Patent Application
20060118305
The present invention relates generally to hydrocarbon production, and more particularly to a method of increasing hydrocarbon production in an existing well by forming a substantially horizontal transverse fractured wellbore, which intersects the existing well and injecting a fluid into the reservoir to sweep the hydrocarbons into the substantially horizontal transverse fractured wellbore.
In certain subterranean formations, fluid is injected into the reservoir to displace or sweep the hydrocarbons out of the reservoir. This method of stimulating production is sometimes referred to as a method of “Enhanced Oil Recovery” and may be called waterflooding, gasflooding, steam injection, etc. For the purpose of this specification, the general process will be defined as injecting a fluid (gas or liquid) into a reservoir in order to displace the existing hydrocarbons into a producing well. The primary issue with injecting fluid to enhance oil recovery is how to sweep the reservoir of the hydrocarbon in the most efficient manner possible. Because of geological differences in a reservoir, the permeability may not be homogenous. Because of such permeability differences between the vertical and horizontal directions or the existence of higher permeability streaks, the injecting fluid may bypass some of the reservoir and create a path into the producing well.
The industry has come up with numerous methods to improve the sweep efficiency and the overall reservoir that is swept by individual wells. These methods include fracturing and the use of horizontal wells. The industry currently uses horizontal wells as injectors in an attempt to expose more of the reservoir to the injecting fluid. The goal is to create a movement of injection fluid evenly across the reservoir. This is sometimes referred to as line drive. The industry also uses horizontal wells as producers, again the goal being to evenly produce the reservoir so to form a line drive.
SPE Paper 84077 presents a method referred to as toe-to-heel waterflooding where a horizontal lateral is used to produce the reservoir with a vertical injector located nearer the toe (end) of the lateral. The method referred to in this paper is limited, since the horizontal lateral only covers a limited area in the reservoir. It therefore does not maximize the amount of surface area that can be used to recover the hydrocarbons. This method also suffers from an inability to control the influx of injection fluid at the toe to improve recovery.
Part of the efficiency of the sweep is reducing the production of the injection fluid. The industry has created several techniques from the use of chemicals that block the injection fluid, to injection fluids that improve the matrix flow through the reservoir to reduce channeling. Some injection programs include attempts to plug high permeability streaks and natural fractures in the reservoir. This is done to force the injection fluid out into more of the reservoir to displace hydrocarbons.
When the injection fluid is produced, such as water, it is usually removed from the hydrocarbons at the surface using multi-phase separation devices. These devices operate to agglomerate and coalesce the hydrocarbons, thereby separating them from the water. A drawback of this approach, however, is that no separation process is perfect. As such, some amount of the hydrocarbons always remains in the water. This can create environmental problems when disposing of the water, especially in off-shore applications. Also, the multi-phase separation devices are rather large in size, which is another disadvantage in off-shore applications, as space is limited. Yet another drawback is that these devices can require additional maintenance or repair if solids are part of the produced fluid stream. A further, and perhaps greatest drawback of these solutions, is that they do nothing to increase or maximize the amount of hydrocarbons being produced. Their only focus is removing the water from the production.
Specialized downhole tools have also been developed, which separate the water from the hydrocarbons downhole. These tools are designed to leave the water in the formation as the hydrocarbons are produced. While these devices can remove a significant amount of water from the hydrocarbons, they are also often less than perfect in removing the water from the hydrocarbons. They also suffer from the same drawback of the surface separation devices in that they do nothing to increase or maximize the amount of hydrocarbons being produced.
A solution is therefore desired that not only improves the efficiency and economics of enhanced oil recovery through injection, but that also reduces the amount of injection fluid that infiltrates the hydrocarbon production of an existing well.
The present invention is directed to a method of increasing hydrocarbon production in an existing well in a hydrocarbon reservoir, which minimizes the drawbacks of prior art methods and apparatuses. In one embodiment, the method includes the steps of forming a substantially horizontal transverse fractured wellbore; and injecting a fluid in the reservoir so as to form a fluid front that sweeps the hydrocarbons into the horizontal transverse fractured wellbore.
In another embodiment, the method according to the present invention includes the steps of drilling a substantially horizontal wellbore that intersects the existing well and forming at least one transverse fracture in the reservoir along the substantially horizontal wellbore. In one exemplary embodiment, a plurality of transverse fractures are formed. The method further includes the steps of drilling an injection well into the reservoir and injecting a fluid into the reservoir through the injection well so as to sweep the hydrocarbons toward the plurality of transverse fractures. The hydrocarbons can then be drained into the plurality of transverse fractures.
