Mud pulse telemetry

Details Mud pulse telemetry Mud pulse telemetry

1999-10-08

2002-07-16

Edwards, Jr., Timothy (Department: 2635)

Communications, electrical: acoustic wave systems and devices

Wellbore telemetering

Through well fluids

C340S853200, C340S855400

Reexamination Certificate

active

06421298

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 relates generally to measurement while drilling and logging while drilling technologies. More specifically, the invention relates to detecting telemetry from downhole sensors in a drilling operation by analyzing interaction patterns between pressure pulses. Drilling engineers have ordinary skill in this art.
2. Description of the Related Art
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 commonly is referred to as “logging.” Logging has been known in the industry for many years as a technique for providing information regarding the particular earth formation being drilled and can be performed by several methods. In conventional oil well wireline logging, a probe 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.
Wireline logging is useful in assimilating information relating to formations downhole but it has certain disadvantages. For example, before the wireline logging tool can be run in the wellbore, the drillstring and bottomhole assembly must first be removed, or tripped, from the borehole, resulting in considerable cost and loss of drilling time for the driller (who typically is paying daily fees for the rental of drilling equipment). In addition, because wireline tools are unable to collect data during the actual drilling operation, drillers possibly must make decisions (such as the direction to drill, etc.) without sufficient information, or else incur the cost of tripping the drillstring to run a logging tool to gather more information relating to conditions downhole. In addition, because wireline logging occurs a relatively long period after the wellbore is drilled, the accuracy of the wireline measurement can be questionable. As one skilled in the art will understand, wellbore conditions tend to degrade as drilling fluids invade the formation in the vicinity of the wellbore. Additionally, the borehole shape may begin to degrade, reducing the accuracy of the measurements.
Because of the limitations associated with wireline logging, there recently has been an increasing emphasis on the collection of data during the drilling process itself. By collecting and processing data during the drilling process, without the necessity of tripping the drilling assembly to insert a wireline logging tool, the driller can make accurate modifications or corrections “real-time”, as necessary, to optimize drilling performance. For example, the driller may change the weight-on-bit to cause the bottomhole assembly to tend to drill in a particular direction. Moreover, the measurement of formation parameters during drilling, and hopefully before invasion of the formation by the drilling fluid, increases the usefulness of the measured data. Further, making formation and borehole measurements during drilling can save the additional rig time which otherwise would be required to run a wireline logging tool.
Techniques for measuring conditions downhole, and the movement and location of the drilling assembly contemporaneously with the drilling of the well, have come to be known as “measurement-while-drilling” techniques, or “MWD.” Similar techniques, concentrating more on the measurement of formation parameters of the type associated with wireline tools, commonly have been referred to as “logging while drilling” techniques, or “LWD.” While distinctions between MWD and LWD may exist, the terms MWD and LWD are often used interchangeably. For the purposes of this disclosure, the term LWD will be used with the understanding that the term encompasses both the collection of formation parameters and the collection of information relating to the position of the drilling assembly while the bottomhole assembly is in the well. The measurement of formation properties during drilling of the well by LWD systems improves the timeliness of measurement data and, consequently, increases the efficiency of drilling operations. Typically, LWD measurements are used to provide information regarding the particular formation in which the borehole is traversing.
Referring to
FIG. 1
, there is illustrated an MWD system. A well bore or borehole
54
contains a drillstring or drill pipe
36
which includes a hollow center region, and defines an annulus
44
(the region between the outside of the drill string and periphery of the borehole). Also shown are stand pipe
34
, drill bit
42
, and transmitter
40
. Stand pipe
34
connects above the earth's surface (or rig floor)
58
to desurger
26
, pressure transducer
60
, signal processor
62
(through a transmission line
50
), mud pump
24
and drillstring
36
. Drill bit
42
attaches to drillstring
36
at the lower end of the drillstring. Transmitter
40
, part of a bottomhole assembly (not shown in its entirety), is located near the bottom of the drillstring, proximate to drill bit
42
.
Typically, a pit at the surface of the earth (not shown) contains drilling fluid or mud. Mud pump
24
forces the drilling fluid into the drillstring, where it flows in a downstream direction as indicated by arrow T. Eventually, it exits the drillstring via ports in the drill bit
42
and circulates upward via annulus
44
. The drilling fluid thereby lubricates the bit and carries formation cuttings to the surface of the earth. The drilling fluid is returned to the pit for recirculation.
Transmitter or pulser
40
generates an information signal representative of measured downhole parameters. This information signal typically is a pressure pulse signal that travels along the mud column at the speed of sound. Pulsers are known and typically transmit at low data transmission rates around 1 bps. Other devices are known which are capable of creating the mud pressure pulses. For instance, a mud siren, which typically creates acoustic waves within the drilling fluid in a frequency range of 12 to 24 Hertz, could be modified to generate the drilling fluid pressure pulses this invention is designed to detect. Pressure transducer
60
receives the mud pressure pulse at an upstream location, such as at the surface of the earth and converts the pressure signals to electronic signals. Transducer
60
outputs the received waveform across communication path
50
to signal processor
62
which operates to process and decode the received signals.
In an ideal system, each and every mud pressure pulse created downhole would propagate upstream and be easily detected by a pressure transducer at the surface of the earth. However, drilling mud pressure fluctuates significantly and contains noise because of several drilling parameters. The primary sources of noise in the pressure signal comprise: (1) the mud pump; (2) torque noise; and (3) bit noise. Bit noise is created by vibration of the drill bit during the drilling operation. As the bit moves and vibrates, bit jets where the drilling fluid exhausts can be partially or momentarily restricted, creating a high frequency noise in the pressure signal. Torque noise is generated downhole by the action of the drill bit sticking in a formation, causing the drillstring to torque up. The subsequent release of the drill bit relieves the torque on the drilling string and generates a low frequency, high amplitude pressure surge. Finally, the mud pumps themselves create cyclic noise as the pistons within the mud pump force the drilling mud into the drillstring.
Most drilling systems contain a dampener or desurger
26
. The desurger is fluidly connected to the high pressure drilling mud on a drilling mud

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