Abstract:
A system and method for creating a controlled geyser well with sustained periodical production includes a cap ( 16 ) which prevents gas from entering a well tubing ( 14 ) while allowing liquid to enter and accumulate in the tubing, means for compressing the gas, and means for injecting the gas in the annulus so that the gas enters the bottom end of the well tubing ( 14 ), thereby creating a controlled geyser effect which blows out most of the liquid residing in the well tubing ( 14 ). The gas being compressed can be a produced gas or a supplied gas

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates generally to systems, apparatuses and methods for bringing to the surface liquids contained in underground reservoirs. Specifically, the invention relates to systems, apparatuses and methods for creating a geyser-type flow and controlling it in such a way as to safely bring to the surface liquids contained in a reservoir. 
         [0002]    A plunger pump reciprocated by a pump jack (or beam pumping unit) is the typical means used to extract liquid hydrocarbons (“oil”) from an underground reservoir when the well can no longer naturally flow. However, pump jacks can have difficulty extracting oil from high gas-oil-ratio (GOR) reservoirs or from wells deeper than 10,000 ft. 
         [0003]    Gas lift is an artificial-lift method used for high production rate wells (Le., typically 2,000 barrels per day or greater) in which gas is injected into the well tubing to reduce the hydrostatic pressure of the liquid column, thereby permitting liquids to enter the tubing at a higher flow rate. Typically, the injected gas is conveyed down the annulus located between the tubing and the well casing and enters the tubing through a series of gas-lift valves located at different depths along the length of tubing. A packer must be positioned at the bottom of the casing-tubing annulus in order to isolate the annulus from the bottom end of the tubing. Gas injection continues as the liquids flow at the desired rate. 
         [0004]    While gas lift is desired in certain down hole applications, “severe slugging” (or “heading”) is not desired in any application. Severe slugging occurs when gas continues to accumulate in a reservoir cavity or in the casing-tubing annulus, with the liquid level rising in the well tubing. As gas pushes down the liquid level in the annulus and enters the tubing, the tubing hydrostatic pressure is reduced, thereby creating a lower downstream pressure. Expansion of the gas then provides the driving force to rapidly expel the liquid, along with the gas, out of the well. 
         [0005]    Because catastrophic consequences to operators and severe damage to downstream facilities can occur during a severe slugging event, professionals in the field take measures to detect severe slugging and prevent it from occurring. This is one reason, for example, why gas lift makes extensive use of valves and chokes to stabilize the injection rate. 
         [0006]    However, severe slugging has properties which can be useful for extracting oil from medium productivity wells (which can produce several hundred barrels per day) and from low productivity wells, such as those commonly labeled as stripper wells. A stripper well is usually defined as any oil or gas well which produces an average of 15 or less equivalent barrels of oil and gas per day. Therefore, a need exists for a system, apparatus and method to intentionally create, and then control in a safe manner, a severe slugging event. 
       SUMMARY OF THE INVENTION 
       [0007]    A system and method according to this invention creates a controlled severe slugging event or eruption (similar as what occurs in a natural geyser) below a liquid residing in the column of a well tubing. 
         [0008]    The eruption or blowout occurs when a compressed gas, which has been accumulated or injected in the annulus located between the tubing and the well casing, exits the bottom end of the annulus and enters the lower end of the well tubing. This greatly reduces the hydrostatic pressure in the tubing and increases the differential pressure, thereby accelerating the upward flow of the liquid residing in the well tubing. After the blowout has occurred, the well is depressurized and the liquid and gas accumulations start again. 
         [0009]    Depending on the depth of the well (e.g. 5,000 feet), the volume of liquid in the column can be substantial. Additionally, the volume of the annulus can accumulate a significant amount of gas, thereby reducing the size requirement of the surface storage vessel or tank used to store or compress the gas. 
