Communications: electrical – Wellbore telemetering or control – Using a specific transmission medium
Reexamination Certificate
2000-09-29
2004-03-30
Edwards, Timothy (Department: 2635)
Communications: electrical
Wellbore telemetering or control
Using a specific transmission medium
C340S855400, C340S856400, C367S084000
Reexamination Certificate
active
06714138
ABSTRACT:
FIELD OF THE INVENTION
The current invention is directed to a method and apparatus for transmitting information from a down hole location in a well to the surface, such as that used in a mud pulse telemetry system employed in a drill string for drilling an oil well.
BACKGROUND OF THE INVENTION
In underground drilling, such as gas, oil or geothermal drilling, a bore is drilled through a formation deep in the earth. Such bores are formed by connecting a drill bit to sections of long pipe, referred to as a “drill pipe,” so as to form an assembly commonly referred to as a “drill string” that extends from the surface to the bottom of the bore. The drill bit is rotated so that it advances into the earth, thereby forming the bore. In rotary drilling, the drill bit is rotated by rotating the drill string at the surface. In directional drilling, the drill bit is rotated by a down hole mud motor coupled to the drill bit; the remainder of the drill string is not rotated during drilling. In a steerable drill string, the mud motor is bent at a slight angle to the centerline of the drill bit so as to create a side force that directs the path of the drill bit away from a straight line. In any event, in order to lubricate the drill bit and flush cuttings from its path, piston operated pumps on the surface pump a high pressure fluid, referred to as “drilling mud,” through an internal passage in the drill string and out through the drill bit. The drilling mud then flows to the surface through the annular passage formed between the drill string and the surface of the bore.
Depending on the drilling operation, the pressure of the drilling mud flowing through the drill string will typically be between 1,000 and 25,000 psi. In addition, there is a large pressure drop at the drill bit so that the pressure of the drilling mud flowing outside the drill string is considerably less than that flowing inside the drill string. Thus, the components within the drill string are subject to large pressure forces. In addition, the components of the drill string are also subjected to wear and abrasion from drilling mud, as well as the vibration of the drill string.
The distal end of a drill string, which includes the drill bit, is referred to as the “bottom hole assembly.” In “measurement while drilling” (MWD) applications, sensing modules in the bottom hole assembly provide information concerning the direction of the drilling. This information can be used, for example, to control the direction in which the drill bit advances in a steerable drill string. Such sensors may include a magnetometer to sense azimuth and accelerometers to sense inclination and tool face.
Historically, information concerning the conditions in the well, such as information about the formation being drill through, was obtained by stopping drilling, removing the drill string, and lowering sensors into the bore using a wire line cable, which were then retrieved after the measurements had been taken. This approach was known as wire line logging. More recently, sensing modules have been incorporated into the bottom hole assembly to provide the drill operator with essentially real time information concerning one or more aspects of the drilling operation as the drilling progresses. In “logging while drilling” (LWD) applications, the drilling aspects about which information is supplied comprise characteristics of the formation being drilled through. For example, resistivity sensors may be used to transmit, and then receive, high frequency wavelength signals (e.g., electromagnetic waves) that travel through the formation surrounding the sensor. By comparing the transmitted and received signals, information can be determined concerning the nature of the formation through which the signal traveled, such as whether it contains water or hydrocarbons. Other sensors are used in conjunction with magnetic resonance imaging (MRI). Still other sensors include gamma scintillators, which are used to determine the natural radioactivity of the formation, and nuclear detectors, which are used to determine the porosity and density of the formation.
In traditional LWD and MWD systems, electrical power was supplied by a turbine driven by the mud flow. More recently, battery modules have been developed that are incorporated into the bottom hole assembly to provide electrical power.
In both LWD and MWD systems, the information collected by the sensors must be transmitted to the surface, where it can be analyzed. Such data transmission is typically accomplished using a technique referred to as “mud pulse telemetry.” In a mud pulse telemetry system, signals from the sensor modules are typically received and processed in a microprocessor-based data encoder of the bottom hole assembly, which digitally encodes the sensor data. A controller in the control module then actuates a pulser, also incorporated into the bottom hole assembly, that generates pressure pulses within the flow of drilling mud that contain the encoded information. The pressure pulses are defined by a variety of characteristics, including amplitude (the difference between the maximum and minimum values of the pressure), duration (the time interval during which the pressure is increased), shape, and frequency (the number of pulses per unit time). Various encoding systems have been developed using one or more pressure pulse characteristics to represent binary data (i.e., bit
1
or
0
)—for example, a pressure pulse of 0.5 second duration represents binary 1, while a pressure pulse of 1.0 second duration represents binary 0. The pressure pulses travel up the column of drilling mud flowing down to the drill bit, where they are sensed by a strain gage based pressure transducer. The data from the pressure transducers are then decoded and analyzed by the drill rig operating personnel.
Various techniques have been attempted for generating the pressure pulses in the drilling mud. One technique involves the use of axially reciprocating valves, such as that disclosed in U.S. Pat. Nos. 3,958,217 (Spinnler); 3,713,089 (Clacomb); and 3,737,843 (Le Peuvedic et al.), each of which is hereby incorporated by reference in its entirety. Another technique involves the use of rotary pursers. Typically, rotary pulsers utilizes a rotor in conjunction with a stator. The stator has vanes that form passages through which the drilling mud flows. The rotor has blades that, when aligned with stator passages, restrict the flow of drilling mud, thereby resulting in an increase in drilling mud pressure, and, when not so aligned, eliminate the restriction. Rotation of the rotor is driven by the flow of drilling mud or an electric motor powered by a battery. Typically, the motor is a brushless DC motor mounted in an oil-filled chamber pressurized to a pressure close to that of the drilling mud to minimize the pressure gradient acting on the housing enclosing the motor.
In one type of rotary pulser, sometimes referred to as a “turbine” or “siren,” the rotor rotates more or less continuously so as to create an acoustic carrier signal within the drilling mud. A siren type rotary pulser is disclosed in U.S. Pat. Nos. 3,770,006 (Sexton et al.) and 4,785,300 (Chin et al.), each of which is hereby incorporated by reference in their entirety. Encoding can be accomplished based on shifting the phase of the acoustic signal relative to a reference signal—for example, a shift in phase may represent one binary bit (e.g., 1), while the absence of a phase shift may indicate another bit (e.g., 0).
In another type of rotary pulser, in which the rotor is typically driven by the mud flow, the rotor increments in discrete intervals. Operation of a latching or escapement mechanism, for example by means of an electrically operated solenoid, may be used to actuate the incremental rotation of the rotor into an orientation in which its blades block the stator passages, thereby resulting in an increase in drilling mud pressure that may be sensed at the surface. The next incremental rotation unblocks the stator passages, thereby resulting in a reduction in drillin
Biglin, Jr. Denis P.
Turner William Evans
APS Technology, Inc.
Edwards Timothy
Woodcock & Washburn LLP
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