Effect of Loading Rate and Time Delay on the Tangent Modulus Method (TMM) in Coal and Coal Measured Rocks

Non-destructive techniques of in-situ stress measurement from oriented cored rocks have great potential to be developed as a cost cost-efective and reliable alternative to the conventional overcoring and hydraulic fracturing methods. The tangent modulus method (TMM) is one such technique that can be applied to oriented cored rocks to measure in-situ stresses. Like the deformation rate analysis (DRA), the rock specimen is subjected to two cycles of uniaxial compression and the stresstangent modulus curve for the two cycles is obtained from the stress–strain curve. A bending point in the tangent modulus curve of the frst cycle is observed, separating it from the tangent modulus curve of the second cycle. The point of separation between the two curves is assumed to be the previously applied maximum stress. A number of experiments were conducted on coal and coal measured rocks (sandstone and limestone) to understand the efect of loading conditions and the time delay. The specimens were preloaded, and cyclic compressions were applied under three diferent modes of loading, four diferent strain rates, and time delays of up to one week. The bending point in the stress-tangent modulus curves occurred approximately at the applied pre-stress levels under all three loading modes, and no efect of loading rate was observed on the bending points in TMM. However, a clear efect of time delay was observed on the TMM, contradicting the DRA results. This could be due to the sensitivity of TMM and the range of its applicability, all of which need further investigation for the in-situ stress measurement.Zulfqar Ali, Murat Karakus, Giang D. Nguyen, Khalid Amrouc

Geomechanical modelling and consequences for fluid-flow in complex rifted settings: A case study in the Otway Basin, Australia

Poster presented at the EGU General Assembly 2019Geomechanical modelling of dilation tendency has been completed on more than 900 faults from nine three dimensional seismic surveys within the Otway Basin, Australia. As the in-situ stress regime within the basin is currently debated, scenarios of normal, strike-slip and reverse regimes of in-situ stress have been modelled. Additionally, the stability of natural fractures from seven wellbore image logs has been modelled under the same scenarios, with the consequences for each explored. NW-SE striking faults that define the basin’s major structural fabric are at critical risk of dilation irrespective of the regime of in-situ stress, while similarly striking fractures require very low (<5MPa under a strike-slip scenario) increases in pore pressure in order to be reactivated. N-S striking and W-E striking faults show lower risks for reactivation although their propensity to dilate is still significant. Our results in part explain why fault seal within the Otway Basin has been historically so poor, and suggest that while natural fracture networks may be optimally oriented for reactivation in order to increase secondary permeability – promising for unconventional prospectively - there is a high associated risk with respect to up-dip contamination along regional faults. This case study also provides insight into possible fluid flow pathways within other more frontier passive margin settings.Hugo Burgin, Khalid Amrouch, David Kulikowski, Simon Holford, and Philippe Robio

Fluid pressure evolution in overpressured limestone reservoir at basin-scale: example of the Bighorn Basin (Wyoming, USA) and lessons from comparison with other reservoirs

Nicolas Beaudoin, Olivier Lacombe, Nicolas Bellahsen, Khalid Amrouch, and Jean-Marc Danie

Software-Managed Read and Write Wear-Leveling for Non-Volatile Main Memory

In-memory wear-leveling has become an important research field for emerging non-volatile main memories over the past years. Many approaches in the literature perform wear-leveling by making use of special hardware. Since most non-volatile memories only wear out from write accesses, the proposed approaches in the literature also usually try to spread write accesses widely over the entire memory space. Some non-volatile memories, however, also wear out from read accesses, because every read causes a consecutive write access. Software-based solutions only operate from the application or kernel level, where read and write accesses are realized with different instructions and semantics. Therefore different mechanisms are required to handle reads and writes on the software level. First, we design a method to approximate read and write accesses to the memory to allow aging aware coarse-grained wear-leveling in the absence of special hardware, providing the age information. Second, we provide specific solutions to resolve access hot-spots within the compiled program code (text segment) and on the application stack. In our evaluation, we estimate the cell age by counting the total amount of accesses per cell. The results show that employing all our methods improves the memory lifetime by up to a factor of 955×

Combining geophysical data and calcite twin stress inversion to refine the tectonic history of subsurface and offshore provinces: a case study on the Cooper-Eromanga Basin, Australia

The use of core samples, borehole image logs, and seismic data is common practice for obtaining valuable structural data; however, these data are often obtained in isolation from other methods and not usually used for paleostress inversion processes. Therefore, for the first time, we present a new approach for constraining paleoprincipal stress orientations and regimes by integrating geophysical data (seismic and well data) with calcite twin principal stress orientation inversion analysis to refine the evolution of entirely subsurface or offshore basins; a case study on the subsurface Cooper‐Eromanga Basin, Australia. Calcite samples were collected from oriented core, natural fracture data collected from borehole image logs, and fault data interpreted from three‐dimensional seismic surveys. The analysis of microscale, mesoscale and macroscale data constrained the paleoprincipal stress orientations and regimes of six successive tectonic events: (1) NNW‐SSE oriented strike‐slip Carboniferous Alice Springs event; (2) SE‐NW oriented compressional Mid‐Permian event; (3) NE‐SW oriented strike‐slip Late Permian Daralingie event; (4) E‐W compressional Late Triassic Hunter‐Bowen event; (5) E‐W compressional Late Cretaceous event; and (6) N‐S compressional Paleogene event. This study shows the applicability of integrating geophysics with calcite twin stress inversion to decipher the tectonic evolution of entirely subsurface and offshore provinces.David Kulikowski and Khalid Amrouc

4D modelling of fault reactivation using complete paleostress tensors from the Cooper-Eromanga Basin, Australia

