Multiple zone isolation method

Multiple producing zones separated by a non-producing zone are gravel packed together. The non-producing zone has locations to take returns so as to get a consistent pack in the non-producing zone. The production string features external seals and/or an internal plug so that no matter which producing zone is aligned to produce, the screens in the non-producing zone are selectively isolated so that the producing zone that is not intended to be produced has only the path through the gravel pack to get to the actual zone being produced. Since the annulus can be long and full of gravel this path will make flow from the zone that is not of interest minimal into the flow from the zone of interest without using a packer between pairs of spaced apart producing zones.

FIELD OF THE INVENTION

The field of the invention is multi-zone subterranean completions and more particularly those that are performed in a single trip where the gravel itself rather than an external packer provides zonal isolation.

BACKGROUND OF THE INVENTION

Producing zone completions involve insertion of a screen assembly that can be as long as several pay zones with long non-producing formations in between the producing zones. The surrounding annulus around the screens is filled with gravel using a tool called a crossover tool that takes the gravel slurry coming down the tubing string from the surface and redirects it out to the annular space below an isolation packer and outside the screen. The gravel remains in the annular space outside the screens while the carrier fluid goes through the screen and into a wash pipe connected to the crossover. The crossover allows the returning fluid to get through the isolation packer and back to the surface through the upper annular space above the isolation packer.

If the producing zones are far apart, the length of borehole between them is spanned by blank pipe and a packer that allows the screen sections to be properly located at the various producing locations. Typically the delivered gravel goes to the furthest (lowest) screen downhole and fills the annulus around it. When that screen is covered, the crossover tool and wash pipe are shifted to allow the setting of a packer in the annulus (between the two zones) to fully isolate the lower zone before further gravel deposition fills the non-producing zone. After the packer is set, pumping of the slurry is resumed, and gravel is deposited on top of the packer, while the returning fluid finds another path of least resistance and starts going through the next higher production screen as the lowermost screen now fully surrounded by gravel is said to “screen out” or resist flow to an extent that sends the returns to the next higher screen. This technique is illustrated in IACC/SPE 77214 by Corbett and Vickery entitled Multiple Zone Open Hole Gravel Packing Techniques with Zonal Isolation. It is limited to separating two zones with a packer in a single trip but is impractical for more than two zones.

US Publication 2008/0164026 shows a method of gravel packing multiple zones together and then setting packers into the gravel pack to isolate the producing zones.

What is needed and not available is a way to more economically perform a gravel pack of multiple zones that are spaced apart and get a good pack in an intervening non-producing zone while getting effective zonal isolation in the pack between the producing zones without employing packers. Those skilled in the art will appreciate each of the aspects of the present invention, some of which are individually listed above, from a review of the detailed description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be found in the appended claims.

SUMMARY OF THE INVENTION

Multiple producing zones separated by a non-producing zone are gravel packed together. The non-producing zone has locations to take returns so as to get a consistent pack in the non-producing zone. The production string features external seals and/or an internal plug so that no matter which producing zone is aligned to produce, the screens in the non-producing zone are selectively isolated so that the producing zone that is not intended to be produced has only the path through the gravel pack to get to the actual zone being produced. Since the annulus can be long and full of gravel this path will make flow from the zone that is not of interest minimal into the flow from the zone of interest without using a packer between pairs of spaced apart producing zones.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1shows producing zone A separated from producing zone C by non-producing zone B. The entire illustrated wellbore is divided into regions1-10to simplify the discussion of how the gravel packing will proceed. It should be noted that while two producing zones A and C are shown separated by a non-producing zone B, the pattern can repeat and the distance between producing zones can vary and can be many meters down to a very small gap. The basic idea is to limit cross flow between zones A and C when only one is desired to be produced without using barriers in the annulus12below the production packer14. The annulus12is filled with gravel16. If only one of zones A and C are aligned to produce such as, for example if zone A is aligned to produce as indicated by arrows18and20, any flow from zone C indicated by arrows22and24will only be able to reach zone A through the annulus12, as indicated by arrows26. Zone C will not flow into producing screen28because the production string30can have a plug32at its lower end34when the string30has its lower end shown inFIG. 2inserted into a sealing relationship with the production packer14shown inFIG. 1. The string30has a sliding sleeve38to selectively cover port40. The sleeve38can be initially in the desired position and can be shifted with a known shifting tool either initially to open it as well as subsequently to close it to isolate any desired zone for a variety of reasons, such as when it produces excess water, for example. When the string30is inside packer14, the ported sub36is opposite screen42in zone A. If it is known from the beginning that zone A is to be produced first, the port40can be run in open and the plug32in position at the lower end34of the string30. While attaining a no flow condition from zone C to zone A when producing only from zone A would be ideal, there may be some minimal amount of infiltration from zone C to zone A through the gravel16in annulus12. The flow resistance between the producing formations A and C depends on many variables such as the distance between them, the density of the packed gravel, the fluid viscosity and the gravel particle size and void volume, to name a few variables.

