RU2732542C1 - Gas generator for oil and gas condensate wells - Google Patents

Abstract

FIELD: oil production; gas production.

SUBSTANCE: invention can be used in thermal gas-chemical treatment of bottomhole zones of oil and gas condensate wells. Gas generator comprises main charge of solid fuel arranged in perforated housing. There is an ignition unit. It is placed in cylindrical housing filled with gas. This unit has membrane units in upper and lower parts with membrane clamping rings. A movable plunger is fixed in the upper part of the cylindrical casing. Above the lower membrane unit there is a temperature promoter. Device has upper and lower flanges. In the lower part of the cylinder of the ignition unit there additionally is a unit for fixation of the plunger position after gas compression in the ignition unit. Said assembly comprises split tapered spring ring arranged on cylinder inner surface and collecting plunger with movable washer, shank and core, having possibility of interaction with split conical spring ring in position of maximum compression of gas and engagement with said ring. To ensure higher tightness of ignition unit in plunger there are lower and upper seals arranged between plunger housing and movable washer, and between plunger housing and shank.

EFFECT: technical result is improvement of solid propellant primary charge ignition reliability.

4 cl, 6 dwg

Description

The invention relates to the field of oil production, namely, to devices for increasing the productivity of oil and gas condensate wells by thermo-, gas-chemical impact on the bottomhole zone of wells. In this case, a solid fuel charge burns with the formation of high-temperature gaseous products, which penetrate into the bottomhole zone of the well under high pressure. Getting into small cracks in the rock, the gaseous combustion products, together with water vapor and liquid, possessing wedging pressure, expand and lengthen them. At the same time, since there are hydrogen halides among the combustion products, the latter can interact with rock components to form soluble compounds, thus increasing its permeability.

The gas generator design includes two blocks connected to each other. The first block - the ignition block provides ignition of the main charge of solid fuel. The second - the charging block creates a high-temperature flow of the vapor-gas mixture, penetrating under high pressure into the bottomhole formation zone and forming a system of cracks in the bottomhole zone. From the point of view of oil well productivity, rock fracturing has the greatest impact on well productivity. The latter depends on the magnitude of the pressure surges during the combustion of solid fuel, their frequency and amplitude. Of no small importance for the productivity of wells is the temperature effect on the oil fluid with a high-temperature vapor-gas mixture (especially for viscous mixtures). There is a melting of paraffins and resinous substances and the release of the pore space from weeds. At the same time, the created gas generating devices must meet the requirements of safety, simple operation, low cost and autonomy, which is important for field conditions.

These requirements are met by gas generating devices with an ignition system based on adiabatic gas compression, which do not require work with a wireline and are further discussed in this invention.

Known device for the treatment of oil and gas condensate wells, allowing to increase their productivity (Koltsova EM, Glebov MB, Lazarev VM, Zhensa AV Gas generator for oil and gas wells. RF Patent No. 2456443 C1, IPC E21B 43/263 (2006/01). Published: 20.07.2012 BI No. 20). The device includes the main charge of solid fuel, a cylindrical ignition device with sealing units in the upper and lower parts and a fixed piston in the upper part of the cylindrical body with the possibility of cutting it at a given external pressure, a temperature promoter. A design feature is the presence of a tube connecting the tubing string with the top of the igniter located at the bottom of the charger with the main charge of solid fuel. This allows both a faster combustion of the fuel charge from the bottom up and a higher rate of pressure rise in the wellbore, which leads to the creation of an extensive network of fractures in the bottomhole formation zone.

The device works as follows. After lowering the gas generator on the tubing to the bottomhole level by applying a pressure surge in the tubing, the initiating pressure pulse is transmitted through the inner tube to the lower igniter. The upper rupture disc ruptures and the piston compresses the gas inside the ignition unit. The temperature and pressure of the gas under the piston rise sharply, the temperature promoter ignites and the lower rupture disc ruptures. Hot gases and a temperature promoter are ejected by a gas stream onto the main charge of solid fuel and the main charge of the fuel is burned. The pressure and temperature in the wellbore and bottomhole zone of the well increase sharply. There is melting of paraffins and heavy oil fractions, the formation and development of cracks in the bottomhole formation zone, as well as the chemical interaction of acidic combustion products (HC1, HF) with the rock. As a result, an increase in the permeability of the rock in the bottomhole formation zone is achieved and, as a consequence, an increase in the productivity of oil wells.

