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Line 28: + + − The figure below shows an example of a magnetic profile on an interpreted seismic section from Logan County, Arkansas. The dark band corresponds to Cambrian through Mississippian sedimentary rocks. Note correlation between the location of the four normal faults interpreted in the seismic section and the location of faults in the magnetic profile (marked by diamonds).+ − [[file:using-magnetics-in-petroleum-exploration_fig14-12.png|thumb|{{figure number|14-12}}Magnetic basement mapping in petroleum exploration can be applied to the search for leads or prospects that can be quickly and economically developed by comparing known traps or structure (and/or stratigraphy) with the basement fault block pattern. Some areas have never been tested by the drill where the structure at basement level is analogous to that over nearby producing properties. Some of these leads become viable prospects when subjected to follow-up seismic profiling or other appropriate exploration techniques. A common type of structural or stratigraphic data used to correlate to the magnetic data is subsurface mapping, developed from well data. However, on overseas projects or in frontier areas, the best (or only) data available may be 2-D seismic surveying. In either case, the procedure is to search for “look-alikes” on the magnetic data that correspond to features over known producing fields. Since the magnetic data can be acquired in continuous fashion over large areas at a very economical price, many good leads can be developed in a short time.]]+ + + + + + + + + − + − − [[file:using-magnetics-in-petroleum-exploration_fig14-14.png|thumb|{{figure number|14-14}}]]
Magnetics: petroleum exploration applications (view source)
Revision as of 19:50, 21 January 2014
, 19:50, 21 January 2014no edit summary
* Aiding in exploration programs based primarily on subsurface (well) data
* Aiding in exploration programs based primarily on subsurface (well) data
* Estimating depth to basement over broad areas
* Estimating depth to basement over broad areas
[[file:using-magnetics-in-petroleum-exploration_fig14-12.png|thumb|left|{{figure number|1}}]]
==Interpreting fault location in seismic sections==
==Interpreting fault location in seismic sections==
Magnetics can be very valuable in [[interpreting seismic data]] by plotting residual magnetic profiles along seismic sections. This technique is valuable in looking for (1) subtle stratigraphic changes that can occur along basement block boundaries and (2) subtle fault offsets or other structural and stratigraphic features. The locations of the basement weakness zones provide focal points for examining the seismic data more closely.
Magnetics can be very valuable in [[interpreting seismic data]] by plotting residual magnetic profiles along seismic sections. This technique is valuable in looking for (1) subtle stratigraphic changes that can occur along basement block boundaries and (2) subtle fault offsets or other structural and stratigraphic features. The locations of the basement weakness zones provide focal points for examining the seismic data more closely.
[[:ile:using-magnetics-in-petroleum-exploration_fig14-12.png|Figure 1]] shows an example of a magnetic profile on an interpreted seismic section from Logan County, Arkansas. The dark band corresponds to Cambrian through Mississippian sedimentary rocks. Note correlation between the location of the four normal faults interpreted in the seismic section and the location of faults in the magnetic profile (marked by diamonds).
==Developing leads from analogs==
Magnetic basement mapping in petroleum exploration can be applied to the search for leads or prospects that can be quickly and economically developed by comparing known traps or structure (and/or stratigraphy) with the basement fault block pattern. Some areas have never been tested by the drill where the structure at basement level is analogous to that over nearby producing properties. Some of these leads become viable prospects when subjected to follow-up seismic profiling or other appropriate exploration techniques. A common type of structural or stratigraphic data used to correlate to the magnetic data is subsurface mapping, developed from well data. However, on overseas projects or in frontier areas, the best (or only) data available may be 2-D seismic surveying. In either case, the procedure is to search for “look-alikes” on the magnetic data that correspond to features over known producing fields. Since the magnetic data can be acquired in continuous fashion over large areas at a very economical price, many good leads can be developed in a short time.
[[file:using-magnetics-in-petroleum-exploration_fig14-13.png|thumb|{{figure number|2}}.]]
==Laying out seismic programs==
Suppose we have developed a basement fault block pattern as shown in [[:file:using-magnetics-in-petroleum-exploration_fig14-13.png|Figure 2]]. Also suppose this area has been tectonically active and is characterized by a fair degree of faulting. This being the case, we can expect that many of the basement shear zones have been reactivated and are now the locus of faults and fractures in the sedimentary section. Thus, A, D, and F in [[:file:using-magnetics-in-petroleum-exploration_fig14-13.png|Figure 2]] are the wrong places to run 2-D seismic lines because of the probable poor seismic definition due to fracturing along these zones and the possibility of sideswipe. Lines B, C, and E, on the other hand, are good places to run seismic surveys because of the probable lack of fracturing and faulting at these localities. In addition, gravitational compaction structures are generally found within these blocks; thus, line B or C would have found West Campbell field (WCF) but Line A would not.
[[file:using-magnetics-in-petroleum-exploration_fig14-14.png|left|thumb|{{figure number|3}}]]
==Interpreting fault location in map view==
==Interpreting fault location in map view==
Magnetics can be quite useful in interpreting existing seismic programs after they have been shot. In the example below, two 2-D seismic lines have been placed purposely in the worst possible positions relative to the basement fault block pattern.
Magnetics can be quite useful in interpreting existing seismic programs after they have been shot. In [[:file:using-magnetics-in-petroleum-exploration_fig14-14.png|Figure 3]], two 2-D seismic lines have been placed purposely in the worst possible positions relative to the basement fault block pattern.
Assuming all the basement shear zones represent faults in the sedimentary section, then “hooking-up” the faults in this area is a problem. Fault pick C on line 1, for example, does not connect straight across to fault pick G on line 2, nor even to H or I, which are some distance away. Instead, it hooks up to J, making this fault very oblique to the seismic lines. This is not a very common way of connecting faults on most seismic interpretations. The connection of B to H is straightforward but, again, is diagonal to the seismic lines, whereas F–K runs diagonally in the opposite direction. Fault picks D, G, E, and I do not connect to the other seismic line at all; they terminate somewhere in between.
Assuming all the basement shear zones represent faults in the sedimentary section, then “hooking-up” the faults in this area is a problem. Fault pick C on line 1, for example, does not connect straight across to fault pick G on line 2, nor even to H or I, which are some distance away. Instead, it hooks up to J, making this fault very oblique to the seismic lines. This is not a very common way of connecting faults on most seismic interpretations. The connection of B to H is straightforward but, again, is diagonal to the seismic lines, whereas F–K runs diagonally in the opposite direction. Fault picks D, G, E, and I do not connect to the other seismic line at all; they terminate somewhere in between.
==Depth estimates==
==Depth estimates==