A method of downhole injection of a firelighting fuel

Abstract

The present application relates to the technical field of underground coal gasification, and particularly relates to an underground injection method of ignition fuel. The method sequentially injects ignition fuel and main fuel which are isolated from each other into a continuous pipe, mixes the ignition fuel and the main fuel when the ignition fuel and the main fuel are located at the position of an igniter, introduces oxygen into the continuous pipe, and starts the igniter to ignite. The ignition fuel and the main fuel are isolated by an isolation capsule or an isolation liquid. The method has simple steps, strong operability, and short operation period. The method only needs to use ignition fuel and main fuel to cooperate with ignition without adding other auxiliary fuel or components, can effectively reduce cost, and greatly improves reliability.

Description

Technical Field

[0001] This invention relates to the field of underground coal gasification technology, and more specifically, to a method for injecting ignition fuel underground. Background Technology

[0002] As oil and gas field exploration and development in my country gradually moves towards deep and ultra-deep wells, the exploration difficulty is increasing. With the growing urgency of energy transformation and upgrading, there is an urgent need to develop clean energy extraction and utilization. Underground coal gasification (UCG) is a powerful measure that can effectively resolve the contradiction between energy demand and clean energy use. my country has abundant underground coal resources, especially in medium-deep formations, with a large undeveloped volume. Therefore, UCG technology has become an important means of clean energy extraction in China. In practical engineering, UCG technology needs to focus on solving issues such as reliability, safety, and efficiency.

[0003] The key to downhole ignition is that the ignition fuel and the main fuel are injected into the igniter in a certain ratio. However, due to the continuous tube being thousands of meters long, there are tortuous flows in the vertical and horizontal sections, and there is liquid in the tube. The injection is affected by multiphase flow, which means that when the ignition fuel threshold injected from the surface reaches the igniter, the concentration cannot be accurately controlled, and the ignition requirements cannot be met, ultimately resulting in ignition failure.

[0004] Currently, there are no readily feasible solutions or measures in China. The main technologies fall into two categories. One involves simultaneously injecting the main fuel and ignition fuel, increasing the concentration of the ignition fuel before injection to ensure the concentration threshold at the ignition point. However, losses are prone to occur during ignition fuel injection, resulting in insufficient ignition fuel concentration reaching the igniter and causing ignition failure. To guarantee successful ignition, a sufficient amount of ignition fuel must be injected, but the cost of ignition fuel is extremely high, easily leading to fuel waste. The second category involves forced oxidation, utilizing the spontaneous combustion characteristics of coal. Through multiple cycles of drainage and heating, an air heating device is activated, and oxygen is introduced to enhance coal seam combustion, raising the calorific value of the coal gas to a certain level before it enters the subsequent gasification process. This method requires multiple drainage and heating operations to achieve forced oxidation, resulting in a complex process, low reliability, and a long operating cycle. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for injecting ignition fuel downhole.

[0006] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0007] This invention provides a method for injecting ignition fuel downhole, wherein ignition fuel and main fuel, which are isolated from each other, are sequentially injected into a continuous tube to the position of the igniter, and then the two are mixed; a mixed gas containing oxygen is introduced into the continuous tube, and the igniter is activated to ignite the fuel.

[0008] Furthermore, the ignition fuel and the main fuel are separated by an isolation capsule or an isolation fluid.

[0009] Furthermore, when the ignition fuel and the main fuel are isolated by an isolation capsule, the injection method includes the following steps:

[0010] S1-1. Encapsulate the ignition fuel into the isolation capsule;

[0011] S1-2. Nitrogen gas is used to inject the isolation capsule containing the ignition fuel into the continuous tube and blow it to the position of the igniter;

[0012] S1-3. Inject the dissolving solution into the continuous tube to dissolve the isolation capsule;

[0013] S1-4. Inject the main fuel into the continuous tube to the position of the igniter, and mix the main fuel with the ignition fuel;

[0014] S1-5. Introduce a mixture of oxygen-containing gas into the continuous tube, start the igniter, and complete the ignition.