In another embodiment, the method according to the present invention includes the steps of drilling a substantially horizontal wellbore that intersects the existing well, forming a plurality of transverse fractures in the reservoir along the substantially horizontal wellbore, and installing a tubing in the substantially horizontal wellbore with an end of the tubing being disposed at a toe portion of the substantially horizontal wellbore, downhole of the farthest transverse fracture. The terms “downhole” and “uphole” are defined herein to describe locations away from and toward, respectively, the existing well. In other words, one object which is downhole of another is farther away from the existing well than the other object and one object which is uphole of another is closer to the existing well than the other object. This embodiment further includes the steps of installing a packer between the tubing and a sidewall forming the substantially horizontal wellbore uphole of the farthest transverse fracture, injecting a fluid into the reservoir through the end of the tubing at the toe of the substantially horizontal wellbore to sweep the hydrocarbons toward the plurality of transverse fractures, and draining the hydrocarbons into the plurality of transverse fractures. No separate injection well is drilled with this embodiment.
In yet another embodiment, the method according to the present invention includes the steps of drilling a first substantially horizontal wellbore that intersects the existing well and forming a plurality of transverse fractures in the reservoir along the first substantially horizontal wellbore. This method also includes the steps of drilling a second substantially horizontal wellbore that intersects the existing well, and forming at least one transverse fracture in the reservoir along the second substantially horizontal wellbore. This method further includes the steps of sealing the at least one transverse fracture formed along the second substantially horizontal wellbore and draining the hydrocarbons into the plurality of transverse fractures formed along the first substantially horizontal wellbore.
In yet another embodiment, the method according to the present invention includes the steps of drilling a pair of oppositely disposed substantially horizontal injection wellbores that intersect the existing well, drilling a plurality of substantially horizontal producing wellbores that intersect the existing well and are disposed between the injection wellbores and forming a plurality of transverse fractures in the reservoir along each of the plurality of substantially horizontal producing wellbores. The method further includes the step of injecting a fluid into the reservoir from the pair of oppositely disposed substantially horizontal injection wellbores and draining the hydrocarbons into the plurality of transverse fractures formed along the plurality of substantially horizontal producing wellbores.
In still another embodiment, the method according to the present invention includes the steps of drilling a pair of oppositely disposed substantially horizontal injection wellbores that intersect the existing well, drilling a pair of oppositely disposed substantially horizontal producing wellbores that intersect the existing well and are disposed between the injection wellbores, each producing wellbore being formed with a plurality of laterals, and forming a plurality of transverse fractures in the reservoir along each of the plurality of laterals. This method further includes the steps of injecting a fluid into the reservoir from the pair of oppositely disposed substantially horizontal injection wellbores and draining the hydrocarbons into the plurality of transverse fractures formed along the plurality of laterals.
In another embodiment, the transverse fractures along the wellbore are created in stages during the production of the well rather than at the outset. For example, a transverse fracture at the toe is created and produced, then another transverse fracture is created uphole and injection fluid is pumped into the end fracture to sweep the formation between the two fractures. After a period of time either scheduled or determined by performance of the well more transverse fractures can be added along the wellbore to sweep more of the formation intersected by the lateral.
As part of these embodiments using transverse fractures, the flow from the transverse fractures is controlled by injecting chemicals into the transverse fractures to seal or partially seal the fracture in order to reduce the movement of the injection fluid into the fracture and force the injection fluid out into the reservoir away from the wellbore so as to increase the sweep area.
The features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of the exemplary embodiments, which follows.
A more complete understanding of the present disclosure and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings, which:
The details of the present invention will now be described. The present invention is directed to a method of increasing hydrocarbon recovery from an existing well through injecting fluid to displace the hydrocarbons from the reservoir while simultaneously reducing the influx of water and other non-hydrocarbon fluids, such as carbon dioxide, into the existing well. In its most basic form, the present invention achieves its goal by providing at least one substantially horizontal wellbore having a plurality of transverse fractures, sealing at least one of the transverse fractures and injecting a flood fluid, such as water, into the formation so as to force the hydrocarbons into the remaining transverse fractures. As those of ordinary skill in the art will appreciate from the disclosure that follows, there are many different ways of arranging the substantially horizontal wells, many different ways of injecting the fluid into the formation, and many different ways of recovering the hydrocarbons into the transverse fractures. A number of exemplary ways of performing these functions are disclosed herein.
