Contributions of pore-throat size distribution to reservoir quality and fluid distribution from NMR and MIP in tight sandy conglomerate reservoirs

Chen, Meng; Dai, Junhu; Liu, Xiangjun; Kuang, Yan; Qin, Minjun; Wang, Zhongtao

doi:10.1007/s12517-018-4153-7

Cited by 20 publications

(21 citation statements)

References 22 publications

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“…Equation (2) indicates that there is a linear relation between the relaxation time T 2 and the pore diameter D. Thus, it is recognized that to calculate the pore diameters in a porous mediums based on its ρ 2 value. In several researches, ρ 2 values were calculated by comparing the T 2 spectrum curves with POSD results from mercury injection porosimetry technique as presented by Chen et al [33] and nitrogen gas adsorption technique as presented by Jahwar et al [34]. Besides, the ρ 2 values can be calculated by empirical formulas of permeability.…”

Section: Theoretical Background Of Nmri Analysismentioning

confidence: 99%

Pore Distribution Characteristics of Thawed Residual Soils in Artificial Frozen-Wall Using NMRI and MIP Measurements

Kong

2020

Applied Sciences

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Artificial ground freezing method is widely applied in the construction of metro tunnel and significantly impact the microstructure of soils in artificial frozen-walls. To delve into the pore distribution characteristics of thawed residual soils, Nuclear Magnetic Resonance Imaging (NMRI) measurements were performed to investigate the relaxation time (T2) spectrums and T2-weighted images of saturated samples after freezing at different temperatures. The pore volume distributions were determined from T2 spectrums based on the surface relaxation coefficient ( ρ 2 ) and the pore structures were visualized by T2-weighted images. Subsequently, the pore size distribution curves from NMRI were compared and validated by mercury intrusion porosimetry (MIP) tests. According to the results, the peak areas of T2 spectrums were linearly related to freezing temperatures in a positive manner. Pore volume distribution curves of thawed soils have two peaks, which are the major peaks with diameters of 0.5–20 μm and the secondary peaks with diameters of 20–500 μm. As the freezing temperature drops, the volumes of pores with different diameters all increased. The damage degree of microstructure in thawed soils increases as the temperature drops, according to the visualized pore structure. Besides, NMRI measurements of saturated soils are more accurate to reflect the full diameter range of pores, compared to MIP method.

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Section: Theoretical Background Of Nmri Analysismentioning

confidence: 99%

Pore Distribution Characteristics of Thawed Residual Soils in Artificial Frozen-Wall Using NMRI and MIP Measurements

Kong

2020

Applied Sciences

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“…where (T 2 ) total is the transverse relaxation time; (T 2 ) B is the bulk fluid relaxation time; (T 2 ) S is the surface relaxation time; and (T 2 ) D is the diffusion relaxation time (all in ms). Because the diffusion relaxation and bulk fluid relaxation times are negligible compared with the surface relaxation time, the total relaxation time of the rock depends on surface relaxation [28,38]. e surface relaxation is related to the specific surface area of rocks (the ratio of pore surface area to pore volume).…”

Section: Nmr Eorymentioning

confidence: 99%

“…Each has its own advantages and disadvantages. Mercury intrusion testing can analyze the pore throats of pore structures, but the pores and throats cannot be identified separately [28,29]. SEM can describe rock micropore structures but can only test a relatively small extent of the rock surface and so cannot provide overall pore structure information nor dynamically observe changes in pore structure.…”

Section: Introductionmentioning

confidence: 99%

NMR Experimental Study on Dynamic Process of Pore Structure and Damage Mechanism of Sandstones with Different Grain Sizes under Acid Erosion

Wang

et al. 2020

Shock and Vibration

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In many engineering projects, it is critical to consider the acid erosion of rock. This study investigates dynamic changes in pore structure and damage mechanisms in sandstones subjected to acid erosion. Specimens with three grain sizes were immersed in acid solution and tested by the nuclear magnetic resonance technique. Changes in solution pH, specimen mass and porosity, T2 spectrum distribution, and area were analyzed. Damage mechanisms are discussed, and relationships between porosity and acid erosion damage variables are established. The results show that acid erosion has significant effects on pore structure and erosion damage in sandstone. With increasing soaking time, new micropores formed in sandstone, while existing micropores and mesopores gradually expanded into macropores, causing the T2 spectrum distributions to change greatly. The porosity, acid erosion damage, and T2 spectral areas of sandstones with different grain sizes all increased gradually. Under acid erosion, sandstones became gradually weakened, but the effects varied greatly according to grain size. Pore structure changes and acid erosion damage were greatest in coarse-grained sandstone, followed by medium- and fine-grained sandstone.

