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CROSS-REFERENCE TO RELATED APPLICATION 
   The present invention is related to the subject matter of U.S. patent application Ser. No. 09/946,849 entitled “Downhole Drilling Assembly with Independent Jet Pump” and Ser. No. 09/971,308 entitled “Concentric Casing Jack”, both of which are incorporated herein by reference. 

   FIELD OF INVENTION 
   The present invention relates generally to oilfield drilling devices and methods and specifically, to an apparatus and method for inducing under balanced drilling conditions by artificially lifting the drilling fluid and the formation fluid with a jet pump assembly affixed to an inner casing section while simultaneously drilling with a drill bit and drill pipe that passes through the jet pump assembly. 
   BACKGROUND 
   In order to produce fluids such as oil, gas, and water from subterranean rock formations, a well is drilled into the fluid-bearing zone. Most wells are generally drilled with a drilling rig, a drill bit, a drill pipe, and a pump for circulating fluid into and out of the well bore. The drilling rig rotates and lowers the drill pipe and drill bit to penetrate the rock. Drilling fluid, sometimes referred to as drilling mud, is pumped down the drill pipe through the drill bit to cool and lubricate the action of the drill bit as it disaggregates the rock. In addition, the drilling fluid removes particles of rock, known as cuttings, generated by the rotational action of the drill bit. The cuttings become entrained in the column of drilling fluid as it returns to the surface for separation and reuse. The column of drilling fluid also serves a second purpose by providing pressure in the form of hydrostatic weight, which prevents seepage from the formation into the well. When the weight of the column of drilling fluid is used to prevent seepage, the hydrostatic pressure of the column of drilling fluid exceeds the pressure contained within the formation, a drilling condition referred to as over balanced drilling. 
   A desired condition when drilling is to prevent drilling fluids from penetrating the surrounding rock and contaminating the reservoir. Another desired condition is to allow any fluid such as oil contained in the reservoir to flow into the well bore above the drill bit so that production can be obtained during the drilling process. Both of these conditions can be achieved by lowering the bottom hole pressure, or in other words, lowering the hydrostatic pressure that is exerted by the column of fluids in the well bore to a point that is below the pore pressure which exists within a rock formation. Lowering the bottom hole pressure within a well bore while drilling below the formation pressure to accomplish either of these goals is referred to as under balanced drilling. 
   Conventional under balanced drilling intentionally reduces the density of fluids contained in the well bore. In conventional under balanced drilling, the reduction in the density of the fluids causes the hydrostatic pressure of the fluid column to be lower than the pressure contained within the pores of the rock formation being drilled. When a reduction in density causes the hydrostatic pressure of the fluid column to be lower than the pore pressure, fluids in the reservoir may flow into the well bore while it is being drilled. Under balanced drilling has gained popularity in the upstream oil and gas industry because it does not allow the drilling fluids to penetrate the surrounding rock and damage the permeability of the reservoir. 
   The under balanced condition is usually achieved by injecting a density reducing agent such as air, nitrogen, exhaust, or natural gas into the fluids that are being pumped down the drill pipe during the process of drilling a well. The injected gas combines with the drilling fluid and reduces its density and thus lowers the hydrostatic pressure that exists in the annulus between the drill pipe and the wall of the well bore. The concentric casing technique is a common method for delivering the gas to the bottom of the well by utilizing a second string of casing hung in the well bore inside the production casing. The injected gas flows down to the bottom of the well through the outer annulus created by the two strings of casings. The drilling fluid, delivered via the drill pipe, and any produced fluid combine with the injected gas as it flows upwards through the inner annulus between the second or concentric string of casing and the drill pipe. The process may be reversed such that the inner annulus is used for injection and the outer annulus is used for well effluent. The use of gas as a density reducing agent has distinct disadvantages. First, if air is used, the risk of down hole fires and corrosion problems are invited. Second, if an inert gas such as nitrogen is used, the expense may be prohibitive. In either case, the cost of compression that is required by all types of gas at the surface is significant. 