The disadvantage of this design of the gas generator is the need to introduce an inner tube, which complicates the design, and the insufficient reliability of the operation of the membrane-piston device at maximum pressures at the stage of compression by the gas piston (gaskets on the piston can pass gas, or the piston itself can be thrown in the opposite direction by the forces of back pressure) ...

It is also known a device (gas generator) that provides a thermo-, gas-chemical effect on the bottomhole formation zone during the treatment of oil and gas condensate wells (Koltsova E.M., Glebov M.B., Zhensa A.V., Lazarev V.M., Gas generator to increase the productivity of oil and gas wells RF Patent No. 2363840 C1, IPC Е21В 43/263 (2006/01). Published: 10.08.2009 BI No. 22), which was chosen as a prototype. The generator contains a series-connected ignition block and a block with the main charge of solid fuel. The ignition unit is a cylinder, in the upper and lower parts of which there are sealing assemblies with the possibility of cutting them off when a given pressure is reached. Rupture discs with a specially made notch are used as sealing units. The diaphragms are fastened to the body of the igniter unit by means of threaded stops. Inside the cylindrical body of the ignition unit, in its upper part, there is a piston with a sealing lip, which is fixed in the body by means of a cut-off annular rim. A temperature promoter is placed in the lower part of the ignition block above the bursting disc.

The block with the main charge of solid fuel is an assembly of cylindrical non-hermetic body elements connected to each other and the ignition block by coupling joints. Solid fuel with longitudinal channels for faster combustion of the charge is placed inside the housing elements.

The gas generator works as follows.

After lowering the gas generator on the tubing to the required depth, a pressure surge is applied in the tubing, which triggers the upper bursting disc of the gas generator ignition unit. Under the influence of the pressure drop, the piston breaks off and the gas is compressed in the chamber of the ignition unit. Under the action of the forces of pressure and inertia of the piston, the compressed gas is heated to temperatures that significantly exceed the temperature of the chemical decomposition of the promoter. This leads to an even greater rise in temperature. The compressed gas pressure exceeds the lower bursting disc threshold, and the heated mixture of gas and temperature promoter is thrown into the chamber with the main charge of solid fuel. Highly heated particles of the temperature promoter, falling on the surface of the solid fuel, ignite it, initiating the combustion of the main fuel charge.

The disadvantage of the considered design of the gas generator (prototype) is the unreliability of the ignition of the promoter and the rupture of the lower rupture disc due to insufficient sealing of the piston with gaskets and possible displacement of the piston by backpressure forces in the opposite direction. The consequence of this is the insufficient reliability of the ignition and combustion of the main charge of solid fuel, which can lead to unnecessary unjustified costs when treating wells with the thermo-, gas-chemical method.

The objective of the invention is to create a new design of a gas generator to increase the productivity of oil wells based on the use of thermo-, gas-chemical method with ignition of the main fuel charge by adiabatic compression of gas, in which the reliability of ignition of the main charge of solid fuel is increased.

The problem is solved by a gas generator for oil and gas condensate wells, which includes the main charge of solid fuel placed in a perforated housing, an igniter in a cylindrical housing with membrane blocks in the upper and lower parts and a fixed movable plunger in the upper part of the cylindrical housing, a temperature promoter located above the lower membrane block. At the same time, a unit for fixing the position of the plunger after gas compression in the ignition unit is additionally introduced into the lower part of the cylinder of the ignition unit, including a split conical spring ring and a plunger core with a conical head in the form of a protrusion, and also to ensure greater tightness of the ignition unit, the lower and top seals located between the plug body and the movable washer and between the plug body and shank. At the same time, two intermediate flanges are introduced into the ignition unit, located between the upper flange and the membrane unit, as well as between the lower flange and the membrane unit, which ensure the removal and tight installation of the membrane assemblies. In addition, the ignition unit is sealed with tightening bolts, and the diaphragm clamping ring on the lower side of the plunger has a hole diameter smaller than the plunger diameter, which is necessary to stop the plunger movement, and the temperature promoter is located in the lower clamping ring.

