RU2563510C1 - Bottom-hole heater and method for improvement of oil recovery using it - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: heating method of a hydrocarbon-bearing formation by a bottom-hole heater consists in installation of the bottom-hole heater and supply to it of current so that the bottom-hole heater provides heating performed by electric resistance of at least one section of the formation. Heat power of the bottom-hole heater is changed depending on the state of its surrounding medium. The bottom-hole heater includes a cylindrical or tubular housing with heating elements and a current lead in the upper part. The heater has an additionally installed hydroprotection device representing an elastic membrane filled with a liquid heat carrier. With that, the upper part of the elastic membrane is fixed by means of a clamp on an intermediate bush attached to the housing, and the lower part is attached with a clamp by means of a bush to a pipe. Heat carrier is contained in the space restricted by the head, the pipe, the housing, the intermediate bush and the elastic membrane. Additionally, well liquid flowing through the heater is heated by the heater.

EFFECT: increasing operating life of a bottom-hole heater, improving its reliability and increasing operating safety of the well.

4 cl, 4 dwg, 4 tbl

Description

The invention relates to the oil industry and is intended for thermal effects on the bottomhole zone and the oil reservoir to prevent the formation of paraffin hydrate deposits in the perforation zone and under pumping equipment, to increase the permeability of the oil reservoir and to increase oil recovery in general.

Heat treatment of the bottom-hole zone of the reservoir is intended to melt and remove paraffin and asphalt-tar deposits, to increase the filtration properties of the rocks that make up the oil reservoir, and lower the viscosity of the reservoir oil.

Bottom-hole heating of the bottom-hole zone helps to melt the paraffin and tar deposits and increase the permeability of the bottom-hole zone, reduce the viscosity of the oil and improve its fluidity.

Currently, there are several types of different devices for thermal stimulation of a formation:

- electrode electric heaters [Utility model patent No. 92087, 125249, Patents No. 2206717, 2208145, Applications No. 95107491/03, No. 2004111016/03, No. 96123652/03].

The disadvantage is heating by means of electrolyte currents, which significantly limits the temperature of the heater and reduces reliability. It is difficult to monitor the state of the heater and the electrolyte itself, and the conductivity of electrolytes increases with increasing temperature, which will lead to an undesirable effect - an increase in the thermal power of the heater as the temperature rises. These effects will require the installation of temperature sensors in the heater, the organization of temperature control of the heater by ground equipment, which will complicate the system as a whole.

- induction electric heaters due to induced inductive currents carry out heating of the heater body, special tubes in which the conductors are laid or directly downhole equipment - tubing or casing [Patent RU 2200228, RU 2249096]. The disadvantage is the complex ground equipment, high frequency currents, respectively, large losses.

- electro-gas-chemical - use the heat of chemical reactions [Patent RU 2235870], electricity is necessary only to start heat-generating processes. The disadvantage is a short duration of action.

- pumping a heat agent from the surface of the well [Patent RU 2471064]. The disadvantage is the large losses during transportation of the heat agent. The need for another hydraulic channel for the delivery of coolant to the bottom of the well.

- electrical, based on the principle of converting electrical energy into heat. Electric heaters are the simplest of all of the above. They can be performed both for dynamic processes - carrying out tripping operations to remove paraffin-hydrate plugs by melting them, and for stationary installation, for example, in the bottom-hole zone of a well for thermal impact and enhanced oil recovery.

A well-known electric heater [Patent RU 120697], comprising a hollow body with an electric heating element and a current lead, characterized in that the body is made flow-through with an open lower end and upper side holes, and the electric heating element is made in the form of a coaxial stacking with the body.

Known electric downhole heater [Patent RU 24854] for removing hydrate-paraffin formations in an oil or gas well containing a heating element, a wave-like body, the wave diameter of which increases from the bow of the body, the instrument head for connecting to a cable head, characterized in that the waves are made inclined grooves, the angle of inclination of which is made from the condition of overlapping the gap of the groove at the entrance to it and exit from it in a direction parallel to the axis of the housing, and the direction of inclination of the grooves to adjacent the waves of the housing is made in one or in different directions.

