Pore Pressure Coefficient Anisotropy Measurements for Intrinsic and Induced Anisotropy in Sandstone

2008 ◽  
Author(s):  
Ashraf Mohammed Al-Tahini ◽  
Younane N. Abousleiman
Keyword(s):  
Pore Pressure ◽  
Pressure Coefficient ◽  
Induced Anisotropy

Pore-Pressure-Coefficient Anisotropy Measurements for Intrinsic and Induced Anisotropy in Sandstone

2010 ◽  
Vol 13 (02) ◽  
pp. 265-274 ◽  
Author(s):  
Ashraf Al-Tahini ◽  
Younane Abousleiman
Keyword(s):  
Pore Pressure ◽  
Elastic Moduli ◽  
Pressure Coefficient ◽  
Induced Anisotropy ◽  
Transverse Anisotropy ◽  
Significant Control ◽  
Bedding Planes ◽  
Rock Structure ◽  
Stress Induced Anisotropy ◽  
The Difference

Summary In this study, we determine experimentally the effect of inherent and stress-induced anisotropy on stiffness components, elastic moduli, and Biot's pore-pressure coefficients (PPCs) for Lyons outcrop Colorado sandstone, which exhibits a clear transverse isotropic rock structure. Both dynamic and quasistatic methods were used under a nonhydrostatic state of stress to perform the measurements on dry core samples. Our assumption of apparent transverse anisotropy was confirmed initially with acoustic velocity measurements and at a later stage in the loading with experimental transverse anisotropic failure analysis. The objective of this study is to identify and isolate the effect of stress-induced anisotropy from the inherent transverse anisotropy on the measured stiffness components, elastic moduli, and Biot's PPCs. The effect of stress-induced anisotropy appears to have significant control on measured stiffness components, elastic moduli, and Biot's PPCs in comparison to the inherent-transverse-anisotropy effect. Our work shows that the stiffness components, Mij and thus the computed elastic moduli, are highly influenced by the stress-induced anisotropy, especially the off-diagonal stiffness components, M12 and M13, where the increase in their magnitudes from the dynamic measurements before failure is determined to be 100 and 81%, respectively. The difference in the magnitude between the axial and lateral Biot's PPCs in line with bedding planes and perpendicular to them is measured to be 24 and 16% from the quasistatic and dynamic methods, respectively; whereas, the effect of stress-induced anisotropy reduced the dynamic average magnitude of the Biot's PPCs along the bedding planes and transverse to these planes by 63% across a stress range of 145 MPa.

scholarly journals Identification and Prediction of Allo-Source Overpressure Caused by Vertical Transfer: Example from an HTHP Gas Reservoir in the Ledong Slope in the Yinggehai Basin

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-20
Author(s):  
Caiwei Fan ◽  
Changgui Xu ◽  
Chao Li ◽  
Aiqun Liu ◽  
Hu Li ◽  
...  
Keyword(s):  
Pore Pressure ◽  
Pressure Coefficient ◽  
Vertical Transfer ◽  
Yinggehai Basin ◽  
High Magnitude ◽  
Key Issues ◽  
Vertical Effective Stress ◽  
Gas Bearing ◽  
Measured Pressure

The Yinggehai Basin is a typical high temperature and high pressure (HTHP) gas-bearing basin. The pressure coefficient exceeds 2.2 in deeply-buried Miocene reservoirs in the Ledong Slope, a nondiapir zone in the Yinggehai Basin. Determining the overpressure mechanisms and predicting the pore pressure are key issues for natural gas exploration and development in the Ledong Slope. In this paper, overpressure mechanisms were investigated according to the analysis of vertical effective stress-logging responses and geological evaluations, and the pore pressure was predicted using the Bowers method. The loading-unloading crossplots indicated that the overpressure that existed in reservoirs mainly consists of two types: neighbor-source and allo-source overpressure. The neighbor-source overpressure is mainly caused by the pressure transmission from the adjacent mudstone to the reservoir, with a pressure coefficient less than 1.5 ~ 1.6. The high-magnitude overpressure points with pressure coefficients greater than 1.6 show a typical unloading response, indicating elevated sandstone pressures rather than in situ mudstone pressures, which are most likely to be generated by overpressure vertical transfer. The high-magnitude overpressure fluid generated by the high mature ultradeep buried N1s source rock migrated to the shallower reservoirs via hidden faults/microfractures, which led to the vertical transfer of overpressure. Vertically transferred overpressure was generated at 1.5 ~0.2 Ma, which is beneficial for the preservation of overpressure in lenticular sandbodies. The estimated pore pressure by the Bowers method is in good agreement with the measured pressure and provides a meaningful reference for predrilling pressure prediction in nondiapir or diapir zones in the Yinggehai Basin.

