Geological and geophysical studies of buried valleys and their fills near Elora and Rockwood, Ontario

1994 ◽  
Vol 31 (12) ◽  
pp. 1838-1848 ◽  
Author(s):  
J. P. Greenhouse ◽  
P. F. Karrow
Keyword(s):  
Epithermal Neutron ◽  
Single Point ◽  
Low Frequency ◽  
Last Interglacial ◽  
Sedimentary Sequences ◽  
Transient Electromagnetic ◽  
Quaternary Sequences ◽  
Natural Gamma ◽  
Geophysical Logs ◽  
Well Data

Buried bedrock valleys are of economic interest for groundwater and engineering studies, and of scientific interest for the sedimentary sequences they may contain. Two buried valleys, about 60 m deep, north and northeast of Guelph, Ontario, are tributary to the major Dundas Valley southwest of Guelph. Located initially from water well data, their locations and geometry were refined with surface geophysics, including very low frequency resistivity, terrain conductivity, resistivity, transient electromagnetic, gravity, and seismic methods. Useful data are obtained roughly in proportion to cost. Cored and rotary holes in the two valleys were followed by geophysical downhole logging with normal electric, spontaneous potential, single-point resistance, calliper, neutron – epithermal neutron, gamma–gamma, and natural gamma methods. Cores revealed multi-till sequences in the upper parts of the holes and, together with geophysical logs and their interpreted electrofacies, indicate the presence of underlying uniform, pollen-bearing (pine and spruce dominate) lacustrine fills. These fills and the buried valleys containing them are interpreted to be perhaps as old as the last interglacial. Buried valleys are fruitful targets for the discovery of older Quaternary sequences.

Application of Geophysical Logging to Groundwater Studies in Southeastern Saskatchewan

1972 ◽  
Vol 9 (1) ◽  
pp. 78-94 ◽  
Author(s):  
J. H. Dyck ◽  
W. S. Keys ◽  
W. A. Meneley
Keyword(s):  
Epithermal Neutron ◽  
Single Point ◽  
Good Resolution ◽  
Spontaneous Potential ◽  
Gravel Beds ◽  
Natural Gamma ◽  
Water Well ◽  
Resistivity Logs ◽  
Routine Basis ◽  
Sand And Gravel

Single-point resistance and spontaneous potential logs in fresh-water filled rotary-drilled test-holes provide data useful in geohydrologic studies in Saskatchewan. These geophysical logs are made by many of the water well drilling contractors in Saskatchewan on a routine basis. The logs provide good resolution of various lithologic units and provide data required to estimate the salinity of water in sand beds prior to constructing a well.Caliper logging offers a potentially useful method for evaluating hole conditions and the effect of drilling techniques on the formation in completion zones. The casing collar locator log run in a previously constructed well near Estevan demonstrates that this device can provide an accurate and objective measurement of the position and length of each joint of casing, the position of the screen assembly, and the location of screened and blanked intervals within the screen assembly. This tool should find general application in water well construction and maintenance practice.The neutron-epithermal neutron log provides a method of measuring the porosity of sand and gravel beds. The response of the gamma log is similar to that of the spontaneous potential log and the neutron-epithermal neutron log deflects in a fashion similar to the resistance and resistivity logs. Nuclear logs offer the advantage that they can be run in cased or uncased boreholes which may be filled with any type of fluid. They require more complicated and expensive instrumentation and slow-speed logging to obtain the required resolution. The normal resistivity logs offer the possibility of determining the concentration of dissolved solids in the formation water. The gamma-gamma log is a poor alternative to the natural gamma and neutron log for stratigraphic correlations.

Use of seismoscope records to determine ML and peak velocities

1984 ◽  
Vol 74 (1) ◽  
pp. 315-324
Author(s):  
David M. Boore
Keyword(s):  
Lower Bound ◽  
San Francisco ◽  
Peak Velocity ◽  
Response Spectrum ◽  
Single Point ◽  
Empirical Relation ◽  
Low Frequency ◽  
Simulation Method ◽  
Horizontal Velocity ◽  
Earthquake Moment

