In general, the present invention relates to a device, system or method including a hydraulically assisted top-mounted pulser system, including a main pulser and a rotary servo valve for actuating the pulser, for generating pressure pulses in a fluid column during the process of drilling a subterranean borehole with the intent of using said pressure pulses to encode information and telemeter such information to the surface in real time.
In the drilling of deep bore holes, the rotary drilling technique has become a commonly accepted practice. This technique involves using a drill string which consists of numerous sections of hollow pipe connected together and to the bottom end of which a drill bit is attached. By imparting axial forces onto the drilling bit and by rotating the drill string either from the surface or using a hydraulic motor attached to the drill string, a reasonably smooth and circular bore hole is created. The rotation and compression of the drilling bit causes the formation being drilled to be crushed and pulverized. Drilling fluid is pumped down the hollow center of the drill string through nozzles on the drilling bit and then back to the surface around the annulus of the drill string. This fluid circulation is used to transport the cuttings from the bottom of the bore hole to the surface where they are filtered out and the drilling fluid is recirculated as desired. The flow of the drilling fluid also provides other secondary functions such as cooling and lubricating the drilling bit cutting surfaces and exerts a hydrostatic pressure against the borehole walls to help contain any entrapped gases or fluids that are encountered during the drilling process. To enable the drilling fluid to travel through the hollow center of the drill string, the restrictive nozzles in the drilling bit and to have sufficient momentum to carry cutting and debris back to the surface, the fluid circulation system at the surface includes a pump or multiple pumps capable of sustaining sufficiently high pressures and flow rates, piping, valves and swivel joints to connect the piping to the rotating drill string.
The need to measure certain parameters at the bottom of a bore hole and provide this information to the driller has long been recognized. These parameters include, but are not limited to the temperature, pressure, inclination and direction of the bore hole, vibration levels, inclination, azimuth, toolface (rotational orientation of the drill string), but also include various geophysical and lithological measurements and formation geophysical properties such as resistivity, porosity, permeability, and density as well as in situ formation analysis for hydrocarbon content. The challenge of measuring these parameters in the hostile environment at the bottom of a borehole during the drilling process and conveying this information to the surface in a timely fashion has led to the development of many devices and practices.
It is an advantage to be able send data from the bottom of a bore well to the surface, while drilling, and without the use of wires or cables, and without the continuous and/or frequent interruption of drilling activity. Thus, tools commonly referred to as “measurement while drilling” or “MWD” tools have been developed. Several types of MWD tools have been contemplated in the prior art and are discussed in brief below.
MWD tools may transmit data in several ways, including: creating EM (low frequency radio waves or signals, currents in the earth or magnetic fields) waves to propagate signals through the earth; imparting high frequency vibrations to the drill string which can be used to encode and transmit data to the surface; and creating pressure pulses to encode and transmit data to the surface of the earth from the bottom of a borehole.
MWD tools using pressure pulses can operate in a number of ways, such as: closing or opening a valve in the drill string so as to create a substantial pressure pulse that is detectable at the surface when a particular parameter reaches a pre-selected or particular value or threshold, or creating a series or group of pulses depending upon the parameter's value, or by using the time between the pressure pulse signals in addition to the total number of pressure pulse signals to encode information. Opening and closing and sensing may be accomplished mechanically or electronically or electromechanically, or by a combination thereof.
An MWD drilling tool may include a pulsing mechanism (pulser) coupled to a power source (e.g, a turbine generator capable of extracting energy from the fluid flow), a sensor package capable of measuring information at the bottom of a well bore, and a control mechanism that encodes the data and activates the pulser to transmit this data to the surface as pressure pulses in the drilling fluid. The pressure pulses may be recorded at the surface by means of a pressure sensitive transducer and the data decoded for display and use to the driller.
A pulser may create pressure pulses in a number of fashions. In one embodiment, a servo mechanism opens and closes the main pulsing mechanism indirectly. U.S. Pat. No. 9,133,950 B2 discloses servo pulser mechanisms, and is incorporated by reference in its entirety. Here, the difference in pressure caused by changes in the fluid flow do most of the work of opening and closing the main valve to generate pulses to transmit data. Such a servo mechanism assisted pulser may also be called a hydraulically assisted pulser.
A hydraulically assisted pulser of a lifting knob type typically has an obstruction, or poppet, used to create a controllable obstruction in an orifice (and a resultant pressure drop thereacross), such hydraulically assisted pulsers are driven by a servo or pilot valve.
In many cases, operators may also desire to use logging-while-drilling (LWD) sensors, which entails including one or more well logging tools downhole into the well borehole as part of the downhole tool. LWD can permit the properties of a formation to be measured during the drilling process. However, LWD sensors traditionally reside below (downhole or downstream of) the MWD platform to be as close as possible to the bit. Therefore, having a top-mounted pulser simplifies wiring and flow path integration, in-part by not requiring electrical or signal wiring to pass upstream or downstream of the main pulsing mechanism, which typically fully occupies the piece of drill pipe in which it resides. As a result, some pulser systems are designed to be top-mounted, and intended to be mounted above or upstream of the rest of the MWD and LWD system(s).
Bottom-mount pulsers, that is pulsers that are mounted towards the lower extremity of the MWD tool, are typically retrievable, i.e. they can be removed upward through the hollow center of the drill pipe, without withdrawing the drill pipe itself, usually in situations where the drill pipe is stuck in the borehole and the removal of the MWD tool from the borehole and drill pipe is desired. This ability can offer an advantage in time and costs should servicing or other access be needed. Retrievability also typically involves the servo valve being unfixed to portions of the main valve, and instead being mounted using a helix-end system, fitted into a muleshoe receiver on the main valve, and the helix end portion of the servo valve and the remainder of the MWD tool must also be sufficiently small enough in diameter to be retrieved through the inner diameter of all the drill pipe above the MWD tool. In such a system, the helix end of the servo valve must have a sufficiently small diameter to fit well within the I.D. of that muleshoe in the main valve. Thus, retrievability may come at the cost of requiring such retrievable components to have a small diameter, which in turn may have detrimental effects in the MWD system's ability to generate mud pulses of sufficient amplitude, or in the MWD system's ability to resist abrasive wear caused by the flow of drilling mud.
A top-mount pulser is usually non-retrievable and as such need not fit within the smaller I.D. that would be required if it were to be retrievable. Thus, it can have a greater cross-sectional area. This additional cross-sectional area allows for a greater power density in the driving mechanisms (motors or solenoids) and allows for greater forces to be generated relative to smaller diameter bottom-mount retrievable designs. Having a larger cross-sectional area also means that fluid flow paths can be made bigger and the mud pulse valve itself can be larger. This reduces flow velocities during the non-pulsing time and allows for better wear life, and increased resistance to blockages caused by high fluid densities which necessarily require the addition of weighting components (solids) to the drilling fluid or the addition of granular or otherwise obstructive materials (Lost Circulation Material, LCM) used to condition the borehole against fluid losses into or fluid gains from the borehole.
A top-mount design is also typically rigidly mounted to the other mechanical components of the downhole drill pipe. The ability to restrict the movement of the MWD tool and avoid impact damage caused in high vibration environments is a potential advantage.
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