Depressurization system of annuli between casings in producing wells

Abstract

A depressurization system for the annular spaces (3) between casings in the drilling activity for wells producing oil or other fluids, so as to guarantee effective hydraulic communication between the pressurized annular space (3) and the base of the exposed rock zone (4) to be broken during depressurization, which has the solid deposit with the consequent hydraulic isolation. The system is made up of a flow control device (11); a conveyance pipe (12) between two points of the annular space (3); and an isolation device (13) linked to a centralizer in the shallow casing string (1), allowing the pressurized fluid outlet and the well wall to be close together, whereby the system used will not become clogged with solid deposits over time during the sinking of these well casings.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon, claims the benefit of, priority of, and incorporates by reference, the contents of Brazilian Patent Application No. PI 0803646-2 filed Aug. 29, 2008.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention concerns a depressurization system of annuli between casings in the drilling activity for producing wells so as to guarantee effective communication between the pressurized annular space and the rock to be broken during depressurization, which has the solid deposit creating the consequent hydraulic isolation between the pressurized fluid and said rock. This proposed invention possesses characteristics that guarantee that the system used will not become clogged with solid deposits over time after these wells have been drilled and the casings have been cemented in.

2. Fundamentals of the Invention

In high temperature wells producing oil and/or water, the increase in temperature and pressure occurs within the annular spaces between the deepest casing string (placed outside the drill column removed after reaching the depth of the reservoir) and the most shallow casing string (inside the well wall), through the thermal expansion of the fluids contained in these.

In special cases, the increase in temperature may produce an increase in the pressure of the annular space, resulting from the expansion of the drilling fluids remaining in this cavity, in such a great amount that it can exceed the limits of tensile strength causing the collapse of the casings affected.

One common form of attenuation of the problem is to maintain the cement head below the shallow-set casing shoe (part of the foundation upon which the walls are raised) so that depressurization may take place in this annular space by the formation of the fracture in the base of the well wall or below this shoe. In special cases, the beginning of production can take place several months after the completion of the well, with particles being deposited from the drilling fluid (bentonite or barytes) in the lower area of (or below) this annular space to the point of producing a hydraulic isolation between the pressurized annular space and the rock positioned below the depth of the shallow-set casing shoe, making it impossible to depressurize this annular space.

This invention has the objective of guaranteeing effective hydraulic communication between the pressurized annular space and the rock to be broken, using a depressurization system in this annular space between the casings, even though solid deposition occurs resulting in hydraulic isolation.

This innovation possesses combinations that guarantee that the system proposed will not become clogged by solid deposits over the passage of time. This invention should be used in well drilling activities, with its installation during the descent of the casings in these wells.

3. State of the Art

Drilling an oil well, performed through a rotating probe, consists of a feed obtained by the rotation and the weight applied by a drill bit located at the end of a drill string. The fragments (gravel) of the drilled rock are continuously removed by a drilling fluid.

Once the depth of the reservoir is reached, the drill column is withdrawn and the steel casing string is placed inside the drilled well. Thereafter an amount of cement is pumped between the external surface of the string and the drilled well wall, in such a way that it will fasten the casing in this position. Once the drilling is finished, the activities surrounding the string, cementing and, if necessary, blasting (creation of openings for communication between the inside of the casing and the producing formation or rock) will follow. This stage is called the completion, in other words, the set of activities destined to set up a well for the production of oil or gas.

The annular space between the casing strings and the well walls is cemented in order to isolate the rocks pierced by the drill bit, allowing at that time the initiation of safe drilling.

The casing program basically consists of a systemized process of inserting piping with pre-established specifications, followed by cementing, and in this way isolating the fluids from various permo-porous formations pierced during the construction of the well at the time when this well begins to produce.

The casing functions to prevent collapses, to avoid the contamination of potable water, to control pressure, to avoid the migration of fluids, to support the well head structure, to sustain other casings, to isolate the water from the producing formation, to house artificial lifting equipment, and to confine the production.

When an oil well is drilled, a balanced system may generate a certain amount of instability. To be able to know what phenomena are involved, to be able to quantify their intensity and minimize their force in the operations performed, is a great engineering challenge encountered when sinking an oil well.

The use of a fluid is essential in well sinking and the success of the operation depends on the composition and the properties of the fluid chosen which may perform several functions, among them, controlling the pressure to avoid the entrance of oil, gas, or water flows coming from the drilled rock and creating a quasi impermeable film on the well wall by depositing solid particles present in the fluid for the same purpose. These solid particles remain in suspension in the fluid if it is moving, but tend to settle over time if the liquid remains immobile long enough. The problem of pressure increase in the annular of wells has already produced a lot of damage, with the total loss of several producing wells in the Gulf of Mexico.

