Abstract:
A pressure pulse generator for a downhole drilling tool is provided. The pressure pulse generator includes a stator with an orifice through which a stream of fluid passes, and a rotor intended to rotate opposite the stator to allow the flow of more or less liquid exiting the orifice of the stator. The rotor is equipped with an orifice, and the two orifices present a communicating area for the passage of the stream of fluid. The rotor is capable of passing fluid therethrough. A turbine with blades rotatable in response to fluid flow through the rotor may also be provided. The turbine is operatively connected to the rotor via a drive shaft. The fluid flow through the rotor may be used to rotate the turbine and provide power usable in the downhole tool.

Description:
BACKGROUND OF INVENTION  
         [0001]    This invention relates to a pressure pulse generator. Such a pressure pulse generator is usable in particular in the area of drilling, and more specifically in a logging-while-drilling and/or measuring-while-drilling tool.  
           [0002]    In these techniques, drilling is accomplished using a string of drillpipe that terminates in a drilling tool. The logging and/or measuring tools are located near the drilling tool, downhole, in a drillpipe in the string. Logging or measurement data are transmitted to the surface.  
           [0003]    There are various existing methods of achieving this transmission. It may be achieved through electrical signals using the electrical conductors that pass through the drillpipe string. Transmission may also be achieved through acoustic signals transmitted through the drillpipes in the string. These methods permit a relatively high transmission flow rate. But the former of these techniques is relatively expensive to implement and poses problems for the connection of the conductors at the joint between drillpipes in the string. As for the latter, it lacks reliability due to the high degree of noise generated during drilling.  
           [0004]    A conventional data transmission technique uses the drilling fluid as a means of transmitting depth-modulated acoustic waves representative of the logging and/or measurement tool response.  
           [0005]    [0005]FIG. 1 illustrates a drilling device capable of making such logs and/or measurements. This device can be equipped with a pressure pulse generator according to the invention.  
           [0006]    A drilling fluid  1  contained in a tank  14  is injected by a pump  4  from the surface  2  to the inside of a drillpipe string  3  intended to drill into a geological formation  7 . The drilling fluid  1  arrives at a drill bit  5  at the end of the drillpipe string  3 . The drilling fluid  1  exits the drillpipe string  3  and returns to the surface  2  through the space  6  between the drillpipe string  3  and the geological formation  7 . The route of the drilling fluid  1  is illustrated by the arrows.  
           [0007]    One of the drillpipes  3 . 1  in the drillpipe string  3  that is near the drill bit  5  is instrumented. This instrumented drillpipe  3 . 1  contains at least one measurement device  8  intended among other things to evaluate the physical properties of the geological formation, such as its density, porosity, resistivity, etc. This measurement device  8  is part of a logging-while-drilling or LWD tool  13 .  
           [0008]    When this measuring device  8  measures drilling-related parameters such as temperature, pressure, drilling tool orientation, etc., it is part of a measuring-while-drilling or MWD tool.  
           [0009]    The instrumented drillpipe  3 . 1  is generally a drill collar. This is a drillpipe that is heavier than the others. It applies sufficient weight to the drill bit  5  to drill into the geological formation  7 .  
           [0010]    In order to produce a pressure fluctuation in the drilling fluid  1 , and thereby transmit data, a pressure pulse generator  9  is placed in the instrumented drillpipe  3 . 1  just above the area that contains the measurement devices  8 . The pressure pulse generator  9  is part of a telemetry module  12  whose function is to control data transmission between the downhole measurement device  8  and the pressure sensors  10  at the surface. The telemetry module  12  is part of the logging- and/or measurement-while-drilling tool.  
