A comparative study of the anisotropic dynamic and static elastic moduli of unconventional reservoir shales: Implication for geomechanical investigations

Geophysics ◽  
2016 ◽  
Vol 81 (3) ◽  
pp. D245-D261 ◽  
Author(s):  
Jaime Meléndez-Martínez ◽  
Douglas R. Schmitt
Keyword(s):  
Bedding Plane ◽  
Horizontal Stress ◽  
Pressure Sensitivity ◽  
S Wave ◽  
Fracture Pressure ◽  
Highly Nonlinear ◽  
Rock Anisotropy ◽  
Minimum Stress ◽  
Sonic Logging ◽  
Static Elastic Moduli

We obtained the complete set of dynamic elastic stiffnesses for a suite of “shales” representative of unconventional reservoirs from simultaneously measured P- and S-wave speeds on single prisms specially machined from cores. Static linear compressibilities were concurrently obtained using strain gauges attached to the prism. Regardless of being from static or dynamic measurements, the pressure sensitivity varies strongly with the direction of measurement. Furthermore, the static and dynamic linear compressibilities measured parallel to the bedding are nearly the same whereas those perpendicular to the bedding can differ by as much as 100%. Compliant cracklike porosity, seen in scanning electron microscope images, controls the elastic properties measured perpendicular to the rock’s bedding plane and results in highly nonlinear pressure sensitivity. In contrast, those properties measured parallel to the bedding are nearly insensitive to stress. This anisotropy to the pressure dependency of the strains and moduli further complicates the study of the overall anisotropy of such rocks. This horizontal stress insensitivity has implications for the use of advanced sonic logging techniques for stress direction indication. Finally, we tested the validity of the practice of estimating the fracture pressure gradient (i.e., horizontal stress) using our observed elastic engineering moduli and found that ignoring anisotropy would lead to underestimates of the minimum stress by as much as 90%. Although one could ostensibly obtain better values or the minimum stress if the rock anisotropy is included, we would hope that these results will instead discourage this method of estimating horizontal stress in favor of more reliable techniques.

scholarly journals How Nanopores Influence Dry-Frame VP Pressure Sensitivity

2021 ◽  
Vol 9 ◽  
Author(s):  
Rohit Raj ◽  
Priyank Jaiswal ◽  
Yulun Wang ◽  
G. Michael Grammer ◽  
Ralf J. Weger
Keyword(s):  
Fluid Model ◽  
Confining Pressure ◽  
P Wave ◽  
Pore Shape ◽  
Pressure Sensitivity ◽  
S Wave ◽  
Shape Distribution ◽  
Transit Times ◽  
Three Samples ◽  
The Individual

This paper investigates how nanopore size distribution influences dry-frame P-wave velocity (VP) pressure sensitivity. The study uses a set of twenty-three samples belonging to a single vertical core from the Mississippian-age Meramec formation of the mid-continent US. Individual samples had their facies interpreted, composition estimated, He-gas porosity (ΦHe) determined, and P-wave and S-wave transit times systematically measured for dry core-plugs in a 5–40 MPa loading and unloading cycle. Data from the unloading cycle were linearized in the log scale, and the slope of the best fitting line was considered as a representative of the dry-frame VP pressure sensitivity. A series of photomicrographs from each sample were analyzed using image processing methods to obtain the shape and size of the individual pores, which were mostly in the nanopore (10−6–10–9 m) scale. At the outset, the pore-shape distribution plots were used to identify and discard samples with excessive cracks and complex pores. When the remaining samples were compared, it was found that within the same facies and pore-shape distribution subgroups VP pressure sensitivity increased as the dominant pore-size became smaller. This was largely independent of ΦHe and composition. The paper postulates that at the nanopore scale in the Meramec formation, pores are mostly isolated, and an increase in the confining pressure increased the bulk moduli of the fluids in the isolated pores, which in turn increased the VP pressure sensitivity. The study proposes incorporating this effect quantitatively through a dual-fluid model where the part of the fluid in unconnected pores is considered compressible while the remaining is considered incompressible. Results start to explain the universal observation of why the presence of microporosity quintessentially enhances VP pressure sensitivity.

scholarly journals Prior Analysis in Determination of TI Anisotropy Type through Well-Based Modelling: A Case Study on the Deep Water Environment

2021 ◽  
Vol 873 (1) ◽  
pp. 012102
Author(s):  
Madaniya Oktariena ◽  
Wahyu Triyoso ◽  
Fatkhan Fatkhan ◽  
Sigit Sukmono ◽  
Erlangga Septama ◽  
...  
Keyword(s):  
Wave Velocity ◽  
Deep Water ◽  
Initial Conditions ◽  
Transverse Isotropy ◽  
Water Environment ◽  
Horizontal Stress ◽  
P Wave ◽  
S Wave ◽  
Geomechanical Analysis ◽  
Vertical Transverse Isotropy

