Patent Publication Number: US-6983802-B2

Title: Methods and apparatus for enhancing production from a hydrocarbons-producing well

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to methods and apparatus for enhancing the production of hydrocarbons from a well, and in a particular, preferred context of use to methods and apparatus for producing low pressure gas wells containing water. 
   2. Description of the Prior Art 
   The usefulness of the present invention is probably best illustrated with reference to this preferred, non-limiting context of use. In this regard, gas producing formations often experience significant water encroachment as the gas is produced thereby reducing the gas formation pressure. The water builds up in the well bore penetrating the formation and eventually prevents the low pressure gas remaining from being produced. In order to return the gas formations containing low pressure gas and water to production, the water is artificially lifted to the surface thereby allowing the gas to be produced. The low formation pressure in most of the water-containing gas formations does not allow the use of artificial gas lift and plunger lift. The use of conventional rod pumping units is generally difficult due to the well depths and amounts of water that must be lifted. Mechanical and corrosion problems contribute to making the use of rod pumping units difficult. 
   A preferred form of artificial lift that has been used for low pressure water-containing gas wells utilizes an electrical submersible pump. A significant number of electrical submersible pumps are presently being used for producing low pressure gas wells containing water. However, due to the continuing decrease in water volumes in some of the gas fields utilizing electrical submersible pumps, the pumped water has fallen below the electrical submersible pump operating design. As a result, the electrical submersible pumps have often failed. 
   Thus, there are continuing needs for methods of reducing failures of electrical submersible water pumps in wells where the amounts of water produced by the wells have become substantially diminished. 
   SUMMARY OF THE INVENTION 
   The present invention provides methods and apparatus for producing low pressure gas wells containing water utilizing electrical submersible pumps which meet the needs described above and overcome the deficiencies of the prior art. Essentially the same methods and apparatus can, however, be adapted to address a number of other production-limiting issues in hydrocarbon-producing wells generally, including for example the formation of gas hydrates, high viscosities in crude oil production and paraffin buildup. 
   Accordingly, from a broader perspective the present invention provides methods and apparatus for enhancing production from a hydrocarbons-producing well, characterized in that an electrical submersible pump is attached to the bottom end of a string of pipe joints or tubing and is placed in the well bore (by means of such string) below a hydrocarbons-producing interval. Thereafter, a liquid comprising crude oil or water is flowed from the surface through a string of pipe joints or tubing to a point below the hydrocarbons-producing interval, whereupon the liquid exits the string and is joined with a liquid comprising oil, water or both from the hydrocarbons-producing interval. The combined liquids are then pumped to the surface by the electrical submersible pump. 
   A method of this invention for producing a water-containing gas interval in a subterranean formation penetrated by a well bore uses water as the liquid that is supplied from the surface, whereby with low gas formation pressures sufficient water is continuously made available to the pump to prevent pump overheating and subsequent failure leading to water build-up in the well bore that reduces or prevents gas production from the water-containing gas interval, and/or whereby water containing chemical treatments for the prevention of gas hydrates, corrosion, scale and the like may be supplied. A method for producing hydrocarbons including a high viscosity crude oil component would use a lighter, less viscous crude oil as the liquid supplied from the surface to improve the recovery of the formation crude oil, while paraffin buildup can be addressed by the method of the invention by using heated oil or heated water. 
   An apparatus of this invention for producing hydrocarbons from an interval in a subterranean formation penetrated by a well bore includes the following components. An electrical submersible pump is attached to the bottom end of a string of pipe joints or tubing extending in the well bore from the surface to below the hydrocarbons-producing interval. A surface source of a liquid comprising crude oil or water is connected to a string of pipe joints or tubing at the surface for supplying and controlling a flow of the liquid through the string into the well bore to below the interval, so that the liquid is combined with a liquid comprised of oil, water or both from the interval and the combination is pumped by the electrical submersible pump to the surface and to a storage or disposal location thereon. 
   The objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of preferred embodiments which follows. 

   
     DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side, partially sectional view of a cased and perforated well bore penetrating a low pressure water-containing gas interval including an electrical submersible pump attached to the bottom end of a string of pipe joints or tubing having one or more openings therein at a bottom end for providing water from the surface, and to a further string of pipe joints or tubing for conveying water via the pump to the surface. 
       FIG. 2  is a cross-sectional view taken along line  2 — 2  of  FIG. 1 . 
       FIG. 3  is a cross-sectional view taken along line  3 — 3  of  FIG. 1 . 
       FIG. 4  is a side view of a portion of the casing  11  extending above the surface and the first and second strings of pipe joints or tubing  16  and  18  extending therefrom, the first string  16  (corresponding to the string supplying water from the surface) having a flow meter  28  disposed therein in association with a valve  22  and the second string  18  (for conveying water to the surface) having a flow meter  26  disposed therein. 
       FIG. 5  is a side, partially sectional view of the cased and perforated well bore penetrating a low pressure water-containing gas interval shown in  FIG. 1 , but with the first string of pipe joints or tubing  16  positioned outside of the second string of pipe joints or tubing  18 . 
       FIG. 6  is a cross-sectional view taken along line  6 — 6  of  FIG. 5 . 
       FIG. 7  is a cross-sectional view taken along line  7 — 7  of  FIG. 5 . 
   

