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Collaborating Authors
Results
A program to calculate the state of stress in the vicinity of an inclined borehole through an anisotropic rock formation
Li, Wei (Southwest Petroleum University, University of Alberta, China University of Geosciences (Beijing)) | Schmitt, Douglas R. (University of Alberta) | Tibbo, Maria (University of Toronto) | Zou, Changchun (China University of Geosciences (Beijing))
ABSTRACT A borehole existing in any geologic formation concentrates the far-field tectonic and overburden stresses amplifying the magnitudes of certain stress components near the borehole. It is important to understand the magnitudes and patterns of this stress concentration because these lead to damage and can even collapse the borehole if sufficiently strong. The solution of the stress distributed near a borehole can be complicated considering the elastic anisotropy of rocks. We have developed programs (ASCIB3D) in MATLAB and Python to model the stress distribution around an inclined borehole in an arbitrarily oriented anisotropic medium. The program is built on the Lekhnitskij-Amadei solution. The input orientation of the far-field stresses and the elastic stiffness matrix of the medium into the program are geology angles instead of the rotation angles shown in previous studies, making the code more convenient for users. The sign convention for the inverse function, which is ignored in previous studies, is discussed in detail. The results indicate that the program ASCIB3D is a useful tool for modeling the stress distributed around an inclined borehole in the anisotropic formation and analyzing the effect of anisotropy and borehole inclination on stress distribution. The inclination and azimuth of the borehole and the anisotropy of the rocks affect the orientation and strength of the stress concentration.
- Asia (0.68)
- North America > Canada > Alberta (0.46)
- North America > United States > Texas (0.46)
- North America > Canada > Ontario (0.28)
- Geophysics > Borehole Geophysics (1.00)
- Geophysics > Seismic Surveying (0.68)
- Well Drilling (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Open hole/cased hole log analysis (1.00)
ABSTRACT Bitumen retains significant solid-like behavior even in temperatures in excess of 50°C. Traditional ultrasonic wave-propagation studies have, however, largely ignored the existence of the shear modulus in such materials, and they have mostly assumed that the observed longitudinal (P) wave speeds solely depend on the fluid’s bulk modulus. To further study this, we have measured ultrasonic longitudinal (P) wave transmission speeds through viscous bitumen at different pressures (0.1–15 MPa) and temperatures (7–132°C) using an adapted version of the technique that consists of two piezoelectric receivers placed at unequal lengths from the transmitter. As such, we are able to calculate the P-wave attenuation and velocity that is used to derive the material’s complex longitudinal modulus. Using parallel measurements of the bitumen’s complex shear modulus, we find that the bulk modulus differs from the longitudinal modulus particularly at lower (reservoirs) temperatures. The results, together with the realization that bitumen experiences a sequence of various compositional and thermophysical phase that is primarily temperature-dependent, can be implemented to improve the fluid-substitution analyses of rock-physics studies of bitumen-saturated reservoirs.
- North America > United States (0.67)
- North America > Canada > Alberta (0.47)
- Geophysics > Seismic Surveying (1.00)
- Geophysics > Time-Lapse Surveying > Time-Lapse Seismic Surveying (0.68)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Oil sand, oil shale, bitumen (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Facilities Design, Construction and Operation > Unconventional Production Facilities > Oil sand/shale/bitumen (1.00)
Estimation of δ and C13 of organic-rich shale from laser ultrasonic technique measurement
Xie, Jianyong (Chengdu University of Technology (CDUT), China University of Petroleum, China University of Petroleum, University of Alberta) | Di, Bangrang (China University of Petroleum, China University of Petroleum) | Schmitt, Douglas R. (University of Alberta) | Wei, Jianxin (China University of Petroleum, China University of Petroleum) | Chen, Yangkang (Oak Ridge National Laboratory)
ABSTRACT The laser ultrasonic technique (LUT) has many advantages in dealing with the anisotropy of organic-rich shale over the transducer ultrasonic contacting measurement. We have developed a systematic procedure to estimate anisotropic parameter and elastic parameter in organic-rich shale from LUT measurement. A novel filtering method called the structural-oriented space-varying median filter (SOSVMF) is proposed for removing the erratic noise from the recorded data. We apply the proposed algorithm onto one synthetic example and real recorded data in artificial bakelite and organic-rich shale by using LUT to show the successful performance. Compared with the original recorded data, the denoised waveform by SOSVMF will also help to obtain more accurate parameter estimations of the anisotropic parameter and elastic parameter . More importantly, the presented systematic procedure may extend the application of LUT to the study of attenuation anisotropy in organic-rich shale and scale physical modeling. In addition, the surface-modification method may be an effective method to enhance the laser-ultrasonic conversion efficiency.
