Patent Grant
7905281
This invention relates to a method for determining the size of casing or other tubular pipe to be inserted in a borehole. Such methods find application, for example, in the casing and completion of boreholes such as oil and gas wells.
When constructing wells such as oil or gas well, it is common to drill a borehole and then line it using a steel casing. The steel casing is formed by joining a number of tubular casing sections end to end and running them into the borehole. Once the casing is in place, cement is pumped down the casing so as to exit at its lower end and return to the surface and fill the annulus between the outside of the casing and the borehole wall.
During the drilling process, boreholes sometimes take on a “corkscrew” or helical path. This most often occurs in deviated wells, and may be the result of inappropriate bottom hole assembly selection, excessive weight-on-bit, or the need for continuous trajectory corrections. As a result, when the driller tries to run casing into the borehole, problems may be encountered. The profile of the borehole may very close to a perfect circle of diameter greater than that of the casing to be run. If the casing to be run is very flexible, it will be able to follow the turns of the borehole, and all will be well. Realistically, however, casings are relatively stiff. As a result, they are often unable to comply with the borehole trajectory and may, in the limit, not be able to go downhole. In a “corkscrewed” borehole, the borehole may be locally circular, but the centre of this circle when traced along the borehole describes neither a straight line nor a smooth curve (as might be expected in a deviated well), but instead traces a helical path. This can result from the drilling process. In such a situation, a 16″ diameter borehole may be so tortuous that a 13.375″ diameter casing can become stuck due to contact with the borehole wall before it can be fully run into place. The cost of getting stuck in such situations can be very high, running into millions of dollars in extreme situations.
The problem is to determine the maximum diameter of casing that will pass through the borehole without being unduly affected by its tortuosity, irrespective of the local diameter of the borehole.
Previous proposals have been made to determine curvature and deformation of cased or lined boreholes. For example, the CALTRAN™ software product package of C-FER TECHNOLOGIES™ that uses raw caliper-log data from a multi-sensor caliper tool to determine the 3D shape of downhole tubulars. 3D drift diameter accounts for curvature and ovalisation and allows an estimate of what size tool will fit downhole.
This invention seeks to provide a method which is applicable to uncased or unlined (i.e. ‘open’) boreholes and to cased or lined wells.
This invention provides a method for determining the size of tubular pipe to be inserted into an interval of borehole, comprising:
Preferably, the method further comprises defining a point in each window to which the determined maximum pipe diameter is assigned, This will typically be the mid-point of the window. Each window is preferably separated from its neighbours by a predetermined distance, such as one data sample for a typical logging tool.
A particularly preferred way of determining the position of the borehole wall comprises making a series of calliper measurements at different depths in the borehole. In this case, the step of defining a polygon preferably comprises connecting calliper measurement points around the borehole in the window.
Typically, the step of determining the position of the borehole wall is performed using a measurement toot comprising a tool body that is moved through the borehole, the method comprising determining any rotation of the toot body as it is moved through the well and using the determined rotation to correct the determination of the position of the borehole wall. The method can also further comprise determining any lateral displacement of the tool body as it is moved through the borehole, and using the determined lateral displacement to correct the determination of the position of the borehole wall.
Selection of the window length can be made according to the bending stiffness of the pipe.
Selecting the size of the pipe to be less that the minimum maximum pipe diameter determined in any window in the interval is particularly desirable.
The invention has the advantage that it enables a casing size to be selected which minimises contact with the wall of the borehole and so helps reduce sticking problems when running into the boreholes. It can be applied in open or cased holes and used for determining the size of any tubular to be inserted into the borehole, for example casing, completion tubulars, etc.
This invention provides a method for determining a maximum tool diameter that will fit in a borehole that has a tortuous path. For the purposes of this description the borehole is considered as one that has been drilled imperfectly so that, although the local profile of the borehole at each depth is approximately circular, the centre of this “local circle” traces a helical path in space as we move along the borehole 10 (see
At one extreme, a measurement tool for measuring the local borehole profile can be considered as an infinitely short cylindrical logging tool 12a (see
As the tool 12a is moved along the borehole 10, the entire tool body will be displaced laterally as the path of the borehole changes. The lateral movement of the tool 12a can be inferred using an accelerometer (such as are typically provided in such logging tools), and doubly-integrating the acceleration. As this lateral movement describes the helix which is the locus of the centre of the borehole 10, the precise form of the borehole in three-dimensional space, referred to the rock and not the tool axis, may be computed by combining the movement of the tool's axis (as determined from the accelerometer measurements) with the tool's finger measurements (giving the local borehole profile at each measurement station.
