gravedad y magneticos 3

7/27/2019 Gravedad y Magneticos 3

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METODOS DE GRAVEDAD YMAGNETICOS PARA LA

EXPLORACION PETROLERA

LA CIENCIA DE DECIDIR DONDEPERFORAR


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DESCUBRIR DEPOSITOS DEPETROLEO O GAS REQUIEREN LAINTEGRACION DE INFORMACIONEXTRAIDA DE DISCIPLINAS COMO LAGEOLOGIA, GEOQUIMICA,GRAVITOMETRIA, MAGNETOMETRIA,

SSMICA, PERFORACION Y MUCHASMAS.


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GRANDES EXTENCIONES DE TERRENO PUEDEN EXPLORARSE DE MANERASATELITAL Y AEREA


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Exploracin del petrleo Gravimetra (I)

La gravedad depende de la altitud, latitud,y densidad de la corteza terrestre.

La gravedad puede medirse tanto sobre lacorteza, desde un avin o un satlite

SatliteGrace


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There are a number of important and useful suchapplications for gravity in oil and gas exploration. Airbornegravity gradiometry can contribute to any of these,

providing

significantly lower noise and higher resolution data thanairborne gravimetry and faster coverage with reducedaccess

issues than surface gravimetry.In general, the major areas of application are those that

provide extra information when seismic data is limited or inmapping large areas in order to target an expensive

seismicsurvey effectively.


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AVIONES NOTRIPULADOS


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PARA FOCALIZAR MAS SE UTILIZATECNOLOGIA SOBRE EL TERRENO


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INDISPENSABLE EN EL MAR


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DISEO DE LA

EXPLORACION


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http://www.archaeologicalfieldmethods.org/wiki/File:Archeo_GridAssemblyComplete.png


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Resultados Magnetometra


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Resultados de la Magnetometra.

El mtodo magntico es el mtodo geofsico de prospeccinms antiguo el cual nos arroja cierto datos muy interesantesdependiendo del rea aplicada:

prospeccin

petrolfera

exploraciones

mineras

artefactos arqueolgicos.


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En esta el mtodo magntico arrojainformaciones acerca de la profundidad de lasrocas pertenecientes al basamento.

A partir de estos conocimientos se puedelocalizar y definir la extensin de las cuencassedimentarias ubicadas encima del basamento,

que posiblemente contienen reservas depetrleo.

La prospeccin petrolfera


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En esta el mtodo magnticonos arroja informacion directa

de minerales magnticos y deminerales no magnticosasociados con los minerales,que ejercen un efecto

magntico mensurable en lasuperficie terrestre.

Exploraciones mineras


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Adems el mtodo magntico nos puedearrojar datos exacto sobre dondeencontramos agua subterrnea.


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8- The negative magnetic susceptibility of salt causes a local decrease in thestrength of the Earths magnetic field in the vicinity of a salt dome. Readings

have been corrected for large-scale variations of the magnetic field withlatitude, longitude and time. The contours reflect only those variationsresulting from variations in the magnetic properties of the subsurface. On this

map, as expected, the salt dome (in purple) creates a negative


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This map illustrates a magnetic anomaly. It represents the intensity of

the Earths Magnetic field corrected for regional field (dipole effect) anddiurnal (HF variations) effects. Magnetic anomalies are the differencebetween observed and corresponding computed values or thedifference from the general surrounding values. Such differences areoften induced by geological features.


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9- A reduction to the pole (RTP) map of magnetics, as the one

illustrated above, corresponds to the conversion of the anomaliesinto their equivalent form at the north magnetic pole. This processusually simplifies the magnetic anomalies


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10- This RTE map of magnetics represents what the data would

have looked like if the magnetic field had been horizontal (zeroinclination). Comparing this map with the magnetic anomaly map 8),the advantages of a RTE map is quite evident.


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11- the second vertical derivative (SVD) of the reduction to the pole

(RTP) map enhances subtle magnetic anomalies, which can later becorroborated or not by geological data. Enhancement of classicpotential fields allows a better localization of the sources. Do not forgetthat the derivative of a curve is its tangent. During the night, when youdrive


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12- This map represents the second vertical derivative (SVD) of the reduction to the

equator (RTE) of the magnetic anomaly (see Plate 8), which enhancing the potentialfield switch order a better localization of the magnetic source. To understand suchenhancements suppose a long quite flat road, in which several bumpers were put inplace by the local police. When driving during the daytime, the bumpers, when notpainted, are difficult to locate. However, when driving during the night, they are easilylocated by the abrupt changes of the lights of headlights of the car moving in opposite

direction (first derivative of the road).