   Another method for lowering bottom hole pressure is by artificially inducing lift to remove fluids from a well by using a jet pump and a power fluid. The use of jet pumps is common in production operations where drilling activity has stopped. In this case, the drill pipe and drill bit have been extracted and a jet pump is lowered into the well on the end of a tubing string. A surface pump delivers high-pressure power fluid down the tubing and through the nozzle, throat, and diffuser of the jet pump. The pressure of the power fluid is converted into kinetic energy by the nozzle, which produces a very high velocity jet of fluid. The drilling and production fluids are drawn into the throat of the jet pump by the stream of high velocity power fluid flowing from the nozzle into the throat of the jet pump. The drilling and production fluids mix with the power fluid as they pass through the diffuser. As the fluids mix, the diffuser converts the high velocity mixed fluid back into a pressurized fluid. The pressured fluids have sufficient energy to flow to the surface through the annulus between the production casing and the tubing that carried the jet pump into the well. 
   While jet pumps are used for removing fluid from a well by lowering down hole pressure in production wells, the advantages of under-balanced drilling would be enhanced significantly if a jet pump could be combined with drilling operations. The jet pump could be employed to achieve under-balanced conditions while the drill string is down in the hole and the drill bit is operating. By using a power fluid such as water, the disadvantages of gas could be avoided altogether thereby increasing safety and decreasing costs. Attempts have been made to place jet pumps into drill bits. However, when the jet pump is placed in the drill bit, the drilling fluid serves a dual purpose and becomes the power fluid before entering the nozzle of the jet pump. When the power fluid and the drilling fluid are one in the same and enter the nozzle of the jet pump, the extreme abrasiveness of the drilling fluid can cause the jet pump to wear out prematurely. 
   Casing jacks are also well known in the art. A casing jack is an apparatus for raising and lowering a casing string suspended in a well bore. Casing jacks are the subject matter of U.S. patent application Ser. No. 09/971,308 entitled “Concentric Casing Jack” as well as U.S. Pat. Nos. 6,019,175 and 6,009,941. Persons skilled in the art are aware of other methods of raising and lowering a casing string in a well bore. As casing jacks are a common piece of equipment used in drilling operations, a need exists for an apparatus and method of inducing under balanced drilling conditions in which the jet pump bladder element is actuated using a casing jack or similar apparatus. 
   What is needed beyond the prior art is a jet pump connected to a concentric casing string that will induce artificial lift while allowing the drill bit to operate independently of the jet pump. What is further needed beyond the prior art is a jet pump connected to a concentric casing string that will keep the power fluid separate from the drilling fluid until after the power fluid has passed through the nozzle of the jet pump. What is still further needed beyond the prior art is a concentric casing jet pump that can be actuated using a casing jack. 
   SUMMARY OF INVENTION 
   A concentric casing actuated bladder element of the jet pump is disclosed that induces artificial lift to remove the drilling and production fluid from a well bore during drilling operations by means of a single or multiple hydraulic jet pumps attached to a concentric string of casing. The invention includes a drill string that passes through the jet pump assembly so that the power fluid is separated from the drilling fluid until it enters the jet pump. The jet pump assembly is joined to a concentric casing string. The jet pump also contains a bladder element that inflates or expands to redirect the flow of the drilling and production fluid from the inner annulus into the jet pump assembly. Vertical displacement of the inner casing string by a casing jack causes the bladder to redirect the flow of drilling fluid from the inner annulus into the jet pump assembly. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: 
       FIG. 1  is a cross-sectional elevation view of the present invention showing the inner casing upper section in the raised position; 
       FIG. 2  is a cross-sectional elevation view of the present invention showing the inner casing upper section in the lowered position; 
       FIG. 3  is a cross-sectional plan view of the present invention taken along line  3 — 3  in  FIG. 1 ; 
       FIG. 4  is a cross-sectional plan view of the present invention taken along line  4 — 4  in  FIG. 1 ; 
       FIG. 5  is a cross-sectional plan view of the present invention taken along line  5 — 5  in  FIG. 1 ; 
       FIG. 6  is a cross-sectional plan view of the present invention taken along line  6 — 6  in  FIG. 1 ; 
       FIG. 7  is a cross-sectional elevation view of a concentric casing jack with the inner casing in the lowered position; and 
       FIG. 8  is a perspective view of the surface equipment typically used to perform drilling operation using the present invention. 
