Boring or penetrating the earth – With signaling – indicating – testing or measuring – Tool position direction or inclination measuring or...
Reexamination Certificate
2001-12-21
2004-05-18
Bagnell, David (Department: 3672)
Boring or penetrating the earth
With signaling, indicating, testing or measuring
Tool position direction or inclination measuring or...
C033S303000
Reexamination Certificate
active
06736221
ABSTRACT:
BACKGROUND OF INVENTION
1. Field of the Invention
The invention relates generally to wellbore surveys. More particularly, the invention relates to the estimation of wellbore positions based on analytical techniques.
2. Background Art
Fluids, such as oil, gas and water, are commonly recovered from subterranean formations below the earth's surface. Drilling rigs at the surface are often used to bore long, slender wellbores into the earth's crust to the location of the subsurface fluid deposits to establish fluid communication with the surface through the drilled wellbore. The location of subsurface fluid deposits may not be located directly (vertically downward) below the drilling rig surface location. A wellbore that defines a path, which deviates from vertical to some laterally displaced location, is called a directional wellbore. Downhole drilling equipment may be used to directionally steer the wellbore to known or suspected fluid deposits using directional drilling techniques to laterally displace the borehole and create a directional wellbore.
The path of a wellbore, or its “trajectory,” is made up of a series of positions at various points along the wellbore obtained by using known calculation methods. “Position,” as the term is used herein, refers to an orthogonal Cartesian (x, y, z) spatial position, referenced to some vertical and/or horizontal datum (usually the well-head position and elevation reference). The position may also be obtained using inertial measurement techniques, or by using inclination and azimuth with known calculation methods. “Azimuth” may be considered, for present purposes, to be the directional angular heading, relative to a reference direction, such as North, at the position of measurement. “Inclination” may be considered, also for present purposes, to be the angular deviation from vertical of the borehole at the position of measurement.
Directional wellbores are drilled through earth formations along a selected trajectory. Many factors may combine to unpredictably influence the intended trajectory of a wellbore. It is desirable to accurately estimate the wellbore trajectory in order to guide the wellbore to its geological and/or positional objective. This makes it desirable to measure the inclination, azimuth and depth of the wellbore during wellbore operations to estimate whether the selected trajectory is being maintained.
The drilled trajectory of a wellbore is estimated by the use of a wellbore or directional survey. A wellbore survey is made up of a collection or “set” of survey-stations. A survey station is generated by taking measurements used for estimation of the position and/or wellbore orientation at a single position in the wellbore. The act of performing these measurements and generating the survey stations is termed “surveying the wellbore.”
Surveying of wellbores is commonly performed using downhole survey instruments. These instruments typically contain sets of orthogonal accelerometers, magnetometers and/or gyroscopes. These survey instruments are used to measure the direction and magnitude of the local gravitational, magnetic field and/or earth spin rate vectors respectively, herein referred to as “earth's vectors”. These measurements correspond to the instrument position and orientation in the wellbore, with respect to earth vectors. Wellbore position, inclination and/or azimuth may be estimated from the instrument's measurements.
One or more survey stations may be generated using “discrete” or “continuous”measurement modes. Generally, discrete or “static” wellbore surveys are performed by creating survey stations along the wellbore when drilling is stopped or interrupted to add additional joints or stands of drillpipe to the drillstring at the surface. Continuous wellbore surveys relate to thousands of measurements of the earth's vectors and/or angular velocity of a downhole tool obtained for each wellbore segment using the survey instruments. Successive measurements of these vectors during drilling operations may be separated by only fractions of a second or thousandths of a meter and, in light of the relatively slow rate of change of the vectors in drilling a wellbore, these measurements are considered continuous for all practical analyses.
Known survey techniques as used herein encompass the utilization of a variety of means to estimate wellbore position, such as using sensors, magnetometers, accelerometers, gyroscopes, measurements of drill pipe length or wireline depth, Measurement While Drilling (“MWD”) tools, Logging While Drilling (“LWD”) tools, wireline tools, seismic data, and the like.
Surveying of a wellbore is often performed by inserting one or more survey instrument into a bottom-hole-assembly (“BHA”), and moving the BHA into or out of the wellbore. At selected intervals, usually about every 30 to 90 feet (10 to 30 meters), BHA, having the instrument therein, is stopped so that measurement can be made for the generation of a survey station. An additional measurement not performed by the survey instruments is the estimation of the along hole depth (measured depth “MD”) or wellbore distance between discrete survey stations. The MD corresponds to the length of joints or stands of drillpipe added at the surface down to the BHA survey station measurement position. The measurements of inclination and azimuth at each survey station along with the MD are then entered into any one of a number of well-known position calculation models to estimate the position of the survey station to further define the wellbore trajectory up to that survey station.
Existing wellbore survey computation techniques use various models, including the Tangential method, Balanced Tangential method, Average Angle method, Mercury method, Differential Equation method, cylindrical Radius of Curvature method and the Minimum Radius of Curvature method, to model the trajectory of the wellbore segments between survey stations.
Directional surveys may also be performed using wireline tools. Wireline tools are provided with one or more survey probes suspended by a cable and raised and lowered into and out of a wellbore. In such a system, the survey stations are generated in any of the previously mentions surveying modes to create the survey. Often wireline tools are used to survey wellbores after a drilling tool has drilled a wellbore and an MWD and/or LWD survey has been previously performed.
Uncertainty in the survey results from measurement uncertainty, as well as environmental factors. Measurement uncertainty may exist in any of the known survey techniques. For example, magnetic measuring techniques suffer from the inherent uncertainty in global magnetic models used to estimate declination at a specific site. Similarly, gravitational measuring techniques suffer from movement of the downhole tool and uncertainties in the accelerometers. Gyroscopic measuring techniques, for example, suffer from drift uncertainty. Depth measurements are also prone to uncertainties including mechanical stretch from gravitational forces and thermal expansion, for example.
Various considerations have brought about an ever-increasing need for more precise wellbore surveying techniques. More accurate survey information is necessary to ensure the avoidance of well collisions and the successful penetration of geological targets.
Surveying techniques have been utilized to estimate the wellbore position. For example, techniques have also been developed to estimate the position of wellbore instruments downhole. U.S. Pat. No. 6,026,914 to Adams et al. relates to a wellbore profiling system utilizing multiple pressure sensors to establish the elevation along the wellbore path. U.S. Pat. No. 4,454,756 to Sharp et al. relates to an inertial wellbore survey system, which utilizes multiple accelerometers, and gyros to serially send signals uphole. U.S. Pat. No. 6,302,204 B1 to Reimers et al. relates to a method of conducting subsurface seismic surveys from one or more wellbores from a plurality of downhole sensors. U.S. Pat. No. 5,646,611 to Dailey et al. rel
Aklestad Darren Lee
Chia Christopher R.
Phillips Wayne J.
Bagnell David
Jeffery Brigitte L.
Ryberg John
Salazar J.L. Jennie
Schlumberger Technology Corporation
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