CN106437669B - A kind of thermal cracking seam method and system for deep hot dry rock formation production - Google Patents

Abstract

The invention provides a thermal cracking fracture-making method and system for mining deep dry hot rock formations. The method includes: injecting oxidant, fuel and water into the target position of the formation in the injection well section to generate main fractures; injecting oxidant, fuel and water until the formed fracture reaches a predetermined extension length or the formed fracture can enable injection A connection is formed between the well and the production well; the proppant and the sand-carrying fluid are evenly mixed and then pumped into the main fracture, the displacement fluid is pumped, the well is shut down, and the thermal cracking fracture creation is completed. The thermal cracking system includes a supply device, a coiled tubing, a guide, an anchor, a high-pressure hose and a combustion reaction device; the top of the coiled tubing is connected to the supply device, and the bottom is connected to the top of the guide; the bottom of the guide is The end is connected with the anchor, and the side wall of the guide is provided with a communication port. The technical solution provided by the invention has the advantages of good effect of increasing production and injection, high safety, low mining cost, relatively simple system structure and the like.

Description

A thermal cracking fracture-making method and system for mining deep dry hot rock formations

technical field

The invention relates to a thermal cracking cracking method and system suitable for mining deep dry hot rock formations, and belongs to the technical field of energy mining.

Background technique

Geothermal energy is a clean energy with abundant reserves. It can be used for power generation, heating, auxiliary oil recovery, etc. The development and utilization potential of geothermal energy is very huge. my country is rich in geothermal resources, but at present, the shallow geothermal resources are mainly developed, and the deep geothermal resources need to be developed urgently.

At present, the utilization of geothermal energy at home and abroad is mostly focused on hot water geothermal energy, and the development of hot dry rock is still in the experimental stage. Hot dry rock refers to underground high-temperature rock mass with a buried depth of more than 2000m and a temperature of more than 150°C. It is characterized by the fact that there are few underground fluids in the rock mass. Hot dry rock is mainly used to extract its internal heat. For example, cold water is injected from the ground through the wellbore into the deep hot dry rock formation, and it is extracted from the ground after heat exchange. Therefore, the seepage capacity of the deep hot dry rock formation affects the internal energy The utilization efficiency is very important.

At present, many technologies have been developed to modify the permeability of formations, such as downhole explosion technology, nuclear explosion technology, high-energy gas fracturing, hydraulic fracturing and acidizing technology. Commonly applied to geothermal reservoirs are high-energy gas fracturing, hydraulic fracturing and acidizing techniques.

The downhole explosion method includes the detonation and deflagration of solid, liquid and gaseous explosives in the wellbore. The purpose is to create multiple fractures in the formation around the wellbore, which not only eliminates the skin damage caused during drilling, but also connects the natural fracture system with the wellbore. However, the compressive stress wave caused by the downhole explosion causes irreversible plastic deformation of the rock around the well, and a large number of cracks formed in the early stage of the explosion are either reclosed due to the action of the residual stress field, or blocked by the explosion residue, and sometimes the rock formation is infiltrated. It is only possible to increase production in some cases, and the wellbore is easily damaged by a downhole explosion.

Nuclear explosive oil recovery will create and communicate various cavities, thereby increasing the permeability of the rock around the wellbore. The energy of a nuclear explosion is huge, and the reservoir must have a certain thickness to be able to carry out a nuclear explosion and form cracks of a certain scale. The nuclear device must not only be buried deep enough to prevent radioactive leakage, but not too deep to prevent rock static pressure. cracks reclosed. The United States and the former Soviet Union conducted underground experiments using nuclear devices to stimulate oil and gas layers in the 1960s and 1970s, but they have not been commercially applied. In the 1980s and 1990s, my country also carried out the planning and field experiment design of nuclear explosion oil recovery, but it has not been implemented due to various reasons, and the economics of nuclear explosion method is still controversial.

High-energy gas fracturing was developed on the basis of explosive fracturing in the 1960s and 1970s. High-energy gas fracturing uses gunpowder, propellant or a mixture of propellant and explosive in the wellbore, and utilizes the wedging of a large amount of high-temperature, high-pressure gas generated by their deflagration. The basic principle is that the chemical deflagration is not detonation, and the pressure peak and pressure rise can be controlled. speed. Whether multiple fractures can be generated is directly related to the pressure rise rate in the wellbore. However, the fractures formed by high-energy gas fracturing are limited to the near-wellbore zone, and only when combined with other technologies can it play its due role in increasing production and injection.