   

   DESCRIPTION OF PREFERRED EMBODIMENT 
   As used herein, the term jet pump means an apparatus having a nozzle, a throat, and a diffuser which transfers energy from a power fluid to a drilling and/or production fluid to artificially lift and remove drilling and produced fluids from a well thereby decreasing the hydrostatic weight of the combined fluid column. As used herein, the term bladder means a device that inflates from a first position into a second position to make contact with a drill string or casing and diverts the return flow of fluids through the jet pump. 
   As seen in  FIG. 1 , the well bore is lined with production casing  102 , which separates outer annulus  140  from the earth. Packer  104  expands to fit production casing  102 . The inner casing is concentric with and has a smaller diameter than production casing  102 . The inner casing comprises inner casing upper section  106 , inner casing middle section  120 , and inner casing lower section  136 . The inner casing extends downwardly from the surface and is affixed to packer  104 . The inner casing and production casing  102  form outer annulus  140 , which extends up to the surface and is closed at the bottom by packer  104 . Outer annulus  140  contains a power fluid, which is pressurized from the surface. Drill string  108  is inserted inside the inner casing and inner annulus  138  is created between drill string  108  and the inner casing. A drilling fluid flows from the surface through the middle of drill string  108  to the bottom of the well bore and then flows upwards through the annular region between drill string  108  and production casing  102 . When the drilling fluid reaches packer  104 , it flows up through inner annulus  138 . 
   Inner casing lower section  136  screws into and extends upwardly from packer  104 . Jet pump inlet  132  comprises a plurality of apertures in inner casing lower section  136 . Chamber wall  130  extends upwardly and outwardly from inner casing lower section  136  and contains chamber  128 . Chamber  128  is a cavity in chamber wall  130  and allows the power fluid in outer annulus  140  to flow through a small aperture in nozzle  134 . Throat  126  is located above nozzle  134 . Throat  126  is the area where the power fluid and the drilling fluid mix when the concentric casing actuated jet pump  100  is utilized. The throat  126  is defined by chamber wall  130  and nozzle  134  on its lower side and by diffuser wall  122  on its upper side. The upper portion of throat  126  leads into diffuser  124  where the combination of drilling fluid and power fluid homogenizes. 
   Diffuser wall  122  is also connected to inner casing middle section  120 . Inner casing middle section  120  contains a cylindrical cavity  118 . A cavity fluid such as water or oil fills cavity  118 . Cavity  118  is defined by inner casing middle section  120  on its bottom side and its outside. Cavity  118  is defined by bladder  116  on its inside. Cavity  118  is defined by cylindrical ram  112  on its upper side. Ram  112  is sized to completely fill cavity  118  when the inner casing is moved into the lowered position. When ram  112  is lowered into cavity  118 , the cavity fluid will deform bladder  116  outwardly into inner annulus  138 . Bladder  116  is held in place by bladder element supports  115 . Jet pump outlets  110  are a plurality of apertures in inner casing upper section  106 , similar to jet pump inlets  132  in inner casing lower section  120 . Inner casing upper section  106  extends upwardly from concentric casing actuated jet pump  100  to the surface. 
   With the inner casing in the raised position, as seen in  FIG. 1 , the drilling fluid bypasses jet pump inlet  132  and continues upwardly through inner annulus  138 . The drilling fluid continues upwardly through jet pump bypass  114  and past jet pump outlets  110 . With the inner casing in the raised position, the drilling fluid will continue upwardly through inner annulus  138  until it reaches the surface. 
