METHOD AND APPARATUS FOR CENTRALIZED THERMAL RECOVERY BASED ON AN OIL RESERVOIR BY ELECTRIC HEATING EDGE AND BOTTOM WATER LAYERS WITH HORIZONTAL WELLS

Abstract

A method for centralized thermal recovery, comprising: first, providing a horizontal well in the upper part of the water layer in which a heating system is configured; then centralized preheating the oil reservoir via electrically heating the water layer, then starting centralized producing the oil after the top of the oil layer reaches an expected temperature. An electric heating system for horizontal well to heat the water, comprising, an inner liner with the upper half slotted, a heat insulation board, a sealing board, a vacuum chamber, an electric heater, a ferrite permanent magnet rod.

Claims

1. A method for centralized thermal recovering oil, for an oil reservoir with a water layer and an oil layer, comprising: providing a horizontal well in the upper part of the water layer, centralized preheating the oil reservoir via centralized heating the water layer, and starting centralized producing the oil after the top of the oil layer reaches an expected temperature.

2. the method according to claim 1, wherein, comprising side-drilling the horizontal well from an old well extending into the top water layer, or drilling the horizontal well that meets the water layer directly.

3. the method according to claim 2, wherein, comprising drilling multi-branch horizontal wells in the top water layer.

4. the method according to claim 1, wherein, comprising arranging the horizontal wells in a plane in the water layer, and determining the depth position of the horizontal section of the horizontal well based on the oil reservoir volume, and completing the horizontal well with gravel open-hole.

5. the method according to claim 1, wherein, comprising providing a heating system inside the horizontal well.

6. the method according to claim 5, wherein, comprising providing an electric-heating system inside the horizontal well.

7. the method according to claim 1, wherein, comprising centralized heating the overall oil reservoir in each individual trap when electrically heating the water layer.

8. the method according to claim 1, wherein, comprising keeping the pressure of the oil reservoir lower than the fracture pressure of the reservoir when electrically heating the water layer.

9. the method according to claim 1, wherein, comprising starting to electrically heat formation water at high-power, and then reducing power to heat water, comprising keeping the temperature of the horizontal well lower than Curie temperature.

10. the method according to claim 8, 9, wherein, comprising decreasing the pressure or temperature of the oil reservoir to keep the pressure of the oil reservoir lower than the fracture pressure and the temperature lower than Curie temperature.

11. the method according to claim 1, wherein, comprising stopping electrically heating after the centralized oil producing.

12. the method according to claim 1, wherein, comprising: preheating the oil reservoir until the top oil becomes movable and recoverable.

13. the method according to claim 1, wherein, comprising: after centralized producing the oil, separating the residual oil and the water by gravity differentiation, and reheating the water for secondary oil recovery.

14. An electric-heating system for horizontal well, comprising, an inner liner having a cavity; a heat insulation board inserting into the cavity along the diameter of the inner liner; two sealing boards provided on each side of the lower liner; an electric heater provided on the heat insulation board in the middle of the upper cavity; and a ferrite permanent magnet rod fixed on the inner of the upper inner liner; wherein the lower half of the inner liner, the heat insulation board, and the sealing board form a vacuum chamber.

15. the electric-heating system according to claim 13, wherein, the insulation board and the vacuum-enclosed chamber is configured to reduce downward transmission of thermal energy.

16. the electric-heating system according to claim 13, wherein, the sealing board is configured to be made of a high density insulation plate.

17. the electric-heating system according to claim 13, 15, comprising, the sealing boards provided on each side of the lower liner keep the inner liner stable; and the insulation board is configured to be level and the slotted upper inner liner is configured to be on the top.

18. the electric-heating system according to claim 13, wherein, the slotted upper half of the inner liner is configured to allow water and heat to flow.

19. the electric-heating system according to claim 13, comprising, the electric heater is configured to be waterproof, spiral, and in series connection, and to reduce the scale formation.

20. the electric-heating system according to claim 13, wherein, the ferrite permanent magnet rod is configured to remove the scale.

21. the electric-heating system according to claim 13, wherein, the insulation board and the vacuum chamber are configured to keep from the downward heat loss.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0056] FIG. 1 is a schematic diagram of a structure of an electric heating system positioned in a horizontal well.

