Geometrical instruments – Indicator of direction of force traversing natural media – Borehole direction or inclination
Reexamination Certificate
2003-09-05
2004-11-30
Gutierrez, Diego (Department: 2859)
Geometrical instruments
Indicator of direction of force traversing natural media
Borehole direction or inclination
C033S313000, C175S045000
Reexamination Certificate
active
06823602
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to continuous measurement-while-drilling surveying methods and apparatuses.
BACKGROUND OF THE INVENTION
To obtain hydrocarbons such as oil and gas, boreholes are drilled by rotating a drill bit attached at a drill string end. A large proportion of the current drilling activity involves directional drilling, i.e., drilling deviated and horizontal boreholes to increase the hydrocarbon production and/or to withdraw additional hydrocarbons from the earth's formations. Modem directional drilling systems generally employ a drill pipe having a drill bit at the bottom that is rotated by a drill motor or a “mud motor”. Pressurized drilling fluid or “mud” or “drilling mud” is pumped into the drill pipe to rotate the drill motor and to provide lubrication to various members of the drill string including the drill bit. The drill bit and drill motor form part of what is known as the bottom hole assembly (“BHA”). As required the drill pipe is rotated by a prime mover, such as a motor, to facilitate directional drilling and to drill vertical boreholes.
Measurement-While-Drilling (MWD) surveying for directional and horizontal drilling processes is performed to provide the orientation and the position of the BHA [Conti, 1999]. Azimuth, the inclination and the tool face angles determine the orientation of the BHA, while latitude, longitude and altitude determine the position of the BHA. The altitude directly determines the true vertical depth of the BHA. State of the art MWD surveying techniques are based on magnetic surveying which incorporates three-axis magnetometers and three-axis accelerometers arranged in three-mutually orthogonal directions. The three-axis accelerometers monitor the Earth gravity field to provide the inclination and the tool face angles. This information is combined with the magnetometer measurements of the Earth magnetic field to provide the azimuth [FIG. 1, Russel et al., 1979].
The magnetic surveying system determines the BHA orientation at certain survey stations with the assumption that the error which modifies the Earth's magnetic field vector at the surveying instrument is in the direction of the borehole [Russel et al., 1979]. This assumption is justified by installing these magnetometers inside a non-magnetic housing. Such housing system necessitates the use of non-magnetic drill collars around the surveying equipment at a cost approaching $30,000 per single installation [Rehm et al., 1989].
Although simple, the magnetic surveying system suffers from several inadequacies especially within the drilling environment [Thorogood, 1990; Thorogood et al., 1986]. The presence of downhole ore deposits deviate the measurements of the Earth magnetic field even with the non-magnetic drill collars surrounding the surveying instruments. In addition, magnetic surveying tools located in non-magnetic drill collars are subject to the influence of the other steel components of the drill string. It has been shown that drill string induced surveying error increases with inclination and as the borehole direction approaches the east-west azimuth. Drill string magnetic interference is particularly noticeable when inclination exceeds 30°. Although it has been reported that the effect of the drill string magnetic interference could be reduced (mitigated but never entirely eliminated) by running long lengths of non-magnetic materials above and below the survey instruments [Grindord et al., 1983], this solution could affect the cost benefits of the horizontal drilling technology. The effect of drill string magnetic interference as well as the presence of downhole ore deposits can neither be quantified nor compensated. In addition to these two effects, geomagnetic influences play an important role in the accuracy of the magnetic surveying system [Parkinson, 1983]. Geomagnetic influences are defined by the variation of the dip angle, the declination and the total magnetic field strength with respect to time. The dip angle is the angle between the direction of the Earth's magnetic field and the horizontal plane. The declination is the angle between the magnetic north and the true north. It was recorded that during any given day at a random location the standard deviations of the dip angle, the declination and the magnetic field strength were 0.3°, 0.9° and 0.3 &mgr;-Tesla respectively [Parkinson, 1983]. The variation in the geomagnetic field is quite significant in relation to the performance capabilities of the magnetic surveying tools currently used. Therefore, geomagnetic effects must be taken into account when considering absolute survey accuracy and impose definite limitations on the accuracy levels that can ultimately be achieved.
Several investigations have been reported to improve the magnetic surveying accuracy. Shiells and Kerridge (2000) introduced the interpolated in-field referencing method in which absolute local geomagnetic field data is determined from spot measurements of the Earth's magnetic field. These measurements are taken at local site which is sufficiently close to the drilling site so that the measurement data is indicative of the Earth's magnetic field at the drilling site but is sufficiently remote from the drilling site so that the measurement data is unaffected by magnetic interference from the drilling site. This technique compensates for the geomagnetic influences but the measurements taken by the magnetometers still suffer from the drill string magnetic interference. In addition, measurements of the geomagnetic field in a local site might not be applicable in an area that has many drilling rigs. Moreover, such technique adds more complexity that may give rise to additional cost.
Hartmann (1998) introduced a method to improve the accuracy of borehole surveying. This method is based on determining the uncertainty in the magnetic field measurements by comparing the measured magnetic field with a corresponding known value at specific location. However, this method does not take into account two phenomena. The first phenomenon is the increase of the drill string magnetic interference at high inclinations. The second is the presence of ore deposits that can be found randomly downhole. These two phenomena add additional errors that are not taken into consideration when referencing the theoretical value of the magnetic field to the measured value at the known location.
Dipersio (1995) introduced a new method for the compensation of geomagnetic influences. This method depends on matching both the calculated magnetic field strength and the calculated dip angle to their corresponding nominal values at a particular geomagnetic location. This results in determining an error-free value of the axial component of the magnetic field which is directly used to determine the azimuth. However, at high inclinations, the drill string magnetic interference generates additional errors in the cross-axial directions.
Several other techniques have been described for magnetic MWD surveying [Nicholson, 1995; Engebretson, 1992; Helm, 1991; van Dongen et al., 1987; Trowsdale, 1982]. However, it is clear that the major weaknesses of the present directional sensing instruments stem from the use of magnetometers for monitoring the azimuth and from the hostile environment in which these devices work. The problem encountered with the use of magnetometers is the presence of massive amount of steel around the drilling rig. The abundance of ferromagnetic material necessitates the separation of the magnetometers by non-magnetic drill collars. Aside from the cost of utilizing non-magnetic drill collars, their use introduces a second problem. Since the non-magnetic drill collars impose an additional weight on the drill bit, the surveying tools are separated from the bearing assembly and the drill bit by about 30 feet [Conti, 1989; Rehm at al., 1989]. Elimination of the non-magnetic drill collars could reduce the distance betwee
Irvine-Halliday Dave
Mintchev Martin P.
Noureldin Aboelmagd
Smith Winston
Tabler Herb
Bennett Jones LLP
Gutierrez Diego
Smith R. Alexander
University Technologies International Inc.
LandOfFree
Continuous measurement-while-drilling surveying does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Continuous measurement-while-drilling surveying, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Continuous measurement-while-drilling surveying will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3320266