Analysis of stress and pore pressure in naturally fractured shale formations: a finite element based chemo-thermo-poroplastic model

2010 ◽  
Author(s):  
Hamid Roshan ◽  
Sheik S. Rahman
Keyword(s):  
Finite Element ◽  
Pore Pressure ◽  
Shale Formations ◽  
Naturally Fractured

Pore Pressure Prediction in Sandstone Using a Lateral Transfer Approach

2021 ◽  
Author(s):  
Jose Francisco Consuegra
Keyword(s):  
Pore Pressure ◽  
Seismic Data ◽  
Strong Relationship ◽  
Lateral Transfer ◽  
Earth Model ◽  
Driving Mechanism ◽  
Shale Formations ◽  
Sand Body ◽  
Pore Pressure Prediction ◽  
Normal Trend

Abstract Accurate pore pressure prediction is required to determine reliable static mud weights and circulating pressures, necessary to mitigate the risk of influx, blowouts and borehole instability. To accurately estimate the pore pressure, the over-pressure mechanism has to be identified with respect to the geological environment. One of the most widely used methods for pore pressure prediction is based on Normal Compaction Trend Analysis, where the difference between a ‘normal trend' and log value of a porosity indicator log such as sonic or resistivity is used to estimate the pore pressure. This method is biased towards shales, which typically exhibit a strong relationship between porosity and depth. Overpressure in non-shale formations has to be estimated using a different method to avoid errors while predicting the pore pressure. In this study, a different method for pore pressure prediction has been performed by using the lateral transfer approach. Many offset wells were used to predict the pore pressure. Lateral transfer in the sand body was identified as the mechanism for overpressure. This form of overpressure cannot be identified by well logs, which makes the pore pressure prediction more complex. Building a 2D geomechanical model, using seismic data as an input and following an analysis methodology that considered three type of formation fluids - gas, oil and water in the sand body, all pore pressure gradients related to lateral transfer for the respective fluids were evaluated. This methodology was applied to a conventional reservoir in a field in Colombia and was helpful to select the appropriate mud weight and circulating pressure to mitigate drilling risks associated to this mechanism of overpressure. Seismic data was critical to identifying this type of overpressure mechanism and was one of the main inputs for building the geomechanical earth model. This methodology enables drilling engineers and geoscientists to confidently predict, assess and mitigate the risks posed by overpressure in non-shale formations where lateral transfer is the driving mechanism of overpressure. This will ensure a robust well plan and minimize drilling/well control hazards associated with this mode of overpressure.

The Effects of Geosynthetic-Reinforcement on Consolidation Behavior of Soft Clay Embankment under Step Construction

2018 ◽  
Vol 783 ◽  
pp. 46-50
Author(s):  
Yu Cong Gao ◽  
Rong Chen ◽  
Dong Xue Hao ◽  
Myoung Soo Won
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Pore Pressure ◽  
Clay Soil ◽  
Clayey Soil ◽  
Soft Clay ◽  
Excess Pore Pressure ◽  
Calculation Results ◽  
Consolidation Behavior ◽  
Excess Pore

Geosynthetics–reinforced structures are widely used in embankments and walls. This paper presents the simulation of the embankment under load in order to compare the behavior of clay embankment with and without wrapping-facing-geosynthetics-reinforcement using finite element method (FEM) and to analyse the variation of behavior included of displacement and excess pore pressure under the different over-consolidation ratios (OCR). The calculation results show that embankment with higher OCR showing lower displacement compare to embankment with lower OCR. However, OCR isn’t very sensitive to the dissipation of excess pore pressure. Geosynthetics-reinforcements could reduce the displacement of embankment and accelerate dissipation of excess pore pressure after construction and surcharge. Gravel, geosynthetics-reinforcement and clay soil are properly combined, clayey soil is expected to be useful as embankment material.

