Abstract:
A Down Hole Drilling Assembly (DHDA) that induces artificial lift to remove the drilling fluid from a well bore using a jet pump attached to a casing string. The DHDA includes a drill string that passes through the jet pump assembly. The power fluid is separated from the drilling fluid until after it has passed through the nozzle of the jet pump. The jet pump assembly is joined to a concentric casing string. The jet pump also contains a bladder element that expands to redirect the flow of the drilling fluid from the inner annulus into the jet pump assembly. The jet pump assembly lifts the drilling fluid, lowering the fluid level within a well bore to a point where the hydrostatic pressure near the bottom of the well is lower than the pore pressure of the formation being drilled thereby creating under balanced conditions.

Description:
FIELD OF INVENTION 
   The present invention relates 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 hole that is being drilled. 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 weight to prevent 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 from the reservoir being drilled 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 a 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 called 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 pressures contained within the pores of the rock formation being drilled, 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. 
   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. 
   SUMMARY OF INVENTION 
   The invention that meets the needs identified above is a Down Hole Drilling Assembly (DHDA) for inducing artificial lift of the drilling and formation fluid by means of a hydraulic jet pump attached to a concentric casing string and a drill string including a drill bit and drill string that passes through the jet pump. In this design, the drilling fluid and production fluid do not mix with the power fluid until after the power fluid has passed through the nozzle of the jet pump. The jet pump is joined to an inner casing section of a concentric casing string. The jet pump consists of a nozzle, a throat, and a diffuser. The jet pump assembly also contains a bladder that inflates to redirect the flow of drilling fluid from the inner annulus to the throat of the jet pump. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a view of the preferred embodiment of the CCJP and (DHDA) showing the un-inflated bladder. The inflated bladder position is indicated by the dashed line. 
       FIG. 2  is a cross-sectional view of the preferred embodiment of CCJP and (DHDA) taken along line  2 — 2  in  FIG. 1  showing the jet pumps, drilling fluid chambers, inner annulus, and the outer annulus. 
       FIG. 3  is a cross-sectional view of the preferred embodiment of DHDA taken along line  3 — 3  in  FIG. 1  showing the jet inlet, drilling fluid chambers, inner annulus, and the outer annulus. 
       FIG. 4  is a cross-sectional view of the preferred embodiment of DHDA taken along line  4 — 4  in  FIG. 1  showing the bladder elbow, bladder housing, drilling fluid chamber, inner annulus, outer annulus, and drill string. 
       FIG. 5  is a cross-sectional view of the preferred embodiment of DHDA taken along line  5 — 5  in  FIG. 1  showing the bladder, bladder inlet, bladder elbow, bladder tube, inner annulus, outer annulus, and drill string. 
       FIG. 6  is a view of the preferred embodiment of the DHDA taken along line  6 — 6  in  FIG. 2  showing the inflated bladder and the extension of the drilling fluid chambers to the pump chamber. 
       FIG. 7  is an alternative embodiment of the DHDA showing the unitary construction of the pumps and pump housing. 
       FIG. 8  is a cross-sectional view of the alternative embodiment of DHDA taken along line  8 — 8  in  FIG. 7  showing the jet nozzle, diffuser, pump chamber, inner annulus, and outer annulus. 
       FIG. 9  is a detail view of the DHDA showing the jet pump, throat, and diffuser. 
       FIG. 10  is a cross section of an alternative embodiment of CCJP DHDA in which the drilling fluid chamber inside wall and drilling fluid chamber outside wall act as the diffuser. 
       FIG. 11  is a depiction of the surface equipment used to operate the DHDA. 