Turning to
Next, a plurality of transverse fractures 116 are formed along the horizontal wellbore 110. The transverse fractures 116 are formed along the natural fracture line and generally parallel to one another. There are a number of different ways of carrying out this step. In one exemplary embodiment, the plurality of transverse fractures 116 are formed by using a hydra jetting tool, such as that used in the SurgiFrac® fracturing service offered by Halliburton Energy Services. In this embodiment, the hydra jetting tool forms each fracture of the plurality of transverse fractures 116 one at a time. Each transverse fracture 116 is formed by the following steps: (i) positioning the hydra jetting tool in the substantially horizontal wellbore 110 at the location where the transverse fracture 116 is to be formed, (ii) perforating the reservoir 112 at the location where the transverse fracture 116 is to be formed, and (iii) injecting a fracture fluid into the perforation at sufficient pressure to form a transverse fracture 116 along the perforation. As those of ordinary skill in the art will appreciate, there are many variations on this embodiment. For example, fracture fluid can be simultaneously pumped down the annulus while it is being pumped out of the hydra jetting tool to initiate the fracture or not. Alternatively, the fracturing fluid may be pumped down the annulus and not through the hydra jetting tool to initiate and propagate the fracture, i.e., in this version the hydra jetting tool only forms the perforations.
In another version of this embodiment, the plurality of transverse fractures 116 are formed by staged fracturing. Staged fracturing is performed by (i) detonating a charge in the substantially horizontal wellbore 110 at the location where a transverse fracture 116 is to be formed so as to form a perforation in the reservoir at that location, (ii) pumping a fracture fluid into the perforation at sufficient pressure to propagate the transverse fracture 116, (iii) installing a plug in the substantially horizontal well 110 bore uphole of the transverse fracture 116, (iv) repeating steps (i) through (iii) until the desired number of transverse fractures 116 have been formed; and (v) removing the plugs following the completion of step (iv). As those of ordinary skill in the art will appreciate, there are many variants on the staged fracture method.
In yet another version of this embodiment, the plurality of transverse fractures 116 are formed using a limited entry perforation and fracture technique. The limited entry perforation and fracture technique is performed by (i) lining the substantially horizontal wellbore 110 with a casing string 114 having a plurality of sets of predrilled holes arranged along its length, and (ii) pumping a fracturing fluid through the plurality of sets of predrilled holes in the casing string at sufficient pressure to fracture the reservoir 112 at the locations of the sets of predrilled holes.
In still another version of this embodiment, the plurality of transverse fractures 116 are formed by the steps of (i) installing a tool having a plurality of hydra jets formed along its length into the substantially horizontal wellbore 110, and (ii) pumping fluid through the plurality of hydra jets simultaneously at one or more pressures sufficient to first perforate and then fracture the reservoir 112 at the locations of the hydra jets.
After the substantially horizontal wellbore 110 has been cased and the plurality of transverse fractures 116 have been formed, the transverse fracture farthest from the existing well 100 is sealed. The sealant is installed into the transverse fracture farthest from the existing well 100 by squeezing it into the transverse fracture. This is accomplished by first isolating the perforations adjacent to the fracture using a packer 135 (such as a hydraulically set drillable, retrievable or inflatable packer) on the end of tubing and set in the casing; then pumping the sealant in a fluid state through the tubing, then through the perforations and into the transverse fracture to be sealed until a sufficient volume of sealant has been placed into the transverse fracture to accomplish the barrier to flow by the invading waterflood.
The sealant can be a cement, a linear polymer mixture, a linear polymer mixture with cross-linker, an in-situ polymerized monomer mixture, a resin-based fluid, an epoxy based fluid, or a magnesium based slurry. All of these sealants are capable of being placed in a fluid state with the property of becoming a viscous fluid or solid barrier to fluid migration after or during placement into the fracture. In one embodiment, the sealant is H2Zero™. Other sealants could include particles, drilling mud, cuttings, and slag. Exemplary particles could be ground cuttings so that a wide range of particle sizes would exist producing low permeability as compared to the surrounding reservoir.
An injection well 120 is then drilled remote from, but generally parallel to, existing well 100. In one certain embodiment, injection well 120 is drilled proximate the sealed transverse fracture 116. As those of ordinary skill in the art will appreciate, the injection well 120 can alternatively be formed prior to the formation of the substantially horizontal wellbore 110. Once the injection well 120 has been formed and the transverse fracture farthest from the existing well 100 sealed, flood fluid can be pumped down the injection well 120. As the flood fluid is pumped into the reservoir 112 it forms a propagating flood front 130. The flood front 130 is diverted around the sealed transverse fracture, as indicated in
In one exemplary variant of the method illustrated in
In another exemplary embodiment, a new transverse fracture is created during the sealing process in the near wellbore area. One method of pumping the sealing material is to use the SurgiFrac® fracturing service available from the assignee herein. If this process is used, then a fracture can be created and sealed in one step without the need of mechanical isolation.