At the other extreme, the tool 12b can be considered as infinitely long and very stilt and unable to bend to follow the helical path of the borehole (see
In a real case, the tool length will be neither infinitely long nor infinitely short. In addition, the tool may rotate about its own axis as it moves along the borehole (such motion is common in logging tools). The behaviour to be expected of the lateral acceleration and finger measurements may therefore be expected to fall somewhere between the two extreme theoretical cases described above. However, combination of data from the accelerometer and the tool's finger measurements allows the precise form of the borehole in three-dimensional space to be determined. Relatively simple geometrical calculations may be used to estimate the maximum diameter of rigid pipe that may be run through a given section of the borehole with minimal risk of sticking.
In its simplest form, the methods provided by the invention comprise two steps:
Determination True Location of the Borehole Wall
In the case where lateral displacement of the tool is ignored (the “infinite tool” case of
Computation of the Maximum Pipe Diameter
As the tool moves along the borehole, one can think of the borehole profile at the depth of the fingers as being excentralised, and rotating about the toot axis. This is illustrated in
Implementation of this method comprises taking the minimum displacement from the tool axis at each azimuth over a certain length of borehole interval (the “Filter window”), and from this constructing a two-dimensional polygon. In the case of
The filter window is then advanced along the interval, for example by one measurement station (6 inches/15 cm) and the computation repeated. Repeating this for the whole of the interval of interest allows a log to be constructed of the computed maxima. The casing or tubular to be installed in this section of the well can then be selected to be below the lowest maximum computed for this interval.
The length of the filter window can be chosen to be representative of the bending stiffness of the pipe, casing or tubular, as some conformance to non-linear boreholes is to be expected. Indeed without such bending it would be impossible to run casing in any deviated borehole with a vertical section near surface. A filter length of 120 ft (36 m) has been found to give useful results for intervals of 1000 ft (300 m) in a 16 inch (41 cm) diameter borehole in certain circumstances but this is dependent on conditions and filter lengths between 30 ft (9 m) and 150 ft (45 m) may be appropriate in other cases.
A more detailed implementation of methods according to the invention comprise the further step of computing the lateral displacement of the tool body during its progress along the interval as it makes measurements. This step essentially involves doubly-integrating the transverse acceleration components versus time, assuming that certain boundary conditions (zero transverse velocity and displacement) are, met at time zero. In practice, however, filtering may be required to ensure that the transverse displacement of the tool is constrained to physically plausible values. Kalman filtering techniques may be used, in a manner analogous to those used for speed-correcting data for logging tool measurements.
The step of determining the true location of the borehole wail then comprises performing a vector addition of the tool-axis-displacements computed as indicated in the previous section, and the vector that each finger measurement represents.
The computation of the maximum pipe diameter is then performed in the manner described above.
The methods can be varied within the scope of the invention. For examples the measurement of borehole profile can be made up of measurements from a number of different tools or techniques. Other changes will be apparent.
While the invention has been described above in relation to a helical, open (uncased) borehole, it can be applied to any form of borehole. For example, the path may not be helical, but may deviate unpredictably along the length of interest. Also, the borehole may be cased and the tubular can be any long tubular that needs to be inserted into the well, e.g. completion tubulars, screens etc. In cased boreholes, it is the position of the innermost casing surface that is measured to find the position of the borehole wall.
| Number | Date | Country | Kind |
|---|---|---|---|
| 06126866 | Dec 2006 | EP | regional |
| Number | Name | Date | Kind |
|---|---|---|---|
| 2595241 | Goble | May 1952 | A |
| 3364464 | Dellinger | Jan 1968 | A |
| 3961683 | Delignieres | Jun 1976 | A |
| 6044326 | Huiszoon | Mar 2000 | A |
| 6078867 | Plumb et al. | Jun 2000 | A |
| Number | Date | Country | |
|---|---|---|---|
| 20080149331 A1 | Jun 2008 | US |