         [0010]    A system and method according to this invention creates a controlled severe slugging (or geyser-type) event to expel or blowout liquid residing in a well tubing. The system includes a cap located at the lower end of the well tubing which prevents gas from entering the well tubing during an accumulation of the liquid in the well tubing. (A gap formed between the cap and the bottom end of the tubing permits liquid to enter the tubing.) When the liquid accumulates within the well tubing to a predetermined level, compressed gas is injected into the upper end of the annulus. The injected compressed gas pushes the liquid level down and exits a lower end of the annulus and enters a lower end of the well tubing, thereby reducing the hydrostatic pressure and causing a portion of the liquid residing in the well tubing to rapidly flow upwards and exit (erupt or blowout of) the well tubing. 
         [0011]    At least one control valve communicates with the injection means. At no point in the system or method is the compressed gas injected directly into the well tubing via gas-lift valves or other means. And unlike gas lift, the injecting step stops once the liquid begins to flow upwards. Additionally, no packer is required at the bottom of the casing-tubing annulus. 
         [0012]    The gas may be a gas produced by the reservoir in communication with the well tubing or, in the case of a man-made reservoir (e.g., a water fountain, pond or pool), the gas could be a supplied gas. When the gas is produced by the reservoir, the gas may be allowed to accumulate in the annulus and can be allowed to exit the upper end of the annulus and routed to a storage vessel, a separator vessel, or some combination of the two. The stored gas may then be routed to the gas compressor. Similarly, the produced liquid and gas can be routed to a separator vessel or other downstream processing equipment. 
         [0013]    Objectives of the invention are to: 
         [0014]    1. create a controlled geyser well, either in a natural reservoir formation or in a man-made formation such as a fountain, pond or pool; 
         [0015]    2. take advantage of severe slugging effects by artificially creating and controlling a severe slugging event; and 
         [0016]    3. improve the production of low productivity wells. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a preferred embodiment of a system and method made according to this invention. When submerged in liquid, a cap prevents gas bubbles from entering the lower end of the well tubing. The gas accumulates in the annulus between the well tubing and casing and/or flows to a surface storage vessel where the pressure increases with the gas input. At the same time, oil flows into the tubing through a gap formed between the cap and the bottom end of the well tubing. 
           [0018]      FIG. 2  continues the system and method of  FIG. 1 , showing the oil level in the annulus reaching the bottom end of the tubing as compressed gas is accumulated and/or injected into the annulus. As the compressed gas reaches the bottom of the well tubing, it enters the lower end of tubing. When the gas flows into the tubing, it replaces oil and reduces the fluid mixture density wherein. The hydrostatic pressure in the tubing decreases. 
           [0019]      FIG. 3  continues the system and method of  FIGS. 1-2 , showing that the compressed gas flows faster into the tubing from the annulus due to lower downstream pressure. This further reduces the density of the fluid mixture and the hydrostatic pressure in the tubing, resulting in higher flow rate. At the same time, gas expands and is released from solution in the oil. The high speed flow from the tubing to the separator is similar as the steam-water eruption of a natural thermal geyser. Oil and gas are separated in the separator and are transferred to downstream facilities for further processing. 
           [0020]      FIG. 4  continues the system and method of  FIGS. 1-3 , showing most of the oil being blown out of the tubing by high speed gas flow. This causes the pressure in the storage vessel to get close to the pressure of the separator. The well is depressurized and a new cycle begins. 
           [0021]      FIG. 5  continues the system and method of  FIGS. 1-4 , showing how the lower end of the well tubing can be set at a certain distance from the perforation and free of standing water. 
           [0022]      FIG. 6  shows how the system and method can be used in connection with a vertical or deviated well connected to one or more horizontal sections with section perforations or fractures. 
           [0023]      FIG. 7 . is another preferred embodiment of a system and method made according to this invention and used in connection with a man-made reservoir such as a water fountain, pond or pool. Compressed air pushes water down in the annulus channel, and water flows upward in the riser tube to the water pool. Meanwhile, the pressure in the air tank increases. This pressure equals the hydrostatic pressure due to the water level difference between the water pool and the annulus channel. 
