WO2000014381A1

WO2000014381A1 - Method adapted in order to prevent water from coning into an oil recovery well

Info

Publication number: WO2000014381A1
Application number: PCT/NO1999/000268
Authority: WO
Inventors: Thor Martin Hegre; Rune Woie
Original assignee: Shore-Tec Services As
Priority date: 1998-09-04
Filing date: 1999-08-26
Publication date: 2000-03-16
Also published as: NO984105D0; NO308914B1; GB0105712D0; GB2357791B; GB2357791A; NO984105L; AU5539199A

Abstract

The invention relates to a method whose object it is to prevent water from coning into an oil-bearing layer (1) of a subsoil formation during the recovery of oil from the formation. This is realized by water being extracted from a water-bearing layer (2) located in connection with the oil-bearing layer (1). Said water is carried directly into a well (4) formed in the formation, through at least one inlet (6) in the wall of the well arranged close to the oil-bearing layer (1). Then the water is returned from the well (4) to the water-bearing layer (2), possibly to another stratum of the formation, through at least one outlet (8) in the wall of the well arranged at a distance from the oil-bearing layer (1). In the well (4) are arranged packers (10) sealing against the well/tubing (5) for the recovery of oil. The packers (10) are placed on the respective side of the oil-bearing layer (1). Whenever required, the well may comprise pumping equipment, such as at least one hydraulic pump (11) to be used for the return of water. Said pump (11) may be driven by means of water which is pumped down from the surface and then injected into the water-bearing layer (2), possibly into the other stratum of the formation, concurrently with the water from the water-bearing layer (2).

Description

METHOD ADAPTED IN ORDER TO PREVENT WATER FROM CONING INTO AN OIL RECOVERY WELL

The invention relates to a method which is adapted so that water is prevented from coning into an oil-bearing stratum of a subsoil formation during the recovery of oil.

Difference in specific gravity leads to water, oil and gas normally settling in layers above one another in the petroleum-bearing part of the subsoil formation. Then, when oil is recovered from the oil layer of the deposit, the pressure drops within the oil layer round the well. Thereby the oil recovery results in the creation of a pressure gradient between the oil close to the well entrance and the water underneath the oil layer. Further said pressure gradient results in water from the underlying water layer penetrating, coning, into the oil layer. If the oil layer is thin, the water could reach all the way to the well entrance and be lead into the well, so that recovered oil may have an undesired content of water from the water layer. The water coning into the oil layer and being extracted together with the oil, leads to, among other things, a reduction in the amount of oil which may be produced from the well per time unit, and the amount of oil which may be recovered from the deposit. Besides, there will be a need for equipment that can separate the water from the oil.

So far, attempts have been made to find solutions that can limit the problem caused by water coning into the oil-bearing layer of the subsoil formation. One solution has been to make use of long horizontal wells in the oil layer. Said horizontal wells are provided with several entrances, so that the pressure gradient will be smaller than if the well were vertical with only one single entrance. Another solution has been to provide vertical wells with at least two tubings, so that water may be recovered from the under- lying water-layer concurrently with the oil. However, these known solutions have not adequately prevented a reduction in the amount of oil which may be produced from the well, or which may be recovered from the deposit. Neither have the solutions lead to any noteworthy reduction in the need for treatment of the water recovered.

The main object of the present invention is to prescribe a method which is adapted in order to prevent water from coning into the oil-bearing layer when oil is being extracted, so that the above drawbacks may be avoided/reduced. The particular feature of the method is that water is recovered from the water-bearing layer of the formation. Then the water is returned to the water-bearing layer, or possibly another stratum of the formation, without having been brought to the surface. The recovery takes place in the way that the water is taken into a well which is formed in the formation. The water is admitted through at least one inlet arranged in the well by the water-bearing layer, and preferably close to the oil- bearing layer. Then the water is returned through at least one outlet in the well, arranged by the water-bearing layer, possibly by the other stratum of the formation, and at a distance from the oil-bearing layer. The advantage of water be- ing recovered concurrently with the oil, is that a corresponding pressure drop occurs in the water-bearing layer near the oil-bearing layer, so that no pressure gradient is created between the layers. The advantage of the water being returned, is that the pressure may be maintained, and thereby contribute to facilitating the recovery of the oil from the formation. Other advantageous features of the invention will appear from the claims and the specification.

Embodiments of the invention will be explained in further detail in the following part of the specification and with ref- erence to the set of figures, in which

Fig. 1 shows a schematic section of a well for the recovery of water, the well being formed in association with a well for the recovery of oil;

Fig. 2 shows a schematic section of separate wells for the recovery of oil and water, the respective well being formed with a horizontal section in the relevant layer of the formation; and

Fig. 3 shows the same as Fig. 1, except that the pump is arranged within a lower extension of the oil tubing.

As mentioned, the invention relates to a method meant to prevent water from coning into the oil-bearing layer 1 of the formation during the recovery of oil. This is done in the way that water from a water-bearing layer 2 is extracted from the formation concurrently with the oil. The extraction is performed by the water being carried from the water-bearing layer 2 directly into a well 4 formed in the formation. Water is carried into the well 4 through at least one inlet 6 by the water-bearing layer. Said inlet 6 is arranged in the wall of the well close to the oil-bearing layer 1 and may be formed by perforation of the wall of the well. Then the water is returned to the water-bearing layer 2, possibly to another stratum of the formation, without having been brought out of the well 4. This happens by the water being carried out of the well 4 through at least one outlet 8 by the water-bearing layer 2, possibly by the other stratum. Said outlet 8 is provided in the wall of the well at a distance from the oil- bearing layer 1, and may be formed by perforation of the wall of the well. The extraction from and the return to the waterbearing layer 2 preferably takes place near an oil recovery well .