           [0011]    U.S. Pat. No. 3,309,656 describes a rotating pressure pulse generator. Rotating at a constant speed, it partially but repeatedly interrupts the flow of the drilling fluid  1 . The interruptions cause the pressure pulse generator to generate pressure pulses at a carrier frequency that is proportional to the interruption rate. Accelerating or decelerating the generator modulates the phase or the frequency of the pressure waves to transmit the data associated with the measurements made by the measurement device  8  to the surface  2 . Pressure sensors  10  at the surface  2  receive the pressure waves that are propagated in the drilling fluid  1 . Before being demodulated, the acoustic signal representing the pressure waves sensed at the surface is filtered in a processing device  11  to eliminate the noise which is inevitable. The assembly formed by the telemetry module  12  including the pressure pulse generator  9 , the processing device  11 , and the pressure sensors  10  is hereinafter called the “telemetry system.” 
           [0012]    Due to the drilling fluid, which is generally mud, the acoustic signal recovered at the surface is highly attenuated. This limits the performance of pressure pulse telemetry systems.  
           [0013]    Although rotating pressure pulse generators have been improved in the past ten years, they still have weaknesses. U.S. Pat. No. 6,219,301 describes a conventional but more recent pressure pulse generator. Referring to FIGS. 2A and 2B, the pressure pulse generator  9  shown has a stator  20  with several peripheral orifices  21  and a rotor  22  with blades  23  in the form of a cross. The rotor  22  is rotated near the stator  20  by a motor (not shown). The drilling fluid, whose displacement is illustrated by the arrows in the figures, goes through the peripheral orifices  21  of the stator  20 . As the rotor  20  rotates it partially blocks the stator orifices  21  and either significantly restricts the passage of the fluid or else allows it to pass massively. In FIG. 2A, the pressure pulse generator is in the so-called “open” position. The rotor blades  23  do not coincide with the orifices  21  and the flow of fluid through the pressure pulse generator is maximal. A communicating area can be defined for the fluid passage, corresponding to the stator orifices, for example triangles whose sides are approximately 20, 30, and 30 millimeters.  
           [0014]    In FIG. 2B, the pressure pulse generator is in the so-called “closed” position. The rotor blades partially block the orifices  21  of the stator  20  and the fluid flow through the pressure pulse generator is minimal. The pressure pulse generator does not totally prevent the passage of the fluid. Since this fluid serves to lubricate the drilling tool, it is necessary for it to permanently circulate in the drillpipe string so that drilling operations can continue. When the blades  23  of the rotor  22  are opposite the stator orifices  21 , the orifices  21  have an unblocked space  24 . The communicating area for the fluid is the spaces  24 , for example rectangles approximately 28×4 millimeters.  
           [0015]    As the rotor  22  rotates, it generates a fluid flow downstream of the pressure pulse generator in which the pressure falls and rises at the rate of rotation. The pressure pulses generated by the generator rotate at constant speed and are not perfectly sinusoidal. As can be seen in FIG. 4, these pulses are represented with the reference A in FIG. 4. A perfect sinusoid is referenced B. Clipping occurs. Energy is lost in the form of harmonics. These harmonics can interfere with the demodulation of the signal at the surface.  
           [0016]    Inevitably, the fluid contains solid particles or debris. In order to be easily removable, this debris must not be too large because it must pass through the peripheral orifices  21  of the stator  20 . Since larger debris often appears, the drive motor must be powerful enough so that the rotor can grind it up. When the debris is ground up, it can then be discharged. But grinding up this debris may cause wear to the rotor. If the motor power is not sufficient, the pressure pulse generator seizes and clogs, and this can cause the drillpipe string to be clogged.  
           [0017]    In an effort to provide necessary power, pressure pulse generators have been used in combination with turbines. U.S. Pat. No. 5,517,464 describes an integrated modulator and turbine-generator with a turbine impeller coupled by a drive shaft to a modulator rotor downstream from the impeller. The turbine impeller is used to drive the modulator rotor, which is coupled to an alternator. Despite this advancement in downhole energy conservation, there is an ever-increasing need for more power in downhole operations. What is needed is a system that is capable of channeling and/or utilizing the force of fluid flowing through the generator to create additional power.  