[0015] Furthermore, the isolation capsule is made of a mixture of urea-formaldehyde resin and aluminum sulfate, and the dissolving solution is a urea solution with a mass percentage of 15-25%; the mass ratio of the isolation capsule to the dissolving solution is 7:2.

[0016] Furthermore, when the ignition fuel and the main fuel are isolated by an isolation fluid, the injection method includes the following steps:

[0017] S2-1. Sequentially inject the ignition fuel, the isolation fluid, and the main fuel into the continuous tube until the igniter is in position;

[0018] S2-2. At the position of the igniter, bring the ignition fuel into contact with the main fuel, introduce a mixture of oxygen into the continuous tube, start the igniter, and complete the ignition.

[0019] Furthermore, the separating liquid is a mixture of an alkaline solution and a surfactant, wherein the mass ratio of the alkaline solution to the surfactant is 1:3; the alkaline solution is a sodium hydroxide solution or a sodium carbonate solution, and the surfactant is a sodium silicate solution or an emulsifier.

[0020] Furthermore, the volume ratio of the isolation liquid to the ignition fuel is 1:5.

[0021] Furthermore, the ignition fuel is triethylborane, and the main fuel is heptane; the mass of triethylborane is 0.66 kg to 6.6 kg, and the mass flow rate of heptane is 8.16 kg / h to 16.32 kg / h.

[0022] Furthermore, the oxygen-containing mixed gas contains oxygen and nitrogen, with oxygen comprising 25% by volume and the remainder being nitrogen.

[0023] Furthermore, before injecting ignition fuel, which is isolated from the main fuel, into the continuous tube, the continuous tube is first purged with nitrogen.

[0024] The beneficial effects of this invention are as follows:

[0025] (1) The ignition fuel downhole injection method of the present invention involves injecting ignition fuel and main fuel separately into a continuous tube, and mixing the two at the position of the igniter to achieve ignition at the same time; the steps are simple, highly operable, and have a short operation cycle;

[0026] (2) The ignition fuel downhole injection method of the present invention uses an isolation capsule to encapsulate the ignition fuel, so that the ignition fuel can pass smoothly through the vertical section and the horizontal section turning point, avoiding the influence of multiphase flow, thereby preventing the concentration change of the ignition fuel when the threshold reaches the igniter, resulting in ignition failure.

[0027] (3) The ignition fuel downhole injection method of the present invention uses an isolation capsule to encapsulate the ignition fuel, and with the use of a dissolving liquid, it can achieve precise control over the dissolution of the isolation capsule, thereby making the ignition process precise and controllable, and further ensuring the ignition success rate;

[0028] (4) The ignition fuel injection method of the present invention only requires the use of ignition fuel and main fuel for ignition without the need to add other auxiliary fuels or components, which can effectively reduce costs and greatly improve reliability. Attached Figure Description

[0029] Figure 1 This is a flowchart illustrating the isolation process using an isolation capsule in the ignition fuel downhole injection method of the present invention.

[0030] Figure 2 This is a flowchart illustrating the isolation process using an isolation fluid in the downhole injection method for ignition fuel of the present invention. Detailed Implementation

[0031] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0032] The ignition fuel downhole injection method of the present invention involves sequentially injecting mutually isolated ignition fuel and main fuel into a continuous tube. When the ignition fuel and main fuel are in the position of the igniter, they are mixed. Oxygen is introduced into the continuous tube, and the igniter is activated for ignition.

[0033] The present invention discloses a downhole injection method for ignition fuel, which involves injecting ignition fuel and main fuel separately into a continuous tubing and mixing them at the igniter location to achieve simultaneous ignition. This method is simple, highly operable, and has a short operation cycle; it is also low-cost, highly reliable, effectively reduces the downhole ignition failure rate, and minimizes the waste of both ignition fuel and main fuel.