DYNAMIC RESPONSES OF INTERVERTEBRAL DISC DURING STATIC CREEP AND DYNAMIC CYCLIC LOADING: A PARAMETRIC POROELASTIC FINITE ELEMENT ANALYSIS

2013 ◽  
Vol 25 (01) ◽  
pp. 1350013 ◽  
Author(s):  
Mohammad Nikkhoo ◽  
Mohammad Haghpanahi ◽  
Mohamad Parnianpour ◽  
Jaw-Lin Wang
Keyword(s):  
Finite Element ◽  
Elastic Modulus ◽  
Intervertebral Disc ◽  
Pore Pressure ◽  
Void Ratio ◽  
Disc Height ◽  
Poisson's Ratio ◽  
Height Loss ◽  
Loading Frequency ◽  
Loading Conditions

Low back pain is a common reason for activity limitation in people younger than 45 years old, and was proved to be associated with heavy physical works, repetitive lifting, impact, stationary work postures and vibrations. The study of load transferring and the loading condition encountered in spinal column can be simulated by finite element models. The intervertebral disc is a structure composed of a porous material. Many physical models were developed to simulate this phenomenon. The confounding effects of poroelastic properties and loading conditions on disc mechanical responses are, nevertheless, not cleared yet. The objective of this study was to develop an axisymmetric poroelastic finite element model of intervertebral disc and use it to investigate the confounding effect of material properties and loading conditions on the disc deformation and pore pressure. An axisymmetric poroelastic model of human lumbar L4–L5 motion segment was developed. The model was validated by comparing the height loss and intradiscal pressure of the L4–L5 intervertebral disc with in vitro cadaveric studies. The effect of permeability, void ratio, elastic modulus, and Poisson's ratio on disc height and pore pressure was investigated for the following three loading conditions: (1) 1334 N creep loading, (2) peak-to-peak, 1000-to-1600 N, 1 Hz cyclic loading, and (3) same loading magnitude, but at 5 Hz loading frequency. The disc height loss and pore pressure of the three loading conditions were analyzed. The predictions of the disc height loss and intradiscal pressure of the current FE model are well comparable with the results of in vitro cadaveric studies. After model validation, the parametric study of disc poroelastic properties on the disc mechanical responses shows that the increase of permeability and void ratio increases the disc height loss and decreases the pore pressure, and these effects are sensitive to external loading frequency. Higher elastic modulus reduces the disc deformation and the pore pressure, but this reduction is not sensitive to the loading frequency. The effect of Poisson's ratio on disc height loss and pore pressure is negligible. In conclusion, the hydraulic permeability describes the fluid flow capability within tissue matrix which has a higher sensitivity on the saturation time for disc deformation and pore pressure. Void ratio directly affects the amount of mobile water within disc and changes time-dependent response of disc. Increase in loading frequency reduces time for fluid inflow and outflow, which fades out the role of permeability and void ratio. Values of elastic modulus and Poisson's ratio, which demonstrates stiffness and bulging capacity, respectively, do not affect the overall dynamic response of disc.

An effective stress model for creep of clay

1995 ◽  
Vol 32 (5) ◽  
pp. 819-834 ◽  
Author(s):  
Mohammed M. Morsy ◽  
D.H. Chan ◽  
N.R. Morgenstern
Keyword(s):  
Finite Element ◽  
Pore Pressure ◽  
Effective Stress ◽  
Pore Water Pressure ◽  
Water Pressure ◽  
Surface Model ◽  
Interpolation Technique ◽  
Stress Integration ◽  
Integration Algorithms ◽  
Double Yield

An effective stress constitutive model to study the problem numerically of creep in the field is presented. A double-yield surface model for the stress–strain–time behaviour of wet clay is described. The model adopts the concept of separating the total deformation into immediate and delayed components. The yield surfaces employed are the modified Cam-clay ellipsoid and the Von Mises cylinder inscribed in the ellipsoid. The proposed numerical scheme incorporates the pore pressure based on field observations into a finite element analysis. An interpolation technique is used to determine the pore pressure at every element. A field example is presented to illustrate the interpolation technique procedure. The scheme not only avoids the complexity of making predictions of pore-water pressure, but also allows the analysis to be carried out in terms of effective stresses based on the actual observed pore pressure. Two stress integration algorithms based on the implicit calculation of plastic strain are implemented and tested for the double-yield surface model. A numerical simulation of stress-controlled drained creep tests confirms the numerical procedure. Key words : constitutive equations, creep, finite element, stress integration algorithms, effective stress approach, pore-water pressure.

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