Boring or penetrating the earth – With signaling – indicating – testing or measuring – Tool position direction or inclination measuring or...
Reexamination Certificate
2000-03-30
2002-06-18
Neuder, William (Department: 3672)
Boring or penetrating the earth
With signaling, indicating, testing or measuring
Tool position direction or inclination measuring or...
C175S061000
Reexamination Certificate
active
06405808
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present relates generally to methods and apparatus for improving the efficiency of the drilling process and also conducting surveys of drilled wells, particularly directional wells having wellbores that transition from vertical to inclined to horizontal orientation for intersecting a desired subsurface anomoly or target. More specifically, the present invention is directed to a method for increasing the efficiency of the drilling operation by minimizing the number of high accuracy stationary measurements by integrating or augmenting that measurement sequence with an additional sequence of lower accuracy measurements that can be made without having to suspend the drilling operation. A particular embodiment of this invention is a method for developing a well survey wherein continuous inclination data, typically achieved by a measuring while drilling (“MWD”) tool, is integrated with or used to augment the minimum radius of curvature approximation of the trajectory shape between conventional survey points taken along a wellbore trajectory to define individual arcs and tangents in the trajectory and thereby improve the accuracy of the wellbore's position.
2. Description of the Related Art
In drilling a directional well, it is common to use a bottom hole drilling assembly (BHA) that is attached to a drill collar as part of the drill string. This BHA typically includes, in descending order, a drilling motor assembly, a drive shaft system including a bit box and a drill bit. In addition to the motor, the drilling motor assembly may include a bent housing assembly which has a small bend angle in the lower portion of the BHA. This bend angle causes the borehole being drilled to curve and gradually establish a new borehole inclination and/or azimuth. During the drilling of a borehole, if the drill string is not rotated, but merely slides downward as the drill bit is being driven only by the motor, the inclination and/or the azimuth of the borehole will gradually change, in other words, curve, due to the bend angle, thus forming a curved wellbore section. Depending upon the tool face angle, that is, the angle at which the drill bit is pointing relative to the high side of the borehole, the borehole can be made to curve at a given azimuth and inclination. If however, the rotation of the drill string is superimposed over that of the output shaft of the motor, the bend point will simply travel around the axis of the borehole so that the bit normally will drill straight ahead at whatever inclination and azimuth have been previously established, thus forming a straight wellbore section. The type of drilling motor that is provided with a bent housing is normally referred to as a steerable drilling system. When drilling with a steerable drilling system of this nature, various combinations of sliding and rotating drilling procedures can be used to control the borehole trajectory in a manner such that eventually the drilling of a borehole will proceed to a targeted formation. Stabilizers, a bent sub, and a kick pad also can be used to control the angle build rate in sliding drilling, or to ensure the stability of the wellbore trajectory in the rotating mode. Thus, when the drill string is not being rotated and the drill bit is being rotated by the drilling motor in a steerable or directional drilling system, the wellbore segment being drilled will be of curved geometry. Likewise, when the drill string is being rotated and the drilling motor is also being operated, the resulting wellbore section being drilled will be substantially straight.
During well drilling, to confirm the spatial position of the wellbore being drilled as it progresses through the formation, it is necessary to conduct periodic well surveys, either using a well survey instrument or using the various sensors of a measuring while drilling (MWD) tool that is incorporated within the well drilling string. These periodic well surveys establish survey stations at selected intervals along the length of the wellbore. Typically, between survey stations the wellbore will be defined by a number of straight wellbore sections or tangents which result from drilling with the drill motor and simultaneously rotating the drill string and a number of curved wellbore sections or arcs which result from drilling only with the drill motor without rotating the drill string, so that the drill string merely slides along the curved wellbore section being drilled. While the survey stations are typically located at substantially equally spaced locations along the wellbore, typically determined by the lengths of the drill pipe sections or the length of the stands of drill pipe, the lengths of the arcs and tangents will vary according to bent motor orientation during drilling. It is typical to compute the trajectory of a wellbore by using a minimum radius of curvature algorithm which assumes that the geometry of a wellbore between survey stations lies along a smoothly curved arc. Well surveys being calculated from the data and the survey points can have significant error because the actual geometry of the drilled wellbore in most cases will not lie along a curve of fixed curvature but rather will consist of a plurality of arcs and tangents arranged end to end and having a bend angle at the juncture of the arcs and tangents. Thus, the spatial position of the wellbore at any given depth can be sufficiently in error that an intended target can be missed.
The same general wellbore geometry is established, as indicated above, when rotary steerable drilling systems are employed for well drilling activities. A rotary steerable drilling tool typically includes a drill collar that is rotated by a drill string and supports a bit shaft to which a drill bit is fixed. The bit shaft is angularly adjusted relative to the drill collar about a pivot mount within the drill collar. As rotary drilling progresses, the angular position of the bit shaft and thus the drill bit is adjusted, in other words, steered by steering control signals communicated from the surface or by on-board sensor responsive steering signals to define straight borehole sections or curved borehole sections having periodically controlled inclination and azimuth to progress the wellbore toward an intended subsurface target. The result of this steerable drilling with a rotary steerable drilling tool is that the wellbore being drilled will be defined by a series of arcs and tangents in the same manner as discussed above. For accurately determining the spatial position of the wellbore at any desired location between the survey points that are achieved at intervals when drilling is discontinued, the trajectory shape of the wellbore between the survey points is desired.
Historically, well surveys were, and in many cases are conducted by running into a wellbore a well survey sonde having a housing that is selectively positioned by cable equipment. The cable equipment typically incorporates electrical conductors for conducting various position signals from on-board sensors of the survey tool to surface equipment for receiving and processing the signals. The survey instrument will typically incorporate one or more inclinometers and an orthogonal triad of accelerometers for measuring the angle of the local vertical with respect to the sonde. Since the sonde handling cable does not control rotational positioning of the sonde, it is necessary that the surveying instrument have the capability for measuring probe orientation to provide a reference for the inclinometer measurements and thus enable measurement of the azimuth of the borehole at the survey point or station. Sonde orientation may be measured with gyroscopes or magnetometers which may be utilized independently or in conjunction with other position sensing systems. When a borehole is surveyed using a sonde or survey instrument of this nature the result is typically a series of survey points or stations at fairly widely spaced intervals along the wellbore. The survey points, which are accurate from t
Edwards John E.
Lovell John R.
J. L. Jennie Salazar
Neuder William
Schlumberger Technology Corporation
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