RU2559975C1 - Heating method of well bottom hole area and device for its implementation - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: heating method of well bottom hole area is characterized in that in the bottom hole area of the well in the perforation interval in the shank of the tubing leak below the downhole submersible equipment depending on the desired length and the heating capacity, one or several interconnected downhole electrical resistance heaters are lowered. The controlled warming of near-wellbore of the bottom hole area and the reservoir fluid entering into the well is carried out. The device for implementing the method is composed of interconnected downhole heater in the form of heating elements controlled from the surface and the air compression chamber or unit of seal section, with the ability of compensation of the compression impact of the heated coolant. The device also comprises an internal temperature sensor and a regulator of power supplied to the downhole heater formed as a thyristor rectifier unit, controlled by the connection with it by the programmable controller of the heating control station with the main indicator in the form of temperature characteristics of the device operation.

EFFECT: increase in efficiency of thermal influence on the near-wellbore in the vicinity of installation of the downhole heater, increasing the flow of fluid from the reservoir, and reducing the viscosity of the borehole fluid in front of the receiving filter of the borehole pump.

4 cl, 5 dwg

Description

The invention relates to the oil and gas industry and is intended for thermal effects on the bottom-hole zone, reducing the viscosity of the wellbore fluid before receiving the submersible pump and to prevent the formation of asphaltene-paraffin-hydrate deposits.

A known method of influencing an oil reservoir (patent RU No. 2379495), including the descent of a borehole electric heater on a string of tubing in the interval of the oil reservoir with subsequent heating and production of heated products from the well. The production of pre-heated well products is carried out with periodic injection of pre-heated well products back into the oil reservoir. The volume and pressure of the injection of heated products and, accordingly, the depth of penetration of the heated products into the oil reservoir are increased with each period until the maximum permissible pressure of the injection of products into the oil reservoir is reached. In each of the periods, the volume of injection of heated products back into the oil reservoir is several times less than the volume of extracted heated products from the well. The device includes a downhole electric heater with a current lead, placed on the tubing string. The tubing string is above the borehole electric heater, but below the dynamic level of production in the borehole, equipped with a packer hermetically separating the annulus of the borehole. Radial holes are made below the packer in the tubing string, and an inserted sucker-rod deep pump is installed in the tubing string above the packer. The tubing string is drowned from below, which increases the heat transfer area in the tubing string section from the plug to the radial holes.

The disadvantage of this method is that the production of pre-heated well products is carried out with periodic injection of pre-heated well products back into the oil reservoir, respectively, during the injection, production stops, which leads to downhole downtime. Given that the method is intended for wells equipped with sucker rod pumps characterized by low flow rates, it does not have practical effectiveness.

A well-known electric heater (patent RU No. 2198284) containing a current lead with a tubular body mounted under it with a long heating element on its surface in the form of a cable with the possibility of supplying voltage through it from the source through the current lead is known. This heater differs in that it is grounded to the tubular body and it uses a cable with low electrical resistance installed in a ferromagnetic tube along the tubular body with the possibility of forming a closed loop and supplying from a source of supplying alternating voltage. In this case, a cable with low electrical resistance is installed in the ferromagnetic tube along the tubular housing along its perimeter in the form of a multi-pass sequence of parallel long-length heating elements. Moreover, the ferromagnetic tube is made divided into sections, the number of which is determined by calculation depending on the intensity of the curvature of the production string and overall dimensions. The method of its application includes the descent of the borehole electric heater on the tubing string into the interval of the oil reservoir, followed by heating and production of heated products from the well.

The disadvantage of this method is its low efficiency due to a slight increase in oil recovery of the oil reservoir, since the heating radius is small, and this does not ensure the flow of oil to the well from a zone remote from the well. Moreover, as a result of the practical application of this method, it was found that the largest increase in oil production was achieved in low-production (up to 2.0 tons / day) production wells. In production wells with an initial flow rate of 3-5 tons / day, the relative increase in flow rate due to the use of this electric heater is significantly lower. It follows that the use of this electric heater in order to intensify oil production is advisable only in low-rate producing wells (with a flow rate of up to 2.0 tons / day).

The disadvantages of both analogues are:

- their complex constructive device;

- most heaters have a high electrical resistance of the heating element, which requires the application of high electrical power, so they do not work on deeper layers;

- at low flows, a large amount of unregulated heat is released per small unit of length and therefore they work for a short time and not reliably;

- lack of efficiency for heat treatment of thick formations, as well as to prevent the formation of asphaltene-paraffin-hydrate deposits;

- low efficiency for heating and reducing the viscosity of well products at the reception of deep pumps;

- lack of operational control over the temperature of the heater and automatic control of heating.

