RIASSUNTO
Abstract
Conventional drillstrings frequently pose problems when used to drill relatively small size holes. Pin Up, a new, simple technology, affords economical solutions to problematic hole sizes and conditions. The improvement realized by using Pin Up drillstrings is helping the industry drill higher quality wells, while lowering drilling cost.
Introduction
As drilling goes deeper and hole sizes become smaller, the stresses exerted on conventional drillstrings frequently exceed their design and structural limits. When this occurs, failure in the individual drillstring components is likely. A new technology was needed to address drilling problems that had become so commonplace as to be expected and budgeted for.
This paper investigates these problems and introduces a technology that is successfully conquering the efficiencies inherent in small-diameter conventional drillstrings.
Pin Up Drillstrings Maximize Value Pin Up Drillstrings Maximize Value Running drillstrings pin up is not a totally new concept. Over the years, many contractors have and still continue to rotate their drillstrings. One well is drilled with the drill pipe run box up and the next well is drilled with the pipe run pin up. This box up/pin up rotation of drill pipe, spreads slip-area wear on both ends of the pipe, and increases appreciably the service life of a drillstring. pipe, and increases appreciably the service life of a drillstring. Although this procedure offers a financial gain by prolonging the life of an expensive asset, it offers little else.
However, the new approach to running drillstrings pin up allows one to run ""one size larger"" components and still retain fishability. The use of drill collars, heavy-wall drill pipe and regular drill pipe in larger sizes or outer diameters (ODs), greatly increases. the stiffness, strength and hydraulic horsepower of the drillstring.
Pin Up technology applies in hole sizes 8 3/4 in. and smaller. As the Pin Up technology applies in hole sizes 8 3/4 in. and smaller. As the hole sizes decrease, the advantages of using Pin Up drillstring components increase. In an 8 1/2 in. hole, frequently the primary concern is control of wellbore direction. Typically 5-in. drill pipe is run conventionally (box up). This size drill pipe is sufficiently strong and keeps pressure losses to a minimum in that section of the drillstring. However, increased stiffness in the bottomhole assembly (BHA) often is desired.
A Pin Up BHA (Figure 1) allows drill collars up to 7% in. OD to be run instead of conventional 61/2 in. collars. A conventional 7% in. box-up drill collar with the appropriate 61/2 in. fishing neck requires a relatively weak connection size (4 in. IF/NC 46) and since connection strength is primarily dependent on box OD and pin ID, a reduction in the box OD either thins the walls of the box or forces the use of a smaller connection size, or both. The problem is compounded because although the BHA now has larger, stiffer drill collars, those drill collars have weak, high-stress level connections.
However, the Pin Up design turns the drill collar pin up and places the fishing neck under the pin, producing a 7% in. OD drill collar with a larger connection (NC56). The NC56 connection is stiffer and stronger, both torsionally and in tensile yield strength. The reduced neck OD does not compromise connection strength nor does it require a smaller connection to be used as is the case when running the drillstring box up. The overshot-retrievable drill collar produced also is 107% stiffer (I=84 vs. I=174), 84% stronger torsionally (40,451 ft/lbs vs. 74,479 ft/lbs) and 46.5% stronger in tensile yield strength (1,183,920 lbs vs. 1,734,398 lbs). As can be seen in Figure 2, more weight-on-bit can be run with the larger OD Pin Up collars without increasing deviation.
It is generally agreed that the first 60 to 90 feet of a bottomhole assembly is the most critical in controlling hole direction. Figure 3 illustrates a short, 63-ft packed Pin Up BHA that offers maximum stiffness and strength. The added stiffness greatly reduces the tendency to deviate. With stiffer drill collars between points of stabilization, the stabilizer blades are less prone to dig into the wall of the wellbore and create high torque loadings. This reduction in torque decreases potentially damaging torsional loadings on the entire drillstring. The extra stiffness of the Pin Up BHA permits the bit to drill closer to its true axis center, promoting longer bit life.
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