- North America > United States (1.00)
- Asia > China (0.69)
- North America > Canada > Alberta (0.46)
- Geophysics > Seismic Surveying > Seismic Processing (1.00)
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling (0.46)
- North America > United States > Texas > Fort Worth Basin > Barnett Shale Formation (0.99)
- North America > United States > South Dakota > Williston Basin (0.99)
- North America > United States > North Dakota > Williston Basin (0.99)
- (3 more...)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (1.00)
- Data Science & Engineering Analytics > Information Management and Systems (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management (0.93)
- Information Technology > Data Science (0.68)
- Information Technology > Artificial Intelligence (0.54)
The Society of Exploration Geophysicists (SEG) and the American Geophysical Union (AGU), through the AGU-SEG Collaboration Committee, organize and support joint meetings to bridge the geophysical knowledge among these societies. The workshop, “Upper crust physics of rock,” held 11–14 July 2016 in Hilo, Hawaii, is the latest of these collaborations. The meeting focused on highlighting the latest rock-physics knowledge from a tectonic, volcanology, petroleum, and CO2 sequestration perspective to advance our understanding and calibration of remotely sensed field geophysical observations.
A comparative study of the anisotropic dynamic and static elastic moduli of unconventional reservoir shales: Implication for geomechanical investigations
Meléndez-Martínez, Jaime (University of Alberta, Institute for Geophysical Research, Mexican Petroleum Institute) | Schmitt, Douglas R. (University of Alberta)
ABSTRACT 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.
- North America > United States (1.00)
- North America > Canada > Alberta (1.00)
- North America > Canada > Saskatchewan (0.92)
- (2 more...)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geophysics > Seismic Surveying (1.00)
- Geophysics > Borehole Geophysics (1.00)
- South America > Venezuela > Caribbean Sea > Cariaco Basin (0.99)
- North America > United States > Wyoming > Laramie Basin > Niobrara Formation (0.99)
- North America > United States > Texas > Fort Worth Basin > Barnett Shale Formation (0.99)
- (18 more...)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Open hole/cased hole log analysis (1.00)
ABSTRACT The Devonian Grosmont Formation in northeastern Alberta, Canada, is the world’s largest accumulation of heavy oil in carbonate rock with estimated bitumen in place of . Much of the reservoir unconformably subcrops beneath Cretaceous sediments. This is an eroded surface modified by kartstification known as the Sub-Mannville Unconformity (SMU). We studied the reanalysis and integration of legacy seismic data sets obtained in the mid-1980s to investigate the structure of this surface. Standard data processing was carried out supplemented by some more modern approaches to noise reduction. The interpretation of these reprocessed data resulted in some key structural maps above and below the SMU. These seismic maps revealed substantially more detail than those constructed solely on the basis of well-log data; in fact, the use of only well-log information would likely result in erroneous interpretations. Although features smaller than about 40 m in radius cannot be easily discerned at the SMU due to wavefield and data sampling limits, the data did reveal the existence of a roughly east–west-trending ridge-valley system. A more minor northeast–southwest-trending linear valley also was apparent. These observations are all consistent with the model of a karsted/eroded carbonate surface. Comparison of the maps for the differing horizons further suggested that deeper horizons may influence the structure of the SMU and even the overlying Mesozoic formations. This suggested that some displacements due to karst cavity collapse or minor faulting within the Grosmont occurred during or after deposition of the younger Mesozoic sediments on top of the Grosmont surface.
- Phanerozoic > Mesozoic (1.00)
- Phanerozoic > Paleozoic > Devonian > Upper Devonian (0.48)
- Geology > Structural Geology (1.00)
- Geology > Sedimentary Geology (1.00)
- Geology > Petroleum Play Type > Unconventional Play > Heavy Oil Play (1.00)
- (2 more...)
- North America > Canada > Saskatchewan > Western Canada Sedimentary Basin > Alberta Basin (0.99)
- North America > Canada > Northwest Territories > Western Canada Sedimentary Basin > Alberta Basin (0.99)
- North America > Canada > Manitoba > Western Canada Sedimentary Basin > Alberta Basin (0.99)
- (35 more...)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Oil sand, oil shale, bitumen (1.00)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Carbonate reservoirs (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- (4 more...)
No perfectly elastic medium exists in the earth. In an anelastic medium, seismic waves are distorted by attenuation and velocity dispersion. Velocity dispersion depends on the petrophysical properties of reservoir rocks, such as porosity, fractures, fluid mobility, and the scale of heterogeneities. However, velocity dispersion usually is neglected in seismic data processing partly because of the insufficiency of observations in the exploration seismic frequency band (∼5 through ). The feasibility of determining velocity dispersion in this band is investigated. Four methods are used in measuring velocity dispersion from uncorrelated vibrator vertical seismic profile (VSP) data: the moving window crosscorrelation (MWCC) method, instantaneous phase method, time-frequency spectral decomposition method, and cross-spectrum method. The MWCC method is a new method that is satisfactorily robust, accurate, and efficient in measuring the frequency-dependent traveltime in uncorrelated vibrator records. The MWCC method is applied to the uncorrelated vibrator VSP data acquired in the Mallik gas hydrate research well. For the first time, continuous velocity dispersion is observed in the exploration seismic frequency band using uncorrelated vibrator VSP data. The observed velocity dispersion is fitted to a straight line with respect to log frequency to calculate . This provides an alternative method for measurement.
