scholarly journals Impacts of Pore-Throat System on Fractal Characterization of Tight Sandstones

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-17 ◽  
Author(s):  
Dengke Liu ◽  
Zhaolin Gu ◽  
Ruixiang Liang ◽  
Junwei Su ◽  
Dazhong Ren ◽  
...  
Keyword(s):  
Experimental Data ◽  
Prediction Models ◽  
Dominant Role ◽  
Fractal Theory ◽  
Fractal Dimensions ◽  
Optical Observations ◽  
Reservoir Quality ◽  
Pore Throat ◽  
Tight Sandstone ◽  
Reservoir Type

The pore-throat structures play a dominant role in the evaluation of properties of tight sandstone, but it remains difficult to determine the related parameters and understand their impact on reservoir quality. Hence, toward this end, we analyze the experimental data that are indicative of the pore-throat system, then we investigate the effect of fractal dimensions of pore-throat structures on petrologic and physical properties, and finally, the optical observations, fractal theory, and prediction model were integrated to explore the qualities of various reservoir types in tight sandstones. The results show that the fractal dimensions of the mercury intrusion curve correspond to three pore-throat types and those of the mercury extrusion curve could correspond to two pore-throat types. Five types of reservoirs were identified, the best reservoir type has a high percentage of interparticle and dissolution pores but a low proportion of clay-related pores, and the differences in pore-throat connectivity of various types affect storage capacity significantly. The storage ability prediction models of various reservoir types are raised by integrated experimental data. This work employed a comprehensive fractal theory based on capillary pressure curves and helps to explore how pore-throat systems influence reservoir quality in tight sandstones.

scholarly journals A reservoir quality evaluation approach for tight sandstone reservoirs based on the gray correlation algorithm: A case study of the Chang 6 layer in the W area of the as oilfield, Ordos Basin

2021 ◽  
pp. 014459872199851
Author(s):  
Yuyang Liu ◽  
Xiaowei Zhang ◽  
Junfeng Shi ◽  
Wei Guo ◽  
Lixia Kang ◽  
...  
Keyword(s):  
Quality Evaluation ◽  
Comprehensive Evaluation ◽  
Ordos Basin ◽  
Reservoir Quality ◽  
Pore Throat ◽  
Tight Sandstone ◽  
Evaluation Approach ◽  
Correlation Algorithm ◽  
Gray Correlation ◽  
Sandstone Reservoir

As an important type of unconventional hydrocarbon, tight sandstone oil has great present and future resource potential. Reservoir quality evaluation is the basis of tight sandstone oil development. A comprehensive evaluation approach based on the gray correlation algorithm is established to effectively assess tight sandstone reservoir quality. Seven tight sandstone samples from the Chang 6 reservoir in the W area of the AS oilfield in the Ordos Basin are employed. First, the petrological and physical characteristics of the study area reservoir are briefly discussed through thin section observations, electron microscopy analysis, core physical property tests, and whole-rock and clay mineral content experiments. Second, the pore type, throat type and pore and throat combination characteristics are described from casting thin sections and scanning electron microscopy. Third, high-pressure mercury injection and nitrogen adsorption experiments are optimized to evaluate the characteristic parameters of pore throat distribution, micro- and nanopore throat frequency, permeability contribution and volume continuous distribution characteristics to quantitatively characterize the reservoir micro- and nanopores and throats. Then, the effective pore throat frequency specific gravity parameter of movable oil and the irreducible oil pore throat volume specific gravity parameter are introduced and combined with the reservoir physical properties, multipoint Brunauer-Emmett-Teller (BET) specific surface area, displacement pressure, maximum mercury saturation and mercury withdrawal efficiency parameters as the basic parameters for evaluation of tight sandstone reservoir quality. Finally, the weight coefficient of each parameter is calculated by the gray correlation method, and a reservoir comprehensive evaluation indicator (RCEI) is designed. The results show that the study area is dominated by types II and III tight sandstone reservoirs. In addition, the research method in this paper can be further extended to the evaluation of shale gas and other unconventional reservoirs after appropriate modification.

FRACTAL ANALYSIS OF GAS DIFFUSION IN POROUS NANOFIBERS

Fractals ◽  
2015 ◽  
Vol 23 (01) ◽  
pp. 1540011 ◽  
Author(s):  
BOQI XIAO ◽  
JINTU FAN ◽  
ZONGCHI WANG ◽  
XIN CAI ◽  
XIGE ZHAO
Keyword(s):  
Experimental Data ◽  
Fractal Dimension ◽  
Fractal Theory ◽  
Fractal Dimensions ◽  
Fractal Model ◽  
Gas Diffusion ◽  
Physical Mechanisms ◽  
Gas Diffusivity ◽  
Model Predictions ◽  
Good Agreement

