Pore-scale characterization of tight sandstone in Yanchang Formation Ordos Basin China using micro-CT and SEM imaging from nm- to cm-scale

Li, Xuefeng; Jian-fu, Wang; Guo, Lin; Hu, Fengxia; Li, Chaoliu; Li, Xia; Yu, Jun; Xu, Huaimin; Lu, Shuangfang; Xue, Qingzhong

doi:10.1016/j.fuel.2017.07.068

Cited by 112 publications

(43 citation statements)

References 25 publications

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“…The 3D images of the pore characterization of tight sandstone were measured by a Phoenix Nanotom M scanner with a working voltage of 90 kV, and tomogram image spatial resolution of around 3 µm. In this method, an X-ray with conical beam penetrates the specimen and then attenuates depending on the sample density, mineral compositions and contents, and the thickness along the beam direction, and this attenuation is mainly associated with the decreasing sample density [22,53]. Finally, based on the threshold value segmentation method, rock matrix with high density and void space with low density can be determined [22].…”

Section: Experimental Methodsmentioning

confidence: 99%

“…Although many methods can be used to characterize pore structures, no sole direct and indirect experiment can be used to determine pore structures traits due to its own limitations and strengths [18]: TS and SEM can reveal pore morphology and occurrence qualitatively, but these techniques were unable to obtain quantitative pore structure-related data [19,20]. CT is an effective technique to quantitatively characterize the three-dimensional images of pore networks, but it has drawbacks in the calculation of pores larger than 3 µm and is often restricted by expense [2,21,22]. PCMI is understood to be a widely-used method of estimation of pore structures because it can detect a broad spectrum of PSD on account of relatively high injection pressure according to the Washburn equation [23]; however, this technique fails to acquire an exact count of large pores because of the shielding effect of small pores [24].…”

Section: Introductionmentioning

confidence: 99%

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Experimental Investigation of Pore Structure and Movable Fluid Traits in Tight Sandstone

2019

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Whether the variation of pore structures and movable fluid characteristics enhance, deteriorate, or have no influence on reservoir quality has long been disputed, despite their considerable implications for hydrocarbon development in tight sandstone reservoirs. To elucidate these relationships, this study systematically analyzes pore structures qualitatively and quantitatively by various kinds of direct observations, indirect methods, and imaging simulations. We found that the uncertainty of porosity measurements, caused by the complex pore-throat structure, needs to be eliminated to accurately characterize reservoir quality. Bulk water was more easily removed, while surface water tended to be retained in the pores, and the heterogeneity of pore structures was caused by the abundance of tiny pores. The rates of water saturation reduction in macropores are faster than those for tiny pores, and sandstones with poor reservoir quality show no marked descending of lower limits of movable pore radius, indicating that the movable fluid would advance exempted from the larger pores. This study suggests that the deterioration of reservoir quality is strongly affected by the reduction of larger pores and the aqueous phases tended to remain in the tiny pores in the forms of surface water.

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Section: Experimental Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Experimental Investigation of Pore Structure and Movable Fluid Traits in Tight Sandstone

2019

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“…A sample can be analyzed nondestructively using the CT scanning technique, and 3D pore distribution data can be obtained by 3D digital reconstruction based on sample scanning slices [36]. Micro-CT was carried out on the high-resolution 3D X-ray microXCT-400 imager, produced by Xradia, USA, with a maximum theoretical 3D spatial resolution of less than 3 Geofluids 1 μm.…”

Section: Microcomputer Tomography (Micro-ct)mentioning

confidence: 99%

Quantitative Characterization of Pore Connectivity and Movable Fluid Distribution of Tight Sandstones: A Case Study of the Upper Triassic Chang 7 Member, Yanchang Formation in Ordos Basin, China