Abstract The existence of anisotropy phenomena in the subsurface will affect the image quality of seismic data. Hence a prior knowledge of the type of anisotropy is quite essential, especially when dealing with deep water targets. The preliminary result of the anisotropy of the well-based modelling in deep water exploration and development is discussed in this study. Anisotropy types are modelled for Vertical Transverse Isotropy (VTI) and Horizontal Transverse Isotropy (HTI) based on Thomsen Parameters of ε and γ. The parameters are obtained from DSI Logging paired with reference δ value for modelling. Three initial conditions are then analysed. The first assumption is isotropic, in which the P-Wave Velocity, S-Wave Velocity, and Density Log modelled at their in-situ condition. The second and third assumptions are anisotropy models that are VTI and HTI. In terms of HTI, the result shows that the model of CDP Gather in the offset domain has a weak distortion in Amplitude Variation with Azimuth (AVAz). However, another finding shows a relatively strong hockey effect in far offset, which indicates that the target level is a VTI dominated type. It is supported by the geomechanical analysis result in which vertical stress acts as the maximum principal axis while horizontal stress is close to isotropic one. To sum up, this prior anisotropy knowledge obtained based on this study could guide the efficiency guidance in exploring the deep water environment.

3D Alford rotation analysis for the Diamond M Field, Midland Basin, Texas

2014 ◽  
Vol 2 (2) ◽  
pp. SE63-SE75 ◽  
Author(s):  
Oswaldo E. Davogustto Cataldo ◽  
Timothy J. Kwiatkowski ◽  
Kurt J. Marfurt ◽  
Steven L. Roche ◽  
James W. Thomas
Keyword(s):  
Vertical Component ◽  
Horizontal Stress ◽  
Compressional Wave ◽  
Carbonate Reservoir ◽  
S Wave ◽  
Stress Regime ◽  
Compressional Waves ◽  
Principal Axes ◽  
Wave Splitting ◽  
Processing Effort

The 2C by 2C S-wave survey generated significant excitement in the mid-1980s, but then it fell out of favor when S-wave splitting initially attributed to fractures was also found to be associated with an anisotropic stress regime. In general, 2C by 2C data require more expensive acquisition and more processing effort to obtain images comparable to 1C “compressional wave” data acquired with vertical component sources and receivers. Because S-waves are insensitive to fluids, and hence the water table, the effective S-wave weathering zone is greater than that for compressional waves, making statics more difficult. S-wave splitting due to anisotropy complicates residual statics and velocity analysis as well as the final image. S-wave frequencies and S-wave moveout are closer to those of contaminating ground roll than compressional waves. Since Alford’s introduction of S-wave rotation from survey coordinates to the principal axes in 1986, geoscientist and engineers retain their interest in fractures but are also keenly interested in the direction and magnitude of maximum horizontal stress. Simultaneous sweep and improved recording technology have reduced the acquisition cost to approximate that of 1C data. Alford’s work was applied to 2C by 2C poststack data. We extended the Alford rotation to prestack data using a modern high-fold 2C by 2C survey acquired over a fractured carbonate reservoir in the Diamond M Field, Texas. Through careful processing, the resulting images were comparable and in many places superior to that of the contemporaneously acquired 1C data. More importantly, we found a good correlation between our derived fracture azimuth map and the fracture azimuth log data from wells present in the field.

scholarly journals Comparison of elastic moduli from seismic diving-wave and ice-core microstructure analysis in Antarctic polar firn

2019 ◽  
Vol 60 (79) ◽  
pp. 220-230 ◽  
Author(s):  
Rebecca Schlegel ◽  
Anja Diez ◽  
Henning Löwe ◽  
Christoph Mayer ◽  
Astrid Lambrecht ◽  
...  
Keyword(s):  
Elastic Moduli ◽  
Seismic Velocity ◽  
Ice Core ◽  
S Wave ◽  
Uncertainty Range ◽  
Wave Refraction ◽  
Refraction Seismic ◽  
Dynamic Elastic Moduli ◽  
Static Elastic Moduli ◽  
Firn Core