In this study, with the consideration of pore size distribution and tortuosity of capillaries, the analytical model for gas diffusivity of porous nanofibers is derived based on fractal theory. The proposed fractal model for the normalized gas diffusivity (De/D0) is found to be a function of the porosity, the area fractal dimensions of pore and the fractal dimension of tortuous capillaries. It is found that the normalized gas diffusivity decreases with increasing of the tortuosity fractal dimension. However, the normalized gas diffusivity is positively correlated with the porosity. The prediction of the proposed fractal model for porous nanofibers with porosity less than 0.75 is highly consistent with the experimental and analytical results found in the literature. The model predictions are compared with the previously reported experimental data, and are in good agreement between the model predictions and experimental data is found. The validity of the present model is thus verified. Every parameter of the proposed formula of calculating the normalized gas diffusivity has clear physical meaning. The proposed fractal model can reveal the physical mechanisms of gas diffusion in porous nanofibers.

scholarly journals Analysis of pore throat characteristics of tight sandstone reservoirs

2020 ◽  
Vol 12 (1) ◽  
pp. 977-989
Author(s):  
Xinli Zhao ◽  
Zhengming Yang ◽  
Xuewei Liu ◽  
Zhiyuan Wang ◽  
Yutian Luo
Keyword(s):  
Fractal Dimension ◽  
Fractal Theory ◽  
Pressure Curve ◽  
Tight Oil ◽  
Pore Throat ◽  
Tight Sandstone ◽  
Throat Radius ◽  
Testing Technology ◽  
Fractal Characteristics ◽  
Effective Development

AbstractThe characterization of pore throat structure in tight reservoirs is the basis for the effective development of tight oil. In order to effectively characterize the pore -throat structure of tight sandstone in E Basin, China, this study used high-pressure mercury intrusion (HPMI) testing technology and thin section (TS) technology to jointly explore the characteristics of tight oil pore throat structure. The results of the TS test show that there are many types of pores in the tight sandstone, mainly the primary intergranular pores, dissolved pores, and microfractures. Based on the pore throat parameters obtained by HPMI experiments, the pore throat radius of tight sandstone is between 0.0035 and 2.6158 µm. There are two peaks in the pore throat distribution curve, indicating that the tight sandstone contains at least two types of pores. This is consistent with the results of the TS experiments. In addition, based on the fractal theory and obtained capillary pressure curve by HPMI experiments, the fractal characteristics of tight sandstone pore throat are quantitatively characterized. The results show that the tight sandstones in E Basin have piecewise fractal (multifractal) features. The segmentation fractal feature occurs at a pore throat radius of approximately 0.06 µm. Therefore, according to the fractal characteristics, the tight sandstone pore throat of the study block is divided into macropores (pore throat radius > 0.06 µm) and micropores (pore throat radius < 0.06 µm). The fractal dimension DL of the macropores is larger than the fractal dimension DS of the micropores, indicating that the surface of the macropores is rough and the pores are irregular. This study cannot only provide certain support for characterizing the size of tight oil pore throat, but also plays an inspiring role in understanding the tight pore structure of tight sandstone.

Evaluation of the matrix influence on the microscopic pore-throat structures of deep-water tight sandstone: A case study from the Upper Triassic Chang 6 oil group of the Yanchang Formation in the Huaqing area, Ordos Basin, China

2020 ◽  
Vol 8 (4) ◽  
pp. T763-T776
Author(s):  
Zhaobing Chen ◽  
Chuangfei Zhou ◽  
Xinjing Chen ◽  
Yujie Zhu ◽  
Yushuang Zhu
Keyword(s):  
Deep Water ◽  
Ordos Basin ◽  
Fractal Dimensions ◽  
Crystal Form ◽  
Pore Throat ◽  
Tight Sandstone ◽  
Clastic Rocks ◽  
The Matrix ◽  
Intercrystalline Pores

Former studies have suggested that the matrix of clastic rocks is unfavorable for the storage-percolation of reservoirs. However, the contribution of the matrix to the microscopic pore-throat structures in deep-water tight sandstone cannot be ignored. Aiming at the deep-water tight sandstone of the Chang 6 reservoir in the Ordos Basin (China), we have evaluated the characteristics of the matrix and the secondary pores in the matrix based on a multiscale microscopic identification and testing method, to reveal the influence of the matrix on the types, distribution, and heterogeneity of the pore throats. The results show that, unlike cements, the composition of the matrix is complex, characterized by its poor crystal form with no cement generation relationship. The structure of the matrix components is not completely dense. Intercrystalline pores and dissolved matrix pores are developed in the matrix after diagenetic modification, with a pore diameter of 20–1000 nm. These pores form a complex matrix secondary pore network. The matrix controls the number and volume of 0–1 μm pore throats. The matrix is constructive to the distribution of pore throats when its content is ≤7%. This positive effect gradually decreases with the increase of the matrix content, intensifying the compaction of the reservoir. The matrix controls the heterogeneities of the pore throat structures in deep-water tight sandstone. Large pore throats are gradually separated and disintegrated into a large number of micro-/nanopores by the matrix with the increase of the matrix content. Meanwhile, the fractal dimensions approached 3, increasing the complexity of the pore structures. Therefore, the matrix is favorable and unfavorable to the microscopic pore throat structures of the reservoir. The matrix not only results in the loss of intergranular pores but also generates a large number of secondary micro-/nanopore throat networks with complex structures, constituting an effective space for hydrocarbon accumulation and percolation in deep-water tight sandstone.

