Problem of Monitoring of Arbitrary Oriented Trajectories of Boreholes with Small Diameters by Means of Strapdown Gyroscopic Inclinometers and its Solution Methods

Abstract

The possibility to use two-axis gyro rate sensor (GRS) in principle for measurement of trajectory parameters is shown., in the present report. The angular momentum vector of this sensor is oriented along the longitudinal axis of the borehole device. The errors and limits of this scheme utilization are defined, when operating in gyrocompassing mode. A method of utilization of the scheme with a longitudial gyro is original for two operation modes (gyrocompassing and analytical directional gyro) near the line West-East. The errors intrinsic to such a combined operation mode are analyzed. In order to eliminate the restrictions typical for inclinometer with a longitudinal gyro, it was proposed to arrange GRS with angular momentum in the cross-section plane of the borehole. And with this, a method of inclinometer utilization was develop, which permits not only to solve the "accuracy loss zone" problem but also to eliminate effect of the gyro drift changeability caused both by its utilization period and the gyro start-up errors. For the first time calibration of the gyro during operation is proposed by slewing the gyro housing about two multually perpendicular axes: the main sensor axis and the boring column axis.Algorithms on multiposition gyrocompassing of such a single-gyro system are proposed and analyzed. Experimental results confirming the main conclusions of the teoretical investigations are presented. Introduction Wide implementation of directional (controlled) drilling in the last years, and first of all - drilling of inclined and horizontal shafts of oil and gas boreholes, became the main factor that stipulated development of navigation systems including directional survey systems intended either for tracking of drilling process or for a posteriori measurement of borehole trajectory parameters. And with this, in a number of tasks related to measurement of parameters of cased borehole trajectories and also to branched-horizontal drilling of so-called secondary shafts from the ones cased before, there arose a problem of gyroscopic orientation in azimuth. This problem pertains also to the tasks related to measurement of cased holes trajectories and branched-horizon drilling [1]. Depending on the measured object and type of task in the underground course detection, several designs of inclinometers may be used: inertial, gyroazimuth or compass. The last one, which is called point-to-point inclinometer, seems to be the most preferable. This name reflects discrete nature of measurement execution, since it is done in points, where a downhole instrument is motionless. Due to natural restrictions in the use of gimbals, at present, as a rule, analytical compassing mode is implemented in such instruments with the reference to data obtained from gyro rate sensors (GRS).

Advanced Borehole Attitude Determination without Measuring Axial Angular Rate Component

“…But the aforesaid method used for the borehole azimuth determination is not a unique one. Earlier the authors have shown [1] that it is possible to calculate the azimuth value using only the first expression from (7), i.e. to calculate the desired angle with the help of arcsin function, namely:…”

“…Such statement of the problem was not considered earlier, probably, due to seeming evidence of the conventional algorithm, in which arctg function is used. It was shown in the authors' paper [1] that there exists another azimuth calculation algorithm with the use of arcsin function. In this case the properties of the desired angle are changing: in particular, the limitation area for the use of "axial" scheme is substantially narrowed down, i.e.…”