         SUMMARY OF INVENTION  
         [0018]    This invention proposes a pressure pulse generator, also called a turbo-modulator, which remedies the above disadvantages and/or provides further advantages.  
           [0019]    More specifically, the invention proposes a pressure pulse generator that can easily discharge large debris, even in closed position, without grinding it up. The risks of seizing and clogging are considerably reduced. Since the debris can be discharged without being ground up, the pressure pulse generator according to the invention operates with less power. The invention also proposes a pressure pulse generator that generates nearly sinusoidal pressure pulses, so as to increase the efficiency of the telemetry system using such a generator. The invention is provided with a turbine used in combination with the generator to produce downhole power.  
           [0020]    In order to achieve this, this invention is a pressure pulse generator containing a stator with an orifice through which a stream of fluid flows and a rotor also equipped with an orifice. The rotor is intended to turn opposite the stator to allow more or less fluid coming out of the stator orifice to flow. The two orifices present a communicating area for the flow of the fluid stream. This communicating area varies between a maximum and a minimum area depending on the position of the rotor with respect to the stator. The communicating area can vary in basically a sinusoidal manner.  
           [0021]    This communicating area comprises one section located in a central area of the stator-rotor assembly regardless of the position of the rotor with respect to the stator.  
           [0022]    The stator orifice may have a central section located in the central area of the stator and at least one lobe that communicates with the central section. Similarly, the rotor orifice may have a central section located in a central area of the rotor and at least one lobe that communicates with the central section. Advantageously, this central section is preferably circular. The lobe may be part of a sector of a circle.  
           [0023]    In an alternative, the lobe is preferably part of a trapezoid.  
           [0024]    The number of lobes of an orifice contributes to determining the period of the pressure pulses. A particularly interesting shape for at least one of the orifices is preferably a rectangular shape. This rectangle is preferably centered. In this configuration, the pressure pulses are preferably sinusoidal when the rotor rotates preferably at a constant speed. Another particularly interesting shape for at least one of the orifices is a cross shape.  
           [0025]    The amplitude of the pressure pulses is determined by the difference between the maximum and minimum cross-sections.  
           [0026]    With a pulse generator according to the invention, the debris contained in the fluid is carried by the rotor towards the section located in the central area of the stator-rotor assembly.  
           [0027]    This invention also concerns a logging-while-drilling tool that has a pressure pulse generator characterized in this way.  
           [0028]    This invention also concerns a measuring-while-drilling tool that has a pressure pulse generator characterized in this way.  
           [0029]    This invention also concerns a telemetry system that has a pressure pulse generator characterized in this way.  
           [0030]    In at least one aspect, the invention relates to a pressure pulse generator comprising a stator with an orifice intended for the passage of a stream of fluid and a rotor adapted to rotate opposite the stator in order to permit the through flow of fluid to exit the orifice of the stator. The generator is characterized by the fact that the rotor is also equipped with an orifice, both orifices presenting a communicating area for the passage of the stream of fluid. The generator may also include a turbine connected to the rotor.  
           [0031]    In another aspect, the invention relates to a pressure pulse generator comprising a stator with a stator orifice intended for the passage of a stream of fluid, a rotor adapted to rotate opposite the stator for selectively permitting the flow of fluid exiting the orifice of the stator to pass through the rotor, and a turbine operatively connected to the rotor. The rotor equipped with a rotor orifice. The orifices defining a communicating area for the passage of the stream of fluid. The turbine having blades rotatable in response to the flow of fluid through the rotor.  
           [0032]    In another aspect, the invention relates to a pressure pulse generator for a downhole drilling tool. The downhole drilling tool has a fluid passing therethrough. The pressure pulse generator comprises a stator, a rotor and a turbine. The stator has a stator orifice adapted to permit the fluid to flow therethrough and defines a plurality of stator lobes. The rotor is positioned adjacent the stator orifice and has a rotor orifice defining a plurality of rotor lobes of corresponding dimension to the stator lobes. The rotor is adapted to rotate with respect to the stator such that the fluid selectively passes therethrough. The rotor has a channel therethrough and at least one port to permit the fluid to exit the rotor. The turbine is connected to the rotor and has at least one blade. The turbine is rotationally driven by the flow of fluid through the rotor and over the at least one blade whereby power is provided to the downhole tool.  