           [0024]      FIG. 8  continues the system and method of  FIG. 7 . The process continues until the water level in the annulus channel reaches the bottom inlet of the riser tube. Air starts to flow into the riser tube which replaces water and reduces the fluid mixture density therein and the hydrostatic pressure in the riser tube decreases. 
           [0025]      FIG. 9  continues the system and method of  FIGS. 7-8 . Compressed air flows faster into the riser tube through the annulus channel due to lower downstream pressure. This further reduces the density of the fluid mixture and the hydrostatic pressure in the riser tube, resulting in higher air flow rate. At the same time, air expands due to the pressure drop. An air-water eruption, similar as the steam-water eruption of a natural thermal geyser, from the riser tube is formed. 
           [0026]      FIG. 10  continues the system and method of  FIGS. 7-9 . After most of the water in the riser tube is swept out by the high speed air flow and the compressed air is exhausted, the pressure in the air tank is close to the atmospheric pressure. Water starts to flow back into the riser tube and the annulus channel, until the pressure in the air tank equalizes with the hydrostatic pressure in the riser tube. Then, a new cycle begins. 
           [0027]      FIG. 11  shows how the casing pipe can be replaced by a tube which connects the air tank to the inlet of the riser tube at the bottom of the well. 
           [0028]      FIG. 12  shows how a down corner can be used for the water to flow back from the top water pool to the bottom of the riser tube. The water flow is regulated with a valve. 
           [0029]      FIG. 13  is yet another preferred embodiment of a system and method according to this invention. The water tank is fully or partially filled with water and a riser tube is connected to the water tank from the top with its inlet extended to near the bottom of the water tank. The riser tube can be set vertically or deviated from vertical to a certain degree. The height of the riser tube determines the strength of the geyser it creates. 
           [0030]      FIG. 14  continues with the system and method of  FIG. 13 . As the water level in the water tank reaches the inlet of the riser tube, water stops flowing into the riser tube and the pressure in the water tank reaches its maximum value. Air then starts to enter the riser tube, thereby replacing water and reducing the fluid mixture density therein. Because of this the hydrostatic pressure in the riser tube decreases and the compressed air in the water tank flows faster into the riser tube. This further reduces the density of the fluid mixture and the hydrostatic pressure in the riser tube, resulting in higher air flow rate. At the same time, air expands due to pressure drop. 
           [0031]      FIG. 15  continues with the system and method of  FIGS. 13-14 . An air-water eruption from the riser tube is formed, similar to the steam-water eruption of a natural thermal geyser. 
           [0032]      FIG. 16  continues with the system and method of  FIGS. 13-15 . The water starts to flow back into the water tank through the riser tube until the pressure in the water tank equalizes again with the hydrostatic pressure in the riser tube. A new cycle begins. 
           [0033]      FIG. 17  is a further variation of the system of  FIG. 13 . At least one down corner can be used for the water to flow back from the top water pool to the water tank and regulated with a valve. 
           [0034]      FIG. 18  is a side view of a preferred embodiment of the cap used to prevent gas from entering the tubing during liquid accumulation. Liquid is allowed to enter the tubing through a gap formed between the cap  16  and the bottom end of the tubing. 
           [0035]      FIG. 19  is a top view of the cap of  FIG. 18 . 
