Method for preventing pressure channeling and casing deformation through cooperation of micro-nano bubbles and oxidation liquid in shale gas reservoir

Abstract

The invention discloses a method for preventing pressure channeling and casing deformation of a shale gas reservoir through cooperation of micro-nano bubbles and oxidation liquid, and the method comprises the following steps: injecting micro-nano bubble liquid into a main fracture, forming a plugging zone on the wall surface of the fracture and in matrix pores, and preventing lateral filtration of fluid; when the main crack reaches a certain distance, stopping injecting the micro-nano bubble liquid, injecting an oxidation liquid, inducing the periphery of the main crack to form a micro-crack network through an oxidation reaction, and realizing fluid diversion; and then well closing treatment is conducted, sand-carrying fluid is injected, and staged regulation and control of the crack expansion process are achieved through multiple times of circulation. Through the synergistic effect of micro-nano bubble plugging and oxidation liquid induced fracture, inter-well pressure channeling can be effectively inhibited, and stress disturbance of the stratum around the well in the fracturing construction process is reduced, so that the risk of deformation of the casing pipe is reduced, and adverse effects on sand-carrying conveying and later production capacity are avoided while the complexity of the fracture is guaranteed.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of unconventional oil and gas development and reservoir reconstruction engineering, in particular to a method for preventing channeling and casing deformation control applied in the process of staged hydraulic fracturing of shale gas reservoirs, and more particularly to a sequenced injection method based on the synergistic effect of micro-nano bubbles and oxidizing fluid. BACKGROUND

[0002] With the continuous expansion of deep shale gas development, horizontal well staged fracturing has become the main stimulation measure; however, during the fracturing process, the common interwell channeling and casing deformation (referred to as "casing deformation") phenomena seriously affect the single well productivity and the overall benefit of the platform; the channeling phenomenon mainly manifests as the undesired connection or fluid communication between adjacent wells, and the channeling mechanism can be summarized into three categories: (1) Artificial fracture-artificial fracture connection: the fracturing fractures extend and penetrate each other; (2) Artificial fracture-natural fracture connection: artificial fractures and natural fractures are connected, and natural fractures act as a bridge to cause communication; (3) Fracture and wellbore direct connection: the fracture or short channel directly connects with the wellbore or completion member of the adjacent well.

[0003] The uncontrolled extension of fracturing fractures and abnormal fluid channeling not only increase the risk of interwell communication, but also may induce local stress concentration or fault activity, thereby increasing the probability of casing deformation; the existing channeling prevention measures include: reducing the discharge, optimizing the cluster spacing, adding temporary plugging balls or fibers, etc.; however, these methods generally have the problems of uncontrollable plugging, affecting the sand carrying effect, or damaged productivity; therefore, in the process of fracturing construction, simultaneously inhibiting the excessive extension of fractures and reducing the stress disturbance of the wellbore has become a technical problem to be solved for safe and efficient development of shale gas reservoirs.

[0004] In recent years, micro-nano bubbles have been introduced into the plugging research of unconventional oil and gas development due to their surface charge stability and the characteristics of being able to stay in microfractures or pore throats; oxidizing fluid has potential in modifying shale pore and fracture structure due to its characteristics of inducing near-fracture microfracture networks, changing local stress field and seepage channel; however, how to combine the two to form a synergistic process that can not only control the excessive extension of main fractures, but also actively create a microfracture diversion channel for preventing channeling and casing deformation, has not been disclosed so far. SUMMARY

[0005] In view of the problem that, in the process of existing shale gas reservoir segmented hydraulic fracturing, uncontrolled fracture extension causes interwell channeling, and further increases the risk of casing deformation, and the problem that the existing anti-channeling measures cannot control the plugging position, and affect the sand carrying effect or productivity, the present application aims to provide a method for reducing the risk of interwell channeling and casing deformation by first forming a local plugging layer around the main fracture with micro-nano bubble liquid to limit lateral filtration, and then inducing micro-fracture expansion around the main fracture with oxidizing liquid to divert the fluid in the main fracture; the technical key points are: The present application provides a method for preventing channeling and casing deformation of shale gas reservoirs by micro-nano bubble and oxidizing liquid, characterized in that it comprises the following steps: (1) injecting fluid beyond the fracture pressure to form a main fracture; (2) injecting micro-nano bubble liquid into the main fracture to form a plugging zone in the fracture wall and matrix pore to prevent lateral filtration of fluid; (3) stopping the injection of micro-nano bubble liquid when the main fracture reaches a certain distance; (4) injecting oxidizing liquid, with a single injection duration T p ; (5) stopping the pump and allowing the well to soak for a certain period of time before injecting sand-carrying liquid; (6) repeating steps (4) and (5) until the main fracture reaches the designed main fracture length.