           [0033]    In yet another aspect, the invention relates to a method of generating power in a downhole tool. The steps include selectively passing a fluid through an orifice of a stator and a corresponding orifice of a rotor in the downhole tool, passing the fluid through the rotor and out one or more exit ports therein and generating rotational energy by passing the fluid from at least one exit port over at least one turbine blade of a turbine operatively connected to the rotor.  
           [0034]    Other aspects will be discernable from the following description. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0035]    This invention will be better understood by reading the description of the examples given purely for information and without limitation, referring to the attached drawings, in which:  
         [0036]    [0036]FIG. 1 (already described) shows a drilling device equipped with a logging-and/or measuring-while-drilling tool that can be equipped with a pressure pulse generator according to the invention;  
         [0037]    [0037]FIGS. 2A, 2B (already described) show a prior art pressure pulse generator in the open and closed positions, respectively;  
         [0038]    [0038]FIGS. 3A, 3B show an example of a pressure pulse generator according to the invention in the open and closed positions, respectively;  
         [0039]    [0039]FIG. 4 shows the pressure pulses generated by the pulse generator in FIG. 2 (curve A) and FIG. 3 (curve C), to be compared to a pure sinusoid (curve B);  
         [0040]    [0040]FIGS. 5A, 5B show the front of the stator-rotor assembly of a pressure pulse generator according to the invention in the open and closed positions, respectively;  
         [0041]    [0041]FIG. 6 shows debris lodged in the prior art pressure pulse generator;  
         [0042]    [0042]FIGS. 7A, 7B show the trajectory followed by the debris before being evacuated in a pressure pulse generator according to the invention;  
         [0043]    [0043]FIGS. 8A, 8B show the front of a pressure pulse generator according to the invention with four-lobed orifices, and the shape of the pressure pulses generated;  
         [0044]    [0044]FIGS. 9A, 9B show the front of a pressure pulse generator according to the invention with two sector lobe orifices and the shape of the pressure pulses generated;  
         [0045]    [0045]FIGS. 10A and 10B show the front of a pressure pulse generator according to the invention with optimized two-lobed orifices and the shape of the pressure pulses generated.  
         [0046]    [0046]FIG. 10C shows a three dimensional view of a pressure pulse generator according to the invention.  
         [0047]    [0047]FIGS. 11A, 11B,  11 C and  11 D show the front of a pressure pulse generator according to the invention with three-lobed orifices and the shape of the pressure pulses generated.  
         [0048]    [0048]FIGS. 11E and 11F show a schematic view, partially in cross-section, and a three-dimensional view, respectively, of a pressure pulse generator with a turbine according to the invention. 
     
    
       [0049]    In these figures, the identical or similar elements are designated by the same reference characters. For the sake of clarity, the figures are not necessarily to scale.  
       DETAILED DESCRIPTION  
       [0050]    Referring to FIGS. 3A, 3B, which show a pressure pulse generator according to the invention, this pulse generator is intended to generate pressure pulses in a stream of fluid, which may be a drilling fluid used in a drilling device equipped with a telemetry system like the one in FIG. 1.  
         [0051]    Note that there is a stator  40  that cooperates with a rotor  43 , and the stator  40 -rotor  43  assembly is placed inside a drillpipe  30  in a drillpipe string. The stator  40  has an orifice  41 . The rotor  43  also has an orifice  44 . In order to generate the pressure pulses in the fluid stream, illustrated by the arrows, the fluid enters the pressure pulse generator from the stator  40  side. The fluid passes through the orifice  41  of the stator  40 . When it leaves the orifice  41  of the stator  40 , the fluid goes to the orifice  44  of the rotor  43 , which is opposite the stator  40 . A motor (not shown) drives the rotating rotor  43  around an axis xx′ parallel to the fluid stream.  