   

   DESCRIPTION OF PREFERRED EMBODIMENT 
   As seen in  FIG. 1 , well bore  160  is lined with production casing  120 , which separates outer annulus  210  from earth  130 . Packer  140  expands to fit production casing  120 . Inner casing  150  is concentric with and has a smaller diameter than production casing  120 . Inner casing  150  extends downwardly from the surface and is affixed to packer  140 . Inner casing  150  and production casing  120  form outer annulus  210 , which extends up to the surface and is closed at the bottom by packer  140 . Outer annulus  210  contains power fluid  100 , which is pressurized from the surface. Drill string  110  is inserted inside inner casing  150  and inner annulus  230  is created between drill string  110  and inner casing  150 . Drilling fluid  101  flows from the surface through the middle of drill string  110  to the bottom of well bore  160  and then flows upwards through the annular region between drill string  110 , and production casing  120 . When drilling fluid  101  reaches packer  140 , it flows up through inner annulus  230 . The flow of drilling fluid  101  can be reversed between drill string  110  and inner annulus  230 . 
   DHDA  300  is affixed to inner casing  150  and positioned above packer  140 . 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 production fluid to artificially lift and remove drilling and produced fluids from a well thereby decreasing the hydrostatic weight of the combined fluid column in the annulus between the concentric casing string and drill pipe above the jet pump. Drilling fluid inlet housing  310  screws onto and extends up and out from inner casing  150 . Drilling fluid inlet housing  310  has approximately the same inside diameter as inner casing  150  so that drilling fluid  101  may continue to flow up to the surface through inner annulus  230  if desired. Drilling fluid inlet housing  310  also contains drilling fluid inlet  240 , which is an aperture in drilling fluid inlet housing  310  that allows drilling fluid  101  to flow into drilling fluid chamber  242 . Drilling fluid chamber  242  is an annular region that allows drilling fluid  101  to flow from drilling fluid inlet  240  to pump chamber  216 . 
   As seen in  FIG. 4 , drilling fluid chamber  242  is defined on its outside by drilling fluid chamber outer wall  312 , which screws onto and extends up from drilling fluid inlet housing  310 . Drilling fluid chamber  242  is defined along its inside by bladder housing  318 , drilling fluid chamber inner wall  314 , and pump housing  320 . Drilling fluid chamber inner wall  314  extends up along drilling fluid chamber  242  and is welded to bladder housing  318 . Bladder housing  318  holds bladder  316  in place and consists of a pair of cylinders at the upper and lower end of bladder  316 , which have the same outer diameter as the inside wall of drilling fluid chamber inner wall  314 . 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 and divert the return flow of fluids through the jet pump. The lower cylinder of bladder housing  318  is welded to drilling fluid inlet housing  310 . The upper cylinder of bladder housing  318  is welded to the inside wall of drilling fluid chamber inner wall  314 . 
   Bladder  316  is cylindrical and interlocks with bladder housing  318 . Bladder  316  has the same outer diameter as the inside wall of drilling fluid chamber inner wall  314 . Bladder  316  is made of an expansive material, such as rubber, that expands inwardly from drilling fluid chamber inner wall  314  to drill string  110  when inflated. Bladder tube  332  is screwed into drilling fluid inlet housing  310 . Bladder tube  332  extends up through drilling fluid chamber  242  and is screwed into bladder elbow  334 . Bladder elbow  334  is welded to drilling fluid chamber inner wall  314 . As seen in  FIGS. 1 and 5 , bladder inlet  222  allows power fluid  100  to flow through drilling fluid chamber inner wall  314  between bladder elbow  334  and bladder  316 . Power fluid  100  flows from outer annulus  210  through bladder tube  332 , bladder elbow  334 , and bladder inlet  222  to bladder  316 . As the pressure of power fluid  100  increases, power fluid  100  will fill bladder fill zone  224  and bladder  316  will expand until it contacts drill string  110 . When bladder  316  contacts drill string  110 , bladder  316  diverts the flow of drilling fluid  101  within inner annulus  230  and forces drilling fluid  101  to flow through drilling fluid inlet  240  into drilling fluid chamber  242 . 
