Defining structural permeability in Australian sedimentary basins

2015 ◽  
Vol 55 (1) ◽  
pp. 119 ◽  
Author(s):  
Adam Bailey ◽  
Rosalind King ◽  
Simon Holford ◽  
Joshua Sage ◽  
Martin Hand ◽  
...  
Keyword(s):  
Regional Scale ◽  
Sedimentary Basins ◽  
In Situ Stress ◽  
Natural Fracture ◽  
Enhanced Geothermal Systems ◽  
Structural Development ◽  
Geothermal Systems ◽  
Stress Regime ◽  
Orientation Data

Declining conventional hydrocarbon reserves have triggered exploration towards unconventional energy, such as CSG, shale gas and enhanced geothermal systems. Unconventional play viability is often heavily dependent on the presence of secondary permeability in the form of interconnected natural fracture networks that commonly exert a prime control over permeability due to low primary permeabiliy of in situ rock units. Structural permeability in the Northern Perth, SA Otway, and Northern Carnarvon basins is characterised using an integrated geophysical and geological approach combining wellbore logs, seismic attribute analysis and detailed structural geology. Integration of these methods allows for the identification of faults and fractures across a range of scales (millimetre to kilometre), providing crucial permeability information. New stress orientation data is also interpreted, allowing for stress-based predictions of fracture reactivation. Otway Basin core shows open fractures are rarer than image logs indicate; this is due to the presence of fracture-filling siderite, an electrically conductive cement that may cause fractures to appear hydraulically conductive in image logs. Although the majority of fractures detected are favourably oriented for reactivation under in situ stresses, fracture fill primarily controls which fractures are open, demonstrating that lithological data is often essential for understanding potential structural permeability networks. The Carnarvon Basin is shown to host distinct variations in fracture orientation attributable to the in situ stress regime, regional tectonic development and local structure. A detailed understanding of the structural development, from regional-scale (hundreds of kilometres) down to local-scale (kilometres), is demonstrated to be of importance when attempting to understand structural permeability.

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.

Subsurface in situ stress magnitudes from oil-well drilling records: an example from the Venture area, offshore eastern Canada

1987 ◽  
Vol 24 (9) ◽  
pp. 1748-1759 ◽  
Author(s):  
W. B. Ervine ◽  
J. S. Bell
Keyword(s):  
Feed Rate ◽  
Fluid Pressure ◽  
Sedimentary Basins ◽  
In Situ Stress ◽  
Depth Interval ◽  
Principal Stresses ◽  
Eastern Canada ◽  
Stress Regime ◽  
Clastic Rocks

This report describes a method of obtaining information on in situ stress magnitudes at depth in sedimentary basins by using information gathered while drilling oil wells. If we assume that one of the principal stresses is vertical at a well site, principal stress magnitudes can be estimated in the following manner. Sv is equated with overburden load, which is obtained by integrating density log records. SHmin is equated with leak-off test pressures measured over short open-hole intervals and also from selected initial feed-rate pressures. SHmax is derived from the equation SHmax = 2P1 − P0, where P1 is the leak-off pressure or the initial feed-rate pressure, and P0 is the fluid pressure over a specified depth interval. This relationship is a simplified approximation of Hubbert and Willis' well-known equation Pb = T + 3SHmin − SHmax − P0, describing hydraulic fracturing around a borehole.Using this approach, stress magnitudes were estimated for 44 depth intervals in four wells drilled over the Venture structure on the Scotian Shelf, offshore eastern Canada. The information obtained between subsea depths of 815 and 5783 m provides a consistent record and points to a stress regime where SHmax > Sv > SHmin. At approximately 6000 m, Sv and SHmin may become equal. Inferred stress magnitudes in the upper 3000 m are comparable to those measured in clastic rocks in western Canada.

