An offshore oilfield environmental protection water injection and formation damage control regulation method

Abstract

This invention discloses a method for environmentally friendly water injection and formation damage control in offshore oilfields, relating to the field of oilfield production water reinjection technology. The method includes: collecting geological condition data and basic state data of the injection medium for the target offshore oilfield water injection layer, and making unified judgments to obtain a set of basic formation state information; adjusting the water injection operation process based on the initial water injection state information to coordinate changes in injection pressure and volume, forming a stable water injection state; implementing water injection operations under the stable water injection state, controlling the formation damage state generated during the water injection operation to form a formation damage control operation state, and implementing water injection capacity release control under the stable water injection state to form an environmentally friendly water injection operation state. This invention continuously improves the effectiveness of the water injection channel under non-backflow conditions while ensuring the safe operation of the entire injection wellhead equipment and completion string, reducing the risk of formation damage.

Description

Technical Field

[0001] This invention relates to the field of oilfield production water reinjection technology, and in particular to a method for environmentally friendly water injection and formation damage control in offshore oilfields. Background Technology

[0002] With the continuous expansion of offshore production water reinjection, the injection volume per well has increased from several thousand cubic meters to tens of thousands of cubic meters per day. Water injection technology is also gradually evolving from traditional single-method injection to multi-condition coordinated water injection. Related technologies are continuously evolving around water injection medium adaptation, formation chemical modification, and fine-tuning of water injection parameters, and are being integrated with wellhead devices and completion tubing such as wellheads, water injection strings, and sand control strings. In long-term water injection operations, the injection process needs to adapt to water media with high salinity and high solids content, as well as complex pore structures, prompting water injection technology to continuously advance towards continuous, refined, and large-scale completion devices.

[0003] Existing offshore oilfield water injection technologies generally involve combined acidizing and de-plugging operations with water injection during engineering implementation. However, with the increasing size of completion equipment, the coordinated control between water injection operations and formation reaction processes remains challenging. This is especially true under conditions where large-diameter water injection tubing is used without backflow, making it difficult to precisely constrain the final state of the acidizing reaction, which can easily lead to formation disturbances and affect water injection stability. Existing methods often focus on single-stage water injection regulation, lacking continuous correlation control between the completion state of the acidizing reaction, the initial water injection conditions, the completion equipment and tubing, the stable water injection state, and capacity release. Consequently, it is difficult to achieve a balance between enhanced water injection capacity and controlled formation damage under long-term sealed operation of the wellhead and water injection tubing. Summary of the Invention

[0004] In view of the aforementioned existing problems, the present invention is proposed.

[0005] Therefore, this invention provides a method for environmentally friendly water injection and formation damage control in offshore oilfields to solve the problem of difficulty in synergistically achieving improved water injection capacity and controllable formation damage during water injection in offshore oilfields under non-reflow conditions.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] This invention provides a method for environmentally friendly water injection and formation damage control in offshore oilfields, comprising:

[0008] Geological condition data and basic state data of the injection medium of the target offshore oilfield's water injection layer are collected and uniformly assessed to obtain a set of basic formation state information. Based on this set, a non-flowback acidizing and unblocking fluid system is constructed, and its function in the formation is controlled to form final state control parameters for the non-flowback acidizing reaction. Initial water injection conditions are set according to these parameters, and water injection operations are performed under these conditions to generate initial water injection state information. Based on this information, the water injection process is adjusted to ensure coordinated changes in injection pressure and volume, resulting in a stable water injection state. Water injection is then performed under this stable state, and the formation damage generated during the process is regulated to form a formation damage control operation state. Finally, water injection capacity release control is implemented under the stable water injection state to achieve an environmentally friendly water injection operation state.

[0009] As a preferred embodiment of the offshore oilfield environmental water injection and formation damage control method of the present invention, the geological condition data includes formation lithology type, formation pore structure characteristics, formation original permeability and formation mineral composition characteristics.

[0010] The basic state data of the water injection medium includes the salinity composition of the water injection medium, the content of reactive ions in the water injection medium, and the content of suspended solids in the water injection medium.

[0011] As a preferred embodiment of the offshore oilfield environmental protection water injection and formation damage control method of the present invention, the steps for obtaining the formation basic state information set are as follows:

[0012] The geological condition data and basic state data of the injection medium of the target offshore oilfield water injection layer are uniformly quantified to form a formation structure state vector and a water injection medium reaction potential vector.

[0013] A unified scale mapping and coupling determination are performed on the formation structure state vector and the water injection medium response potential vector to generate a formation-medium coupling state index.

[0014] The formation structure state vector, the water injection medium reaction potential vector, and the formation-medium coupling state index are integrated into a set of basic formation state information.

[0015] As a preferred embodiment of the offshore oilfield environmentally friendly water injection and formation damage control method of the present invention, the steps for constructing the acidizing and unblocking fluid system under non-backflow conditions are as follows:

[0016] Coupled analysis was performed on the set of basic formation state information to determine the synergistic relationship between the formation structure state and the reaction potential of the water injection medium, and the coupled analysis results were obtained.

