Investigation of pore-throat structure and fractal characteristics of tight sandstones using HPMI, CRMI, and NMR methods: A case study of the lower Shihezi Formation in the Sulige area, Ordos Basin

Wu, Yuping; Liu, Cheng‐Lin; Ouyang, Siqi; Luo, Bin; Zhao, Dingding; Sun, Wei; Awan, Rizwan Sarwar; Lu, Zhendong; Li, Guoxiong; Zang, Qibiao

doi:10.1016/j.petrol.2021.110053

Cited by 35 publications

(30 citation statements)

References 58 publications

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“…The fractal dimension D of the pore-throat microstructure can be calculated according to the slope of the straight line. In fractal theory, the lower limit of D is 2, which represents regular pore shape or completely smooth pore surface; the upper limit of D is 3, which represents rough or completely irregular surface morphology of the pore throat . The fractal dimension D increases with the complexity and heterogeneity of the rock pore-throat microstructure.…”

Section: Methodsmentioning

confidence: 99%

Quantifying Controls on Threshold Pressure during CO₂ Injection in Tight Gas Reservoir Rocks

et al. 2022

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The simultaneous flow of gas and water is controlled by a threshold pressure gradient (TPG) effect during CO 2 injection of tight gas reservoirs. The TPG effect is dynamic because it varies with both the effective stress and the water saturation. The sensitivity of TPG to effective stress and mobile water is affected by the porethroat microstructure. In this paper, we report the results of dynamic TPG tests on six cores with similar permeability. The influence of the pore-throat microstructure on the sensitivity of the TPG to stress and to mobile water was also quantitatively studied using a fractal method, and the distribution of the threshold pressure and corresponding gas production loss were calculated during CO 2 injection in tight gas reservoirs. The test results show that TPG decreases logarithmically with the increase of the pore fluid pressure during CO 2 injection, a change of 0.1−50 MPa in the pore fluid pressure corresponding to a 1.8−3.5 times increase of the TPG variation. The TPG increases exponentially by 3.5−6.7 times from irreducible water saturation to a mobile water saturation of 30%. The fractal dimension (D) of the heterogeneity of the rock pore-throat microstructure has a linear relationship with both the stress sensitivity coefficient (λ) and mobile water sensitivity coefficient (η), with the larger values of λ and η being associated with more heterogeneous pore-throat microstructures. The reservoir threshold pressure showed a significant nonlinear distribution in near-well reservoirs at low bottom-hole flow pressures of the production well during CO 2 injection. The calculated gas well production loss as a result of a dynamic threshold pressure is 7−16% higher than that of the fixed threshold pressure, and the difference is larger at low pressures.

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Section: Methodsmentioning

confidence: 99%

Quantifying Controls on Threshold Pressure during CO₂ Injection in Tight Gas Reservoir Rocks

et al. 2022

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“…Therefore, several molecular simulation approaches have been recently proposed to study the occurrence characteristics of hydrocarbons in shale. − However, because of the complex petroleum molecules and shale composition, , only simplified petroleum molecules and shale components can be used for modeling, resulting in limited findings. Additionally, NMR technology has been widely applied to study shale pore structure and fluid characteristics. − Pore distribution characteristics of the shale matrix obtained by 1D-NMR ,, and the occurrence characteristics of various hydrogen components in shale such as kerogen, asphalt, oil, and water can be obtained by 2D-NMR. ,, However, hydrogen components in oil-rich shale may overlap and have similar distribution positions . Therefore, it is still debatable how to correctly identify shale oil in various physical states.…”

Section: Discussionmentioning

confidence: 99%

“…Additionally, NMR technology has been widely applied to study shale pore structure and fluid characteristics. 79−83 Pore distribution characteristics of the shale matrix obtained by 1D-NMR 81,84,85 and the occurrence characteristics of various hydrogen components in shale such as kerogen, asphalt, oil, and water can be obtained by 2D-NMR. 82,83,86 However, hydrogen components in oil-rich shale may overlap and have similar distribution positions.…”

Section: Occurrence State and Space Of Shale Oil 421 Occurrence Space...mentioning

confidence: 99%

Occurrence Space and State of Petroleum in Lacustrine Shale: Insights from Two-Step Pyrolysis and the N₂ Adsorption Experiment

Liu

Jiang

et al. 2022

Energy Fuels

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The pore structure and occurrence state of hydrocarbons in shale reservoirs are significant factors affecting shale oil production. However, how pore structure affects the occurrence of shale oil remains unclear. This paper aims at analyzing the major distribution space of shale oil with various physical states in shale pores using experimental approaches. Therefore, the original samples and solvent-extracted samples of lacustrine shale from the Permian Fengcheng Formation in Junggar Basin were investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Rock-Eval pyrolysis, and N 2 adsorption/desorption methods. The findings demonstrate that the Fengcheng shale has high oil content, with free oil accounting for 57.17% of the total oil yield. The pore size distribution characteristics of original and solvent-extracted shale samples indicate that shale oil is mainly stored in mesopore pores with diameters between 5 and 40 nm. The threshold limit of pore diameter for the movable oil in shale reservoirs is between 3.5 and 19 nm. Also, by comparing shale oil mobility in various basins, it is found that petroleum mobility occurs when the total oil yield in the shale reaches 6 mg HC/g Rock. Meanwhile, the threshold value of petroleum mobility in different basins is related to the pore shape. Parallel plate pores within shales are more favorable for petroleum mobility. This research presents the mobility of the shale oil threshold, which is critical for shale oil exploration and exploitation.

