RU2783030C1 - Method for thermochemical treatment of an oil reservoir - Google Patents

Abstract

FIELD: oil industry.

SUBSTANCE: invention relates to the oil industry. The method for thermochemical treatment of an oil reservoir includes the determination of reservoir capacity and primary measurements of temperature and pressure in the interval of well perforation, depending on which the volumes and order of injection of reagents are determined: a solution of a binary mixture containing ammonium nitrate and sodium nitrite, as well as a reaction activator, and the control of temperature and pressure are performed during the processing of the oil reservoir. Before pumping the reagents, the buffer valve on the wellhead assembly is closed, the downhole submersible pump is stopped in a position that excludes their penetration into the pump during the injection of reagents, and the oil collector is disconnected from the outlet line of the wellhead assembly. Reagents are injected through the inter-tube space between the production column and the tubing with installed deep pumping equipment with a pressure 20-30% lower than the pressure of the production column. Between the injection of the binary mixture solution and the injection of the reaction activator, the high-pressure lines, the inter-tube space and part of the borehole are pre-washed between the deflated deep pumping equipment and the perforation interval, through which reagents are injected into the oil reservoir, with andisplacement inert liquid in a volume of at least a single volume of pipes through which the binary mixture solution and the reaction activator move.

EFFECT: optimization of the process of thermochemical treatment of the oil reservoir, reducing the volume of preparatory and final work.

1 cl, 1 dwg

Description

Technical field:

The invention relates to the oil industry, namely, to methods of thermochemical formation treatment to stimulate the oil production process.

Prior Art:

There is a known method of thermochemical fracturing, in which, before pumping solutions of a combustible-oxidizing mixture (FOS), tubing and a packer with a hydraulic anchor are lowered into the well, a Christmas tree is installed at the wellhead, the working pressure of which must correspond to the pressure of the production casing and the expected pressure, arising during the treatment, and a safety valve is installed in the annulus, while the injection of the GOS is carried out through the Christmas tree and the tubing string. (Patent RF No. 2527437, publ. 2013).

The disadvantage of this method is a significant increase in the cost of well treatment due to the need to prepare the well for thermal gas chemical treatment, which requires the involvement of an underground well workover team (WRS), whose work is carried out within 2-3 days, as well as the presence of special X-mas trees for injecting reagents and most cases of special (technological) tubing. Also, to maintain a given pressure in the annulus during the injection of reagents, it is necessary to have a separate pumping unit (for example, TsA-320 type).

After the treatment of the reservoir with chemical reagents and the end of their reaction time in the reservoir, the drilling team also participates in the development of the well by swabbing, causing inflow from the reservoir. Then, before running the tubing + GNO assembly, the well is killed using a given volume of killing solution, which negatively affects the effect obtained from the thermochemical treatment of the formation, namely, leads to a drop in oil flow from the formation to the wellbore.

The closest analogue is the method of thermochemical treatment of an oil reservoir, which consists in injecting into the reservoir the required volume of a binary mixture containing ammonium nitrate and sodium nitrite in combination with an initiating composition, in pumping an activating solution and controlling temperature and pressure in the process of treating the reservoir, moreover, before injection of the binary composition determine the injectivity of the reservoir, and also produce primary measurements of temperature and pressure in the interval of perforation of the well, depending on which determine the volumes and modes of supply of the binary mixture. (Patent RF No. 2696714, publ. 2019).

This method allows, due to the chemical decomposition of large volumes of reagents injected into the reservoir, to significantly increase the reservoir temperature and pressure in the reaction zone, reduce the fluid viscosity, increase the sweep factor and thereby increase oil recovery.

To implement this method, it is necessary to carry out a large amount of preliminary work, which is necessary to prepare the well for thermal gas chemical treatment. Such work is usually carried out by an underground well workover (IS) team and usually includes the following activities:

1. Preparation of the well pad for work, installation and fastening of the tower of the lifting unit, installation of auxiliary equipment.

2. Preparation of the required volume of killing fluid, shutdown of downhole pumping equipment, injection of killing fluid into the annulus of the well.

3. Dismantling of wellhead fittings, lifting of tubing string (tubing string) with downhole pumping equipment (DPE), if necessary, normalization and backfilling.

4. Flushing the wellbore. Determination and preparation (scrapering) of the packer landing site.

5. Lowering the tubing string with a funnel and packer to the wellhead with reference to the location of the funnel and packer, setting the packer in the required interval.

