A new empirical method for constructing capillary pressure curves from conventional logs in low-permeability sandstones

Feng, Cheng; Shi, Yuqing; Li, Jiahong; Chang, Liang-Cheng; Li, Gao‐Ren; Mao, Zhiqiang

doi:10.1007/s12583-016-0913-6

“…According to basement property, tectonic evolution, and current tectonic pattern of the basin, it can be divided into 6 first-order tectonic units (Figure 1(b)). The internal structure is relatively simple with a stable formation and the inclination angle less than 1°g enerally, while the disrupted fold is relatively developed along the margin of the basin [23][24][25]. The study area is at the lower-middle parts of the border between Tianhuan depression and North Shaanxi slope, which extends from Dingbian county in the north to Zhenyuan county in the south and stretches from Mahuang mountain in the west to Youfangzhuang village in the east across the Tianhuan depression tectonic belt (Figure 1(b)).…”

Section: Methodsmentioning

confidence: 99%

Estimation of the Resistivity Index via Nuclear Magnetic Resonance Log Data Based on Fractal Theory

Feng

¹

,

Han

²

,

Duan

³

et al. 2020

Geofluids

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The resistivity index is an important parameter for determining the rock saturation index. However, the saturation index changes greatly in unconventional reservoirs, which leads to oil saturation estimation with great difficulty. Hence, we try to establish the relationship between the resistivity index and log data. Firstly, a novel model of estimating the resistivity index with T 2 time was derived based on fractal theory, the relationship between nuclear magnetic resonance (NMR) T 2 spectrum and capillary pressure curve ( T 2 - P c ), and Archie formula. It regards the logarithm of the resistivity index as the dependent variable, with T 2 time and T 2 time when water saturation is 100% as the independent variables. Second, 17 cores were drilled, and T 2 spectrum and the relationship between the resistivity index and water saturation ( I r - S w ) were jointly measured. Next, the experimental results were substituted into the established model to get the model parameters via the multivariate statistics regression method. Then, the experimental data engaged and not engaged in modeling were used to test the established model. The average relative errors of estimated resistivity indices and experimental results are smaller than 8%, and those of the regressed saturation index are smaller than 5%. Finally, the established model was applied in log data processing and interpretation with good effects. It thus proves that the method of the estimating resistivity index with T 2 time is reliable, which provides a novel solution for determining rock electrical parameter of unconventional reservoirs.

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“…8,9 With the improvement and development of experimental methods, research of microscopic pore structures in reservoirs has gradually transitioned from basic physical analysis to advanced experimental tests and methods. [18][19][20] Ideal results cannot be achieved by a single technological method because of the lithology of tight oil reservoirs, diversity, and heterogeneity of rock pores and the limitation of experimental methods. However, each technique has advantages and disadvantages.…”

Section: Introductionmentioning

confidence: 99%

“…Moreover, high-pressure mercury injection experiments require drying of the samples, which alters the porosity, permeability, and fabric of samples with high clay contents. [18][19][20] Ideal results cannot be achieved by a single technological method because of the lithology of tight oil reservoirs, diversity, and heterogeneity of rock pores and the limitation of experimental methods. 21,22 Although there has been much research characterizing the pore structure of tight oil reservoirs, the contribution of different pore throat types toward the reservoir accumulation capacity and producing degree has been ignored for the most part.…”

Section: Introductionmentioning

confidence: 99%

Influence of micro‐pore structure in tight sandstone reservoir on the seepage and water‐drive producing mechanism—a case study from Chang 6 reservoir in Huaqing area of Ordos basin