[0057] FIG. 1a is a schematic diagram of the longitudinal profile of an electric heating system positioned in a horizontal well.

[0058] FIG. 1b is a schematic diagram of the cross section of an electric heating system positioned in a horizontal well.

[0059] FIG. 1c is a side view of the line of an electric heating system positioned in a horizontal well.

[0060] FIG. 2 is a schematic diagram of wellbore structure of an electric heating horizontal well for centralized thermal recovery method based on an oil reservoir by electric heating edge and bottom water layers with horizontal wells.

[0061] FIG. 3 is a schematic diagram of horizontal heating well for centralized thermal recovery.

[0062] FIG. 4 is a schematic diagram of heat transfer direction of electric heating system in horizontal wells

The solid arrow indicates the direction of direct radiant heat energy from the electric heater, and
the dotted arrow indicates the direction of heat energy transfer after being reflected by the heat insulation board.

[0063] FIG. 5 is a schematic diagram of temperature distribution curves in oil reservoir under 15 MPa pressure during centralized thermal recovery by numerical simulation. E1 and E2 respectively represent Profile Temperature of Electrically Heated Horizontal wells, and

P stands for Inter-well profile temperature of electric-heating horizontal wells, and the shaded area is the vaporized area when the bottom water invades under the condition of 15 MPa.

DETAILED DESCRIPTION

[0064] Label 1 in each figure refers to a slotted upper inner liner. Its function mainly has two points: one is to suspend the permanent magnet rods to protect the electric heater from the pressure of the upper stratum; the other is to allow the formation water to enter and leave the slotted screen pipe freely, so that the water and the electric heater can fully contact, so as to better play the thermal conductivity of water.

[0065] Label 2 refers to ferrite permanent magnet rods used to prevent scaling. According to FIG. 5 the prediction diagram of the relationship between water boiling point temperature and pressure, the higher the formation pressure is, the higher the water boiling point temperature is, and the corresponding fitting mathematical relationship is as follows:

Y=178.27x.sup.0.2509 [0066] Note: y: Boiling point temperature; x: pressure MPa.
Under the condition of electrically heated formation water, the boiling point temperature corresponding to formation water under 15 MPa is predicted to be 350 degrees Celsius and that corresponding to 28 MPa is about 450 degrees Celsius. Therefore, as long as formation pressure and the boiling point temperature of formation water are controlled to be lower than the Curie temperature 450 degrees Celsius of ferrite permanent magnet, the magnetism of permanent magnet will not be destroyed. At the same time, it must be noted that when the electric heater is DC, the magnetic pole of the ferrite permanent magnet rod must be in the same direction as the electromagnetic field produced by the electric heater. Otherwise, the magnetic force of the permanent ferrite magnet rod will gradually weaken.

[0067] Label 3 refers to a waterproof spiral electric heater connected in series. The electric heater is connected to the ground power supply through a coaxial cable. When current is applied, the spiral electric heater will generate resistance heat to heat the edge and bottom water directly, the heated edge and bottom water will transfer mainly upwards and cold water will move downwards, which makes the surrounding water moving up and down produce electromagnetic induction heat. During this period, when the direction of the magnetic field is the same as that of the electromagnetic field, the ferrite permanent magnet rods will enhance the intensity of the electromagnetic field produced by the electric heater, and vice versa, weaken the induction phenomenon of the electromagnetic field.

[0068] Label 4 refers to the heat insulation board. As shown in FIG. 4, the heat energy from the electric heater radiates to the surrounding area, and the upward heat is transferred with the upward movement of formation water, while the downward heat energy is reflected by the insulation plate, and only a very small amount of heat energy is transmitted downward. Another function of the heat insulation board 4 is to sustain the waterproof spiral electric heater connected in series 3.

[0069] Label 5 refers to a sealing board. Label 15 indicates the sealed vacuum chamber enclosed by the heat insulation board, the sealing board and the lower half of the inner liner. It keeps heat from transferring downward together with the heat insulation board.