   The method of inducing lift to remove drilling and production fluid involves injecting power fluid through a nozzle so that when the power fluid exits the nozzle, a pressure differential is created that draws in drilling and production fluid. The power fluid enters the throat where the power fluid combines with the drilling fluid and the production fluid. When the power fluid combines with the drilling fluid and the production fluid, the high velocity power fluid converts the drilling fluid and production fluid into a combined pressurized fluid called an effluent, which has sufficient energy to flow to the surface. This process reduces the pressure of effluent, by reducing the hydrostatic weight of the fluid column above concentric casing actuated jet pump  100 . The reduction in the hydrostatic weight in turn reduces the pressure in the well bore below concentric casing actuated jet pump and allows the production fluid in the reservoir to flow into well bore. This method of inducing lift can be utilized during the drilling process and is attached to inner casing upper section  106  rather than drill string  108 . 
     FIG. 2  is an illustration of concentric casing actuated jet pump  100  with the inner casing in the lowered position. Ram  112  has filled cavity  118  and displaced the cavity fluid. The displaced cavity fluid deforms bladder  116  such that it contacts drill string  108  and stops the flow of drilling fluid through jet pump bypass  114 . With jet pump bypass  114  blocked, the drilling fluid is forced to enter jet pump inlet  132 . After passing though jet pump inlet  132 , the drilling fluid enters throat  126  and surrounds nozzle  134 . 
   After lowering of the inner casing, a surface pump begins to pump the power fluid into outer annulus  140 . The power fluid circulates down the outer annulus  140  and into chamber  128 . As the power fluid passes through nozzle  134 , its velocity increases. The high speed power fluid then enters throat  126  where it mixes with the drilling fluid and forms the effluent. The effluent passes through the diffuser  124  where the effluent becomes a relatively homogenous mix of drilling fluid, production fluid, drilling fines, and power fluid. The effluent then passes through jet pump outlets  110  and back into inner annulus  138 . The effluent then proceeds to the surface where it is separated by a surface separator. 
     FIG. 3  is a cross-sectional view looking downward at the concentric casing actuated jet pump  100  taken along line  3 — 3  in FIG.  1 . Drill string  108  is shown in the center of FIG.  3 . Jet pump bypass  114  is shown bordered by drill string  108  and bladder element support  115 . Bladder element support  115  is adjacent to ram  112 . Eight diffusers  124  can be seen depicted in the embodiment in FIG.  3 . Diffuser wall  122  separates the diffusers  124  from the outer annulus  140 . Production casing  102  is also shown. 
   In  FIG. 3 , the power fluid flows downward (into the page) through outer annulus  140 . The drilling fluid flows downward through the center on the drill string  108 . The drilling fluid with the drilling fines then flows back up (out of the page) though jet pump bypass  114 . If the inner casing is lowered as depicted in  FIG. 2 , then the effluent would flow upward through diffusers  124 . 
     FIG. 4  is a cross-sectional view looking downward at the concentric casing actuated jet pump  100  taken along line  4 — 4  in FIG.  1 . Drill string  108  is shown in the center of FIG.  4 . Jet pump bypass  114  is shown bordered by drill string  108  and bladder  116 . Bladder  116  separates jet pump bypass  114  and cavity  118 . Inner casing middle section  120  is also shown. Eight diffusers  124  can be seen depicted in the embodiment in FIG.  4 . Diffuser wall  122  separates the diffusers  124  from the outer annulus  140 . Production casing  102  is also shown. 
   In  FIG. 4 , the power fluid flows downward through outer annulus  140 . The drilling fluid flows downward through the center on the drill string  108 . The drilling fluid with the drilling fines then flows back up though jet pump bypass  114 . If the inner casing is lowered as depicted in  FIG. 2 , then the effluent would flow upward through diffusers  124 . 
     FIG. 5  is a cross-sectional view looking downward at the concentric casing actuated jet pump  100  taken along line  5 — 5  in FIG.  1 . Drill string  108  is shown in the center of FIG.  5 . Inner annulus  138  is shown adjacent to drill string  108 . Jet pump inlet  132  allows the drilling fluid to pass from inner annulus  138  to throat  126 . Eight nozzles  134  can be seen depicted in the embodiment in FIG.  5 . Diffuser wall  122  separates throats  126  from the outer annulus  140 . Production casing  102  is also shown. 
