Changes

===Structural applications===

===Structural applications===

Superficially, the determination of structural dip from a dipmeter seems simple and straightforward. In practice, it may be tricky. Difficulties arise from questions of scale and perspective. ''Structural dip'' by definition is the dip of recognizable lithological unit boundaries in the general vicinity of the borehole. However, a sharp change in lithology, such as from a shale to a sandstone, is the signature of a catastrophic event in geological history. Therefore, such a contact is liable to be highly irregular over the extremely short section exposed by the borehole. On an outcrop, a field geologist would astutely measure the dip of an eyeball average of the contact. The stringent confines of the borehole offer no such luxury of perspective, and the section of the contact exposed is liable to be highly unrepresentative of the average structural dip. Outcrop perspectives cannot be extrapolated to the borehole, so a different approach is needed.

Superficially, the determination of structural dip from a dipmeter seems simple and straightforward. In practice, it may be tricky. Difficulties arise from questions of scale and perspective. ''Structural dip'' by definition is the dip of recognizable lithological unit boundaries in the general vicinity of the borehole. However, a sharp change in lithology, such as from a shale to a sandstone, is the signature of a catastrophic event in geological history. Therefore, such a contact is liable to be highly irregular over the extremely short section exposed by the borehole. On an outcrop, a field geologist would astutely measure the dip of an eyeball average of the contact. The stringent confines of the borehole offer no such luxury of perspective, and the section of the contact exposed is liable to be highly unrepresentative of the average structural dip. [http://www.merriam-webster.com/dictionary/outcrop Outcrop] perspectives cannot be extrapolated to the borehole, so a different approach is needed.

Because shale is a low energy deposit, it is generally deposited in thin laminations that are parallel, planar, and horizontal at the time of deposition. In the subsurface, then, shale laminations tend to be parallel to one another and parallel to the average of most lithological bed boundaries. In dipmeter computations, there are a number of ways in which the influence of parallel bedding can be accentuated, thus biasing the results toward structural dip. Essentially these are stacking filter effects that can be applied at various stages in the computation chain, such as in the following:

Because shale is a low energy deposit, it is generally deposited in thin laminations that are parallel, planar, and horizontal at the time of deposition. In the subsurface, then, shale laminations tend to be parallel to one another and parallel to the average of most lithological bed boundaries. In dipmeter computations, there are a number of ways in which the influence of parallel bedding can be accentuated, thus biasing the results toward structural dip. Essentially these are stacking filter effects that can be applied at various stages in the computation chain, such as in the following: