Geometrical instruments – Indicator of direction of force traversing natural media – Borehole direction or inclination
Reexamination Certificate
2002-05-07
2003-10-14
Gutierrez, Diego (Department: 2859)
Geometrical instruments
Indicator of direction of force traversing natural media
Borehole direction or inclination
C033S304000, C033S324000, C073S152540
Reexamination Certificate
active
06631563
ABSTRACT:
BACKGROUND OF THE DISCLOSURE
1. Field of the Invention
The present disclosure is directed to a wellbore survey method and apparatus, and more particularly to a survey system which enables mapping of the well borehole path while moving a survey instrument along the well borehole during drilling
2. Background of the Art
Well borehole survey can be defined as the mapping of the path of a borehole with respect to a set of fixed, known coordinates A survey is required during the drilling of many oil and gas wells, and is of particular importance in the drilling of well which is deviated significantly from an axis perpendicular to the earth surface. Often two or three surveys will be required during the drilling process. In addition, a final survey is often required in a highly deviated well.
In drilling an oil well, it is rather easy to drill straight into the earth in a direction which is more or less vertical with respect to the surface of the earth. Indeed, regulatory agencies define a vertical well by tolerating a few degrees of deviation from the vertical. The interruption of the drilling operation and cost of the surveys is minimal in that situation. By contrast, highly deviated wells are required in a number of circumstances.
Onshore, it is necessary to drill a deviated well to enter formations at selected locations and angles. This may occur because of the faulting in the region. It is also necessary to do this around certain types of salt dome structures. As a further example of onshore, deviated drilling, a tremendous amount of interest has been developed in providing surveys of wells that have been deviated from a vertical portion toward the horizontal. Recently, a number of older wells drilled into the Austin chalk formation in the south central United States have played out and production has been lost. This has been a result of the loss of formation pressure. The Austin chalk producing strata is easily located and easily defined. It is however relatively thin. Enhanced production from the Austin chalk has been obtained by reentering old wells, milling a window in the casing, and reentry into the formation. The formation is typically reentered by directing the deviated well so that it is caught within the producing strata. In instances where the strata is perfectly horizontal with respect to the earth, that would require horizontal hole portion after curving into the strata. As a practical matter, the producing formations may also dip and so the last leg of the well may extend outwardly at some extreme angle such as 40 to 70°. Without being definitive as to the particular formation dip, such drilling is generally labeled horizontal drilling. The end result is that the borehole does not simply penetrate the formation, but is directed or guided follow the formation so that several hundred feet of perforations can then be placed to enable better production. To consider a single example, assume that the formation is 20′ thick measured from the top to the bottom face. Assume as an example that the formation has a dip of 30°. By proper direction of the well during drilling, several hundred feet of hole can be drilled between the top and bottom faces of the formation. After drilling, but before casing has been completed, it is often necessary to conduct a concluding survey to assure that the production is obtained below the leasehold property. In addition, other surveys are required.
In offshore production, once a producing formation has been located, it is typically produced from a centrally positioned platform. Assume that the producing formation has an extent of four or five miles in lateral directions. Assume further that the formation is located at 5,000 feet or deeper. A single production platform is typically installed at a central location above the formation and supported on the ocean bottom. A production platform supports a drilling rig which is moved from place to place on the platform so that a number of wells are drilled. It is not uncommon to drill as many as 32 or more wells from a single production platform. From the inception, all the wells are parallel and extend downwardly with parallel portions, at least to a certain depth. Then, they are deviated at some angle. At the outer end of the deviated portion, vertical drilling may again be resumed. While a few of the wells will be more or less vertically drilled, many of the wells will be drilled with three portions, a shallow vertical portion, an angled portion, and a termination portion in the formation which is more or less vertically positioned. Again as before, one or two surveys are required during drilling, and a completion survey is typically required to be able to identify clearly the location of the well in the formation. Field development requires knowledge of the formation itself and also requires knowledge of the termination points of the wells into the formation. This means accurate and precise surveys are used to direct the wells in an optimum fashion to selected locations to get proper production from the formation.
The use of magnetic survey instrumentation is widely applied, but this technology has its limitations. For example, locally, magnetic survey instrumentation accuracy can be limited, since the earth's magnetic field strength and dip angles change, causing erroneous magnetic survey readings. Furthermore, magnetic survey accuracy can also be distorted due to non magnetic drill collars or so called “hot-spots”. In addition, the magnetic survey accuracy can also be negatively affected by the presence of adjacent wells, from which the steel casing may severely influence the earth's magnetic field thereby generating erroneous magnetic readings within the well being surveyed. Other issues which affect the magnetic survey accuracy are the platform mass from which the survey is being conducted, geomagnetic interferences, and changes in the earth's magnetic field from one location to another location. Of course, these changes can be accurately measured, but in practice it is not a routine procedure and it further requires well trained field engineers and sophisticated instrumentation. Magnetic survey technology is also not applicable for use in wellbore which have been cased with steel casing.
The mapping apparatus, containing a rate gyroscope and accelerometers, remotely measures the earth's spin axis, and is lowered into the wellbore, while the system is held stationary at predetermined locations. In addition, the apparatus applies a rotary drive mechanism, functionally connected with the gyroscope and the accelerometers to rotate the gyroscope about its instrument or housing axis. Furthermore, the mapping apparatus contains a downhole power supply and data section for processing the sensor outputs to determine the heading direction of the wellbore at predetermined wellbore depths. This invention also discloses a method to measure azimuth very accurately regardless the wellbore deviation angle and latitude, while traversing continuously through a wellbore. A major advantage over U.S. Pat. No. 4,611,405 is the absence of a feed back controlled mechanism, i.e. the absence of a resolver means which is connected with a drive mechanism. In addition, the absence of a costly, power consuming feed back controlled mechanism reduces, significantly, development, operation and maintenance costs.
Survey instruments introduced in the 1980's featured rate gyroscopes and inclinometers in various configurations have been used for a number of years. A representative survey system of that sort is shown in U.S. Pat. No. 4,468,863 and also in U.S. Pat. No. 4,611,405. These instruments do not utilize a measure of the earth's magnetic filed, and can therefore be used in cased boreholes, and further overcome other previously discussed shortcomings of magnetic surveys. In these systems, a gyroscope is mounted with an axis of rotation coincident with the tool body or housing. The housing is an elongate cylindrical structure. Accordingly, the long housing is coincident with the axis
Brosnahan James
Neubauer Greg
Uttecht Gary
Wright Eric
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