Term
| Exploration for natural gas |
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Definition
1. begins with geologists examining the surface of the earth's structure
2. determine areas where it is geologically likely that petro or gas deposists might exist (like in anticlinal slopes) |
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Term
| What are anticlinal slopes? |
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Definition
| the earth has folded up on itself, forming the dome shape that is characterisitic of a great number of reservoirs |
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Term
| How can geologists extrapolate which areas are most likely to contain a petrol or natural gas reservoir? |
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Definition
| by surveying and mapping the surface and sub surface |
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Term
| The information that the geologists collect is all combined to make inferences about what? |
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Definition
1. fluid content
2. porosity
3. permeability
4. age and formation sequence of the rocks undernearth the surface of a particular area |
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Term
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Definition
| the study of how energy, in the form of seismic waves moves through the Earth's crust and interacts differently with various types of underground formations |
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Term
| Who developed the seismograph in 1855? |
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Definition
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Term
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Definition
| instrument used to detect and record earthquakes; picks up and records the vibration of the earth that occurs during an earthquake; applied to petrol industry in 1921 |
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Term
| How does seismic exploration work? |
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Definition
1. The earth's crust is composed of different layers and each has its own properties
2. the energy traveling underground interacts differently with each of these layers and the seismic waves emitted from a source will travel through the earth but also be relfected back towards the source by different underground layers
3. Geophysicts artifically create vibrations on the surface and record how these vibrations are reflected back to the surface |
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Term
| How do geologists use seismographs to map underground geologic formations? |
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Definition
| by artifically creating seismic waves and the reflections are then picked up by sensitive pieces of equipment called geophones; the data is then trasmitted to a seismic recording truck |
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Term
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Definition
| senstitive instrument that picks up seismic waves and the refections |
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Term
| What is a seismic recording truck? |
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Definition
| records the data for further interpretation by geophysists and petroleum reservoir engineers |
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Term
| Are explosive charges needed to generate the needed seismic waves? |
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Definition
No; use non-explosive technology that consists of a large heavy wheeled or tracked vehicle carrying special equipment designed to create a lareg impact or series of vibrations
- the large piston in the middle is used to create vibrations on the surface of the earth, sending seismic waves that are used to generate useful data |
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Term
| What method is used for offshore seismology? |
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Definition
| a ship is used to pick up seismic data and instead of geophones, offshore exploration uses hydrophonesn which are designed to pick up seismic waves underwater |
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Term
| What is used to pick up seismic waves underwater? |
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Definition
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Term
| What happens with a seismic ship? |
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Definition
| A large air gun releases bursts of compressed air under the water, creating seismic waves that can travel through the Earth's crust and generate the seismic reflections |
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Term
| Why are the magnetic properites of underground formations measured? |
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Definition
| to generate geological and geophysical data |
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Term
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Definition
| Devices which measure the small differences in the Earth's magnetic field |
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Term
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Definition
| a NASA satellite magnetometer that allows for continental measurements (study of underground rock formations and the Earth's mantle on a larger scale; provides clues as to tectonic plate movement and the location of the deposits of petroleum, natural gas, and other minerals |
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Term
| What can geophysicts also measure to gain a better understanding of what is underground? |
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Definition
| the difference in the Earth's gravitational field |
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Term
| What is the gravitational field that surrounds the Earth affected by? |
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Definition
| the different underground formations and types of rock |
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Term
| What is the best way to gain a full understanding of a subsurface geology and the potential for natural gas deposist? |
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Definition
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Term
| What does an exploratory well consist of? |
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Definition
| digging into the earths crust to allow geologists to study the compositiohn of the underground layers in detail (examine the drill cuttings and fluids); use logging |
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Term
| When are exploratory wells used? |
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Definition
| When other data has indicated a high probability of petroleum formations there |
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Term
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Definition
| performing tests during or after the drilling process to allow geologists and drill operators to monitor the progress of the well drilling and to gain a clearer picture of subsurface formations |
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Term
| What are the various tests used in logging? |
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Definition
1. standard
2. electric
3. acoustic
4. radioactivity
5. density
6. induction
7. caliper
8. directional
9. nuclear |
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Term
| What are the 2 important types of logging? |
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Definition
| standard logging and electric logging |
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Term
| What is standard logging? |
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Definition
| examining and recording the physical aspects of a well (drill cuttings are examined and recorded) |
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Term
| What is electric logging? |
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Definition
| lowering a device used to measure the electric resistance of the rock layers in the "down hole" portion of the well; running an electric current through the rock formation and measuring the resistance that it encounters along the way |
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Term
| What is induction electric logging? |
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Definition
| a newer version of electric logging provides the same types of readings but it is more easily performed and provides data that is more easily interpreted |
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Term
| What is the first contact that a geologist or petro enginner has with the actual contents of the subsurface geology? |
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Definition
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Term
| In its many forms, what does logging consist of? |
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Definition
| using this opportunity to gani a fuller understanding of what actually lies beneath the surface |
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Term
| What do geologists do with data from explorations and logging? |
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Definition
| Create a model or educated guess as to the structure of the layers of the rock undergroup; hand or computer generated visual interpretation |
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Term
| What ist he only way of being sure that a petroleum or natural gas reservoir exists? |
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Definition
| drill an exploratory well |
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Term
| What is 2 D seismic interpretation? |
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Definition
- uses data from seismic exploration to develop a cross-sectional picture of the underground rock formations
- deveoop a conceptional model of the composition and thickness of the various layers of rock underground
- white bands called "bright spots" could indicate deposits of hydrocarbons (but this does not hold universally) this technique of using basic seismic data is known as direct detection |
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Term
| What is direct detection? |
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Definition
| technique of using basic seismic data |
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Term
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Definition
| Computer assisted exploration |
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Term
| What are 3 types of computer assisted exploration models? |
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Definition
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Term
| How is a visualization of the underground gromation created? |
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Definition
| by incorporating the data from different types of tests, such a logging, production inforamtion and gravimetric testing |
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Term
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Definition
| uses seismic field data to denerate a 3D pictrue of underground formations and geologic features; coud be used to estimate the porbability of gas and oil formations existing in a patricual area |
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Term
| How much has 3D seismic imaging increased the likelihood of successful reservoir location:? |
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Definition
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Term
| What is the cost of 3D seismic imaging? |
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Definition
| $1 million per 50 square mile |
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Term
| What are some benefits of 3D seismic imaging? |
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Definition
1. allows for more accurate plaement of wells to be drilled
2. can increase the productives wells 40-50%
3. Nearly 80% of wells drilled in the gulf were based on 3D seismic data |
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Term
| What is 2D Seismic imaging? |
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Definition
| generates an image of subsurface geology; generate maps more quickly than with 2D method without comptuers; use color graphic displays; simpler and may be used in areas where it is likely to contain natural gas deposts and not likely enough to justify the full cost and time commitment required by 3D imaging; can increase recovery rates 25-30% |
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Term
| What is 4D Seismic Imaging? |
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Definition
| one of the latest breakthroughs in seismic exploration; the changes in structures and properties of underground formations are observed over time; the fourth dimension is time; aka 4D "time lapse" imaging; various seismic readings are taken at different times and this sequence of data is fed into a powerful computer; images create a "movie"; geolists gain a better understanding of many properties of the rock, including underground fluid flow, viscosity, temperature, saturation; can also be used by petrol geologists to evaluate the properties of a reservoir and hot it is expected to deplete once petrol extraction has begun; recover rates of 65-70% |
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