[0017] Based on the results of the coupling analysis, the composition and synergistic relationship of each functional component in the unblocking fluid are determined, and a construction scheme for the unblocking fluid is formed.

[0018] By combining the corresponding functional components according to the unblocking fluid construction scheme and completing the configuration, an acid unblocking fluid system suitable for non-backflow conditions is obtained.

[0019] As a preferred embodiment of the offshore oilfield environmentally friendly water injection and formation damage control method of the present invention, the steps for forming the final state control parameters of the non-backflow acidizing reaction are as follows:

[0020] The acidizing unblocking fluid system is introduced into the formation and an unblocking reaction occurs within the formation. The reaction state information of the acidizing unblocking fluid system in the formation changes with the action time is obtained to form a reaction state sequence.

[0021] The reaction state sequence is continuously determined to identify the critical state in which the acid unblocking reaction transitions from the enhanced stage to the stable stage, thus forming the final state determination result of the reaction.

[0022] Based on the final state determination results, the termination timing and intensity boundary of the acid unblocking reaction are determined, forming the final state control parameters for the non-backflow acid unblocking reaction.

[0023] As a preferred embodiment of the offshore oilfield environmental protection water injection and formation damage control method of the present invention, the steps for setting the initial water injection conditions are as follows:

[0024] The reaction termination timing and action intensity boundary in the final state control parameters of the non-backflow acidification reaction are transformed into constraints for the water injection start-up stage, forming water injection start-up constraint information.

[0025] Based on the water injection start-up constraint information, the initial value of water injection pressure and the rate of change of water injection volume during the water injection start-up phase are calculated to form candidate initial water injection conditions.

[0026] The candidate initial water injection conditions are checked for consistency, and the initial water injection pressure and the rate of change of water injection volume that pass the consistency check are determined as the initial water injection conditions.

[0027] As a preferred embodiment of the offshore oilfield environmental protection water injection and formation damage control method of the present invention, the steps for generating initial water injection state information are as follows:

[0028] The water injection operation is initiated according to the initial value of the water injection pressure and the rate of change of the water injection volume. The formation is unblocked by the acid unblocking fluid system, and records of water injection pressure change and water injection volume change are generated.

[0029] The records of changes in water injection pressure and water injection volume are correlated and organized to identify changes in the state of the formation channel during the water injection start-up phase, and to form the water injection start-up response results.

[0030] The results of the water injection start-up response are summarized to generate water injection initial state information.

[0031] As a preferred embodiment of the offshore oilfield environmental protection water injection and formation damage control method of the present invention, the steps for forming a stable water injection state are as follows:

[0032] Based on the initial state information of water injection, the characteristics of water injection pressure change and water injection volume change during the water injection operation start-up phase are extracted to form a basis for coordination judgment.

[0033] Based on the coordination judgment, the relationship between the changes in water injection pressure and water injection volume during the water injection operation is adjusted synchronously to generate a coordinated control result.

[0034] The results of coordination and control will be continuously applied to the water injection operation process, and the current water injection operation status will be solidified under the condition that the water injection pressure and water injection volume remain in coordinated change, thus forming a stable water injection status.

[0035] As a preferred embodiment of the offshore oilfield environmental protection water injection and formation damage control method of the present invention, the steps for establishing the formation damage control operating state are as follows:

[0036] Based on the stable water injection state, the records of water injection pressure change and water injection volume change are compared and organized to generate the formation damage state quantity.

[0037] Based on the formation damage state, the rate of change of water injection pressure and water injection volume during the water injection operation is constrained and adjusted to form the formation damage control result.

[0038] The formation damage control results are continuously applied to the water injection operation process, and the current water injection operation state is solidified while the formation damage state remains under controlled change, thus forming the formation damage control operation state.

[0039] As a preferred embodiment of the offshore oilfield environmentally friendly water injection and formation damage control method of the present invention, the steps for establishing the environmentally friendly water injection operation state are as follows:

[0040] Using the formation damage control operation status as an operational constraint, the water injection operation process is continuously monitored to generate operational constraint information;

[0041] Under stable water injection conditions, the rate of change of water injection volume during the water injection operation is gradually relaxed based on the operational constraint information, resulting in the regulation and control of water injection capacity release.

[0042] The results of water injection capacity release regulation are continuously applied to the water injection operation process, and the current water injection operation status is solidified under the condition of meeting the operational constraints, thus forming an environmentally friendly water injection operation status.

