Some Problems about Pore Pressure Prediction from Effective Stress Theorem

2018 ◽  
Vol 08 (07) ◽  
pp. 1113-1122
Author(s):  
鸿升 王
Keyword(s):  
Pore Pressure ◽  
Effective Stress ◽  
Pore Pressure Prediction

Pore pressure prediction based on the Full Effective Stress (FES) method

2020 ◽  
Author(s):  
G. Richards ◽  
D. Roberts ◽  
A. Bere ◽  
S. Martinez ◽  
M. Tilita ◽  
...  
Keyword(s):  
Pore Pressure ◽  
Effective Stress ◽  
Pore Pressure Prediction

Pore-pressure prediction challenges in chemical compaction regimes: An alternative VP/VS-based approach

2016 ◽  
Vol 4 (4) ◽  
pp. T443-T454 ◽  
Author(s):  
Ajesh John
Keyword(s):  
High Temperature ◽  
Pore Pressure ◽  
Effective Stress ◽  
Text Analysis ◽  
Correction Coefficient ◽  
S Wave ◽  
Wave Velocities ◽  
Temperature Regimes ◽  
Pore Pressure Prediction ◽  
High Degree

Understanding pressure mechanisms and their role in porosity-effective stress relationship is crucial in pore-pressure prediction estimation, particularly in complex geologic and high-temperature regimes. Overpressures are commonly associated with undercompaction and/or unloading mechanisms; those associated with undercompaction generally possess a direct relationship between effective stress and porosity, whereas those associated with unloading do not provide such direct indications from porosity trends. The type of associated unloading mechanism can be correlated when the effective stress and velocity become distorted with the onset of unloading. In the Ravva field, the pore-pressure distribution and overpressure mechanism in the Miocene and below it is a classic example of the unloading mechanism related to chemical compaction, thereby making it difficult to resolve the magnitude and trend of pore pressures. Here, the ratio of P- and S-wave velocities ([Formula: see text]) is analyzed from the drilled locations to understand the effects of lithology, pressure, and fluids on formation velocities and indicates a distinct decreasing trend across the overpressure formations, which I have corresponded to excess pressure resulting from chemical compaction. Across the high-pressured zones, [Formula: see text] ratios show low values compared with normally pressured zones possibly due to the presence of hydrocarbon and/or overpressures. A velocity correction coefficient ranging 0.83–0.71 is resolved for overpressure zones by normalizing the [Formula: see text] values across the normally pressured formations, and thereby assuring that a pore-pressure estimation using corrected velocity from [Formula: see text] analysis shows a high degree of accuracy on prediction trends. Pore-pressure predictions based on [Formula: see text] are a more effective and valid approach in high-temperature settings, in which numerous factors can contribute to pressure generation and a direct effective stress-porosity relationship deviates from the trend.

Analysis of overpressure and its generating mechanisms in the northern Carnarvon Basin from drilling data

2012 ◽  
Vol 52 (1) ◽  
pp. 375
Author(s):  
Iko Sagala ◽  
Mark Tingay
Keyword(s):  
Pore Pressure ◽  
Effective Stress ◽  
Late Triassic ◽  
Effective Stress Analysis ◽  
Pore Pressure Prediction ◽  
Pressure Indicators ◽  
Northern Carnarvon Basin ◽  
Vertical Effective Stress ◽  
Prediction Techniques ◽  
Carnarvon Basin

The Northern Carnarvon Basin is one of Australia’s most prolific hydrocarbon basins. Overpressure has been encountered in numerous wells drilled in the Northern Carnarvon Basin. Knowledge of overpressure distribution is important for drilling and exploration strategies, and understanding the origin of overpressure is essential for applying reliable pore pressure prediction techniques. Unconventional pore pressure indicators—primarily drilling kicks and the presence of connection gas—were used to improve an updated distribution of overpressure and to investigate the origin of overpressure in the Northern Carnarvon Basin. This unconventional dataset was compiled from 45 wells. Overpressures are observed in 40 wells and tend to occur near, or on, the Rankin Platform, Alpha Arch, and Barrow Trend. The presence of overpressure in this area coincides with the region of maximum Cenozoic deposition. Overpressured strata in the Northern Carnarvon Basin occurs through a wide stratigraphic range, from Late Triassic to Paleocene sequences. Generally, post Paleocene sequences in the Northern Carnarvon Basin are considered to be normally pressured. Porosity-vertical effective stress analysis in shale lithologies was used to investigate the origin of overpressure in the Northern Carnarvon Basin. Porosity-vertical effective stress plots from 28 wells in the Northern Carnarvon Basin identified 20 wells where the overpressure appears to be generated by disequilibrium compaction, and eight wells where the overpressure appears to be generated by a component of fluid expansion. Disequilibrium compaction mechanisms were the predominant cause of overpressure in wells around the Rankin Platform and areas located further away from the coast. Conversely, fluid expansion mechanisms were the predominant cause of overpressure in wells around the Alpha Arch and Bambra Trend, and an area located closer to the coast. These results broadly confirm those obtained from earlier studies and highlight the usefulness of kick and connection gas data in overpressure analysis.