ABSTRACTWe compared elastic moduli in polar firn derived from diving wave refraction seismic velocity analysis, firn-core density measurements and microstructure modelling based on firn-core data. The seismic data were obtained with a small electrodynamic vibrator source near Kohnen Station, East Antarctica. The analysis of diving waves resulted in velocity–depth profiles for different wave types (P-, SH- and SV-waves). Dynamic elastic moduli of firn were derived by combining P- and S-wave velocities and densities obtained from firn-core measurements. The structural finite-element method (FEM) was used to calculate the components of the elastic tensor from firn microstructure derived from X-ray tomography of firn-core samples at depths of 10, 42, 71 and 99 m, providing static elastic moduli. Shear and bulk moduli range from 0.39 to 2.42 GPa and 0.68 to 2.42 GPa, respectively. The elastic moduli from seismic observations and the structural FEM agree within 8.5% for the deepest achieved values at a depth of 71 m, and are within the uncertainty range. Our observations demonstrate that the elastic moduli of the firn can be consistently obtained from two independent methods which are based on dynamic (seismic) and static (tomography and FEM) observations, respectively, for deeper layers in the firn below ~10 m depth.

Estimating geomechanical parameters from microseismic plane focal mechanisms recorded during multistage hydraulic fracturing

Geophysics ◽  
2017 ◽  
Vol 82 (1) ◽  
pp. KS1-KS11 ◽  
Author(s):  
Wenhuan Kuang ◽  
Mark Zoback ◽  
Jie Zhang
Keyword(s):  
Hydraulic Fracturing ◽  
Pore Pressure ◽  
Principal Stress ◽  
Focal Plane ◽  
Amplitude Ratio ◽  
Horizontal Stress ◽  
Focal Mechanisms ◽  
P Wave ◽  
S Wave ◽  
Multistage Hydraulic Fracturing

We extend a full-waveform modeling method to invert source focal-plane mechanisms for microseismic data recorded with dual-borehole seismic arrays. Combining inverted focal-plane mechanisms with geomechanics knowledge, we map the pore pressure distribution in the reservoir. Determining focal mechanisms for microseismic events is challenging due to poor geometry coverage. We use the P-wave polarities, the P- and S-wave similarities, the SV/P amplitude ratio, and the SH/P amplitude ratio to invert the focal-plane mechanisms. A synthetic study proves that this method can effectively resolve focal mechanisms with dual-array geometry. We apply this method to 47 relatively large events recorded during a hydraulic fracturing operation in the Barnett Shale. The focal mechanisms are used to invert for the orientation and relative magnitudes of the principal stress axes, the orientation of the planes slipping in shear, and the approximate pore pressure perturbation that caused the slip. The analysis of the focal mechanisms consistently shows a normal faulting stress state with the maximum principal stress near vertical, the maximum horizontal stress near horizontal at an azimuth of N60°E, and the minimum horizontal stress near horizontal at an azimuth of S30°E. We propose a general method that can be used to obtain microseismic focal-plane mechanisms and use them to improve the geomechanical understanding of the stimulation process during multistage hydraulic fracturing.

Experimental Investigation of Reservoir Stress Path Hysteresis During Production-Injection Periods

2014 ◽  
Author(s):  
Mojtaba P. Shahri ◽  
Stefan Z. Miska
Keyword(s):  
Pore Pressure ◽  
Poisson’S Ratio ◽  
Stress Path ◽  
Horizontal Stress ◽  
Poisson's Ratio ◽  
Injection Process ◽  
Fracture Pressure ◽  
Industry Standards ◽  
Depletion Period ◽  
Stress Changes

There has been an increasing consciousness regarding stress changes associated with reservoir depletion as the industry moves towards more challenging jobs in deep-water or depleted reservoirs. These stress changes play a significant role in the design of wells in this condition. Therefore, accurate prediction of reservoir stress path, i.e., change in horizontal stresses with pore pressure, is of vital importance. In this study, the current stress path formulation is investigated using a Tri-axial Rock Mechanics Testing Facility. The reservoir depletion scenario is simulated through experiments and provides a better perspective on the currently used formulation and how it’s applicable during production and injection periods. The effect of fluid re-injection into reservoirs on the horizontal stress is also analyzed using core samples. According to the results, formation fracture pressure would not be equal to its initial value if pressure builds up using re-injection. The irrecoverable formation fracture pressure has a power law relation with pore pressure drawdown range. In order to avoid higher permanent fracture pressure reduction, it’s recommended to start the injection process as soon as possible during the production life of reservoirs. According to the experimental results, rocks behave differently during production and injection periods. Poisson’s ratio is greater during pressure build-up as compared to the depletion period. According to the current industry standards, Poisson’s ratio is usually obtained using fracturing data; i.e., leak-off test or mini-fracture test, or well logging methods. However, we are not able to use the same Poisson’s ratio for both pressure drawdown and build-up scenarios according to the experimental data. Corresponding to Poisson’s ratio values, the change in horizontal stress with pore pressure during drawdown (production) is higher than during build-up (injection) period. The outcomes of this study can significantly contribute to well planning and design of challenging wells over the life of reservoirs.