[0043] The beneficial effects of this invention are as follows: By combining the wellhead, water injection string, sand control string, and completion string, the coordinated operation of water injection pressure and water injection volume is solidified into a stable water injection foundation. Based on this stable water injection, a water injection capacity release mechanism constrained by formation damage is introduced, ensuring that the increase in water injection capacity is controlled by the formation structure stability requirements, thus achieving an orderly release of water injection volume. While ensuring the safe operation of the entire wellhead assembly and completion string, the effectiveness of the water injection channel under non-backflow conditions is continuously improved, reducing the risk of formation damage. Simultaneously, it meets the stringent environmental requirements of water injection operations, providing reliable support for the long-term stable operation of the entire wellhead assembly and completion string, and significantly improving the overall operational quality and sustainability of oilfield water injection operations. Attached Figure Description

[0044] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0045] Figure 1 A flowchart for environmentally friendly water injection and formation damage control methods in offshore oil fields.

[0046] Figure 2 A flowchart for generating basic geological state information.

[0047] Figure 3 A flowchart for establishing a stable water injection state.

[0048] Figure 4 A flowchart for establishing the environmentally friendly water injection operation status. Detailed Implementation

[0049] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0050] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0051] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0052] Reference Figures 1-4 This is one embodiment of the present invention, which provides a method for environmentally friendly water injection and formation damage control in offshore oil fields, comprising the following steps:

[0053] S1. Collect geological condition data and basic state data of water injection medium of the target offshore oilfield water injection layer, and make unified judgments to obtain a set of basic state information of the formation.

[0054] S1.1: Geological condition data includes stratigraphic lithology, stratigraphic pore structure characteristics, original permeability of stratigraphy, and stratigraphic mineral composition characteristics;

[0055] It should be noted that the lithological type of the formation refers to the material composition and diagenetic characteristics of the rocks in the water injection layer, specifically including sandstone, limestone and dolomite, which are used to reflect the basic physical conditions of the formation for fluid entry and flow.

[0056] Formation pore structure characteristics refer to the spatial morphology and connectivity of pores and throats within the injection layer, including pore size distribution, pore-throat ratio, and pore connectivity.

[0057] The original permeability of a formation refers to the objective reflection of the formation's ability to allow fluid to pass through before water injection operations, in a state unaffected by water injection and chemical effects. Specifically, it is the level of fluid permeability allowed by the formation under original pressure conditions.

[0058] The mineral composition characteristics of a formation refer to the main minerals and their relative content that make up the rocks of the water-bearing layer, including quartz, feldspar, clay minerals and carbonate minerals.

[0059] S1.2: Basic state data of the injection medium includes the salinity composition of the injection medium, the content of reactive ions in the injection medium, and the content of suspended solids in the injection medium.

[0060] It should be noted that the salinity composition of the injection medium refers to the types and relative contents of various dissolved salts in the injection medium, which is used to reflect the overall ionic environment and mineralization degree of the injection medium.

[0061] The content of reactive ions in the water injection medium refers to the types and concentrations of ions in the water injection medium that may participate in chemical reactions under water injection and acidification conditions, in order to determine the reaction potential between the water injection medium and the formation minerals.

[0062] The suspended solids content of the water injection medium refers to the content of undissolved solid substances in the water injection medium that exist in particulate form. It is used to assess the degree of risk of blockage of formation pore channels during the water injection process.

[0063] S1.3: The geological condition data and basic state data of the injection medium of the target offshore oilfield water injection layer are uniformly quantified to form the formation structure state vector and the injection medium reaction potential vector.

[0064] Specifically, the geological condition data of the target offshore oilfield water injection layer are classified and graded according to the lithological type, pore structure characteristics, original permeability, and mineral composition characteristics of the formation. This allows geological condition data from different sources and with different dimensions to form clear state level identifiers on the same quantitative scale. The data are then combined in a fixed order of lithological type, pore structure characteristics, original permeability, and mineral composition characteristics to form a formation structure state vector.

[0065] The salinity composition, reactive ion content, and suspended solids content of the injection medium in the basic state data of the injection medium are classified into states respectively, so that the injection medium forms a consistent state level label in terms of ionic environment characteristics, reactivity characteristics, and particle characteristics. The injection medium is then integrated in a fixed order of salinity composition, reactive ion content, and suspended solids content to form a reaction potential vector of the injection medium.

[0066] It should be noted that the lithological types of the formation are divided into three discrete state levels according to the lithological category. The first lithological state level corresponds to sandstone water-injection layers, the second lithological state level corresponds to carbonate rock water-injection layers, and the third lithological state level corresponds to water-injection layers of other lithological types.

[0067] The formation pore structure characteristics are divided into three state ranges based on the preset pore connectivity threshold. When the pore connectivity is lower than 0.3 Darcy, it corresponds to a low connectivity level; when the pore connectivity is between 0.3 and 0.7 Darcy, it corresponds to a medium connectivity level; and when the pore connectivity is higher than 0.7 Darcy, it corresponds to a high connectivity level.