       
    
    
     ELEMENT NUMBERING USED IN THE DRAWINGS AND DETAILED DESCRIPTION 
       [0000]    
       
         Perforations or Fractures  10   
         Casing  12   
         Tubing  14   
         Cap  16   
         Annulus between Casing and Tubing  18   
         Valves  20 ,  26 ,  30 ,  32 ,  36 ,  38   
         Flow Meter  22   
         Gas Tank  24   
         Separator  28   
         Compressor  34   
         Horizontal Wells  40   
         Well  110   
         Riser tube  112   
         Annulus between Casing and Tubing  113   
         Casing pipe  114   
         Air compressor  116   
         Air tank  118   
         Water pool  120   
         Check valve  122   
         Valves  124 ,  130   
         Water supply  126   
         Tube  128   
         Down corner  132   
         Water tank  134   
         Drainage  136   
       
     
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0061]    Referring to the drawings in detail,  FIGS. 1 through 4  illustrate diagrammatic views of one preferred system and method in accordance with the present invention. 
         [0062]    A well is drilled into an oil and gas reservoir. It is then completed with a casing  12  and perforations (or hydraulic fractures)  10  corresponding to the reservoir thickness. A tubing  14  is inserted in the casing  12 , with its bottom end covered with a cap  16  to prevent gas from entering the tubing  14  during liquid accumulation. Liquid is allowed to enter the tubing  14  through a gap formed between the cap  16  and the bottom end of the tubing  14 . The top end of the tubing  14  is connected to a gas-liquid separator  28 . The outer diameter of the tubing  14  is smaller than the inner diameter of the casing pipe  12 , forming an annulus channel or annulus  18  in between. The casing pipe  12  is connected to a gas tank  24 . Under a varying pressure drawdown, oil and gas flow from reservoir into the well. The bottom end of the tubing  14  is submerged by oil. 
         [0063]    As shown in  FIG. 1 , gas bubbles move upward through the oil due to buoyancy and enter the annulus  18 . The cap  16  prevents the gas bubbles from entering the tubing  14 . If the annulus volume is insufficient, gas further flows to the tank  24  where the pressure increases with the gas input. At the same time, oil flows into the tubing  14  through the gap between the cap  16  and the bottom end of the tubing  14 . The increasing oil level creates a hydrostatic pressure at the bottom of the tubing  14  to balance the pressure in the annulus  18 . This process continues until the oil level in the annulus  18  reaches the bottom end of the tubing  14 , as shown in  FIG. 2 . 
         [0064]    At this moment, gas starts to flow into the tubing  14 . The pressure in the gas tank  24  reaches its maximum value, which equals the hydrostatic pressure in the tubing  14  plus the pressure in the separator  28 . When gas flows into the tubing  14 , it replaces oil and reduces the fluid mixture density wherein. The hydrostatic pressure in the tubing  14  decreases. Compressed gas in the gas tank  24  flows into the tubing  14  through the annulus  18  due to lower downstream pressure. This further reduces the density of the fluid mixture and the hydrostatic pressure in the tubing  14 , resulting in higher gas flow rate. At the same time, gas expands and is released from solution in oil due to the pressure drop. 
         [0065]    A high speed flow from the tubing  14  to the separator  28  is formed (as shown in  FIG. 3 ), similar as the steam-water eruption of a natural thermal geyser. Oil and gas are separated in the separator  28  and are transferred to downstream facilities for further processing. 
         [0066]    After most of the oil in the tubing  14  is blown out by the high speed gas flow and the compressed gas is exhausted, the pressure in the gas tank  24  is close to the pressure in the separator  28 . Oil film on the tubing inside wall starts to fall back and the tubing bottom end is again blocked by oil, as shown in  FIG. 4 . A new cycle begins. 
         [0067]    The blowout can be controlled by valves  20  and  26 . If the produced gas exceeds the need for blowout, it can be released to the separator  28  through valve  32 . If the produced gas is not sufficient, gas from the previous blowout may be recycled by a compressor  34  which draws the gas from the separator  28  and charges the gas into the gas tank  24  with a higher pressure. 
         [0068]    As shown in  FIG. 5  when free water exists in the reservoir, the tubing  14  may be set with its bottom end at a certain distance from the perforation  10 . This helps separate oil from water and produce less water. 