Abstract More information about ground motion can be extracted from seismoscope records than a single point on a response spectrum. To demonstrate this, the relation between seismoscope response and Wood-Anderson instrument output and peak horizontal ground velocity has been studied by simulating the various responses for a range of distances and magnitudes. The simulations show that the relation used by Jennings and Kanamori (1979) to convert from peak seismoscope readings to the peak response of a Wood-Anderson instrument has a distance- and magnitude-dependent systematic error. The error is negligible, however, for modern seismoscopes at distances of a few tens of kilometers. At several hundred kilometers, the relation underestimates the Wood-Anderson response by as much as a factor of two. The spread in Jennings and Kanamori's estimate of ML for the 1906 San Francisco earthquake, recorded on seismoscopes having relatively low natural frequencies (0.26 and 0.5 Hz), is reduced by the results in this paper—the upper value, from a seismoscope in Carson City, Nevada, at 290 km from the fault, going from ML = 7.2 to ML = 7.0 and the lower value, from Yountville, California (R ≈ 60 km), going from about 6.3 to 6.4. About 0.3 units of the remaining spread may be due to local geologic site conditions. If the 0.3 units is distributed equally between the Yountville and Carson City recordings, the estimates of ML for the San Francisco earthquake then become 6.5 and 6.8, somewhat lower than Jennings and Kanamori's final estimates of 634 to 7. Although the error in using the relation of Jennings and Kanamori to estimate Wood-Anderson response was at most a factor of 1.6 for the 1906 earthquake, the error can be substantially larger for smaller earthquakes recorded on similar low frequency seismoscopes. The relation between Wood-Anderson and seismoscope response used by Jennings and Kanamori can be combined with an empirical relation between peak horizontal velocity and Wood-Anderson response to predict peak velocity from seismocope recordings. The simulations show that this relation (vmax = 8.1Awa, where vmax is the peak horizontal velocity in centimeters/second and Awa is one-half the range of the Wood-Anderson motion in meters) forms a lower bound for estimates of peak velocity from seismoscope recordings. The relation is good for stations within about 100 km of earthquakes with moment magnitudes of about 4.5 to 6.5, and it underestimates peak velocity by factors up to 2 or 3 for larger earthquakes at distances within 100 km. An application of the simulation method to the 1976 Guatemala earthquake (moment magnitude = 7.6) results in 37 cm/sec as a lower bound to vmax, with 66 cm/sec as a more likely value, from the seismocope recording in Guatemala City (approximately 25 km from the Motagua fault).

Topographic Correction for the Data of SQUID-based TEM Using a Ground Loop

2019 ◽  
Vol 24 (1) ◽  
pp. 111-117
Author(s):  
Yanju Ji ◽  
Yi Zhao ◽  
Shangyu Du ◽  
Dongsheng Li ◽  
Yi Zhang ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Quantum Interference ◽  
Low Frequency ◽  
High Sensitivity ◽  
Absolute Error ◽  
Correction Method ◽  
Topographic Effects ◽  
Topographic Correction ◽  
Transient Electromagnetic ◽  
Ground Loop

Superconducting quantum interference device (SQUID) can be used to detect the signal of transient electromagnetic method (TEM) due to its superiority of high sensitivity in the low frequency range. However, the measuring direction of SQUID is hardly consistent with the normal direction of the transmitting coil of a TEM system because of the undulating topography in the field. In this case, the central magnetic field measured by SQUID is only a component of the theoretical central magnetic field. There will be larger errors if we directly use the measured central magnetic field for geological interpretation. To solve this problem, we propose a topographic correction method for the data of SQUID-based TEM using ground loop. The theoretical central magnetic field of the ground loop is calculated after the trapezoidal transmitting current wave is turned off. Then, we use the theoretical central magnetic field of the ground loop as the reference to correct the measured central magnetic field of SQUID-based on the trigonometric function relation between the measuring direction of SQUID and the topographic inclination. The experiment of SQUID-based TEM using a ground loop was carried out in the field. The result shows that at the measurement point with larger topographic inclination, the average absolute error of the measured central magnetic field reduces significantly with the proposed correction method. This method can also be applied to the correction of complex topographic effects when using SQUID to measure three components of magnetic field.