[0068] The pore connectivity threshold is set based on the connectivity of the pore structure and the development of pore throats. The specific setting steps include determining the pore connectivity range that can effectively support water injection operations and avoid excessive damage to the formation based on the pore connectivity performance of different rock types (such as sandstone, limestone, and claystone) and geological environments. Through multiple engineering tests, the median value of the pore connectivity range is selected as the pore connectivity threshold. An exemplary value range is 0.3~0.7 Darcy. When it is below 0.3, the connectivity between pores is poor, leading to difficulties in water injection and unstable fluid storage. When it is above 0.7, the fluid flow between pores is too fast, leading to fluid waste, damage to the pore structure, and formation instability.

[0069] The original permeability of the formation is divided into three continuous levels according to the preset formation permeability threshold. When the permeability is higher than 500mD, it corresponds to the high permeability range. When the permeability is between 50mD and 500mD, it corresponds to the medium permeability range. When the permeability is lower than 50mD, it corresponds to the low permeability range.

[0070] The formation permeability threshold is set based on the formation pore structure, fluid flowability, and engineering requirements. The specific setting steps include: analyzing the permeability performance of different formations, combining the lithological characteristics, porosity, and fluid flowability requirements of the formation to determine the effective range of permeability; selecting a permeability range within the effective range that can support stable water injection and avoid formation damage based on historical water injection operation data and laboratory permeability tests; and using the stable median value within the permeability range as the formation permeability threshold. An exemplary value range is 50 mD to 500 mD. When the permeability is higher than 500 mD, the fluid flowability is strong, which can easily lead to an overly loose formation structure; when the permeability is lower than 50 mD, the fluid flowability is poor, making it difficult to effectively maintain water injection operations.

[0071] The mineral composition characteristics of the strata are divided into three levels based on the proportion of major minerals and their influence on the stability of pore structure. The state dominated by stable minerals such as quartz corresponds to the stable mineral level, the state in which stable minerals and easily reactive minerals coexist corresponds to the transitional mineral level, and the state dominated by clay minerals and minerals that are prone to hydration and dissolution corresponds to the variable mineral level.

[0072] The salinity composition of the injection medium is divided according to a preset salinity difference threshold. When the salinity difference is less than 5%, it corresponds to a low impact level; when the salinity difference is 5% to 20%, it corresponds to a medium impact level; and when the salinity difference is greater than 20%, it corresponds to a high impact level.

[0073] The salinity difference threshold is set based on the balance between the difference between the original ionic environment of the formation and the salinity of the injection medium and the impact on mineral solubility and structure. The specific setting steps include: analyzing the original ionic environment of different formations and the salinity composition of common injection media to determine the salinity difference range that can effectively avoid mineral dissolution and structural disturbance; and selecting the median value within this range as the salinity difference threshold to ensure formation stability and avoid excessive reactions during injection. An exemplary range is 5% to 20%, which can effectively prevent mineral reactions and formation structure damage caused by excessive salinity differences. When the salinity difference exceeds 20%, it easily triggers dissolution reactions of formation minerals, leading to a decrease in formation stability. When the salinity difference is less than 5%, it is difficult to effectively adjust formation conditions, affecting the injection effect.

[0074] The content of reactive ions in the injection medium is classified according to the preset ion influence threshold. When the ion content is below 1000 ppm, it corresponds to a low influence level; when the ion content is between 1000 ppm and 5000 ppm, it corresponds to a medium influence level; and when the ion content is above 5000 ppm, it corresponds to a high influence level.

[0075] The ion impact threshold is set based on the influence of the reactive ion content in the injection medium on the stability and pore structure of formation minerals. The specific setting steps include: analyzing the impact of reactive ions (such as sodium, calcium, and magnesium) in different injection media on the reaction of formation minerals (such as clay and carbonate rocks), determining the range of influence of ion content, and selecting the ion content within the range that has no negative impact on formation stability and fluid flow as the ion impact threshold through quantitative analysis. An exemplary value range is 1000ppm to 5000ppm. That is, when the reactive ion content is controlled between 1000ppm and 5000ppm, the reaction process is controllable and will not have a significant impact on the formation; when the ion content is higher than 5000ppm, it is easy to induce formation mineral reactions and structural changes, leading to formation damage; when the ion content is lower than 1000ppm, it cannot effectively improve the water injection effect, resulting in low water injection operation efficiency.

[0076] The suspended solids content of the injection medium is classified according to a preset solids impact threshold. When the solids content is below 10 mg / L, it corresponds to a low impact level; when the solids content is between 10 mg / L and 100 mg / L, it corresponds to a medium impact level; and when the solids content is above 100 mg / L, it corresponds to a high impact level. Parameters from different sources and with different dimensions are uniformly converted into state level identifiers with the same level meaning, so as to achieve unified quantification of geological condition data and basic state data of injection medium.

[0077] The solids impact threshold is set based on the influence of suspended solids content in the injection medium on formation pore channels. The specific setting steps include: analyzing the impact of suspended solids content in different injection media on formation pore channels to determine a reasonable range for suspended solids content; combining the relationship between solids content and formation stability, selecting an intermediate value within the reasonable range that will not cause severe formation blockage and deposition as the solids impact threshold; an exemplary range is 10 mg / L to 100 mg / L, meaning that when the suspended solids content is controlled between 10 mg / L and 100 mg / L, the reaction process is controllable and will not significantly affect the pore channels; when the suspended solids content is higher than 100 mg / L, it will lead to pore channel blockage; when the suspended solids content is lower than 10 mg / L, the reaction kinetics are insufficient, resulting in poor injection effect.

