Method and apparatus for directional well logging

Patent metadata

Field	Value
Publication number	US-9360580-B2
Application number	US-200913128261-A
Country	US
Kind code	B2
Filing date	Nov 23, 2009
Priority date	Dec 10, 2008
Publication date	Jun 7, 2016
Grant date	Jun 7, 2016

Abstract

A method and apparatus are provided for making directional measurements toward a formation of different resistivity that is proximate to the borehole, but which is not penetrated by the borehole. The methods and apparatus include the use of at least one insulated gap and at least one magnetometer positioned within a non-magnetic housing that is disposed within a non-magnetic tubular. An electric current is applied across the insulated gap, which results in current leaking into the surrounding formations. When a formation of contrasting resistivity is proximate to the logging apparatus, the magnetometer detects a secondary magnetic field due to the contrasting formation. The direction of the secondary magnetic field can be used to determine the direction to the contrasting formation. The magnitude of the secondary magnetic field can be used to determine the distance position to the contrasting formation.

First claim

What is claimed is:

1. A method of electromagnetic resistivity measurement to determine distance and direction to a boundary within a formation, comprising:
deploying a conductive tubular in a wellbore in a first formation having a first resistivity, the conductive tubular having a drill bit that axially extends the wellbore, a gap, and a magnetometer configured to receive a magnetic signal from an adjacent formation having a contrasting resistivity;
while axially extending the wellbore in the first formation, generating a current along the conductive tubular and across the gap wherein the current induces a primary magnetic field arising from the current in the tubular, the current leaking into the first formation and induces a secondary magnetic field;
measuring a direction of the secondary magnetic field;
determining a direction of the adjacent formation from the direction of the secondary magnetic field;
measuring a magnitude of the secondary magnetic field; and
determining a distance to the adjacent formation wherein the wellbore does not pass based on a non-zero magnitude of the measured secondary magnetic field and is steered away from the adjacent formation.

2. The method according to claim 1 , further comprising steering additional axial extension of the wellbore with the drill bit based on the distance to the adjacent formation.

3. The method according to claim 1 , wherein the conductive tubular comprises one of a drill collar, a bottomhole assembly, a wireline sonde, and a coiled tubing conveyance apparatus.

4. The method according to claim 1 , further comprising measuring a phase of the current generated on the conductive tubular.

5. The method according to claim 4 , further comprising determining whether the formation boundary is uphole or downhole based on the phase of the current on the conductive tubular.

6. The method according to claim 1 , further comprising measuring the amplitude of the generated current on the conductive tubular.

7. The method according to claim 6 , further comprising inputting an estimate for a resistivity contrast C and performing an inversion computation to solve for the distance according to an equation of the form:

d
=

1
β

⁢
ln
⁢

{

α

B
->

1

⁢

(

C
-
1

C
+
1

)

}

.

where d is the distance from a BHA to the adjacent formation, α and β are constants that depend on BHA geometry and {right arrow over (B)} 1 is a measured value of the secondary magnetic field.

8. A drilling system, comprising:
a conductive tubular in a wellbore in a first formation having a first resistivity, the conductive tubular comprising:
a drill bit that axially extends the wellbore,
an electric current driving tool having an gap that generates a current along the conductive tubular and across the gap, wherein the current generates a primary magnetic field and leaks into the first formation generating a secondary magnetic field, and
a magnetometer configured to receive magnetic signal of an adjacent formation of contrasting resistivity, wherein the magnetometer is shielded from the primary magnetic field and measures a direction and a magnitude of the secondary magnetic field to determine a direction and a distance from the adjacent formation;

the drilling system further comprising:
a MWD tool transmits the measurements to the surface;
a surface control computer system that determines the presence of the adjacent formation through which the wellbore does not pass based on a non-zero magnitude of the measured secondary magnetic field; and
a steerable system that receives a driller command based on the determined presence of the adjacent formation through which the wellbore does not pass and steers the drill bit in a given trajectory in the formation based on the driller command.

Assignees

• Goswami Jaideva
• Clark Brian
• Rong Betty
• Pabon Miguel F
• Morley Jan S
• Schlumberger Technology Corp

Inventors

• Goswami Jaideva
• Clark Brian
• Rong Betty
• Pabon Miguel F
• Morley Jan S

Classifications

• G01V3/26 Primary

  operating with magnetic or electric fields produced or modified either by the surrounding earth formation or by the detecting device (with electromagnetic waves G01V3/30) · CPC title

• E21B49/00

  Testing the nature of borehole walls; Formation testing; Methods or apparatus for obtaining samples of soil or well fluids, specially adapted to earth drilling or wells · CPC title

• E21B47/026

  of penetrated ground layers · CPC title

• E21B47/0228

  using electromagnetic energy or detectors therefor · CPC title

• E21B47/02216

  Fixed Constructions · mapped topic