A known heater [Patent RU 37521], comprising a housing with a tubular electric heater (TEN) inside, a cable head, means of current supply to the TEN with a seal of current-carrying cable conductors, characterized in that a cone is made in the cable head with the cone tip pointing inside the heater and with a partition, in which holes for current-carrying conductors of the cable are made, a conical plug of elastic material is mounted in the cone of the cable head and with holes for current-carrying conductors, a push-in sleeve is installed between the cable head and the heater left, a centralizer is located on the heater body.

Closest to the proposed one is the downhole electric heater according to the patent [Patent RU 2006571], comprising a hollow cylindrical body with a heating element and a current lead in its upper end, characterized in that it is equipped with a metal heat-conducting core located inside the hollow cylindrical body and a monolithic metal radiator of heat directional flows located at the lower end of the hollow cylindrical body, and the electric heating element is placed on an external turn NOSTA metallic thermally conductive core, a monolithic metallic radiator heat flow directional is in contact with the metal heat-conductive core and the cylinder cavity is filled with insulating material.

The disadvantage of all of the above inventions is either the limited power of the downhole heaters, or their low reliability. These provisions are explained by the fact that the well heater needs to convert electrical energy into heat and transfer it to the well fluid. In this case, overheating of the downhole heater can cause its failure and violate the safety of work in the well.

The technical problem solved by the claimed invention is to simplify and improve the reliability of the control system of a downhole heater, simplifying the design of its housing.

The technical problem is achieved by the fact that it is proposed the use of heating elements from a certain group of materials or a temperature control system and the use of hydraulic protection for the well heater body.

Heat transfer processes are limited by the area of the bodies between which heat transfer occurs. Basically, electric heaters have a solid or tubular metal body, through which heat is transferred from the downhole heater to the downhole fluid. A design of a downhole heater is proposed in which the heating elements interact with a coolant (for example, Penta-410) that transfers heat to the outer walls of the downhole heater. The working temperature of the coolant in a closed circuit is up to 300 degrees, above which its destruction begins.

In some cases of well operation, preconditions may arise for overheating of the well heater, for example, when the latter is in continuous contact with the gas medium. This is fraught with failure of the downhole heater and poses a threat to the safety of work in the well. To prevent overheating of the downhole heater, the easiest way is to use the effect of thermal stabilization through the use of suitable materials as heating elements.

To analyze the effectiveness of the use of various materials as heating elements, we present the following calculations:

R = R ₀ · (1 + α-ΔT),

where R is the final resistance of the material of the heating element;

R ₀ is the resistance of the material of the heating element at 20 ° C;

α is the temperature coefficient of resistance.

Temperature coefficient of resistance

Conductor α, 10 ^-3 * C ^-1 Aluminum 4.2 Tungsten 5 Iron 6 Gold four Constantan (Ni-Cu + Mn alloy) 0.05 Brass 0.1-0.4 Magnesium 3.9 Manganin (an alloy of copper, manganese and nickel - instrument) 0.01 Copper 4.3 Nickel silver (alloy of copper, zinc and nickel) 0.25 Nickel (an alloy of copper and nickel) 0.1 Nickel 6.5 Nichrome (an alloy of nickel, chromium, iron and manganese) 0.1 Tin 4.4 Platinum 3.9 Mercury one Lead 3,7 Silver 4.1 Steel 4.00 February (Cr (12-15%); Al (3.5-5.5%); Si (1%); Mn (0.7%); + Fe) 0.1 Zinc 4.2

For nichrome traditionally used in heaters, an increase in the temperature of the heating element by 100 ° C will lead to an increase in resistance by 1%, at 200 degrees - 2%. Those. the power allocated by the heater remains virtually unchanged, which entails a significant probability of failure of the downhole heater due to overheating. This can happen when the flow of the well fluid stops or the fluid is replaced by gas, i.e. under external conditions, significantly impairing the heat sink from the downhole heater, or malfunctions in the temperature control system.

For a nickel heating element, an increase in the temperature of the heater by 100 degrees will lead to an increase in ohmic resistance by 1.65 times, at 200 degrees the resistance will increase by 2.3 times, respectively, which will lead to a decrease in the heater power by 2.3 times. Thus, the effect of thermal stabilization is manifested and the reliability of the downhole heater is increased.

Iron and copper have similar temperature properties.

Another way to prevent heater overheating is to use a temperature control system that changes the power transmitted to the heating elements by installing additional temperature control sensors directly on the well heater or a temperature control system located in the ground station.