In yet another variant of the method illustrated in
Another alternative method to setting packers includes installing a plug made of cement or other material that sets. The plug in the wellbore thus may be the same chemical or material used to seal the transverse fractures.
In one certain embodiment, a device 150 for monitoring the amount of infiltration of the flood fluid into the hydrocarbons being produced in the substantially horizontal wellbore 110 is installed adjacent to one or more of the fractures that have not been sealed. Examples of such devices include, but are not limited to, fluid flow meters, electric resistivity devices, oxygen decay monitoring devices, fluid density monitoring devices, pressure gauge devices, and temperature monitoring devices. Data from these devices can be obtained through electric lines, fiber-optic cables, retrieval of bottom hole sensors or other methods common in the industry. Another solution involves installing a sampling line into the production flow path. This could be a tubing (coiled or jointed) that takes a sample of the fluid at a point in the wellbore. If the sampling line is continuous tubing, then the well can be continuously monitored. In yet another embodiment, a sampling chamber is formed in the production flow path so that discrete samples of fluid can be taken. With such devices/solutions, the percentage of injection fluid to hydrocarbons can be measured at the surface, so that a judgment can be made whether to close a transverse fracture.
Turning to
Turning to
Fluid is injected into the reservoir 512 through toe section 540 of substantially horizontal wellbore 511 through the end of tubing 560. Flood front 530 propagates outward in the direction indicated by the arrows in
A device for monitoring the amount of non-hydrocarbon fluid in the hydrocarbon production 550 may also be employed in substantially horizontal wellbore 510. The hydrocarbon production flows in the direction of the arrows moving up the annulus and wellbore 510 into existing wellbore 500.
Turning to
In one embodiment, the transverse fractures farthest downhole from existing well 600 are all sealed and plugged with drillable plugs 635. The opposing substantially horizontal injection wells 601 and 602 may or may not be cased depending upon the nature of the reservoir 612. Those of ordinary skill in the art will appreciate those circumstances under which wellbore 601 and 602 should be cased. Tubing 660 and 662 are inserted respectively into wellbore 601 and 602. Flood fluid is injected into reservoir 612 through the ends of tubing 660 and 662 and the toe sections of wellbore 601 and 602. In this embodiment, the flood front sweeps inward toward the existing well 600. As the fluid flood ratio increases with the hydrocarbon production, over time successive transverse fractures uphole from the sealed fractures at the toes of horizontal wells 620 through 629 can be sealed to reduce the production of flood fluids. This process can be repeated until all of the transverse fractures have been sealed. In the embodiment of
Turning to
Front fluid is injected into the reservoir 712 through a plurality of injection ports formed along tubing 760 and 762 disposed in opposing substantially horizontal injection wellbore 701 and 702, respectively. In this embodiment the fluid front moves away from existing well 700. Accordingly, the transverse fractures closest to existing well 700 are the first to be sealed. Hydrocarbons are swept into the remaining transverse fractures and recovered up the existing well through annuli formed in each of the substantially horizontal production wellbores 720 through 729. As the flood front propagates outward and the ratio of flood fluid and the hydrocarbon production increases beyond an acceptable level additional transverse fractures are sealed successively outward until all of the transverse fractures in the substantially horizontal production wellbores 720 through 729 are sealed. As with all the other embodiments, a flood fluid monitoring device may be disposed in each of the substantially horizontal production wellbores 720 through 729.
Turning to
In yet another embodiment, transverse fractures 916 (shown in
Therefore, 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 the invention has been depicted, described, and is defined by reference to exemplary embodiments of the invention, such a reference does not imply a limitation on the invention, and no such limitation is to be inferred. The invention is capable of considerable modification, alteration, and equivalents in form and function, as will occur to those ordinarily skilled in the pertinent arts and having the benefit of this disclosure. For example, as those of ordinary skill in the art will appreciate, the exact number, size and order of the transverse fractures formed is not critical. The depicted and described embodiments of the invention are exemplary only, and are not exhaustive of the scope of the invention. Consequently, the invention is intended to be limited only by the spirit and scope of the appended claims, giving full cognizance to equivalents in all respects.
