Patent Application
20250003309
The invention relates generally to oil and gas extraction and, more particularly, to a dissolvable release acidizing plug.
Oil and gas are a primary source of energy for much of the world, and are the raw materials from which many plastics, pharmaceuticals, and other products are made. The transportation industry relies almost exclusively on gasoline, kerosene, other products derived from oil drilling, and heating is largely provided by natural gas. Natural gas is typically found in pockets or reservoirs in the ground where remains of prehistoric plants and animals have decomposed in the absence of oxygen to form carbon-rich organic compounds that with heat and pressure over time became products such as natural gas and crude oil. These products tend to accumulate in porous limestone or sandstone, but can also be found in shale where such accumulation has not happened or is incomplete.
Geologists search for oil and gas by using seismology and other methods to look for accumulations of oil and gas in such pockets, or by looking for shale deposits likely to have high oil and gas content. Once an area of interest is found, a well is drilled such as by using a large bit to bore a hole through rock and sediment while water or other material is circulated through the drill pipe and out the bored hole to clear the hole of drilled debris. A casing or large diameter pipe is then placed in the bored hole to stabilize the hole, and cement is pumped between the casing and the bored hole to stabilize the bored hole.
When a bore hole is complete, a perforating gun is typically lowered to a point at which oil or gas is believed to be present, and explosive charges create holes in the casing through which oil and gas can flow. The perforated casing typically will not result in a “gusher” of oil as is popularly seen on television and in the movies, but may require acid etching, pressurized steam, hydraulic fracturing, or other treatment of the geology surrounding the perforated area of the bore hole casing to result in oil flow. A pump coupled to the bore hole at the ground surface is typically employed to create suction in the bore hole to extract oil and gas from the bored hole.
Where oil and gas have not yet accumulated in large reservoirs but are still trapped in geologic formations, a process known as fracking or hydraulic fracturing is used to create fractures in the shale surrounding the perforations in the casing before trying to extract oil or gas. Gas exploration similarly often uses a method known as acidizing, in which hydrochloric acid is introduced rather than fracking fluid to etch away geologic formations that have trapped natural gas deposits.
Because a bore hole may run thousands of feet, especially for horizontal drilling, it is often desirable to perform these fracturing or acidizing processes at intervals along the bore casing to better harvest oil and/or gas from a large area along the bore hole. To do this, a type of fracking called plug-and-perf is employed, in which a segment of the bore hole is perforated before a fracking fluid is pumped in under high pressure to fracture the surrounding rock, that segment is plugged or isolated, and the next segment is perforated and fractured. This process is repeated until the entire region of interest is perforated and fractured, and the plugs used as part of the process are drilled out.
But, the plugs used for processes such as acidizing must be able to withstand the hostile environment created by pumping hydrochloric acid into the bore hole without moving within the bore hole, while also being removable after the acidizing process is complete so that natural gas can be extracted. Traditional plugs often take more than a significant time to drill out per plug, and can be difficult to drill out if various complications arise, such as if they become dislodged or spin during the drilling process. For these and other reasons, an improved acidizing plug is desired.
One example embodiment comprises an acidizing plug assembly having a mandrel, sealing element, upper and lower backup rings, upper and lower cones, upper and lower slips each having teeth configured to engage a well casing, and a shoe. An external surface of the acidizing plug is configured to be acid-resistant, and one or more breakable plugs prevents acid from reaching an acid-vulnerable portion of the acidizing plug. The breakable plugs are broken when the acidizing plug is no longer needed to permit acid such as hydrochloric acid to dissolve at least a substantial portion of the acidizing plug.
The details of one or more examples of the invention are set forth in the accompanying drawings and the description below. Other features and advantages will be apparent from the description and drawings, and from the claims.
In the following detailed description of example embodiments, reference is made to specific example embodiments by way of drawings and illustrations. These examples are described in sufficient detail to enable those skilled in the art to practice what is described, and serve to illustrate how elements of these examples may be applied to various purposes or embodiments. Other embodiments exist, and logical, mechanical, electrical, and other changes may be made.
Features or limitations of various embodiments described herein, however important to the example embodiments in which they are incorporated, do not limit other embodiments, and any reference to the elements, operation, and application of the examples serve only to define these example embodiments. Features or elements shown in various examples described herein can be combined in ways other than shown in the examples, and any such combinations is explicitly contemplated to be within the scope of the examples presented here. The following detailed description does not, therefore, limit the scope of what is claimed.
