Patent Application
20120168180
The field of this invention is zone isolation for treatment and more particularly where the barriers are temporary and do not need to be milled out at the conclusion of the treatment but instead are otherwise removed.
In the past one system that allowed fracturing an interval included a series of external isolators such as open hole packers and a plurality of sliding sleeve valves. These valves could be operated with dropped balls of different sizes that would get progressively larger as sliding sleeve valves closer to the surface had to be operated by larger balls later in the procedure. Because of the size of the bottom hole assembly, there were only so many discrete ball sizes that could be used. The more zones that needed treatment in a given interval, the fewer the openings for treatment fluid that could be used in each zone. One example relevant to this concept is U.S. Pat. No. 7,591,312.
Some operators want a more even distribution of fracturing or acid treating fluids in each isolated zone in an interval. In the past one technique has been to install a plug, perforate the zone/section, and treat the zone just perforated. The next plug is installed to isolate the zone just treated and another gun is fired in the adjacent zone and the process is repeated until the entire interval is treated. At the end of the treatment all the plugs have to be milled out. The plugs are made from easily milled materials to expedite this process. This process is time consuming and therefore expensive and it generates a lot of cuttings that have to be removed from the borehole.
The present invention addresses an alternative technique to milling out all the plugs that were used to isolate intervals with an option to remove the plugs by making them disappear or by physically forcing them to hole bottom or grabbing them and removing them from the wellbore.
The concept of using tubular barriers in general that can disappear, usually with a chemical reaction, or by dissolving or using magnetic fields are illustrated in the following references: U.S. Pat. Nos. 6,568,470; 6,926,089 (FIGS. 4 and 5); 6,779,600; 6,145,593; 7,533,721; 7,493,956 and 5,425,424. Also of interest is US Publication 2005/0023004.
Those skilled in the art will better appreciate the details of the invention from a review of the detailed description of the preferred embodiment and the associated drawings while appreciating that the full scope of the invention is to be found in the appended claims.
An interval can be divided into zones by inserting a series of plugs that register with specific profiles at predetermined intervals along a section of pipe. Each plug supports a releasable perforating gun that can release from the plug and perforate an interval for treatment such as fracturing or acidizing. A subsequent plug then isolates the just treated zone and the process is repeated working up toward the surface. When the full interval is treated the plugs can then be removed by making the blocking member in the cores partly or totally disappear using a reaction or dissolving techniques. If there is a partial elimination the residue can be allowed to fall further in the hole or circulation can bring the residue from the borehole. Mechanical alternative that push all the plugs to hole bottom or that retrieve them together or individually are possible alternative techniques for removal of the plugs from the treated interval before production is initiated.
In one embodiment the plug assembly 16 can have a metallic housing 18 that has projections 20 and 22 to engage a given profile such as 14 as shown in
At the conclusion of the treating of the interval with all the plug assemblies in position in the interval or even before all the plugs to span the interval have been delivered, the removal process can take place that opens the casing or liner 10 in the interval treated in one of several ways. If there is a disappearing barrier that forms the core 24 in each of the plugs the stimulus that makes the cores disappear can be introduced or activated so that all the cores open to production flow. This can preferably be done with introduction of acid for a long exposure so that the cores 24 dissolve or are reacted to a condition where they release from the housing 18 of the plug assembly 16. It can also be done with temperature of wellbore fluids or with a magnetic or other field. It should be noted that as soon as another plug is about to be introduced, the acid or other stimulus can be activated for the plug that will now be covered with a higher landed plug. While the zones are treated with acid, or some other stimulus such as brine or heat for example, the cores 24 remain intact since the duration of the procedure is short enough to maintain the integrity of the cores 24. At the end of the procedure there is more time or the composition of the acid can be altered to induce core failure and the opening up to flow from the interval of all the plug assemblies 16. Other stimuli that can get the same result are envisioned such as thermal, electromagnetic or the introduction of a substance that catalyzes a reaction with the material of the cores 24 to mention some possibilities.
As an alternative to removal of the cores 24 there is also the option of removing all the plug assemblies such as those shown in
Another alternative is to run a tool into the well that can apply a physical force to the topmost plug to allow it to release from its associated profile while being selectively retained by the string and grapple tool that grips the topmost plug. Once the topmost plug is released the string is lowered so that the lower end of the topmost plug engages and retains the plug below. Weight is again set down and the process is repeated until the string is selectively supporting all the plugs. The assembly of all the plugs can be run to the hole bottom and released or the assembly can be brought to the surface to remove all the plugs from the casing or liner 10 while leaving the profile sleeves in the deeper recess. The profile sleeves can be slit so that moving into the deeper recess allows them to grow in diameter to allow the plugs to pass on the way out of the casing or liner 10, if that option is being used.
For example, in
Those skilled in the art will recognize that the milling out of a series of plugs as was done in the past is not required. The plugs can all be opened up internally such as by removal of a core using a variety of stimuli with the preferred technique being dissolving or reacting away the cores 24 such as using acid pumped into the casing or liner 10 at the conclusion of the fracturing or acidizing or other completion step. Alternatively, the plugs do not need disappearing cores but instead have a mechanism to release from the profile where they are supported. They can collectively be allowed to go to hole bottom or they can be captured to each other and removed all together from the casing or liner 10. Alternatively the plugs can be blown into a released position from the profile that supports them but that approach adds pressure to the formation that in some cases is not advantageous to maximizing production. In yet another approach the plugs can be pulled out one at a time but that process is more time consuming and hence expensive than pulling them all out at once or simply opening a passage through them all in a simple operation that removes their cores.
The above description is illustrative of the preferred embodiment and many modifications may be made by those skilled in the art without departing from the invention whose scope is to be determined from the literal and equivalent scope of the claims below.