The objective of the invention is the creation and application of an effective method of heating the bottom-hole zone of the well on the perforation interval, direct heating of the wellbore fluid in the area of installation of the wellbore heater, reducing the viscosity of the wellbore fluid, as well as preventing the formation of asphaltene-paraffin-hydrate deposits. Achievable technical result of the use of the heater is to increase the efficiency of thermal effects on the near-wellbore space in the area of installation of the downhole heater, increase the flow of fluid from the reservoir and reduce the viscosity of the downhole fluid in front of the downhole pump intake filter.

The task and the technical result achieved are provided in the claimed method of heating the bottom-hole zone of the well, characterized in that one or more connected downhole wells are lowered into the bottom-hole zone of the well in the perforation interval on the liner from the tubing below the downhole submersible equipment, depending on the required length and heating power electric resistive heaters and produce controlled heating of the near-wellbore space of the bottom-hole zone and the formation entering the well second fluid. In this case, slot holes are made in the lower pipe on which the heater is fixed, through which the heated well fluid is freely transferred from the annulus to the tubing interior and back, and the well heater itself is used both with rod-type deep pumps and with electric centrifugal and screw pumps and in fountain and gas lift wells.

At the same time, with the help of the control station, the set temperature of the heater is automatically maintained and the temperature of the outgoing stream from the heater and the temperature of the outgoing liquid flow at the wellhead are controlled, and the supply of the required power to the heater, taking into account the control measurements, is automatically controlled by the programmed controller of the station to control the set temperature of the heater. Thus, the necessary thermal effect is exerted on the bottomhole zone of the well. A variation of the operation of the necessary heat exposure in the claimed method is that in the bottomhole zone of the well in the perforation interval simultaneously with the well heater in the power cable, the capillary tube is lowered and chemical reagents are supplied. As a result, at the same time, a complex thermal and chemical effect is exerted on the bottomhole zone of the well.

The task and the technical result achieved are also provided using the claimed device for implementing a method for heating the bottom-hole zone of a well, composed of interconnected downhole heaters in the form of surface-controlled heating elements and an air compression chamber or a hydraulic protection unit, with the possibility of compensating for the compression effects of the heated coolant . The device also includes an internal temperature sensor and a power regulator supplied to the downhole heater, made in the form of a thyristor rectifier unit controlled by a programmable controller of the heating control station connected to it with the main indicator in the form of temperature characteristics of the device. The power cable inserted into the device connecting the control station and the downhole heater is composed of measuring sensors, power cores for transmitting electrical power, measuring cores for transmitting control signals and a capillary channel for supplying chemical inhibitors and surfactants to the bottomhole zone of the well.

In the claimed device, the heater can be mounted from identical sections of the same or different power with the number of sections of the heater selected in the range from 2 to 12.

The claimed method and device, it is advisable to schematically illustrate using the following figures of the drawings

In FIG. 1 shows a schematic diagram of the submersible part of the device: 1a) for electrical and 1b) for mechanical submersible equipment.

In FIG. 2 shows a schematic diagram of the submersible part of the device: 2a) for electric and 2b) for the mechanical mining method.

In FIG. 3 shows a schematic diagram of the ground part of the device: 3a) a diagram of ground equipment and 3b) a diagram of ground equipment with a metering unit.

In FIG. 4 shows a cross section of a power submersible electric cable: 4a) with measuring cores and 4b) with measuring cores and with a capillary channel built in.

In FIG. 5 shows the schematic diagrams of a sectional downhole heater: 5a) of the upper heating section, 5b) of the intermediate heating section, 5c) of the lower heating section.