scholarly journals Seismic Anisotropy and  Stress of the Canterbury  Plains

2021 ◽  
Author(s):  
◽  
Rob Holt
Keyword(s):  
Seismic Anisotropy ◽  
Horizontal Stress ◽  
Tectonic Stress ◽  
Aftershock Sequence ◽  
S Wave ◽  
Principal Stresses ◽  
Seismic Properties ◽  
Average Value ◽  
North East ◽  
Slip Regime

<p>The Mѡ=7.1 Darfield (Canterbury) earthquake struck on 4 September 2010, approximately 45 km west of Christchurch, New Zealand. It revealed a previously unknown fault (the Greendale fault) and caused billions of dollars of damage due to high peak ground velocities and extensive liquefaction. It also triggered the Mw=6.3 Christchurch earthquake on 22 February 2011, which caused further damage and the loss of 185 lives. The objective of this research was to determine the relationship between stress and seismic properties in a seismically active region using manually-picked P and S wave arrival times from the aftershock sequence between 8 September 2010-13 January 2011 to estimate shear-wave splitting (SWS) parameters, VP =VS-ratios, anisotropy (delay-time tomography), focal mechanisms, and tectonic stress on the Canterbury plains. The maximum horizontal stress direction was highly consistent in the plains, with an average value of SHmax=116 18 . However, the estimates showed variation in SHmax near the fault, with one estimate rotating by as much as 30° counter-clockwise. This suggests heterogeneity of stress at the fault, though the cause remains unclear. Orientations of the principal stresses predominantly indicate a strike-slip regime, but there are possible thrust regimes to the west and north/east of the fault. The SWS fast directions (ø) on the plains show alignment with SHmax at the majority of stations, indicating stress controlled anisotropy. However, structural effects appear more dominant in the neighbouring regions of the Southern Alps and Banks Peninsula.</p>

Hydraulic fracture-height containment by permeable weak bedding interfaces

Geophysics ◽  
2018 ◽  
Vol 83 (3) ◽  
pp. MR137-MR152 ◽  
Author(s):  
Xiaowei Weng ◽  
Dimitry Chuprakov ◽  
Olga Kresse ◽  
Romain Prioul ◽  
Haotian Wang
Keyword(s):  
Coefficient Of Friction ◽  
Hydraulic Fracture ◽  
Shear Failure ◽  
Mechanistic Model ◽  
Bedding Plane ◽  
Horizontal Stress ◽  
Height Growth ◽  
Vertical Stress ◽  
Weak Interface ◽  
Minimum Horizontal Stress

In laminated formations, the vertical height growth of a hydraulic fracture can be strongly influenced by the interaction of the fracture tip with the bedding interfaces it crosses. A weak interface may fail in shear and then slip, depending on the strength and frictional properties, the effective vertical stress at the interface, and the net pressure. Shear failure and slippage at the interface can retard the height growth or even stop it completely. A 2D analytical model called the FracT model has been developed that examines the shear slippage along the bedding interface adjacent to the fracture tip and the resulting blunting of the fracture tip at the interface, as well as the stress condition on the face opposite from the hydraulic fracture tip for possible fracture nucleation that leads to fracture crossing. The growth of the shear slippage along the interface with time is coupled with the fluid flow into the permeable interface. A parametric study has been carried out to investigate the key formation parameters that influence the crossing/arrest of the fracture at the bedding interface and the shear slippage and depth of fluid penetration into the interface. The study suggests that the interfacial coefficient of friction and the ratio of the vertical to minimum horizontal stress are two of the most influential parameters governing fracture arrest by a weak interface. For the fracture tip to be arrested at the interface, the vertical stress acting on the interface must be close to the minimum horizontal stress or the interfacial coefficient of friction must be very small. The FracT model has also been integrated into a pseudo-3D-based complex hydraulic fracture model. This quantitative mechanistic model that incorporates a bedding-plane slip-driven mechanism is a necessary step to understand and bridge the characterization (sonic) and monitoring (microseismic) observations.

scholarly journals Magnetic fabric of Siwalik sediments (Nepal): implications to time-space evolution of stress field