- North America > Canada > Ontario (0.28)
- North America > Canada > Alberta (0.28)
- North America > Canada > Saskatchewan > Athabasca Basin (0.99)
- North America > Canada > Alberta > Athabasca Basin (0.99)
The seismic reflection characterizations of a thin layer are important for reservoir geophysics. However, discussions on the reflection for a thin layer are usually restricted to precritical angle incidence. In this work, an exact analytical solution is derived to model the reflection amplitude and amplitude variation with offset (AVO) responses of a single thin bed for arbitrary incident angles. The results show that the influence of an ultrathin bed is great for oppositepolarity reflections and is small for identicalpolarity reflections. Oppositepolarity precritical reflection amplitudes first decrease in magnitude with the wavelength/thickness ratio to a local minimum, then increase to a maximum, and finally decrease gradually to zero as the layer vanishes. Oppositepolarity postcritical reflections monotonically decrease from near unity to zero, proportional to the thickness of the layer. Identicalpolarity precritical reflection amplitudes first increase in magnitude with the wavelength/thickness ratio to a local maximum, then decrease to a minimum, and finally increase to the amplitude of a single bottom reflection when the layer vanishes. Identicalpolarity postcritical reflections have magnitudes near unity. The AVO responses for both opposite and identicalpolarity acoustic thin beds gradually increase with angle. The influence of the Poisson's ratio of the thin bed is small for either small incidence angles or thicknesses less than 7 of the seismic wavelength, but is large for high incidence angles or thicknesses greater than 13 of the wavelength. A decrease of Poisson's ratio causes a pronounced AVO response that reaches its maximum at the quarterwavelength tuning thickness.
- Geology > Rock Type (1.00)
- Geology > Geological Subdiscipline > Stratigraphy (1.00)
- North America > Canada > Saskatchewan > Western Canada Sedimentary Basin > Alberta Basin (0.99)
- North America > Canada > Northwest Territories > Western Canada Sedimentary Basin > Alberta Basin (0.99)
- North America > Canada > Manitoba > Western Canada Sedimentary Basin > Alberta Basin (0.99)
- (2 more...)
Rayleighwave dispersion is used to study the nearsurface elastic properties of a thick, lacustrine clay to approximately 10 m depth. Ten repeated sets of Rayleigh dispersion curves were obtained through late spring to early fall. A variety of methodologies were used to extract the dispersion curves, but a modified frequencyray parameter (fp) method most successfully yields dispersion curves for the first three Rayleigh modes. The Rayleighwave velocities varied from 100 to 350 m/s with frequency over the band from 75 to 10 Hz. Over this band, these velocities did not measurably vary during the study period. The observed phase velocity curves were inverted with Pwave and density values obtained from shallow coring to obtain the shearwave velocity structure at the site down to > 14 m. This case study highlights the robust, repeatable, nature of surface wave dispersion methods when care is taken in the acquisition of field data.
- Geology > Rock Type > Sedimentary Rock (0.46)
- Geology > Sedimentary Geology > Depositional Environment > Continental Environment > Lacustrine Environment (0.35)
Contrasts in the elastic-wave velocities and densities of rocks are the most important physical properties influencing the overall seismic response of an orebody. The wave velocities depend on the in-situ elastic properties, which in crystalline metamorphic and igneous rocks are controlled by mineralogical content, damage, stress, in-situ fractures, pressure, and saturation. The elastic properties of core samples of rocks at standard conditions usually will not be representative of those for the same material at depth within the earth. Elastic-wave and density geophysical wireline logs provide important information to constrain the in-situ elastic properties, but a practitioner must be aware of what effects can influence the final interpretation of the logs. Two examples of combined density and full waveform sonic logs highlight the utility of such logs in delineating massive sulfide orebodies and the use of such logs to estimate the in-situ elastic impedances needed for modeling of the seismic wavefield.
- North America > Canada (0.93)
- North America > United States > Texas > Coleman County (0.24)
- Overview (0.46)
- Instructional Material > Course Syllabus & Notes (0.40)
- Geology > Rock Type > Igneous Rock (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geophysics > Borehole Geophysics (1.00)
- Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling (0.93)
- Geophysics > Seismic Surveying > Seismic Processing (0.88)
- Geophysics > Seismic Surveying > Borehole Seismic Surveying (0.67)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Open hole/cased hole log analysis (1.00)