APPLICATION OF GUIDELINE CHARTS IN DECISIONMAKING ON WELL TRAJECTORY AND MUD WEIGHT PROGRAM

2001 ◽  
Vol 41 (1) ◽  
pp. 609
Author(s):  
X. Chen ◽  
C.P. Tan ◽  
C.M. Haberfield
Keyword(s):  
Stability Analysis ◽  
Case Studies ◽  
In Situ Stress ◽  
Wellbore Stability ◽  
Material Strength ◽  
Stress Regime ◽  
Wellbore Instability ◽  
Well Trajectory

To prevent or minimise wellbore instability problems, it is critical to determine the optimum wellbore profile and to design an appropriate mud weight program based on wellbore stability analysis. It is a complex and iterative decisionmaking procedure since various factors, such as in-situ stress regime, material strength and poroelastic properties, strength and poroelastic anisotropies, initial and induced pore pressures, must be considered in the assessment and determination.This paper describes the methodology and procedure for determination of optimum wellbore profile and mud weight program based on rock mechanics consideration. The methodology is presented in the form of guideline charts and the procedure of applying the methodology is described. The application of the methodology and procedure is demonstrated through two field case studies with different in-situ stress regimes in Australia and Indonesia.

DYNAMIC FAULT/FRACTURE SEAL BEHAVIOUR AND GEOMECHANICAL ANALYSIS OF THE GREATER GOBE AREA, SOUTHERN HIGHLANDS PROVINCE, PAPUA NEW GUINEA

2001 ◽  
Vol 41 (1) ◽  
pp. 251
Author(s):  
M.C. Daniels ◽  
D.T. Moffat ◽  
D.A. Castillo
Keyword(s):  
Papua New Guinea ◽  
Shear Failure ◽  
New Guinea ◽  
In Situ Stress ◽  
Stress Regime ◽  
Well Spacing ◽  
Geomechanical Analysis ◽  
Near Shore ◽  
Performance Results

The Gobe Main and SE Gobe Fields were discovered in the early 1990s in the Papuan Fold Belt in the Highlands of Papua New Guinea. Heavily karstified Darai Limestone at the surface and heli-supported drilling made field appraisal problematic and expensive. With initial well spacing upwards of several kilometres, these fields were thought to be ‘tank’ type models, with field-wide extrapolations of gas-oil and oil-water contacts.The main Iagifu Sandstone reservoir in the Gobe fields comprises several fluvial and near-shore sand bodies, which are readily correlatable across the fields. The reservoir units display discrete coarsening upward sequences containing medium (~17%) porosity, medium to high permeability (>100 mD) sandstones. Although several different depositional facies are interpreted within the Iagifu reservoir, sand units are extensive on the scale of the Gobe structures and do not appear to be producing significant lateral boundaries or reservoir compartmentalisation.Geomechanical analysis has enabled the calculation of in-situ stress magnitudes and establishment of a geomechanical model for Gobe. Locally, the Gobe Main Field appears to be in a strike-slip stress regime (SHmax>Sv>Shmin). SHmax directions vary from NNE– SSW to NE–SW. Stress magnitudes indicate the structure is near frictional equilibrium, with a high proportion of natural fractures and faults critically stressed for shear failure. Since first oil in early 1998, performance results have indicted pressure segregation of many of the wells in both the Gobe Main and SE Gobe fields. Although only one fault has been positively identified at the reservoir level, the mapped faults appear to have sand-on-sand juxtaposition with minimal (

scholarly journals The Role of In Situ Stress in Organizing Flow Pathways in Natural Fracture Networks at the Percolation Threshold

Geofluids ◽  
2019 ◽  
Vol 2019 ◽  
pp. 1-14 ◽  
Author(s):  
Chuanyin Jiang ◽  
Xiaoguang Wang ◽  
Zhixue Sun ◽  
Qinghua Lei
Keyword(s):  
Fluid Flow ◽  
Percolation Threshold ◽  
Fractured Reservoirs ◽  
Fracture Network ◽  
In Situ Stress ◽  
Natural Fracture ◽  
Fracture Aperture ◽  
Dilation Effect ◽  
Stress Dependent

We investigated the effect of in situ stresses on fluid flow in a natural fracture network. The fracture network model is based on an actual critically connected (i.e., close to the percolation threshold) fracture pattern mapped from a field outcrop. We derive stress-dependent fracture aperture fields using a hybrid finite-discrete element method. We analyze the changes of aperture distribution and fluid flow field with variations of in situ stress orientation and magnitude. Our simulations show that an isotropic stress loading tends to reduce fracture apertures and suppress fluid flow, resulting in a decrease of equivalent permeability of the fractured rock. Anisotropic stresses may cause a significant amount of sliding of fracture walls accompanied with shear-induced dilation along some preferentially oriented fractures, resulting in enhanced flow heterogeneity and channelization. When the differential stress is further elevated, fracture propagation becomes prevailing and creates some new flow paths via linking preexisting natural fractures, which attempts to increase the bulk permeability but attenuates the flow channelization. Comparing to the shear-induced dilation effect, it appears that the propagation of new cracks leads to a more prominent permeability enhancement for the natural fracture system. The results have particularly important implications for predicting the hydraulic responses of fractured rocks to in situ stress fields and may provide useful guidance for the strategy design of geofluid production from naturally fractured reservoirs.