[0006] Further, the micro-nano bubbles meet any one of the following conditions: (1) the diameter of the micro-nano bubbles is greater than the average matrix pore diameter and between 0.7 and 0.9 times the target reservoir micro-fracture width; (2) the diameter of the micro-nano bubbles is between 0.8 and 1.3 times the average pore throat diameter of the reservoir.

[0007] Further, the timing of stopping the injection of micro-nano bubble liquid or starting the injection of oxidizing liquid includes but is not limited to any of the following: (1) microseismic monitoring shows that the fracture extends to 0.7-0.9 times the designed main fracture length; (2) the pressure-volume curve shows a platform or pressure increasing trend.

[0008] Further, the single injection duration T p of the oxidizing liquid is determined by the following formula: (1.1); wherein, V inj V is the single injection volume of the oxidizing liquid, m³; Q Q is the injection rate, unit m³ / s; R targetThe preset radius of action is in meters. D eff m is the effective diffusion / convective transport coefficient of the oxidant in the fracture-matrix system. 2 / s; k is the first-order consumption constant of the oxidant in the system (s -1 Estimated through experiments; C0 is the initial concentration, in mg / L; C e The effective concentration threshold is expressed in mg / L. γ is the safety factor, which is generally 0.8 to 1.

[0009] Furthermore, the well shut-in time is based on the wellhead pressure reduction rate not exceeding 5% within one hour or a certain period after pump shutdown.

[0010] Furthermore, this invention provides a method for preventing pressure channeling and casing deformation in shale gas reservoirs using micro-nano bubbles in conjunction with oxidation liquid, characterized in that the micro-nano bubbles are sealed at a distance of radius from the main fracture wall. δ(t) Estimated by the following formula: (1.2); in, δ(t) Distance, in meters; C 𝐿 Carter filtration coefficient, unit m / (s) 0.5 The value is determined by the rock's permeability, porosity, viscosity, and pressure differential. t The duration of filtration loss is expressed in seconds (s).

[0011] Beneficial effects: Compared with the prior art, the present invention has the following advantages: This invention effectively seals fractures by introducing micro-nano bubble liquid in conjunction with oxidizing liquid during fracturing. It forms a sealing band on the fracture wall and in the matrix pores, and releases or transforms this sealing effect in subsequent stages. This not only inhibits uncontrolled fracture propagation but also avoids adverse effects on subsequent sand transport and seepage capacity in the production stage. It overcomes the problem that traditional anti-fracture measures are uncontrollable and easily affect sand transport or production capacity.

[0012] Compared to conventional hydraulic fracturing methods that rely solely on mechanical fracturing to form fractures, this invention induces the development of near-fracture microfractures through the reaction of oxidizing fluid with reservoir minerals surrounding the main fracture, which helps reduce the amount of water used in the fracturing process.

[0013] This invention reduces stress concentration and abnormal fluid flow at the tip of the main fracture by controlling the fracture propagation process in stages, thereby reducing the stress disturbance amplitude of the formation around the well during fracturing operations. This helps to reduce the risk of casing deformation and improve the stability of the wellbore structure while suppressing inter-well hydraulic cross-flow. Attached Figure Description

[0014] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below; in all the drawings, similar elements or parts are generally identified by similar reference numerals; in the drawings, the elements or parts are not necessarily drawn to actual scale.

[0015] Figure 1 A schematic diagram illustrating the formation of the main fracture after exceeding the formation fracturing pressure according to an embodiment of the present invention; Figure 2 A schematic diagram illustrating the formation of a local sealing band from micro-nano bubbles according to an embodiment of the present invention; Figure 3 A schematic diagram of the oxidation liquid injection stage after the main crack extends to a certain length according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the well-sealing treatment and subsequent injection of sand-carrying fluid according to an embodiment of the present invention; Figure 5 A schematic diagram illustrating the re-injection of oxidizing fluid followed by well suffocation treatment and then re-injection of sand-carrying fluid according to an embodiment of the present invention; Figure 6 This is a schematic diagram illustrating the construction effect according to an embodiment of the present invention; In the figure, a-prepared liquid; b-micro-nano bubbles; c-oxidizing liquid; d-sand-carrying liquid. Detailed Implementation