The current designs of downhole heaters are equipped with a massive body, necessary to withstand significant downhole pressure, reaching 300 bar. In this regard, it is proposed to use hydraulic protection, which consists in the following - the borehole fluid through the channels in the body acts on an elastic diaphragm filled with a liquid coolant [Kaplan L.S. Oil and associated gas production operator. Ufa 2005]. Deformation of the diaphragm entails a decrease in volume and an increase in coolant pressure. The alignment of the external and internal pressures of the downhole heater occurs and, accordingly, the casing is unloaded from mechanical stresses.

In addition, an increase in the temperature of the coolant causes its expansion, which can lead to damage to the housing. Hydroprotection will solve this problem.

Figure 1 shows a downhole heater.

Figure 2 shows a downhole heater with hydroprotection.

According to figure 1, the downhole heater consists of a head 1 with internal or external thread for connection with a tubing string or umbilical end, rigidly connected to the head 1 by a pipe 2 located on the head 1 of the current lead 3, with wires 4 connected to it by one the end, and the second to the heating elements 5, mounted on the pipe 2 by means of holders 6. On the head 1 is fixed a housing 7 with a sleeve 8 attached thereto. In the space bounded by the head 1, the pipe 2, the housing 7 and the sleeve 8 there is a coolant spruce 9, for pouring head 1 in which openings are provided, closing stoppers 10 between the head 1 and the housing 7 as well as between the housing 7 and the sleeve 8 are installed sealing elements 11.

The proposed downhole heater operates as follows:

after connecting the head 1 to the tubing string or the umbilical tip with a corresponding connection of the power line to the current lead 3, the downhole heater is delivered to the zone necessary for heating, after which electric current is supplied to the heating elements 5, the heat from which is transferred through the heat carrier 9 to the housing 7, head 1 and sleeve 8, due to which the bottom-hole zone is heated. In addition, heat is transferred from the heating elements 5 through the holders 6 to the pipe 2, which heats the borehole fluid passing through it.

According to figure 2, the downhole heater consists of a head 1 with internal or external thread for connection with a tubing string or umbilical end, rigidly connected to the head 1 by a pipe 2 located on the head 1 of the current lead 3, with wires 4 connected to it by one the end, and the second - to the heating elements 5, mounted on the pipe 2 by means of holders 6. On the head 1 is fixed a housing 7 with an intermediate sleeve 12 attached to it, on which, in turn, the lower housing 13 is fixed, having holes 14 with p the sleeve 8 attached to it. On the intermediate sleeve 12, with the clamp 15, the upper part of the elastic diaphragm 16 is fixed, the lower part of which is attached with the clamp 15 via the sleeve 17 to the pipe 2. In the space bounded by the head 1, pipe 2, the housing 7, the intermediate sleeve 12 and elastic diaphragm 16, there is a coolant 9, for filling which in the head 1 and the intermediate sleeve 12 holes are provided that are closed by plugs 10. At the contact points of the housing 7 with the head 1 and the intermediate sleeve 12, sealing elements are installed cients 11.

The principle of operation of such a downhole heater is similar to that described above, except that when the downhole heater is immersed in the well, the downhole fluid through the holes 14 enters the lower housing 13 and puts pressure on the elastic diaphragm 16, which causes a decrease in its volume and a corresponding increase in the pressure of the coolant 9 to approximately equal to the value of the pressure of the well fluid. In addition, when heated, the coolant 9 expands and puts pressure on the elastic diaphragm 16, which causes an increase in its volume and reduces the load on the housing 7.

The technical result of the claimed invention is to increase the life of the downhole heater, increase its reliability and increase the safety of well operation.

Known methods for stationary heat treatment of the bottom-hole zone of the formation, namely, that in the well in the interval of the formation below the pumping equipment, stationary heating devices are installed and the formation is heated during operation continuously or according to a predetermined mode [Oil production reference book. Ed. Sh.K. Gimatudinova, Moscow: Nedra, 1974].

Closest to the proposed is a method of heating a hydrocarbon-containing formation with a heater, which means that a heater is installed in the formation and current is supplied to the heater in such a way that the heater provides heating through at least a portion of the formation by electrical resistance [Patent RU 244113 8].

