Information obtained from surface structure

In areas where the rocks outcrop at the surface, a careful study of the surface and its structural relations may be considered to be a guide to the subsurface conditions and thus aid in predicting the most favorable sits for the location of a test well to be drilled.

The surface survey should be directed by a competent geologist, who may know in advance whether or not petroliferous strata are likely to be found beneath the area under observation. Then the problem resolves itself into the locating and mapping of structure favourable for drilling. The possible thickening or thinning of formations and the probability of overlapping and unconformable relations of strata must be taken into account, as the presence or absence of either will determine whether or not the surface outcrops and the surface strata are closely related.

Even though the surface outcrops are favourable, and petroliferous strata are known to underlie the area, no concentrations of oil in commercial quantities will exist unless the surface structures are favourable, as well. This, of course, can be determined accurately only by drilling a test well, since the surface strata often do not conform to the surface bed. But with a clear knowledge of the nature and relationships of structure, the careful geologist will devote much time and effort to make the proper deductions as to the existence of favourable underground conditions before any drilling is commenced. All possible area for drilling purposes, the presence or absence of bituminous outcrops, gas emanations, and oil seeps should be investigated; and the dip strike of the outcropping rocks must be carefully measured to make a surface contour map of the area. An aerial map will also assist, as it will indicate the positions of the outcrops and point out the relative position of any faults that are in evidence at the surface. In addition to this, a detailed study of the fossil remains in the surface rocks should be made if the geologic age and sequence of the strata are unknown. Also, surface outcrops several miles distant may furnish an appreciable amount of direct evidence as to the subsurface conditions of the sediments beneath area under observation.