Data processing: measuring – calibrating – or testing – Measurement system in a specific environment – Earth science
Reexamination Certificate
2002-10-30
2004-09-21
McElheny, Donald (Department: 2857)
Data processing: measuring, calibrating, or testing
Measurement system in a specific environment
Earth science
C702S010000
Reexamination Certificate
active
06795774
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to induction well logging. More particularly, the invention relates to a correction method for induction well logging measurements.
2. Background of the Invention
Modern petroleum drilling and production operations demand a great quantity of information relating to parameters and conditions downhole. Such information typically includes characteristics of the earth formations traversed by the wellbore, in addition to data relating to the size and configuration of the borehole itself. The collection of information relating to conditions downhole, which commonly is referred to as “logging,” can be performed by several methods. Oil well logging has been known in the industry for many years as a technique for providing information to a driller regarding the particular earth formation being drilled. In conventional oil well wireline logging, a probe or “sonde” is lowered into the borehole after some or all of the well has been drilled, and is used to determine certain characteristics of the formations traversed by the borehole. The sonde may include one or more sensors to measure parameters downhole and typically is constructed as a hermetically sealed cylinder for housing the sensors, which hangs at the end of a long cable or “wireline.” The cable or wireline provides mechanical support to the sonde and also provides an electrical connection between the sensors and associated instrumentation within the sonde, and electrical equipment located at the surface of the well. Normally, the cable supplies operating power to the sonde and is used as an electrical conductor to transmit information signals from the sonde to the surface. In accordance with conventional techniques, various parameters of the earth's formations are measured and correlated with the position of the sonde in the borehole, as the sonde is pulled uphole.
The sensors used in a wireline sonde usually include a source device for transmitting energy into the formation, and one or more receivers for detecting the energy reflected from the formation. Various sensors have been used to determine particular characteristics of the formation, including nuclear sensors, acoustic sensors, and electrical sensors.
For a formation to contain petroleum, and for the formation to permit the petroleum to flow through it, the rock comprising the formation must have certain well-known physical characteristics. One characteristic is that the formation has a certain measurable resistivity (or conductivity), which can be determined by inducing an alternating electromagnetic field into the formation by a transmitter coil arrangement. The electromagnetic field induces alternating electric (or eddy) currents in the formation in paths that are substantially coaxial with the transmitter. These currents in turn create a secondary electromagnetic field in the medium, inducing an alternating voltage at the receiver coil. If the current in the transmitter coil is kept constant, the eddy current intensity is proportional to the conductivity of the formation. Consequently, the conductivity of the formation determines the intensity of the secondary electromagnetic field, and thus, the amplitude of the voltage at the receiver coil.
A number of different induction tools are known in the art. One known induction tool is the “high resolution array induction tool” or HRAI as taught in U.S. Ser. No. 09/460,553, U.S. Pat. No. 6,606,565, filed Dec. 14, 1999, which is hereby incorporated by reference for all purposes. This is an array induction tool, operating with two frequencies and ten subarrays of six characteristic spacings. HRAI raw measurements are processed through skin-effect correction, borehole correction and software focusing to provide logs of six depth of investigation (10″, 20″, 30″, 60″, 90″, and 120″) with three vertical resolutions (1 ft, 2 ft and 4 ft). The use of this tool is not a limitation on the invention, however.
FIG. 1
shows an induction well logging instrument
10
disposed in a wellbore
2
drilled through earth formations. The earth formations are shown generally at
6
,
7
,
8
,
9
,
12
,
13
and
14
. The instrument
10
is typically lowered into the wellbore
2
at one end of an armored electrical cable
22
by means of a winch
28
or similar device known in the art.
The instrument
10
can include a telemetry/signal processing unit
20
(SPU).
The SPU
20
can include a source of alternating current (not shown separately). The alternating current is generally conducted through a transmitter
16
disposed on the instrument
10
. Receivers
18
A-
18
F can be disposed at axially spaced apart locations along the instrument
10
. The SPU
20
can include receiver circuits (not shown separately) connected to the receivers
18
A-
18
F for detecting voltages induced in each of the receivers
18
A-
18
F. The SPU
20
can also impart signals to the cable
22
corresponding to the magnitude of the voltages induced in each of the receivers
18
A-
18
F. It is to be understood that the number of transmitters and receivers, and the relative geometry of the transmitter
16
and the receivers
18
A-
18
F shown in the instrument in
FIG. 1
is not meant to be a limitation on the invention.
As is understood by those skilled in the art, the alternating current passing through the transmitter
16
induces eddy currents in the earth formations
6
,
7
,
8
,
9
,
12
,
13
,
14
. The eddy currents correspond in magnitude both to the electrical conductivity of the earth formations
6
,
7
,
8
,
9
,
12
,
13
,
14
and to the relative position of the particular earth formation with respect to the transmitter
16
. The eddy currents in turn induce voltages in the receivers
18
A-
18
F, the magnitude of which depends on both the eddy current magnitude and the relative position of the earth formation with respect to the individual receiver
18
A-
18
F.
The signals, corresponding to the voltages induced in each receiver
18
A-
18
F, can be transmitted along the cable
22
to surface electronics
24
. The surface electronics
24
can include detectors (not shown separately) for interpreting the signals transmitted from the instrument
10
, and a computer
26
to perform the process according to the present invention on the signals transmitted thereto. It is to be understood that the SPU
20
could also be programmed to perform the process of the present invention.
The voltages induced in each receiver
18
A-
18
F correspond to apparent electrical conductivity of all of the media surrounding the instrument
10
. The media comprise the earth formations
6
,
7
,
8
,
9
,
12
,
13
,
14
and the drilling mud
4
in the wellbore
2
. The degree of correspondence between the voltages induced in a particular receiver, and the electrical conductivity of the particular earth formation axially disposed between the particular receiver and the transmitter
16
, can depend on the relative inclination of the layers of the earth formations, such as formation
12
, and the axis of the instrument
10
.
The eddy currents induced by the transmitter coils tend to flow in circular paths that are coaxial with the transmitter coils. For a vertical borehole traversing horizontal formations, each line of current flow ideally remains in the same formation along its entire flow path, and never crosses a bed boundary. Thus, one simplifying assumption that is made in relating the receiver voltage measurements to the conductivity of the earth formations is that the ground loops are positioned entirely within a portion of the earth formation having substantially circumferentially uniform conductivity. This assumption fails in cases where layers of the earth formations are not perpendicular to, but are inclined with respect to, the axis of the wellbore (and consequently the axis of the instrument). A boundary separat
Conley & Rose, P.C.
Halliburton Energy Service,s Inc.
McElheny Donald
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