Dynamic effective pressure coefficient calibration

Geophysics ◽  
2015 ◽  
Vol 80 (1) ◽  
pp. D65-D73 ◽  
Author(s):  
Hua Yu
Keyword(s):  
Pore Pressure ◽  
Effective Stress ◽  
Oil And Gas ◽  
Pressure Coefficient ◽  
Oil And Gas Industry ◽  
Velocity Variation ◽  
Effective Pressure ◽  
Overburden Pressure ◽  
Gas Industry ◽  
Pore Pressure Prediction

Pore pressure prediction provides an important risk assessment in the oil and gas industry. Most predrill pore-pressure prediction methods from seismic and/or well-log sonic velocities are based on the effective stress principle, which relates velocity variation to the combined effect of overburden stress and pore pressure. In the current practice of pore pressure prediction, the effective stress coefficient [Formula: see text] is often assumed as unity, which is not always the case, especially when sediments are deeply buried and consolidated. To understand the variation of [Formula: see text] with depth, I analyzed density and velocity trends from more than 100 Gulf of Mexico wells near the Louisiana continental shelf edge. In the study area, overpressure zones are present in most wells and compaction disequilibrium is the dominant overpressure mechanism. Normal compaction trends for velocity and density were built. The overburden pressure model was refined by taking into account that the density gradient approaches zero at the onset depth of overpressure. Based on the effective pressure principle, values for [Formula: see text] in the overpressure intervals were estimated in the study area. The average [Formula: see text] values varied from 0.6 to 0.9 inclusive of errors associated with assuming the gradient of mud weight and pore pressure is the same.

A comparative study on methods for determining the hydraulic properties of a clay shale

2020 ◽  
Vol 224 (3) ◽  
pp. 1523-1539
Author(s):  
Lisa Winhausen ◽  
Alexandra Amann-Hildenbrand ◽  
Reinhard Fink ◽  
Mohammadreza Jalali ◽  
Kavan Khaledi ◽  
...  
Keyword(s):  
Pore Pressure ◽  
Effective Stress ◽  
Ion Beam ◽  
Applied Pressure ◽  
Pressure Oscillation ◽  
Stress Conditions ◽  
Data Set ◽  
Clay Shale ◽  
Permeability Coefficients ◽  
Effective Stresses

SUMMARY A comprehensive characterization of clay shale behavior requires quantifying both geomechanical and hydromechanical characteristics. This paper presents a comparative laboratory study of different methods to determine the water permeability of saturated Opalinus Clay: (i) pore pressure oscillation, (ii) pressure pulse decay and (iii) pore pressure equilibration. Based on a comprehensive data set obtained on one sample under well-defined temperature and isostatic effective stress conditions, we discuss the sensitivity of permeability and storativity on the experimental boundary conditions (oscillation frequency, pore pressure amplitudes and effective stress). The results show that permeability coefficients obtained by all three methods differ less than 15 per cent at a constant effective stress of 24 MPa (kmean = 6.6E-21 to 7.5E-21 m2). The pore pressure transmission technique tends towards lower permeability coefficients, whereas the pulse decay and pressure oscillation techniques result in slightly higher values. The discrepancies are considered minor and experimental times of the techniques are similar in the range of 1–2 d for this sample. We found that permeability coefficients determined by the pore pressure oscillation technique increase with higher frequencies, that is oscillation periods shorter than 2 hr. No dependence is found for the applied pressure amplitudes (5, 10 and 25 per cent of the mean pore pressure). By means of experimental handling and data density, the pore pressure oscillation technique appears to be the most efficient. Data can be recorded continuously over a user-defined period of time and yield information on both, permeability and storativity. Furthermore, effective stress conditions can be held constant during the test and pressure equilibration prior to testing is not necessary. Electron microscopic imaging of ion-beam polished surfaces before and after testing suggests that testing at effective stresses higher than in situ did not lead to pore significant collapse or other irreversible damage in the samples. The study also shows that unloading during the experiment did not result in a permeability increase, which is associated to the persistent closure of microcracks at effective stresses between 24 and 6 MPa.

Combining porosity and resistivity logs for pore pressure prediction

2021 ◽  
pp. 108819
Author(s):  
Augustine Uhunoma Osarogiagbon ◽  
Olalere Oloruntobi ◽  
Faisal Khan ◽  
Ramachandran Venkatesan ◽  
Paul Gillard
Keyword(s):  
Pore Pressure ◽  
Resistivity Logs ◽  
Pore Pressure Prediction
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