   DESCRIPTION OF PREFERRED EMBODIMENTS 
   The present invention provides methods of producing low pressure water-containing gas intervals in subterranean formations penetrated by well bores whereby gas production-limiting water level build-up or loss of water level in the well bores does not occur. The methods are basically comprised of the following steps. An electrical submersible pump attached to the bottom end of a string of pipe joints or tubing is placed in the well bore below the water-containing gas interval. The same string of pipe joints or tubing extends to the surface whereby water pumped by the electrical submersible pump is conducted to a storage or disposal location. A further string of pipe joints or tubing is placed in the well bore having one or more openings therein at the bottom end thereof, which string also extends below the water-containing gas interval. Water from the surface is flowed through the further string of pipe joints or tubing so that the water exits the string of pipe joints or tubing and is pumped by the electrical submersible pump along with water from the water-containing gas interval to the surface, with the flow of water from the surface being adjusted so that the electrical submersible pump constantly pumps sufficient water to prevent pump overheating due to the lack of water and while the water level in said well bore is maintained below the water-containing gas interval. 
   The well bore preferably includes casing therein and is perforated in the water-containing gas interval. The respective conduit strings for removing water to the surface and for supplying needed additional water can be strings of pipe joints or tubing, for example, coil tubing, small screw tubing or the like. The second, fluid return string of pipe joints or tubing (item  18  in the drawings) conventionally will be sized to accommodate a greater flow of liquid (e.g., water) than the first, surface fluid supply string (item  16 ) of pipe joints or tubing, as liquid from the formation will be added in the second string. 
   Referring now to the drawings and particularly  FIGS. 1 through 3 , a first preferred embodiment of the apparatus of the invention is illustrated. In  FIG. 1  particularly, a bottom portion of a cased and perforated well bore  10  penetrating a low pressure water-containing gas interval  12  is illustrated. Disposed within the casing  11  that contains perforations  20  is an electrical submersible pump  14  attached to and in fluid communication with the bottom end of a second, fluid return string of pipe joints or tubing  18 , preferably coil tubing. The electrical submersible pump  14  is connected to a source of electrical power at the surface by a power cable (not shown). As shown in  FIGS. 1 through 3 , the electrical submersible pump  14  includes a shroud  15  having an opening  17  at the bottom end thereof through which water from the interior of the well bore  10  flows and is pumped by the pump  14  into the second string of pipe joints or tubing  18 . The string of pipe joints or tubing  18  extends from the electrical submersible pump  14  to the surface (not shown). The electrical submersible pump  14  is positioned in the well bore  10  below the water-containing gas interval  12 . 
   A first string of pipe joints or tubing  16  having one or more openings therein at the bottom end thereof is also disposed in the well bore for carrying fluid from the surface into the well bore below the interval  12 . In the arrangement shown in  FIGS. 1 through 3  of the drawings, the first string of pipe joints or tubing  16  is preferably a string of production tubing and the second string of pipe joints or tubing  18  is preferably coil tubing disposed within the first string of pipe joints or tubing  16 . As shown in  FIG. 1 , the bottom end of the first string of pipe joints or tubing  16  can be attached to the electrical submersible pump  14  to thereby maintain the second string of pipe joints or tubing  18  in a central position within the string of pipe joints or tubing  16 . 
   In a second or alternate preferred embodiment of the apparatus of the present invention as shown in  FIGS. 5 through 7 , the first string of pipe joints or tubing  16  can be located outside the second string of pipe joints or tubing  18  and can be unattached to the electrical submersible pump  14 . In the arrangement shown in  FIGS. 5 through 7 , the second string of pipe joints or tubing  18 , preferably tubing, is attached to the electrical submersible pump  14  as shown. The first string of pipe joints or tubing  16 , preferably pipe joints, is open ended and not attached to the pump  14  (but is preferably banded to the second string  18  and to the power cable (not shown)). The electrical submersible pump  14  and the lower open end of the first string of pipe joints or tubing  16  are positioned below the water-containing gas interval. As will be understood by those skilled in the art, the strings of pipe joints or tubing  16  and  18  can be formed of pipe strings, tubing or other conduits formed of different materials. 
   As mentioned above, the casing  10  and the water-containing gas interval  12  contain a plurality of perforations  20  through which gas and water flow into the well bore. The water flows downwardly in the well bore as shown by the arrows into the bottom portion of the well bore and the gas flows upwardly in the well bore as shown by the arrows to the surface. 
   In operation, water from the surface is flowed through the first string of pipe joints or tubing  16  so that the water exits the string of pipe joints or tubing  16  below the water-containing gas interval  12 . The water flowed from the surface through the first, surface fluid supply string of pipe joints or tubing  16  is pumped by the electrical submersible pump  14  along with water that enters the well bore from the water-containing gas interval  12  to the surface. Thus, the electrical submersible pump  14  constantly pumps sufficient water to prevent pump overheating due to the lack of water and to prevent water build-up in the well bore that reduces or prevents gas production. 
   The flow rate of water supplied through the first string of pipe joints or tubing  16  is controlled so that the water pumped through the second, fluid return string of pipe joints or tubing  18  by the electrical submersible pump  14  is generally maintained at a rate whereby the water level in the well bore is below the water-containing gas interval  12 . As shown in  FIG. 4 , this control can be accomplished manually by opening or closing a valve  22  in a water line  24  on the surface connected to the first string of pipe joints or tubing  16  based on the reading of a flow meter  26  disposed in the second, fluid return string of pipe joints or tubing  18  at the surface. A second flow meter  28  can be disposed in the line  24 . As is well understood by those skilled in the art, the flow of water through the first, surface fluid supply string of pipe joints or tubing  16  can optionally be controlled automatically by a control valve and flow controller (not shown) in combination. 
   Thus, the apparatus for producing a low pressure water-containing gas interval in a subterranean formation penetrated by a well bore may be generally summarized as follows. An electrical submersible pump is attached to and in fluid communication with the bottom end of a string of pipe joints or tubing extending in the well bore from the surface to below the water-containing gas interval, whereby water can be pumped to the surface from the well bore by means of such string. A further string of pipe joints or tubing having one or more openings therein at the bottom end thereof also extends in the well bore from the surface to below the water-containing gas interval, and is used to supply water from the surface into the well bore. Means are provided at the surface in association with these strings of pipe joints or tubing for supplying and controlling the flow of water from the surface to below the water-containing gas interval. This flow is controlled so that the supplied water along with water from the water-containing gas interval is constantly pumped by the electrical submersible pump to the surface and to a storage or disposal location thereon at a sufficient rate to prevent the electrical submersible pump from overheating due to lack of water and to prevent water build-up in the well bore that reduces or prevents gas production. 
   The methods and apparatus of this invention can also be used to lift iron-sulfide complex solids to the surface formed as a result of the production of sour gas (H 2 S) from the water-containing gas interval. The iron-sulfide complex solids that normally accumulate in the well bore are lifted to the surface as a result of the high water rates made possible by the present invention. 
   The methods and apparatus of this invention can also be used to inject aqueous or hydrocarbon liquids containing various chemical treatment additives into the well bore such as chemicals for inhibiting one or more of corrosion, scale or the formation of gas hydrates. Also, light oil such as a less viscous crude oil can be circulated through the well bore to cut viscous crude oil therein and/or heated water or heated oil can be circulated to prevent paraffin build-up. 
   A preferred method of this invention for enhancing production from a hydrocarbons-producing interval in a subterranean formation penetrated by a well bore comprises the steps of:
         (a) placing an electrical submersible pump attached to and in fluid communication with the bottom end of a string of pipe joints or tubing in said well bore below said interval; and   (b) flowing a liquid comprising crude oil or water from the surface through a string of pipe joints or tubing in said well bore to below said interval whereby the liquid exits said string and combines with a liquid comprising oil, water or both produced from said interval; and   (c) pumping the combined liquids to the surface through said string of pipe joints or tubing attached to said electrical submersible pump by means of said electrical submersible pump.       