As a working medium in the ignition unit, both a chemically stable gas when heated and a gas that decomposes when heated with an increase in volume (for example, ammonia) can be used.

The temperature promoter in the proposed design is located in the lower part of the ignition unit above the lower membrane.

The use of the proposed design of a gas generator for processing oil wells will allow, due to the creation of a higher pressure and temperature in the ignition unit, to significantly reduce the risk of non-ignition of the main charge of solid fuel by the temperature promoter and increase the reliability of the gas generator. At the same time, due to the formation of a network of cracks in the bottomhole zone of the well, the melting of resinous and paraffinic hydrocarbons, the chemical interaction of acidic combustion products with the rock, the productivity of oil wells increases.

The effect of increasing the reliability of the gas generator is achieved by placing a conical split spring washer in the lower part of the ignition unit with an inner diameter smaller than the internal diameter of the ignition unit housing, and on the plunger core - an annular conical protrusion with the largest external diameter exceeding the internal diameter of the washer, but smaller than the internal diameter of the housing ignition unit. In addition, for better sealing of the gas compression zone, the piston is equipped with two self-sealing gaskets. The consequence of this will be higher values of pressure and temperature in the compression zone, guaranteed rupture of the lower membrane of the ignition unit and more reliable ignition of the main charge of solid fuel.

FIG. 1, 2, 3, 4 shows the device of the proposed design of the gas generator.

The ignition unit of the gas generator (Fig. 1) consists of a cylinder 1, an upper inlet flange 5, a lower outlet flange 8, an upper intermediate flange 6, a lower intermediate flange 7, a split spring ring 2 located between the lower end of cylinder 1 and the lower intermediate flange 7. In the upper part of the ignition unit, under the upper membrane block 10, an assembly plunger 12 is fixed. The upper 10 and lower AND membrane blocks are pulled together by bolts 3 through washers 9. The upper flange on the cylinder 14 and the lower flange on the cylinder 15 are attached to the cylinder 1 by a threaded and welding connection. The upper and lower diaphragm blocks 10, 11, the upper inlet flange 5 and the lower outlet flange 8, the upper flange on the cylinder 14, the lower flange on the cylinder 15 are pulled together through the washers 9 by bolts 3. The core 13 of the assembly plunger 12 has a conical head with a protrusion, allowing engagement with a split spring ring 2. The tightness of the ignition unit is ensured by installing gaskets 4.

A temperature promoter (for example, ammonium dichromate, etc.) is placed in the lower part of the ignition unit above the sealing rupture membrane of the membrane unit 11 - a substance that ensures reliable ignition of the main charge of solid fuel. Inside the cylindrical body 1 of the ignition unit between the temperature promoter and the plunger 12 is a gas (for example, air or other gas), which is compressed by the plunger 12 to a high temperature and pressure when the ignition unit is triggered.

The assembled plunger (Fig. 2) consists of four parts, interconnected by threaded connections through gaskets. The plunger includes a core 16 with a conical protrusion, a movable washer 17, a plunger body 18, a shank 19, which seals the lower and upper seals 20, 21, self-sealing under pressure on the core 16.

The upper and lower diaphragm blocks (Fig. 3.) have the same design and differ in the magnitude of the pressure for which the diaphragms are designed. The diaphragm block includes: two clamping rings 22, performing the function of fixing the diaphragm, a bursting diaphragm 23, a mounting plate 24 and screws 25, which are necessary for mounting the diaphragm unit in the structure of the gas generator.