Hydraulic fracturing technology is to use high-pressure pumps on the surface to squeeze fracturing fluid with high viscosity into the oil layer through the wellbore. When the rate of injection of fracturing fluid exceeds the absorption capacity of the oil layer, a very high pressure will be formed on the oil layer at the bottom of the well. When this pressure exceeds the fracture pressure of the rock in the oil layer near the bottom of the well, the oil layer will be pressed open and fractures will occur. Then inject the sand-carrying fluid with proppant to ensure that the fractures are not closed. However, hydraulic fracturing activities will cause groundwater pollution. During the fracturing process, fracturing fluid containing a large amount of chemical additives is injected into the ground, and the formation is fractured under high pressure. Therefore, the fracturing fluid will pollute the groundwater body and fracture the oil and gas reservoir rocks. Afterwards, oil and gas may also escape into the groundwater layer, causing pollution to the groundwater. In addition, hydraulic fracturing activities may also cause seismic activity, and the cost of fracturing equipment and materials is relatively high, and there is a certain risk of failure.

Acidizing refers to the restoration or improvement of the permeability of formation interface gaps and fractures through the dissolution and dissolution of acid liquid on rock cement, formation interface gaps, and plugs in fractures. However, in the acidizing process, the insoluble matter generated by the reaction may block the interface gap, and the chemical additives may pollute the groundwater. In addition, the acidizing technology has high requirements for the adaptability of the formation, so it can only be applied to carbonate formations, and the application range is limited. .

It can be seen from the above that there is currently no cost-effective and widely used method that can be used to realize large-scale commercial utilization of geothermal resources in deep dry hot rock formations.

Contents of the invention

In order to solve the above technical problems, the present invention provides a thermal cracking fracture-making method and system for mining deep hot dry rock formations. The thermal cracking method for hot dry rock mining can economically and effectively improve deep dry hot rock formations and improve the utilization rate of deep geothermal energy.

In order to achieve the above object, the present invention provides a thermal cracking method for deep dry hot rock formation mining, which comprises the following steps:

Inject oxidant, fuel and water into the target position of the formation in the injection well section, crack the formation rock at the target position, and generate main fractures;

Continue to inject oxidant, fuel and water to make the oxidant and fuel enter the generated main fractures, extend and crack the main fractures, and generate secondary fractures until the formed fractures reach the predetermined extension length or the formed fractures can make injection Connectivity between wells and production wells;

Mix the proppant and sand-carrying fluid evenly and pump it into the main fracture, and then pump the displacement fluid to make the proppant evenly distributed in the main fracture;

Shut in the well and complete thermal cracking fracture creation. After the well is shut in, the main fracture will be closed on the proppant under the action of in-situ stress (that is, the proppant will be included when the main fracture is closed), forming a channel with high conductivity.

Deep hot dry rock formations are generally located below 2000m below the surface, and their high-temperature and high-pressure environment (P>22.13MPa, T>374℃) can make the injected water in a supercritical state, and the density, viscosity, conductivity, and medium The basic properties such as electrical constant are very different from ordinary water, showing properties similar to non-polar organic compounds. Therefore, supercritical water can be completely miscible with non-polar substances (such as hydrocarbons) and other organic substances, while inorganic substances, especially salts, have very low ionization constants and solubility in supercritical water; at the same time, supercritical water can be mixed with Gases such as air, oxygen, nitrogen and carbon dioxide are completely miscible. When the injected water is in a supercritical state downhole, the fuel and oxidant will undergo a supercritical water oxidation reaction downhole, and together with the generated supercritical water, they will act on the formation rocks, cracking the formation rocks around the target position and forming fractures.

During the cracking process, on the one hand, part of the supercritical water will enter into the newly created cracks due to its low viscosity, so that the cracks will continue cracking; In the main fractures, and continue to react in the fractures, the main fractures are extended and cracked to form secondary fractures, thereby improving the physical properties of the deep hot dry rock formation. After the thermal cracking effect of supercritical water is used to create fractures, the secondary cracks will form uneven surfaces due to the thermal cracking effect, and the crack walls cannot be completely closed, so they have better flow conductivity.

