SYSTEM AND METHOD FOR RECOMPLETION OF OLD WELLS
A system for recompletion of an old well in order to achieve an increased oil recovery from a reservoir, said system comprising a pipe inserted into the old well, at least two constrictors or swell packers being arranged along the length of the recompleted well and defining a well section between two successive constrictors or swell packers, said system further comprising at least one autonomous valve arranged in said well section defined between said two successive swell packers or constrictors. Disclosed is also a method for recompletion of an old well in order to achieve an increased oil recovery from a reservoir.
Latest STATOIL ASA Patents:
The present invention relates to a system and method for recompletion of old wells. More specifically the invention relates to a system and a method as disclosed in the preamble of claim 1 and 7, respectively.
In a preferred embodiment of the invention a plurality of autonomous valves or flow control devices are substantially as those described in WO 2008/0048745 A1, belonging to the applicant of the present application.
Devices for recovering of oil and gas from long, horizontal and vertical wells are known from US patent publications Nos. 4,821,801, 4,858,691, 4,577,691 and GB patent publication No. 2169018. These known devices comprise a perforated drainage pipe with, for example, a filter for control of sand around the pipe. A considerable disadvantage with the known devices for oil/and or gas production in highly permeable geological formations is that the pressure in the drainage pipe increases exponentially in the upstream direction as a result of the flow friction in the pipe. Because the differential pressure between the reservoir and the drainage pipe will decrease upstream as a result, the quantity of oil and/or gas flowing from the reservoir into the drainage pipe will decrease correspondingly. The total oil and/or gas produced by this means will therefore be low. With thin oil zones and highly permeable geological formations, there is further a high risk that of coning, i.e. flow of unwanted water or gas into the drainage pipe downstream, where the velocity of the oil flow from the reservoir to the pipe is the greatest.
From World Oil, vol. 212, N. 11 (11/91), pages 73-80, is previously known to divide a drainage pipe into sections with one or more inflow restriction devices such as sliding sleeves or throttling devices. However, this reference is mainly dealing with the use of inflow control to limit the inflow rate for up hole zones and thereby avoid or reduce coning of water and or gas.
WO-A-9208875 describes a horizontal production pipe comprising a plurality of production sections connected by mixing chambers having a larger internal diameter than the production sections. The production sections comprise an external slotted liner which can be considered as performing a filtering action. However, the sequence of sections, of different diameter creates flow turbulence and prevent the running of work-over tools.
U.S. Pat. No. 5,435,393 describes a production pipe with a lover drainage pipe divided into sections and with one or more inflow restriction devices which controls the flow of oil or gas from the reservoir into the drainage pipe based on the precalculated loss of friction pressure along the drainage pipe, the precalculated production profile of the reservoir and the precalculated inflow of gas or water. This publication does thus not relate to recompletion of old wells, nor to the use of autonomous flow control devices in said recompletion.
When extracting oil and or gas from geological production formations, fluids of different qualities, i.e. oil, gas, water (and sand) is produced in different amounts and mixtures depending on the property or quality of the formation. None of the above-mentioned, known devices are able to distinguish between and control the inflow of oil, gas or water on the basis of their relative composition and/or quality.
With the autonomous valve as described in WO 2008/0048745 A1 is provided an inflow control device which is self adjusting or autonomous and can easily be fitted in the wall of a production pipe and which therefore provide for the use of work-over tools. The device is designed to “distinguish” between the oil and/or gas and/or water and is able to control the flow or inflow of oil or gas, depending on which of these fluids such flow control is required.
The device as disclosed in WO 2008/0048745 A1 is robust, can withstand large forces and high temperatures, needs no energy supply, can withstand sand production, is reliable, but is still simple and very cheap.
A problem with the prior art is that the well, with or without inflow control devices, has to be abandoned since the well is not able to produce anymore due to gas and/or water breakthrough.
In existing wells large quantities of oil will remain along the path of the well due to “short-circuit” effects, i.e. that only parts of the well are producing oil. As shown in the enclosed
Short-circuit effects might also appear in low oil zones with zones comprising gas and/or water above or below them.