[0034] In this invention, the ignition fuel and the main fuel are specifically separated by an isolation capsule or an isolation liquid.

[0035] like Figure 1 As shown, when the ignition fuel and the main fuel are separated by an isolation capsule, the injection method includes the following steps:

[0036] S1-1. The ignition fuel is sealed into an isolation capsule.

[0037] S1-2. Nitrogen gas is used to inject the isolation capsule containing ignition fuel into the continuous tube and blow it to the position of the igniter.

[0038] S1-3. Inject the dissolving solution into the continuous tube to dissolve the isolation capsule.

[0039] S1-4. Inject the main fuel into the continuous tube and mix the main fuel with the ignition fuel.

[0040] S1-5. Introduce oxygen into the continuous tube, start the igniter, and complete the ignition.

[0041] For the isolation capsule, it must meet the following requirements: sealed space, immiscible with ignition fuel and main fuel, insoluble in water, non-flammable, and not easily broken. At the same time, the isolation capsule also needs to have a certain degree of elasticity. This is because the downhole coiled tubing has vertical and horizontal sections, and the isolation capsule needs to be able to pass smoothly through the junction of the vertical and horizontal sections.

[0042] The dissolving solution must be able to dissolve the isolation capsule, and it must also be non-flammable and insoluble in ignition fuel. After the dissolving solution is introduced, it must dissolve the isolation capsule that has reached the igniter without mixing with the ignition fuel.

[0043] Therefore, according to the above requirements, preferably, the material of the isolation capsule of the present invention is a mixture of urea-formaldehyde resin and aluminum sulfate, and the dissolving solution is a urea solution with a mass percentage of 15-25%; the mass ratio of the isolation capsule to the dissolving solution is 7:2.

[0044] More preferably, the urea solution has a mass percentage of 20%.

[0045] like Figure 2 As shown, when the ignition fuel and the main fuel are separated by a separating fluid, the injection method includes the following steps:

[0046] S2-1. Inject ignition fuel, isolation fluid and main fuel into the continuous tube in sequence.

[0047] S2-2. When the ignition fuel, isolation fluid, and main fuel are all in the igniter position, oxygen is introduced into the continuous tube to start the igniter and complete the ignition.

[0048] It should be noted that when the ignition fuel, isolating fluid, and main fuel are located at the igniter position, the ignition fuel can come into contact with and burn the main fuel, and the isolating fluid no longer isolates the two. This process is achieved through the specific structure of the continuous tube and the igniter: an igniter is located at one end of the continuous tube, inside the wellbore, and the diameter of the wellbore is larger than the outlet of the igniter. When the ignition fuel, isolating fluid, and main fuel are ejected, they enter the larger space of the wellbore, where the ignition fuel can mix with the main fuel and ignite through the igniter.

[0049] For the isolation fluid, it needs to meet the performance characteristics of being insoluble in the main fuel and ignition fuel, while being non-flammable and having good fluidity.

[0050] Therefore, based on the above requirements, preferably, the separating liquid is a mixture of an alkaline solution and a surfactant; the alkaline solution is a sodium hydroxide solution or a sodium carbonate solution, and the surfactant is a sodium silicate solution or an emulsifier.

[0051] It should be noted that when using an isolation fluid for isolation, the order of the three liquids when the ignition fuel, isolation fluid, and main fuel arrive at the igniter will no longer be sequential. The ignition fuel can come into contact with the main fuel, and after oxygen is introduced, the ignition fuel undergoes an oxidation reaction, producing an open flame, releasing heat, and igniting the main fuel.

[0052] Since the isolation fluid does not participate in the combustion reaction, its amount only needs to be sufficient to isolate the ignition fuel from the main fuel, and there are no particularly strict limitations.