Determining fault activity through time has typically utilised high-resolution seismic data to identify stratigraphic thickness changes or displacement vs distance plots; however, this approach is not possible in regions with low-resolution seismic data. We present a new approach for determining fault reactivation (tensile and shear) through time by integrating three-dimensional seismic data, geomechanical modelling and complete paleostress tensors from calcite twin stress inversion. The Cooper–Eromanga Basin is used as a case study to model the stress conditions present during six tectonic events that have affected the basin and, in doing so, constrain the effective paleostress magnitudes through time. Results show that the likelihood of dilation and shear reactivation of individual fault sets varies through time, with N–S- and E–W-striking faults likely to have been open to fluid flow after the critical moment in the hydrocarbon system. These results have substantial implications for hydrocarbon migration pathway models and structural and stratigraphic models for the Cooper–Eromanga Basin. This approach would benefit other provinces with low-resolution seismic data preventing fault growth analysis, or in regions where hydrocarbon migration pathways are poorly defined.D. Kulikowski ans K. Amrouc

3D seismic analysis investigating the relationship between stratigraphic architecture and structural activity in the intra-cratonic Cooper and Eromanga basins, Australia

This research uses four three-dimensional (3D) seismic surveys located in Australia's largest onshore hydrocarbon province, the intra-cratonic Cooper and Eromanga basins, to present an approach that extracts important structural and stratigraphic information from geophysical data that can then be used to define the tectonostratigraphic evolution of subsurface provinces. The methodology consists of: (1) analysing isopach maps; (2) cross-section interpretation of stratigraphic features, erosional surfaces, and faults; and (3) constraining the evolution of fault activity. Most faults within this province are basement-involved with high dip angles. The primary fault set is NE-SW striking, with secondary sets striking N-S, E-W and NW-SE. These high angle faults most likely developed as normal faults before being reactivated by five of the six major tectonic events. Field scale NW-SE strike-slip faults are prolific and can often be overlooked due to the low seismic resolution. A close relationship between on-lapping features and present-day structural highs was found during each of the major structural events, particularly within hydrocarbon-rich Permian stratigraphy, inferring that present-day structures were present throughout basin development and intermittently reactivated. Significant stratal-package thinning, and a high presence of on-lapping features, were associated with regional basement-involved faults, particularly along the Gidgealpa-Merrimelia-Innamincka and Murteree-Nappacoongee ridges. Initial structural trap development occurred during the early Permian, but was most significant during the Late Triassic. Hydrocarbon accumulations were unaffected by structural growth after the critical moment in the petroleum system (90 Ma), as the final period of fault activity was during the Late Cretaceous. This research constrains the tectonostratigraphic evolution of the intra-cratonic Cooper and Eromanga basins, while detailing an approach that extracts and analyses important structural and stratigraphic information from geophysical data, where outcrop is not accessible.David Kulikowski, Khalid Amrouc

4D quantification of stress and strain tensors at Sheep Mountain Anticline (Wyoming, USA) using calcite twin analysis

We use the calcite twin analysis to investigate the relationship between fold development, stress and strain distribution. We chose for this study the Sheep Mountain Anticline (Wyoming, USA) as a natural laboratory. Because it's asymmetric and basement-cored fold, this anticline was formed during the Laramide orogeny in the Early Tertiary.The calcite twin have been measured in folded Lower Carboniferous to Permian age carbonates and sandstones. Calcite twin recorded both in the matrix and in the veins, highlight three different tectonic stages: the first phase is a pre-folding compression parallel to fold axis, a second one is also pre- folding compression but it's perpendicular to the future fold axis and the third stage is also perpendicular to the fold axis but it's a post-folding compression. Furthermore, calcite twin data provide information about the evolution of stress (Etchecopar's method) and strain (Groshong's method) through time and space. Both pre- folding and post-folding NE-directed compressional stress and/or shortening were recorded within pre-folding veins (set I) as well as in fold-related veins (sets II and III). Set III veins also recorded outer rim extension along the fold hinge line.Besides, calcite twin analysis allow us to quantify stress and strain. Our results point out both temporal and spatial evolution of stress and strain tensors. Spatially, we notice that both strain and particularly differential-stress in the backlimb are higher than in the forelimb. We are also able to show that differential-stress drops both in the backlimb and in the forelimb between pre-folding and post-folding stages. Our new dataset should putting better constrains on numerical models in order to increase our knowledge on fold mechanics.Amrouch, K.; Lacombe, O.; Daniel, J

Mapping permeable subsurface fracture networks: a case study on the Cooper Basin, Australia

The spatial distribution of permeable fracture networks is constrained in the subsurface Cooper Basin (Australia) through the integration of most positive curvature (K₊) analysis of five three dimensional (3D) seismic surveys, wellbore fracture data, and geomechanical modelling. The K₊ provides the likely distribution of subsurface extensional fractures based on the stress redistribution along the outer arc of an anticline. These results are reprocessed into the semblance (similarity) attribute to improve the signal-noise ratio prior to being extracted along the gas-rich and low permeability Patchawarra Formation. The subsurface fracture distribution maps show the geometry and density of extensional fractures that have been shown to facilitate fluid migration in this province, particularly those striking SE-NW and E-W, as these are properly oriented to undergo tensile reactivation. The density of these permeable SE-NW and E-W striking fracture sets is predicted to significantly increase along E-W elongate anticlines and may contribute to improved hydrocarbon recovery in this low permeability stratigraphic interval. We show that wellbore fracture data (n=917) in the Patchawarra Formation presents a close relationship to K₊ results and can be used to generate high density structural data in this basin, with the methodology applicable to other subsurface and offshore provinces.David Kulikowski, Khalid Amrouch, Hugo B. Burgi