Drilling for natural gas is becoming increasingly difficult, as much of the natural gas that is the easiest to extract has already been located and extracted. Complex drilling techniques, such as horizontal drilling, hydraulic fracturing or fracking, acidizing, and the like have therefore become commonplace in oil and gas fields around the world. Further, the depth of such wells is becoming increasingly deeper to reach yet untapped oil reserves, with horizontal wells extending 5,000 feet to 10,000 feet or more being common. For example, many horizontal wells now extend well beyond 5,000 feet through geologic structures that which must be acidized, hydraulically fractured, or both to release natural gas or oil from the many pockets typical geologic formations.
A typical oil and gas well is drilled such as by using a large bit, such as from 5-10 inches in diameter, to bore a hole through rock and sediment while water or other liquid is circulated through a drill pipe and out the bored hole to clear the hole of drilled debris. A casing or large diameter pipe is then placed in the bored hole to stabilize the hole, and cement is pumped between the casing and the bored hole to stabilize the casing in the bored hole. The completed hole is then prepared for fracking or acidizing by lowering a perforating gun in the casing and using explosive charges to crate holes in the casing through which fracking fluid or hydrochloric acid can be pumped to create a passage between pockets of oil and gas in the shale formation and the casing.
Acidizing generally works by using an acid such as hydrochloric acid to dissolve part of a geologic formation, freeing oil and gas to be extracted. Hydraulic fracturing or fracking similarly works by using high pressure fracking fluid to break apart or fracture geologic formations to free trapped oil and gas. Acidizing is often further categorized as matrix acidizing, in which acid is pumped into the well at pressures below the formation fracturing pressure and completes its work by dissolving rather than fracturing the geologic formations, and fracture acidizing, in which acid is pumped into the well at pressures up to thousands of pounds per square inch such that the acid both fractures and dissolves the geologic formations. Although acidizing is often associated with natural gas wells and hydraulic fracturing is often associated with oil wells, both oil and gas may be extracted from wells using either method.
In deep bore holes, the acidizing process may be repeated many times over the length of the bore hole, and plugs are used to seal completed deeper portions of the bore hole while subsequently acidizing shallower regions. This process is often called plug-and-perf, because a plug separates portions of the bore hole that have already been perforated and acidized from the portion currently being acidized. Once the plug-and-perf process is complete, the plugs are all drilled from the bore hole so oil and gas can be extracted. Because acidizing plugs must be able to hold their position within the casing under the caustic environment of hydrochloric acid, they are often difficult to drill out so that oil and gas can be extracted after the acidizing process is complete. Further, as bore holes extend many thousands of feet deep, the plugs become increasingly difficult to drill out from the surface, often taking an hour or more per plug if no problems arise. If the plugs become dislodged or spin during the drilling process, plugs may take many hours to drill out or may not be drilled out at all.
For reasons such as these, some example embodiments of the invention presented herein comprise an acidizing plug that is at least partially soluble in an acid such as hydrochloric acid upon breaking or removing part of the plug, such that the plug can be either substantially dissolved or freed from the casing sufficiently to be moved or removed. In a further embodiment, the acid soluble part of the plug comprises aluminum, magnesium or an aluminum and/or magnesium alloy.
In a more detailed example, a plug comprising a mandrel has a treated area that is resistant to acid and an untreated area that is more vulnerable to being dissolved by acid than the treated area. One or more breakable plugs, such as a ceramic plug or other plug configured to be strong enough to withstand the acidizing process but weak or brittle enough to be able to readily breakable when needed, shields the untreated area from acidizing acid until the plug is broken. Once the breakable plug is broken, the mandrel and optionally one or more other parts of the acidizing plug dissolve in acid such as hydrochloric acid at a substantially faster rate (e.g., 5×, 10×, 20×, or 50× faster) than before the untreated or acid-vulnerable area was exposed to acid.
