Method for inducing controllable collapse of interlayer in construction process of ultra-deep salt cavern reservoir

Abstract

The invention discloses a method for inducing controllable collapse of an interlayer in a construction process of an ultra-deep salt cavern reservoir, which mainly comprises the following steps of: early-stage preparation and parameter design: completing exposure of a target interlayer, and obtaining mechanical parameters of the target interlayer through geological data and logging data; based on this, the peak value, valley value, rate and dwell time of the pressure cycle are designed. And fatigue load application: strictly executing designed pressure circulation through a wellhead pumping and flowback system. The rapid pressure reduction stage is the key of inducing crack propagation. Monitoring and feedback control: utilizing sonar to measure the cavity, and tracking the interlayer state and the collapse process. And adjusting cycle parameters according to a monitoring result to realize closed-loop control. According to the method, the damage of the interlayer is converted from passive waiting to active induction, the whole process is carried out under artificially set parameters, and the controllability is high.

Description

Technical Field

[0001] This invention relates to the field of underground energy storage engineering technology, and more specifically to a method for inducing controlled collapse of interlayers during the construction of ultra-deep salt cavern storage facilities. Background Technology

[0002] Salt rock, due to its low permeability, creep, and self-healing properties, is considered an ideal medium for energy (natural gas, oil, hydrogen, compressed air) storage and disposal. Water-soluble cavity construction techniques are commonly used in salt cavern construction. However, natural salt rock deposits often contain interlayers of non-salt rocks such as gypsum, mudstone, and glaucophane. The mechanical properties (such as strength and creep) of these interlayers differ significantly from those of salt rock.

[0003] In shallow salt caverns, interlayers typically collapse naturally as the salt rock dissolves. However, in ultra-deep salt deposits such as the Ordovician salt fields of northern Shaanxi, which are buried at depths exceeding 2600 meters, the geological stress is high, and interlayers are frequently present. Under these geological conditions, traditional cavity-building methods face severe challenges. High risk of natural collapse: After the interlayer is exposed, it may not collapse for a long time under extremely high ground stress, but its stability is difficult to predict. Once a large-scale collapse occurs suddenly, the huge impact energy may damage the wellbore and production casing, causing a catastrophic accident.

[0004] Uncontrollable cavity shape: Unpredictable interlayer collapse can form extremely irregular cavity shapes, which seriously affects the operational efficiency and safe lifespan of the storage facility.

[0005] Limited treatment options: For ultra-deep salt caves, conventional physical or chemical interventions are extremely costly and risky, and there is a lack of effective artificial control methods.

[0006] Therefore, there is an urgent need in this field for a technology that can actively and safely induce the collapse of thick interlayers in ultra-deep salt caverns, so as to achieve precise control of salt cavern morphology and safe construction. Summary of the Invention

[0007] In view of this, the present invention provides a safe, efficient and controllable method for treating ultra-deep salt cavern interlayers. By artificially applying periodic pressure loads, fatigue damage is induced in the interlayers, causing them to break into small pieces and fall, thereby eliminating the risk of large-scale sudden collapse.

[0008] This invention treats the sandwich layer as an engineering structure, inducing "fatigue" failure by applying periodic alternating loads. Specifically, by controlling the fluid pressure inside the salt cavern, the sandwich layer is repeatedly subjected to cycles of "high stress (compression)" and "low stress (tension / shear)". Under the cumulative effect of fatigue, microcracks initiate, propagate, and connect within the sandwich layer, ultimately leading to the loss of overall stability and the fragmentation into smaller blocks that fall.

[0009] To achieve the above objectives, the present invention adopts the following technical solution: A method for inducing controlled collapse of interlayers during the construction of ultra-deep salt cavern storage facilities, the main steps of which include: Preliminary preparation and parameter design: Complete the exposure of the target interlayer and obtain its mechanical parameters through geological data and well logging data. Based on this, design the peak value, valley value, rate and holding time of pressure circulation.

[0010] Fatigue loading: The designed pressure cycle is strictly executed through wellhead pumping and flowback systems. The rapid depressurization phase is crucial for inducing fracture propagation.

[0011] Monitoring and feedback control: Sonar cavity is used to track the interlayer status and collapse process. Loop parameters are adjusted based on monitoring results to achieve closed-loop control.