[0053] Preferably, the ignition fuel is triethylborane, and the main fuel is heptane; the mass of triethylborane is 0.66 kg to 6.6 kg, and the mass flow rate of heptane is 8.16 kg / h to 16.32 kg / h; during use, the main fuel is continuously supplied to maintain combustion.

[0054] Preferably, the oxygen-containing gas mixture is a mixture of oxygen and nitrogen, wherein the volume percentage of oxygen is 25% and the remainder is nitrogen; during use, the oxygen-containing gas mixture is continuously introduced to maintain combustion.

[0055] Preferably, before injecting ignition fuel, which is isolated from the main fuel, into the igniter, the continuous tube is purged with nitrogen.

[0056] Example 1

[0057] In this embodiment, an isolation capsule is used to isolate and inject the ignition fuel and main fuel. This embodiment uses a ground-based simulation experimental device for ignition experiments, which has a simulated continuous tubing similar to that of a downhole continuous tubing system and an igniter.

[0058] This embodiment uses triethylborane as the ignition fuel and heptane as the main fuel. The combustion formula for the downhole fuel chemical reaction of triethylborane is as follows:

[0059] (CH3CH2)3B(l)+3H2O(l)=H3BO3(l)+3C2H6(g).

[0060] 2(CH3CH2)3B(l)+21O2(g)=2H3BO3(l)+12CO2(g)+12H2O(l)

[0061] Based on the requirements that the capsule must be spatially sealed, immiscible with ignition fuel and main fuel, insoluble in water, non-flammable, and not easily broken, while also possessing a certain degree of elasticity to allow smooth flow at the junction of vertical and horizontal sections in the well, and not be scratched by the pipe wall when flowing in continuous tubing, and also be soluble, urea-formaldehyde resin (UF) was selected as the material. It was manufactured into a capsule shape, ignition fuel was encapsulated inside, and nitrogen gas was introduced to propel it to the downhole igniter.

[0062] The required amount of ignition agent for a single test is 0.66 kg to 6.6 kg, and the main fuel is injected at a mass flow rate of 8.16 kg / h to 16.32 kg / h. After the capsule reaches the igniter, a 20% urea solution is injected at a ratio of 2:7 (solution to capsule mass) to rupture and dissolve the capsule. Finally, a mixed gas containing 25% oxygen by volume is introduced to provide an oxygen-rich environment downhole, causing the ignition fuel to undergo an oxidation reaction, releasing heat and generating an open flame to ignite the main fuel.

[0063] Experiments have shown that this embodiment can effectively achieve ignition.

[0064] Repeated implementation of this embodiment revealed an ignition success rate greater than 90%.

[0065] Example 2

[0066] In this embodiment, an isolation fluid is used to isolate and inject the ignition fuel and main fuel. The ground simulation experimental device, ignition fuel, and main fuel used in this embodiment are exactly the same as in Embodiment 1.

[0067] Based on the requirements that the isolation fluid must be insoluble in both the main fuel and the ignition fuel, non-flammable, and possess good fluidity, a chemical degreasing fluid was selected as the isolation fluid. In the coiled tubing, the ignition fuel, isolation fluid, and main fuel were injected sequentially, and nitrogen was used to push them to the downhole igniter. At this point, the order of the three liquids was shuffled, and the ignition fuel came into contact with the main fuel. The required amount of ignition fuel for a single test was 0.66 kg to 6.6 kg, and the main fuel was injected at a mass flow rate of 8.16 kg / h to 16.32 kg / h; the volume ratio of the isolation fluid to the ignition fuel was 1:5.

[0068] Finally, oxygen at a ratio of 25% is introduced to provide an aerobic environment, causing the ignition fuel to undergo an oxidation reaction, releasing heat, producing an open flame, and igniting the main fuel.

[0069] Experiments have shown that this embodiment can effectively achieve ignition.

[0070] Repeated implementation of this embodiment revealed an ignition success rate greater than 90%.

