Showing 25 pages using this property.
|2-M Probe Survey +||The temperature at 1-2 m below the ground is measured by a thermocouple probe or a thermistor. There are different methods to create the hole in which the thermocouple probe or thermistor is inserted into to acquire the data. Some examples include using a hand soil auger or using a hammer drill. The best method is dependent on the soil type at the site and any time constraints.|
|Acoustic Logs +||Most acoustic-velocity probes employ magnetorestrictive or piezoelectric transducers that convert electrical energy to acoustic energy. Most of the transducers are pulsed from 2 to 10 or more times per second, and the acoustic energy emitted has a frequency in the range of 20 to 35 kHz. Acoustic probes are centralized with bow springs or rubber fingers so the travel path to and from the rock will be of consistent length. Some of the energy moving through the rock is refracted back to the receivers. The receivers reconvert the acoustic energy to an electrical signal, which is transmitted up the cable. At the surface, the entire signal may be recorded digitally for acoustic waveform logging, or the transit time between two receivers may be recorded for velocity logging. Amplitude of portions of the acoustic wave also may be recorded; that technique is described later under waveform logging.|
|Aerial Photography +||Today, current high-resolution aerial photography can be found for most locations on many internet mapping sites. Historical aerial photographs can be obtained from local aerial photography services.|
|Airborne Electromagnetic Survey +||A primary man-made alternating magnetic field is established by passing a current through a coil. The field is measured with a receiver which consists of a sensitive electronic amplifier and meter or a potentiometer bridge. If the source and receiver are flown over a more conductive zone, such as an area with higher metallic content, a measurable secondary magnetic field will be created. This secondary magnetic field is compared to the original and is usually reported proportionally to the primary magnetic field. For airborne electromagnetic systems, the receiver coils are usually in a towed bird and the transmitter may be a large coil encircling a fixed wing aircraft. Or another set up is with one or more small coils in the same bird that houses the transmitting coils.|
|Analytical Modeling +||Matching the analytical model solutions with measured data can provide verification of assumptions on the geothermal reservoir.|
|Caliper Log +||Caliper logs are usually measured mechanically, with only a few using ultrasonic devices which provide full azimuthal coverage with high resolution. The tools measure diameter at a specific chord across the well.|
|Cement Bond Log +||A circuit is employed to convert the difference in time of arrival of the P-wave at the two detectors to transit time (t) in ms/ft.|
|Cuttings Analysis +||Cuttings are obtained from the well, brought to the surface by drilling fluids (mud), and separated from the mud using a shaker. Preliminary analysis of the cuttings is done under a low magnification microscope, and if more information is necessary then other techniques can be used. If more detailed information is desired a higher power microscope may be used, thin sections may be made, or an XRD analysis may be done with the particular cuttings of interest.|
|Density Log +||The data acquired is based on the average density of the rock between the sensor and the detector.|
|Downhole Fluid Sampling +||Temperature, pressure, and pH data are typically measured in the field at the time of sampling, and are recorded in conjunction with the sampling coordinates. The flow rate is also measured at the wellhead gauge. Sampled waters are typically subjected to [[Compound and Elemental Analysis|chemical]] and [[Isotopic Analysis- Fluid|isotopic]] analyses in order to characterize hydrothermal systems and allow for estimation of reservoir temperatures through the application of various chemical [[Geothermometry|geothermometers]]. Data from these analyses can also provide useful information regarding the source of thermal fluids and help to constrain the age of the hydrothermal system.|
|Fault Mapping +||Preliminary analysis often begins with air photos or DEMs to identify surficial features, ranging from headscarps, stream channel offsets, mud volcanoes, hydrothermal mineralization, etc. There are many ways to characterize a fault, most of which rely on geomorphology of the area. The more challenging aspect of fault mapping is determining the direction of slip, slip-rate, whether it is still active or not, and if it is circulating fluids. Since faults do not always have obvious surficial features, there can be several ways to locate and document their existence. But the most critical information for geothermal exploration is whether the fault is a conduit for hydrothermal fluids, this can be an easy or very challenging and expensive factor to determine. It is obvious that a fault system is transporting hydrothermal fluids if there are hot springs or other features (a few mentioned above) associated with the structure. It can be very challenging and expensive to determine whether a fault is circulating hot fluids if the structure has no surficial features, in this case geophysical techniques (subsurface mapping or hyperspectral imaging) or drilling is required.|
|Flow Test +||Flow test data is acquired at the well head by various tools in the field that measure flow rate, temperature, fluid composition, etc. This information is recorded and can be monitored at the well site or remotely.|
|Fluid Inclusion Analysis +||Depending on what the fluid inclusion looks like it is possible to determine the approximate conditions in which it formed. If there is a halite crystal within the inclusion at room temperature, it is inferred that the fluid contains more than 26 wt% NaCl. If the vapor bubble is small, it can be assumed that the fluid originated from a liquid-like fluid because of its relatively high density. If the vapor bubble is very large, it can be inferred that the fluid was derived from a vapor-like fluid because of its relatively low density. The conditions of a minimum temperature of formation for a particular fluid inclusion (or assemblage) can be determined by heating the fluid inclusion to its homogenization temperature. The homogenization temperature is a temperature at which the bubble within the fluid inclusion disappears and all that remains is a single phase fluid. At that particular temperature there is an isochore (line of constant density) that can be projected from the liquid-vapor line on a temperature vs pressure phase diagram. If the pressure conditions are well constrained and appropriately estimated then the temperature of entrapment can be found where the isochore crosses the estimated pressure value.<br:/>To determine the salinity of the fluid, the fluid inclusion (or assemblage) must undergo freezing, usually below the eutectic temperature. As the temperature of the fluid inclusion drops and eventually freezes completely, the vapor bubble will deform and possibly move slightly. After freezing, the sample is gradually heated, the first melting occurs at the eutectic temperature which is representative of the fluid-salt composition. This can be determined by the vapor bubble “unlocking” from the frozen liquid and returning to its normal shape. Continued heating leads to the last bits of ice to melt, the temperature at which the last ice crystals melt can determine the weight percent of salt in the fluid using a salt vs temperature phase diagram.|
|Gamma Log +||A detector located within a wireline probe is lowered into the well and typically measures the gamma ray intensity when raised from the bottom. The detector can either be a scitillation counter (Thallum doped sodium iodice crystal) or Geiger-Muller tubes record and transmit the total radioactivity that is displayed as the gamma ray log.|
|Geodetic Survey +||<br>
* Geodesy data is collected via <b>satellite</b>.
