A gas reservoir water lock solution method based on adsorption-desorption dynamic balance regulation

Abstract

The application is suitable for the technical field of oil and gas field stimulation and reconstruction, and provides a gas reservoir water lock releasing method based on adsorption-desorption dynamic balance regulation and control. The method first injects a low-concentration water lock releasing agent solution into a reservoir to form a non-saturated adsorption layer; then, a high-concentration water lock releasing agent is injected in a slug mode, and the surfactant component is redistributed and rearranged on the interface driven by the concentration gradient; by controlling the residence time, the interface molecules are partially desorbed and re-adsorbed to establish adsorption-desorption dynamic balance; combined with injection parameter window regulation and control, the periodic reconstruction of the interface structure and the release of water lock are realized. Through the synergistic mechanism of "staged injection-concentration gradient-residence regulation", the surfactant component presents a dynamic conversion behavior, effectively weakens the stability of the water film and promotes the release of bound water. The application does not depend on the structure of a specific chemical agent, has wide application range and strong interface regulation and control capability, and is suitable for the release of water lock in low-porosity and low-permeability and tight gas reservoirs.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas field production enhancement and transformation technology, and in particular relates to a method for water lock removal in gas reservoirs based on dynamic balance regulation of adsorption-desorption. Background Technology

[0002] During drilling, completion, fracturing, and workover operations in low-porosity, low-permeability gas reservoirs, a large amount of external working fluid and formation water inevitably intrudes into the reservoir's pore structure, forming continuous or semi-continuous water films on the rock surface and in the micropore throats. When the gas-phase driving force is insufficient to overcome the capillary pressure generated by this water film, the gas flow channels are significantly impeded or even completely blocked, resulting in a water-locking effect. This leads to increased well start-up pressure, reduced effective flow channels, and a significant decrease in production capacity.

[0003] From a microscopic perspective, the water-locking effect is controlled by the coupling of rock wettability, pore-throat-scale structure, and gas-water interface behavior. In hydrophilic reservoirs, the aqueous phase preferentially occupies the rock surface and forms a stable adsorbed water film in the micro- and nano-scale pore throats. This water film exhibits strong stability under capillary forces. Especially in low-porosity, low-permeability, and tight gas reservoirs, the water-locking effect is more severe and more difficult to resolve due to the small pore-throat radius, large specific surface area, and significantly enhanced capillary pressure.

[0004] Existing technologies generally take "chemical agent system optimization" as the core approach. Their mechanism of action mainly relies on the adsorption behavior of surfactants at the solid-liquid interface. By increasing the interface coverage, wettability is changed or the interface tension is reduced. Essentially, it belongs to a static injection-static adsorption control mode.

[0005] Existing technologies generally lack a systematic control design for the coupling relationship between the injection process and the interface response, and still belong to a static control mode. It is difficult to achieve dynamic adjustment of the interface behavior in the reservoir, resulting in limited depth of water-locking action, low reagent utilization efficiency, incomplete water film removal, and easy decay of water-locking effect, which makes it difficult to meet the needs of efficient development of low-porosity, low-permeability and tight gas reservoirs. Summary of the Invention

[0006] The purpose of this invention is to provide a method for water lock release in gas reservoirs based on dynamic equilibrium regulation of adsorption-desorption, aiming to solve the problems existing in the background art.

[0007] This invention is implemented as follows: a gas reservoir water-locking method based on adsorption-desorption dynamic equilibrium regulation. By constructing a synergistic mechanism of "staged injection - concentration gradient regulation - residence time control - parameter window constraint", it induces the surface active components to generate controllable adsorption-desorption dynamic transformation behavior at the gas-liquid-solid interface, causing the interface structure to undergo periodic reconstruction in time and space, and driving the reservoir wetting state to be controllably regulated along the path of "strong hydrophilicity - transitional wetting state - weak hydrophobicity or neutral wetting state".

[0008] Meanwhile, by introducing the coupling relationship between the injection parameter window (pressure, injection rate, and slug volume) and the interface response criteria (interfacial tension change ΔIFT and contact angle change), quantitative control of interface behavior can be achieved. This allows for effective disruption of pore throat water film stability, reduction of capillary resistance, and restoration of gas phase permeation channels without relying on a specific chemical structure system. It also significantly reduces irreversible adsorption loss of reagents and increases the depth of action, making the method highly feasible in engineering and adaptable to the field.