[0071] Comparative Example

[0072] This comparative example uses traditional ignition technology for ignition.

[0073] Traditional ignition technology involves injecting the main fuel and ignition fuel simultaneously, increasing the concentration of the ignition fuel before injection to ensure the concentration threshold at the ignition point.

[0074] Because traditional ignition technology is costly and difficult to repeat under experimental conditions, the ignition success rate of this comparative example is obtained from continued practical experience and related research, with an ignition success rate of 20% to 30%.

[0075] The comparison shows that the method of the present invention can effectively improve the ignition success rate compared with the comparative example. At the same time, it uses less ignition fuel, which greatly reduces the cost and makes it more suitable for practical use.

[0076] In the description of this invention, it should be noted that the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0077] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0078] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for injecting ignition fuel downhole, characterized in that, Sequentially inject separate ignition fuel and main fuel into the continuous tube to the igniter position, and then mix them; introduce the oxygen-containing mixed gas into the continuous tube and start the igniter to ignite; The ignition fuel and the main fuel are separated by an isolation capsule or an isolation liquid; When the ignition fuel and the main fuel are isolated by an isolation capsule, the injection method includes the following steps: S1-1. Encapsulate the ignition fuel into the isolation capsule; S1-2. Nitrogen gas is used to inject the isolation capsule containing the ignition fuel into the continuous tube and blow it to the position of the igniter; S1-3. Inject the dissolving solution into the continuous tube to dissolve the isolation capsule; S1-4. Inject the main fuel into the continuous tube to the position of the igniter, and mix the main fuel with the ignition fuel; S1-5. Introduce a mixture of oxygen-containing gas into the continuous tube, start the igniter, and complete the ignition; The isolation capsule is made of a mixture of urea-formaldehyde resin and aluminum sulfate, and the dissolving solution is a urea solution with a mass percentage of 15-25%; the mass ratio of the isolation capsule to the dissolving solution is 7:

2. When the ignition fuel and the main fuel are isolated by an isolation fluid, the injection method includes the following steps: S2-1. Sequentially inject the ignition fuel, the isolation fluid, and the main fuel into the continuous tube until the igniter is in position; S2-2, At the position of the igniter, the ignition fuel is brought into contact with the main fuel, and a mixture containing oxygen is introduced into the continuous tube to start the igniter and complete the ignition. One end of the continuous tube is equipped with an igniter, which is located inside the wellbore. The diameter of the wellbore is larger than the outlet of the igniter. When the ignition fuel, the isolation fluid, and the main fuel are ejected, they enter the larger wellbore. At this time, the ignition fuel can mix with the main fuel and be ignited by the igniter.

2. The method for injecting ignition fuel downhole according to claim 1, characterized in that, The isolation fluid is a mixture of an alkaline solution and a surfactant, wherein the mass ratio of the alkaline solution to the surfactant is 1:

3. The alkaline solution is a sodium hydroxide solution or a sodium carbonate solution, and the surfactant is a sodium silicate solution or an emulsifier.

3. The method for injecting ignition fuel downhole according to claim 2, characterized in that, The volume ratio of the isolation fluid to the ignition fuel is 1:

5.

4. A method for injecting ignition fuel downhole according to any one of claims 1 to 3, characterized in that, The ignition fuel is triethylborane, and the main fuel is heptane; the mass of triethylborane is 0.66 kg to 6.6 kg, and the mass flow rate of heptane is 8.16 kg / h to 16.32 kg / h.

5. The method for injecting ignition fuel downhole according to claim 4, characterized in that, The oxygen-containing gas mixture contains oxygen and nitrogen, with oxygen comprising 25% by volume and the remainder being nitrogen.

6. A method for injecting ignition fuel downhole according to any one of claims 1 to 3, characterized in that, Before injecting ignition fuel, which is isolated from the main fuel, into the continuous tube, the continuous tube is first purged with nitrogen.

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