![]() ![]() The PDM bent-housing motor assembly is then run into the cased well to divert the trajectory of the drill so that the apparatus can point toward the targeted deposit.Īs more-demanding formations are encountered-such as in ultradeep, high-pressure, high-temperature, abrasive rock and shales-wear and tear on the mud motors and bits causes frequent “trips.” (Trips involve pulling worn-out mechanical bits and motors from the well, attaching replacements, and reentering the well to continue drilling.) To answer these challenges, modern technologies incorporate an RSS capable of drilling vertical, curved, and horizontal sections in one trip. Later, a casing whipstock is used to mill (or grind) through the existing casing. In order to accomplish this, a drill string is prepared to isolate the other producing zones. ![]() ) In mature fields where engineers and drilling staff target smaller deposits of oil that were bypassed previously, it is not uncommon to use existing well bores to develop the bypassed zones. (Sidetracking is drilling horizontal lateral lines out from existing well bores. PDM bent-housing motor assemblies are most commonly used to “sidetrack” out of existing casing. The bent housing misaligns the bit face away from the line of the drill string, which causes the bit to change the direction of the hole being drilled. A more recent technique makes use of steerable motor assemblies containing positive-displacement motors (PDMs) with adjustable bent-housing mud motors. The drill bit was thereby forced to move off in the proper direction. This consisted of an inclined plane on the bottom of the drill pipe that was oriented in the direction the well was intended to take. The original tool for “kicking off” such a well was a mechanical device called the whipstock. The borehole, in effect, ends up making a large arc to reach its objective. ![]() In order to achieve a large deviation angle, therefore, a number of small deviations must be made. Since the nearly inflexible drill pipe must be able to move and rotate through the entire depth, the angle of the borehole can be changed only a few degrees per tens of feet at any one time. This is done by drilling the well vertically to start and then angling it at a depth that depends on the relative position of the target. In such cases, the surface equipment must be offset and the well bore drilled at an angle that will intersect the underground formation at the desired place.
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