rotary drilling
274
rotary drilling the chief method of drilling deep wells, esp. for oil and gas. A drill
bit at the end of a rotating drill pipe grinds a hole in hard rock or tears into
soft sediment. A muddy fluid is pumped down through the drill pipe, passes out through the bit and returns to the surface in the annular space
between the wall of the hole and the pipe. The drilling fluid brings the cuttings to the surface, cools the bit and prevents the walls of the well from caving. Oil and gas exploitation in continental shelf areas involves such drilling,
where besides the spoiling oil in the environment, the drilling fluid contaminates the surrounding of drilling platforms. Under optimal conditions, disturbances of the benthic system can be restricted to a 500- to lOOO-m-wide area
around the platform.
Rotifera (rotifers) phylum of minute animals which swim and feed by means of
typically ciliated bands forming the corona, which is situated around the
mouth. Formerly confused with ciliated Protozoa, who are, however, unicellular organisms contrary to the multicellular rotifers. The bilaterally symmetrical unsegmented body can be cylindrical to oval with or without a tail, and
is covered by a cuticula that can be thickened into an armor. The alimentary canal is mostly straight and ends with an posterior anus. Behind the
mouth is a muscular pharynx with specialized jaws. They have an excretory
system with flame cells joining the hind gut to form a cloaca. There is no blood
system and no respiratory organ, and a very simple nervous system. There
is a large perivisceral cavity which is not a coelom. The sexes are separate, but
Rotifera. (Riedl 1983)
274
rotary drilling the chief method of drilling deep wells, esp. for oil and gas. A drill
bit at the end of a rotating drill pipe grinds a hole in hard rock or tears into
soft sediment. A muddy fluid is pumped down through the drill pipe, passes out through the bit and returns to the surface in the annular space
between the wall of the hole and the pipe. The drilling fluid brings the cuttings to the surface, cools the bit and prevents the walls of the well from caving. Oil and gas exploitation in continental shelf areas involves such drilling,
where besides the spoiling oil in the environment, the drilling fluid contaminates the surrounding of drilling platforms. Under optimal conditions, disturbances of the benthic system can be restricted to a 500- to lOOO-m-wide area
around the platform.
Rotifera (rotifers) phylum of minute animals which swim and feed by means of
typically ciliated bands forming the corona, which is situated around the
mouth. Formerly confused with ciliated Protozoa, who are, however, unicellular organisms contrary to the multicellular rotifers. The bilaterally symmetrical unsegmented body can be cylindrical to oval with or without a tail, and
is covered by a cuticula that can be thickened into an armor. The alimentary canal is mostly straight and ends with an posterior anus. Behind the
mouth is a muscular pharynx with specialized jaws. They have an excretory
system with flame cells joining the hind gut to form a cloaca. There is no blood
system and no respiratory organ, and a very simple nervous system. There
is a large perivisceral cavity which is not a coelom. The sexes are separate, but
Rotifera. (Riedl 1983)