[0070] Label 6 in FIG. 2 refers to the water and oil interface. The electric heating system is configured to be positioned in a horizontal well filled with gravel for open hole completion, as label 8. Label 7 refers to reservoir top interface, and labels 6 to 7 are reservoir thickness. Label 9 refers to a coaxial cable connecting the power supply and electric heater. Closed waterproof treatment is needed at the joint of the coaxial cable and electric heating system. Label 10 refers to a power supply, provided either a DC or AC. Label 11 in FIG. 2 and FIG. 3 refers to a single electric heating horizontal well extending in edge and bottom water layers.

[0071] Label 12 in FIG. 3 refers to an oil reservoir, label 13 refers to the edge and bottom water layers, at least one or more single electric heating horizontal wells are provided in at least one or more edge and bottom water layers on a horizontal plane 14 below oil-water interface 6. The single horizontal wells can be substituted by branched electric heating horizontal wells in order to increase electric heating efficiency and reduce the operating cost of single horizontal wells.

[0072] FIG. 5 shows that as the boiling point temperature of water corresponding to the formation pressure of 15 MPa is 350 degrees Celsius, the shaded area is the vaporized area when the bottom water invades under the condition of 15 MPa. FIG. 5 also shows that some of the formation crude oil will be pyrolyzed, resulting in a small amount of pyrolytic gas. These factors are conducive to improving the efficiency of centralized oil recovery. When the electric heating stops and enters the production stage, the temperature inside the reservoir will drop below the boiling point temperature of water step by step, and the generation of this part of water vapor and pyrolysis gas will end.

Example

[0073] A numerical simulation result shows that the static pressure in the reservoir quickly changes to thermal expansion pressure after electric heating edge and bottom water layer, and the pressure distribution is relatively uniform, which corresponds to the boiling point temperature of formation water one by one. When the electric heating stops and enters the production stage, the reservoir enters the step-down production stage, and the pressure drop is relatively fast until the end of production, and the pressure drops to 2 MPa. Obviously, the magnitude of thermal expansion pressure plays an important role in the process of oil recovery.

[0074] The temperature distribution curves in oil reservoir during centralized thermal recovery shows that the characteristics of temperature is different from that of the pressure distribution, the temperature in the oil reservoir undergoes a gradual accumulation process during the centralized electric heating process. The temperature at the bottom of the reservoir is obviously higher than that at the top, and the temperature above the electric heating horizontal well is higher than that between wells. When the electric heating is stopped, the well closure is conducive to the further uniform diffusion of unbalanced heat in the oil reservoir. In the stage of centralized production, the reservoir temperature gradually decreases with the production of crude oil and becomes more uniform. Due to the thermal insulation of the formation water, the reservoir temperature remained at a high level of about 180 degrees Celsius until the end of production.

[0075] FIG. 5 is a schematic diagram of temperature distribution curves in oil reservoir under 15 MPa pressure at the time of stopping electric heating by numerical simulation. The boiling point temperature of water corresponding to the formation pressure of 15 MPa is 350 degrees Celsius, that is to say, in the oblique shaded part of the figure, wherein the temperature is up to 650 degrees Celsius which is much higher than 350 degrees Celsius, pore water in the oil reservoir exists in a vapor state. At the same time, some of the formation crude oil will be pyrolyzed, resulting in a small amount of pyrolytic gas. These factors are conducive to improving the efficiency of centralized oil recovery. When the electric heating stops and enters the production stage, the temperature inside the reservoir will drop below the boiling point temperature of water step by step, and the generation of this part of water vapor and pyrolysis gas will end.

[0076] After centralized electrically heating the bottom water for 1100 days, the top temperature of the reservoir reaches 150 degrees Celsius. The production peak period produces 65-90 t/d of oil per day, the stable production time is 1405 days, and the recovery degree of primary production is as high as 53.8%.

[0077] Another example of centralized electric heating the bottom water for 730 days, the top temperature of the reservoir reaches 80 degrees Celsius. The stable production time is 1249 days, and the recovery degree of primary production is as high as 34.5%.

INDUSTRIAL APPLICABILITY

[0078] the method and the electric-heating system are applied to thermally recover heavy oil reservoirs and high pour-point oil reservoirs with edge and bottom water layers, especially for those oil reservoirs in the depth of middle-super deep depth which are difficultly recovered, and are widely adapted to thermal recovery of other similar types of mineral resources.