Stress-Dependent Porosity and Permeability of Porous Rocks Represented by a Mechanistic Elastic Cylindrical Pore-Shell Model

2019 ◽  
Vol 129 (3) ◽  
pp. 885-899 ◽  
Author(s):  
Faruk Civan
Keyword(s):  
Shell Model ◽  
Porous Rocks ◽  
Cylindrical Pore ◽  
Porosity And Permeability ◽  
Stress Dependent

Compressibility, Porosity, and Permeability of Shales Involving Stress Shock and Loading/Unloading Hysteresis

SPE Journal ◽  
2019 ◽  
Vol 24 (06) ◽  
pp. 2458-2481 ◽  
Author(s):  
Faruk Civan
Keyword(s):  
Kinetic Model ◽  
Shell Model ◽  
Effective Stress ◽  
Hysteresis Phenomenon ◽  
Universal Method ◽  
Cylindrical Pore ◽  
Porosity And Permeability ◽  
Slope Discontinuity ◽  
Stress Dependent ◽  
Stress Shock

Summary This paper presents the theory, formulation, and correlation of the compressibility, porosity, and permeability of shale reservoirs by considering the effects of stress shock causing a slope discontinuity and loading/unloading hysteresis. The slope discontinuity occurs because the relative contributions of the matrix or fracture change at a critical effective stress depending on whether the process is loading or unloading. The hysteresis phenomenon occurs because of partially reversible and irreversible deformations of the various shale rock constituents by various processes during loading and unloading. Two successful modeling approaches are developed for describing the stress dependency of the petrophysical properties of porous rock formations. The first approach implements a kinetic model leading to a modified power–law equation, and the second approach applies an elastic cylindrical pore–shell model leading to a semianalytical equation. The primary advantage of the kinetic model is its applicability to any stress–dependent property, including strain, void ratio, porosity, pore compressibility, and permeability, thus making it a universal method. The semianalytical equation derived from an elastic cylindrical pore–shell model is applicable only for correlation of permeability. Both approaches are shown to yield high–quality correlations of the properties of porous rocks with effective stress by honoring the slope discontinuity observed at a critical effective stress.

scholarly journals Structural control on fluid flow and shallow diagenesis: insights from calcite cementation along deformation bands in porous sandstones

Solid Earth ◽  
2020 ◽  
Vol 11 (6) ◽  
pp. 2169-2195
Author(s):  
Leonardo Del Sole ◽  
Marco Antonellini ◽  
Roger Soliva ◽  
Gregory Ballas ◽  
Fabrizio Balsamo ◽  
...  
Keyword(s):  
Fluid Flow ◽  
Structural Control ◽  
Control Flow ◽  
Porous Rocks ◽  
Deformation Bands ◽  
Seismic Resolution ◽  
Porous Sandstone ◽  
Reservoir Compartmentalization ◽  
Porosity And Permeability ◽  
And Control

Abstract. Porous sandstones are important reservoirs for geofluids. Interaction therein between deformation and cementation during diagenesis is critical since both processes can strongly reduce rock porosity and permeability, deteriorating reservoir quality. Deformation bands and fault-related diagenetic bodies, here called “structural and diagenetic heterogeneities”, affect fluid flow at a range of scales and potentially lead to reservoir compartmentalization, influencing flow buffering and sealing during the production of geofluids. We present two field-based studies from Loiano (northern Apennines, Italy) and Bollène (Provence, France) that elucidate the structural control exerted by deformation bands on fluid flow and diagenesis recorded by calcite nodules associated with the bands. We relied on careful in situ observations through geo-photography, string mapping, and unmanned aerial vehicle (UAV) photography integrated with optical, scanning electron and cathodoluminescence microscopy, and stable isotope (δ13C and δ18O) analysis of nodules cement. In both case studies, one or more sets of deformation bands precede and control selective cement precipitation. Cement texture, cathodoluminescence patterns, and their isotopic composition suggest precipitation from meteoric fluids. In Loiano, deformation bands acted as low-permeability baffles to fluid flow and promoted selective cement precipitation. In Bollène, clusters of deformation bands restricted fluid flow and focused diagenesis to parallel-to-band compartments. Our work shows that deformation bands control flow patterns within a porous sandstone reservoir and this, in turn, affects how diagenetic heterogeneities are distributed within the porous rocks. This information is invaluable to assess the uncertainties in reservoir petrophysical properties, especially where structural and diagenetic heterogeneities are below seismic resolution.