The system and method according to the invention seeks to reduce or eliminate the above and other problems or disadvantages by inserting a pipe with a at least one, and preferably a plurality of autonomous valves into an existing well, and thus increase oil recovery with limited investments. The invention might thus be regarded as an improvement of an existing stinger solution in which an impervious pipe section having solid walls are arranged on a location in the well in which gas breakthrough previously has been experienced.
The system and method according to the invention are characterized by the features as disclosed in the characterizing clause of claim 1 and 7, respectively.
Advantageous embodiments are set forth in the dependent claims.
The present invention will be further described in the following by means of examples and with reference to the drawings, where:
The present invention exploits the effect of Bernoulli teaching that the sum of static pressure, dynamic pressure and friction is constant along a flow line:
When subjecting the disc 9 to a fluid flow, which is the case with the present invention, the pressure difference over the disc 9 can be expressed as follows:
Due to lower viscosity, a fluid such as gas will “make the turn later” and follow further along the disc towards its outer end (indicated by reference number 14). This makes a higher stagnation pressure in the area 16 at the end of the disc 9, which in turn makes a higher pressure over the disc. And the disc 9, which is freely movable within the space between the disc-shaped bodies 4, 7, will move downwards and thereby narrow the flow path between the disc 9 and inner cylindrical segment 6. Thus, the disc 9 moves dawn-wards or up-wards depending on the viscosity of the fluid flowing through, whereby this principle can be used to control (close/open) the flow of fluid through of the device.
Further, the pressure drop through a traditional inflow control device (ICD) with fixed geometry will be proportional to the dynamic pressure:
where the constant, K is mainly a function of the geometry and less dependent on the Reynolds number. In the control device according to the present invention the flow area will decrease when the differential pressure increases, such that the volume flow through the control device will not, or nearly not, increase when the pressure drop increases. A comparison between a control device according to the present invention with movable disc and a control device with fixed flow-through opening is shown in
This represents a major advantage with the present invention as it can be used to ensure the same volume flowing through each section for the entire horizontal well, which is not possible with fixed inflow control devices.
When producing oil and gas the control device according to the invention may have two different applications: Using it as inflow control device to reduce inflow of water, or using it to reduce inflow of gas at gas break through situations. When designing the control device according to the invention for the different application such as water or gas, as mentioned above, the different areas and pressure zones, as shown in
-
- A1, P1 is the inflow area and pressure respectively. The force (P1·A1) generated by this pressure will strive to open the control device (move the disc or body 9 upwards).
- A2, P2 is the area and pressure in the zone where the velocity will be largest and hence to represents a dynamic pressure source. The resulting force of the dynamic pressure will strive to close the control device (move the disc or body 9 downwards as the flow velocity increases).
- A3, P3 is the area and pressure at the outlet. This should be the same as the well pressure (inlet pressure).
- A4, P4 is the area and pressure (stagnation pressure) behind the movable disc or body 9. The stagnation pressure, at position 16 (
FIG. 2 ), creates the pressure and the force behind the body. This will strive to close the control device (move the body downwards).
Fluids with different viscosities will provide different forces in each zone depending on the design of these zones. In order to optimize the efficiency and flow through properties of the control device, the design of the areas will be different for different applications, e.g. gas/oil or oil/water flow. Hence, for each application the areas needs to be carefully balanced and optimally designed taking into account the properties and physical conditions (viscosity, temperature, pressure etc.) for each design situation.
The spring element 18 is used to balance and control the inflow area between the disc 9 and the inlet 10, or rather the surrounding edge or seat 19 of the inlet 10. Thus, depending on the spring constant and thereby the spring force, the opening between the disc 9 and edge 19 will be larger or smaller, and with a suitable selected spring constant, depending on the inflow and pressure conditions at the selected place where the control device is provided, constant mass flow through the device may be obtained.
When producing oil and/or gas the conditions may rapidly change from a situation where only or mostly oil is produced to a situation where only or mostly gas is produced (gas breakthrough or gas coning). With for instance a pressure drop of 16 bar from 100 bar the temperature drop would correspond to approximately 20° C. By providing the disc 9 with a thermally responsive element such as a bi-metallic element as shown in
The above examples of a control device as shown in
An embodiment of a method according to the invention preferably comprises the following steps (not necessarily in said order):
-
- Providing an old well 24,
- Providing a new pipe 27 comprising a plurality of autonomous valves 2 arranged along the length of the pipe 27,
- passing said pipe 27 into said old well 24 for recompleting the old well 24,
- providing a plurality of swell packers or constrictors 29 along the well to seal between the inserted pipe 27 and the old well 24 and to define a plurality of well sections between two successive constrictors or swell packers 29 in each of which sections at least one autonomous valve 2 is to be located,
- in order to create a substantially uniform inflow into the recompleted well 24, 27 and thus an increased oil recovery.
