Range of explored depths

The range of explored depths in the earth's crust, which have to be dealt with when resolving various geological problems, starts from first two-three meters and proceeds to dozens of kilometers. Seismic exploration deals with the first meters when determining level of underground waters (a very important objective when searching for water in arid regions to design irrigation systems and implement melioration) or identifying thickness of crumbly sediments that must be removed prior to construction of large facilities and open-pit development of minerals. Seismic exploration also has to deal with dozens of kilometers when investigating the earth's crust and upper mantle.

The range of depths from 1000 to 6000 meters is typical for oil and gas searching, where seismic exploration is the key tool of exploration geophysics. Inaccuracy in determining location of any objects in the thickness of rocks in this case must not exceed 1 – 2% with several kilometers thickness of capping sediments. It should be noted that properties of rocks, as a rule, significantly change both vertically (with depth) and horizontally. Further, actual geological bodies significantly differ from ideal elastic bodies in their properties and have sufficiently complex structure.

All of this results in tremendous mathematical difficulties even at the stage of resolving direct problems - calculating field of displacements on the medium surface based on established location of elastic waves source. Differences in elastic properties, and first of all in the capacity to absorb elastic waves, enormous variety in combinations of rocks of different types, changeability of rocks in immediate proximity to the surface do not allow without appropriate experimental surveys answering the question, which capacity should the source of elastic waves have to ensure reaching the target exploration depth.

Text 6

Read, translate the text "Diamond bits" and make the annotation of it.

Diamond bits

Diamond bits are designed to crush nonabrasive rocks of medium hardness and hard rocks by abrasion (micro cutting). Diamond bit consists of steel housing with connecting toll-joint thread and shaped diamond-bearing head (matrix). Matrix is divided into sectors with radial (or spiral) flushing channels, which are connected to the bit housing cavity through flushing ports.

Diameters of diamond bits are 2 — 3 mm less than relevant diameters of roller-cutter bits. This is made to create conditions required for transition to drilling with diamond bits after roller-cutter bits, which, as a rule, are decreased in diameter with deterioration. Key advantages of diamond bits are good centralizing capacity on the well bottom and development of circular bottom hole (opposite to triangular bottom hole with rounded tops when drilling with roller-cutter bits).

Significant disadvantages of diamond bits include: first, extremely low mechanical drilling rate. Maximal mechanical drilling rate, as a rule, does not exceed 3 m/h. For comparison - maximal mechanical rate of drilling with roller-cutter bits is about 120 m/h. Second, diamond bits have small range of application (abrasive rocks are excluded) and third, higher requirements to preliminary preparation of well bore and bottom are set.

Text 7

Read, translate the text "Spontaneous well deviation" and make the annotation of it.