Abstract
The Bakken Formation is a typical tight oil reservoir and oil production formation in the world. Pore structure is one of the key factors that determine the accumulation and production of the hydrocarbon. In order to study the pore structures and main controlling factors of the Bakken Formation, 12 samples were selected from the Bakken Formation and conducted on a set of experiments including X-ray diffraction mineral analysis (XRD), total organic carbon (TOC), vitrinite reflectance (Ro), and low-temperature nitrogen adsorption experiments. Results showed that the average TOC and Ro of Upper and Lower Bakken shale is 10.72 wt% and 0.86%, respectively. The Bakken Formation develops micropores, mesopores, and macropores. However, the Upper and Lower Bakken shale are dominated by micropores, while the Middle Bakken tight reservoir is dominated by mesopores. The total pore volume and specific surface area of the Middle Bakken are significantly higher than those of the Upper and Lower Bakken, indicating that Middle Bakken is more conducive to the storage of oil and gas. Through analysis, the main controlling factors for the pore structure of the Upper and Lower Bakken shale are TOC and maturity, while those for Middle Bakken are clay and quartz contents.
Highlights
The unconventional reservoirs such as shale gas and tight oil have been paid more attention since the production of conventional oil and gas decreased [1,2,3]
For the pore volume determination, it was calculated as the total volume of approximately 3 g of 40 to 80 mesh samples were first dried under vacuum for 12 h at high temperature nitrogen adsorbed at the relative pressure of 0.99
We analyze the correlations of the average pore diameter, the specific surface area, and the total analyze correlations ofthe thecorrelation, average pore diameter, thecorrelation specific surface area, and study the total pore We volume
Summary
The unconventional reservoirs such as shale gas and tight oil have been paid more attention since the production of conventional oil and gas decreased [1,2,3]. A growing number of studies have applied low-pressure N2 adsorption to explore the pore structure characteristics of unconventional shale and tight sandstone, such as pore volume, specific area, and pore size distributions [23,24]. Su et al [27] combined the LTNA and low-temperature CO2 adsorption method to characterize the pore structure of shale oil reservoirs in the Zhanhua Sag, Bohai Bay Basin, China. The X-ray diffraction (XRD), total organic carbon (TOC) analysis, vitrinite reflectance (Ro ) and low-temperature N2 adsorption experiments were conducted on these samples Pore structure parameters, such as pore morphology, specific surface area, and pore size distribution, were analyzed based on low-pressure N2 adsorption curves.
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