RU2439312C1 - Heat gas generator for improvement of formation filtration in its well bore zone - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: heat gas generator includes container, container suspension device in the well in the form of a pipe string, at least two gas-generating charges of solid fuel with various gas-generating capacity. Gas-generating charges are placed into the container in zones of radial holes distributed on side surface of the container. Besides, heat gas generator includes burning initiator of one of the solid fuel charges with lower gas-generating capacity, channel of burning transfer from one gas-generating charge to the other gas-generating charge with the specified burning time. Burning transfer channel has the possibility of preventing mutual penetration of combustion products. At that, length of burning transfer channel is 10-25% of the length of the preceding charge with lower gas-generating capacity and provides together with gas-generating charges a common mode of non-stationary action on well bore zone with the specified amplitude, time of action and rise of action power.

EFFECT: increasing operating efficiency of the device.

8 cl, 1 dwg

Description

The invention relates to the oil industry and can be used to increase the filtration properties of a perforated reservoir by creating cracks in it.

Known gas generator for solid fuel with an adjustable pressure pulse for stimulation of wells (RF patent No. 2175059, 10/06/1999). It includes tubular charges of solid fuel, an igniter charge placed under them, a geophysical cable, and structural fasteners. The duration of burning charges varies from a few hundredths to several tenths of a second. The disadvantage of this device is the short exposure time to the reservoir. In addition, a significant part of the energy released by the charges goes to the rise of fluid in the casing. All this does not allow for the processing of formations of high power or formations with spaced layers.

Known heat generator, adopted for the prototype, to improve the filtration of the reservoir in its near-wellbore area, including a container with solid fuel charges, means for connecting the container to the pipe string for delivery to the required interval of the well, solid fuel in the form of a cylinder with an axial through channel and placed in the container , a means of initiating the combustion of solid fuels (patent RU No. 2312984, 11.29.2006).

The initiation of combustion is based on an exothermic reaction of an acid, for example, hydrochloric acid with alkaline earth metals, for example sodium. According to the known invention, during the descent into the well, the pipe string is filled with liquid from the wellhead. From the wellhead through the pipe string, excess pressure is transferred to the initiation device for exothermic reaction, which is accompanied by a sharp increase in temperature and ignition of solid fuel occurs. It is possible to work with a packer located in the upper part of the container or on a pipe string to reduce gas losses along the wellbore. During operation of the device, the combustion products of a charge of solid fuel penetrate into the well and perforation channels in the formation, creating a burst pressure and cracks in them.

A disadvantage of the known device is the low impact on formations in which the zones of impaired permeability are large enough (can reach up to 10 m) or on formations with spaced layers. To improve well productivity, it is necessary that the length of the cracks be greater than the radius of the impaired permeability. The longer the pulse, the greater the length of the crack. To increase the length of the fracture, it is necessary to provide the ability to control the duration of the pressure pulse, while the pressure amplitude should not lead to damage to the wellhead and other emergency situations. In the known device, this is not possible. Another disadvantage of the known device is that acid and alkaline earth metals or combinations of these metals are used as components of the combustion initiator. Working with such components in the well is a hazard. In addition, the need for continuous filling of the pipe string with liquid from the wellhead during their descent into the well complicates the technology of work.

The technical result of the invention is to increase the efficiency of the device, which consists in improving the filtration properties of the formation due to the formation of more extended and branched cracks in it, the safety of initiating charges of solid fuel in the container and simplifying the technology of work.

The technical result is achieved by the fact that the heat and gas generator for the well includes a container with groups of radial holes, at least two, dispersed along its side surface, means for suspending the container in the well in the form of a pipe string, gas-generating charges of solid fuel, at least two, with different gas-generating ability, placed in a container in the zones of radial openings, the initiator of the combustion of one of the charges of solid fuel with less gas-generating ability, the transmission channel of combustion from one gas-generating charge to another gas-generating charge with a given burning time, made with the possibility of preventing mutual penetration of the combustion products, the length of the combustion transfer channel being 10-25% of the length of the previous charge with lower gas-generating ability and, in combination with gas-generating charges, provides a general mode of unsteady influence on a borehole zone with a given amplitude, exposure time and increase in the impact power.