The charging unit of the gas generator (Fig. 4) is a non-sealed cylindrical body 30, inside of which there are solid propellant blocks 28, 29 of different geometry and with different burning rates in contact with each other. The connection of the charging unit to the ignition unit is carried out by means of an adapter 26 by a threaded connection. The main charge of fuel is connected to the adapter by means of a union nut 27 by a threaded connection.

The gas generator works as follows.

The gas generator is mounted at the lower end of the tubing string and lowered to a predetermined well depth. Operations are underway to prepare the well for treatment. From the wellhead, a pressure surge is created in the tubing, leading to the operation of the upper rupture disc of the gas generator ignition unit. Under the influence of the resulting pressure drop (pressure supplied from the wellhead plus the hydrostatic pressure of the liquid column above the plunger), the plunger begins to accelerate and compresses the gas between the plunger and the promoter above the lower rupture disc. Under the action of the force of pressure, the plunger compresses the gas to pressures and temperatures significantly exceeding the temperature of chemical decomposition of the promoter. The conical head with the projection 13 of the plunger core extends over the spring ring 2 (Fig. 1) and rigidly fixes the plunger position. Under the influence of high temperature, the temperature promoter decomposes with the release of a large amount of the resulting gases. The pressure under the plunger increases even more. However, the retaining spring ring 2 and the conical head of the plunger 13 (Fig. 1) abut against each other and do not allow the plunger to move in the opposite direction. Overpressure below the plunger acts on the self-sealing gaskets that prevent gas from leaking through the plunger. The pressure under the plunger due to the chemical decomposition of the promoter increases even more to values exceeding the ultimate strength of the lower rupture disc of the membrane block 11 (Fig. 1) and its rupture occurs. Highly heated gases together with the particles of the burning promoter under the action of excessive pressure are thrown onto the surface of the solid fuel checker 28 (Fig. 4) and it is ignited. Combustion of solid fuel sticks is transferred to the main charge of solid fuel 29 in contact with it (Fig. 4). Due to the selection of the type of fuel and its geometry, combustion occurs with a peak increase in speed and pressure, which causes a cyclic well treatment mode.

When the main charge of solid fuel burns, highly heated gases (N ₂ , HCl, HF, H ₂ , etc.) are released, which, together with vapors of the liquid medium of the well under high pressure through perforations, spread into the bottomhole zone of the well, heating it up, forming cracks, melting asphaltenes, paraffins in pores and chemically interacting with carbonate particles to form soluble compounds.

In order to confirm the increase in the reliability of the proposed design of the gas generator in comparison with the prototype, an experimental and calculated verification of the operation of the nodes of the proposed design of the gas generator was carried out.

Example 1. To test the performance of the ignition unit of the prototype gas generator, a laboratory sample of the gas generator with a reduced charging unit was created. The inner diameter of the adiabatic compression chamber was 30 mm, and the length of the gas compression zone was 800 mm. The plunger was made of aluminum alloy and its weight was 200 g.

In the experiments, the possibility of compressing air to high pressures was checked using sealing rings located on the plunger with varying the shape of the cross-section of the rings (round, oval, trapezoidal) and the material of the rings (rubber, polymer). For this, the assembled laboratory gas generator was installed on a high-pressure test bench and a compressor was supplied to the inlet of the ignition unit of the gas generator by a pressure that simulates the pressure in the tubing. The supplied pressure was recorded in time by a Karat DI strain gauge pressure sensor and an analog-to-digital converter of the B-480G ADC signal from the pressure sensor to a computer with Power Graph 3.3 Pro software installed to process signals from the pressure sensor and graphically display the signal in time. Upon reaching the set pressure, the upper diaphragm was triggered (ruptured) and the plunger compressed the air under it. At the same time, in some cases, the air compressed by the plunger ruptured the lower membrane, but in other cases the lower membrane did not rupture. The reason for this was determined by the distribution of the residues of the burnt temperature promoter (ammonium dichromate) above and below the plunger compressing the air (these residues have a pronounced green color).

