For purposes of preparing a well for the production of oil or gas, at least one perforating gun may be run into the well via a deployment mechanism, such as a wireline or a coiled tubing string. The shaped charges of the perforating gun(s) are fired when the gun(s) are appropriately positioned to perforate a casing of the well and form perforating tunnels into the surrounding formation. One or more stimulation operations (a hydraulic fracturing, for example) may be performed in the well to increase the well's permeability. These operations may be multiple stage operations, which may involve several runs, or trips, into the well.
In an embodiment, plugs are deployed along a wellbore to form fluid barriers for associated stages. The plugs include a first plug that includes a first material that reacts with a first agent and does not react with a second agent and a second plug that includes a second material that reacts with the second agent and does not react with the first agent. A first stimulation operation is performed in the stage that is associated with the first plug; and a first agent is communicated into the well to react with the first material to remove the first plug. A second stimulation operation is performed in the stage that is associated with the second plug. The second agent is communicated into the well to react with the second material to remove the second plug.
In the following description, numerous details are set forth to provide an understanding of features of various embodiments. However, it will be understood by those skilled in the art that the subject matter that is set forth in the claims may be practiced without these details and that numerous variations or modifications from the described embodiments are possible.
As used herein, terms, such as “up” and “down”; “upper” and “lower”; “upwardly” and downwardly”; “upstream” and “downstream”; “above” and “below”; and other like terms indicating relative positions above or below a given point or element are used in this description to more clearly describe some embodiments. However, when applied to equipment and methods for use in environments that are deviated or horizontal, such terms may refer to a left to right, right to left, or other relationships as appropriate. Likewise, when applied to equipment and methods for use in environments that are vertical, such terms may refer to lower to upper, or upper to lower, or other relationships as appropriate.
In general, systems and techniques are disclosed herein for purposes of performing multiple stage (or “multi-stage”) stimulation operations (fracturing operations, acidizing operation, etc.) in multiple zones, or stages, of a well using plugs that are constructed to form fluid tight barriers (also called “fluid barriers” herein) in the well. Before the stimulation operations commence, the plugs may be installed at predetermined positions along a wellbore (inside a tubular string that extends in the wellbore, for example) to create fluid barriers for associated isolated zones, or stages. More particularly, each plug may form the lower boundary of an associated stage; and after the plugs are installed, the stimulation operations proceed in heel-to-toe fashion (i.e., in a direction moving downhole) along the wellbore. In this manner for a given stage, a stimulation operation is performed in the stage and then the associated plug at the downhole end of the stage is removed to allow access to the next stage for purposes of performing the next stimulation operation.
Reactive agents are introduced into the well to selectively remove the plugs as the stimulation operations progress downhole. For this purpose, alternate materials are used for the plugs: some of the plugs contain a material (called “material A” herein) that is degradable (dissolvable, for example) using a particular reactive agent (called “agent A” herein); and some of the plugs contain another material (called “material B” herein) that is degradable using another reactive agent (called “agent B” herein). Material A does not react or degrade in the presence of agent B, and likewise, material B does not react or degrade in the presence of agent A. Plugs containing the A and B materials are alternated in an ordered spatial sequence along the wellbore, which prevents the reactive agent that is used to dissolve the material of one plug in a given stage from dissolving the material of another plug in the adjacent stage.
For example, when the stimulation operation for a given stage is complete, a reactive agent (agent A, for example) may be introduced into the stage to remove the associated plug (having material A, for example) for purposes of allowing access to the next stage. Because the plug in the next stage is made from a material (material B, for example) that does not react with the reactive agent (agent A, for example), the integrity of this plug is preserved, thereby allowing the stimulation operation in the next stage to rely on the fluid barrier provided by this plug.
Referring to
It is noted that although
In the following non-limiting examples, it is assumed that the stimulation operations are conducted in a direction from the heel end to the toe end of the wellbore 15. Moreover, for the following non-limiting examples, it is assumed that operations may have been conducted in the well prior to the beginning of the stimulation operations to enhance fluid communication with the surrounding reservoir.
One way to enhance fluid communication with the surrounding reservoir is by running one or more perforating guns into the tubular string 20 (on a coiled tubular string or wireline, as non-limiting examples) before any plugs have been installed in the tubular string 20. In general, a perforating gun includes shaped charges that, when the perforating gun is fired, form perforating jets that pierce the wall of the tubular string 20 and forms perforation tunnels that extend into the surrounding reservoir. The figures depict sets 40 of perforation tunnels that are formed in each stage 30 (through one or more previous perforating operations) and extend through the tubular string 20 into the surrounding formation(s). It is noted that each stage 30 may have multiple sets of perforation tunnels 40.