[0009] To achieve the above objectives, this invention provides a method for water unlocking in gas reservoirs based on dynamic equilibrium regulation of adsorption-desorption, comprising the following steps: S1. Inject a low-concentration water-locking agent solution into the gas reservoir. The water-locking agent has a mass concentration of 0.01%–0.1wt%, an injection rate of 0.1–0.5m³ / h, an injection pressure lower than 60%–80% of the formation fracture pressure, and an injection volume of 0.05–0.2PV. This allows the surface-active components to form an unsaturated adsorption layer on the pore surface, establishing an initial interfacial activity distribution state and avoiding excessive adsorption in the near-wellbore area. S2. Subsequently, a high-concentration water-locking agent solution is injected into the reservoir using a slug injection method. The water-locking agent has a mass concentration of 0.1%–1.0wt%, a single slug volume of 0.1–0.5PV, an injection rate of 0.3–1.5m³ / h, and an injection pressure of 70%–95% of the formation pressure. An interval of 0.5–6 hours is set between adjacent slugs. Through concentration transition and slug advancement, the interfacial active molecules are induced to redistribute and rearrange, forming an interfacial tension gradient and triggering dynamic reconstruction of the interfacial structure. S3. After the slug injection is completed, the residence time is controlled to be 2–24 hours, so that the adsorbed surface active molecules will undergo partial desorption under the action of diffusion and concentration gradient, and redistribute within the pores to form an adsorption-desorption dynamic equilibrium state, thereby achieving continuous renewal of interfacial active components. S4. By controlling the injection parameter window, including injection pressure, injection rate, and slug volume, the interfacial response intensity is adjusted to induce periodic disturbances at the gas-liquid-solid interface on the pore scale. The interfacial response parameters are then monitored or experimentally calibrated to ensure that the system meets the requirements of an interfacial tension reduction ΔIFT ≥ 30% (relative to IFT0) and a contact angle change Δθ ≥ 20°. If the above conditions are not met, optimization can be achieved by increasing the slug concentration or volume, adjusting the injection rate (within the range of 0.1–2 m³ / h), and increasing the number of slug cycles (2–5 cycles). S5. Through the adsorption-desorption dynamic equilibrium and periodic interface reconstruction, the stability of the water film is weakened, the bound water is gradually released, and the gas phase permeation channel is restored, ultimately achieving water lock release and production capacity restoration.

[0010] In the method described in this invention, the key control parameters satisfy the following ranges: concentration gradient of 0.01% to 1.0%, injection rate of 0.1–2 m³ / h, injection pressure of 60%–95% of formation pressure, slug volume of 0.1–1.0 PV, and residence time of 2–24 h. The above parameter windows together constitute the "controllable operating range" of the interface dynamic response.

[0011] In the method described in this invention, the water-locking agent is a nonionic surfactant, an amphoteric surfactant, or a compound system thereof, and the specific molecular structure is not limited; the method is applicable to low-porosity, low-permeability or tight gas reservoirs with permeability less than 10 mD, and is applicable to reservoirs with temperatures of 80–150℃ and high salinity conditions.

[0012] The present invention provides a method for water-locking gas reservoirs based on dynamic equilibrium regulation of adsorption-desorption, which has the following beneficial effects: 1. A method for staged injection and synergistic regulation of concentration gradients was constructed. This invention combines low-concentration pre-adsorption, high-concentration slug injection, and residence time control to form a synergistic system of "staged injection – concentration gradient regulation – residence regulation," which transforms the distribution of the water-locking agent in the reservoir from traditional continuous and uniform injection to a non-steady-state dynamic distribution, thus differing from the traditional single injection method in its methodological approach.

[0013] 2. A novel mechanism for dynamic equilibrium regulation of interfacial adsorption-desorption has been achieved. This invention, through concentration gradient and time control, enables surface-active components to no longer exhibit monotonous adsorption behavior at the solid-liquid interface, but rather a dynamic transformation between adsorption and desorption. Through continuous desorption-readsorption and orientation rearrangement of molecules, the periodic reconstruction of the interfacial structure and the dynamic adjustment of interfacial free energy are achieved, thereby driving a controllable change in the wetting state and effectively disrupting the stable water film structure in the pore throat.

[0014] 3. A quantitative coupling relationship between the injection parameter window and the interface response criterion was established. This invention introduces parameter windows such as injection pressure, injection rate, and slug volume, and combines them with the interface tension change ΔIFT and contact angle change Δθ as interface response criteria to achieve quantitative control of the water-locking process, transforming interface behavior control from an experience-based approach to a controllable engineering process.