MODELING FOR HYDRAULIC PERMEABILITY AND KOZENY–CARMAN CONSTANT OF POROUS NANOFIBERS USING A FRACTAL APPROACH

Fractals ◽  
2015 ◽  
Vol 23 (03) ◽  
pp. 1550029 ◽  
Author(s):  
BOQI XIAO ◽  
XING TU ◽  
WEN REN ◽  
ZONGCHI WANG
Keyword(s):  
Experimental Data ◽  
Present Model ◽  
Fractal Theory ◽  
Fractal Dimensions ◽  
Hydraulic Permeability ◽  
Fractal Approach ◽  
Microstructural Parameters ◽  
Fractal Models ◽  
Model Predictions ◽  
Analytical Expressions

In this study, the analytical expressions for the hydraulic permeability and Kozeny–Carman (KC) constant of porous nanofibers are derived based on fractal theory. In the present approach, the permeability is explicitly related to the porosity and the area fractal dimensions of porous nanofibers. The proposed fractal models for KC constant is also found to be a function of the microstructural parameters (porosity, area fractal dimensions). Besides, the present model clearly indicates that KC constant is not a constant and increases with porosity. However, KC constant is close to a constant value which is 18 for ϕ > 0.8. Every parameter of the proposed formulas of calculating permeability and KC constant has clear physical meaning. The model predictions are compared with the existing experimental data, and fair agreement between the model predictions and experimental data is found for different porosities.

scholarly journals Dynamic characteristics and fractal representations of crack propagation of rock with different fissures under multiple impact loadings

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Bing Sun ◽  
Shun Liu ◽  
Sheng Zeng ◽  
Shanyong Wang ◽  
Shaoping Wang
Keyword(s):  
Fractal Dimension ◽  
Crack Propagation ◽  
Crack Growth ◽  
Impact Test ◽  
Fractal Theory ◽  
Dynamic Change ◽  
Fractal Dimensions ◽  
Peak Stress ◽  
Dynamic Mechanical Properties ◽  
Gravitational Potential Energy

AbstractTo investigate the influence of the fissure morphology on the dynamic mechanical properties of the rock and the crack propagation, a drop hammer impact test device was used to conduct impact failure tests on sandstones with different fissure numbers and fissure dips, simultaneously recorded the crack growth after each impact. The box fractal dimension is used to quantitatively analyze the dynamic change in the sandstone cracks and a fractal model of crack growth over time is established based on fractal theory. The results demonstrate that under impact test conditions of the same mass and different heights, the energy absorbed by sandstone accounts for about 26.7% of the gravitational potential energy. But at the same height and different mass, the energy absorbed by the sandstone accounts for about 68.6% of the total energy. As the fissure dip increases and the number of fissures increases, the dynamic peak stress and dynamic elastic modulus of the fractured sandstone gradually decrease. The fractal dimensions of crack evolution tend to increase with time as a whole and assume as a parabolic. Except for one fissure, 60° and 90° specimens, with the extension of time, the increase rate of fractal dimension is decreasing correspondingly.

scholarly journals Revisiting Kelvin equation and Peng–Robinson equation of state for accurate modeling of hydrocarbon phase behavior in nano capillaries

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Ilyas Al-Kindi ◽  
Tayfun Babadagli
Keyword(s):  
Experimental Data ◽  
Surface Tension ◽  
Equation Of State ◽  
Phase Behavior ◽  
Pore Radius ◽  
Microfluidic Chips ◽  
Tight Sandstone ◽  
Kelvin Equation ◽  
Rock Samples ◽  
Robinson Equation

AbstractThe thermodynamics of fluids in confined (capillary) media is different from the bulk conditions due to the effects of the surface tension, wettability, and pore radius as described by the classical Kelvin equation. This study provides experimental data showing the deviation of propane vapour pressures in capillary media from the bulk conditions. Comparisons were also made with the vapour pressures calculated by the Peng–Robinson equation-of-state (PR-EOS). While the propane vapour pressures measured using synthetic capillary medium models (Hele–Shaw cells and microfluidic chips) were comparable with those measured at bulk conditions, the measured vapour pressures in the rock samples (sandstone, limestone, tight sandstone, and shale) were 15% (on average) less than those modelled by PR-EOS.

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