[0016] Example 1: Application based on well L203H53-1 in southern Sichuan; (1) Well conditions and fracturing background; The horizontal well spacing between the parent well and the daughter well of the L203H53 platform in a certain block in southern Sichuan is about 300m. The single-stage fracturing length is about 78m, with a total of 8 clusters and 48 perforations. The pumping rate is generally 14m³ / min, the pumping pressure is 65~85MPa, the single-stage fluid volume is about 2930m³, and the total sand addition per stage is about 300 tons. Microseismic monitoring shows that the half-length of the fracture in the fracturing section of this well can reach 212~237m, which exceeds the half-distance (150m) between the parent well and the daughter well. There is a risk of uncontrolled extension of the fracturing fracture and connection with adjacent wells. At the same time, it may cause stress concentration in the formation around the well, increasing the probability of casing deformation.

[0017] (2) The formation of the main crack and the injection of micro-nano bubble liquid; During the fracturing operation of this well, pre-fracturing fluid was first injected according to conventional fracturing techniques. Once the bottom hole pressure exceeded the formation fracturing pressure, the main fracture was formed. Figure 1 Subsequently, according to the method of the present invention, micro-nano bubbles are injected into the fracture after the main fracture is formed; in this embodiment, the diameter of the selected micro-nano bubbles is controlled within the range of 10~30μm, and meets one of the following conditions: the diameter of the micro-nano bubbles is greater than the average matrix pore size of the reservoir, and is between 0.7 and 0.9 times the width of the micro-fractures in the target reservoir, or the diameter of the micro-nano bubbles is between 0.8 and 1.3 times the average pore throat diameter of the reservoir.

[0018] After the micro-nano bubble liquid enters the main fracture, it is retained and accumulates on the fracture wall and in the matrix pores around the fracture, forming a local sealing zone around the main fracture. Figure 2 This mode aims to reduce the amount of fracturing fluid lost laterally to the reservoir.

[0019] (3) Estimation of the effective radius of micro / nano bubble plugging; First, the radius of the micro / nano bubble plug from the main seam wall. δ(t) Estimated by the following formula: (1.1); In deep shale, φ=0.06; C 𝐿 =10 −6 ~3×10 −5 m / (s 0.5 ); Using the effective duration of the preceding segment t=5 / 10 / 20min, interval estimation is performed to obtain the values ​​under different conditions. δ(t) As shown in Table 1: Table 1. Estimation of radius from the main seam wall for micro / nano bubble plugging under different conditions. ; Calculations show that the radius φ from the main slit wall can be achieved using micro / nano bubbles. max ≈0.5~35mm; therefore, micro- and nano-bubbles mainly seal near-seam micro-cracks and pore zones, but are not expected to seal over long distances.

[0020] (4) The timing of injecting micro / nano bubble liquid or starting to inject oxidation liquid; During the fracturing operation of this well, real-time microseismic monitoring and construction pressure curve analysis were used to determine when the main fracture extension reached approximately 70%–90% of the designed main fracture length, and the pump pressure-volume curve showed a plateau or increasing pressure trend. At this point, the injection of micro / nano bubble fluid was stopped, and the operation transitioned to the oxidation fluid injection stage, forming… Figure 3 The pattern.

[0021] (5) Prepare the oxidizing solution and calculate the duration of oxidizing solution injection; Prepare a persulfate (Na2S2O8) oxidation solution with a mass fraction of 1.0–2.0%. If necessary, add corrosion inhibitors and slow-release agents to adapt to the high-temperature shale environment. Use an intermittent mode, with each slug having a volume of 15–30 m³. The duration is determined according to the following formula: The oxidizing solution is injected in a pulsed or intermittent manner, with a single injection duration of [duration missing]. T p Determine by the following formula: (1.2); in, V inj The volume of the oxidizing solution injected in a single batch is in m³. Q Injection displacement, in m³ / s; R target The preset radius of action is in meters. D eff m is the effective diffusion / convective transport coefficient of the oxidant in the fracture-matrix system. 2 / s; k is the first-order consumption constant of the oxidant in the system (s -1 Estimated through experiments; C0 is the initial concentration, in mg / L; C e The effective concentration threshold is expressed in mg / L. γ is the safety factor, which is generally 0.8 to 1.

