The effective pressure law for permeability of clay-rich sandstones

The permeability k of porous rocks is known to vary with confining pressure pc and pore fluid pressure pf. But it is, in principle, possible to replace the two‐variable function k(pf, pc) by a function k(peff) of a single variable, peff(pf, pc), called the effective pressure. Our goal in this paper is to establish an experimental method for determining a possibly nonlinear, effective pressure law (EPL) for permeability, i.e., find the function κs(pf, pc) such that the effective pressure is given by peff = pc − κs(pf, pc) pf. We applied this method to a set of 26 sandstone cores from various hydrocarbon reservoirs in China. We found that κs greatly varied, from sample to sample, in magnitude and range, sometimes even reaching theoretically prohibited values (i.e., greater than 1 or lower than porosity). One interesting feature of κs(pf, pc) is that it could be approximately described in all rocks but one as a decreasing function κs(pc − pf) of Terzaghi's differential pressure. We also investigated the dependence of permeability on peff for each of our samples. Three models from the literature, i.e., exponential (E), power law (P), and the Walsh model (W), were tested. The (W) model was more likely to fit the experimental data of cores with a high pressure dependence of permeability whereas (E) occurred more frequently in low‐pressure‐sensitive rocks. Finally, we made various types of two‐ and three‐dimensional microstructural observations that generally supported the trend mentioned above.

show abstract

“…However, extrapolation can be avoided via a method recently proposed by Zhao et al . []. The method is sketched in Figure .…”

Section: Nonlinear Effective Pressure Lawmentioning

confidence: 99%

Nonlinear effective pressure law for permeability

Xiao

Bernabé

et al. 2014

JGR Solid Earth

View full text Add to dashboard Cite

show abstract

“…Meanwhile, in other studies, the effective stress is corrected by the introduction of a constant n value, which translates into a better estimation of the stress effect of permeability. The improved effective stress law is frequently used but the approach for obtaining n varies (Chen et al, 2017; Heller et al, 2014; Zhao et al, 2011). The study by Letham and Bustin (2016a) shows that the n value is affected by the gas slippage effect.…”

Section: Introductionmentioning

confidence: 99%

Laboratory Research on Gas Transport in Shale Nanopores Considering the Stress Effect and Slippage Effect

Sun

Zhou

et al. 2020

JGR Solid Earth

View full text Add to dashboard Cite

The low permeability of shale, in accretionary complexes and passive continental margins, influences pore pressure generation, and thus induces deformation and fault slip behavior. It is also key in hindering the ability to evaluate shale gas production. Gas is commonly used in measuring the permeability of shale and generally yields high values than that of liquids, due to slippage effect. Separation of the slippage effect from gas permeability is a critical task in the study of low‐permeability media. This study measured the gas permeability (Kg) of the Longmaxi shale parallel to bedding (L1P) and perpendicular to bedding (L1V) under different confining pressures (Cp) and pore pressures (Pp), while simultaneously measuring porosity for different values of Cp. Additionally, a new approach is proposed to define the effective stress coefficient and boundary condition for the Klinkenberg correction. The results show that the Kg of L1P is almost unaffected by the slippage effect, while, for L1V, the Klinkenberg correction is required. The Klinkenberg plot of L1V follows the quadratic model from the study by Ashrafi Moghadam and Chalaturnyk (2014, https://doi.org.10/1016/j.coal.2013.10.008), rather than the classic linear Klinkenberg equation. The results also show that, as the Cp increases and/or the Pp decreases, the contribution of the slippage effect to the L1V Kg increased from 20% to 86.5%. Finally, based on the Knudsen number (Kn), the flow regime of L1P changes from Darcy flow (Kn < 0.01) to slip flow (0.01 < Kn < 0.1), and that of L1V is slip flow.

show abstract

“…In order to highlight the flow mechanism of tight reservoirs, the stress sensitivity of tight reservoirs is considered to study stress sensitivity effects of matrix and fracture permeability. There are kinds of types of stress-sensitive models, including binomial, logarithmic, power law, and exponential relationship (Jones, 1975;David et al, 1994;Zhao et al, 2011;Xiao et al, 2016).…”

Section: Stress Sensitivity In Tight Reservoirsmentioning

confidence: 99%

Numerical Simulation of a Horizontal Well With Multi-Stage Oval Hydraulic Fractures in Tight Oil Reservoir Based on an Embedded Discrete Fracture Model

Yang

Wang²,

Zhang³

et al. 2020

Front. Energy Res.

View full text Add to dashboard Cite

Tight oil is a kind of unconventional oil and gas resource with great development potential. Due to the unconventional characteristics of low porosity and low permeability in tight oil reservoirs, single wells generally have no natural productivity, and industrial development is usually conducted in combination with horizontal wells and hydraulic fracturing techniques. To capture the flow behavior affected by fractures with complex geometry and interaction, we adopted embedded discrete fracture models (EDFMs) to simulate the development of fractured reservoirs. Compared with the traditional discrete fracture models (DFMs), the embedded discrete fracture models (EDFMs) can not only accurately represent the fracture geometry but also do not generate a large number of refine grids around fractures and intersections of fractures, which shows the high computational efficiency. To be more consistent with the real characteristic of the reservoir and reflect the advantage of EDFMs on modeling complex fractures, in this work, the hydraulic fractures are set as oval shape, and we adopted 3-dimensional oil–gas two-phase model considering capillary forces and gravity effects. We developed an EDFM simulator, which is verified by using the fine grid method (FGM). Finally, we simulated and studied the development of tight oil without and with random natural fractures (NFs). In our simulation, the pressure varies widely from the beginning to the end of the development. In real situation, tight oil reservoirs have high initial pressure and adopt step-down bottom hole pressure development strategy where the bottom hole pressure of the last stage is below the bubble point pressure and the free gas appears in the reservoir. Modeling studies indicate that the geometry of fracture has a great influence on the pressure and saturation profiles in the area near the fractures, and dissolved gas flooding contributes to the development of tight oil, and NFs can significantly improve production, while the effect of the stress sensitivity coefficient of NFs on production is more significant in the later stage of production with lower reservoir pressure.

show abstract

The effective pressure law for permeability of clay-rich sandstones

Cited by 28 publications

References 8 publications

Nonlinear effective pressure law for permeability

Nonlinear effective pressure law for permeability

Laboratory Research on Gas Transport in Shale Nanopores Considering the Stress Effect and Slippage Effect

Numerical Simulation of a Horizontal Well With Multi-Stage Oval Hydraulic Fractures in Tight Oil Reservoir Based on an Embedded Discrete Fracture Model

Contact Info

Product

Resources

About