et al. 2020

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The pore connectivity and distribution of moveable fluids, which determines fluid movability and recoverable reserves, are critical for enhancing oil/gas recovery in tight sandstone reservoirs. In this paper, multiple techniques including high-pressure mercury intrusion porosimetry (MIP), nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), and microcomputer tomography scanning (micro-CT) were used for the quantitative characterization of pore structure, pore connectivity, and movable fluid distribution. Firstly, sample porosity and permeability were obtained. Pore morphology and the 3D distribution of the pore structures were analyzed using SEM and micro-CT, respectively. The pore-size distribution (PSD) from NMR was generally broader than that from MIP because this technique simply characterized the connected pore volume, whereas NMR showed the total pore volume. Therefore, an attempt was made to calculate pore connectivity percentages of pores with different radii (<50 nm, 50 nm–0.1 μm, and 0.1 μm–1 μm) using the difference between the PSD obtained from MIP and NMR. It was found that small pores (r<0.05 μm) contributed 5.02%–18.00% to connectivity, which is less than large pores (r>0.05 μm) with contribution of 36.60%–92.00%, although small pores had greater pore volumes. In addition, a new parameter, effective movable fluid saturation, was proposed based on the initial movable fluid saturation from NMR and the pore connectivity percentage from MIP and NMR. The results demonstrated that the initial movable fluid saturation decreased by 14.16% on average when disconnected pores were excluded. It was concluded that the effective movable fluid saturation has a higher accuracy in evaluating the recovery of tight sandstone reservoirs.

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“…The study of pore throat characteristics in tight sandstone reservoirs has become a research focus. The types, origin, morphology, sizes and distribution of pores have been the focus of researchers through various methods and techniques, such as direct observation (e.g., SEM and X-ray micro-computed tomography), quantitative measurement (e.g., high pressure mercury intrusion) and the application of fractal theory (Hu et al, 2012;Giri et al, 2012;Bai et al, 2013;Ge et al, 2015;Dou et al, 2017;Liu et al, 2017). Inspections through thin -section petrography and SEM are universally used to qualitatively or semi-quantitatively describe pore throat structures (Pittman, 1992), which can provide information about the shapes, sizes, positions and digenetic evolution.…”

Section: Introductionmentioning

confidence: 99%

Pore‐Throat Combination Types and Gas‐Water Relative Permeability Responses of Tight Gas Sandstone Reservoirs in the Zizhou Area of East Ordos Basin, China

Guo

et al. 2019

Acta Geologica Sinica (Eng)

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With the aim of better understanding the tight gas reservoirs in the Zizhou area of east Ordos Basin, a total of 222 samples were collected from 50 wells for a series of experiments. In this study, three pore-throat combination types in sandstones were revealed and confirmed to play a controlling role in the distribution of throat size and the characteristics of gas-water relative permeability. The type-I sandstones are dominated by intercrystalline micropores connected by cluster throats, of which the distribution curves of throat size are narrow and have a strong single peak (peak ratio >30%). The pores in the type-II sandstones dominantly consist of secondary dissolution pores and intercrystalline micropores, and throats mainly occur as slice-shaped throats along cleavages between rigid grain margins and cluster throats in clay cement. The distribution curves of throat size for the type-II sandstones show a bimodal distribution with a substantial low-value region between the peaks (peak ratio <15%). Primary intergranular pores and secondary intergranular pores are mainly found in type-III samples, which are connected by various throats. The throat size distribution curves of type-III sandstones show a nearly normal distribution with low kurtosis (peak ratio <10%), and the micro-scale throat radii (>0.5 μm) constitute a large proportion. From type-I to type-III sandstones, the irreducible water saturation (S wo ) decreased; furthermore, the slope of the curves of K rw /K rg in two-phase saturation zone decreased and the two-phase saturation zone increased, indicating that the gas relative flow ability increased. Variations of the permeability exist in sandstones with different porethroat combination types, which indicate the type-III sandstones are better reservoirs, followed by type-II sandstones and type-I sandstones. As an important factor affecting the reservoir quality, the pore-throat combination type in sandstones is the cumulative expression of lithology and diagenetic modifications with strong heterogeneity.

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Pore-scale characterization of tight sandstone in Yanchang Formation Ordos Basin China using micro-CT and SEM imaging from nm- to cm-scale

Cited by 112 publications

References 25 publications

Experimental Investigation of Pore Structure and Movable Fluid Traits in Tight Sandstone

Experimental Investigation of Pore Structure and Movable Fluid Traits in Tight Sandstone

Quantitative Characterization of Pore Connectivity and Movable Fluid Distribution of Tight Sandstones: A Case Study of the Upper Triassic Chang 7 Member, Yanchang Formation in Ordos Basin, China

Pore‐Throat Combination Types and Gas‐Water Relative Permeability Responses of Tight Gas Sandstone Reservoirs in the Zizhou Area of East Ordos Basin, China

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