The list of elements numbered in the figures of the drawings:

1 Downhole heater (Fig. 2),

2 heater housing,

3 upper head,

4 lower head,

5 current lead block,

6 heating elements,

7 Inner pipe (Fig. 1),

8 upper filler plug,

9 Stopper plug

10 lower drain plug,

11 coolant,

12 Internal heater temperature sensor,

13 Air Compensation Cavity ,,

14 The lower pipe of the shank (Fig. 2),

15 Slotted holes of the lower pipe (Fig. 2),

16 Shank,

17 downhole heater clutch,

18 Engine submersible pumping equipment,

19 Well submersible pump (Fig. 2),

20 coupling of submersible equipment,

21 tubing string,

22 Power cable downhole heater (Fig. 2),

23 Power cable for submersible pumping equipment,

24 fastening belts (clamps),

25 production string,

26 perforation interval,

27 Oil reservoir (Fig. 2),

28 Cable entry of the power cable (Fig. 3),

29 Wellhead temperature sensor,

30 Flip manifold (Fig. 3),

31 Fountain fittings (Fig. 3),

32 terminal (gas separation) box,

33 Power cable strapping outdoor equipment (Fig. 3),

34 control station,

35 step-up transformer,

36 Dosing device (Fig. 3),

37 Current-carrying core (Fig. 4),

38 Insulation sheath,

39 Isopolymer protective fabric,

40 protective metal armor,

41 Measuring core (Fig. 4)

42 capillary tube,

43 Connecting flange for sectional assembly.

It is advisable to describe the proposed method and device in more detail using these illustrations as follows. First, the technological data on the well is studied (practical flow rate, geological forecast, formation or several formation capabilities, pumping equipment installed in the well, well operation mode, formation temperatures, etc.), based on which heater 1 is selected (Fig. 1 , 2) or the assembly of heaters of the required length and the required design power. After that, one or more heaters 1 are mounted on the shank 16 from the tubing, and depending on the production method, the lower pipe 14 may contain slot holes 15, the total area of which allows the well fluid to move freely from the inner space of the tubing to the annular and vice versa, and the upper pipe 16 is mounted on the lower sleeve 17 of the submersible pumping equipment 18.

The power cable of the downhole heater 22 is connected to the current lead block of the downhole heater 5 through a special plug, and for the convenience of the staff, both the heater block 5 and the cable plug are made similar to the current lead plug of the submersible equipment. At the same time, both block 5 and the plug, depending on the design of the well, heater and downhole equipment, can be performed in various versions, most suitable in each particular case. Then, the submersible pumping equipment 18-19 is installed through the coupling 20 onto the tubing string 21 and the tubing 21 string is lowered into the well so that the upper part of the downhole heater 1 is at the same level with the upper boundary of the perforation zone 26. The size of the submersible pumping equipment 18 is selected so so as to ensure free passage of the downhole heater power cable 22 between the pump casing 19 (engine 18) and the production (casing) string 25. The downhole heater 22 and submersible power cables pine equipment 23 can be attached to the tubing in various ways, depending on the equipment, equipment and qualifications of the underground repair crews: only with 24 fastening belts (clamps), using protective treads, centralizing treads made of various materials, from plastic to stainless steel .

The output of power cables 22 and 23 from the annulus of the well is carried out through standard cable entries 28 (Fig. 3) of the submersible equipment installed in the faceplate of the fountain valve 31. During the installation of the wellhead equipment on the flow manifold 30 of the fountain valve 31 (preferably up to the fitting), it is mounted wellhead temperature sensor 29 control the temperature of the outlet stream. Then the power cable of the heater 22 through the gas separation (terminal) box 32 and the power cable strapping ground equipment 33 is connected to the heating control station 34. In this case, in some cases, you can use the step-up transformer 35. The capillary channel 42 is removed from the power cable 22 and connected to the metering device 36.

The combined power cable of the downhole heater 22 power supply itself (Fig. 4) itself is a set of three current-carrying conductors (two of which are power 37 and the third measuring 41), covered with an insulating sheath 38. Additionally, the power cable may include capillary the tube 42. The cores 37, 41 and the capillary 42 in the sheath 38 are wrapped in an isopolymer protective fabric 39, and then covered with metal armor 40. The cable with the capillary is led out of the well through a standard cable entry 28 of the fountain a Mathura 31.

After the descent of the tubing string and installation of the wellhead equipment is completed, before the start of the well, a downhole heater is turned on to heat the surrounding and superior downhole fluid. The temperature of the downhole heater is maintained by the control station within 30-95% of the maximum allowable. Due to thermal convection, the heated liquid rises to the pump, which reduces the load on the submersible pumping equipment at the time of start-up. Monitoring the increase in temperature of the borehole fluid is carried out using instrumentation (TMS) at the entrance of the submersible equipment. In this case, the perforation interval of the well is simultaneously heated.