[0015] 4. Significantly improves water-locking efficiency and reduces reagent adsorption loss. Due to the establishment of the adsorption-desorption dynamic equilibrium, surface-active components continuously migrate and renew in the reservoir, avoiding the problem of irreversible high adsorption zones forming near-wellbore in traditional systems. This improves reagent utilization efficiency and expands the depth of action. At the same time, it significantly reduces capillary pressure and restores gas phase permeability through interfacial structure reconstruction.

[0016] 5. It has good reservoir adaptability and engineering feasibility. The method of this invention is applicable to low-porosity, low-permeability and tight gas reservoirs, and can maintain the dynamic response capability of the interface even under high temperature and high salinity conditions; at the same time, the injection steps and parameter control involved in this method can be achieved by conventional oilfield construction equipment, without the need for additional complex equipment, and has good field operability.

[0017] 6. Achieving designability of wetting control paths. Unlike existing technologies that change wetting properties in a single direction, this invention achieves path-based transformation of the wetting state through dynamic interface reconstruction, making the wetting control process more controllable and adaptable to multi-scale interface behavior in complex pore-throat structures.

[0018] 7. The method is highly versatile and does not depend on a specific chemical agent system. The method of this invention does not strictly limit the specific chemical structure of the water-locking agent, and can be applied to nonionic, amphoteric, or their compound systems, thus having good versatility and promotional value. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0020] When implementing the gas reservoir water-locking method based on adsorption-desorption dynamic equilibrium control as described in this invention, the basic parameters of the target gas reservoir are first tested, including the original interfacial tension IFT0 (mN / m), the original contact angle θ0 (°), formation pressure, and permeability, which serve as the benchmark parameters for subsequent control.

[0021] Then, proceed with the following steps: (1) Initial Adsorption Construction Stage: A low-concentration water-locking agent solution is injected into the reservoir. The water-locking agent has a mass concentration of 0.01%–0.1wt%, an injection rate of 0.1–0.5 m³ / h, an injection pressure lower than 60%–80% of the formation fracturing pressure, and an injection volume of 0.05–0.2 PV. In this stage, the surface-active components form an unsaturated adsorption layer on the pore surface, establishing the initial interfacial activity distribution state and avoiding excessive adsorption in the near-wellbore area.

[0022] (2) Interface Strengthening and Reconstruction Stage: A high-concentration water-locking agent solution is injected into the reservoir using a slug injection method. The water-locking agent has a mass concentration of 0.1%–1.0 wt%, a single slug volume of 0.1–0.5 PV, an injection rate of 0.3–1.5 m³ / h, and an injection pressure of 70%–95% of the formation pressure. An interval of 0.5–6 hours is set between adjacent slugs. Through concentration transitions and slug advancement, the active molecules at the interface are induced to redistribute and rearrange, forming an interfacial tension gradient, thereby triggering dynamic reconstruction of the interface structure. The slug injection can be performed using a multi-slug cyclic injection method, with 2–5 slug injections.

[0023] (3) Residence-Desorption Regulation Stage: After slug injection is completed, the residence time is controlled to be 2–24 hours. During this process, the adsorbed molecules undergo partial desorption under the influence of concentration gradient and diffusion, and are redistributed inside the pores, forming an adsorption-desorption dynamic equilibrium state, thereby achieving continuous renewal of interfacial active components.

[0024] (4) Interface response criterion control stage: By monitoring or experimentally calibrating the interface response parameters, the injection parameter window is adjusted to ensure that the system meets the requirements of a reduction in interface tension ΔIFT ≥ 30% (relative to IFT0) and a change in contact angle Δθ ≥ 20°. When the above conditions are not met, optimization is achieved by increasing the slug concentration or volume, adjusting the injection rate (within the range of 0.1–2 m³ / h), and increasing the number of slug cycles (2–5 cycles), thereby achieving a controllable increase in the intensity of interface disturbance.

[0025] (5) Water lock release stage: Under the dynamic equilibrium of adsorption-desorption and the periodic reconstruction of the interface, the stability of the water film is weakened, the bound water is gradually released, the gas phase permeation channel is restored, and finally the water lock is released and the production capacity is restored.

[0026] During the above implementation process, the key control parameters meet the following ranges: concentration gradient of 0.01% to 1.0%, injection rate of 0.1–2 m³ / h, injection pressure of 60%–95% of formation pressure, slug volume of 0.1–1.0 PV, and residence time of 2–24 h. These parameter windows together constitute the "controllable operating range" of the interface's dynamic response.