The proppant and sand-carrying fluid are evenly mixed and then pumped into the main fracture, and then the displacement fluid is pumped to make the proppant evenly distributed in the main fracture and prevent the fracture from closing; when the well is shut down, the main fracture will be closed on the proppant, thereby Sand-filled fractures with a certain geometric size and high conductivity are formed in the formation near the bottom of the well, so that the well can achieve the purpose of increasing production and injection.

In the above method, preferably, continue to inject oxidant, fuel and water, make the oxidant and fuel enter the generated primary fractures, extend and crack the primary fractures, and generate secondary fractures including the following process:

Close the wellhead. After the downhole thermal cracking reaction is complete, open the wellhead and continue to inject oxidant and fuel until the formed fracture reaches the predetermined extension length or the formed fracture can connect the injection well and the production well. Among them, the process of closing the well and injecting oxidant and fuel can realize the re-reaction of downhole fractures, and this process can be repeated according to the actual situation of the formation. Through repeated injections, the fractures will gradually extend to the set length. Or until the fracture reaches the vicinity of the production well, the effective communication between the injection well and the production well is realized, and the formation permeability is improved.

In the above method, preferably, during the cracking process of thermal cracking, the cracking and extension rate of the fracture can be adjusted by controlling the injection rate of water, fuel and oxidant.

In the above method, the injection well may be a vertical well or a radial horizontal well located in a deep hot dry rock formation.

In the above method, the high-temperature supercritical fluid produced by the combustion reaction can cause the downhole rock to expand under heat. Since the thermal expansion rates of various mineral components inside the rock are different, thermal cracking will cause uneven thermal stress inside the rock, thus forming a geothermal stress. Extended crack controlled by stress direction.

In the above method, preferably, before injecting oxidant, fuel and water into the target position of the formation in the injection well section, the method further includes the step of running a high temperature resistant packer in the injection well, and the high temperature resistant packer can Prevent backflow of the resulting supercritical fluid.

The present invention also provides a thermal cracking fracture-making system, which can be applied to the above-mentioned thermal cracking fracture-making method, and the thermal cracking fracture-making system includes a supply device, a coiled tubing, a guide, and an anchor , high-pressure hose and combustion reaction device;

The top end of the coiled tubing is connected to the supply device, the bottom end of the coiled tubing is connected to the top end of the guide, the bottom end of the guide is connected to the anchor, and the guide There is a communication port on the side wall near the bottom of the device; among them, the guider controls and adjusts the injection direction of fuel and oxidant by combining coiled tubing and high-pressure hose; the anchor is mainly used to improve the stress state of the pipe string and reduce the fatigue of the pipe string damage, control the expansion and contraction of the pipe string, and prolong the life of the pipe string;

One end of the high-pressure hose is connected to the combustion reaction device, and the other end is connected to the coiled oil pipe through the communication port; an outlet is provided on the combustion reaction device, and liquid and/or gas can be discharged from the outlet flow out.

In the thermal cracking system described above, preferably, the coiled tubing includes an inner pipe and an outer pipe, the outer pipe is sheathed outside the inner pipe, and a void is formed between the inner pipe and the outer pipe. cavity.

In the thermal cracking system above, preferably, the supply device includes a water supply device, a fuel supply device, an oxidant supply device, a displacement liquid supply device and a sand-carrying liquid supply device; wherein, the water supply device, fuel supply device, The replacement liquid supply device and the sand-carrying liquid supply device are respectively connected with the inner pipe; the oxidant supply device is connected with the outer pipe.

In the above thermal cracking system, preferably, the system also includes a flowback liquid treatment device and a production casing; the production casing is set on the coiled tubing, the guide, the anchor and the combustion reaction device External: the flowback liquid treatment device is connected with the production casing, and is used for processing the flowback liquid and cuttings produced in the process of thermal cracking and fracturing.

In the thermal cracking system above, preferably, the supply device further includes a displacement liquid supply device, and the displacement liquid supply device is connected to the inner pipe.

In the thermal cracking system described above, preferably, a one-way valve is provided on the pipeline connecting one end of the coiled tubing to the supply device.

In the above thermal cracking fracture creation system, preferably, the thermal cracking fracture creation system further includes a packer, and the packer is located in the cavity between the production casing and the coiled tubing.