The well 4 which is used for the extraction and return of water, may either be formed in association with the oil re- covery well, or as a separate well. Likewise, the wells for the recovery of water and oil may each be configured with a horizontal section in the respective layer and preferably with inlets along the major part of each horizontal section. Said horizontal section of the well 4 for the extraction of water, extends close to the oil-producing well and the oil layer 1. The water may be pumped from the inlet 6 and back into the respective layer through an outlet 8 of the well 4. Clearly, the well 4 will have to be formed with the required casings and liners, and with packers 10 etc., so that oil and water may be kept separate in the well 4. Besides, the well 4 must have pumping equipment 11, 12, so that water may be pumped through the well 4 and out into the formation across the outlets 8. Said pumping equipment 11, 12 is preferably formed of at least one hydraulically operated pump 11, 12. The pump 11, 12 is preferably driven by means of surface water supplied through a suitable supply pipe 13. Water from the water-bearing layer 2 is drawn into the pump 12 through a suitable pipe socket 15. Through a suitable outlet pipe 14 the water supplied for the operation of the pump 11, 12 is then injected into the water-bearing layer 2, possibly into another stratum of the formation. The injection of the water driving the pump 11, 12 is carried out concurrently with the injection of the water from the water-bearing layer 2.

In the set of figures the supply pipe 13 for liquid for the operation of the pump 11, 12 extends to the surface. Clearly, the supply pipe 13 may, however, just as well be terminated at the packer 10 above the oil-bearing layer 1, cfr. Figs. 1 and 3, alternatively as a pipe socket on the pump 11, 12, cfr. Fig. 2. In that case, the liquid for the operation of the pump is fed to the supply pipe 13 through the annulus between the tubing 5 for oil and the well 4, alternatively through the well 4.

Fig. 3 shows how the pump 11, 12 may be arranged within a lower extension of the oil tubing. The tubing 5 is equipped with a packer 16 sealing against the pump 11, 12, and openings for pipe sockets in the pump 11, 12. Said pipe sockets form at least one inlet and one outlet for the liquid driving the pump, and at least one inlet for the water extracted from the water-bearing layer 2. In addition the well must at least be provided with further packers 10 below the perforations forming inlets for the oil in the well 4 and the tubing 5. Otherwise, it should be mentioned briefly that it is the properties of the formation in question, which will be decisive for the positioning of inlets and outlets for water in the well, and to what is required in terms of pump capacity, packers, casings and liners etc. It should also be mentioned that the set of figures is highly distorted in terms of longitudinal and transversal dimensions .

Claims

C l a i m s

1. A method adapted in order to prevent water from coning into an oil-bearing layer (1) of a subsoil formation during the recovery of oil from the formation, charac t eri z ed i n that water is extracted from a water-bearing layer (2) of the formation, that the water is carried directly into at least one well (4) which is formed in the formation, said water being lead into the well (4) through at least one inlet (6) ar- o ranged in the wall of the well, preferably close to the oil-bearing layer (1) , and that the water is carried back from the well (4) to the water-bearing layer (2) , possibly another layer of the formation, the water being carried out of the well (4) through at least one outlet s (8) arranged in the wall of the well at a distance from the oil-bearing layer (1) .

2. A method according to claim 1, chara c t e r i z e d i n that the water is pumped from said inlet (6) out through said outlet (8) in the well (4) .

o 3. A method according to claim 1 or 2 , c ha ra c t e r i z e d i n that the water is preferably pumped by means of at least one hydraulic pump (11, 12) positioned in the well (4) .

4. A method according to claim 3, cha ra c t e r i z e d 5 i n that said pump (11, 12) is driven by means of water pumped from the surface, said water being injected into the water-bearing layer (2) , possibly into the other stratum of the formation, concurrently with water from the water-bearing layer (2) .

5. A method according to claim 3, c h a r a c t e r i z e d i n that said pump (11, 12) is positioned within an ex- tension of a tubing (5) for oil, said tubing being formed with a packer (16) above the pump (11, 12) and with openings for at least one inlet and outlet socket for the liquid driving said pump (11, 12) , and at least one inlet socket for the water from the water-bearing o layer (2) of the formation.

6. A method according to any one of the preceding claims, c h a r a c t e r i z e d i n that the well (4) is formed in association with the well for the recovery of oil.

s 7. A method according to any one of the preceding claims, c h a r a c t e r i z e d i n that the well (4) is formed as a separate well for the extraction of water.

8. A method according to any one of the preceding claims, c h a r a c t e r i z e d i n that the well (4) is o formed with vertical sections, possibly a horizontal section, extending close to the oil-producing well, possibly the oil-bearing layer (1) of the formation.

9. A method according to any one of the preceding claims, c h a r a c t e r i z e d i n that the water is extraced 5 concurrently, possibly alternately, with the recovery of oil.