Communications: electrical – Wellbore telemetering or control – Diagnostic monitoring or detecting operation of...
Reexamination Certificate
2001-11-13
2004-05-25
Wong, Albert K. (Department: 2635)
Communications: electrical
Wellbore telemetering or control
Diagnostic monitoring or detecting operation of...
C367S083000, C340S854600, C175S040000, C175S048000, C375S232000, C375S346000, C375S347000, C375S350000
Reexamination Certificate
active
06741185
ABSTRACT:
TECHNICAL FIELD
The invention relates generally to data telemetry methods and apparatus used with measurement-while-drilling (MWD) and logging-while-drilling (LWD) systems. More particularly, the invention relates to a method and apparatus for reducing the effects of harmonically-related tone noise, especially noise from mud pumps, that is intended to improve signal detection in the telemetry used with MWD and LWD systems.
BACKGROUND ART
MWD and LWD systems provide drilling operators greater control over the construction of a well by providing information about conditions at the bottom of a wellbore substantially in real time as the wellbore is being drilled. Certain information is of interest to drilling operators, which is preferably obtained from the bottom of the wellbore substantially in real time. This information includes directional drilling variables such as inclination and direction (azimuth) of the drill bit, and geological formation data, such as natural gamma ray radiation levels and electrical resistivity of the rock formation. Typically, MWD tools or instruments make the directional and other drilling-related measurements, and LWD tools or instruments make the geological formation measurements. Often MWD and LWD tools are integrated into a single instrument package and are called MWD/LWD tools. In the description which follows, the term “MWD system” will be used collectively to refer to MWD, LWD, and combination MWD/LWD tools or instruments. The term MWD system should also be understood to encompass equipment and techniques for data transmission from within the well to the earth's surface.
MWD systems measure parameters (such as the previously mentioned examples) within the wellbore, and can transmit the acquired data to the earth's surface from within the wellbore. There are several different methods for transmitting data to the surface, including “mud pulse” telemetry and electromagnetic telemetry.
In mud-pulse telemetry, data is transmitted from the MWD system in the wellbore to the surface by means of generating pressure waves in the drilling fluid (drilling “mud”) that is pumped through the drill string by pumps on the surface.
FIG. 1
illustrates a drilling system
100
that is equipped for MWD system operation using mud-pulse telemetry. As shown in
FIG. 1
, the drilling system
100
includes a drill string
112
hanging from a derrick
150
. The drill string
112
extends through a rotary table
152
on the rig floor
151
into the wellbore
121
. A drill bit
111
is attached to the end of the drill string
112
. Drilling is accomplished by rotating the drill bit
111
while some of the weight of the drill string
112
is applied to the bit. The drill bit
111
may be rotated by rotating the entire drill sting
112
from the surface using the rotary table
152
which is adapted to drive a kelly
153
, or alternatively by using a top drive (not shown). Alternatively, operating a positive displacement motor known as a “mud motor”
110
disposed in the drill string
112
above the drill bit
111
, drilling can be accomplished without rotating the entire drill string
112
.
While drilling, drilling mud is pumped by mud pumps
115
on the surface through surface piping
117
, standpipe
118
, rotary hose
119
and swivel
154
, kelly
153
and down the drill string
112
. Pulsation dampeners
116
, also known as desurgers or accumulators, are located near the outputs of the mud pumps
115
to smooth pressure transients in the mud discharged from the mud pumps
115
. The mud in the drill string
112
is forced out through jet nozzles (not shown) in the cutting face of the drill bit
111
. The mud is returned to the surface through an annular space (the well annulus
113
) between the well
121
and the drill string
112
. One or more sensors or transducers
101
are located in a measurement module
102
in a bottomhole assembly portion of the drill string
112
to measure selected downhole conditions. For example, the transducer
101
may be a strain gage that measures weight-on bit (axial force applied to the bit
111
) or a thermocouple that measures temperature at the bottom of the well
121
. Additional sensors may be provided as necessary to measure other drilling and formation parameters such as those previously described.
The measurements made by the transducers
101
may be transmitted to the surface through the drilling mud in the drill string
112
. To do this, first, the transducers
101
send signals that are representative of the measured downhole condition to a downhole electronics unit
103
. The signals from the transducers
101
may be digitized in an analog-to-digital converter (not shown separately). The downhole electronics unit
103
then collects the measurements from the transducers
101
and arranges them into a selected telemetry format, usually a digital representation of the measurements made by the transducers
101
. Extra digital bits used for synchronization, and error detection and correction may be added to the telemetry format. The telemetry format is then passed to a modulator
104
, which groups bits into symbols and then uses a process called modulation to impress the symbols onto a baseband or carrier waveform that can be transmitted through the mud in the drill string
112
. A symbol consists of a group of one or more bits. The modulated signals serve as input to an acoustic “transmitter”
105
and valve mechanism
106
that generates a telemetry pressure wave that ultimately carries data to the surface. One or more pressure transducers
130
,
132
located on the standpipe
118
, or surface piping
117
, generate signals that are representative of variations in the pressure of the mud. The outputs
131
,
133
of the pressure transducers
130
,
132
can be digitized in analog-to-digital converters and processed by a signal processing module
134
, which recovers the symbols from the pressure variations and then sends data recovered from the symbols to a computer
135
where the transmitted information can be accessed by the drilling operators.
There are several mud-pulse telemetry systems known in the art. These include positive-pulse, negative-pulse, and continuous-wave. In a positive-pulse system, valve mechanism
106
of the transmitter
105
creates a pressure pulse at higher pressure than that of the drilling mud by momentarily restricting flow in the drill string
112
. In a negative mud-pulse telemetry system, the valve mechanism
106
creates a pressure pulse at lower pressure than that of the mud by venting a small amount of the mud in the drill string
112
through a valve
106
to the well annulus
113
. In both the positive-pulse and negative-pulse systems, the pressure pulses propagate to the surface through the drilling mud in the drill string
112
and are detected by the pressure transducers
130
,
132
. To send a stream of data, a series of pressure pulses are generated in a pattern that is recognizable by the signal processing module
134
.
The pressure pulses generated by positive-pulse and negative-pulse systems are discrete pressure waves. Continuous wave telemetry can be generated with a rotary valve or “mud siren.” In a continuous-wave system, the valve mechanism
106
rotates so as to repeatedly interrupt the flow of the drilling mud in the drill string
112
. This causes a periodic pressure wave to be generated at a rate that is proportional to the rate of interruption. Information is then transmitted by modulating the phase, frequency, or amplitude of the periodic wave in a manner related to the downhole measured data.
The telemetry pressure wave that carries information from the transmitter
105
to the pressure transducers
130
,
132
is subjected to attenuation, reflections, and noise as it moves through the drilling mud. The signal attenuation as it passes through the mud channel may not be constant across the range of component frequencies present in the telemetry pressure wave. Typically, lower frequency components are subject to less attenuation than higher frequency compon
Brady David
Reyes Sandra D.
Shi Pengyu
Tennent Robert
Jeffery Brigitte L.
Ryberg John J.
Salazar Jennie (JL)
Schlumberger Technology Corporation
Wong Albert K.
LandOfFree
Digital signal receiver for measurement while drilling... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Digital signal receiver for measurement while drilling..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Digital signal receiver for measurement while drilling... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3185448