   A preferred method of this invention for producing a low pressure water-containing gas interval in a subterranean formation penetrated by a well bore whereby production-limiting water level build-up or loss of water level in the well bore does not occur, comprises the steps of: (a) placing an electrical submersible pump attached to and in fluid communication with the bottom end of a string of pipe joints or tubing in the well bore below the water-containing gas interval, the string of pipe joints or tubing extending to the surface whereby water pumped by the electrical submersible pump is conducted to a storage or disposal location; (b) placing a further string of pipe joints or tubing in the well bore having one or more openings therein at the bottom end thereof, the bottom end of this string of pipe joints or tubing extending below the water-containing gas interval; and (c) flowing sufficient water from the surface through the further string of pipe joints or tubing so that the water exits the string of pipe joints or tubing and is pumped by the electrical submersible pump along with water from the water-containing gas interval at a rate whereby the electrical submersible pump does not overheat due to a lack of water and whereby water build-up in the well bore that reduces or prevents gas production from the water-containing gas interval does not occur. 
   A preferred apparatus of this invention for producing a low pressure water-containing gas interval in a subterranean formation penetrated by a well bore comprises:
         an electrical submersible pump attached to and in fluid communication with the bottom end of a string of pipe joints or tubing extending in the well bore from the surface to below the water-containing gas interval;   a further string of pipe joints or tubing having one or more openings therein at the bottom end thereof extending in the well bore from the surface to below the water-containing gas interval;   means associated with the strings of pipe joints or tubing at the surface for supplying and controlling a flow of water from the surface to below the water-containing gas interval so that the supplied water along with water from the water-containing gas interval is constantly pumped by the electrical submersible pump to the surface and to a storage or disposal location thereon at a rate sufficient to prevent the electrical submersible pump from overheating due to a lack of water and to prevent water build-up in the well bore that reduces or prevents gas production.       

   Thus, the present invention is well adapted to carry out the objects and attain the ends and advantages mentioned as well as those which are inherent therein. While numerous changes may be made by those skilled in the art, such changes are encompassed within the spirit of this invention as defined by the appended claims.