Analysis of Effective Porosity and Effective Permeability in Shale-Gas Reservoirs With Consideration of Gas Adsorption and Stress Effects

SPE Journal ◽  
2017 ◽  
Vol 22 (06) ◽  
pp. 1739-1759 ◽  
Author(s):  
Y.. Pang ◽  
M. Y. Soliman ◽  
H.. Deng ◽  
Hossein Emadi
Keyword(s):  
Pore Pressure ◽  
Shale Gas ◽  
Gas Adsorption ◽  
Effective Porosity ◽  
Gas Production ◽  
Gas Reservoirs ◽  
Adsorption Effect ◽  
Shale Gas Reservoirs ◽  
Porosity And Permeability ◽  
Stress Dependent

Summary Nanoscale porosity and permeability play important roles in the characterization of shale-gas reservoirs and predicting shale-gas-production behavior. The gas adsorption and stress effects are two crucial parameters that should be considered in shale rocks. Although stress-dependent porosity and permeability models have been introduced and applied to calculate effective porosity and permeability, the adsorption effect specified as pore volume (PV) occupied by adsorbate is not properly accounted. Generally, gas adsorption results in significant reduction of nanoscale porosity and permeability in shale-gas reservoirs because the PV is occupied by layers of adsorbed-gas molecules. In this paper, correlations of effective porosity and permeability with the consideration of combining effects of gas adsorption and stress are developed for shale. For the adsorption effect, methane-adsorption capacity of shale rocks is measured on five shale-core samples in the laboratory by use of the gravimetric method. Methane-adsorption capacity is evaluated through performing regression analysis on Gibbs adsorption data from experimental measurements by use of the modified Dubinin-Astakhov (D-A) equation (Sakurovs et al. 2007) under the supercritical condition, from which the density of adsorbate is found. In addition, the Gibbs adsorption data are converted to absolute adsorption data to determine the volume of adsorbate. Furthermore, the stress-dependent porosity and permeability are calculated by use of McKee correlations (McKee et al. 1988) with the experimentally measured constant pore compressibility by use of the nonadsorptive-gas-expansion method. The developed correlations illustrating the changes in porosity and permeability with pore pressure in shale are similar to those produced by the Shi and Durucan model (2005), which represents the decline of porosity and permeability with the increase of pore pressure in the coalbed. The tendency of porosity and permeability change is the inverse of the common stress-dependent regulation that porosity and permeability increase with the increase of pore pressure. Here, the gas-adsorption effect has a larger influence on PV than stress effect does, which is because more gas is attempting to adsorb on the surface of the matrix as pore pressure increases. Furthermore, the developed correlations are added into a numerical-simulation model at field scale, which successfully matches production data from a horizontal well with multistage hydraulic fractures in the Barnett Shale reservoir. The simulation results note that without considering the effect of PV occupied by adsorbed gas, characterization of reservoir properties and prediction of gas production by history matching cannot be performed reliably. The purpose of this study is to introduce a model to calculate the volume of the adsorbed phase through the adsorption isotherm and propose correlations of effective porosity and permeability in shale rocks, including the consideration of the effects of both gas adsorption and stress. In addition, practical application of the developed correlations to reservoir-simulation work might achieve an appropriate evaluation of effective porosity and permeability and provide an accurate estimation of gas production in shale-gas reservoirs.

scholarly journals Deformation Bands and Associated FIP Characteristics From High-Porous Triassic Reservoirs in the Tarim Basin, NW China: A Multiscale Analysis

2021 ◽  
Vol 9 ◽  
Author(s):  
Wenyuan Yan ◽  
Ming Zha ◽  
Jiangxiu Qu ◽  
Xiujian Ding ◽  
Qinglan Zhang
Keyword(s):  
Thin Section ◽  
Oil And Gas ◽  
Fluid Dynamic ◽  
Shear Bands ◽  
Raman Laser ◽  
Homogenization Temperature ◽  
High Porosity ◽  
Porous Rocks ◽  
Deformation Bands ◽  
Porosity And Permeability

Deformation bands are widely formed and distributed in Triassic high-porous rocks as a result of multistage tectonic movement. In this research, core observation, the rock thin section (fluorescence and casting thin section), FIB-SEM, X-ray diffraction, Raman laser, and thermometry of fluid inclusions were employed to describe the macro- and micro characteristics of deformation bands and their associated relationship with microfractures. Results indicate that the main types of deformation bands formed in the Lunnan Triassic high-porosity sandstone during the Yanshanian and Himalayan periods under different temperature and pressure conditions are compaction shear bands, and their quantity increases evidently with the distance of thrust faults. The density of deformation bands near the fault is about 15/m; porosity and permeability decrease sharply compared with those of the host rock. Microscopically, two obtained fluid-inclusion planes (FIPs) can be distinguished as 51 samples collected from 12 wells by the cutting relationship and mechanical characteristics. The homogenization temperature of associated aqueous inclusion is generally characterized by two peaks, mainly 70–80°C and 110–120°C, which were formed in the Late Yanshanian and Late Himalayan periods. The formation period of deformation bands induced by the intragranular microfractures improved the reservoir seepage capacity. In the later stage, as the interlayer and barrier with low porosity and low permeability affects the distribution of oil and gas, which is an important factor in this study of the local fluid dynamic field and high-quality reservoir evolution distribution.

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