METHOD AND APPARATUS FOR PRODUCING PRESSURE VARIATIONS IN A DRILLING FLUID

Abstract: A method and apparatus are disclosed for producing pressure variations in a drilling fluid flowing through a pipe string within a borehole. The method comprises establishing fluidic oscillation in a stream of drilling fluid and amplifying the oscillating flow of drilling fluid to establish a series of high pressure gradients in the drilling fluid stream. The apparatus comprises a fluidic oscillator means (1) and a fluidic amplifier (7) downstream from the fluidic oscillator means. The amplifier is preferably a vortex amplifier having the radial inlet port (7B) connected to one outlet conduit of a fluidic oscillator of the Coanda type and having the tangential inlet port (7A) connected to the other outlet of the fluidic oscillator.

Description: The invention relates to a method and apparatus for producing pressure variations in a stream of drilling fluid present in a pipe string within a borehole. British patent No. 1,198,328 discloses a fluidic oscillator having an inlet conduit of which two opposite sides are in communication with two bores respectively, which bores are not in communication with each other. The fluidic oscillator switches a stream of drilling fluid between two outlets which generates pressure variations in the main stream of the drilling fluid. Said pressure variations are transmitted to a cavity inside the bit which is down in the drilling hole. In this way Helmholz resonators are formed, which are resonant at the operating frequency of the fluidic oscillator unit. This resonance creates resonant pressure variations in the drilling fluid that produce a hammering action of the drill bit. Such an arrangement leads to objections in as much as the effect of these resonant pressure variations is severely limited. At the one hand, the high bottom hole pressures in deep holes reduce the maximum pressure gradients which can be reached with this type of apparatus. At the other hand, the inertia of the quite heavy drilling fluid reduces the possible frequency band, so that only a relatively slow hammering action on the drilling bit can be obtained. The latter instance fails to provide an appreciable improvement of the drilling conditions, in order to raise the drilling rate. Furthermore, these pressure variations are not strong enough to jar and loosen a drill pipe string that is stuck in the borehole. US patent No. 4,323,991 discloses a telemetry system for transmitting fluid pulses from a fluidic pulser in a drill string to a receiver. The known system has the disadvantage that vulnerable electrical equipment is required in the drill string in order to create the fluid pulses, which equipment is in the form of an electrical actuator receiving power from a generator driven by a mud turbine. The pulser has two control channels which are separated from each other by the electrical actuator, which control channels are in communication with opposite sides of an inlet conduit of the pulser. The object of the invention is to remove these and other objections and provide a method and apparatus for producing pressure variations in a drilling fluid present in a borehole that better satisfy the requirements of practice. In particular, it is an object of the present invention to increase the pressure gradients that can be obtained, so that these increased pressure gradients enhance the drilling conditions and thus drilling rates. Further, the jarring and liberation of stuck drill strings is also possible with the increase in pressure gradients. In accordance with the invention, this object is achieved by a method for producing pressure variations in a stream of drilling fluid in a pipe string within a borehole, said method comprising introducing said stream into an inlet conduit of a fluidic oscillator thereby establishing a cyclic fluidic oscillation in two outlet flows emerging from the oscillator; amplifying the oscillating flow of drilling fluid to establish a series of high pressure gradients in the drilling fluid by receiving a first outlet flow from the fluidic oscillator in a radial inlet of a fluidic vortex amplifier and receiving a second outlet flow from the fluidic oscillator in a tangential inlet of the fluidic vortex amplifier; and directing a flow from a central outlet of the fluidic vortex amplifier towards the bottom of the borehole, characterized in that the step of introducing said stream into the fluidic oscillator comprises introducing said stream into a Coanda type fluidic oscillator of which opposite sides of the inlet conduit are in fluid communication with each other via a feedback loop conduit thereby automatically establishing said oscillation. The apparatus according to the invention comprises at least one fluidic oscillator mounted in said pipe string for producing pressure variations in the stream of drilling fluid, said oscillator being provided with an inlet conduit, a first and a second outlet conduit; and at least one fluidic amplifier mounted in said pipe string downstream from the fluidic oscillator disposed to receive the oscillating flow of the stream of drilling fluid from the fluidic oscillator and to establish a series of high pressure gradients in the