The search for stratigraphic traps is basically the search for barriers to the movement of fluids. Such barriers can be identified more surely by pressure information than by stratigraphic correlation. We think of normal reservoir pressure as "that necessary to sustain a column of water to the surface." However, when oil or gas is in lenticular sands, the initial reservoir pressures may be much less or much more than "normal." Examples of low pressures are found in the Cretaceous of New Mexico and Alberta, and the Morrow of western Oklahoma. Abnormally high pressures are found in many areas of the world, especially in Tertiary sediments, but also in the Pennsylvanian Morrow sandstones of central Oklahoma. In Blaine County there are about 10 separate Morrow reservoirs. All the wells in each reservoir have similar initial pressures and subsequent pressure-decline histories, which differ markedly from one reservoir to another. It should be possible from well performance, or even good drillstem-test data, to tell which reservoir a wildcat well has penetrated, or whether it has found an entirely new reservoir. Thus the regional extent of each reservoir can be ascertained very early during exploration.

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