University of Wyoming Near-Surface Geophysical Instrument Center & Wyoming Center for Environmental Hydrology and Geophysics

Transcription

1 University of Wyoming Near-Surface Geophysical Instrument Center & Wyoming Center for Environmental Hydrology and Geophysics UWNSG & WyCEHG Groundwater Studies on the Brule Formation near Pine Bluffs, Wyoming: What can near-surface geophysics tell us about tops and fracturing in the upper Brule Formation. Brad Carr, Ph.D. University of Wyoming

2 Acknowledgments University of Wyoming-Department of Geology and Geophysics Near-Surface Geophysics Instrument Center (UWNSG) University of Wyoming-Office of Research and Economic Development Wyoming Center for Environmental Hydrology and Geophysics (WyCEHG) -- NSF grant EPS UWNSG 2017 summer personnel: Matthew Elliot and Evan Cox Dahlgren Consulting, Inc.. Russ Dahlgren, P.G. and Shana Wolff

3 University of Wyoming Near-Surface Geophysical Instrument Center & Wyoming Center for Environmental Hydrology and Geophysics What is UWNSG? The Univ. of Wyoming cost center (like the Stable Isotope lab) for geophysical equipment and data support for: environmental hydrology, environmental engineering, natural hazards, near surface petrophysics, and near surface geophysics and hydrogeophysics. UWNSG serves the geophysical community, water science, engineering and watershed management by providing cutting-edge tools to managers, scientists, public educators and private sectors. Funded by equipment rentals and project work. Started April, 2017 Currently find our personnel at: and our equipment at:

4 University of Wyoming Near-Surface Geophysical Instrument Center & Wyoming Center for Environmental Hydrology and Geophysics UWNSG & WyCEHG Geophysical Tools Seismic Refraction, Reflection and Surface Wave 240 channel capability, impact sources, 4.5Hz/10Hz/40Hz geophones, 2 24 channel borehole/marine hydrophone arrays Ground Penetrating Radar 3 - systems with 100MHz/250MHz/500MHz and 800MHz antennae DC Resistivity/Induced Polarization/Self-Potential 5 systems with ~ 56 electrode capability, 60 Non-Polarizable electrodes, 2 56 electrode borehole/marine cables Electromagnetics (shallow and deep) Surface loop EM system (WalkTEM), 2 handheld soil conductivity meters (DualEM and GEM2) Magnetics & Magnetotellurics Proton Precession Base Station and Cesium Vapor Gradiometer CSAMT - StrataGEM Nuclear Magnetic Resonance Surface (GMR) and Borehole (Javelin & Dart) Gravity CG-5 microgravimeter Borehole Geophysical Logging Caliper, Optical Televiewer, Acoustic Televiewer, Natural Gamma, Fluid Temperature/Conductivity, Spectral Gamma, Spinner Flowmeter, Heat Pulse Flowmeter, Electromagnetic/Magnetic Susceptibility, Full Waveform Sonic (3 receiver), Resistivity (normal 8,16, 32, 64 ) & Induced Polarization, and Fluid Sampler. Direct Push Sampling/Rotary Coring/HPT-EC Direct Imaging Geoprobe 7822DT

5 Geophysical Instrumentation Shallow drilling/coring Ground-Penetrating Radar Seismic Refraction Electrical Resistivity Microgravity Magnetic Resonance Sounding

6 University of Wyoming Near-Surface Geophysical Instrument Center & Wyoming Center for Environmental Hydrology and Geophysics Audio magnetotellurics Downhole Logging Time-domain EM Electromagnetic Induction Magnetic Gradiometry

7 University of Wyoming Near-Surface Geophysical Instrument Center & Wyoming Center for Environmental Hydrology and Geophysics Geophysical Pilot Study to Image the top of the Brule Formation near Pine Bluffs, Wyoming

8 University of Wyoming Near-Surface Geophysical Instrument Center & Wyoming Center for Environmental Hydrology and Geophysics Project Goals: 1) Use surface geophysics (Seismic Refraction and DC Resistivity) to image the top of the Brule Fm. 2) Use borehole geophysical logging to study in situ fractures in the upper Brule Fm.

