Determination of true formation resistivity

Patent metadata

Field	Value
Publication number	US-10295697-B2
Application number	US-201314650748-A
Country	US
Kind code	B2
Filing date	Jan 30, 2013
Priority date	Jan 30, 2013
Publication date	May 21, 2019
Grant date	May 21, 2019

Abstract

Various embodiments include apparatus and methods to determine true formation resistivity. Such apparatus and methods may use techniques to effectively reduce or eliminate polarization horn effects at boundaries between formations of different resistivity. The techniques may use combinations of geosignals and adjustments of measurement data to evaluate true formation resistivity for formation layers investigated. Such techniques and associated analysis may be conducted real time. Additional apparatus, systems, and methods are disclosed.

First claim

What is claimed is:

1. A method for reducing a horn effect to more accurately determine a true formation resistivity using an electromagnetic tool, the method comprising:
lowering the electromagnetic tool into a wellbore, wherein the electromagnetic tool comprises
a transmitter attached to the electromagnetic tool, wherein the transmitter comprises a transmitter antenna,
a first receiver attached to the electromagnetic tool, wherein the first receiver comprises a receiver antenna at a first tilt angle with respect to a longitudinal axis of the electromagnetic tool, and wherein the first receiver and the transmitter are axially separated;

generating a signal with the transmitter;
measuring voltage values from the first receiver based on a measurement by the first receiver of the signal, wherein measuring voltage values comprises making measurements during a rotation of the electromagnetic tool, the rotation of the electromagnetic tool partitioned into a number of bins, in which completion of the number of bins is one complete rotation of the electromagnetic tool, wherein the number of bins is greater than one;
determining virtual voltage values at a second tilt angle based on the voltage values, the number of bins, a first ratio, and a second ratio, wherein the first ratio is based on the first tilt angle and the second tilt angle, and wherein the second ratio is based on the number of bins and a difference between the first tilt angle and the second tilt angle; and
determining an estimate of the true formation resistivity based on the virtual measurement voltage values.

2. The method of claim 1 , wherein determining virtual voltage values at the second tilt angle comprises determining V R ind T ind ′(i) according to

V

R
ind

T
ind

′

⁡

(
i
)

=

V

R
ind

T
ind

⁡

(
i
)

×

sin
⁢

⁢

θ

r
⁢

⁢
2

sin
⁢

⁢

θ

r
⁢

⁢
1

+

2
N

⁢

∑

i
=
1

N

⁢

V

R
ind

T
ind

⁡

(
i
)

×

sin
⁡

(

θ

r
⁢

⁢
1

-

θ

r
⁢

⁢
2

)

sin
⁡

(

2
⁢

⁢

θ

r
⁢

⁢
1

)

,

⁢

i
=
1

,
2
,
…
⁢

Assignees

• Halliburton Energy Services Inc

Inventors

• Wu Hsu-Hsiang
• Bittar Michael S

Classifications

• G01V3/34

  Transmitting data to recording or processing apparatus; Recording data · CPC title

• G01V3/30 Primary

  operating with electromagnetic waves · CPC title

• G01V8/20

  using multiple transmitters or receivers · CPC title

• G01V3/36

  Recording data (G01V3/34 takes precedence) · CPC title

• G01V8/12

  using one transmitter and one receiver · CPC title