Further, the inserted pipe 27 preferably covers substantially the whole length of the old well 24.
In a most basic embodiment according to the invention, the pipe 27 just covers a limited length to be arranged at a very distinct location in the well 24 in which breakthrough is to be prevented, i.e. a distinct fraction in the formation or reservoir 26 intersected by the well 24. This location will then be isolated by providing one constrictor or swell packer 29 on each side of said fraction, and with just one autonomous valve 2 arranged in such a single isolated section of the well.
With the valve or control device described in WO 2008/0048745 A1, due to the constant volume rate, a much better drainage of the reservoir is thus achieved. This result in significant larger production of that reservoir.
Even though the well 24 shown in
As also mentioned in the introductionary part of the description, the autonomous valves 2 preferably are those described in WO 2008/0048745 A1 and above, but any type of autonomous valve (e.g. electronically operated) is conceivable within the context of the invention.
Claims
1. A system for recompletion of an old well in order to achieve an increased oil recovery from a reservoir, said system comprising:
- a pipe inserted into the old well, at least two constrictors or swell packers being arranged along the length of the recompleted well and defining a well section between two successive constrictors or swell packers; and
- at least one autonomous valve arranged in said well section defined between said two successive swell packers or constrictors.
2. A system according to claim 1, wherein a plurality of well sections are defined along the length of the well and that at least one autonomous valve is arranged within each well section.
3. The system according to claim 1, wherein the at least one autonomous valve operates by the Bernoully principle and has a substantially constant flow-through volume above a given differential pressure.
4. The system according to claim 1, wherein the inserted pipe covers substantially the whole length of the old well.
5. The system according to claim 1, wherein the well is a horizontal well.
6. The system according to claim 1, wherein the well is a well of any inclination from horizontal, including vertical.
7. A method for completion of an old well in order to achieve an increased oil recovery from a reservoir, comprising the following steps (not necessarily in said order):
- providing a pipe comprising at least one autonomous valve arranged in the pipe,
- passing the pipe into the old well for recompleting said old well,
- providing at least two swell packers or constrictors along the well to seal between the inserted pipe and the old well to define at least one well section between said two successive constrictors or swell packers in which at least one well section the at least one autonomous valve is arranged.
8. A method according to claim 7, further comprising the step of providing a plurality of well sections along the well in each of which sections at least one autonomous valve is arranged.
9. The method according to claim 8, further comprising the step of covering substantially the whole length of the old well with the inserted pipe.
10. The method according to claim 7, wherein the at least one autonomous valve operates by the Bernoully principle and has a substantially constant flow-through volume above a given differential pressure.
11. The system according to claim 2, wherein the at least one autonomous valve operates by the Bernoully principle and has a substantially constant flow-through volume above a given differential pressure.
12. The system according to claim 2, wherein the inserted pipe covers substantially the whole length of the old well.
13. The system according to claim 3, wherein the inserted pipe covers substantially the whole length of the old well.
14. The system according to claim 2, wherein the well is a horizontal well.
15. The system according to claim 3, wherein the well is a horizontal well.
16. The system according to claim 4, wherein the well is a horizontal well.
17. The system according to claim 2, wherein the well is a well of any inclination from horizontal, including vertical.
18. The system according to claim 3, wherein the well is a well of any inclination from horizontal, including vertical.
19. The system according to claim 4, wherein the well is a well of any inclination from horizontal, including vertical.
20. The method according to claim 8, wherein the at least one autonomous valve operates by the Bernoully principle and has a substantially constant flow-through volume above a given differential pressure.
Type: Application
Filed: Apr 1, 2009
Publication Date: Mar 10, 2011
Applicant: STATOIL ASA (STAVANGER)
Inventors: Vidar Mathiesen (Porsgrunn), Haavard Aakre (Skien)
Application Number: 12/935,958
International Classification: E21B 43/00 (20060101); E21B 33/12 (20060101);