Besides:

a packer is placed on the pipe string above the gas generating charges of solid fuel, and at least one check valve is placed above the packer on said column;

the combustion transfer channel is made in the form of a metal tube having a diameter smaller than the diameter of the container, inside which a solid fuel charge is pressed in with the possibility of burning along the end surface, while metal disks with a central hole for a steel tube are fixed at the ends of the tube, overlapping the annular space between the container and metal tube;

the initiator of combustion of solid fuel is an initiator of combustion of the adiabatic type and is made in the form of a hollow cylinder, in the upper part of which there is an aluminum piston with o-rings, and in the lower part there is an igniter solid propellant charge and a sealing disk. Other initiators, for example, electrical or mechanical, can be taken as a combustion initiator;

the container is made in the form of a set of sections with detachable connections;

solid fuel charges are made in the form of continuous cylinders or cylinders with a central through channel, or cylinders with through peripheral channels;

the container is made of segments of tubing;

the lower part of the container is configured to install a device for measuring pressure and temperature in the well.

SUMMARY OF THE INVENTION

Unlike the prior art, the invention allows you to adjust the amplitude and duration of the pressure pulse in the perforation interval by conducting several exposure cycles of different power. For this, in the container between the charges of solid fuel, at least two, is a combustion transfer channel with charge characteristics different from the characteristics of the charges of solid fuel. With an increase in the number of charges of solid fuel, the number of combustion transfer channels is correspondingly increased. As a result, a delay in the ignition of the lower charge is ensured in comparison with the higher charge. Since the container is leaky, the charges in it burn on the end surface, and the combustion front moves from top to bottom. The length of the combustion transfer channel from one gas-generating charge to another gas-generating charge is essential. With the length of the combustion transfer channel 10–25% of the length of the preceding charge with less gas-generating ability, it is possible, in conjunction with gas-generating charges, to directly affect the formation in the unsteady, as the most effective, effect on the borehole zone with a given amplitude, exposure time and rise power. At short exposure times, the effect does not have time to manifest itself.

The mass of charges of solid fuel is selected so as to achieve fracture pressure in the well and subsequent formation of cracks that can propagate until pressure drops in the well. The pressure drop is associated with the withdrawal of the gas-liquid mixture into the reservoir and heat transfer processes between the combustion products, the liquid and the casing. The increase in pressure above the pressure of the fracturing is impractical due to possible damage to the wellhead. Therefore, for the further development of cracks, it is necessary to carry out one more, at least, pressure increase cycle. This function is performed by the combustion transfer channel from one charge of solid fuel to another. It provides, in essence, a delay in the ignition of additional charges in the container. After this, a secondary increase in pressure in the well to an acceptable value follows and a further increase in the length of the cracks. Of great importance is the unsteadiness of the impact on the borehole zone with a given amplitude, exposure time and power increase. This mode increases the likelihood of obtaining branched cracks of increased length as multifractals.

In addition, it is noted that the packer placed above the combustion initiator isolates the annulus (the space between the casing and tubing string) from the treatment area, which allows to reduce pressure losses and ensures its gradual increase in the well during end-face combustion of charges in the container .

The combustion transfer channel is made in the form of a tube, for example, of steel, inside which a charge-moderator of solid fuel is pressed in. The combustion of the charge-moderator also occurs along the end surface. The time of stimulation of the formation is set by the length of the combustion transfer channel and is recommended by a given range of values according to the simulation data. In this case, the combustion products of the upstream charges do not penetrate to the lower charges, since, for example, disks can be installed at the ends of the tube, each of which has a central hole for coaxial installation on the tube, with the possibility of rigid fixation.