The acidizing plug is in a simple example used to seal the casing of a bore hole of an oil or gas well while it is matrix acidized or fracture acidized, and once the acidization process is complete the breakable plug is broken, exposing an untreated or acid-vulnerable portion of the acidizing plug to acid and allowing the acidizing plug to dissolve much more rapidly. In more complex examples, the acidizing plug is used to isolate one section of a gas and/or oil well from another during processes such as matrix acidizing or fracture acidizing, facilitating exploration and extraction in large or deep wells.
In the simplified example shown in
But, while use of a drill head 314 works fairly well near the surface of the gas well where the wireline or coiled tubing distance to the drill head is fairly short, it works progressively less reliably as the distance underground to the drill head increases. In some embodiments of the invention, the drill head 314 is therefore replaced with or supplemented by a tool that is designed to puncture, shatter, drill, or otherwise open at least one breakable plug in the acidizing plug, exposing a portion of the acidizing plug that is acid-vulnerable to acid present in the casing 302. In a more detailed example, the acidizing plug is treated or coated with a material that resists acid on its exterior, such that it dissolves in acid substantially faster in acid once the breakable plug has been opened to expose the acid-vulnerable portion of the plug than before the breakable plug or plugs are broken.
The acidizing plug in another example has a steel shear stud that is engaged with the setting tool, which in a further example shears in a way that provides access to the one or more breakable plugs. For example, the shear stud may be configured to break along an outer radius of a threaded portion of the shear stud designed to engage the mandrel, which in some examples is greater in diameter than the diameter of the shear stud portion that engages with a setting tool. In alternate examples, the shear stud may be removable from the mandrel, such as by rotating via the setting tool or another tool in a certain direction to separate the shear stud from the mandrel or other portion of the acidizing plug assembly.
Upper cone 514 and lower cone 516 engage upper slip 518 and lower slip 520. When the setting ring 510 is screwed toward the shoe 512, it forces the upper and lower cones together which forces the upper and lower slips outward radially from the axis of the mandrel. When the upper and lower slips are forced radially outward by the upper and lower cones, teeth 522 bite into the casing, securing the acidizing plug in place. Upper sealing element 524 and lower sealing element 526 are also forced outward from the radial axis of the mandrel when the setting ring is forced toward the shoe, and in this example are made of a rubber or composite material that is flexible enough to flex and seal against the wall of the oil and gas well's casing but resilient enough to withstand hydraulic pressure in the thousands to tens of thousands of pounds per square inch and still seal properly. In other examples, the sealing element 508 is soluble in an acid solvent, is made of a metallic or semi-metallic compound, or is a fiber-reinforced polymer. The upper and lower sealing elements in this example have a groove in its center as shown, but in other examples do not have a groove or has multiple grooves. The grooves in some such examples are configured to control the amount of flex in the sealing element, to control the region in which the sealing element flexes, or to control both the amount and region of flex. In further examples, one or more backup rings are also positioned on the mandrel, such as between a sealing element and cone or a sealing element and shoe or setting ring, and further examples are semi-flexible such that they can expand slightly to provide a secondary or backup sealing function when seated against the casing of the oil well.
The acidizing plug is assembled by screwing the shoe 512 onto the mandrel 502, with breakable lower disk 506 and one or more sealing O-rings retained between the mandrel and shoe to seal a lower portion of the acidizing plug. Additional elements such as lower sealing element 526, backup rings, lower cone 516 and lower slip 520, upper cone 514 and upper slip 518, additional backup rings, and upper sealing element 524 are then slid in place over the exterior surface of the mandrel. Setting ring 510 is threaded onto the top end of the exterior of the mandrel 502, securing these elements in place on the mandrel between the setting ring 510 and the shoe 512. Shear stud 508 is screwed into the top end of the mandrel, retaining breakable upper disk 504 and one or more O-rings to seal the breakable upper disc against the mandrel.
The acidizing plug assembly is further treated on its exterior surfaces to be resistant to acid, such as hydrochloric acid often used in acidizing oil and gas wells. In a more detailed example, the exterior surface is anodized, coated with an acid-resistant material, or otherwise treated to be acid-resistant. The inner cylindrical surface of the mandrel located between the breakable upper disk 504 and the breakable lower disk 506 is not treated, and is more vulnerable to acid than the exterior surface of the acidizing plug assembly. In a more detailed example, the mandrel comprises aluminum or magnesium, and the inner acid-vulnerable surface of the mandrel is soluble in acid in 1-5 hours while the acid-resistant exterior is soluble in acid in 1-5 days.