[0027] The water-locking agent is a nonionic surfactant, an amphoteric surfactant, or a compound system thereof, and its specific molecular structure is not limited. This method is applicable to low-porosity, low-permeability or tight gas reservoirs with permeability less than 10 mD, and is suitable for reservoirs with temperatures of 80–150℃ and high salinity conditions.

[0028] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0029] Example 1: Comparative Experiment on the Water Lock Dissolution Effect of Continuous Injection and Segmented Injection (1) Experimental materials and conditions A core sample from a low-permeability tight gas reservoir was selected: permeability 0.85 mD, porosity 8.2%, formation temperature 100℃, and formation water salinity 80,000 mg / L. The water-locking agent used in the experiment was a non-ionic amphoteric compound system, with a concentration range of 0.05%–0.5%. Test parameters included interfacial tension (IFT), contact angle (θ), and permeability recovery rate (R0). k ).

[0030] (2) Experimental Design Control group A (conventional continuous injection): injection concentration 0.2wt% (constant), injection method is continuous injection, injection rate 0.5mL / min, injection volume 0.5PV, no residence time control.

[0031] Experimental Group B (segmented injection of this invention): employing "low-concentration pretreatment + high-concentration slug injection + residence time control". Stage 1: low-concentration pre-adsorption, concentration 0.05wt%, injection volume 0.1PV; Stage 2: high-concentration slug injection, concentration 0.5wt%, single slug volume 0.2PV, slug injection twice; Stage 3: residence time, residence time 8 hours; Stage 4: second slug displacement, concentration 0.3wt%, injection volume 0.2PV.

[0032] (3) ΔIFT change test results

[0033] Segmented injection significantly enhanced interfacial activity, increasing ΔIFT by approximately 1.5 times. Segmented injection induced interfacial molecular rearrangement through concentration transitions, resulting in a more significant reduction in interfacial tension, indicating dynamic reconstruction of the interfacial structure.

[0034] (4) Results of contact angle change

[0035] Segmented injection achieves more significant wettability control, meeting the patent criterion: Δθ≥20°.

[0036] (5) Comparison of penetration rate recovery rate Permeability recovery rate Rk =(treated permeability / original permeability) × 100%.

[0037]

[0038] Improvement: Recovery rate increased by approximately 48%.

[0039] (6) Experimental mechanism analysis Experimental results show that under continuous injection conditions, surfactants form a stable adsorption layer in the near-well region, and the interface regulation process tends to be static, making it difficult to achieve deep-seated effects. Under segmented injection conditions, due to the synergistic effect of concentration gradient and residence time, interfacial active molecules undergo dynamic transformation between adsorption and desorption, resulting in continuous renewal of the interfacial structure. This dynamic process generates periodic disturbances in the microscale pore throats, effectively weakening the stability of the water film and promoting the release of bound water, thereby significantly improving the permeability recovery effect.

[0040] Compared with the traditional continuous injection method, the segmented injection method of the present invention shows significant improvements in the reduction of interfacial tension, wettability control capability and permeability recovery effect, proving that the injection strategy has obvious technical effects in regulating the dynamic balance of adsorption-desorption.

[0041] Example 2: The effect of slug size on water-lock breaking effect The experimental conditions were the same as in Example 1, but the volume of the single-segment plug was changed. The results are as follows:

[0042] When the slug volume is 0.2–0.4 PV, the interface disturbance and transmission efficiency reach the optimal balance; excessively large slugs do not significantly improve the effect.

[0043] Example 3: The effect of residence time on the adsorption-desorption dynamic equilibrium

[0044] The results of controlling the dwell time are as follows:

[0045] After a residence time of ≥6 hours, the adsorption-desorption dynamic equilibrium is fully established, and the interface reconstruction effect tends to stabilize.

[0046] Example 4: The effect of concentration gradient path on interface regulation effect Comparison of three injection methods:

[0047] Increasing concentration pathways are more conducive to the gradual rearrangement and deep migration of interfacial active molecules.

[0048] Example 5: The Influence of Injection Rate on Interface Dynamic Behavior

[0049] A moderate injection rate is beneficial for interfacial molecule migration and rearrangement, while an excessively rapid rate will reduce the efficiency of adsorption-desorption regulation.