One of the features of the invention is to get a good gravel pack in the zone B. Normally, there is just blank pipe and a packer between producing screens28and42in prior systems. This mean that when the gravel gets to the point of causing screen28to screen out, the slurry fluid that carries the gravel has to return to the surface from screen42as it then becomes the path of least fluid resistance. What this means is that gravel and carrier fluid separate at screen42and the gravel has only gravity to carry it down the annulus12below the producing screen42. As a result the pack density of the gravel16between screens42and28is not optimally high.

In the present invention, there are completion screens such as44,46and48located respectively at regions7,5and3. The spacing of these screens and their individual length can vary as can the number of such non-producing zone B seal bores2,4,6, and8. The screens44,46and48should be shorter than the production screens28and42due to their limited service during gravel packing but they can also be the same size or larger. The objective is that after screen28is covered by gravel16and the gravel packing continues, that there are enough return locations for the fluid carrying the gravel to return to the surface at different locations so as to continue to use the fluid velocity to carry the gravel16into the non-producing zone B as it fills the annulus12in a direction from screen28to screen42.This is shown graphically inFIGS. 3-8. InFIG. 3, the gravel covers about half of screen28and fluid represented by arrow50that carried the gravel in annulus12passes through the screen28and returns to the surface through the packer14and a crossover (not shown) through the annulus above the packer14. InFIG. 4the screen28has screened out and the returns represented by arrow52enter screen44as the gravel16builds above the level of screen28and into the non-producing zone B. InFIG. 5the gravel16has reached screen44. InFIG. 6, screen44has screened out and returns represented by arrow now pass through screen46. InFIG. 7, screen46has screened out and returns represented by arrow56go through screen48. InFIG. 8, screen48has screened out and returns represented by arrow58enter through screen42. Continuing the gravel packing until screen42screens out will produce a fully gravel packed annulus12with gravel16over the top of screen42.

With the gravel pack complete as shown inFIG. 1the crossover and any wash pipe attached (not shown) are removed and the production string ofFIG. 2is inserted into the packer14. When that happens, seal assemblies60,62,64and66are placed respectively in regions2,4,6and8so that every screen44,46, and48is straddled so that no flow can come through it. It essentially converts the portion of the completion inFIG. 1between screens28and42into blank pipe. It also provides flow access into the string30through its lower end34if there is no plug32there so that flow can occur into screen28from zone C. Alternatively, the port40can be put into or already be in the open position to allow flow from zone A while shutting the lower end34with plug32to block flow from zone C into screen28.

The seal assemblies60,62,64and66can have one or more external seals to the string30. The seal type can vary as long as the objective of isolating the screens44,46, and48from flow is accomplished after the gravel packing is completed. Screens44,46, and48can be small openings of any shape size and number so as to prevent gravel from getting through during gravel packing. These screens are spaced apart so that the seal assemblies60,62,64and66can land on blank pipe to seal in regions2,4,6and8. The lower end34is in region9inside the screen34. If plug32is used it can be subsequently removed in a variety of ways. If desired, the zone A and C can be produced together. Any number of producing zones can be completed in this manner and produced in any desired order by manipulating sliding sleeves such as38in ported subs36that can be positioned in any of the producing zones. The lowermost zone is preferably produced through an opening at the bottom of the string30.

When the annulus12is tightly packed due to the presence in the non-producing zone of return screens44,46, and48the migration flow between adjacent producing formations can be as low as a few barrels per day or with optimal low pressure differentials between adjacent formations and long spacing between them it is conceivable to effectively get to a no cross flow situation between adjacent producing zones. Clearly, the longer the spacing and the smaller the open hole annulus and the tighter the gravel pack, the amount of cross flow between producing formations is minimized if not eliminated.

While production is mentioned through screens28and42, the term “production” encompasses flow in the reverse direction is contemplated such as in a fracturing mode or in an injection mode such as with steam, for example.

The above description is illustrative of the preferred embodiment and various alternatives and is not intended to embody the broadest scope of the invention, which is determined from the claims appended below, and properly given their full scope literally and equivalently.