Petroleum exploration tools
Maps have always been key tools of petro-leum exploration. Since the early 1900s, ex-plorers
have found many oil and gas fields by drilling domes and anticlines that could be
identified from surface mapping. The size, po-sition, dips and strikes of surface beds are all
recorded with instruments such as plane tables and Brunton compasses. Today, the map of an
explorer includes this “traditional” information, as well as that gleaned from aerial photographs
and satellite pictures. Early geologists made common use of sam-ple and drilling information from wells.
As technology advanced, well log data and core data added a great deal of knowledge. Today, information from such instruments as formation sampling tools can assist in the eval-uation of both rocks and fluids in a wellbore. Among wireline tools that provide valuable in-sights into the subsurface are electric, radioac-tive and acoustic logs, as well as dipmeters, borehole imaging logs and magnetic resonance imaging logs. Data from drillstem tests are also incorporated into a subsurface picture. Even geochemical techniques, which seek to corre-late surface measurements of various chemical compounds with the underground occurrence of hydrocarbons, are sometimes called into play.
Geophysicists also bring some tremen-dous tools to the trade of petroleum ex-ploration. Three common geophysical methods used to look for oil are magnetic, grav-ity and seismic exploration. Magnetic methods measure the strength of the Earth’s magnetic field at a specific point on the surface, while gravity techniques seek to determine the strength of the Earth’s gravity at a location. Both methods are useful in reconnaissance mapping and are usually employed in the early stages of basin evaluation.
Seismic is the real workhorse of the industry, however. In seismic prospecting, acoustic sources such as dynamite, vibrations or sonic impulses from compressed air transmit sound into the ground. As acoustic signals pass into the subsurface, they are reflected and refracted off the various sedimentary layers. Signals that bounce back to the surface are recorded and processed to form an image of the subsurface. Two-dimensional (2-D) seismic yields a cross-sectional view of the subsurface in two planes, length and height, while a 3-D survey delivers a complete volume of data that allows the explorer to image the subsurface in fine de-tail.
A further enhancement is 4-D seismic, which adds the dimension of time to the geo-physical process. In this technique, successive 3-D surveys are acquired over an area to track the movements of fluids in the subsurface. Traditional seismic relies on the information carried in compressional waves, but an emerg-ing approach extracts subsurface information carried in shear waves. This type of seismic, called multi-component or full-wave seismic, is very good at imaging stratigraphic reservoirs and fractured reservoirs.
have found many oil and gas fields by drilling domes and anticlines that could be
identified from surface mapping. The size, po-sition, dips and strikes of surface beds are all
recorded with instruments such as plane tables and Brunton compasses. Today, the map of an
explorer includes this “traditional” information, as well as that gleaned from aerial photographs
and satellite pictures. Early geologists made common use of sam-ple and drilling information from wells.
As technology advanced, well log data and core data added a great deal of knowledge. Today, information from such instruments as formation sampling tools can assist in the eval-uation of both rocks and fluids in a wellbore. Among wireline tools that provide valuable in-sights into the subsurface are electric, radioac-tive and acoustic logs, as well as dipmeters, borehole imaging logs and magnetic resonance imaging logs. Data from drillstem tests are also incorporated into a subsurface picture. Even geochemical techniques, which seek to corre-late surface measurements of various chemical compounds with the underground occurrence of hydrocarbons, are sometimes called into play.
Geophysicists also bring some tremen-dous tools to the trade of petroleum ex-ploration. Three common geophysical methods used to look for oil are magnetic, grav-ity and seismic exploration. Magnetic methods measure the strength of the Earth’s magnetic field at a specific point on the surface, while gravity techniques seek to determine the strength of the Earth’s gravity at a location. Both methods are useful in reconnaissance mapping and are usually employed in the early stages of basin evaluation.
Seismic is the real workhorse of the industry, however. In seismic prospecting, acoustic sources such as dynamite, vibrations or sonic impulses from compressed air transmit sound into the ground. As acoustic signals pass into the subsurface, they are reflected and refracted off the various sedimentary layers. Signals that bounce back to the surface are recorded and processed to form an image of the subsurface. Two-dimensional (2-D) seismic yields a cross-sectional view of the subsurface in two planes, length and height, while a 3-D survey delivers a complete volume of data that allows the explorer to image the subsurface in fine de-tail.
A further enhancement is 4-D seismic, which adds the dimension of time to the geo-physical process. In this technique, successive 3-D surveys are acquired over an area to track the movements of fluids in the subsurface. Traditional seismic relies on the information carried in compressional waves, but an emerg-ing approach extracts subsurface information carried in shear waves. This type of seismic, called multi-component or full-wave seismic, is very good at imaging stratigraphic reservoirs and fractured reservoirs.
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