Parametric Investigation of Shale Gas Production Considering Nano-Scale Pore Size Distribution, Formation Factor, and Non-Darcy Flow Mechanisms

Effect of nanoscale pore size distribution (PSD) on shale gas production is one of the challenges to be addressed by the industry. An improved approach to study multi-scale real gas transport in fractal shale rocks is proposed to bridge nanoscale PSD and gas filed production. This approach is well validated with field tests. Results indicate the gas production is underestimated without considering a nanoscale PSD. A PSD with a larger fractal dimension in pore size and variance yields a higher fraction of large pores; this leads to a better gas transport capacity; this is owing to a higher free gas transport ratio. A PSD with a smaller fractal dimension yields a lower cumulative gas production; this is because a smaller fractal dimension results in the reduction of gas transport efficiency. With an increase in the fractal dimension in pore size and variance, an apparent permeability-shifting effect is less obvious, and the sensitivity of this effect to a nanoscale PSD is also impaired. Higher fractal dimensions and variances result in higher cumulative gas production and a lower sensitivity of gas production to a nanoscale PSD, which is due to a better gas transport efficiency. The shale apparent permeability-shifting effect to nanoscale is more sensitive to a nanoscale PSD under a higher initial reservoir pressure, which makes gas production more sensitive to a nanoscale PSD. The findings of this study can help to better understand the influence of a nanoscale PSD on gas flow capacity and gas production.

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Review of Formation and Gas Characteristics in Shale Gas Reservoirs

Energies ◽

10.3390/en13205427 ◽

2020 ◽

Vol 13 (20) ◽

pp. 5427

Author(s):

Boning Zhang ◽

Baochao Shan ◽

Yulong Zhao ◽

Liehui Zhang

Keyword(s):

Pore Size Distribution ◽

Pore Size ◽

Size Distribution ◽

Shale Gas ◽

Physical Parameters ◽

Gas Reservoirs ◽

Shale Formations ◽

Adsorbed Gas ◽

Shale Gas Reservoirs ◽

Longmaxi Shale

An accurate understanding of formation and gas properties is crucial to the efficient development of shale gas resources. As one kind of unconventional energy, shale gas shows significant differences from conventional energy ones in terms of gas accumulation processes, pore structure characteristics, gas storage forms, physical parameters, and reservoir production modes. Traditional experimental techniques could not satisfy the need to capture the microscopic characteristics of pores and throats in shale plays. In this review, the uniqueness of shale gas reservoirs is elaborated from the perspective of: (1) geological and pore structural characteristics, (2) adsorption/desorption laws, and (3) differences in properties between the adsorbed gas and free gas. As to the first aspect, the mineral composition and organic geochemical characteristics of shale samples from the Longmaxi Formation, Sichuan Basin, China were measured and analyzed based on the experimental results. Principles of different methods to test pore size distribution in shale formations are introduced, after which the results of pore size distribution of samples from the Longmaxi shale are given. Based on the geological understanding of shale formations, three different types of shale gas and respective modeling methods are reviewed. Afterwards, the conventional adsorption models, Gibbs excess adsorption behaviors, and supercritical adsorption characteristics, as well as their applicability to engineering problems, are introduced. Finally, six methods of calculating virtual saturated vapor pressure, seven methods of giving adsorbed gas density, and 12 methods of calculating gas viscosity in different pressure and temperature conditions are collected and compared, with the recommended methods given after a comparison.

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Evaluation of Pore Size Distribution Effects on Phase Behavior of Hydrocarbons Produced in Shale Gas Condensate Reservoirs

10.2118/183833-ms ◽

2017 ◽

Cited By ~ 4

Author(s):

Baoyan Li ◽

Alberto Mezzatesta

Keyword(s):

Pore Size Distribution ◽

Phase Behavior ◽

Pore Size ◽

Size Distribution ◽

Shale Gas ◽

Gas Condensate ◽

Gas Condensate Reservoirs

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Probe material choice for nuclear magnetic resonance cryoporometry (NMRC) measurements of the nano-scale pore size distribution of unconventional reservoirs

Energy Exploration & Exploitation ◽

10.1177/0144598718802475 ◽

2018 ◽

Vol 37 (1) ◽

pp. 412-428

Author(s):

Feng Zhu ◽

Wenxuan Hu ◽

Jian Cao ◽

Biao Liu ◽

Yifeng Liu ◽

...