         [0052]    When the rotor  43  rotates, it allows more or less fluid from the orifice  41  of the stator  40  to flow. The two orifices  41 ,  44  define a communicating area (or intersection)  48  for the passage of the fluid, varying between a minimum and a maximum cross-section. This communicating area  48  includes a section located in a central area of the stator-rotor assembly regardless of the position of the rotor with respect to the stator. The axis xx′ is contained in this communicating area  48 . The central area is an area that includes the center of the rotor-stator assembly. In FIG. 3A, the generator is in the “open” position, in which the communicating area  48  is maximal. In FIG. 3B, the generator is in the “closed” position, in which the communication cross-section  48  is minimal.  
         [0053]    In general, the orifice  41  of the stator  40  includes a central section  42 , i.e., located in a central area of the stator  40 , and at least one lobe  46  that communicates with the central section  42 . This central section  42  and this lobe  46  are visible in FIG. 5B.  
         [0054]    Similarly, the orifice  44  of the rotor  43  includes a central section  45 , i.e., located in a central area of the rotor  43 , and at least one lobe  47  that communicates with the central section  45 . This central section  45  and this lobe  47  are visible in FIG. 5B.  
         [0055]    With such a configuration for the orifices  41 ,  44  of the stator  40  and the rotor  43 , the communicating area  48  is achieved for the passage of the fluid with the section located in a central area of the stator-rotor assembly. Orifices  41 ,  44  of the rotor and stator can be identical as in FIGS. 3A, 3B, but could have been different shapes.  
         [0056]    In FIGS. 5A, 5B, orifices  41 ,  44  are both rectangular and are centered on axis xx′. Then in the center of the rectangle is the central section  42 ,  45  and on either side the two lobes  46 ,  47 . When the rotor is driven at constant speed, such a configuration makes it possible to generate preferably sinusoidal pressure pulses, referenced C in FIG. 4. There is practically no loss of energy in the form of harmonics. The communicating cross-section varies in preferably a sinusoidal manner. The pressure pulse generator has an increased efficiency and better signal demodulation can be achieved at the surface. This shape of pressure pulses was not possible with the prior art generator illustrated in FIGS. 2A, 2B.  
         [0057]    [0057]FIGS. 5A, 5B schematically show the front view of the rotor  43  of the pressure pulse generator according to the invention and, hidden behind the rotor  43 , the stator  40 . The latter is visible only by its orifice  41 . In this embodiment, the orifices  41 ,  44  of the stator  40  and the rotor  43  are preferably identical, rectangular and centered. In FIG. 5A the orifices  41 ,  44  are aligned and coincide. The angle of the rotor  43  to the stator  40  is zero modulo Tr. The area for the passage of the stream of fluid, i.e., the communicating surface area between the two orifices  41 ,  44 , is maximal and is the same as the surface area of the orifices  41 ,  44 . The pressure drop of the stream of fluid through the pressure pulse generator is minimal. The orifices  41 ,  44  may have the following dimensions 75 millimeters×20 millimeters but this invention is not limited to a pressure pulse generator whose rotor and stator orifices have these dimensions. Any debris smaller than the aforesaid dimensions can go through the pressure pulse generator.  
         [0058]    In FIG. 5B, the rotor  43  has rotated π/2 modulo π, and now the two orifices  41 ,  44  are offset with respect to one another. The lobes  46 ,  47  are located on either side of the communicating area.  
         [0059]    The communicating area  48  is minimal and is represented by the intersection between the two orifices  41 ,  44 , i.e., the small central white square. The pressure drop of the stream of fluid through the pressure pulse generator is maximal in this case. The dimensions of the communicating area between the two orifices  41 ,  44  are preferably 20 millimeters×20 millimeters. The central sections of the orifice  41  of the stator  40  and the orifice  44  of the rotor  43  are represented by the communicating area  48  between the two orifices  41 ,  44 . Any debris whose dimensions are smaller than these dimensions can go through the pressure pulse generator. The risk of clogging is much smaller than with the structure in FIG. 2.  