[0078] S1.4: Perform unified scale mapping and coupling determination on the formation structure state vector and the water injection medium response potential vector to generate formation-medium coupling state index;

[0079] Specifically, the formation structure state vector and the injection medium reaction potential vector are unfolded one by one according to their fixed formation order. The state level identifiers in the formation structure state vector and the injection medium reaction potential vector are aligned under the same level system, so that each state level identifier in the formation structure state vector and each state level identifier in the injection medium reaction potential vector have a one-to-one correspondence in position and level. Based on the correspondence between the state level identifiers in the formation structure state vector that reflect pore channel conditions and physical property basis and the state level identifiers in the injection medium reaction potential vector that reflect ion environment characteristics, reactivity characteristics and particle characteristics, each pair of state level identifiers is matched and judged. Based on the degree of matching, a judgment result reflecting the adaptation relationship between formation conditions and the injection medium is formed. The judgment results are summarized into a single formation-medium coupling state index.

[0080] It should be noted that the pairing relationship between the formation structure state vector and the injection medium reaction potential vector is determined according to the principle of consistency of the target. The state level indicators in the formation structure state vector, which reflect the geometry and connectivity of pore channels, are paired with the state level indicators in the injection medium reaction potential vector, which reflect the characteristics of suspended solids. This is used to determine the compatibility of the influence of particles entering pore channels on the channel retention capacity. The state level indicators in the formation structure state vector, which reflect the formation physical properties and seepage stability, are paired with the state level indicators in the injection medium reaction potential vector, which reflect the characteristics of the ionic environment and the reactivity. This is used to determine the compatibility of the influence of the chemical action of the injection medium on the formation physical property stability.

[0081] "Same level system" refers to the state intervals at the same level of the formation structure state vector and the water injection medium response potential vector in a unified three-level state evaluation system. The low-level interval corresponds to the state where the interaction between the formation and the water injection medium has little impact and does not disturb the channel and physical property stability. The medium-level interval corresponds to the state where the interaction between the formation and the water injection medium affects the channel or physical property but is still under control. The high-level interval corresponds to the state where the interaction between the formation and the water injection medium disturbs the pore channel and formation physical property stability. When the two state level indicators after pairing are both in the same level system, they are judged to be in a mutually compatible interval. When they belong to different level intervals, they are judged to be incompatible.

[0082] S1.5: Integrate the formation structure state vector, the water injection medium reaction potential vector, and the formation-medium coupling state index into a set of basic formation state information.

[0083] Specifically, the formation-medium coupling state index is arranged in parallel with the formation structure state vector and the injection medium response potential vector. The formation structure state vector is used to represent the conditions of the injection layer itself, the injection medium response potential vector is used to represent the characteristics of the injection medium, and the formation-medium coupling state index is used to represent the compatibility relationship between the injection layer and the injection medium. The formation structure state vector, the injection medium response potential vector, and the formation-medium coupling state index are collected as a unified state description to form a set of basic formation state information.

[0084] S2. Based on the set of basic formation state information, construct an acidizing and unblocking fluid system under non-flowback conditions, and control the function of the acidizing and unblocking fluid system in the formation to form the final state control parameters of the non-flowback acidizing reaction.

[0085] S2.1: Perform coupled analysis on the set of basic formation state information to determine the synergistic relationship between the formation structure state and the reaction potential of the injection medium, and obtain the coupled analysis results;

[0086] Specifically, following the fixed order in which the formation structure state vector and the injection medium reaction potential vector are formed, the state level indicators reflecting formation properties and pore channel conditions in the formation structure state vector are compared and confirmed item by item with the state level indicators reflecting ion environment characteristics, reactivity characteristics, and particle characteristics in the injection medium reaction potential vector. This clarifies the mutual influence relationship between formation conditions and injection medium characteristics at the same level. Combined with the overall fit reflected by the formation-medium coupling state index, the mutual influence relationship between formation conditions and injection medium characteristics is uniformly summarized, and the synergistic relationship between formation structure state and injection medium reaction potential is determined, resulting in the coupling analysis results.

[0087] It should be noted that before constructing the acidizing and plugging fluid system under non-flowback conditions, core damage assessment experiments were conducted based on core samples obtained from the water injection layer of the target offshore oilfield. Comparative tests were performed to assess changes in core pore channels, seepage capacity, and particle migration under the influence of the water injection medium, resulting in core damage assessment results. These results reflect the degree of damage and recoverability of the core pore structure and seepage channels under different water injection medium conditions and reaction environments. They serve as experimental evidence alongside the formation basic state information set, providing experimental support for determining the synergistic relationship between formation structure state and the reaction potential of the water injection medium.