After warming the wellbore fluid to the required temperature (usually 5-50 ° C higher than the primary one, depending on the well’s conditions, heater operating time, liner length, etc.), the well is put into operation. Simultaneously with the acceleration of the well and the conclusion of the well to the optimal mode of pumping equipment, the parameters of the well heater are adjusted taking into account the gradual heating of the near-wellbore space. For this, the power supplied to the downhole heater is initially set so that the temperature of the downhole heater in the first days of operation is within 50-90% of the maximum allowable. In the future, simultaneously with the gradual heating of the bottom-hole zone and near-wellbore space, the temperature of the downhole heater gradually rises to the established 80-95% of the maximum allowable.

A device for implementing this method consists of an electric resistive downhole heater 1, mounted on a shank of tubing 16 mounted on the lower sleeve 17 of the downhole equipment 18, the lower pipe of the shank 14 of which may contain slotted holes 15, of the power cable 22 designed to transfer electrical power from the control station to the heater, and which may contain a capillary channel 42 for supplying chemical inhibitors. Through the cable entry 28 of the fountain fittings 31, the power cable 22 through the gas separation (terminal) box 32 and the strapping cable 33 is connected to the heating control station 34.

The power supplied to the downhole heater 1 is controlled by a thyristor rectifier unit controlled by a programmable controller of the heating control station 34. Since when using downhole heaters at great depths, there is a large loss of power according to the voltage supplied to the heater, a boost can be included in the device’s power supply circuit transformer 35.

A device for heating the bottom-hole zone of a well works as follows.

The principle of operation of a borehole electric resistive heater is to transfer heat from the heating elements through the coolant to the bottomhole zone of the borehole and to heat the borehole fluid passing outside the heater and through the internal hydraulic channel of the heater.

When starting the downhole heater assembly (Fig. 1) into operation simultaneously with heating the downhole fluid in the perforation interval, heat is transferred to the inner walls of the production string and then to the bottom hole zone. As a result, the borehole fluid warms up, located not only inside the production string, but also in the near-wellbore space, and a stagnant zone of the heated product is formed on the perforation interval. Thermal convection of the fluid allows you to increase the zone of heating of the well not only within the heater, but also higher, including the receiving zone of the pumping equipment, which can significantly reduce the load when starting up the pumping equipment.

After the well is put into operation, the well fluid coming from the formation into the well partially passes along the walls of the production string in contact with the outer surface of the heater, and the other part passes through the inner tube of the downhole heater. In this case, the maximum transfer of thermal power from the heater of the borehole fluid, and through it to the near-wellbore space, takes place.

The heated downhole fluid enters the pump, then through the tubing comes to the surface. An increase in the temperature of the well fluid by 10-30 ° C before taking the submersible pump reduces the viscosity of the fluid entering the pump from 2 to 8 times, which has a significant effect on the speed and conditions of the passage of the well fluid through the tubing. The combined use of the downhole heater and chemical inhibitors fed through the capillary tube of the power cable can significantly reduce the load on the submersible pumping equipment, which leads to a significant increase in the service life of submersible equipment, an increase in the overhaul period of the well and, as the main indicator of the operation of the device, a significant increase in production wells.

Downhole electric resistance heater 1 contains:

- a heater body 2 with a female thread in the upper head 3 for screwing a shank 14 with slotted holes 15 and a hole for the current lead block 5 onto the lower tubing;

- a block of heating elements 6 mounted in the outer casing 2 of high-strength or stainless steel (to prevent corrosion of the surface material in aggressive conditions at elevated temperatures) and mounted on the upper head 3;

- inside the housing, the heating elements 4 are poured with a special coolant 11, which ensures maximum heat transfer on the surface of the heater;

- a temperature sensor (thermistor) 12 is installed in the upper part of the downhole heater casing 1. One end of the sensor is connected to the cable entry contact and the other end to the heater casing. Thus, the ground equipment uses two conductors 37 of the supply cable to power the heating elements, and the third core 41 of the power cable is used to measure the temperature of the coolant. In this case, the sensor readings are used to change the power supplied to the heaters, providing a given temperature mode of operation.

Depending on the need, the downhole heater is equipped with:

- in a single installation - the lower head 4 with an external thread for attaching filters and other devices;

- when installing several heaters - flange connections 43 for sectional assembly and blocks and plugs 5 of the current lead.