The Great Australian Bight – from AVO prospectivity screening to potentially drillable targets in one of the world's remaining untapped basins

2017 ◽  
Vol 57 (2) ◽  
pp. 793
Author(s):  
Dushyan Rajeswaran ◽  
Marcin Przywara
Keyword(s):  
Low Frequency ◽  
Structural Complexity ◽  
Source Rocks ◽  
High Definition ◽  
Depth Migration ◽  
Velocity Models ◽  
Structural Style ◽  
Petroleum Resource ◽  
Dual Sensor ◽  
Well Data

The Ceduna Sub-basin in Australia’s southern margin offers an untapped opportunity for significant petroleum resource as part of the global exploration portfolio. Analogous to the prolific Niger delta in both size and structural style, this highly-extensional province contains up to 15 km of largely untested post-rift sediments including two widespread Late Cretaceous deltas linked to world-class oil-prone marine Cretaceous source rocks. Regional interpretation of legacy 2D seismic across the Bight Basin brings the sheer scale and structural complexity of this giant Cretaceous depocentre into perspective, but it is only through the detailed analysis of 8001 km2 of dual-sensor towed streamer 3D seismic that its true potential can be quantified. Rigorous phase and amplitude AVO QC of the pre-stack information, coupled with optimised velocity models fed into the depth migration sequence, have ensured amplitude fidelity and phase stability across all offset ranges. This has enabled a systematic and robust exploration workflow of AVO analysis and pre-stack inversion despite limited well data. Numerous dual-sensor case studies have nevertheless demonstrated these Relative Acoustic Impedance and Vp/Vs volumes to be reliably robust for prospect de-risking because of the extended low frequency bandwidth. Frontier screening supported by a partially-automated high-resolution stratigraphic framework has led to the identification of numerous prospects at multiple stratigraphic levels across the survey area. This includes isolation of laterally extensive and vertically amalgamated fan-like structures within the shallow Hammerhead delta using horizon-constrained high-definition spectral decomposition, and the extraction of potential AVO anomalies within the deeper structurally-controlled White Pointer sands draped across large gravity-driven listric growth faults.

Climate studies with a coupled atmosphere-upper-ocean-ice-sheet model

1989 ◽  
Vol 329 (1604) ◽  
pp. 249-261 ◽  
Keyword(s):  
Seasonal Cycle ◽  
Low Frequency ◽  
Coupled Model ◽  
Upper Ocean ◽  
Glacial Cycle ◽  
Last Interglacial ◽  
The North ◽  
Technical Report ◽  
Averaged Model

A two-dimensional zonally averaged model has been developed for simulating the seasonal cycle of the climate of the Northern Hemisphere. The atmospheric component of the model is based on the two-level quasi-geostrophic potential vorticity system of equations. At the surface, the model has land—sea resolution and incorporates detailed snow and sea-ice mass budgets. The upper ocean is represented by an integral mixed-layer model that takes into account the meridional advection and turbulent diffusion of heat. Comparisons between the computed present-day climate and climatological data show that the model does reasonably well in simulating the seasonal cycle of the temperature field. In response to a projected CO 2 trend based on the scenario of Wuebbles et al. (DOE/ NBB-0066 Technical Report 15 (1984)), the modelled annual hemispheric mean surface temperature increases by 2 °C between 1983 and 2063. In the high latitudes, the response undergoes significant seasonal variations. The largest surface warmings occur during autumn and spring. The model is then asynchronously coupled to a model that simulates the dynamics of the Greenland, the Eurasian and the North American ice sheets in order to investigate the transient response of the climate to the long-term insolation anomalies caused by orbital perturbations. Over the last interglacial-glacial cycle, the coupled model produces continental ice-volume changes that are in general agreement with the low-frequency part of palaeoclimatic records.

Accuracy of wavelets, seismic inversion, and thin-bed resolution

2017 ◽  
Vol 5 (4) ◽  
pp. T523-T530
Author(s):  
Ehsan Zabihi Naeini ◽  
Mark Sams
Keyword(s):  
Seismic Data ◽  
Reservoir Characterization ◽  
Low Frequency ◽  
Seismic Inversion ◽  
Inversion Method ◽  
Frequency Content ◽  
Frequency Model ◽  
North West ◽  
The North ◽  
Well Data

Broadband reprocessed seismic data from the North West Shelf of Australia were inverted using wavelets estimated with a conventional approach. The inversion method applied was a facies-based inversion, in which the low-frequency model is a product of the inversion process itself, constrained by facies-dependent input trends, the resultant facies distribution, and the match to the seismic. The results identified the presence of a gas reservoir that had recently been confirmed through drilling. The reservoir is thin, with up to 15 ms of maximum thickness. The bandwidth of the seismic data is approximately 5–70 Hz, and the well data used to extract the wavelet used in the inversion are only 400 ms long. As such, there was little control on the lowest frequencies of the wavelet. Different wavelets were subsequently estimated using a variety of new techniques that attempt to address the limitations of short well-log segments and low-frequency seismic. The revised inversion showed greater gas-sand continuity and an extension of the reservoir at one flank. Noise-free synthetic examples indicate that thin-bed delineation can depend on the accuracy of the low-frequency content of the wavelets used for inversion. Underestimation of the low-frequency contents can result in missing thin beds, whereas underestimation of high frequencies can introduce false thin beds. Therefore, it is very important to correctly capture the full frequency content of the seismic data in terms of the amplitude and phase spectra of the estimated wavelets, which subsequently leads to a more accurate thin-bed reservoir characterization through inversion.