[0088] When the state level indicators in the water injection medium reaction potential vector do not weaken the pore channel conditions reflected by the formation structure state vector, a positive synergistic relationship is determined between the two; when the water injection medium reaction potential weakens the stability of the pore channel, a restricted synergistic relationship is determined.

[0089] S2.2: Based on the results of the coupling analysis, determine the composition and synergistic relationship of each functional component in the unblocking fluid, and formulate a construction scheme for the unblocking fluid;

[0090] Specifically, based on the synergistic relationship between the formation structure and the reaction potential of the injection medium in the coupled analysis results, functional components for improving pore channel conditions, regulating the chemical reaction environment, and inhibiting the influence of particles are determined to form the unblocking fluid. According to the strength of the synergistic relationship, the composition mode and sequential synergistic relationship of each functional component in the unblocking fluid are determined so that each functional component can coordinate and cooperate during the process. The determined composition mode and sequential synergistic relationship of the functional components are unified and organized to form the unblocking fluid construction scheme.

[0091] It should be noted that the functional components in the unblocking fluid include channel-improving components (e.g., organic acids, inorganic acids, acidic complexing agents, and surfactants with wetting reversal effects) for improving formation pore channel conditions, reaction-regulating components (e.g., slow-release acid systems, buffers, and reaction inhibitors) for adjusting the chemical reaction environment within the formation, and particle-inhibiting components (e.g., dispersants, anti-deposition agents, and particle stabilizers) for inhibiting particle migration and deposition effects.

[0092] Based on the coupling analysis results, when the state level indicators reflecting pore connectivity and pore throat development in the formation structure state vector are in the low-level range, and the corresponding formation-medium coupling state indicators show insufficient channel adaptation, the channel-improving component is identified as the priority component in the unblocking fluid construction scheme. When the state level indicators reflecting reactive ion activity and reaction environment sensitivity in the water injection medium reaction potential vector are in the level range that easily triggers formation reactions, and the correspondence with the formation structure state vector shows a reaction mismatch, the reaction regulating component is identified as the dominant regulating component in the unblocking fluid construction scheme. When the state level indicators reflecting suspended solids characteristics in the water injection medium reaction potential vector are in the level range that easily causes pore channel blockage, and the coupling analysis results show that particle influence is the main limiting factor, the particle inhibition component is identified as the synergistic limiting group in the unblocking fluid construction scheme.

[0093] The functional components form a synergistic relationship in the order of improving channel conditions, regulating the reaction environment, and suppressing the influence of particles, thus constituting a solution for unblocking fluids suitable for non-backflow conditions.

[0094] S2.3: Combine the corresponding functional components according to the unblocking fluid construction scheme and complete the configuration to obtain an acid unblocking fluid system suitable for non-backflow conditions.

[0095] Specifically, according to the composition and synergistic relationship of the functional components, the functional components are combined in a predetermined order. The functional components that improve pore channel conditions, regulate the chemical reaction environment, and suppress the influence of particles are added to the same preparation process in sequence to form a mixture. The mixture is continuously stirred and allowed to stand so that the functional components are uniformly dispersed in the liquid and achieve stable coexistence, forming a liquid system corresponding to the unblocking solution construction scheme. After the liquid system achieves stable coexistence, the liquid system is determined as the acid unblocking solution system.

[0096] It should be noted that the predetermined order refers to the order in which the functional components are added in the unblocking fluid construction scheme. Specifically, the order is: functional components that improve pore channel conditions, functional components that regulate the chemical reaction environment, and functional components that inhibit the influence of particles.

[0097] S2.4: Introduce the acidizing and unblocking fluid system into the formation and allow it to undergo an unblocking reaction within the formation. Obtain the reaction state information of the acidizing and unblocking fluid system within the formation as the reaction time changes, and form a reaction state sequence.

[0098] Specifically, the acidizing and unblocking fluid system is introduced into the target offshore oilfield's water-injection layer through a water injection channel, allowing the system to contact the formation medium within the water-injection layer and gradually initiate the unblocking process. At predetermined time intervals, changes in water injection pressure and volume, as well as the channel patency reflected by the correlation between these changes, are continuously recorded during the unblocking process. This ensures the records reflect the state changes of the acidizing and unblocking fluid system at different stages of the process. The recorded results at each time point are then organized chronologically to form a reaction state sequence.

[0099] It should be noted that the time interval refers to the observation interval corresponding to the fixed operation monitoring cycle that has been adopted in the existing water injection operation of the target offshore oil field;

[0100] The patency of the formation channel is characterized by the correlation between changes in injection pressure and injection volume. Within the same time interval, when the injection volume increases while the change in injection pressure decreases, it indicates that the patency of the formation channel has improved. When the change in injection volume decreases while the injection pressure shows a continuous upward trend, it indicates that the patency of the formation channel has decreased. When the changes in injection pressure and injection volume show a stable correlation within a continuous time interval and no longer show significant deviations, it indicates that the state of the formation channel is stabilizing. By continuously recording the changes in the correlation at different time points, a reaction state sequence reflecting the change of the patency of the formation channel over time is formed.