         [0060]    We now refer to FIG. 6, which shows a front view of the stator-rotor assembly of the pressure pulse generator from FIGS. 2A, 2B. This figure helps explain why the risks of clogging are high in this configuration. The orifices  21  of the stator  20  are peripheral and preferably triangular. When the blades  23  of the rotor  22  are rotating, they push the debris  25  into a corner of a triangular orifice  21  of the stator  20 . The debris is stuck between one of the blades  23  of the rotor  22  and one of the corners of an orifice  21  of the stator  20 , as shown in the figure. If the rotor&#39;s drive motor is powerful enough so that the debris  25  is ground up and discharged, the pulse generator can continue to function, but the blade  23  of the rotor  22  that acted could be damaged.  
         [0061]    If the motor is not powerful enough to grind up the debris  25 , the pressure pulse generator could go into a de-clogging cycle, with the rotor  22  rotating back and forth several times until the debris  25  is ground up. Increased energy consumption will occur and the rotor  22  is even more likely to be damaged.  
         [0062]    If the debris  25  is still not ground up after a certain period, the situation becomes critical. One solution is to stop everything and pull the string of drillpipe up to the surface in order to access the pressure pulse generator.  
         [0063]    We now refer to FIGS. 7A, 7B, which show why the pressure pulse generator according to the invention makes it possible to easily eliminate debris.  
         [0064]    When debris  49  arrives from a peripheral location, it is carried forward by the rotor  43 , which applies a force F to it. This force F is made up of two orthogonal components F 1 , F 2 . This force F tends to move the debris  49  closer to the central area of the stator-rotor assembly and therefore to push it towards the communicating area between the orifice  41  of the stator  40  and the orifice  44  of the rotor  43 .  
         [0065]    When the pressure pulse generator is in the closed position as in FIG. 7B, the force applied to the debris  49  has only one component F 1 . The debris  49  is located at the communicating area  48  and can be discharged if it has the appropriate dimensions. If it is too large, it can be discharged when the rotor  43  is offset π/2 from the position shown in FIG. 7B and the communicating section  48  between the orifice  41  of the stator  40  and the orifice  44  of the rotor  43  becomes maximal. The risk of clogging is considerably reduced compared to the configuration in FIGS. 2 and 6.  
         [0066]    The pressure pulse generator according to the invention makes it possible to eliminate larger debris because there is only one central fluid passage area regardless of the position of the rotor with respect to the stator. In the prior art, the fluid passage area was always broken up.  
         [0067]    The number of lobes either a rotor or a stator orifice has contributes to determining the period of the pressure pulses generated. A two-lobed configuration of both the stator orifice and the rotor orifice, as in FIG. 6, results in a period π, while a four-lobed configuration as in FIG. 8A results in a period π/2. More generally, a configuration with n lobes (n being a whole number other than zero) in both the rotor orifice and the stator orifice results in a period 2 π/n. If the rotor and stator orifices do not have the same number of lobes, this becomes more complicated.  
         [0068]    It should be noted that for maximum passage areas of equal value, configurations with few lobes (one or two) make it possible to discharge the largest debris.  
         [0069]    [0069]FIG. 8A shows an example of a pressure pulse generator according to the invention in which both the stator and the rotor orifices have the shape of a four-legged cross. These orifices take on the shape of two rectangles offset by π/2. The corners of the rectangles are rounded. These orifices  41 ,  44  have a central section  42 ,  45  and four lobes  46 ,  47 , respectively. In the closed position, as in FIG. 8A, the fluid passage area becomes more and more complex as the number of lobes increases.  