drill fluid flow, said amplifier being a vortex amplifier having a radial inlet port connected to the first outlet conduit of the fluidic oscillator and having a tangential inlet port connected to the second outlet conduit of the fluidic oscillator and having a central outlet upstream a drill bit carried by the pipe string, characterized in that the fluidic oscillator comprises a Coanda type fluidic oscillator of which opposite sides of the inlet conduit are in fluid communication with each other via a feedback loop conduit. With the method and apparatus according to the invention fluidic oscillation is created automatically by the application of the Coanda type fluidic oscillator having an inlet conduit of which opposite sides are in fluid communication with each other via the feedback loop conduit. Preferably the apparatus according to the invention is mounted somewhere in the bottom hole assembly of a drill string. The optimum location depends on the drilling circumstances. The invention will now be further described referring to the accompanying schematic drawing of a preferred embodiment, in which: Fig. 1 shows a simplified diagram of the principle of the invention; and Fig. 2 shows a perspective view of a preferred embodiment in which the principle of Fig. 1 is applied. The diagram of Fig. 1 shows firstly a fluidic oscillator which has been generally indicated with reference numeral 1. The oscillator 1 comprises an inlet conduit 2, that receives a fluid feed flow F, in this case drilling fluid, the so-called mud. The inlet conduit 2 bifurcates into two channels 3 and 4. The one outer side of the inlet conduit 2 is at the bifurcation 5 connected by a feedback loop conduit 6 with the other side of said inlet conduit 2. At high enough Reynolds numbers, the flow F is diverted to either one of the two channels 3 and 4. This diversion or switching action can be obtained automatically through the feedback loop conduit 6 that transfers the pressure at the side of either channel. This switching action is caused by the Coanda effect, which is known per se and will therefore not further be discussed. The result being, however, that a continuous inlet flow F is transformed into two discontinuous flows f1 and f2 in channels 3 and 4, respectively. The frequency of the switching action can be controlled by the rate of the inlet flow F. If the flow rate is increased the frequency also increases. Also by varying the length of the feedback loop conduit 6, the frequency can be influenced. If the length of the loop conduit 6 is increased or this one contains a retarding means of the pressure transmission the frequency of switching and thus of the two discontinuous flows f1 and f2 is decreased. The channels 3 and 4 of the oscillator are connected to the two inlet ports 7A and 7B of the fluidic vortex amplifier which has been generally indicated with reference numeral 7. The inlet port 7A is tangential and the inlet port 6 is radial whereas the central outlet 9 of the vortex chamber 8 is axial. When the oscillator 1 discharges fluid through channel 3 into the tangetial inlet port 7A, a vortex is formed in the vortex chamber 8 before the central outlet 9. Consequently there is a large flow resistance and therefore a large pressure drop in the channel 3. This results in a rapid deceleration of the fluid flow f1. When on the other hand the oscillator 1 discharges through the channel 4 into the radial inlet port 7B of the vortex chamber 8, the vortex in there disappears and a radial flow is established to the cental outlet 9. This gives only a small pressure drop and therefore a large flow f2 develops causing a rapid acceleration of the fluid flow f2 in the channel 4. Now the oscillator 1 switches back from inlet port 7A to inlet port 7B, and again a deceleration of the fluid flow f1 occurs. This switching action in combination with the vortex amplifier 7 results in high pressure variations or pulses. Typically a useful range of frequencies is in the order of 1-50 Hz. EXAMPLE In a typical embodiment, the flow f1 through channel 3 is about six times less than the flow f2 through channel 4. The speed of response of the vortex amplifier 7 is of the order of milliseconds (less than the acoustic delay of a typical drill string). An instantaneous change of resistance can then be assumed. From flow calculations based on wave theory and a maximum flow rate of 0.02 m/s, it can be calculated that blows of the order of 3 tons will be delivered at a frequency which can be adjusted by the flow rate through it. Fig. 2 shows a preferred embodiment of the invention. The apparatus has been generally indicated with reference numeral 10 and is preferably mounted in the bottom section of a drill string 11. The apparatus 10 comprises a body 12 having a central bore 13 for transporting drilling fluid or so-called mud (not shown). Into this bore 13 opens the radial inlet conduit 14 of the fluidic oscillator making a 90 degree bend and connecting to the bifurcation 15. From this bifurcation 15 extend two side branch conduits 16, 17 to either side, that are mutually connected by the feedback loop conduit 18. Furthermore two switching channel conduits 19 and 20 diverge from the bifurcation 15 and are connected to the