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The petrographic microscope provides a direct visual means of observing and measuring the chemical and physical properties of sedimentary rocks. Through its use the geologist is able to study the details and relationships of a sediment that have a direct bearing on the majority of our exploration problems. In the past five years numerous exploration offices in the Rocky Mountains have acquired petrographic microscopes for use on routine problems. Petrographic information is being used effectively now to supplement other types of geological and engineering data in the following ways: (a) to assist in the interpretation of depositional environments, textural trends and facies patterns by revealing the primary character of the rock, i,e., composition, texture and fabric; (b) by showing the secondary changes that the rock has undergone since deposition such as mineral alteration, the development of solution cavities, fracturing and cementation; (c) by providing a visual method of analyzing porosity and its relationship to both the primary character and the secondary changes; (d) by revealing the age relationship between cementation, fracturing and porosity development with respect to the times of fluid movement and to the time of oil accumulation, and (e) by providing detailed mineralogic data that can be applied statistically toward the identification and correlation of specific sedimentary bodies.
Variations on standard techniques are being employed to adapt petrographic data to all types of geological and engineering problems. In the future, exploration offices will depend more heavily on petrographic information in helping to define comparable and noncomparable data associated with exploration leads. From this usage will evolve new geological concepts that will materially increase our knowledge of sedimentary rocks, porosity and permeability, fluid migration and oil accumulation.
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