Keyword(s):

Nuclear Magnetic Resonance ◽

Magnetic Resonance ◽

Pore Size Distribution ◽

Porous Materials ◽

Pore Size ◽

Size Distribution ◽

Geological Samples ◽

Nano Scale ◽

Chloride Hexahydrate ◽

Nuclear Magnetic

Nuclear magnetic resonance cryoporometry is a newly developed technique that can characterize the pore size distribution of nano-scale porous materials. To date, this technique has scarcely been used for the testing of unconventional oil and gas reservoirs; thus, their micro- and nano-scale pore structures must still be investigated. The selection of the probe material for this technique has a key impact on the quality of the measurement results during the testing of geological samples. In this paper, we present details on the nuclear magnetic resonance cryoporometric procedure. Several types of probe materials were compared during the nuclear testing of standard nano-scale porous materials and unconventional reservoir geological samples from Sichuan Basin, Southwest China. Gas sorption experiments were also carried out on the same samples simultaneously. The KGT values of the probe materials octamethylcyclotetrasiloxane and calcium chloride hexahydrate were calibrated using standard nano-scale porous materials to reveal respective values of 149.3 Knm and 184 Knm. Water did not successfully wet the pore surfaces of the standard controlled pore glass samples; moreover, water damaged the pore structures of the geological samples, which was confirmed during two freeze-melting tests. The complex phase transition during the melting of cyclohexane introduced a nuclear magnetic resonance signal in addition to that from liquid in the pores, which led to an imprecise characterization of the pore size distribution. Octamethylcyclotetrasiloxane and calcium chloride hexahydrate have been rarely employed as nuclear magnetic resonance cryoporometric probe materials for the testing of an unconventional reservoir. Both of these materials were able to characterize pore sizes up to 1 μm, and they were more applicable than either water or cyclohexane.

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Pore size distribution in shale gas deposits based on adsorption isotherm analyses

Nafta-Gaz ◽

10.18668/ng.2016.08.03 ◽

2016 ◽

Vol 8 ◽

pp. 603-609 ◽

Cited By ~ 3

Author(s):

Lidia Dudek ◽

Keyword(s):

Adsorption Isotherm ◽

Pore Size Distribution ◽

Pore Size ◽

Size Distribution ◽

Shale Gas

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Salinity dependence of the complex surface conductivity of the Portland sandstone

Geophysics ◽

10.1190/geo2015-0426.1 ◽

2016 ◽

Vol 81 (2) ◽

pp. D125-D140 ◽

Cited By ~ 26

Author(s):

Qifei Niu ◽

André Revil ◽

Milad Saidian

Keyword(s):

Relaxation Time ◽

Pore Size Distribution ◽

Pore Size ◽

Size Distribution ◽

Pore Space ◽

Complex Surface ◽

Surface Conductivity ◽

Formation Factor ◽

Polarization Model ◽

Fluid Conductivity

Induced polarization can be used to estimate surface conductivity by assuming a universal linear relationship between the surface and quadrature conductivities of porous media. However, this assumption has not yet been justified for conditions covering a broad range of fluid conductivities. We have performed complex conductivity measurements on Portland sandstone, an illite- and kaolinite-rich sandstone, at 13 different water salinities (NaCl) over the frequency range of 0.1 Hz to 45 kHz. The conductivity of the pore water [Formula: see text] affected the complex surface conductivity mainly by changing the tortuosity of the conduction paths in the pore network from high to low salinities. As the fluid conductivity decreases, the magnitude of the surface conductivity and quadrature conductivity was observed to decrease. At relatively high salinities ([Formula: see text]), the ratio between the surface conductivity and quadrature conductivity was roughly constant. At low salinities ([Formula: see text]), the ratio decreased slightly with the decrease of the salinity. A Stern layer polarization model was combined with the differential effective medium (DEM) theory to describe this behavior. The tortuosity entering the complex surface conductivity was salinity dependent following the prediction of the DEM theory. At high salinity, it reached the value of the bulk tortuosity of the pore space given by the product of the intrinsic formation factor and the connected porosity. The relaxation time distributions were also obtained at different salinities by inverting the measured spectra using a Warburg decomposition. The mode of the relaxation time probability distribution found a small but clear dependence on the salinity. This salinity dependence can be explained by considering the ions exchange between Stern and diffuse layers during polarization of the former. The pore-size distribution obtained from the distribution of the relaxation time agreed with the pore-size distribution from nuclear magnetic resonance measurements.

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