inlet conduits 21 and 22, respectively, of the fluidic vortex amplifier generally indicated with 23. The inlet conduits 21 and 22 make a 90 degree bend and discharge tangentially and radially, respectively, into the bowl-shaped vortex chamber 24 having a central axial outlet 25. This outlet 25 is in this case a continuation of the central bore 13 of the body 12 of the apparatus. One method of producing pressure variations is leading the full flow F of drilling fluid through the apparatus 10, by which the pressure gradient is established. The activation of the apparatus 10 can be made, for example, by dropping an object (not shown), such as a ball, into the fluid bore 13. This closes a valve (not shown). If the pulses that are created are matched with the resonant frequency of the drill string in the hole, this drill string can be exited and amplify these resonant forces. These resonant forces can be used for different applications. If there are high axial forces, these can be used for controlling at least one jarring means when the drill string has become stuck in the drill hole. If the axial forces are moderate to small, these can be used for improving the drilling conditions and especially the drilling rate of the bit. The resulting blows of the bit against the hole bottom increases the penetration rate and may reduce the number of drill collars. Another field of application is in horizontal drilling, where the drill string is not rotated. Then the apparatus can be used to keep the drill string in motion so as to reduce frictional forces between the drill string/hole interface. The pressure pulses can also be used as a source for seimic interpretation, e.g., for locating the downhole position of the bit.

Claims: A method for producing pressure variations in a stream of drilling fluid in a pipe string within a borehole, said method comprising introducing said stream into an inlet conduit of a fluidic oscillator thereby establishing a cyclic fluidic oscillation in two outlet flows emerging from the oscillator; amplifying the oscillating flow of drilling fluid to establish a series of high pressure gradients in the drilling fluid by receiving a first outlet flow from the fluidic oscillator in a radial inlet of a fluidic vortex amplifier and receiving a second outlet flow from the fluidic oscillator in a tangential inlet of the fluidic vortex amplifier; and directing a flow from a central outlet of the fluidic vortex amplifier towards the bottom of the borehole, characterized in that the step of introducing said stream into the fluidic oscillator comprises introducing said stream into a Coanda type fluidic oscillator of which opposite sides of the inlet conduit are in fluid communication with each other via a feedback loop conduit thereby automatically establishing said oscillation. A method in accordance with claim 1, further comprising mounting said fluidic oscillator and amplifier in a bottom hole assembly of a drill string which carries a drill bit. A method in accordance with claim 2, further comprising selecting the location for the fluidic oscillator and amplifier within the bottom hole assembly as a function of the drilling circumstances. A method in accordance with claim 2, further comprising tuning a frequency of the pressure variation to a resonant frequency of the drill string by adjusting the rate of flow of drilling fluid through the fluidic oscillator and amplifier. A method in accordance with claim 1, further comprising triggering the production of pressure variations by dropping an object into the drill string. An apparatus for producing pressure variations in a stream of drilling fluid present in a pipe string within a borehole, comprising at least one fluidic oscillator mounted in said pipe string for producing pressure variations in the stream of drilling fluid, said oscillator being provided with an inlet conduit, a first and a second outlet conduit; and at least one fluidic amplifier mounted in said pipe string downstream from the fluidic oscillator disposed to receive the oscillating flow of the stream of drilling fluid from the fluidic oscillator and to establish a series of high pressure gradients in the drill fluid flow, said amplifier being a vortex amplifier having a radial inlet port connected to the first outlet conduit of the fluidic oscillator and having a tangential inlet port connected to the second outlet conduit of the fluidic oscillator and having a central outlet upstream a drill bit carried by the pipe string, characterized in that the fluidic oscillator comprises a Coanda type fluidic oscillator of which opposite sides of the inlet conduit are in fluid communication with each other via a feedback loop conduit. An apparatus in accordance with claim 6, wherein the apparatus is arranged in the lower section of the pipe string, somewhere in the bottom hole assembly near the drill bit. An apparatus in accordance with claim 7, further comprising means in the bottom hole assembly adapted for cooperation with an object dropped into the pipe string to activate the apparatus.

Inventors: KITSIOS, EFSTATHIOS EUGENE
Applicants: SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1988
Main classification: E21B7
IPC codes: E21B47, E21B31, E21B7, G01V1