[0101] For example, in the initial stage after introducing the acidizing and unblocking fluid system into the formation, if the injection volume gradually increases within adjacent time intervals while the corresponding change in injection pressure decreases relatively, it indicates that the acidizing and unblocking reaction is improving pore channel conditions, and the formation channel patency is in an upward phase. As the treatment time continues, if the injection volume changes tend to stabilize within a continuous period and the injection pressure no longer shows an increasing or decreasing trend, it indicates that the formation channel conditions have reached a stable state, and the corresponding channel patency has entered a stable phase. If, within a certain time interval, the change in injection volume decreases while the injection pressure continues to increase, it indicates that the formation channel is becoming restricted, and the state at the corresponding time point needs to be marked as a state of declining channel patency.

[0102] S2.5: Continuously determine the reaction state sequence, identify the critical state at which the acid unblocking reaction transitions from the enhancement stage to the stable stage, and form the final state determination result of the reaction.

[0103] Specifically, based on the continuous changes in water injection pressure, water injection volume, and channel patency at each time point in the reaction state sequence, the reaction state sequence is compared and judged hour by hour to ensure that the trend of state change between adjacent time points is continuously reflected. When the state change reflected in the reaction state sequence changes from continuous enhancement to stabilization, and the state characteristics reflected by multiple consecutive time points remain basically consistent, the corresponding time point is determined as the critical state in which the acid unblocking reaction transitions from the enhancement stage to the stable stage. The critical state is used as the basis for determining the degree of completion of the acid unblocking reaction to form the final state determination result.

[0104] S2.6: Based on the final state determination results, determine the termination timing and intensity boundary of the acid unblocking reaction, and form the final state control parameters for the non-backflow acidification reaction.

[0105] Specifically, the critical state in the final reaction determination result is taken as the termination time of the acidizing and unblocking reaction, and the continuous recording of water injection pressure changes, water injection volume changes, and channel patency status before and after the critical state in the reaction state sequence is used as the basis for confirming the termination time; the range of continuous and stable changes in water injection pressure, water injection volume, and channel patency status before and after the critical state in the reaction state sequence is selected as the boundary of the sustainable function of the acidizing and unblocking liquid system in the water injection layer; the termination time and the boundary of the function are unified and organized to form the final state control parameters of the non-backflow acidizing reaction.

[0106] S3. Set the initial water injection conditions based on the final state control parameters of the non-backflow acidification reaction, and carry out water injection operations under the initial water injection conditions to generate initial water injection state information.

[0107] S3.1: Transform the reaction termination timing and action intensity boundary in the final state control parameters of the non-backflow acidification reaction into the constraint conditions of the water injection operation start-up stage, forming water injection start-up constraint information;

[0108] Specifically, the time node corresponding to the reaction termination timing in the final state control parameters of the non-backflow acidification reaction is used as the time constraint for allowing the start of water injection operations, and the water injection pressure change range, water injection volume change range, and channel unobstructed state range defined by the action intensity boundary are used as the operational constraints for the start-up phase of water injection operations. The time constraints and operational constraints are unified and organized so that the water injection behavior in the start-up phase of water injection operations can be limited within the change range allowed by the final state control parameters of the non-backflow acidification reaction, thus forming water injection start-up constraint information.

[0109] S3.2: Based on the water injection start-up constraint information, calculate the initial value of water injection pressure and the rate of change of water injection volume during the water injection start-up phase to form candidate initial water injection conditions;

[0110] Specifically, based on the water injection start-up constraint information, the initial value of water injection pressure and the rate of change of water injection volume during the water injection start-up phase are calculated, and the initial value of water injection pressure and the rate of change of water injection volume are compiled and used as candidate initial water injection conditions that can be adopted during the water injection start-up phase.

[0111] The expression for calculating the initial value of injection pressure and the rate of change of injection volume is as follows:

[0112] ;

[0113] ;

[0114] in, This indicates the initial water injection pressure value during the water injection operation startup phase. The upper limit of the allowable water injection pressure is determined by the range of water injection pressure changes that remain stable near the critical state in the reaction state sequence, and the maximum allowable water injection pressure in the stable range is taken as the upper limit of the allowable water injection pressure. This indicates the injection pressure level corresponding to the boundary of the action intensity in the final state control parameters of the non-backflow acidification reaction; This indicates the rate of change of water injection volume during the initial stage of the water injection operation. This indicates the upper limit of the allowable water injection volume. The range of water injection volume change corresponding to the reaction state sequence near the critical state is identified as the stable range, and the maximum allowable water injection volume within the stable range is taken as the upper limit of the allowable water injection volume. This indicates the water injection volume at the initial moment of the water injection operation. This indicates the duration of the water injection start-up phase given in the water injection start-up constraint information.