Currently, this problem has been turned around using pressure release valves installed in the shallow casing for drainage of pressure from the annular. These release valves act as shear devices and they have the disadvantage of reducing the maximum internal pressure allowable for this shallow casing and reduce reliability in the accuracy of the rupture pressure of these valves.

Another alternative is the use of production columns with thermal insulation. This column, called “vacuum insulated tubing” (VIT), has a very high cost; it damages and delays the operation of sinking production columns into wells.

U.S. Pat. No. 6,520,254 describes a system and process for generating an alternative route to the flow used in the fracture operations and “gravel pack” (sand containment) in the completion of well drilling.

The system proposed differs from the prior patent because it is not installed in gravel pack screens and the mechanism proposed does not have the objective of actively participating in the operations surrounding the pumping of liquid. The system proposed is simple and inexpensive. It is a pipe having a small diameter installed in the outer part of the deepest casing that makes up part of the annular space.

The system proposed is a passive mechanism and is driven by the natural increase in pressure, from the increase in temperature of the confined liquid and, at a later time, at the end of any pumping operation, carried out in the annular space concerned.

SUMMARY OF THE INVENTION

This invention proposes a depressurization system for the annular spaces between the casings in producing wells that is made up by three devices that guarantee effective communication between the pressurized annular space and the rock base to be broken during the depressurization process, in which solid deposits occurs with a consequent hydraulic isolation.

BRIEF DESCRIPTION OF THE DRAWINGS

So that it is possible to have a clearer understanding of the invention, the attached Figures illustrate the form of application and installation of the system proposed that may be checked along with the description of the invention.

FIG. 1 illustrates the typical design of a well for producing oil or another liquid;

FIG. 2 illustrates the typical design of a well for producing oil or other liquid after particles from the drilling fluid have precipitated;

FIG. 3 illustrates the typical design of a well for producing oil or other liquid with the depressurization system for the casings' annular spaces installed; and

FIG. 4 shows a front view of the components of the depressurization system of the annuli between casings.

DETAILED DESCRIPTION OF THE INVENTION

The system proposed seeks to avoid that the pressure in the isolated annular space exceed a level that would produce damage in the casing strings due to collapse (external pressure in the string) or because of the internal pressure.

FIG. 1 illustrates the typical design of a well producing oil or another liquid containing: most shallow casing string (1); production column (2) with flow of fluids at high temperatures; annular space (3) with mud and other drilling fluids; region of exposed rock (4) that may be broken to depressurize the annular space (3); deepest casing string (5); geological formations (6) penetrated by the well; shallow-set casing (1) shoe (7) and cementing (8) of the base of the casings.

The objective of this system is to maintain the internal pressure of the annular space (3), comprised between the deepest casing string (5) to be protected from failure due to collapse and the shallow casing string (1) (previously installed) below the pressure limit determined to cause collapse of the casing.

FIG. 2 illustrates the typical design of a well producing oil or other liquid after particles from the drilling fluid have been precipitated into the annular space (3) with a pressurized zone (9), that when the temperature is elevated, the pressure is trapped and unless it is drained, on account of the formation of a zone with solid deposits (10) which are present in the drilling fluid.

The innovation proposed promotes depressurization of this annular space (3) by hydraulic conveyance between the pressurized zone (9) and the exposed rock zone (4), which is capable of draining this pressure by absorbing various amounts of fluids (liquids and/or gaseous) through the rock having any type of formation. The elevated pressure of the fluid makes it possible to inject the fluid contained in the annular space (3).

FIG. 3 illustrates the typical design of a well producing oil or other liquid showing the depressurization system for the casings' annular spaces containing: flow control device (11); conveyance pipe (12) between two points of the annular space (3); linked isolation device (13) to a centralizer in the shallow casing string (1), allowing the pressurized fluid outlet and the well wall to be close together. The conveyance pipe (12) may be made up of one or more interconnected or continuous pipes, with cross-sections, including circular, elliptical, rectangular sections or, even, with pipes aligned concentrically with the shallow casing string (5) for protection. The shallow end of said conveyance mechanism must be close to the top of the deepest casing string (5) and its deepest end below the depth of the shallow-set casing (1) shoe (7).

Said depressurization system makes it possible for fluids to flow between a pressurized zone (9) and a solid deposit zone (10) in the annular space (3) described above and that they remain hydraulically isolated from the solids precipitated from the original fluid present in this annular space (3), or in atypical cases are hydraulically isolated by devices specifically installed to promote this isolation or by mechanical, sedimentary obstacles, or due to chemical or geological deposits in this space.

One of the principal characteristics of the system proposed is the filling of the hydraulic conveyance system, comprised thusly by: flow control device (11); conveyance pipe (12); linked isolation device (13), with a fluid of appropriate density and viscosity, and having a physical and chemical stability that impedes the precipitation of particles into its interior, in such a way as to avoid eventual clogging of the hydraulic conveyance mechanism after its installation into the well.