* Data is collected over a period of years, which often does not fit into an exploration programs timeline. Data may already exist, however, for some areas with geothermal potential.
* Geodetic surveys are often an academic pursuit, measuring long-term tectonic uplift and plate motion.|
|Geothermal Literature Review +||A geothermal literature review relies on past data, not recording new data. The literature review should compile different data from multiple sources and studies into one comprehensive report.|
|Groundwater Sampling +||Temperature and pH data are typically measured in the field at the time of sampling, and are recorded in conjunction with the sampling coordinates. The flow rate is also typically measured at the wellhead gauge for flowing wells. Sampled waters are typically subjected to [[Compound and Elemental Analysis|chemical]] and [[Isotopic Analysis- Fluid|isotopic]] analyses in order to estimate mixing ratios and recharge of the hydrothermal system. Data from these analyses can also provide useful information regarding the source of thermal fluids and help to constrain the age of the hydrothermal system.|
|Hyperspectral Imaging +||Hyperspectral data collection requires sunny days - the images are not as clear when collected on cloudy days.|
|Image Logs +||[[File: OTV-Dike.jpg|thumb|center|400px| An example of well log images from an [[Optical Televiewer]]; (left) a flat 360° view; (right) 180° virtual core view.]]|
|LiDAR +||Places to get data
*Non-military federal government LiDAR data is not collected for general use by the public, so it must be obtained commercially.
*Research-grade, public datasets are available through the National Center for Airborne Laser Mapping ([http://www.ncalm.cive.uh.edu/ NCALM]) for no cost, but coverage is very limited.
*Some states agencies (e.g., Oregon Department of Geology and Mineral Industries) have contracts with LiDAR collection companies to collect and provide LiDAR data to the public for the entire state.|
|Modeling-Computer Simulations +||See [[Numerical Modeling]]|
|Multispectral Imaging +||Multispectral data from NASA’s [http://earthexplorer.usgs.gov/ LANDSAT] and [http://asterweb.jpl.nasa.gov/data.asp ASTER] satellites are freely available to the public at no cost.|
|Neutron Log +||Neutron logging tools commonly use chemical sealed sources, generally Americium-241/Beryllium (AmBe). These sources emit fast neutrons that are eventually slowed down by collisions with hydrogen atoms found in fluids such as oil, gas or water until they are captured at the receiver. When the sourced neutrons are received they produce a secondary emission which is detected and counted. The higher the count means that fewer of the sourced neutrons were slowed down by hydrogen atoms between the source and the receiver.|
|Petrography Analysis +||Data acquisition begins with a rock sample from outcrop, drill core, or cuttings. Once macroscopic details about the formation or rock sample have been determined by visually inspecting an outcrop or hand sample, a petrographic thin section is typically made to characterize the microscopic features. Thin sections are great for identifying the minerals present, porosity, inter-granualr volume (IGV), alteration, microstructures, and provenance. However, thin sections are only two dimensional, to get a three dimensional understanding of the micro-features a scanning electron microscope (SEM) is typically used. SEM’s can reveal micron scale surface features of a rock sample. One of the consequences of a rock interacting with an electron beam in an SEM is that characteristic X-rays are released, which can be measured to determine a relatively qualitative elemental composition of the specific grain being investigated. This process is called energy dispersive X-ray spectrometry, or EDS, and can be very helpful in providing basic elemental composition of a sample. To acquire quantitative bulk rock compositions XRD is a common technique. There are various XRD machines and techniques, but typically a rock sample is crushed into a fine powder which is packed and mounted onto a stage that is analyzed by X-rays. The X-ray detector captures this information which gets plotted onto a diffractogram where characteristic peaks can be identified as specific minerals.|
|Portable X-Ray Diffraction (XRD) +||Portable XRD analysis is rapid compared to its lab-based counterparts, usually taking no more than a minute or two for a single analysis. Samples can also be quickly scanned for their major and trace element constituents (Ca through U) using the device’s XRF capability.|