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13- As illustrated, a monocline geological model dipping westward with asmall sedimentary trough, striking North-South and located in the westernpart of the map, is corroborated by the previous magnetic maps (8 to 12).Significant normal faults striking roughly north-south, seem to havelengthened the sediments. A magnetic source is likely in the north-easternarea. The proposed geological model must be tested by gravimetric andfinally by seismic and subsurface data.


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Gravimetry

Considering the gravitational attraction of aspherical non-rotating, homogeneous Earth

of mass M and a radius R on a small massm on its surface

where G is the Gravitational Constant


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14- The Bouguer anomaly (BA) corresponds roughly to the difference between theestimated regional gravity field and the observed gravity. In fact, this difference mustbe corrected by free-air correction (FAC), the Bouguer correction (BA), and theterrain correction (TC) or Etvs correction (EC) when the gravity measurements aretaken in a moving vehicle. Residual gravity anomalies are conventionally displayedon profiles or as isogal maps.


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15- This map illustrates the negative gravity anomaly over the GrandSaline Salt Dome (see magnetic anomaly on 7). The gravitational

readings have been corrected for effects resulting from (i) Earths rotation,(ii) Irregular surface relief and (iii) Regional geology. The contours reflectjust variations in shallow density structures of the area induced by localgeology. As depicted in 6, the low density of the salt, generally between2.15 and 2.17 g/cm3, induces a negative gravity anomaly.


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6-The relatively low density of salt with respect to its surroundingsrenders the salt dome a zone of anomalously low mass. Earthsgravitational field is perturbed by subsurface mass distributions andthe salt dome therefore gives rise to a gravity anomaly that isnegative with respect to surrounding areas, as illustrated on theBouguer anomaly.


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16- The magnetic and gravity anomalies illustrated on Plates 7 and 15 wereperformed over a salt dome that later was completely identified by this seismicline (Grand Saline Salt Dome, Texas, USA). Potential methods can roughly putin evidence the exact location and geometry of salt domes. They do not allowan exhaustive understanding of the geometry of the salt structures.Nevertheless, they can be used to test the coherence of the geologicalinterpretations. In this particular example, the bulb and stem of the salt domeare quite evident as well as the associated rim synclines.


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17- This map illustrates the Bouguer Gravity of the area covered bythe magnetic anomaly depicted in 8. It represents the gravityanomaly corrected for topographic and elevation effects.


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Corrections for the differing elevations of the gravity stations ismade in three parts:1) Free-Air Correction (FAC)It corrects the decrease in gravity with height in free air

resulting from increased distance from the centre of the Earth,

according to Newton's Law.

2) Bouguer Correction (BC)It removes the gravitational effect of the rock present betweenthe observation point and datum.3) Terrain Correction (TC)It takes into account the topographic relief in the vicinity of the

gravity station. This correction is always positive.


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f) Gravity Interpretation (Plate 22)

e) Second Vertical Derivative (SVD) of

Residual Gravity (21)

c) Residual Gravity (19)

b) Regional Gravity (18)The estimated regional field is calculated using the

observed gravity as shown on (14).


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18- This map illustrates the Regional Gravity. Itrepresents the long wavelength of the gravimetricanomaly associated with deeper sources.


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19- This Residual Gravity represents the short wavelengths of theanomaly related to shallower sources. In other words, it representsthe gravity anomalies when the regional field is removed.


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20- Here is illustrated the second vertical derivative map ofBouguer anomaly of the area covered by 18. Theenhancement induced by the derivative allows a betterlocalization of the sources.


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21- As for the Bouguer anomaly, the residual is here enhanced by thesecond derivative. The location of the gravimetric sources is moreevident than in the residual map (19).


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22- An extensional geological monocline,as illustrated above, fits with thegravimetric data (17 to 21).


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represents the density difference between the heart of the anticline and thesurrounding sediments. Such a difference is a consequence of sedimentary

burial.

23- Geological model of an anticline structure and its gravity response with for a

d


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24- Geological model and gravity response for a thrust fault (orreverse fault), in which the density difference between thehangingwall and the footwall is d = 0.13 g/cm3.


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25- In normal faulting, the hangingwall sediments are denser than thesediments of the upthrown block. Hence, as illustrated in the gravimetryprofile, the associated gravimetric anomaly can be relatively sharp.


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26- On this geological model, the dips of the strata increase indepth. Hence, due to compaction, one can say that averagedensity and acoustical impedance increase too. So, gravityanomalies can be associated with such a tectonic behavior.


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In conclusion:- Gravity maps are seldom used for detailed interpretation.- Seismic surveys are generally more useful for detailed studiesin small areas.- Like magnetic, gravity maps are useful to show the broadarchitecture of sedimentary basins.

- In gravimetry, low-density depocenters appear as negativeanomalies (salt domes, rim synclines).- Buried hills of dense basement rock, in gravimetry, show upas positive anomalies.

gravedad y magneticos 3

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