scholarly journals The baseline wander correction based on improved EEMD algorithm for grounded electrical source airborne transient electromagnetic signals

2020 ◽  
Author(s):  
Yuan Li ◽  
Song Gao ◽  
Saimin Zhang ◽  
Hu He ◽  
Pengfei Xian ◽  
...  
Keyword(s):  
Flight Control ◽  
Detection Efficiency ◽  
Signal To Noise Ratio ◽  
Synthetic Data ◽  
Low Frequency ◽  
Ensemble Empirical Mode Decomposition ◽  
Electromagnetic Signal ◽  
Transient Electromagnetic ◽  
Baseline Wander ◽  
Electrical Source

Abstract. The grounded electrical source airborne transient electromagnetic (GREATEM) system is an important method for obtaining subsurface conductivity distribution as well as outstanding detection efficiency and easy flight control. However, the signals are the superposition of useful signals and various noise signals. The baseline wander caused by the receiving coil motion always exists in the process of data acquisition to affect the measurement results. The baseline wander is one of the main noise sources of data, which has the low frequency, large amplitude, non-periodic and non-stationary and so on. Consequently, it is important to correction baseline wander for inversion explanation of GREATEM. In this paper, we propose improving method EEMD-AF based on ensemble empirical mode decomposition (EEMD) to correction baseline wander. The EEMD-AF method will decompose the electromagnetic signal into multi-stage intrinsic mode function (IMF) components and adaptively filter high-order IMF component which containing the baseline wander. To examine the performance of our introduced method, we used the EEMD-AF method for the signal baseline correction and compared with sym8 wavelet with 10 decomposition levels and EEMD with deleted higher-order components directly. The various methods were applied to process the synthetic data and field data. Through the evaluation of the signal-to-noise ratio (SNR) and mean-square-error (MSE), the correction result indicates that the signal using EEMD-AF method can get higher SNR and lower MSE. Comparing correctional signal using the EEMD-AF and the wavelet-based method in the anomaly curves profile images of the response signal, it is proved that the EEMD-AF method is a practical and effective method for removal of the baseline wander on GREATEM signal.

scholarly journals Suppression of very low frequency radio noise in transient electromagnetic data with semi-tapered gates

2021 ◽  
Vol 10 (1) ◽  
pp. 81-90
Author(s):  
Jakob Juul Larsen ◽  
Stine Søgaard Pedersen ◽  
Nikolaj Foged ◽  
Esben Auken
Keyword(s):  
Standard Error ◽  
Signal To Noise Ratio ◽  
Low Frequency ◽  
Side Lobe ◽  
Late Time ◽  
Very Low Frequency ◽  
Transient Electromagnetic ◽  
Noise Rejection ◽  
Radio Signals ◽  
Subsurface Resistivity

Abstract. The transient electromagnetic method (TEM) is widely used for mapping subsurface resistivity structures, but data are inevitably contaminated by noise from various sources. It is common practice to gate signals from TEM systems to reduce the amount of data and improve the signal-to-noise ratio (SNR). Gating acts as a filter, and optimum gating will pass the TEM signal un-attenuated while suppressing noise. In systems based on analog boxcar integrators, the gating corresponds to filtering with a square window. The frequency response of this window shape has large side lobes, which are often insufficient in attenuating noise, e.g., from radio signals in the very low frequency (VLF) 3–30 kHz band. Tapered gates have better side lobe suppression and attenuate noise better, but tapering with analog boxcar integrators is difficult. We propose using many short boxcar gates, denoted sub-gates, and combine the sub-gates into semi-tapered gates to improve noise rejection at late gates where low signal normally leads to poor SNR. The semi-tapering approach is analyzed and tested experimentally on data from a roving TEM system. We quantify the effect of semi-tapered gates by computing an improvement factor as the ratio between the standard error of data measured with boxcar gates and the standard error of data measured with semi-tapered gates. Data from a test survey in Gedved, Denmark, with 1825 measurements gave mean improvement factors between 1.04 and 2.22 for the 10 late-time gates centered between 78.7 and 978.1 µs. After inversion of the data, we find that semi-tapering increases the depth of investigation by about 20 % for this specific survey. We conclude that the semi-tapered approach is a viable path towards increasing SNR in TEM systems based on analog boxcar integrators.