[0012] More specifically, it includes the following steps: S1. Cavity Construction and Exposure: Using conventional water-soluble cavity construction technology, construct a salt cavern until the target interlayer is fully exposed to the top plate or sidewall of the chamber; the conventional water-soluble cavity construction technology refers to the "Technical Specification for Cavity Construction of Salt Cavern Gas Storage" (SY / T 7307-2016). S2. Circulation parameter design: Based on the mechanical properties, thickness and burial depth of the target interlayer, design the parameters of pressure circulation, including peak pressure, valley pressure, pressurization rate, depressurization rate, holding time and number of cycles; S3. Implement fatigue cycle: periodically inject or discharge fluid into the salt cavern to perform at least one pressure cycle unit, each of the pressure cycle units including: pressurization phase, high pressure holding phase, depressurization phase and low pressure holding phase; S4. Process monitoring and dredging: During step S3 or after each pressure cycle unit, sonar cavity measurement technology is used to monitor changes in cavity morphology and interlayer collapse. S5. Judgment and Iteration: Based on the sonar cavity measurement results, determine whether the target interlayer has completely collapsed as expected; if not, return to step S3, adjust the loop parameters and continue; if completed, end the interlayer processing and continue with subsequent cavity construction or sealing operations.

[0013] Preferably, in step S2, the valley pressure is lower than the minimum principal stress of the formation at that depth, and the peak pressure is higher than the pore pressure of the formation at that depth but lower than the formation fracturing pressure.

[0014] Preferably, in step S2, the parameters of the pressure cycle are optimized using the numerical simulation software FLAC3D, and the numerical simulation is based on the fatigue life model of interbedded rock.

[0015] Preferably, in step S3, the depressurization stage adopts a rapid depressurization method, with the depressurization rate controlled at 0.5-3.0 MPa / h; the pressurization stage adopts a relatively slow pressurization method, with the pressurization rate controlled at 0.1-1.0 MPa / h.

[0016] Preferably, in step S3, during the depressurization stage, the sudden change in wellhead return flow or the micro-fracture events captured by the downhole microseismic monitoring system are used to determine in real time whether the interlayer has experienced local fracture or collapse.

[0017] Preferably, the method is used for salt rock deposits with a burial depth of 2600 meters or more and containing interlayers with a single layer thickness of not less than 1 meter.

[0018] As can be seen from the above technical solution, compared with the prior art, the present invention has the following beneficial effects: Active and controllable: The destruction of the interlayer is transformed from passive waiting to active induction. The entire process is carried out under artificially set parameters, which makes it highly controllable.

[0019] Safe and reliable: It transforms a potentially catastrophic large-scale collapse into a series of predictable small-scale falls, greatly reducing the impact risk and ensuring the safety of the well shaft and cavity.

[0020] High applicability: It provides an effective solution, especially for solving the industry problem of ultra-deep salt cavern interlayers, and broadens the construction scope of salt cavern storage under complex geological conditions.

[0021] Cost-effective: It is achieved simply by controlling fluid pressure, without the need for additional expensive tools or chemical reagents, resulting in relatively low operating costs. It can also effectively optimize the final cavity shape and improve the operational efficiency of the storage facility. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of the overall process of the method of the present invention.

[0024] Figure 2 This is a schematic diagram of a typical pressure cycle unit, showing the relationship between pressure and time (t) (P).

[0025] Figure 3 This is a schematic diagram showing the process of interlayers transitioning from intact to fatigue fracture under alternating stress. Detailed Implementation

[0026] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Example 1 This embodiment provides a method for inducing controlled collapse of interlayers during the construction of an ultra-deep salt cavern storage facility, including the following steps: This embodiment takes an ultra-deep salt cavern reservoir in the Ordovician salt field of northern Shaanxi as an example. The target interlayer is argillaceous dolomite, with a bottom burial depth of 2724.77 meters and a single layer thickness of 1.69 meters, beneath which lies a solution cavity of 87.04 meters. The interlayer below has collapsed. The salt cavern has been constructed using a water-soluble cavity-building process until the target interlayer is completely exposed to the top of the cavity. This embodiment provides a complete method for inducing the controlled collapse of this interlayer, with the specific steps as follows: S1. Cavity Construction and Exposure Using conventional water-soluble cavity construction techniques, a salt cavern was constructed until the target interlayer was completely exposed to the top plate of the chamber. The cavity is 87.04 meters high, with a radius of approximately 80 meters, and the exposed area of ​​the interlayer is approximately 20,000 square meters.

[0028] S2. Loop Parameter Design Based on geological data and well logging data, the mechanical parameters of the target interlayer were obtained: uniaxial compressive strength of 52 MPa, elastic modulus of 28 GPa, Poisson's ratio of 0.26, and tensile strength of 4.8 MPa. According to formation pressure data, the minimum principal stress at this depth is 41.5 MPa, the pore pressure is 28.2 MPa, and the formation fracturing pressure is 49.2 MPa.