In the above thermal cracking system, preferably, the thermal cracking system also includes a manifold car and an instrument device; generally, in actual construction operations, the supply device is relatively large and difficult to move, and the manifold car can realize Movement of supply units.

In the aforementioned thermal cracking fracture creation system, preferably, the production casing and the formation are cemented together through a cement sheath.

In a preferred embodiment, using the above-mentioned thermal cracking fracture creation system to perform thermal cracking fracture creation on dry hot rock formations may include the following steps:

Put the combustion reaction device down at the target position of the formation in the injection well section, inject oxidant, fuel and water into the combustion reaction device with the supply device, crack the formation rock at the target position, and generate main fractures;

Use the supply device to continue to inject oxidant and fuel into the combustion reaction device, so that the main cracks are extended and cracked to generate secondary cracks;

Adjust the injection rate of oxidant, fuel and water to control the rate of fracture extension and cracking, and the cuttings generated during the process of thermal cracking fractures enter the flowback liquid treatment device through the production casing for treatment;

The proppant and sand-carrying fluid are evenly mixed and then pumped into the main fracture through the ground pump unit, and then pumped into the displacement fluid to make the proppant evenly distributed in the main fracture;

Stop the pumping, close the well, close the main fractures on the proppant, and complete the thermal cracking fracture creation.

Beneficial effects of the present invention

Compared with the prior art, the technical solution provided by the present invention mainly has the following advantages:

(1) The effect of increasing production and injection is better: after the supercritical hydrothermal cracking effect is used to create fractures in the rocks near the underground, supercritical water enters the fractures and continues to form secondary fractures in the fractures. At the same time, fuel and oxidant enter the fractures to react. Extending fractures and generating secondary fractures further improves the permeability of the formation;

(2) Higher safety: by reacting underground to generate supercritical water to create fractures, it does not require the pressure of the ground pump set to be too high, and avoids the use of dangerous methods such as underground explosive explosions to increase the formation permeability;

(3) Low mining cost: use fuel, oxidant and water to react underground to generate supercritical water, which avoids the disadvantages of using high-pressure pumps and the need to inject a large amount of water into the formation, and reduces the mining cost;

(4) The system structure is relatively simple: the structural settings of the underground and surface devices and components are relatively simple, so that the method can have a wide range of applications.

Description of drawings

Fig. 1 is the structural representation of the pyrolysis cracking system that embodiment 1 provides;

Fig. 2 is the schematic diagram of connecting the injection well and the production well for the pyrolysis fracture-making method provided in Example 2;

Fig. 3 is a schematic diagram of secondary fractures formed by the thermal cracking method provided in Example 2.

Explanation of main figures and symbols:

1: Displacing liquid supply device; 2: Sand mixing device; 3: Carrying sand liquid supply device; 4: Water supply device; 5: Fuel supply device; 6: Oxidant supply device; 7: The first one-way valve; 8: The second One-way valve; 9: third one-way valve; 10: fourth one-way valve; 11: fifth one-way valve; 12: flowback liquid treatment device; 13: inner pipe; 14: cement ring; 15: outer pipe ;16: production casing; 17: combustion reaction device; 18: deep dry hot rock formation; 19: overlying formation; 20: high-pressure hose; 21: guide; 22: anchor; 23: underlying formation; 24: supercritical water; 25: primary fracture; 26: secondary fracture; 27: packer; 28: production well; 29: proppant.

Detailed ways

In order to have a clearer understanding of the technical features, purposes and beneficial effects of the present invention, the technical solution of the present invention is described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

Example 1

The present invention provides a pyrolysis fracture-making system, the structural diagram of which is shown in Figure 1.