         [0070]    [0070]FIG. 8B shows the appearance of the pressure pulses generated by such a pressure pulse generator. These pulses are preferably sinusoidal and their period is half that shown in FIG. 5. The amplitude of the pressure pulses generated is controlled by the difference between the maximum communication area and the minimum communication area, i.e., the difference between the fluid passage area in the open position and the fluid passage area in the closed position.  
         [0071]    The geometry of the stator and rotor orifices controls the shape of the pressure pulses generated. A centered rectangular shape generates nearly sinusoidal pulses. Other contours are of course possible.  
         [0072]    It is possible, for example, to give the rotor and stator orifices a geometry such as the one illustrated in FIG. 9A. The rotor and stator orifices are preferably identical. Each of the orifices  41 ,  44  preferably has a circular central section  42 ,  45  with two diametrically opposed sector-shaped lobes  46 ,  47 . These sectors are approximately equal to π/2. When the generator is in the closed position, the communicating area at the two orifices  41 ,  44  corresponds to the central section  42 . FIG. 9B shows the shape of the pulses generated with a pressure pulse generator of the type in FIG. 9A. This shape is relatively far from a pure sinusoid.  
         [0073]    It is possible to finely adjust the geometry of the orifices  41 ,  44  in order on the one hand to optimize the shape of the pressure pulses generated and on the other hand to obtain the largest possible minimum communicating area. FIG. 10A shows such an optimized shape for the orifices  41 ,  44  of the stator  40  and the rotor  43 . It is derived from the centered rectangular orifice. Each of the orifices  41 ,  44  preferably has a circular central section  42 ,  45  and two lobes  46 ,  47  that communicate with the central opening  42 ,  45 . These two lobes are diametrically opposed and slightly flared and curved.  
         [0074]    [0074]FIG. 10B illustrates the shape of the pulses generated (curve D) by the pressure pulse generator in FIG. 10A, and this shape can be compared to a perfect sinusoid (curve E).  
         [0075]    [0075]FIG. 10C illustrates a three-dimensional view of a pressure pulse generator according to the invention with the configuration in FIG. 10A. The pressure pulse generator is in the open position. The arrows show the direction of fluid flow. The rotor  43  is shown in its entirety because in the preceding figures it was only schematicized by a first section  43 . 1  nearest the stator  40 . This first section  43 . 1  communicates with a second section  43 . 2  in the shape of a funnel to discharge the stream of fluid exiting the rotor. The first section  43 . 1  is made of a particularly strong material because it receives the brunt of the debris mixed into the fluid. The rotor drive motor (not shown) would be placed downstream of the rotor.  
         [0076]    [0076]FIGS. 11A, 11B and  11 C depict another proposed shape for the orifices  51 ,  54  of a stator  50  and a rotor  53 , respectively. Each of these figures show the rotor in a different rotational position with respect to the stator. FIG. 11A shows the rotor aligned with the stator at zero degrees rotation, or the “open” position. FIG. 11B shows the rotor in an intermediate position with respect to the stator at the thirty degrees rotation. FIG. 11C shows the rotor in non-alignment with the stator at sixty degrees rotation, or the “closed” position.  
         [0077]    The stator orifice  51  preferably has a circular central opening  52  and three lobes  56 ,  57 ,  58  that communicate with the central openings  52 . The rotor orifice  54  preferably has a circular central opening  55  and three lobes  66 ,  67 ,  68  that communicate with the central openings  55 . The lobes are preferably equally spaced and slightly flared and curved. While three, flared lobes are depicted, any number or shape may be used.  
         [0078]    [0078]FIG. 11D illustrates the shape of the pulses generated by the pressure pulse generator of FIGS. 11A, 11B and  11 C. Points H, I and J depict the pressure drop corresponding to the position of the rotor as depicted in FIGS. 11A, 11B and  11 C, respectively.  
