|—the depth of the boreholes, metres|
|—the commercial speed of the drilling, metres per month|
|—the average penetration per one drilling bit per one tripping operation, metres|
DRILLING WORKS (EN: drilling works; DE: Bohrarbeiten; FR: travaux de forage, travaux de sondage; ES: perforacion, sondeo, taladrado; RU: буровые работы) is the determined combination and sequence for the performance of the operations during the construction of the operational and researching boreholes, and during the drilling of the mining-technical boreholes.
The quantity of the drilling works for the petroleum and gas boreholes within the USSR amounts to more than 22 million metres, of the exploratory boreholes amounts to up to 6 million metres, of the mining-technical boreholes amounts to 50 million metres (1980). Within the USSR, the major quantity of the penetration for the petroleum and gas boreholes is performed by the hydraulic bottomhole motors (75.8% of the total quantity of penetration, 1980), while abroad there is used almost exclusively the rotary method for the drilling (up to 1% by the bottomhole motors). The drilling works include the construction of the drilling derrick, and of the near-derrick built structures, the installation (and also the dismantling) of the drilling equipment (see the "Derrick installation works" article), the drilling (including the fixation), the mastering and testing of the boreholes.
Depending on the purpose of the drilling, the composition and the significance of the individual operations during the drilling works may vary (for example, during the drilling of the blastholes and blasting boreholes, their walls are not fixated). The drilling proper is characterized by the continuous advancement of the boreholes, and by the cyclical character of the work, that is, the immediate destruction of the rock at the bottomhole within the borehole by the drilling bit (or by the drilling crown during the retrieval of the core) is replaced by the lifting of the drilling string for the replacement of the drilling bit, which has worn out, by the new drilling bit, and for the lowering of the new drilling bit into the bottomhole. The advancement of the drilling bit assembly and of the rock destructing tool into the bottomhole is conducted with the prescribed axial force and frequency of the rotation; the cleaning of the bottomhole of the products of destruction is performed with the help of the drilling fluid, compressed air, and so on.
The drilling is accompanied by the fixation of the shaft within the borehole (of the parts within the borehole throughout the depth) by the casing pipe strings, and also by the auxiliary and repairing works, which also mostly have the cyclical character. The main criteria for the evaluation of the effectiveness of the drilling works are the speed of the drilling, the cost per the metre of the penetration, the quality of the construction of the boreholes, and the development of these boreholes to the designed depths (see the Figure); besides these criteria, for the geological-exploratory drilling works, there exist the representativeness and reliability of the geological-geophysical and technological information, the growth of the reserves of petroleum and gas per one metre of the penetration, and for the operational works, the yield of the borehole.
The effectiveness of the drilling works increases with the decrease of the quantity of the tripping operations, which are spent for the drilling of the borehole in case of the specific mining-geological conditions, of the time, which is consumed on average per one tripping operation, with the increase of the speed of the cycle of the construction of the borehole, and also with the decrease of the share of all the expenditures, which are associated with the liquidation of the consequences of the accidents, complications, and defects during the work, and of the downtimes of the boreholes according to the organizational causes.
The prospects for the development of the drilling works are: the increase of the tempos for the construction of the boreholes with the depth of more than 4500 metres, the widespread usage of the roller-cone drilling bits with the sealed oil-filled supports, the increase of the tempos, quality, and level of organization for the works on the mastering and testing of the boreholes, the massive mastering of the coastal shelf zone, and of the regions with the permafrost, and so on.
Abroad, the drilling works are characterized by the growth of the quantities of the penetration for the petroleum and gas boreholes, by the stabilization of the average depths for the boreholes (at the level of 1450-1500 metres), by the growth of the average penetration per one drilling bit (up to 320 metres, 1980).
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