection in the Bakken would depend on the analysis of minimum miscibility pressure (MMP) experiments.The Rising Bubble Apparatus (RBA) has been chosen for the purpose of these experiments. The RBA provides results in a short amount of time using small amounts of fluid samples. The RBA consists of a cell gage containing a flat glass tube where oil samples are placed and an injection needle where gas is injected into the flat glass tube. To simulate reservoir conditions, the glass tube is pressurized using de-ionized water, and heating plates surrounding the cell are used to regulate temperature. Visual observation of the injected gas bubble behavior is captured by a camera as it rises and moves upward along the oil column. By observing the shape and dissolution behavior of the bubble, the MMP can be determined.MMP results from a Bakken crude sample are shown to range from 2100 to 3500psi at temperatures from 160 to 240°F using CO2 as the injection fluid. Other injection fluids such as nitrogen and hydrocarbon gases have been tested and also provided reasonable MMP values. MMP results from Bakken crude oil samples were compared to existing correlations, and the correlations were found to produce mostly unreliable MMP results for the Bakken oils evaluated in the study. On the other hand, an equation of state phase behavior program showed similarities with the RBA MMP results.The impact of different injection fluids, inclusive of CO2 and enriched hydrocarbon gases is the subject of this study. MMP results are influenced by the choice of injection fluids, providing valuable information for economic production and increased recovery in the Bakken formation. The results from this study provide a range of MMP data that can be used in planning pilot tests for miscible gas injection in the Bakken.

Net energy analysis of Bakken crude oil production using a well-level engineering-based model

Since 2005, production of oil from the Bakken formation of North Dakota has increased substantially, and the region now supplies about 1.5% of global oil output. This study presents a first engineering-based assessment of the energy intensity of Bakken crude oil production and computes the resulting NER (net energy return) from Bakken hydrocarbon production. The energy required to drill, produce, and process Bakken oil and gas is estimated for over 7000 wells using open-source drilling and production assessment models. The largest energy uses are from drilling and processing of produced fluids (crude/water emulsions and gas). Fluid lifting and injection and embodied energy are also important energy needs. Median energy consumption equals ≈3.4% of net crude and gas energy content, while mean energy consumption equals ≈3.9% of hydrocarbon energy. The median NER is 29.3 MJ/MJ. The interquartile range is 24.3–35.7 MJ/MJ, while the 5%–95% range is 13.3–52.0 MJ/MJ. NERs have declined in recent years, with a decline in median NER of 23% between 2010 and 2014. Results are most sensitive to modeled estimated ultimate recovery, and embodied energy.

Wettability Survey in Bakken Shale With Surfactant-Formulation Imbibition

Summary For ultratight shale reservoirs, wettability strongly affects fluid flow behavior. However, wettability can be modified by numerous complex interactions and the ambient environment, such as pH, temperature, or surfactant access. This paper is a third-phase study of the use of surfactant imbibition to increase oil recovery from Bakken shale. The surfactant formulations that we used in this paper are the initial results that are based on our previous study, in which a group of surfactant formulations was examined—balancing the temperature, pH, salinity, and divalent-cation content of aqueous fluids to increase oil production from shale with ultralow porosity and permeability in the Middle Member of the Bakken formation in the Williston basin of North Dakota. In our previous study, through the use of spontaneous imbibition, brines and surfactant solutions with different water compositions were examined. With oil from the Bakken formation, significant differences in recoveries were observed, depending on compositions and conditions. Cases were observed in which brine and surfactant (0.05 to 0.2 wt% concentration) imbibition yielded recovery values of 1.55 to 76% original oil in place (OOIP) at high salinity (150 to 300 g/L; 15 to 30 wt%) and temperatures ranging from 23 to 120°C. To advance this work, this paper determines the wettability of different parts of the Bakken formation. One goal of this research is to identify whether the wettability can be altered by means of surfactant formulations. The ultimate objective of this research is to determine the potential of surfactant formulations to imbibe into and displace oil from shale and to examine the viability of a field application. In this paper, through the use of modified Amott-Harvey tests, the wettability was determined for cores and slices from three wells at different portions of the Bakken formation. The tests were performed under reservoir conditions (90 to 120°C, 150- to 300-g/L formation-water salinity), with the use of Bakken crude oil. Both cleaned cores (cleaned by toluene/methanol) and untreated cores (sealed, native state) were investigated. Bakken shale cores were generally oil-wet or intermediate-wet (before introduction of the surfactant formulation). The four surfactant formulations that we tested consistently altered the wetting state of Bakken cores toward water-wet. These surfactants consistently imbibed to displace significantly more oil than brine alone. Four of the surfactant imbibition tests provided enhanced-oil-recovery [(EOR) vs. brine water imbibition alone] values of 6.8 to 10.2% OOIP, incremental over brine imbibition. Ten surfactant imbibition tests provided EOR values of 15.6 to 25.4% OOIP. Thus, imbibition of surfactant formulations appears to have a substantial potential to improve oil recovery from the Bakken formation. Positive results were generally observed with all four surfactants: amphoteric dimethyl amine oxide, nonionic ethoxylated alcohol, anionic internal olefin sulfonate, and anionic linear α-olefin sulfonate. From our work to date, no definitive correlation is evident in surfactant effectiveness vs. temperature, core porosity, core source (i.e., Upper Shale or the Middle Member), or core preservation (sealed) or cleaning before use.