For example, when treating a formation with a thickness of 8 m at a depth of 3000 m (fracture pressure of about 75 MPa at a hydrostatic pressure of 30 MPa) after a solid fuel charge of 1 m weighing 5 kg was activated, the pressure drop time from the maximum value of 75 MPa to hydrostatic was preliminary calculated 4 sec At an average rate of combustion of a charge of solid fuel u = 40 mm / s in this pressure range, the length of the charge in the combustion transfer channel will be 4 × 40 = 160 mm, which is 16% of the length of the activated charge above. The next cycle of stimulation of the formation is provided with an increased power by a charge of solid fuel 1.5 m long, and the length of the second charge in the combustion transfer channel will be 240 mm with the same ratio between them to provide a third cycle of action with a further increase in power.

The number of charges of solid fuel and, correspondingly, combustion transfer channels, the ratio between the channel length and the length of upstream charges is determined previously by mathematical modeling taking into account the thickness of the treated formation, the geological and technical characteristics of the well and the ballistic characteristics of the charge and charge compositions in the combustion transfer channel.

The total area of the holes in each of the parts of the container, separated by combustion transfer channels, must be not less than the cross-sectional area of the container. Well tests showed that this ratio ensures equal pressures in the container and under the packer in the perforation interval. This eliminates the possibility of deformation or destruction of the container.

When the tubing string is lowered into the well, it is necessary to fill them with water in order to transfer pressure from the wellhead to the initiation device. To simplify this operation, the means for connecting the container to the pipe string for delivery at a predetermined interval of the well is provided with at least one check valve for continuously filling the pipe string with water from the annulus.

Safe initiation of solid fuel charges in a container is provided, for example, by an adiabatic device made in the form of a hollow cylinder, in the upper part of which there is a piston, for example of aluminum, with o-rings, and in the lower part, a solid fuel igniter charge and a sealing disk. When overpressure is supplied to the piston from the wellhead through a string of pipes, its support girdle is cut off and the piston in the cylinder moves downward, compressing air in the cylinder cavity. The geometric dimensions of the cylinder are chosen so that at a selected excess pressure on the piston, the air during compression would be heated to the ignition temperature of the charge, which for solid fuels is about 300 ° C. During combustion of the igniter charge, the pressure in the cylinder increases, the sealing disk breaks and opens access to the container of combustion products that ignite the charges in the container.

For processing perforated formations of high power or complex-built reservoirs where productive formations are spaced, as well as formations with large radii of impaired permeability (can reach 10 m), the heat and gas generator must contain a sufficient number of charges of solid fuel and an appropriate number of combustion transfer channels. In this case, the container, for the convenience of assembly, is made in the form of a set of sections with detachable connections, and the total area of the holes in each of the parts of the sections separated by the combustion transfer channels should be not less than the cross-sectional area of the container.

The burning of charges in the container occurs along the end surface. In this regard, solid fuel charges can be made in the form of continuous cylinders, cylinders with an axial central through channel and cylinders with through peripheral channels.

For long burning times in the transmission channel, it may contain additional disks installed between two disks at the ends of the tube to reliably prevent the penetration of combustion products of upstream charges to downstream charges.

As noted above, the openings on the sides of the container are selected so as to ensure equal pressures in the container and in the well. This eliminates the deformation or destruction of the container structure. To simplify the assembly, sections of the container can be made of tubing sections.

The drawing shows a General view of a device with a single combustion transfer channel.

The device is lowered into the borehole on the tubing string 1 to the location of the perforation channels 21. The check valve 2 is located above the packer 3 and when the device is lowered, the tubing is continuously filled with water from the space between the casing 20 and tubing 1 (annulus) . The combustion initiator consists of a hollow cylinder 8 connected to the tubing 1 and the container 11 with couplings 4, a support washer 5, a piston 6 with O-rings 7, an igniter charge 9 and a sealing disk 10. The container sections 11 and 16 with the charges 15 and 17 are connected by a coupling 4 and through holes 19 are located on the lateral surfaces of the sections. A combustion transfer channel is installed between charges 15 and 17. A charge 13 of the combustion transfer channel from solid fuel is located in the tube 14. Disks 12 are fixed at the ends of the tube. Charge 17 rests on tip 18.