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“…Currently, various methods can be used to describe the pore structure of tight reservoirs, and low-field nuclear magnetic resonance (NMR) is commonly used in unconventional oil and gas fields. NMR has an individual advantage for describing the micro-pore structure (such as the properties of the reservoir, pore throat characteristics, and pore size distribution), and the fluid in the pore (such as the volume of movable fluid, saturation of movable oil, and distribution of residual oil) (Hamada and AbuShanab 2008;Yang et al 2013;Lai et al 2018;Lyu et al 2018a;Gao et al 2019;Li et al 2019;Wu et al 2022). The pores in a tight reservoir can be classified according to the transverse relaxation time (T 2 ), Peng et al (2018) reported that the pores could be divided into micro-pore (T 2 ≤ 30 ms), mesopore (30-90 ms), macropore (90-200 ms) and super macropore (T 2 > 200 ms).…”

Section: Introductionmentioning

confidence: 99%

“…The pores in a tight reservoir exhibit self-similarity. Compared with classical European geometry, the fractal dimension can describe the heterogeneity and complexity of pores (Krohn and Thompson 1986;Krohn 1988;Jin et al 2017a, b;Guo et al 2019;Wang et al 2019aWang et al , b, 2020Wang et al , 2021Wu et al 2020Wu et al , 2022Yang et al 2021). Pores with fractal dimensions below 2 and above 3 have a weak influence on the pore structure (Guo et al 2019).…”

Section: Introductionmentioning

confidence: 99%

Oil utilization degree at various pore sizes via different displacement methods

Gao

Wang

et al. 2022

J Petrol Explor Prod Technol

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A reasonable displacement method is essential to improve the oil displacement efficiency of tight reservoirs. In this study, three different displacement methods were utilized on the tight core samples obtained from the Yanchang Formation Chang 8 and Chang 9 tight oil reservoirs: spontaneous imbibition displacement, various water flooding rate displacement and water flooding displacement after spontaneous imbibitions; furthermore, the oil utilization degree of the residual oil in various pores was discussed. The oil displacement efficiency of the spontaneous imbibitions was approximately 26.91% and 29.56% for the Chang 8 and Chang 9 samples, respectively. With an increasing water flooding rate, the oil displacement efficiency features an inverse “V”-like tendency, and a water flooding rate of 0.06 mL/min was the optimal value as; the oil displacement efficiency achieved was 63.56% and 60.27% for the Chang 8 and Chang 9, respectively. When compared with spontaneous imbibitions, at a displacement rate of 0.06 mL/min after spontaneous imbibition, the oil displacement efficiency could be further increased to 50.02% and 30.35%, respectively. The differences in the oil displacement efficiency using various displacement methods are primarily related to the degree of utilization of residual oil in various pores. The progressively refined pore classification method is used to study the degree of oil utilization in various pores, and the pores in the tight reservoir can be divided into four types: P1, P2, P3 and P4. Regarding the spontaneous imbibition displacement, the displacement of the residual oil is dominantly determined by the residual oil present in the P2 and P3 pores; as the residual oil massively accumulates in the P2 pores, the discharging of the residual oil in this part finally determines the oil displacement efficiency when the water flooding rates changed. At a water flooding rate of 0.06 mL/min after spontaneous imbibition, the oil utilization degree of residual oil in various pores is enhanced, particularly for the P2, P3, and P4 pores, and the pore structure contributes to the increase in the oil displacement efficiency. Using the progressively refined pore classification method, the complexity of the distribution of residual oil in tight reservoirs could be studied quantitatively and elaborately, and the results can efficiently guide the development of residual oil in tight oil reservoirs.

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Investigation of pore-throat structure and fractal characteristics of tight sandstones using HPMI, CRMI, and NMR methods: A case study of the lower Shihezi Formation in the Sulige area, Ordos Basin

Cited by 35 publications

References 58 publications

Quantifying Controls on Threshold Pressure during CO₂ Injection in Tight Gas Reservoir Rocks

Quantifying Controls on Threshold Pressure during CO₂ Injection in Tight Gas Reservoir Rocks

Occurrence Space and State of Petroleum in Lacustrine Shale: Insights from Two-Step Pyrolysis and the N₂ Adsorption Experiment

Oil utilization degree at various pore sizes via different displacement methods

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Investigation of pore-throat structure and fractal characteristics of tight sandstones using HPMI, CRMI, and NMR methods: A case study of the lower Shihezi Formation in the Sulige area, Ordos Basin

Cited by 35 publications

References 58 publications

Quantifying Controls on Threshold Pressure during CO2 Injection in Tight Gas Reservoir Rocks

Quantifying Controls on Threshold Pressure during CO2 Injection in Tight Gas Reservoir Rocks

Occurrence Space and State of Petroleum in Lacustrine Shale: Insights from Two-Step Pyrolysis and the N2 Adsorption Experiment

Oil utilization degree at various pore sizes via different displacement methods

Contact Info

Product

Resources

About

Quantifying Controls on Threshold Pressure during CO₂ Injection in Tight Gas Reservoir Rocks

Quantifying Controls on Threshold Pressure during CO₂ Injection in Tight Gas Reservoir Rocks

Occurrence Space and State of Petroleum in Lacustrine Shale: Insights from Two-Step Pyrolysis and the N₂ Adsorption Experiment