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“…It is widely used in porosity calculations and permeability and movable fluid content evaluation. 14 , 17 The Mahu conglomerate reservoir has less ferromagnetic materials and larger particles, which is suitable for preparing large-size samples for testing, and NMR is an ideal method for testing its pore throat structure. The key to the test is to determine the conversion relationship between T 2 and the pore radius.…”

Section: Introductionmentioning

confidence: 99%

Pore Structure and Movable Fluid Characteristics of Typical Sedimentary Lithofacies in a Tight Conglomerate Reservoir, Mahu Depression, Northwest China

Yang

Gan

et al. 2021

ACS Omega

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The pore structure and movable fluid characteristics of tight conglomerate reservoirs are complex, which are greatly different from conventional reservoirs. The depositional mechanism is the fundamental factor controlling the physical properties of conglomerate reservoirs. However, there is a lack of systematic research on the pore structure and movable fluid characteristics of conglomerate reservoirs with typical sedimentary facies. This paper investigates the pore structure and movable fluid characteristics of conglomerate of different sedimentary facies based on various experiments. Casting thin sections, X-ray diffraction, scanning electron microscopy, high-pressure mercury injection, and nuclear magnetic resonance experiments were conducted on 32 conglomerates samples from the Mahu Sag, Junggar Basin, China. The quality classification method of tight conglomerate reservoirs is established. The results show that the conglomerate can be divided into three sedimentary facies; traction flow conglomerate (TFC) and pebbled sandstone (PSS) mainly develop intergranular pores and dissolved pores; and the pore diameter curves are mainly a double peak, single peak, and flat peak. Gravity flow conglomerate (GFC) mainly develops dissolved pores and interstitial micropores, and the pore diameter curve is mainly a single peak. PSS includes pebbled gritty sandstone (P(G)SS) and pebbled fine sandstone (P(F)SS). TFC and P(G)SS are favorable class I reservoirs, while GFC and P(F)SS are nonfavorable class II reservoirs. A new parameter, the ratio of the major axis to the minor axis of the pore outer ellipse (axial ratio), is proposed to quantitatively describe the compaction effect. The average axial ratios of the three lithofacies are 3.04, 3.98, and 8.78, respectively, indicating that the compaction is intensified and the pore structure becomes worse. By analyzing the correlation between pore structure parameters and permeability, it is found that the main controlling factors of permeability of GFC and TFC are sorting and connectivity, respectively, and the main flow radius is the most suitable parameter to describe permeability. A linear spectral decomposition method was used to establish a new quantitative calculation method of movable fluid saturation for different types of pores, and the results show that the movable fluid saturation of intergranular pores is the highest (average: 65.43%), and the movable fluid saturation of TFC and P(G)SS with more intergranular pores is the highest. Movable fluid saturation is inversely proportional to the content of I/S and the compaction rate and positively proportional to the content of quartz and feldspar and the cementation rate. The fluid mobility of water-wet samples is weaker. The research results provide theoretical support for the identification of favorable reservoirs and the cognition of a development mechanism.

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Contributions of pore-throat size distribution to reservoir quality and fluid distribution from NMR and MIP in tight sandy conglomerate reservoirs

Cited by 20 publications

References 22 publications

Pore Distribution Characteristics of Thawed Residual Soils in Artificial Frozen-Wall Using NMRI and MIP Measurements

Pore Distribution Characteristics of Thawed Residual Soils in Artificial Frozen-Wall Using NMRI and MIP Measurements

NMR Experimental Study on Dynamic Process of Pore Structure and Damage Mechanism of Sandstones with Different Grain Sizes under Acid Erosion

Pore Structure and Movable Fluid Characteristics of Typical Sedimentary Lithofacies in a Tight Conglomerate Reservoir, Mahu Depression, Northwest China

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