1. A method of determining a casing point in an uncased interval of a well being drilled using a drilling mud, the method comprising:
a) drilling an uncased interval of a well with a drilling mud using a drill bit and drill string at known dip and azimuth angles toward a region of interest in a known subterranean formation without the bit entering the region; and
b) using formation resistivity markers obtained from resistivity measurements obtained while drilling one or more offset wells to identify one or more casing points in the uncased interval of the well while the drill bit advances toward but does not penetrate the region of interest while drilling the well.
2. The method of claim 1 comprising gathering the resistivity markers in the offset wells prior to or simultaneously with the drilling of the uncased interval of the well.
3. The method of claim 2 wherein the resistivity markers are obtained simultaneously with drilling the uncased interval of the well, and the offset well or wells are being drilled simultaneously with the uncased interval of the well.
4. The method of claim 1 further comprising casing the uncased interval of the well based on the identified casing point or points.
5. The method of claim 3 further comprising measuring resistivity in front of the drill bit and using resistivity in front of the drill bit in the uncased interval of the well in conjunction with the resistivity markers from the offset well or wells to determine the casing point in the uncased interval of the well.
6. The method of claim 1 wherein the mud is selected from oil-based muds, water-based muds, and synthetic-based muds.
7. The method of claim 1 wherein the resistivity measurements from one or more offset wells is obtained prior to drilling the uncased interval of the well.
8. The method of claim 1 further comprising adjusting the density, specific gravity, weight, viscosity, water content, oil content, composition, pH, flow rate, solids content, solids particle size distribution, resistivity, conductivity, or any combination of any of these, of the drilling mud based on the resistivity measured in the offset well.
9. The method of claim 1 wherein the gathering of resistivity measurements comprises a method selected from contact resistivity measurement focused in front of the bit, use of a transient electromagnetic survey, continuous deep directional electromagnetic measurements, and use of guided electromagnetic waves along the drill pipe.
10. A method of determining a casing point in an uncased interval of a well during drilling of the well using a drilling mud, the method comprising:
a) drilling an uncased interval of a well with a drilling mud using a drill bit, a drill string, and a resistivity apparatus at known dip and azimuth angles toward a region of interest in a known formation without the bit entering the region;
b) measuring resistivity in front of the drill bit in the uncased interval of the well using the resistivity apparatus;
c) using formation resistivity markers obtained from resistivity measurements obtained while drilling one or more offset wells in conjunction with the resistivity measured in front of the drill bit in the uncased interval of the well to identify one or more casing points in the uncased interval of the well while the drill bit advances toward but does not penetrate the region of interest while drilling the uncased interval of the well.
11. The method of claim 10 further comprising comparing resistivity in front the of the drill bit in the uncased interval of the well to the resistivity markers obtained during drilling of the offset well.
12. The method of claim 10 comprising gathering the resistivity markers in the offset wells prior to or simultaneously with the drilling of the uncased interval of the well.
13. The method of claim 10 further comprising wherein the resistivity markers are obtained simultaneously with drilling the uncased interval of the well, and the offset well or wells are being drilled simultaneously with the uncased interval of the well.
14. The method of claim 10 further comprising casing the uncased interval of the well based on the identified casing point or points.
15. The method of claim 10 wherein the gathering of resistivity measurements data ahead of the bit comprises a method selected from contact resistivity measurement focused in front to the bit, use of a transient electromagnetic survey, continuous deep directional electromagnetic measurements, and use of guided electromagnetic waves along the drill pipe.
16. A method of using resistivity measurements obtained while drilling one or more subterranean offset wells in drilling a subterranean uncased interval of a well using a drilling mud, the method comprising:
a) drilling one or more offset wells;
b) obtaining formation resistivity markers from resistivity measurements obtained while drilling at least one of the offset wells;
c) drilling an uncased interval of a well with a drilling mud using a drill bit and drill string at known dip and azimuth angles toward a region of interest in the formation without the bit entering the region of interest; and
d) using the formation resistivity markers obtained from step (b) to identify one or more casing points in the uncased interval of the well while the drill bit advances toward but does not penetrate the formation while drilling the uncased interval of the well.
17. The method of claim 16 further comprising casing the uncased interval of the well based on the identified casing point or points.
18. The method of claim 17 further comprising measuring resistivity in front of the drill bit in the uncased interval of the well and comparing resistivity in front the of the drill bit in the uncased interval of the well to the resistivity markers obtained during drilling of the offset well.
19. The method of claim 18 wherein the gathering of resistivity data ahead of the bit in the uncased interval of the well comprises a method selected from contact resistivity measurement focused in front to the bit, use of a transient electromagnetic survey, continuous deep directional electromagnetic measurements, and use of guided electromagnetic waves along the drill pipe.
20. The method of claim 16 further comprising adjusting the density, specific gravity, weight, viscosity, water content, oil content, composition, pH, flow rate, solids content, solids particle size distribution, resistivity, conductivity, or any combination of any of these, of the drilling mud used in drilling the uncased interval of the well based on the resistivity measured in the offset well as the drill bit in the uncased interval of the well approaches a depth equal to the depth of the offset wells when the resistivity measurements were taken in the offset wells.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A Current transformer for a compensating current sensor having a primary conductor (1), a secondary winding (2), and a soft-magnetic core (4),
in which the secondary winding (2) does not completely wind around the core (4),
in which the primary conductor (1) and the secondary winding (2) are electrically insulated from one another and are magnetically intercoupled via the core (4), and
in which the primary conductor (1) is provided for injecting a current to be detected and the secondary winding (2) is provided to detect a compensating current,
characterized by
an additional conductor (3), which is electrically connected in parallel to the primary conductor (1) and is arranged in the area of the core (4), at which a flux rise occurs, with the flux rise being at least partially compensated for by the flux, which is caused by the current flowing in the additional conductor (3).
2. The current transformer according to claim 1, characterized in that the additional conductor (3) is arranged beside the core (4) in such a way that only certain areas of the core (4) are detected by its magnetic flow.
3. The current transformer according to one of the previous claims, characterized in that at least a second additional conductor (16, 17) is provided, which is electrically connected in parallel to the other two (1, 3) and is arranged beside the core (4) in such a way that only certain areas of the core (4) are detected by their magnetic flow.
4. The current transformer according to one of the previous claims, characterized in that the primary conductor (1) and the additional conductor(s) (3, 16, 17) conduct currents of different strengths, with the sum of the currents giving rise to the current to be detected.
5. The current transformer according to one of the previous claims, characterized in that the primary conductor (1) and the additional conductor(s) (3, 16, 17) exhibit number of turns that are less than one.
6. The current transformer according to claim 5, characterized in that the primary conductor (1) and the additional conductor(s) (3, 16, 17) are formed by an essentially rectilinear conductor in the area of the core (4).
7. The current transformer according to claim 5, characterized in that the primary conductor (1) and the additional conductor(s) (3, 16, 17) are formed by an essentially U-shaped conductor in the area of the core (4).
8. The current transformer according to claim 5, characterized in that the primary conductor (1) andor the additional conductor(s) (3, 16, 17) are formed by a one-piece slotted conductor.
9. The current transformer according to one of the previous claims, characterized in that a return conductor (5) is provided, which beside the core (4), is arranged on the side of the core (4) opposite the additional conductors (3, 16, 17) and which is traversed in the opposite direction of the additional conductors (3, 16, 17) by the current to be detected.
10. The current transformer according to one of the previous claims, characterized in that the primary conductor (1), the additional conductor(s) (3, 16, 17), the secondary winding (2) and the core (4) are surrounded at least partially by a shielding plate (6).