The disadvantage of this method is the use of linear heating, which negatively affects the efficiency of the downhole heater and entails the possibility of overheating.

As you know, the heat transfer coefficients between a metal wall and a liquid very much depend on the state of the latter and the presence of gas in it, for example:

Heat transfer coefficients W / (m2 * K) Calm water - metal wall 450 Flowing water - metal wall

450 + 2100 $$\sqrt{v}$$

m / s Boiling water - metal wall 4500 Condensing water vapor 10500 Air - smooth surface 5,6 + 4 * v m / s * where v is the flow velocity in m / s. (Handbook of Physics, H. Kuhling, Moscow, MIR, 1983)

As can be seen from the above data, the heat transfer coefficients are very different for different states of the substance surrounding the downhole heater.

Calculation of heat transfer wall of the downhole heater - environment

P = σ · S · ΔT

ΔT = 100 ° C

S = π · d · L - heat transfer area

L = 5 m - the length of the downhole heater

d = 80 mm - diameter of the downhole heater

σ is the heat transfer coefficient

Heat transfer calculation results for the downhole heater wall - environment

Well heater area, m2 1,256 Power transmitted with standing water, W 56520 Power transmitted at a speed of well fluid 1 m / s, W 320 280 Power transmitted by boiling water, W 565,200 Power transmitted by air, W 703

Calculation of the temperature of the well heater for various conditions of the well fluid

ΔT = P / (σ · S)

The results of calculating the temperature of the downhole heater for various conditions of the downhole fluid

The initial temperature of the well fluid twenty ° C Well heater power twenty kW Well heater temperature with standing water 55 ° C Well heater temperature at well fluid velocity of 1 m / s 26 ° C Boiling water well heater temperature 24 ° C The temperature of the downhole heater in the air in the elevator string 612 ° C

The calculation results show that the temperature of the downhole heater varies depending on the state of its environment. In accordance with this, it is necessary to use a temperature control system that will allow to determine the temperature of the downhole heater and change the power transmitted to them, preventing the temperature from rising above the value that is necessary for the destruction of the coolant.

The implementation of the method is shown in FIG. 3 and FIG. 4 and is as follows

On the ground platform 18 next to the drilled well 19, which is equipped with a casing 20 with an open reservoir 21, a mobile ground equipment 22 with a drum or a bay 23 of a flexible load-bearing polymer pipe 24 is placed, containing a power wire 25, the upper end of which is connected to the temperature control system 26 after which a downhole heater 27 is connected to the tip of the flexible load-bearing polymer pipe 24, and the lower end of the power wire 25 is connected to its current lead 3, and connected to the bushing 8 of the downhole heater 27 equipment 28 is needed to lift the borehole substance 29, after which it is launched into the borehole 19 of a flexible load-bearing polymer pipe 24 with a borehole heater 27, after which it is placed in the zone of the productive formation 21, the borehole heater 27 controlled by the temperature control system 26 is heated, from which heat is transferred not only the zone of the reservoir 21, but also the borehole fluid passing through the pipe 2.

The technical result of the proposed method is to increase oil recovery and improving the safety of its operation.

Claims (4)

1. A downhole heater, comprising a cylindrical or tubular body with heating elements and a current lead in the upper part, characterized in that it has an additionally installed hydraulic protection device, which is an elastic diaphragm filled with liquid coolant, and the upper part of the elastic diaphragm is fixed by means of a clamp on the intermediate sleeve, attached to the body, and the lower part is attached with a collar by means of a sleeve to the pipe, the coolant is in the space bounded by the head th, pipe, casing, intermediate sleeve and the elastic diaphragm. 2. The downhole heater according to claim 1, characterized in that the material of the heating elements has a positive temperature coefficient of resistance comparable to copper, nickel or iron. 3. The downhole heater according to claim 1, characterized in that it comprises a temperature control device directly in the heater body or in the ground control station. 4. A method of heating a hydrocarbon-containing formation by a downhole heater, the method being that a downhole heater is installed in the formation and a current is supplied thereto so that the downhole heater provides heating through at least a portion of the formation by electrical resistance, wherein the thermal power of the downhole heater is changed depending on the state of its environment, characterized in that the heater according to any one of paragraphs is used as a heater. 1-3, which additionally heats the borehole fluid passing through it.

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