The thermal cracking system includes a supply device, a coiled tubing, a guide 21, an anchor 22, a high-pressure hose 20, and a combustion reaction device 17; wherein, the supply device includes a displacement fluid supply device 1, a sand-carrying fluid supply device 3, a water supply Device 4, fuel supply device 5, and oxidant supply device 6; the coiled tubing is a tubular structure, which includes an inner tube 13 and an outer tube 15, and the outer tube 15 is sleeved outside the inner tube 13, and the inner tube 13 and the outer tube 15 An annular cavity that allows the medium to flow is formed between them;

The displacing liquid supply device 1, the sand-carrying liquid supply device 3, the water supply device 4 and the fuel supply device 5 are respectively connected to the top end of the inner pipe 13, and each connecting pipeline is provided with a first check valve 7 and a second check valve respectively. 8. The third one-way valve 9 and the fourth one-way valve 10;

The oxidant supply device 6 is connected to the top end of the outer pipe 15, and a fifth check valve 11 is arranged on the connecting pipe;

The bottom end of the coiled tubing is connected to the top end of the guide 21, and the bottom end of the guide 21 is connected to the anchor 22; the side wall of the guide 21 near the bottom end is provided with a connection port;

One end of the high-pressure hose 20 is connected with the combustion reaction device 17, and the other end passes through the connection port on the guide 21 and is connected with the coiled tubing;

The thermal cracking system provided in this embodiment also includes a flowback liquid treatment device 12 and a production casing 16; the production casing 16 is arranged outside the coiled tubing, the guide 21, the anchor 22 and the combustion reaction device 17, The flowback liquid treatment device 12 is connected to the production casing 16; during production operations, the production casing 16 and the formation are cemented together through the cement sheath 14;

The thermal cracking fracture-making system provided in this embodiment may also include a sand mixing device 2 connected to a sand-carrying liquid supply device 3 .

The thermal cracking fracture creation system provided in this embodiment may further include a packer 27, which is arranged in the cavity formed between the production casing 16 and the coiled tubing.

Example 2

This embodiment provides a thermal cracking cracking method for hot dry rock mining. The method is carried out using the thermal cracking cracking system provided in Example 1. The method includes the following steps:

1) In the radial horizontal well drilled by applying the thermal jet method, the downhole combustion reaction device 17 is placed in the horizontal radial well section of the deep hot dry rock formation 18 (as shown in Figure 1);

The deep hot dry rock formation is generally located below 2000m below the surface, and the pressure is generally higher than 22.13MPa. As shown in Figure 1, the upper part of the deep hot dry rock formation 18 is the overlying stratum 19, and the lower part is the overlying stratum 23;

2) respectively open the second one-way valve 8, the fourth one-way valve 10 and the fifth one-way valve 11 on the pipelines connected to the water supply device 4, the fuel supply device 5 and the oxidant supply device 6 and the coiled tubing, and lower the seal Spacer 27 injects oxidant 6, fuel 5 and water 4 into the combustion reaction device 17, so that the oxidant 6 and fuel 5 undergo a combustion reaction downhole;

3) The generated supercritical water 24 flows out through the outlet of the combustion reaction device 17, heating the rocks near the downhole, causing cracks to appear between and inside the mineral particles, and continuing to heat the reservoir rocks to produce main cracks 25 (as shown in Figure 3);

4) After the main fractures 25 are formed in the reservoir rock, the reaction rate can be continuously controlled, so that the generated supercritical water 24 enters the main fractures 25, thereby continuously producing a thermal cracking effect on the reservoir rocks in the main fractures 25, causing the formation of After the main crack 25, a secondary crack 26 is further generated;

5) Continue to inject excess fuel and oxidant, so that the fuel and oxidant enter the generated main cracks 25, continue to react in the main cracks 25, impel the cracks to extend further and generate secondary cracks 26;

Close the wellhead, open the wellhead after the downhole thermal cracking reaction is complete, and continue to inject oxidant and fuel. This process can be repeated many times until the formed fracture reaches a predetermined extension length (as shown in Figure 1) or the formed fracture Fractures enable communication between the injection well and the production well 28 (as shown in Figure 2);

Due to thermal cracking, the secondary cracks form uneven surfaces, and the crack walls cannot be completely closed, so they have good flow conductivity;

During operation, the injection rate of the fuel, oxidizer and water injected into the combustion reaction device 17 can be adjusted to control the temperature of the supercritical water 24 heated by the combustion reaction, thereby controlling the thermal cracking fracture creation and fracture extension. rate; for example, when operating between an injection well and a production well 28, the injection rate may be increased until the fractures formed enable communication between the two wells;

6) Close the second one-way valve 8, the fourth one-way valve 10 and the fifth one-way valve 11 on the pipelines where the water supply device 4, the fuel supply device 5 and the oxidant supply device 6 are connected to the coiled tubing respectively, and open the replacement respectively The first one-way valve 7 and the third one-way valve 9 on the pipeline connected to the liquid supply device 1 and the sand-carrying liquid supply device 3 and the coiled tubing;

