An analytical solution for recovering the complete in-situ stress tensor from Flat Jack tests

2015 ◽  
Vol 78 ◽  
pp. 118-126 ◽  
Author(s):  
Ben-Guo He ◽  
Yossef H. Hatzor
Keyword(s):  
Analytical Solution ◽  
Stress Tensor ◽  
In Situ Stress

scholarly journals Uncertainties in geomechanical models – exhaustive vs. feasible approach

2021 ◽  
Vol 1 ◽  
pp. 187-188
Author(s):  
Moritz Ziegler ◽  
Oliver Heidbach
Keyword(s):  
Standard Deviation ◽  
Stress State ◽  
Stress Tensor ◽  
In Situ Stress ◽  
Rock Properties ◽  
Geomechanical Model ◽  
Rock Property ◽  
Stress Changes ◽  
Stress States

Abstract. The stress state is a key component for the safety and stability of deep geological repositories for the storage of nuclear waste. For the stability assessment and prediction over the repository lifetime, the stress state is put in relation to the rock strength. This assessment requires knowledge of both the future stress changes and the current in situ stress state. Due to the limited number of in situ stress data records, 3D geomechanical models are used to obtain continuous stress field prediction. However, meaningful interpretation of the stress state model requires quantification of the associated uncertainties that result from the geological, stress and rock-property data. This would require thousands of simulations which in a high-resolution model is called an exhaustive approach. Here we present a feasible approach to reduce computation time significantly. The exhaustive approach quantifies uncertainties that are due to variabilities in stress data records. Therefore, all available data records within a model volume are used individually in separate simulations. Due to the inherent variability in the available data, each simulation represents one of many possible stress states supported by data. A combination of these simulations allows estimation of an individual probability density function for each component of the stress tensor represented by an average value and a standard deviation. If weighting of the data records can be performed, the standard deviation can usually be reduced and the significance of the model result is improved. Alternatively, a range of different stress states supported by the data can be provided with the benefit that no outliers are disregarded, but this comes at the cost of a loss in precision. Both approaches are only feasible since the number of stress data records is limited. However, it is indicated that large uncertainties are also introduced by variabilities in rock properties due to natural intra-lithological lateral variations that are not represented in the geomechanical model or due to measurement errors. Quantification of these uncertainties would result in an exhaustive approach with a high number of simulations, and we use an alternative, feasible approach. We use a generic model to quantify the stress state uncertainties from the model due to rock property variabilities. The main contributor is the Young's module, followed by the density and the Poisson ratio. They affect primarily the σxx and σyy components of the stress tensor, except for the density, which mainly affects the σzz component. Furthermore, a relative influence of the stress magnitudes, the tectonic stress regime and the absolute magnitude of rock properties is observed. We propose to use this information in a post-computation assignment of uncertainties to the individual components of the stress tensor. A range of lookup tables need to be generated that compile information on the effect of different variabilities in the rock properties on the components of the stress tensor in different tectonic settings. This allows feasible quantification of uncertainties in a geomechanical model and increases the significance of the model results significantly.

New constraints on stress and fracture orientations in the Shipwreck Trough, Otway Basin: implications for conventional and unconventional exploration and production

2012 ◽  
Vol 52 (2) ◽  
pp. 697
Author(s):  
David Tassone ◽  
Simon Holford ◽  
Rosalind King ◽  
Guillaume Backé
Keyword(s):  
Stress Tensor ◽  
Test Data ◽  
Sedimentary Basins ◽  
Horizontal Stress ◽  
In Situ Stress ◽  
New Method ◽  
Natural Fracture ◽  
Log Data ◽  
Maximum Horizontal Stress

A detailed understanding of the in-situ stress tensor within energy-rich basins is integral for planning successful drilling completions, evaluating the reactivation potential of sealing faults and developing unconventional plays where fracture stimulation strategies are required to enhance low permeability reservoirs. Newly available leak-off test results interpreted using a new method for analysing leak-off test data constrains the minimal horizontal stress magnitude for the offshore Shipwreck Trough wells to be ∼20 MPa/km, which is similar to the vertical stress magnitude derived from wireline data for depths shallower than ∼2–2.5 km. Breakouts interpreted from image log data reveal a ∼northwest–southeast maximum horizontal stress orientation and formation pressure tests confirm near-hydrostatic conditions for all wells. The new method for analysing leak-off test data has constrained the upper limit of the maximum horizontal stress magnitude to be the greatest, indicating a reverse-to-strike-slip faulting regime, which is consistent with neotectonic faulting evidence. Petrophysical wireline data and image log data to characterise extant natural fracture populations within conventional reservoirs and stratigraphic units that may be exploited as future unconventional reservoirs have also been used. These fracture sets are compared with possible fracture populations recognised in contiguous, high-fidelity 3D seismic datasets using a new method for identifying fracture systems based on attribute mapping techniques. This study represents the first of its kind in the Otway Basin. Combined analysis of the in-situ stress tensor and fracture density and geometries provides a powerful workflow for constraining fracture-related fluid flow pathways in sedimentary basins.

CHARACTERISING THE FULL STRESS TENSOR BASED ON OBSERVATIONS OF DRILLING-INDUCED WELLBORE FAILURES IN VERTICAL AND INCLINED BOREHOLES LEADING TO IMPROVED WELLBORE STABILITY AND PERMEABILITY PREDICTION

1998 ◽  
Vol 38 (1) ◽  
pp. 466 ◽  
Author(s):  
C.A. Barton ◽  
D.A. Castillo ◽  
D. Moos ◽  
P. Peska ◽  
M.D. Zoback
Keyword(s):  
Stress Field ◽  
Stress Tensor ◽  
Image Data ◽  
In Situ Stress ◽  
Wellbore Stability ◽  
Efficient Production ◽  
Sand Production ◽  
Inclined Boreholes ◽  
In Situ Stress Field

To minimise wellbore failures in unstable environments, knowledge of the complete stress tensor is crucial to designing optimally-stable borehole trajectories, selecting suitable mud weights, and determining appropriate casing points. Understanding how the in situ stress field interacts with the drilling and production of a well enables one to design for maximum stability and to facilitate intersecting the greatest population of hydraulically-conductive fractures for efficient production. Knowledge of the in situ stress field is also important to reduce uncertainties in sand production prediction to allow more aggressive completion designs and production schedules.A new interactive software system, Stress and Failure of Inclined Boreholes (SFIB) (Peska and Zoback, 1995a) is used to demonstrate how observations of drilling-induced compressive and tensile wellbore failures from acoustic and electrical images in vertical and inclined boreholes can be integrated with routinely-collected drilling data (leak-off and drill stem tests) to construct a well-constrained stress tensor. These techniques can also exploit wellbore image data to constrain in situ rock strength in vertical and inclined wells. This paper illustrates how to apply this knowledge to limit wellbore instability, design optimally stable wellbores, develop constraints that help mitigate problems associated with sand production, and optimise productivity of fractured reservoirs.In addition to mapping drilling-induced wellbore features, image data can also be used to determine the distribution, orientation, and apparent aperture of natural fractures and fault systems. With knowledge of the orientations and magnitudes of the in situ stresses it is possible to identify the subset of fractures that are likely to be hydraulically conductive.Examples of recent applications in the North Sea, Gulf of Mexico, California, and Puerto Rico illustrating how this integrated approach can be used in a variety of tectonic settings.

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