[0050] Example 6: The effect of slug cycle number on water-lock breaking effect

[0051] Multi-stage plug cycles can enhance interface disturbances, but the improvement is limited after more than 3 cycles.

[0052] Example 7: Adaptability Verification of Reservoirs with Different Permeability

[0053] This method is more effective in low-permeability reservoirs, and is especially suitable for tight gas reservoirs.

[0054] The system experiments in Examples 1–7 demonstrate that the segmented injection method based on adsorption-desorption dynamic equilibrium control described in this invention exhibits superior interface control and permeability recovery compared to traditional continuous injection methods under different parameter conditions. In particular, when the slug volume, residence time, and concentration gradient are within a specific parameter window, the reduction in interfacial tension and the effect on wettability control are significantly enhanced. This proves that the method, through injection strategy, has a stable and repeatable technical effect in controlling the dynamic behavior of the interface, and possesses good engineering applicability.

[0055] 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, and improvements 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 water-locking gas reservoirs based on dynamic equilibrium regulation of adsorption-desorption, characterized in that, The gas reservoir water-locking method based on adsorption-desorption dynamic equilibrium regulation includes: S1. Inject a low-concentration water-locking agent solution into the gas reservoir. The water-locking agent has a mass concentration of 0.01%–0.1% to form an unsaturated adsorption layer on the surface of the reservoir pores, thereby establishing an initial interfacial activity distribution state. S2. Subsequently, a high-concentration water-locking agent solution is injected into the reservoir using a slug injection method. The water-locking agent has a mass concentration of 0.1%–1.0%. The concentration gradient drives the redistribution and rearrangement of surface-active components at the gas-liquid-solid interface, inducing dynamic reconstruction of the interface structure. S3. After the slug injection is completed, the residence time is controlled to be 2–24 hours, so that the adsorbed surface active molecules undergo partial desorption and re-adsorption under the action of diffusion and concentration gradient, and establish an adsorption-desorption dynamic equilibrium state. S4. By controlling the injection parameter window, including injection pressure, injection rate and slug volume, the interface response intensity is adjusted to generate periodic disturbances at the gas-liquid-solid interface on the pore scale. S5. Through the adsorption-desorption dynamic balance and periodic interface reconstruction, the reservoir wettability can be controlled and the resistance to water flow can be reduced, thereby releasing water lock and restoring gas phase permeability.

2. The gas reservoir water-locking method based on adsorption-desorption dynamic equilibrium control according to claim 1, characterized in that, In S1, the injection volume is 0.05–0.2 PV and the injection rate is 0.1–0.5 m³ / h; in S2, the single-segment plug volume is 0.1–0.5 PV and the total injection volume is 0.2–1.0 PV; in S3, the injection rate is 0.1–2 m³ / h and the injection pressure is 60%–95% of the formation pressure.

3. The gas reservoir water-locking method based on adsorption-desorption dynamic equilibrium control according to claim 2, characterized in that, The slug injection described in S2 is a multi-slug cyclic injection method, with 2–5 slug injections and an interval of 0.5–6 hours between adjacent slug injections.

4. The gas reservoir water-locking method based on adsorption-desorption dynamic equilibrium control according to claim 1, characterized in that, The concentration of the water-locking agent varies in a gradient at different injection stages. The concentration gradient is one of the following: increasing, decreasing, or alternating. The increasing concentration path is from 0.01%–0.1% to 0.1%–1.0%.

5. The gas reservoir water-locking method based on adsorption-desorption dynamic equilibrium control according to claim 4, characterized in that, The adsorption-desorption dynamic equilibrium is characterized by interface response parameters, which include: The reduction in interfacial tension ΔIFT is ≥30%; The contact angle change Δθ ≥ 20°.

6. The gas reservoir water-locking method based on adsorption-desorption dynamic equilibrium control according to claim 5, characterized in that, When the interface response parameters do not reach the preset range, optimize by adjusting the following parameters: Increase slug concentration and slug volume; Adjust the injection rate and injection pressure; Increase the number of slug cycles and extend the dwell time.

7. The gas reservoir water-locking method based on adsorption-desorption dynamic equilibrium control according to claim 1, characterized in that, The method is applicable to low-porosity, low-permeability, and tight gas reservoirs with permeability less than 10 mD, and is suitable for reservoirs with temperatures of 80–150 °C and high salinity.

8. The application of the gas reservoir water-locking method based on adsorption-desorption dynamic equilibrium control as described in any one of claims 1-7 in improving reservoir permeability and restoring gas well productivity.

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