Blowout of petroleum and gas
BLOWOUT OF PETROLEUM AND GAS (EN: oil and gas outburst; DE: Erdol- und Gasausbruch; FR: degagement instantane du petrole et du gaz; ES: erupcion de petroleo y gas, desprendimiento, instantaneo de petroleo y gas; RU: выброс нефти и газа) is the sudden spontaneous outflowing of the petroleum and (or) gas from the borehole during the process of the drilling.
The blowout proceeds in case of the emergence of the positive difference between the pressure within the petroleum-gas layer, which has been unsealed using the borehole, and the pressure of the column of the drilling fluid within the borehole at the level of this layer. The blowout often starts with the manifestation of the petroleum or gas, which rapidly transitions into the open gushing (into the atmosphere), or into the closed gushing (through the pipelines into the reserve reservoirs). In case of the open gushing, there is possible the ejection of the drilling tools from the borehole, the destruction of the wellhead equipment by the stream of the drilling fluid, which has been mixed with the petroleum and (or) gas (especially the drilling fluid, which has been made heavy, using the hematite or barite), and in the individual cases, the emergence of the fire.
The causes of the blowout are: the unexpected absorption of the drilling fluid within the rocks; the saturation of the drilling fluid within the borehole with the gas, which is released from the rocks, and which decreases the weight of the drilling fluid; the decreasing or increasing of the hydrodynamic pressure onto the bottomhole, which is caused by the drilling fluid, in case of the high speed of the lowering or lifting of the drilling tools (the so called piston effect); the untimely replenishment of the borehole with the drilling fluid during the lifting of the drilling pipes; the non-compliance with the requirements for the technological regime of the drilling, for the density and composition of the drilling fluid. The most widespread sources of the blowout are the zones of the enclosed volumes of the rocks (especially clayish) with the abnormally high layer pressure or pore pressure. For example, the gas-petroleum blowout with the most severe consequences (the yield of the petroleum was 3200-4700 cubic metres per day, the yield of the gas was up to 0.8 million cubic metres per day) has emerged at the I-Source marine drilling installation within Mexico (June of the 1979 - March of the 1980), which has entailed the destruction of the wellhead, the fire, the pollution with the petroleum of the large area of the sea surface, and of the coast of the Mexico and USA.
For the prophylactics and prevention of the blowout of the petroleum and gas, the wellhead is equipped with several preventers, with the system for the joining of the pipes, with the pipelines for the injection of the drilling fluid into the borehole during the shutdown of the fountain, and with other equipment (see the "Shutdown of the boreholes" article).
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