The power cable 22, containing an additional capillary channel 42, visually represents a standard 3-wire cable for powering the submersible pump motor, with a tube installed inside the protective armor, and the material for making the capillary tube may vary, depending on the well conditions and the flow of inhibitors and chemically active substances.

Among the advantages of the declared objects, it is advisable to pay attention to the fact that the new one, which predetermines the achievement of the indicated technical result, is that the method predetermines the controlled thermal effect on the bottom hole zone of the well and the heating of the well fluid using a well heater with adjustable heating power, achieved by:

- increase the total length of the heating part by connecting several heaters 1, which allows you to block the required length of the perforation zone 26;

- increase the total power of the downhole heater 1 by adding the power of each sectional heater;

- the use of an automatic programmable heating control station 34.

Also new is the fact that an additional capillary channel can be introduced into the power cable supplying electric power to the downhole heater, designed to supply chemical active inhibitors and surfactants into the bottomhole zone of the well, the use of which from the perforation interval in combination with elevated temperature of the well fluid can significantly reduce the amount of inhibitor used in the earlier exposure of the inhibitor to the well fluid. New is the fact that the well heater can be used not only with sucker rod pumps, but also with electric centrifugal and screw pumps, while monitoring the temperature of the well fluid avoids overheating of the submersible pump motor.

The achieved technical result, as shown by experimental data, can only be realized by an interconnected set of all the essential features of the claimed objects reflected in the claims. The differences indicated in it give reason to conclude that the technical solution is new, and the totality of the claimed claims in connection with their non-obviousness is about its inventive step, which is also proved by their detailed description given above. Compliance with the criterion of "industrial applicability" of the proposed method and device is proved both by the implementation of its prototypes and by the absence in the claimed claims of any features that are practically not practicable on an industrial scale. The features of the essential features of the claimed technical solution were investigated and formulated on the basis of processing the results of experimental studies, analyzing and summarizing them, as well as using inventive intuition, based on the conditions for achieving the specified technical result.

In conclusion, it is also worth noting that along with the indicated technical result achieved, the use of several interconnected downhole heaters allows the use of this method in wells with high flow rates, especially in fields with high viscosity and heavy bituminous oil, while reducing heat loss due to an increase in the heating surface liquids. In addition, this method allows you to combine thermal effects with chemical, feeding inhibitors and surfactants directly into the heating zone, which can significantly reduce the consumption of chemicals with a more pronounced effect of their use.

Claims (4)

1. The method of heating the bottom-hole zone of the well, characterized in that in the bottom-hole zone of the well during the perforation interval on the liner of the tubing from the tubing) below the borehole submersible equipment, depending on the required length and heating power, lower one or more interconnected borehole electric resistive heaters, produce controlled heating of the near-wellbore space of the bottomhole zone and the formation fluid entering the well, while in the lower pipe, on which a heater, slotted holes are made through which free movement of heated well fluid from the annulus to the tubing interior and vice versa is carried out, and the well heater itself is used both with sucker rod pumps and with electric centrifugal and screw pumps and in fountain and gas lift wells, at the same time, with the help of the control station, the set temperature of the heater is automatically maintained; at the same time, the temperature of the outlet from the flow heater and the temperature of the outgoing fluid flow at the wellhead, and the supply of the required power to the heater, taking into account control measurements, is automatically controlled by the programmed controller of the station to control the set heater temperature, thereby providing the necessary thermal effect on the bottomhole zone of the well. 2. The method according to p. 1, characterized in that the capillary tube is lowered into the bottomhole zone of the well at the same time as the well heater in the power cable and chemical reagents are supplied, and thus the complex thermal and chemical effect is simultaneously exerted on the bottomhole zone of the well. 3. A device for implementing the method of heating the bottom-hole zone of a well, composed of interconnected downhole heaters in the form of surface-controlled heating elements, an air compression chamber or a hydraulic protection unit, with the possibility of compensating for the compression effects of a heated coolant, an internal temperature sensor, and a power regulator supplied to downhole heater, made in the form of a thyristor rectifier unit controlled by a programmable connected to it the controller of the heating control station with the main indicator in the form of temperature characteristics of the device, as well as a power cable connecting the control station and the downhole heater, which is composed of measuring sensors, power cores for transmitting electrical power, measuring cores for transmitting control signals and a capillary channel for feeding chemical inhibitors and surfactants in the bottomhole zone of the well. 4. The device according to p. 2, in which the heater is mounted from identical sections of the same or different power with the number of sections selected in the range from 2 to 12.

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