Experimental Study on Anisotropy of Granite Residual Soil

2012 ◽  
Vol 518-523 ◽  
pp. 4721-4725
Author(s):  
Li Qun Guo ◽  
Yao Xing Huang ◽  
Jian Bing Huang
Keyword(s):  
Pressure Coefficient ◽  
Specimen Size ◽  
Engineering Properties ◽  
Triaxial Tests ◽  
Engineering Practice ◽  
Residual Soil ◽  
Induced Anisotropy ◽  
Inherent Anisotropy ◽  
Strain Relationship ◽  
Granite Residual Soil

Inherent anisotropy and induced anisotropy are two main influencing factors on the engineering properties of granite residual soil. When preparing specimens of granite residual soil for undrained triaxial tests, large-sized specimens can be used to weaken the influence of sampling disturbance and inherent anisotropy, and K0 consolidation is adopted to restore the soil specimens to the state of induced anisotropy. The experimental results indicate that, specimen size has no significant influence on the determination of static lateral pressure coefficient k0, while specimen size and consolidation method obviously affect the stress-strain relationship and shear strength indices of granite residual soil. Undrained triaxial tests using large-sized specimens and the method of K0 consolidation can provide parameters more suitable for engineering practice.

Construction pore pressures in clay foundations under embankments. Part II: generalized behaviour

1978 ◽  
Vol 15 (1) ◽  
pp. 66-82 ◽  
Author(s):  
S. Leroueil ◽  
F. Tavenas ◽  
C. Mieussens ◽  
M. Peignaud
Keyword(s):  
Pore Pressure ◽  
Case History ◽  
Pressure Coefficient ◽  
Geographical Location ◽  
A Value ◽  
Pore Pressures ◽  
Geological Origin ◽  
Observed Behaviour ◽  
Analysis Of Stability ◽  
Vertical Effective Stress

The pore pressures observed under 30 embankments on clays of widely varying geological origin and geographical location are analysed to confirm the validity of the concepts developed from the Saint-Alban case history presented in Part I.It is shown that a significant consolidation does occur in all but one case in the early stages of embankment construction. As a result the vertical effective stress increases rapidly to a value equal to Pc. For further loading on the then normally consolidated clay the pore pressure coefficient [Formula: see text] assumes a value of 1.0.The observed behaviour is interpreted by means of the YLIGHT model of clay behaviour proposed by Tavenas and Leroueil and is shown to apply directly to all clays with an overconsolidation ratio less than 2.5, and with some modifications to heavily overconsolidated clays.The consequences of this behaviour on the analysis of stability and settlements of embankments are presented.

The Pore-Pressure Coefficient in Saturated Soils

Géotechnique ◽  
1960 ◽  
Vol 10 (4) ◽  
pp. 186-187 ◽  
Author(s):  
A. W. Skempton
Keyword(s):  
Pore Pressure ◽  
Pressure Coefficient ◽  
Saturated Soils

A method for calculating pore pressure coefficient directly using ADCIGS

2018 ◽  
Author(s):  
Xu Jialiang ◽  
Wang Jun ◽  
He Dianbo ◽  
Lv Zhenyu YuYa
Keyword(s):  
Pore Pressure ◽  
Pressure Coefficient
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