The in-situ stress state of the Rhine-Ruhr region and its implications for the geothermal energy utilization

2020 ◽  
Author(s):  
Michal Kruszewski ◽  
Giordano Montegrossi ◽  
Tobias Backers ◽  
Erik Saenger
Keyword(s):  
Stress State ◽  
Geothermal Energy ◽  
In Situ Stress ◽  
Wellbore Stability ◽  
Energy Utilization ◽  
Natural Fracture ◽  
Electricity Production ◽  
The Future ◽  
Ruhr Region

<p>The Rhine-Ruhr region is one of the largest metropolitan areas in Europe, with more than 10 million inhabitants, located in western Germany. The region is defined by the rich coal-bearing layers from the upper Carboniferous period, extracted as early as the 13<sup>th</sup> century and belonging to the sub-Variscan Trough. In 2018, after more than 700 years of exploration, the last black coal mine was closed in the area. One of the most promising re-uses of the abandoned coal mines is the exploitation of geothermal energy sources. Additionally, to the geothermal energy extracted from existing mines, potential deep geothermal reservoirs within the Rhine-Ruhr, may exist at depths between 4.5 and 6 km, where Devonian limestones were found. Based on the available temperature profiles from deep exploration wells in the area, geothermal gradient amounts to 36.8<sup>o</sup>C/km and results in reservoir temperatures between 170<sup>o</sup>C and 220<sup>o</sup>C, which will enable not only heat but even electricity production. This study provides a comprehensive investigation of the full in-situ stress state tensor with its anisotropy and presents crucial physical formation and natural fracture properties. The data for this investigation was acquired from the extensive borehole logging and geomechanical campaigns carried out in deep coal exploration wells throughout the 1980s as well as from the recent shallow geothermal research wells. Acquired data allowed assessing critically-stressed, i.e. hydraulically active, fractures undergoing shear displacement, being primarily responsible for the future geothermal reservoir permeability. Extensive sets of microseismic, subsidence and drilling data were used to confirm the results of the analysis. Additionally, wellbore stability analysis and potential drill paths for the future medium-to-deep geothermal wells in the region were assessed. This study is a part of the 3D-RuhrMarie project, which aims to assess the intrinsic seismic risk within the Rhine-Ruhr region to promote safer and economically more efficient exploration and exploitation of the future geothermal resources.</p>

scholarly journals Evaluation of the Influence of In Situ Stress on the Stability of Mine Pit Walls: A Case Study of Songwe Mine

2021 ◽  
Vol 4 (2) ◽  
pp. p1
Author(s):  
Dyson Moses ◽  
Hideki Shimada ◽  
Takashi Sasaoka ◽  
Akihiro Hamanaka ◽  
Tumelo K. M Dintwe ◽  
...  
Keyword(s):  
Active Regions ◽  
Horizontal Stress ◽  
In Situ Stress ◽  
Slope Instability ◽  
Open Pit ◽  
Stress Regime ◽  
Tectonically Active ◽  
The Stability ◽  
The Impact

The investigation of the influence of in situ stress in Open Pit Mine (OPM) projects has not been accorded a deserved attention despite being a fundamental concern in the design of underground excavations. Hence, its long-term potential adverse impacts on pit slope performance are overly undermined. Nevertheless, in mines located in tectonically active settings with a potential high horizontal stress regime like the Songwe mine, the impact could be considerable. Thus, Using FLAC3D 5.0 software, based on Finite Difference Method (FDM) code, we assessed the role of stress regimes as a potential triggering factor for slope instability in Songwe mine. The results of the evaluated shearing contours and quantified strain rate and displacement values reveal that high horizontal stress can reduce the stability performance of the pit-wall in spite of the minimal change in Factor of Safety (FoS). Since mining projects have a long life span, it would be recommendable to consider “in situ stress-stability analyses” for OPM operations that would be planned to extend to greater depths and those located in tectonically active regions.

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