         [0069]    As shown in  FIG. 6 , a vertical or deviated well  12  can also be connected to one or more horizontal sections  40  with section perforations or fractures. A down extension of the well  12  from the perforation can contain the produced solid particles by gravitational separation. 
         [0070]    Referring now to  FIGS. 7 through 12 , another preferred embodiment of a system and method in accordance with the present invention does not rely upon a produced gas in order to create the eruption. 
         [0071]    A well  110  is drilled into a depth required to form the desired geyser eruption height. A casing pipe  114  with closed bottom end is inserted to the bottom of the well  110 . A riser tube  112  is inserted in the casing pipe  114 , with its bottom end extended to near the casing pipe  114  bottom and its top end connected to a water pool  120 . The outer diameter of the riser tube  112  is smaller than the inner diameter of the casing pipe  114 , forming an annulus channel  113  in between. The casing pipe  114  is connected to an air tank  118  which is charged with air by an air compressor  116 . Compressed air flows from the air tank  118  into the annulus channel  113  between the casing pipe  114  and the riser tube  112 . A check valve  122  may be used to prevent water flowing back into the air tank  118 . 
         [0072]    As shown in  FIG. 7 , compressed air pushes water down in the annulus channel  113 , and water flows upward in the riser tube  112  to the water pool  120 . Meanwhile, the pressure in the air tank  118  increases. This pressure equals the hydrostatic pressure due to the water level difference between the water pool  120  and the annulus channel  113 . 
         [0073]    This process continues until the water level in the annulus channel  113  reaches the bottom inlet of the riser tube  112 , as shown in  FIG. 8 . At this moment, water stops flowing into the riser tube  112 . The pressure in the air tank  118  reaches its maximum value which equals the hydrostatic pressure in the riser tube  112 . Air starts to enter the riser tube  112 . When air flows into the riser tube  112 , it replaces water and reduces the fluid mixture density therein. The hydrostatic pressure in the riser tube  112  decreases. Compressed air in the air tank  118  flows faster into the riser tube  112  through the annulus channel  113  due to lower downstream pressure. This further reduces the density of the fluid mixture and the hydrostatic pressure in the riser tube  112 , resulting in higher air flow rate. At the same time, air expands due to the pressure drop. 
         [0074]    An air-water eruption from the riser tube  112  is formed (as shown in  FIG. 9 ), similar as the steam-water eruption of a natural thermal geyser. Water erupted from the riser tube  112  is contained with a shallow pool  120 . The lost water can be compensated by a water supply line  126  and a valve  124 . 
         [0075]    After most of the water in the riser tube  112  is swept out by the high speed air flow and the compressed air is exhausted, the pressure in the air tank  118  is close to the atmospheric pressure. Water starts to flow back into the riser tube  112  and the annulus channel, as shown in  FIG. 10 , until the pressure in the air tank  18  equalizes with the hydrostatic pressure in the riser tube  112 . Then, a new cycle begins. 
         [0076]    As shown in  FIG. 11 , the casing pipe  114  can be replaced by a tube  128 , which connects the air tank to the inlet of the riser tube  112  at the bottom of the well  110 . 
         [0077]    A further variation of this process is shown in  FIG. 12 . A down corner  132  can be used for the water to flow back from the top water pool  120  to the bottom of the riser tube  112 . The water flow is regulated with a valve  130 . The top end of the riser tube  112  is above the water level in the water pool  120 , so that water cannot flow back to the riser tube  112 . The tube  128  connection to the riser tube  112  must be higher than the water down corner  132  connection to the riser tube  112 , so that compressed air cannot flow into the down corner  132 . 
         [0078]    In one non-limiting example of an application of this preferred process, a well, such as a four-inch (10.16 cm) hole diameter well, is drilled to a required depth, for example, 150 feet (45.72 m). A 4-inch (10.16 cm) casing pipe with its tip sealed is inserted into the well. A three-inch (7.62 cm) riser tube is inserted into the casing pipe to near its bottom. A 20 cubic feet (about 0.57 m 3 ) air tank is connected to the top of the annulus channel formed between the riser tube and the casing pipe. A 100 psi (about 690 kpa) and 3 cubic feet per minute (about 0.085 m 3 /min) air compressor is used to charge the air tank. The shallow water pool can be set on the ground to contain the erupted water. 