It turned out that in cases where the lower membrane did not work, the remnants of the burnt ammonium dichromate were distributed along the entire length of the ignition block (both after and before the plunger), which indicates the leakage of the sealing rings. This phenomenon was observed in cases of all forms of sealing rings and material of manufacture. The reason for this is the insufficient resistance of the sealing rings to the longitudinal component of the compressed air pressure forces in the high-pressure region. To solve this problem in the design of the prototype, we proposed to use self-sealing sealing rings in the patented design. The rings are in a closed volume and, with increasing pressure, increase the sealing of the volume under the plunger.

Example 2. Experiments were carried out with the design of the prototype gas generator described in example 1. In the experiments, the lower membranes were used, designed for high pressures (more than 400 atm). It was observed that in many experiments rupture of the lower membrane did not occur. At the same time, disassembly of the structure of the gas generator ignition block after the experiments showed that the block plunger was at a considerable distance (tens of centimeters) from the lower membrane, which indicates that it was thrown in the opposite direction by the back pressure arising under the plunger. This additional backpressure occurs when the temperature promoter burns with the release of gaseous products. For example, during the decomposition of solid ammonium dichromate, gaseous nitrogen and vaporous water are additionally released:

(NH ₄ ) ₂ Cr ₂ O ₇ = Cr ₂ O ₃ + N ₂ + 4H ₂ O

The resulting additional pressure under the plunger as a result of the combustion of the promoter displaces the plunger in the prototype structure in the opposite direction, the temperature drops, and combustion is interrupted.

To exclude such a development of events in the design of the prototype, we proposed to install a device for fixing the plunger in the position of maximum air compression in the ignition unit. This will allow the additional pressure generated during the decomposition of the promoter to be used to rupture the lower membrane and to increase the reliability of the gas generator by reducing the risk of non-ignition of the main charge of the solid fuel.

Example 3.In order to assess the effect of the decomposition of the promoter during adiabatic compression of the gas in the ignition unit on the pressure and temperature created in the unit, two calculations were carried out: adiabatic compression of the gas without decomposition of the promoter (case a) and adiabatic compression of the gas with decomposition of the promoter (case b). Consider both cases, a) Initially, we calculated the pressure and temperature of the air during its adiabatic compression in the design of the gas generator indicated in example 1 (prototype), without a promoter.

The volume of the air compression zone V ₁ in the gas generator is:

where d is the diameter of the gas compression channel, cm; L ₁ - the length of the gas compression channel, see.

The volume of gas V ₂ after adiabatic compression is equal to the volume of the cylindrical recess above the lower membrane and is:

where d ₂ is the diameter of the cylindrical recess above the lower membrane, cm;

L ₂ - the length of the cylindrical recess above the lower membrane, see.

The adiabatic compression of an ideal gas obeys the Poisson equation, i.e.

where γ is the adiabatic index (for air γ = 1.4); Р ₁ , Р ₂ correspond to the gas pressure before and after compression.

If the gas being compressed is air initially at atmospheric pressure in volume V], then when compressed to volume V ₂ its pressure will be:

Accordingly, its temperature T ₂ after compression will be equal (at the initial temperature T ₁ = 298.15 K).

b) Further, the case of adiabatic compression was considered, during which the temperature promoter decomposes. The design of the gas generator corresponds to example 1. The temperature promoter (dispersed mixed solid fuel) is located in a cylindrical cavity with a diameter of 2.5 cm and a height of 1.2 cm above the lower membrane. The proportion of free volume ϕ in the promoter is approximately ϕ = 0.4. The mass m of the temperature promoter in the cylindrical cavity is

m = (1-ϕ) ρV ₂ = 6.01 g,

where the density of the temperature promoter ρ is 1.7 g / cm ³ , and the volume of the cylindrical depression V ₂ is 5.89 cm ³ .

When 1 g of mixed solid fuel is burned, an average of 0.85 liters of gases are formed under normal conditions. Thus, when burning 6.01 g of mixed solid fuel under normal conditions, 5.11 liters of gases will be released. Taking into account the air in the pre-compression ignition unit (0.566 normal liters), the total volume of compressible gases will be 5.676 normal liters.