The fluid that will fill the depressurization system must have a density lower than that of the drilling fluid. For this reason, the upper end of this system will have a difference in the pressure of the inside of the pipe and the annular space (3). For this reason, there is a need for said flow control.

The installation of the hydraulic conveyance system proposed is made by fastening it onto the shallow casing string (1) or onto the deepest casing string (5); which make up the annular space (3) to be depressurized.

A flow control device (11) must be installed on the most shallow end of the hydraulic conveyance system which will impede the entrance of fluid into the interior of the conveyance pipe (12). The pressure external to this system will be below a value determined by the system plan.

This value determined by the plan must guarantee that the increase in pressure within the annular space (3) does not exceed a limit value before this flow control device (11)—a retention or shear valve—allows the entrance of fluid into the inside of the pressure conveyance pipe (12) to the upper end.

The linked isolation device (13) in the lower end or the deepest end of the pressure conveyance system may or may not have a retention value similar to that used on the flow control device (11) in the shallow end of this system. This lower end may terminate in a centralizer in the shallow set casing string (1), in which it may be fasten and positioned in such a way that its end is located close to the well wall.

The hydraulic communication system must be installed laterally and extern to the deepest casing string (5). The mechanism may be fastened to the deepest casing string (5) by metal straps, by brackets made for this purpose or any other fastening system. The installation of this system is performed simultaneously with the drilling and completion activities, and in the latter activity, the deepest casing string is put in place (5).

FIG. 4 shows a front view of the casings' annular depressurization system which comprises:

A flow control device (11), which makes it possible for the fluid on the inside of the system to be lower than the external fluid, resulting in the pressure internal to the system being greater than the external pressure and the retention valve or another device must prevent the flow of fluids before a certain time;

a conveyance pipe (12) between two points within the annular space; a pressurized zone (9) and the exposed rock zone (4) that may be broken;

linked isolation device (13), that may possess horizontal and vertical outlets (13a, 13b, and 13c).

The inside of the pipe will be filled with special fluid that will not permit the precipitation of solids.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. Depressurization system of annuli between casings in producing wells, characterized by being an effective communication system between the pressurized annular space (3) and the exposed rock zone (4) to be broken during depressurization.

2. Depressurization system of annuli between casings in producing wells, in accordance with claim 1, characterized by being a passive system driven by the natural increase in pressure promoted by the increase in temperature of the confined liquid and carried out at the end of any pumping operation.

3. Depressurization system of annuli between casings in producing wells, in accordance with claim 1, characterized by the installation of this system being performed simultaneously with the drilling and completion activities, in which the deepest casing string (5) is put in place.

4. Depressurization system of annuli between casings in producing wells, in accordance with claim 1, characterized by maintaining the internal pressure of the annular space (3), comprised between the deepest casing string (5) to be protected from failure due to collapse and the shallow casing string (1) (previously installed) below the pressure limit determined to cause collapse of the casing.

5. Depressurization system of annuli between casings in producing wells, in accordance with claim 1, characterized by promoting a depressurization of the annular space (3) by hydraulic communication between the pressurized zone (9) and the exposed rock zone (4), and of draining of this pressure by absorbing different volumes of fluids (liquids and/or gaseous) by a rock of any type of formation which high pressure of fluid will promote the injection of said fluid restrained on that annular space (3).

6. Depressurization system of annuli between casings in producing wells, in accordance with claim 1, characterized by having a flow control device (11 ); a conveyance pipe (12) between two points of the annular space (3); and an isolation device (13) linked to a centralizer in the shallow casing string (1), allowing the pressurized fluid outlet and the well wall to be close together.

7. Depressurization system of annuli between casings in producing wells, in accordance with claim 1, characterized by using a flow control device (11) installed on the most shallow end of the hydraulic conveyance system to impede the entrance of fluid into the interior of the conveyance pipe (12).

8. Depressurization system of annuli between casings in producing wells, in accordance with claim 1, characterized by the linked isolation device (13) having a retention value or shear valve, similar to that used on the flow control device (11), located at a lower end of the system positioned close to the well wall.

9. Depressurization system of annuli between casings in producing wells, in accordance with claim 1, characterized by the density of the fluid inside the system being lower than that of the external fluid, resulting in the internal pressure being greater than the external pressure and the inside of the pipe being filled with a special fluid that does not allow solids to precipitate.

10. Depressurization system of annuli between casings in producing wells, in accordance with claim 1, characterized by this system being installed laterally and externally to the deepest casing string (5) and being fastened to it by metal straps, by brackets made for this purpose or by any other fastening system.