   In  FIG. 5 , the power fluid flows downward through outer annulus  140 . The drilling fluid flows downward through the center on the drill string  108 . The drilling fluid with the drilling fines then flows back up though inner annulus  138 . If the inner casing is lowered as depicted in  FIG. 2 , then the drilling fluid would flow upward through jet pump inlet  132  into throat  126 . The high velocity power fluid would also be exiting nozzles  134  in an upwardly direction. 
     FIG. 6  is a cross-sectional view looking downward at the concentric casing actuated jet pump  100  taken along line  6 — 6  in FIG.  1 . Drill string  108  is shown in the center of FIG.  6 . Inner annulus  138  is shown adjacent to drill string  108 . Jet pump inlet  132  allows the drilling fluid to pass from inner annulus  138  to throat  126 . Eight chambers  128  defined by chamber wall  130  can be seen depicted in the embodiment in FIG.  6 . Chamber wall  130  separates chambers  128  from the outer annulus  140 . Production casing  102  is also shown. 
   In  FIG. 6 , the power fluid flows downward through outer annulus  140 . The drilling fluid flows downward through the center on the drill string  108 . The drilling fluid with the drilling fines then flows back up though inner annulus  138 . If the inner casing is lowered as depicted in  FIG. 2 , then the drilling fluid would flow upward through jet pump inlet  132 . The high velocity power fluid would also be flowing upwardly through chamber  128 . 
     FIG. 7  is an illustration of a concentric casing jack. The casing jack is connected to the inner casing upper section  106  and is able to raise and lower the inner casing. Casing jacks are well known in the art as evidenced by U.S. patent application Ser. No. 09/971,308 entitled “Concentric Casing Jack”. Casing jacks are also the subject matter of U.S. Pat. Nos. 6,019,175 and 6,009,941. The casing jack in  FIG. 7  is depicted with the inner casing in the lowered position. 
     FIG. 8  displays the surface equipment that is needed to drill an under balanced well using the present invention. Some of the equipment shown such as drilling derrick  400 , drilling fluid pump  402 , and mud tank/solids control equipment  406  are used in most conventional drilling operations. Other equipment for under balanced drilling, such as four-phase (oil, water, cuttings, and gas) separator  404 , flare stack  405 , oil storage tanks  409 , produced water storage tanks  408 , and drilling fluid storage tanks  407  are also shown. The additional surface equipment needed to operate the present invention is power fluid pump  401  and power fluid filtration equipment  403 . A separate pump is typically used to force the power fluid down outer annulus  140  for two reasons. First, power fluid pump  401  needs to operate at much higher pressures than drilling fluid pump  402 . Second, power fluid  200  needs to be filtered so that it does not prematurely erode nozzles  134  in the jet pump. The drilling fluid  201  that is pumped and circulated down the drill string  108  by drilling fluid pump  402  contains “drilling fines” that are generated from the rock being drilled, hence the name mud, and would not be suitable to pass through a small jet pump nozzle. 
   With respect to the above description then, it is to be realized that the optimum dimensional relationships for the parts of the invention, to include variations in size, materials, shape, form, function and manner of operation, assembly and use, are deemed readily apparent and obvious to one skilled in the art, and all equivalent relationships to those illustrated in the drawings and described in the specification are intended to be encompassed by the present invention.

Summary:
A concentric casing actuated jet pump is disclosed that induces artificial lift to remove the drilling and production fluid from a well bore during drilling operations by means of a single or multiple hydraulic jet pumps attached to a concentric string of casing. The invention includes a drill string that passes through the jet pump assembly so that the power fluid is separated from the drilling fluid until it enters the jet pump. The jet pump assembly is joined to a concentric casing string. The jet pump also contains a bladder element that inflates or expands to redirect the flow of the drilling and production fluid from the inner annulus into the jet pump assembly. Vertical displacement of the inner casing string by a casing jack causes the bladder to redirect the flow of drilling fluid form the inner annulus into the jet pump assembly.