Ren

¹

,

Li

²

,

Fu

³

et al. 2019

Energy Science & Engineering

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To study the influence of pore structure on the seepage and water‐drive producing mechanisms, various methods were combined to describe the micro‐pore structure in the Chang 6 tight sandstone reservoir in the Huaqing area, Ordos Basin, China. Nuclear magnetic resonance (NMR) was combined with displacement experiments to determine the distribution of oil and water in pores of different scales before and after water flooding. There are few micro pores in the reservoir. As permeability increases, the distribution of nano pores decreases, while sub‐micro pores increase. Also, sub‐micro pores are the main pathway within the reservoir. There is a negative power function correlation between the minimum starting pressure gradient of the oil (Swc) and maximum throat radius. Also, with a decrease of permeability, smaller pore throats become more abundant and the nonlinear section of the flow velocity‐differential pressure curves increase. There is a large amount of crude oil gathering in the nano pores. As permeability increases, the main sources of movable oil are from the nano pores (kg < 0.4 × 10−3 μm2), sub‐micro pores (kg ≈ 0.4 × 10−3 μm2‐1.0 × 10−3 μm2), and micro pores (kg > 1.0 × 10−3 μm2). Displacement efficiency is always the highest in sub‐micro pores.

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“…Scanning electron microscopy (SEM) is a useful tool for studying microcracks and macropores, particularly in the size range between 100 nm and 10 μm. Nano CT-scans, field emission scanning electron microscopy (FESEM) and focused ion beam scanning electron microscopy (FIB-SEM) are also used to qualitatively observe the pore types and sizes. − The pore size distributions, volumes, and specific surface areas can be characterized by techniques such as mercury injection capillary pressure (MICP), high-pressure mercury injection (HPMI), nuclear magnetic resonance (NMR), and low-temperature N 2 and CO 2 adsorption. − MICP is the most traditional and widely used approach for pore volume measurements. NMR measurements have been extensively used in the petroleum industry to provide lithology-independent estimates of porosity, pore-size distribution, rock permeability, and fluid saturations. , Low-pressure adsorption (N 2 and CO 2 ) should be combined with MICP to determine the entire pore size spectrum of a tight reservoir, because of the variable access of the probe molecules (N 2 and CO 2 ) at measurement temperatures and pressures …”

Section: Introductionmentioning

confidence: 99%

Investigation of Pore Characteristics and Irreducible Water Saturation of Tight Reservoir Using Experimental and Theoretical Methods

Lai

¹

,

Li

²

,

Zhang

³

et al. 2018

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Characterizing pore structure is one of the most fundamental tasks in reservoir characterization; it is closely related to the calculation/interpretation of other critical parameters, such as permeability and capillary pressure. High-pressure mercury injection (HPMI), a low-pressure nitrogen gas adsorption (LP-N2GA), specific surface area (SSA) analysis, nuclear magnetic resonance (NMR), and fractal theory were used to study the pore structure characteristics and irreducible water saturation of tight reservoir samples from the Chang 7 formation in Ordos Basin, China. In this study, pores are mainly composed of mesopores and macropores. HPMI is more likely to detect macropores, while the distribution of mesopores is better characterized by LP-N2GA and SSA analysis. The capillary curves obtained by HPMI experiments are divided into two categories. The adsorption–desorption isotherms are divided into two groups, according to the rate of change of the desorption curve when the relative pressure is 0.5. The permeability contribution rate of different pore radius was studied through different methods, and the results showed the combination of HPMI and LP-N2GA can describe the microscopic pore structure of a reservoir more comprehensively than either method alone. The irreducible water saturation obtained by NMR test is greater than the irreducible water saturation obtained by HPMI. An irreducible water saturation model was established based on fractal theory and the capillary bundle model. The factors affecting the irreducible water saturation were fractal dimension, maximum connected pore throat radius, minimum pore throat radius, and thickness of the water film. The calculation results are closer to the experimental value when the fractal dimension is greater than 2.7. This comprehensive application of various experimental and theoretical methods gives a better understanding of the pore structure characteristics and fluid distribution in tight reservoir samples.

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A new empirical method for constructing capillary pressure curves from conventional logs in low-permeability sandstones

Cited by 11 publications

References 10 publications

Estimation of the Resistivity Index via Nuclear Magnetic Resonance Log Data Based on Fractal Theory

Estimation of the Resistivity Index via Nuclear Magnetic Resonance Log Data Based on Fractal Theory

Influence of micro‐pore structure in tight sandstone reservoir on the seepage and water‐drive producing mechanism—a case study from Chang 6 reservoir in Huaqing area of Ordos basin

Investigation of Pore Characteristics and Irreducible Water Saturation of Tight Reservoir Using Experimental and Theoretical Methods

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