         [0079]    Various pressure pulse curves are depicted in FIGS. 8B, 9B,  10 B and  11 D corresponding to the flow of fluid in various rotor/stator configurations. FIGS. 8B, 10B and  11 D depict sinusoidal waves generated by rotation of the rotor at constant speed. FIG. 9B is also rotating at a constant speed, but generates a non-sinusoidal wave based on the geometry of the rotor/stator configuration. However, by varying the speed of the rotor/stator configuration of FIG. 9A over each periodp, a sinusoidal wave may also be generated. In this manner, the variation of speeds and geometries may be manipulated to generate the desired wave. Additionally, the distance between the rotor and stator may be adjusted to provide variations in the pressure pulse amplitude. The closer the rotor is to the stator, the higher the pressure pulse amplitude.  
         [0080]    [0080]FIG. 11E illustrates a pressure pulse generator usable in conjunction with the rotor/stator configurations depicted in FIGS. 11A, 11B and  11 C. FIG. 11E is a cross-sectional view of the generator positioned in a downhole tool, such as the drilling device of FIG. 1. The generator includes a stator  50  having an orifice  51  therethrough, and a rotor  53  positioned adjacent the stator  50 . The arrows show the direction of fluid flow through the stator and rotor  53 . A rotor shaft  55  is operatively connected to the rotor and rotational driven by the generator as indicated by the curved arrow. A turbine  65  is connected to the rotor  53  and drive shaft  55 .  
         [0081]    [0081]FIG. 11F is a three-dimensional view of a rotor  53  and turbine  65  forming part of the generator of FIG. 111E. The rotor  53  includes a first section  53 . 1 , a second section  53 . 2 . The rotor  53  has an orifice  54  therethrough, lobes  66 ,  67 ,  68  and a central section  55  corresponding to the rotor as depicted more fully in FIGS. 11A, 11B and  11 C.  
         [0082]    Referring still to FIG. 11F, fluid flows through the downhole tool and past the orifice of the stator and the rotor, and into the generator as indicated by the arrow. Fluid flows through the rotor  53  and exits-three ports  69  in the second section  53 . 2  of the generator. Fluid exiting ports  69  in the rotor flows across one or more of blades  80 ,  81 ,  82  of the turbine  65 . The force of the fluid pushing against the blades rotates the turbine  65 . The rotational force of the blade may then be used to provide power, such as mechanical rotation for the rotor.  
         [0083]    The blades of the turbine are preferably adapted to conform to the force of fluid as it passes through the downhole tool to generate maximum power. As shown in FIG. 11F, the blades are curved to increase the surface contact with the fluid exiting the ports  69 . However, it will be appreciated that one or more of the blades may be straight, angled, or have other geometries adapted to the flow of fluid. Additionally, the exit port  66  may be angled, shaped, configured or otherwise adjusted to direct flow in the desired direction with respect to the blades. The distance between the exit ports  69  and the blades and/or the distance between the rotor and stator may also be adjusted to increase and/or decrease the force of the fluid against the blade. In this manner, the flow of fluid may be optimized to adjust the power generated by the turbine.  
         [0084]    The turbine  65  of FIGS. 11E and 11F is preferably depicted downstream of the rotor  53 . The turbine may be located at various positions along the rotor and in the direction of fluid flow through the generator. Additionally, the generator may be inverted with respect to the flow of fluid and run in a “backwards” position in the downhole tool if the blade inclination is also reversed. The rotor shaft may be positioned uphole or downhole from the stator.  
         [0085]    Referring again to FIG. 1, assume that reference  13  illustrates a logging-while-drilling tool according to the invention and includes the pressure pulse generator  9  according to the invention. It could of course be assumed that reference  13  represents a measuring-while-drilling tool according to the invention.  
         [0086]    Still referring to FIG. 1, the invention also concerns a telemetry system that includes the telemetry module  12  comprising the pressure pulse generator  9  according to the invention  9 , the surface pressure sensors  10 , and the processing device  11 .  
         [0087]    Although several embodiments of this invention have been shown and described in detail, it is understandable that various changes and modifications can be made without going outside the scope of the invention. The rotor and/or the stator could have several orifices, the stator and rotor orifices could be different, and of course the shapes shown are not the only possible shapes.