[0022] Based on the on-site construction conditions, the single injection volume of oxidizing solution... V inj The injection volume is 40~80m³. Q The flow rate is 14 m³ / min; considering the near-fracture stimulation characteristics of shale reservoirs, the preset radius of action of the oxidation fluid is... R target The thickness is 10~50mm; the effective diffusion / convective transport coefficient of the oxidant in the crack-matrix system is taken. D eff 1.0×10 -9 m 2 / s; the first-order loss constant k is 5.0 × 10⁻⁶. -5 s⁻¹, initial concentration C0 is 3000 mg / L, effective concentration threshold C e The concentration is 300 mg / L, and the safety factor γ is 0.9; the corresponding single injection duration T p It takes about 0.5 to 3 minutes.

[0023] (6) The process of well blockage and circulating injection; After the oxidizing fluid injection is completed, pumping is stopped and the well is shut off. In this embodiment, the shut-off time is determined based on the principle that the wellhead pressure drop rate should not exceed 5% within 1 hour after pumping is stopped. After the shut-off is completed, the sand-carrying fluid is injected again to form... Figure 4 The pattern; By repeatedly performing the cycle of "oxidizing fluid injection - well shut-in - sand-carrying fluid injection" ( Figure 5 ), until the main crack extends to the designed main crack length ( Figure 6 ).

[0024] (7) Explanation of implementation results; Without this method, the main fracture half-length can reach 225m, posing a communication risk. With this method, the main fracture half-length is expected to be controlled at 100-130m, below the safety threshold. The pressure rise in adjacent wells is reduced from 10MPa to 5-6MPa. The distribution of microseismic event points is more dispersed, indicating increased fracture complexity and significant diversion effect. It also reduces stress disturbance in the formation around the well, thereby reducing the possibility of casing deformation.

Claims

1. A method for preventing pressure channeling and casing deformation in shale gas reservoirs using micro / nano bubbles in conjunction with oxidation liquid, characterized in that... Includes the following steps: (1) Fluid is injected beyond the rupture pressure to form the main fracture; (2) Inject micro-nano bubble liquid into the main fracture to form a sealing band on the fracture wall and matrix pores to prevent lateral fluid loss; (3) Stop injecting micro-nano bubble liquid when the main seam reaches a certain distance; (4) Inject the oxidizing solution for a duration T. p ; (5) Stop the pump and shut down the well. After shutting down the well for a certain period of time, inject sand-carrying fluid. (6) Repeat steps (4) and (5) until the main seam reaches the designed main seam length.

2. The method according to claim 1, characterized in that, The micro-nano bubbles described satisfy any one of the following conditions: (1) The diameter of the micro-nano bubble is greater than the average matrix pore size and is between 0.7 and 0.9 times the width of the target reservoir microfracture; (2) The diameter of the micro-nano bubble is between 0.8 and 1.3 times the average pore throat diameter of the reservoir.

3. A method for preventing pressure channeling and casing deformation in shale gas reservoirs using micro-nano bubbles in conjunction with oxidation liquid, characterized in that... Radius of micro / nano bubble plugging from the main seam wall δ(t) Estimated by the following formula: in, δ(t) The distance from the main seam wall to the micro / nano bubble sealing is expressed in meters (m). C 𝐿 Carter filtration coefficient, unit m / (s) 0.5 The value is determined by the rock's permeability, porosity, viscosity, and pressure differential. 𝑡 represents the filtration duration, in seconds.

4. The method according to claim 1, characterized in that, The timing for stopping the injection of micro / nano bubble liquid or starting the injection of oxidation liquid includes, but is not limited to, any of the following: (1) Microseismic monitoring showed that the crack extended to 0.7 to 0.9 times the designed main joint length; (2) The pressure-volume curve shows a plateau or a pressure-increasing trend.

5. The method according to claim 1, characterized in that, The duration of a single injection of the oxidizing liquid T p Determine by the following formula: in, V inj The volume of the oxidizing solution injected in a single batch is in m³. Q Injection displacement, in m³ / s; R target The preset radius of action is in meters. D eff m is the effective diffusion / convective transport coefficient of the oxidant in the fracture-matrix system. 2 / s; k is the first-order consumption constant of the oxidant in the system (s -1 Estimated through experiments; C0 is the initial concentration, in mg / L; C e The effective concentration threshold is expressed in mg / L. γ is the safety factor, which is generally 0.8 to 1.

6. The method according to claim 1, characterized in that, The well shut-in time is based on the wellhead pressure reduction rate not exceeding 5% within one hour or a certain period after pump shutdown.

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