9 University of Wyoming Near-Surface Geophysical Instrument Center & Wyoming Center for Environmental Hydrology and Geophysics Generalized Stratigraphy for the Pine Bluffs, WY area:

10 University of Wyoming Near-Surface Geophysical Instrument Center & Wyoming Center for Environmental Hydrology and Geophysics Geophysical Site surrounding the Duello Well

11 University of Wyoming Near-Surface Geophysical Instrument Center & Wyoming Center for Environmental Hydrology and Geophysics Well Summary of the Duello Well from UWNSG geophysical logging data: -- TD = m // ft. bgs -- ID = 16.5 cm // 6.5 in. -- H 2 O level (~6.02 m // ft. bgs) were measured on June 15, The top of the Brule Fm. is at the base of the cased interval (~ 2.8 m // ~ 9.1 ft. bgs). -Fractured Intervals of the upper Brule Fm. were determined from the caliper & optical televiewer tools.

12 University of Wyoming Near-Surface Geophysical Instrument Center & Wyoming Center for Environmental Hydrology and Geophysics Surface Geophysical Methods

13 Resistivity/IP /SP Methods Why is Resistivity Imaging useful? and what can the color/values really represent?

14 Resistivity/IP /SP Methods Photos and data courtesy of Triad Engineering, Inc.

15 Resistivity /IP /SP Methods DC Resistivity (Galvanic): For each measurement, a DC electric current is injected into the ground through two electrodes (A and B) that are planted into the ground. The resulting electric potential is measured between another two electrodes (M and N). Measured data (i.e. apparent resistivity) are inverted to produce true subsurface resistivity distribution. Resistivity distribution is correlated to subsurface geology by a data interpreter I V A B M N Transmitter Receiver ρ a

16 Apparent resistivity Apparent resistivity is a weighted average of the resistivities under the four electrodes. If the ground is homogenous, the apparent resistivity equals the true resistivity r r r r i V a General formula for calculating apparent resistivity Resistivity/IP/SP Methods

17 Resistivity/IP/SP Methods Resistivity of soil and rock is a complicated function of the following parameters: 1) Moisture (water) content, a dominant factor 2) Porosity 3) Pore fluid chemistry (fresh water vs. saltwater) 4) Temperature of pore water (resistivity decreases with increasing temperature) 5) Resistivity of minerals

18 Refraction: Why Care? Seismic refraction data allow us to determine the distribution of seismic velocity in the Earth -- which has a myriad of uses, from small-scale studies of local geology and soil structure to large-scale problems like the structure of continents.

19 Snell s Law: Critical Refraction Guy G. Drijkoningen v 1 v 2 A special case of refraction occurs when 2 =90 (so that sin 2 =1): 2 in this case is called the critical angle c. The resulting refraction travels along the boundary and is called a head wave. Waves such as this are the basis for refraction seismology, about which we ll have more to say later.

20 Refractions (Head Wave): One-Layer Case Here is one form of the onelayer equations, from Mussett & Khan: t = 1 v 2 x + 2h 1 1 v v 2 2 i.e., time = slope distance + intercept (note that I ve changed z to h 1 ) Mussett & Khan

21 Controls on Velocity Confining Pressure Composition (Mineralogy) Temperature Porosity (Voids and cracks) Pore Fluid Composition (gas/water) Pore Pressure Most important for near-surface geophysics

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26 University of Wyoming Near-Surface Geophysical Instrument Center & Wyoming Center for Environmental Hydrology and Geophysics Summary of Interpreted Fracture locations at the site from UWNSG surface geophysical imaging data:

27 University of Wyoming Near-Surface Geophysical Instrument Center & Wyoming Center for Environmental Hydrology and Geophysics

28 University of Wyoming Near-Surface Geophysical Instrument Center & Wyoming Center for Environmental Hydrology and Geophysics Borehole Deviation of the Duello Well

29 Brule Fm. water logs in the Duello Well

30 Brule Fm. water logs in the Duello Well

31 Brule Fm. fracturing in the Duello Well

32 University of Wyoming Near-Surface Geophysical Instrument Center & Wyoming Center for Environmental Hydrology and Geophysics Fracture Strike and Dip of the Duello Well (Southern (Lower) Hemisphere, Kamb contouring, Standard deviations =2) Strike and Dip angle of DS1 Fractures Dip azimuth and dip angle of DS1 Fractures

33 Brule Fm. fracture density/m (yellow) in the Duello Well

34 Bottom of casing in the Duello Well

35 Brule Fm. fracturing in the Duello Well

36 Brule Fm. fracturing & water table in the Duello Well

37 Brule Fm. fracturing in the Duello Well

38 Brule Fm. fracturing in the Duello Well

39 Brule Fm. fracturing at bottom of the Duello Well

40 University of Wyoming Near-Surface Geophysical Instrument Center & Wyoming Center for Environmental Hydrology and Geophysics