In the lower part of the tip 18, a device can be installed, for example, on a threaded connection, for measuring pressure and temperature in the well.

The device operates as follows.

At the command of the operator from the mouth through the tubing string 1, excess pressure, for example, CA-320 aggregate, is applied to the piston 6. After cutting the support belt, the piston, moving downward, compresses the air in cylinder 8, which is adiabatically heated to the ignition temperature of the charge-igniter 9. Products The combustion of this charge sharply increases the pressure in the cylinder 8, the disk 10 is cut off and the combustion products of the charge-igniter 9 enter the container 11 and ignite the charge 15. After the combustion of the charge 15, the charge of the transmission channel ignites and combustion 13, while the disks 12 impede the penetration of the products of combustion of the charge 15 to the charge 17. After the combustion of the charge of the combustion transfer channel ends, the charge 17 ignites.

The above packer 3 eliminates the movement of the wellbore fluid up the well. The products of combustion of the charge 15, flowing into the well through the holes 19, create increasing pressure in the perforation interval. After the combustion of the charge 15, the charge of the combustion transfer channel is ignited, and the pressure increase in the well stops. The combustion of charge 13 lasts for a predetermined estimated time, while the gas intake into the well is practically absent and the pressure in the well decreases to hydrostatic, after which charge 17 is ignited and a second cycle of increase in pressure occurs in the well.

When the charge 15 is activated in the well, the fracture pressure is reached, the gas-liquid mixture penetrates the perforation channels, revealing cracks in the formation, and when the charge 17 is triggered, the growth of cracks continues. The masses of charges 15 and 17 are determined by calculation to create cracks in the formation, the length of which exceeds the radius of the impaired permeability of the formation, which is previously determined according to hydrodynamic studies.

Impact control can be carried out after lifting the device and taking readings of a device that records pressure and temperature in the well.

Claims (8)

1. Heat and gas generator to improve reservoir filtration in its near-wellbore zone, comprising a container with groups of radial holes at least two dispersed along its lateral surface, means for suspending the container in the well in the form of a pipe string, gas-generating charges of solid fuel, at least two with different gas-generating ability, placed in a container in the zones of radial openings, the initiator of combustion of one of the charges of solid fuel with lower gas-generating ability, the combustion transfer channel one gas-generating charge to another gas-generating charge with a predetermined burning time, made with the possibility of preventing mutual penetration of the combustion products, and the length of the combustion transfer channel is 10-25% of the length of the previous charge with lower gas-generating ability and provides, together with gas-generating charges, a general mode of unsteady influence on a borehole zone with a given amplitude, exposure time and increase in the impact power. 2. The heat and gas generator according to claim 1, characterized in that the packer is placed on the pipe string above the gas-generating solid fuel charges, and at least one check valve is placed on the pipe above the packer. 3. The heat and gas generator according to claim 1, characterized in that the combustion transfer channel is made in the form of a metal tube having a diameter smaller than the diameter of the container, inside which a solid fuel charge is pressed in with the possibility of burning along the end surface, while metal disks with a central hole for a steel tube, overlapping the annular space between the container and the metal tube. 4. The heat and gas generator according to claim 1, characterized in that the initiator of combustion of solid fuel is an initiator of combustion of the adiabatic type and is made in the form of a hollow cylinder, in the upper part of which there is an aluminum piston with o-rings, and in the lower part there is an igniter solid fuel charge and sealing disc. 5. The heat and gas generator according to claim 1, characterized in that the container is made in the form of a set of sections with detachable connections. 6. The heat and gas generator according to claim 1, characterized in that the solid fuel charges are made in the form of solid cylinders, or cylinders with a central through channel, or cylinders with through peripheral channels. 7. The heat and gas generator according to claim 1, characterized in that the container is made of segments of tubing. 8. The heat and gas generator according to claim 1, characterized in that the lower part of the container is configured to install a device for measuring pressure and temperature in the well.