When the entire volume of the formed gases is compressed to a volume of V ₂ = 5.89 cm ³ in accordance with the Poisson adiabat, the maximum pressure P ₂ will increase to the following value:

Accordingly, the maximum temperature T ₂ in the compression zone will be:

From the above calculations, the large contribution of the temperature promoter to the achievement of maximum pressures and temperatures in the gas compression zone of the gas generator is obvious.

Of course, the maximum pressure and temperature will not be reached as the lower bursting disc will operate earlier. Nevertheless, it follows from the calculations that the potential margin of the claimed design of the ignition unit due to fixing the position of the plunger in the state of gas compression is significant.

Example 4. Investigation of the operation of bursting discs in the ignition unit.

On the basis of the laboratory gas generator shown in example 1, a study of the shape of the opening of rupture discs when they are triggered was carried out. The shape of the membrane opening largely determines how completely the temperature promoter reaches the surface of the main charge of the solid fuel and, consequently, the reliability of ignition. The most expedient is the central opening of the membrane ("flower opening"), when practically the entire temperature promoter falls on the surface of the main charge of the solid fuel.

The experiments were carried out on brass and stainless steel membranes. The diameters of the membranes (from 20 mm to 30 mm) and the thickness of the membranes (from 0.15 mm to 0.4 mm) were varied. The shape of the membrane rupture and the response pressure were recorded. In all experiments, the central opening of the membranes was observed, which corresponds to their task. FIG. Figures 5, 6 show photographs of the typical shape of the membranes after their actuation.

Conclusion on the results of examples 1-4.

The proposed design of the gas generator provides, in comparison with the prototype, a higher reliability of operation due to the use of the plunger fixation unit in the limiting position of gas compression, the introduction of sealing seals into the assembly plunger design and the introduction of a temperature promoter into the design, which ensures the ignition of the main charge of solid fuel.

Literature

1. Koltsova E.M., Glebov M.B., Lazarev V.M., Zhensa A.V. Gas generator for oil and gas wells. RF patent No. 2456443 C1, IPC E21B 43/263 (2006/01). Published: 20.07.2012 BI No. 20.

2. Koltsova EM, Glebov MB, Zhensa AV, Lazarev VM, Gas generator for increasing the productivity of oil and gas wells. RF patent No. 2363840 C1, IPC E21B 43/263 (2006/01). Published: 10.08.2009 BI №22.

Claims (4)

1. A gas generator for oil and gas condensate wells, including a main charge of solid fuel located in a perforated casing, an ignition unit in a gas-filled cylindrical casing with membrane blocks in the upper and lower parts with diaphragm clamping rings and a fixed movable plunger in the upper part of the cylindrical casing, a temperature promoter located above the lower diaphragm block, the upper and lower flanges, characterized in that a unit for fixing the position of the plunger after gas compression in the ignition unit is additionally introduced into the lower part of the cylinder of the ignition unit, including a split conical spring ring located on the inner surface of the cylinder and an assembly plunger with a movable a washer, a shank and a core that can interact with a split conical spring ring in the position of maximum gas compression and engagement with the said ring, in addition, to ensure greater tightness of the ignition unit into the plunger The upper and lower seals are introduced, placed between the plunger body and the movable washer, as well as between the plunger body and the shank. 2. The gas generator according to claim 1, characterized in that two intermediate flanges are introduced into the ignition unit, located between the upper flange and the membrane unit, as well as between the lower flange and the membrane unit, providing removal and sealed installation of membrane units. 3. The gas generator according to claim 1, characterized in that the ignition unit is sealed with tightening bolts. 4. The gas generator according to claim 1, characterized in that the lower diaphragm clamping ring from the plunger side has a hole diameter smaller than the plunger diameter to enable stopping the plunger movement, while the temperature promoter is located in the lower diaphragm clamping ring.

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