scholarly journals Petrological and Tectonostratigraphic Evidence for a Mid Ordovician Rift Pulse on the Arabian Peninsula

GeoArabia ◽  
1999 ◽  
Vol 4 (4) ◽  
pp. 467-500 ◽  
Author(s):  
W. Heiko Oterdoom ◽  
Mike A. Worthing ◽  
Mark Partington
Keyword(s):  
Tectonic Setting ◽  
Late Ordovician ◽  
Mafic Rocks ◽  
Early Ordovician ◽  
Sedimentary Sequences ◽  
Field Investigations ◽  
Clastic Sediments ◽  
Step Heating ◽  
Well Data ◽  
Uplift And Erosion

ABSTRACT During late Early Ordovician times an increase in the rate of subsidence in the Ghaba Salt Basin and western South Oman Salt Basin is suggested by the thick sequence of continental clastics of the Ghudun Formation. After a phase of rift-shoulder uplift and erosion, related to a renewed pulse of extension which may have initiated diapiric growth of salt structures in the Ghaba Salt Basin, sedimentation resumed again in the Mid Ordovician. During this period, the center of deposition shifted to the Saih Hatat area in North Oman. This paper documents seismic and well data, field investigations and petrological study of potassic mafic rocks from the Huqf area which were intruded in the eastern side of the Ghaba Salt Basin. A Mid Ordovician age of 461 ± 2.4 million years has been established for these rocks by the Argon-Argon step heating method. Analogy with the petrology and setting of similar potassic mafic rocks from the Rio Grande Rift in the western United States of America suggests that they were intruded into the shoulder of an intra-continental rift. The data provide the first clear evidence of a pulse of rift-shoulder uplift in the Huqf area during the Mid Ordovician. The 3-kilometer-thick Mid to Late Ordovician clastic sediments of the Amdeh Formation in North Oman, together with the occurrence of abnormally thick sedimentary sequences and volcanics in the Tabas Graben in Iran, are consistent with a period of break-up of eastern Gondwana. Together, the Ghaba-Saih Hatat and Tabas Basins are considered to be part of a failed rift arm. These observations further improve our regional knowledge of the Early to Late Ordovician tectonic setting of Oman and will assist in unlocking the hydrocarbon potential of classical rift-related structures consisting of early-rift Early Ordovician sand-prone reservoirs sealed by syn-rift Mid to Late Ordovician marine shales.

Improved seismic inversion and reservoir description of the Ichthys gas-condensate field, Browse Basin, Western Australia

2010 ◽  
Vol 50 (2) ◽  
pp. 716
Author(s):  
Masamichi Fujimoto ◽  
Takeshi Yoshida ◽  
Andrew Long
Keyword(s):  
Low Frequency ◽  
Seismic Inversion ◽  
Gas Condensate ◽  
Sensor Technology ◽  
Frequency Model ◽  
Porosity Distribution ◽  
Low Frequencies ◽  
Simultaneous Inversion ◽  
Dual Sensor ◽  
Well Data

Seismic inversion has become a standard geophysical tool to enhance seismic resolution, predict the reservoir porosity distribution, and to discriminate between reservoir and non-reservoir pay zones. Conventional seismic data does not record the low frequencies necessary for inversion. To enable a complete bandwidth, low frequencies are modelled from well data and are typically interpolated throughout the volume using seismic velocities. This often causes the resultant porosity distribution calculated from the inverted P-impedance to be biased by the well data and the geometry of well locations. Dual-sensor GeoStreamer technology was used to acquire a regional multi-client 2D survey by PGS in 2008, including some lines over the Ichthys gas-condensate field in the Browse Basin. Dual-sensor streamer processing recovers a wider frequency bandwidth than conventional seismic. Receiver ghost removal combined with deep streamer towing simultaneously boosts both the low and high frequencies. The improved bandwidth enables a higher quality of velocity analysis, which further improves resolution throughout the section. Simultaneous inversion of the data validated the uplift of the low frequency data, and significantly reduced the bias towards well data for the low frequency model. The resultant P-impedance data demonstrated an excellent tie to well data. The dual-sensor technology promises to improve the description of the porosity distribution within our reservoir model.

Sign in / Sign up

Export Citation Format

Share Document