[0029] The pressure cycle parameters were determined using numerical simulation software (such as FLAC3D) based on a fatigue life model of interbedded rock, and optimization design was performed: Peak pressure: 43MPa Valley pressure: 35MPa Pressurization rate: 0.5 MPa / h Pressure reduction rate: 2.0 MPa / h High pressure holding time: 2.5 hours Low-pressure holding time: 1.5 hours Number of cycles: 10 S3. Implement fatigue cycles Pressure circulation is performed by periodically injecting or draining fluid into the salt cavern through a wellhead pumping and flowback system. Each pressure circulation unit includes: Pressurization phase: The pressure is increased from the valley pressure of 35 MPa to the peak pressure of 43 MPa at a rate of 0.5 MPa / h, taking 16 hours.

[0030] High pressure holding stage: Hold pressure at 43MPa for 2.5 hours.

[0031] Pressure reduction phase: The pressure is reduced from the peak pressure of 43 MPa to the valley pressure of 35 MPa at a rate of 2.0 MPa / h, taking 4 hours.

[0032] Low-pressure holding stage: Hold pressure at 35MPa for 1.5 hours.

[0033] During the depressurization phase, by monitoring sudden changes in wellhead return flow or microseismic events captured by the downhole microseismic monitoring system, it is possible to determine in real time whether the interlayer has experienced local rupture or collapse.

[0034] S4. Process Monitoring and Dredging After 10 pressure cycles, sonar cavity sensing technology was used to monitor changes in cavity morphology and interlayer collapse. Sonar cavity sensing revealed cracks on the interlayer surface that gradually expanded, and the collapsed debris was cleared through a return drainage system.

[0035] S5. Judgment and Iteration According to the sonar cavity measurement results, after the 10th cycle, approximately 80% of the interlayer had collapsed. The circulation parameters were adjusted: the depressurization rate was increased to 2.5 MPa / h, and the number of cycles was increased to 15. After the 15th cycle, the sonar cavity measurement showed complete collapse of the interlayer, with all collapsed blocks less than 0.5 meters in size, indicating no risk of large-scale sudden collapse. The interlayer treatment was terminated, and subsequent cavity construction work continued.

[0036] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0037] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for inducing controlled collapse of interlayers during the construction of an ultra-deep salt cavern storage facility, characterized in that, Includes the following steps: S1. Cavity Construction and Exposure: Using conventional water-soluble cavity construction techniques, a salt cavern is constructed until the target interlayer is fully exposed to the top or sidewall of the cavity; S2. Circulation parameter design: Based on the mechanical properties, thickness and burial depth of the target interlayer, design the parameters of pressure circulation, including peak pressure, valley pressure, pressurization rate, depressurization rate, holding time and number of cycles; S3. Implement fatigue cycle: periodically inject or discharge fluid into the salt cavern to perform at least one pressure cycle unit, each of the pressure cycle units including: pressurization phase, high pressure holding phase, depressurization phase and low pressure holding phase; S4. Process monitoring and dredging: During step S3 or after each pressure cycle unit, sonar cavity measurement technology is used to monitor changes in cavity morphology and interlayer collapse. S5. Judgment and Iteration: Based on the sonar cavity measurement results, determine whether the target interlayer has completely collapsed as expected; if not, return to step S3, adjust the loop parameters and continue; if completed, end the interlayer processing and continue with subsequent cavity construction or sealing operations.

2. The method for inducing controlled collapse of interlayers during the construction of ultra-deep salt cavern storage facilities according to claim 1, characterized in that, In step S2, the valley pressure is lower than the minimum principal stress of the formation at that depth, and the peak pressure is higher than the pore pressure of the formation at that depth but lower than the formation fracturing pressure.

3. The method for inducing controlled collapse of interlayers during the construction of ultra-deep salt cavern storage facilities according to claim 1, characterized in that, In step S2, the parameters of the pressure cycle are optimized using the numerical simulation software FLAC3D, and the numerical simulation is based on the fatigue life model of interbedded rock.

4. The method for inducing controlled collapse of interlayers during the construction of ultra-deep salt cavern storage facilities according to claim 1 or 2, characterized in that, In step S3, the depressurization stage adopts a rapid depressurization method with a depressurization rate controlled at 0.5-3.0 MPa / h; the pressurization stage adopts a relatively slow pressurization method with a pressurization rate controlled at 0.1-1.0 MPa / h.

5. The method for inducing controlled collapse of interlayers during the construction of ultra-deep salt cavern storage facilities according to claim 1, characterized in that, In step S3, during the depressurization stage, the sudden changes in wellhead return flow or micro-fracture events captured by the downhole microseismic monitoring system are used to determine in real time whether the interlayer has experienced local fracture or collapse.

6. The method for inducing controlled collapse of interlayers during the construction of an ultra-deep salt cavern storage facility according to claim 1, characterized in that, The method is applicable to salt rock deposits with a burial depth of 2600 meters or more and containing interlayers with a single layer thickness of not less than 1 meter.

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