6. Pressure testing of the production string, tubing string and packer. Determination of well injectivity by formation water injection.

7. Assembly and installation of X-mas trees at the wellhead. Control of outlet flanges, installation locations of temperature and pressure sensors. Pressure testing of X-mas trees up to the central valve.

The injection of the prepared BS solution occurs through the high-pressure pipelines (HPL) through the X-mas tree and the tubing string. A pumping unit is preliminarily connected to the annular space, which creates and maintains a predetermined pressure to prevent the packer from breaking during pumping of the BS.

At the same time, the economic effect of the treatment of the bottomhole formation zone is defined as the difference between the result obtained from the treatment and the costs of this treatment, including the work of the drilling team, in monetary terms. The cost of the work of the drilling team can be up to 50% of the total cost of treating the bottomhole formation zone. Thus, it is difficult, and sometimes even impossible, to achieve a given economic effect from the thermochemical treatment of an oil reservoir.

Disclosure of the invention:

The task to be solved by the claimed invention is to optimize the process of thermochemical treatment of an oil reservoir by significantly reducing the cost of its implementation by reducing the volume of preparatory and final work and the absence of the need to use some additional equipment.

The technical result is achieved by the fact that in the method of thermochemical treatment of an oil reservoir, including determining the injectivity of the reservoir and primary measurements of temperature and pressure in the perforation interval of the well, depending on which the volumes and order of injection of reagents are determined - a solution of a binary mixture containing ammonium nitrate and sodium nitrite, as well as the reaction activator, and the implementation of temperature and pressure control in the process of treating the oil reservoir, before the injection of reagents, the buffer valve on the wellhead is closed, the downhole submersible pump is stopped in a position that excludes their penetration into the pump during the injection of reagents, and the oil-gathering manifold is disconnected from the outlet wellhead fittings, reagents are injected through the annulus between the production string and the tubing string with downhole pumping equipment installed at a pressure below the pressure test pressure of the production string n and 20 - 30%, and between the injection of the binary mixture solution and the injection of the reaction activator, the high-pressure lines, the annular space and part of the wellbore between the lowered downhole pumping equipment and the perforation interval, through which the reagents are injected into the oil reservoir, are pre-flushed with an inert displacement fluid in a volume of at least a single volume of pipes through which the solution of the binary mixture and the reaction activator move.

The use of a binary mixture and a reaction activator of standard wellhead equipment for injection of a solution and the injection of reagents through the annular space between the production string and the tubing string with installed downhole pumping equipment makes it possible to pump reagents without first extracting the tubing string, which allows significantly reduce the amount of preparatory work, refuse to use the PRS team and some additional equipment, for example, the TsA-320 pumping unit to maintain a given pressure in the annular space with a high-pressure line for its connection, a safety valve, a set of shut-off and control valves, a pressure sensor and others

Injection of a binary mixture and a reaction activator into an oil reservoir with a pressure lower than the production string pressure test pressure by 20 - 30% makes it possible to exclude the violation of the tightness of the production string, its destruction and damage to the well structure.

Between the injection of the binary mixture solution and the injection of the activator, flushing of all lines, namely the high-pressure lines, the annular space and part of the wellbore between the lowered downhole pumping equipment and the perforation interval through which the reagents are injected into the oil reservoir, with a displacement inert liquid in a volume of at least a single volume of pipes, through which the binary mixture and the activator move, ensures the neutralization of the pipelines to avoid abnormal initiation of the reaction between the injected reagents.

The invention is illustrated graphically, where in FIG. 1 shows the scheme of injection of a binary mixture according to the proposed method.

In this diagram, the positions indicate the following elements.

1 - wellhead fittings;

2 - line for supplying reagents - a solution of a binary mixture and a reaction activator;

3 - production string;

4 - column of production tubing (tubing);

5 - annular space;

6 - buffer valve;

7 - discharge line;

8 - downhole pumping equipment (DPP), which includes a downhole submersible pump;

9 - productive (oil) layer.

The method of thermochemical treatment of the formation is carried out as follows.

At the selected well pad of the field, installation of equipment for thermochemical treatment of the oil reservoir is carried out, including pumping and mixing units for preparing solutions of a binary mixture containing ammonium nitrate and sodium nitrite, and a monitoring and control station (MCS) for temperature and pressure control.