In a further example, one or more other elements such as the shoe 512, setting ring 510, upper and lower cones 514 and 516, and upper and lower slips 518 and 520 are soluble in acid, or are more acid-vulnerable on protected surfaces than on surfaces exposed on the exterior of the acidizing plug assembly. Some elements of this example acidizing plug are not acid-soluble, including the steel shear stud 508, carbide teeth 522, and rubber or nitrile O-rings. In the example acidizing plug shown in
Once the plug is assembled, it can be placed using methods such as a wire line to guide the plug into position in an oil and gas well casing. When the plug is in the desired position, the threaded setting ring is rotated relative to the threaded mandrel to drive it toward the shoe, causing elements such as the upper sealing element 524 and lower sealing element 526 to bow out and seal the acidizing plug against the casing. Rotating the threaded setting ring to drive it against the mandrel toward the shoe also causes the upper cone 514 and lower cone 516 to be driven toward each other, causing the upper and lower slips to be forced outward from the mandrel body against the casing. The upper and lower slip's teeth bite into the casing, securing the acidizing plug in place in the casing. A plug setting tool holds the plug in place such as by locking onto the shear stud while turning the setting ring to screw the setting ring toward the shoe during this installation or setting process, breaking away from the plug assembly by breaking the shear stud once a desired mechanical force between the mandrel and the upper slip is reached.
When the acidizing plug has served its purpose and removal is desired, the shear stud 508 is broken at the junction between the threaded stud portion and the threaded portion that engages the mandrel, revealing an opening in the threaded portion that engages the mandrel. This provides an opening to the breakable upper disk from the upper end of the acidizing plug, such that the breakable upper disc, made of a material such as ceramic, can be broken with a tool inserted in the top end of the acidizing plug. The same tool used to break the upper disk also breaks the breakable lower disk 506, enabling fluid such as hydrochloric acid to flow through the mandrel.
Hydrochloric acid is then introduced to flow through the center portion of the mandrel, including the acid-vulnerable portion between the breakable upper disk 504 and breakable lower disk 506. Because this portion of the mandrel is selected to be an acid-soluble material and is not treated to be acid-resistant, it dissolves readily in the acid and the acidizing plug breaks up. Insoluble parts such as the shear stud 508, carbide teeth 522, O-rings, and in a further example the sealing elements 524 and 526 come loose from the acidizing plug assembly and do not substantially obstruct the flow of oil or gas. In a further example, these non-soluble elements can be flushed out of the casing and separated from recovered oil and gas.
In another example, one or more other cavities, grooves, or other such features are incorporated into the acid-vulnerable surface of the mandrel to increase the surface area exposed to acid during the dissolving process, thereby reducing the time needed to dissolve the plug assembly. Soluble in various embodiments means that the mandrel will dissolve in a half hour, an hour, three hours, six hours, twelve hours, or a day.
In an alternate embodiment, the plug of
Rock formations surrounding the perforated portions of the casing are then acidized at 612 by pumping hydrochloric acid down the well. At 614, the driller determines whether all desired regions of the well have been perforated and acidized, and the process repeats for the next segment of the well at 604 if additional regions remain to be acidized. If the perforating and acidizing process is determined to be complete at 614, a tool is inserted to puncture, shatter, or drill the breakable plugs in the acidizing plugs at 618. The acidizing plugs are then removed or dislodged from their places in the casing at 616 using an acid such as hydrochloric acid that dissolves part or all of the plugs. The well is then ready for extracting oil or gas at 620.
The examples presented here illustrate how an acidizing plug for plug-and-perf oil and gas drilling applications can be formed at least partially from a material that is dissolvable or soluble in acid, facilitating easier and more certain removal of the acidizing plug after the acidizing process is complete. Further, dissolvable plugs such as those described here enable plug-and-perf fracking in wells that are deeper than can be currently employed due to the limitations of the traditional drilling process used to remove acidizing plugs.
Although specific embodiments have been illustrated and described herein, any arrangement that achieves the same purpose, structure, or function may be substituted for the specific embodiments shown. This application is intended to cover any adaptations or variations of the example embodiments of the invention described herein. These and other embodiments are within the scope of the following claims and their equivalents.