   As seen in  FIG. 2 , pump housing  320  screws onto both drilling fluid chamber inner wall  314  and drilling fluid chamber outer wall  312 . Drilling fluid chamber  242  splits into four sections as it extends up through pump housing  320  as seen in FIG.  6 . Drilling fluid  101  flows up through drilling fluid chamber  242  and enters pump chamber  216 . Pump chamber  216  is an annular region defined on the inside by pump  322  and on the outside by pump housing  320 . Drilling fluid  101  in pump chamber  216  surrounds pump  322  and is pulled into throat  217  by power fluid  100  exiting pump nozzle  214 . 
   As seen in  FIG. 3 , pump housing  320  contains four pump inlets  212  which allow power fluid  100  to flow from outer annulus  210  to pump  322 . DHDA  300  contains four pumps  322 , which screw into pump housing  320 . Each pump  322  is cylindrical in shape and has pump nozzle  214  fixedly joined to the upper end of pump  322 . Pump nozzle  214  is conical in shape, having an aperture at its apex to let power fluid  100  flow from pump  322  into throat  217 . 
   As seen in  FIG. 9 , power fluid  100  and drilling fluid  101  mix together in throat  217  to form effluent  102 . Effluent  102  flows up through throat  217  and enters diffuser  218 . Diffuser  218  is a conical aperture in diffuser housing  324  which screws into pump housing  320 . Effluent  102  flows up from diffuser  218  and into effluent chamber  244 . Effluent chamber  244  is an annular region defined on its outside by inner casing adapter  326  and on its inside by drill string  110 . Inner casing adapter  326  screws onto pump housing  320  and inner casing  150 . Effluent  102  flows up from effluent chamber  244  into inner annulus  230  and continues to the surface. 
   CCJP and (DHDA)  300  operates as described only when bladder  316  is inflated as indicated in FIG.  6 . When bladder  316  is not inflated, drilling fluid  101  will flow up through inner annulus  230  instead of into drilling fluid inlet  240 . When the pressure of power fluid  100  is increased to expand bladder  316  to fit against drill string  110 , drilling fluid  101  will no longer be allowed to flow up through inner annulus  230 , and will instead be forced into drilling fluid inlet  240 . As seen in  FIG. 10 , an alternate embodiment of DHDA  300  is shown where bladder tube  332  extends up and pump  322  is combined with drilling fluid inlet  240 . The alternate embodiment in  FIG. 10  is advantageous because of the reduction in the number of parts required. Further alternative embodiments are also possible by forming parts of DHDA  300  with unitary construction. In  FIG. 7 , jet pump  322  and pump housing  320  are unitary. Moreover, the number of jet pumps should not be limited to number depicted in the preferred embodiment.  FIG. 8  is an alternative embodiment of DHDA  300  which utilizes six jet pumps.  FIG. 8  is also a view of the top of the jet pump looking down the diffuser showing the jet pump nozzle, throat, and diffuser. 
   The method of inducing lift to remove drilling and production fluid  101  involves injecting power fluid  100  through a nozzle so that when the power fluid exits the nozzle a pressure differential is created that draws in drilling and production fluid  101 . The power fluid enters the diffuser 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 to a combined pressurized fluid that now has the energy to flow to the surface. This process reduces the pressure of effluent  102 , by reducing the hydrostatic weight of the fluid column above DHDA  300 . The reduction in the hydrostatic weight in turn reduces the pressure in well bore  160  below DHDA  300  and allows the production fluid in the reservoir to flow into well bore  160 . This method of inducing lift can be utilized during the drilling process and is attached to inner casing  150  rather than drill string  110 . 
     FIG. 11  displays the surface equipment that is needed to drill an under balanced well using the concentric jet pump. 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 concentric jet pump is power fluid pump  401  and power fluid filtration equipment  403 . A separate pump is needed to force power fluid  100  down the annulus. Drilling fluid pump  302  cannot be used for two reasons. First, power fluid pump  401  needs to operate at much higher pressures than drilling fluid pump  402 . Second, power fluid  100  needs to be filtered so that it does not prematurely erode the nozzles in (DHDA  300 . Drilling fluid  101  that is pumped and circulated down drill string  110  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.