Using a perforating gun is merely an example of one way to establish/enhance fluid communication with the reservoir, as the fluid communication may be established/enhanced through any of a number of techniques. For example, an abrasive slurry communication tool may be run downhole inside the tubular string 20 on a coiled tubing string and used to communicate an abrasive slurry in a jetting operation to selectively abrade the wall of the tubular string 20. As another example, the tubular string 20 may have sliding sleeve valves that are opened for purposes of opening fluid communication with the surrounding formation for the stimulation operations, as discussed further below in connection with
For the example that is depicted in
In some embodiments, the plugs 50 may be run into the tubular string 20 in one or more trips using a plug setting tool that carries and sets multiple plugs or using a plug setting tool that carriers and sets one plug at a time. The plug setting tool may be run downhole on conveyance line, such as a coiled tubing string, a wireline or a slickline, depending on the particular embodiment. In further embodiments, the plugs may be pumped downhole without the use of a conveyance line. In further embodiments, the plugs 50 may be placed in the tubular string 20 at the Earth surface, as the string 20 is being installed.
Regardless of the conveyance mechanism, tool used, or deployment technique in general, the plugs 50 are set in a sequence from the toe end to the heel end of the wellbore 15. Thus, for the example that is depicted in
The plug 50 may have one of numerous forms, depending on the particular embodiment. For example, in some embodiments, the plug 50 may have a resilient outer sealing element that is expanded by the plug setting tool and an interior sealing element that forms the remaining seal for the plug 50. The outer sealing element, the interior sealing element or both sealing elements may form the material that is dissolved by introduction of the appropriate agent into the associated stage 30. As another example, the plug 50 may be a solid material that is dissolved by the introduction of the appropriate agent into the associated stage 30. In this manner, a given plug 50 may, in accordance with some embodiments, be formed by setting a first smaller bridge plug at a predetermined position in the tubular string 20 and then communicating material into the well, which deposits on the first plug to form the plug 50. As another example, the plug 50 may contain an expandable sealing element that is a composite material that contains a material that dissolves in the presence of the appropriate agent. As another example, the plug 50 contains a setting/setting retention mechanism that contains a material that dissolves in the presence of the appropriate agent to cause the plug 50 to lose its seal.
Regardless of the particular form of the plug 50, the plug 50 contains a material that is constructed to degrade (dissolve, for example) in the presence of a certain reactive agent for purposes of removing the fluid barrier that is created by the plug 50. Thus, although
Although
For the following examples, it is assumed that each plug 50 contains one of two materials: a material A that dissolves in the presence of a reactive agent A and does not react or dissolve in the presence of another reactive agent B; and material B that dissolves in the presence of agent B but does not react or dissolve in the presence of agent A. The deployment of the plugs 30 into the tubular string 20 follows an ordered spatial sequence: the plugs associated with odd indices (plugs 50-1 and 50-3, for the example depicted in
It is noted that although for the following examples, it is assumed that the plugs 50 contain two different types of material, more than two types of plugs 50, which contain more than two types of material that are selectively dissolvable using different agents may be used, in accordance with other implementations.
Due to the alternating deployment of the materials A and B, a plug 50 uphole from a lower stage 30 may be removed using an agent, which does not react with the plug 50 that forms the downhole boundary for the lower stage 30. Thus, due to the plugs 50 containing alternating materials A and B, stimulation operations may be performed by first deploying all of the plugs 50 in the well in the above-described alternating fashion and then alternating the use of the agents A and B for purposes of selectively removing the plugs 50 as the stimulation operations proceed downhole.
Turning now to a more specific example, it is assumed, as depicted in
Assuming, for a non-limiting example, that the stimulation operation that is performed in the stage 30-1 is a hydraulic fracturing operation, fracturing fluid is pumped from the Earth surface into the tubular string 20 and the plug 50-1 diverts the fracturing fluid into the perforating tunnels 40 of the stage 30-1. The fracturing operation in the stage 30-1 results in the formation of a corresponding fractured region 60. It is noted that a stimulation operation other than a fracturing operation may be performed, in accordance with other embodiments.
After the stimulation operation is complete in the stage 30-1 or near the time when the stimulation operation is to be completed, agent A is introduced into the well from the Earth surface and enters the stage 30-1, where agent A begins dissolving material A of the plug 50-1, as depicted in
With the removal of the plug 50-1 and the sealing off of reservoir communication for the stage 30-1, a stimulation operation may then begin in the next stage 30-2, which results in a corresponding fractured region 64 that is depicted in
Stimulation operations may be performed in the additional stages 30 (such as stage 30-3 and 30-4, as non-limiting examples) in a similar manner by alternating the reactive agents that are introduced for purposes of removing the plug 50s. Thus, plug 50-3 is removed using agent A, the plug 50-4 is removed using agent B, and so forth.
As non-limiting examples, in accordance with some embodiments, material A may be calcium carbonate, which dissolves in the presence of an acid (hydrochloric acid, for example), which forms agent A; and material B may be a polyacrylic polymer, which dissolves in the presence of a base (sodium hydroxide, calcium hydroxide, magnesium hydroxide, etc., as non-limiting examples), which forms agent B. For this example, it is noted that the calcium carbonate material does not dissolve in the presence of a base, and the polyacrylic polymer material does not dissolve in the presence of an acid.
Referring to
Referring to
Other variations are contemplated and are within the scope of the appended claims. For example, referring to
It is noted that although
While a limited number of examples have been disclosed herein, those skilled in the art, having the benefit of this disclosure, will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations.
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