2008 ◽  
Vol 38 ◽  
pp. 39-48
Author(s):  
Pitambar Gautam
Keyword(s):  
Stress Field ◽  
Bedding Plane ◽  
Horizontal Stress ◽  
Magnetic Polarity ◽  
Magnetic Fabric ◽  
Compression Direction ◽  
Time Space ◽  
Depositional Age ◽  
Tectonic Rotation ◽  
Magnetic Lineations

Magnetic fabric data based on the anisotropy of magnetic susceptibility (AMS) of the sediments constituting the Siwalik sections (Kamali R., Amilia- Tui Road, Surai R., Tinau R., and Rato R.) in Nepal have been analysed for the variability of magnetic lineation and the implications to the time-space evolution of the stress field in this region during the last 16 myrs. This invo lved compilation of (i) the magnetic polarity data that constrain the depositional age of the Nepalese Siwaliks to ca. 16 to 1 Ma, and (ii) the declination of characteristic magnetic remanence to reveal the relative tectonic rotations (17° CCW at Butwal to 9° CW at Amilia). The magnetic fabric, defined mainly by alignment of paramagnetic minerals, corresponds to an oblate ellipsoid with foliation parallel to bedding plane, implying a sedimentary-compactional origin. The magnetic lineations show well defined clusters (confined in or close to the bedding plane). Being subparallel to the fold axes/bedding strikes/thrust fronts, these lineations are assumed to originate from a secondary mild deformation process related to the compression tectonics in the Siwalik foredeep and therefore correspond to the active direction of the minimum principal horizontal stress active during foredeep deposition. Hence, the direction of compression is orthogonal to the mean lineation. The compression direction in the palaeogeographic coordinates can be obtained by introducing an additional correction for the tectonic rotation about the vertical, using the palaeomagnetic declination. Available AMS-based lineations, corrected for rotation about vertical using palaeomagnetic declinations, reveal that the compression direction in the Himalayan foreland remained in general N to NNE with significant deviations in its far western part, in particular around the Amilia- Tui section where the direction was NS8°E.

Estimating SHmax azimuth with P sources and vertical geophones: Use P-P reflection amplitudes or use SV-P reflection times?

2021 ◽  
pp. 1-49
Author(s):  
Bob Hardage ◽  
Mike Graul ◽  
Tim Hall ◽  
Chris Hall ◽  
Mark Kelley ◽  
...  
Keyword(s):  
Incident Angle ◽  
Ground Truth ◽  
Horizontal Stress ◽  
Gradient Estimates ◽  
Michigan Basin ◽  
Reflection Seismology ◽  
S Wave ◽  
Arrival Times ◽  
Maximum Horizontal Stress ◽  
P Sources

We compared two methods for extracting the azimuth of maximum horizontal stress (SHmax) from 3D land-based seismic data generated by a P source and recorded with vertical geophones. In the first method, we used the direct-SV mode that is produced by all land-based P sources. P sources generate SV illumination that radiates in all azimuth directions from a source station and creates SV-P reflections that are recorded by vertical geophones. Unless stratigraphy has steep dip, SV-P raypaths recorded by vertical geophones are the reverse of P-SV raypaths recorded by horizontal geophones. Thus, SV-P data provide the same S-wave sensitivity to stress fields as popular P-SV data do. In the second method, we retrieved P-P reflections and then performed an amplitude-versus-incident-angle (AVA) analysis of the amplitude-gradient behavior of P-P reflection wavelets. We did this analysis in narrow azimuth corridors to determine the gradient of reflection-wavelet amplitudes as a function of azimuth. This P-P AVA amplitude-gradient method has been of great interest in the reflection seismology community since it was introduced in the late 1990s. Each of these methods, AVA analysis of the gradient of P-P reflection amplitudes and azimuth-dependent arrival times of SV-P reflections can be used to determine the azimuth of SHmax stress. We compare the results of the two methods with ground truth measurements of SHmax azimuth at a CO2 sequestration site in the Michigan Basin. SHmax azimuths were determined from P-P and SV-P data at three major boundaries at depths of approximately 3500 ft (1067 m), 5500 ft (1676 m), and 7500 ft (2286 m). Two estimates of SHmax azimuth (one using SV-P data and one using P-P data) were made at each stacking bin inside a 24 mi2 (62 km2) image space. The result was approximately 98,000 estimates of SHmax azimuth across each of these three boundaries for each of these two prediction strategies. Histogram displays of PP AVA gradient estimates had peaks at correct azimuths of SHmax at all three depths, but the spread of the distributions widened with depth and split into two peaks at the deepest boundary. In contrast, each histogram of SHmax azimuth predicted by azimuth-dependent SV-P traveltimes had a single, definitive peak that was positioned at the correct SHmax azimuth at all three boundary depths.

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