Service workers of the customer before pumping reagents perform a small amount of preparatory work, including:

- lowering the static level in the well to a minimum value, closing the buffer valve 6 on the wellhead valve 1, stopping the downhole submersible pump in a position that excludes the penetration of the binary mixture into the pump during injection, for which, when using a pumping unit, the latter creates an excess pressure in column 4 tubing and stop the pumping unit in the upper position of the head of its balancer;

- disconnection of the oil-gathering header from the flow line 7 of the wellhead fitting 1;

- connection to the pump-mixing units for the preparation of a binary mixture of line 2 for supplying reagents to the annular space 5, pressure testing of the discharge lines, checking the operation of the safety valve.

Before injection of reagents, formation injectivity is also determined and primary measurements of temperature and pressure are made in the well perforation interval, depending on which volumes are determined, the order of supply of reagents is a binary mixture solution and a reaction activator.

The injection of reagents is carried out with a completely lowered stopped GNO 8 and tubing string 4 from the line 2 for supplying reagents through the annular space 5 between the production string 3 and the production tubing string 4 with a pressure lower than the pressure of the production string 4 by 20 - 30%. When the reaction activator is supplied after the binary mixture solution is injected, the binary mixture is injected together with the reaction initiator, which is, for example, a solution of formaldehyde or glyoxal. The pumping of the activator, for example, a solution of an inorganic acid or formalin, is carried out mainly after preliminary flushing of all lines with a displacement inert liquid, which is most often used as technical water, in a volume of at least a single volume of pipes through which the solution moves: lines high pressure, annular space and part of the wellbore between the lowered GNO and the perforation interval through which the BS is injected into the reservoir.

When implementing the procedure for supplying reagents, in which the reaction activator is injected before the binary mixture solution is injected, after the activator is injected, all lines are also predominantly flushed with a squeezing inert liquid in a volume of at least a single volume of the pipes through which the solution moves. The injection of a binary mixture solution can be carried out with or without the simultaneous supply of the reaction initiator.

After the end of the reaction of the binary mixture in the reservoir 9, self-discharge of the reservoir fluid is often observed, in which it rises to the wellhead due to a sharp increase in bottomhole pressure. Such an increase is noted due to the cleaning of the bottomhole formation zone from clogging deposits, paraffins and resins, as well as an increase in the bottomhole zone permeability due to the occurrence of additional microfractures, which leads, respectively, to an increase in the productivity coefficient and conductivity of the bottomhole zone.

The liquid obtained during self-discharge is collected in a special technological drainage container and subsequently processed. After the end of the self-discharge, the buffer valve 6 opens, the well is developed using the installed GNO 8 to the drainage tank, followed by switching the flow line 7 to the oil-gathering manifold. The development of the well and putting it into operation are carried out by the established GNO 8, if necessary, adjusting the modes and duration of operation of the pumping equipment.

The proposed method of thermochemical treatment of an oil reservoir provides the following advantages:

1. The total downtime of the well is from 1.75 to 1.85 days, while the downtime with the work of the drilling team is up to 10 days, i.e. downtime is reduced by more than 5 times.

2. There are no direct costs of the customer associated with the payment for the work of the drilling crew and indirect costs associated with downtime of the well during the work of the drilling crew.

3. Since the proposed method excludes the ingress of the binary mixture and the activator into the downhole submersible pump, there is no negative impact of the injected reagents on the operation of the GNO.

4. The development of the well is carried out by a regular GNO, as a result of which there is a faster start-up and commissioning.

5. The payback time for well treatment costs is reduced by about 2 times.

Claims (1)

A method for thermochemical treatment of an oil reservoir, including determining the reservoir injectivity and primary measurements of temperature and pressure in the well perforation interval, depending on which the volumes and order of injection of reagents are determined - a solution of a binary mixture containing ammonium nitrate and sodium nitrite, as well as a reaction activator, and implementation control of temperature and pressure in the process of treating an oil reservoir, characterized in that before the injection of reagents, the buffer valve on the wellhead is closed, the downhole submersible pump is stopped in a position that excludes their penetration into the pump during the injection of reagents, and the oil-gathering manifold is disconnected from the flow line of the wellhead fittings, and the injection of reagents is carried out through the annular space between the production string and the tubing string with installed downhole pumping equipment with a pressure below the production string pressurization pressure by 20-30%, and between by injecting the binary mixture solution and injecting the reaction activator, the high-pressure lines, the annular space and part of the wellbore between the lowered downhole pumping equipment and the perforation interval, through which the reagents are injected into the oil reservoir, are pre-flushed with a displacement inert liquid in a volume of at least a single volume of pipes along which the solution of the binary mixture and the reaction activator move.

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