41 Acoustic Televiewer data from DS-1 Acoustic & Optical Televiewer data from UW Blair-Wallis #6

42 Conclusions: University of Wyoming Near-Surface Geophysical Instrument Center & Wyoming Center for Environmental Hydrology and Geophysics 1) Surface geophysics (Seismic Refraction and DC Resistivity) can be used to image the top of the Brule Fm. (i.e. determine regolith thickness) away from well control. Additionally, these data provide indications of areas with elevated fracture density and bulk porosity. At this site, the area interpreted to show the most fracturing define an elliptical area that encompasses the Duello well(s) and is oriented at ~ N 20 W. This is the same direction that the borehole deviates. 2) Details about Brule Fm. fracture density and orientation can be observed with borehole geophysical logging. 3) In this particular well, fractures strike to the west and dip to north at less than 30 degrees.

43 University of Wyoming Near-Surface Geophysical Instrument Center & Wyoming Center for Environmental Hydrology and Geophysics Thank you

44 Supporting material

45 University of Wyoming Near-Surface Geophysical Instrument Center & Wyoming Center for Environmental Hydrology and Geophysics What is WyCEHG ( Y-Keg )? A center of excellence in environmental hydrology and hydrogeophysics that serves water science and watershed management by providing cutting-edge tools to managers, scientists and educators in the public and private sectors. Funded by a 5-year, $20 M grant from NSF-EPSCoR (plus $4 M match from UW). EPSCoR Track-1 Research Infrastructure Improvement grant Expires June 30, 2017 Two major facilities: The Facility for Imaging the Near- and Sub-surface Environment (FINSE): Geophysical Equipment The Surface and Subsurface Hydrology Lab (SSHL): Hydrological Equipment Long-term: Transition to a self-supporting, UW cost center for hydrogeophysics April 2017 UW NS Geophysical Instrument Center (UWNSG) Find us at:

46 University of Wyoming Near-Surface Geophysical Instrument Center & Wyoming Center for Environmental Hydrology and Geophysics Science Goals 1. Surface water/groundwater interaction. Hyporheic zone Integrated watershed modeling 2. How do snow processes, particularly moisture content (SWE) and the timing of snowmelt, affect the downstream system? 3. Critical Zone science How does regolith vary across landscapes? How does this variation affect ecosystems and watershed hydrology? How do hydrothermal waters interact with surface features at Yellowstone National Park?

47 Resistivity/IP/SP Methods Typical Applications for Resistivity Cavity and sinkhole detection Geotechnical site characterization Groundwater exploration Lithologic mapping Mineral exploration Archaeological site investigation Detection of free products of contaminant plumes. Time lapse monitoring of remediation process such as steam injection, air sparging, injection of various oxidants such as hydrogen peroxide (H 2 O 2 ) and potassium permanganate (KMnO 4 ) Time lapse monitoring of subsurface processes such as groundwater recharge, infiltration, saltwater intrusion, tunneling, and dam leakage

48 Resistivity/IP /SP Methods Typical Ranges of Resistivities for common materials: Rock/material type: Resistivity range (Wm): Igneous 100 1,000,000 Limestone ,000 Sandstone ,000 Sand (both dry & wet sand) 1 10,000 Gravel ,000 Clay (including wet clay) Alluvium 1 1,000 Soil 1 10 Drill mud, hydraul-ez 4.5 Fresh water Salt water Copper (native)

49 Resistivity /IP /SP Methods Fundamental Principle: Ohms law: Resistance = Voltage/Current; -Unit for Resistance is Ohm -Unit for Resistivity is Ohm-meter R V I Think about it like water flowing through a hose: Voltage = Pressure difference at the ends of the hose Current = Flow of water through the hose Resistance = Dirt clogging up the hose

50 Potential and current fields around a point source and sink If we have both a source and a sink of current (i.e., two electrodes with current passing between them), then the potential surfaces are more complex they are the sum of the two potential surfaces created independently by the source (positive) and the sink (negative). current potential Reynolds, 2011

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52 Resistivity/IP/SP Methods

53 Resistivity/IP/SP Methods Resistivity and IP inversion software

54 Resistivity/IP /SP Methods

55 Sources and Receivers: Near- Surface Seismic Refraction

56 Velocities in Different Materials

57 Data Acquisition Acquisition involves generating sound waves with a source (like a sledgehammer) and recording the refracted energy on a line of geophones.

58 Data Example: Seismograms from one shot

59 Travel Times from Many Shots

60 Ray Paths In this example, the geophones were 50 m apart, and each one produces one trace. Note that time is plotted on the vertical axis (increasing upward), and distance from the source to the receiver is on the horizontal axis.

61 Final Velocity Model