         [0079]    An alternate preferred process is illustrated in  FIGS. 13 through 17 . Water tank  134  is fully or partially filled with water. A riser tube  112  is connected to the water tank  134  from the top with its inlet extended to near the bottom of the water tank  134 . The riser tube  112  can be set vertical or deviated from vertical to a certain degree. The height of the riser tube  112  determines the strength of the geyser it creates. 
         [0080]    As shown in  FIG. 13 , compressed air is charged by an air compressor  116  into the water tank  134 . A check valve  122  may be used to prevent back flow. Pressure inside the water tank  134  increases and water level in the riser tube  112  rises. The hydrostatic pressure caused by the liquid level difference between the riser tube  112  and the water tank  134  equals the static pressure inside the water tank  134 . 
         [0081]    This process continues until the water level in the water tank  134  reaches the inlet of the riser tube  112 , as shown in  FIG. 14 . Then, water stops flowing into the riser tube  112 . The pressure in the water tank  134  reaches its maximum value. Air starts to enter the riser tube  112 . As air flows into the riser tube  112 , it replaces water and reduces the fluid mixture density therein. The hydrostatic pressure in the riser tube  112  decreases. The compressed air in the water tank  134  flows faster into the riser tube  112  due to the lower downstream pressure. This further reduces the density of the fluid mixture and the hydrostatic pressure in the riser tube  112 , resulting in higher air flow rate. At the same time, air expands due to pressure drop. 
         [0082]    An air-water eruption from the riser tube  112  is formed (shown in  FIG. 15 ), similar as the steam-water eruption of a natural thermal geyser. The water is contained with a shallow pool  120  at the top of the riser tube  112 . After most of the water in the riser tube  112  is swept out by the high speed air flow and the compressed air is exhausted, the pressure in the water tank  134  is almost equal to the atmospheric pressure. The water starts to flow back into the water tank  134  through the riser tube  112 , as shown in  FIG. 16 , until the pressure in the water tank  134  equalizes again with the hydrostatic pressure in the riser tube  112 . Then, a new cycle begins. 
         [0083]    The lost water can be compensated by a water supply line  126  and a valve  124 . Excessive water due to rain or snow accumulated by the top pool can be drained through the drainage line  136 . 
         [0084]    A further variation of this process is shown in  FIG. 17 . At least one down corner  132  can be used for the water to flow back from the top water pool  120  to the water tank  134  and regulated with a valve  130 . The top of the riser tube  112  is above the water level in the water pool  120 , so that water cannot flow back to the water tank  134  through the riser tube  112 . The bottom end of the down corner  132  must be lower than the inlet of the riser tube  112 , so that compressed air cannot enter the down corner  132 . 
         [0085]    In one non-limiting example of an application of this preferred process, a three barrel (3 bbl) water tank is filled with 2 bbl water. A three-inch (7.62 cm) inner diameter and 100 foot (30.48 m) long riser tube is inserted to near the bottom of the water tank where the majority of water is above the inlet of the riser tube. The riser tube can be set up in vertical or near vertical position on a hill side or along a building. A 60 psi (about 414 kpa) and 3 cubic feet per minute (about 0.085 m 3 /min) air compressor can be used to charge the water tank. The shallow water pool can be set up on the top of a hill or a building to contain the erupted water. 
         [0086]    While the invention has been described with a certain degree of particularity, modifications may be made in the details of construction and the arrangement of components and steps without departing from the spirit and scope of this disclosure. Therefore, the invention is limited by the following claims and not limited to the embodiments presented here for the purpose of explaining the system and method.