7) Use the sand mixing device 2 to mix the proppant 29 and the sand-carrying liquid evenly, and then input the sand-carrying liquid supply device 3, and use the surface pump unit to pump the sand-carrying liquid containing the proppant 29 into the Deep hot dry rock formations18;

8) Use the surface pump unit to pump the displacement fluid in the displacement fluid supply device 1 into the deep hot dry rock formation, so that the proppant 29 is evenly distributed in the fracture 25, and the well is shut down, and the fracture 25 is closed in the proppant under the action of in-situ stress. 29, the formed secondary fractures 26 have uneven surfaces due to thermal cracking, and the fracture walls cannot be completely closed, which increases the flow area of formation fluids, thus forming high-conductivity fractures with a certain geometric size in the formation near the bottom of the well. The sand-filling fractures with high flow capacity can improve the formation permeability, so that the well can achieve the purpose of increasing production and injection.

In summary, the thermal cracking fracture-making method and system suitable for hot dry rock mining provided by the present invention have the advantages of good production and injection increase effects, high safety, low mining cost, simple system structure, etc., and can effectively improve deep fractures. The properties of hot dry rock formations improve the utilization efficiency of geothermal energy and have broad application prospects.

Claims (10)

1. A method for creating cracks by thermal cracking for deep dry hot rock formation mining, comprising the following steps: Inject oxidant, fuel and water into the target position of the formation in the injection well section, crack the formation rock at the target position, and generate main fractures; Continue to inject oxidant, fuel and water to make the oxidant and fuel enter the generated main fractures, extend and crack the main fractures, and generate secondary fractures until the formed fractures reach the predetermined extension length or the formed fractures can make injection Connectivity between wells and production wells; Mix the proppant and sand-carrying fluid evenly and pump it into the main fracture, and then pump the displacement fluid to make the proppant evenly distributed in the main fracture; Shut in the well and complete thermal cracking fracture creation. 2. The thermal cracking fracture-making method according to claim 1, characterized in that, during the thermal cracking crack-making process, the cracking and elongation rate of the crack is regulated by controlling the injection rate of water, fuel and oxidant. 3. The thermal cracking fracture-making method according to claim 1, wherein the injection well is a vertical well or a radial horizontal well located in a deep hot dry rock formation. 4. A thermal cracking seam-making system, which includes a supply device, coiled tubing, a guide, an anchor, a high-pressure hose and a combustion reaction device; The top end of the coiled tubing is connected to the supply device, the bottom end of the coiled tubing is connected to the top end of the guide, the bottom end of the guide is connected to the anchor, and the guide There is a communication port on the side wall of the device; One end of the high-pressure hose is connected to the combustion reaction device, and the other end is connected to the coiled oil pipe through the communication port; an outlet is provided on the combustion reaction device. 5. The thermal cracking system according to claim 4, wherein the coiled tubing comprises an inner pipe and an outer pipe, and the outer pipe is sleeved outside the inner pipe, and the inner pipe and the inner pipe are A cavity is formed between the outer tubes. 6. The thermal cracking system according to claim 5, wherein the supply device comprises a water supply device, a fuel supply device, an oxidizer supply device, a displacement liquid supply device and a sand-carrying liquid supply device; wherein, the The water supply device, the fuel supply device, the displacement liquid supply device and the sand-carrying liquid supply device are respectively connected with the inner pipe; the oxidant supply device is connected with the outer pipe. 7. The thermal cracking fracture-making system according to claim 4 or 5, characterized in that the system also includes a flowback liquid treatment device and a production casing; the production casing is sleeved on the coiled tubing and the guide , the anchor and the exterior of the combustion reaction device, the flowback liquid treatment device is connected with the production casing. 8. The thermal cracking fracture-making system according to claim 6, characterized in that the system further comprises a sand mixing device, and the sand mixing device is connected with the sand-carrying liquid supply device. 9. The thermal cracking system according to claim 4, characterized in that a check valve is provided on the pipeline connecting one end of the coiled tubing to the supply device. 10. The thermal cracking system according to claim 4, characterized in that, the thermal cracking system further comprises a manifold car and an instrument device.