Boring or penetrating the earth – Processes
Reexamination Certificate
2000-09-29
2002-09-03
Dang, Hoang (Department: 3671)
Boring or penetrating the earth
Processes
C166S381000, C175S040000, C702S009000
Reexamination Certificate
active
06443242
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
2. Description of Related Art
Three basic methods for moving items used in subterranean wells, known as conveyance methods (CM) are:
Jointed Pipe (JP)—sections of pipe are screwed together at “joints” to form a “string” of pipe. JP includes drill pipe, production tubing and casing. Drill pipe and drill collars are used to form drill strings.
Coiled Tubing (CT)—continuous tubing or pipe which is coiled onto a reel at the surface, and spooled on and off the reel when being run in and out of a well.
Wireline (WL)—cable. There are several types of WL, including electric cable, braided cable, and “slick-line”.
Computer based models have been developed to calculate many quantities such as the forces, stresses, torques, stretch, etc. associated with these conveyance methods as the pipe, tubing or wireline are run into and out of subterranean wells. U.S. Pat. No. 5,044,198 gives a detailed description of one such model used for drilling. The known prior art, Orpheus software (commercially available from the owner of this invention) models all of these CM. Mathematical models or CMM's (conveyance method models) refer to computer models for the various conveyance methods.
These known CMM's take many parameters into consideration when performing calculations. The parameters may vary between the various CM. For example, JP and CT are pipes, so they may have internal pressure and fluid flow. WL has no internal flow path and thus does not have internal pressure and fluid flow. The following is a list of some of the parameters the CMM's take into consideration:
Well properties—hole geometry, temperature and diameter versus the hole depth
Friction—dynamic and static friction coefficients throughout the well
Pressures—pressures inside and outside along the length of the well
Fluid properties—viscosity, density and flow rates of the fluids inside and outside of systems used in the CM
Material properties—strength and elastic modulus of the material the systems used in the CM are made of
Dimensions of CM systems—inside and outside diameters along the length
Applied torques and forces—torque and/or force applied at the downhole end of the CM system, and/or applied at the surface
Tool properties—length, outside diameter, stiffness, internal diameter, flow restrictions in the tools being conveyed by the CM system, if any
Speeds—axial speed and rate of rotation (RPM).
These known CMM's are then used to determine many things such as:
When the CM system is approaching some limit at which it will break or buckle;
How much the CM system will stretch or shrink due to axial forces, helical buckling, temperature and pressure. This change in length is often needed to accurately calculate the depth of the end of the CM system or the location of the tools it is conveying;
How much force can the CM system apply at the downhole end of the tools, either in tension (as in pulling on a plug) or in compression (as in applying weight on bit (WOB)) while drilling;
How much torque is being applied at the downhole end when a certain amount of torque is applied at surface;
How much twist is in the CM system between the surface and the downhole end;
The torsional and axial dynamic frequencies for stick-slip type movements; and
The point at which the CM system is stuck in a well.
It is often desirable to run these CMM models in “real-time”. Measured parameters such as the force at surface (often called “hook load” for JP drilling or “weight” for CT and WL applications) and other parameters measured in real-time are input to the CMM, and it calculates the desired values such as a depth correction, WOB, etc. also in real-time. These calculated values are then displayed to those operating the system along with the measured parameters. Usually the display of updated values occur in less than 1 or 2 seconds, to be considered real-time. If dynamic effects are being considered, the real-time calculation must be even faster.
However, the CMM's often require complicated calculations, e.g. numerically solving differential equations repeatedly. Due to the length and complexity of the calculations, the computer may not be able to perform these CMM calculations fast enough to perform real-time updates.
To avoid this problem, highly simplified CMM's have been developed, such as the one in U.S. Pat. No. 6,026,912. Simplified CMM's such as this can be run in real-time, but, are typically accurate for only certain specific cases such as vertical well drilling.
SUMMARY OF THE PRESENT INVENTION
The present invention provides a method for complex CMM calculations to be made available in real-time. According to one aspect of the present invention a CMM includes a computer program that calculates desired output parameters for a range of input parameters ahead of time (e.g. several seconds or minutes ahead of real time, or before the operation begins) based upon the best data available at that time. If the CMM is being run only a short time (seconds or minutes ahead of time), actual current measured data is used. If the CMM is being run before the operation, the data will be estimated or predicted. The relationship between the input and output parameters is then modeled using a relatively simple mathematical model technique such as a curve-fit or data table technique. This simple mathematical model (SMM) technique includes a computer program that is then used in an appropriate computer to determine output parameters in real-time based upon the real-time input parameters.
Curve-fit techniques are known to those skilled in mathematics. There are many types of curve-fits. Given a series of n data points, (x
j
,y
j
), calculated by a CMM, where x is an input parameter and y is a calculated parameter, the equation of a line or curve is developed which passes through or close to these points. One common curve-fit is linear, taking the form of:
y=A+Bx
Where A and B are the curve fit constants. This curve-fit forms a linear SMM which calculates the output parameter y for a given input parameter x. It is much easier to calculate than the complex equations in a CMM.
A parabolic (second order polynomial) curve fit would take the form of:
y=A+Bx+Cx
2
In this case A, B and C are the curve fit constants.
A hyperbolic curve-fit may be written in the form:
y=A+B
/(
x−C
)
There are many other types of curve-fits known to those skilled in mathematics including logarithmic, exponential, moving average, etc. Curve-fit techniques are known which allow multiple input parameters to be considered. Any suitable type of curve-fit may be used to create the SMM. The curve-fit constants may or may not have any physical significance (“physical significance” means a constant is related to an actual physical parameter, e.g., but not limited to the buoyant weight of the WL in pounds per foot or density of drilling fluid in pounds per gallon).
With any curve-fit technique, there may be some error. In such a case an SMM will not produce exactly the same calculated result as a CMM. The type of curve-fit used in any specific application is chosen carefully to minimize this error. The curve-fit may, in certain aspects, be chosen at the time the SMM software is developed based upon an understanding of the usual shape of the curve, and thus the type of curve-fit which will most likely work well. Alternatively, multiple curve-fits are developed. For each curve-fit an error is calculated based upon the input data points. The curve-fit with the smallest error is then used for the SMM. Alternatively, multiple curve-fits are made available, and the operator chooses the curve-fit to be used in the SMM.
Alternatively, the n data points calculated by a CMM are placed in a data table available to the real-time software. The real-time software uses the data table and interpolates or extrapolates to obtain a desired value. In this case, the SMM is simply the equations used to interpolate or extrapolate. Interpolation and extrapolation are known to those
McSpadden Albert Rice
Newman Kenneth Ray
CTES L.C.
Dang Hoang
McClung Guy
LandOfFree
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