[0115] S3.3: Perform consistency verification on the candidate initial water injection conditions, and determine the initial water injection pressure and the rate of change of water injection volume that pass the consistency verification as the initial water injection conditions.

[0116] Specifically, the initial water injection pressure and rate of change of water injection volume in the candidate initial water injection conditions are compared and confirmed item by item with the water injection pressure change range, water injection volume change range, and the action intensity boundary corresponding to the final state control parameters of the non-backflow acidification reaction defined in the water injection start-up constraint information, so as to ensure that the candidate initial water injection conditions are consistent with the requirements of start-up time and operation constraints. When the initial water injection pressure and rate of change of water injection volume corresponding to the candidate initial water injection conditions are both within the corresponding change range, and the water injection pressure and water injection volume changes can maintain a coordinated change trend consistent with the characteristics near the critical state in the reaction state sequence during the water injection start-up phase, the candidate initial water injection conditions are judged to have passed the consistency check. The initial water injection pressure and rate of change of water injection volume that have passed the consistency check are uniformly determined as the initial water injection conditions.

[0117] S3.4: Start the water injection operation according to the initial value of the water injection pressure and the rate of change of the water injection volume. Use the acid unblocking fluid system to unblock the formation and generate records of water injection pressure change and water injection volume change.

[0118] Specifically, water injection is initiated according to the initial water injection pressure and the rate of change in water injection volume. This allows the acidizing and unblocking fluid system to enter the formation and unblock any blockages formed within the formation. As the water injection operation continues, the relevant equipment (throttle valve, Christmas tree, and blowout preventer) simultaneously generate corresponding operational records. The throttle valve, Christmas tree, and blowout preventer also generate operational records reflecting changes in water injection pressure and volume during the water injection process. As the acidizing and unblocking fluid system continues to act on the formation, the operational records generated by the throttle valve, Christmas tree, and blowout preventer during the water injection operation are compiled and organized to obtain records of changes in water injection pressure and volume.

[0119] S3.5: Correlate and organize the records of changes in water injection pressure and water injection volume to identify changes in the state of the formation channel during the water injection start-up phase and generate water injection start-up response results;

[0120] Specifically, the records of water injection pressure changes and water injection volume changes are compared and organized according to the same water injection operation period. This ensures that the records of water injection pressure changes and water injection volume changes formed within the same period can correspond to each other. During the comparison and organization process, the synchronization and deviation of pressure changes with water injection volume changes during the water injection operation are identified, forming a correspondence reflecting the relationship between pressure changes and water injection volume changes during the water injection operation. The changes in the correspondence during the water injection start-up phase are continuously compared to identify the state manifestations of water injection pressure changes and water injection volume changes from synchronization to abnormal deviation and from abnormal to stable during the water injection start-up phase. This determines the changes in the formation channel state during the water injection start-up phase and forms the water injection start-up response results.

[0121] S3.6: Summarize the water injection start-up response results and generate water injection initial state information.

[0122] Specifically, the changes in the formation channel state during the water injection start-up phase in the water injection start-up response results are uniformly organized to ensure that the changes in formation channel state in different time periods are consistent; the water injection start-up response results are correlated and merged with the records of water injection pressure changes and water injection volume changes to form a complete correspondence between the water injection behavior during the water injection start-up phase and the changes in formation channel state; the changes in water injection pressure, water injection volume, and formation channel state during the water injection start-up phase are all collected to form the initial state information of water injection.

[0123] S4. Based on the initial water injection status information, adjust the implementation process of the water injection operation to ensure that the water injection pressure and water injection volume change in a coordinated manner during the water injection operation, thereby forming a stable water injection state.

[0124] S4.1: Based on the initial state information of water injection, extract the characteristics of water injection pressure change and water injection volume change during the water injection operation start-up phase to form a basis for coordination judgment;

[0125] Specifically, the records of water injection pressure changes and water injection volume changes in the initial water injection status information are compared with the water quality standards of the injected medium. During the water injection start-up phase, the records of water injection pressure changes and water injection volume changes at the Christmas tree, water injection tubing, and sand control tubing are simultaneously read. This ensures that the initial water injection status information and the water quality standards of the injected medium form a consistent reference in the corresponding operational records of the Christmas tree, water injection tubing, and sand control tubing. Based on this consistent reference, the water injection pressure change process over a continuous time period during the water injection start-up phase is used as the water injection pressure change characteristic. Simultaneously, the change in water injection volume during the start-up process within the same time range is used as the water injection volume change characteristic. The water injection pressure change characteristics and water injection volume change characteristics are compared within the same time period to clarify the synchronous relationship between water injection pressure changes and water injection volume changes during the start-up phase, forming a basis for coordinated judgment.

[0126] S4.2: Based on the coordination judgment basis, the relationship between the changes in water injection pressure and water injection volume during the water injection operation is adjusted synchronously to generate coordination control results;

[0127] Specifically, the characteristics of water injection pressure change and water injection volume change in the coordination judgment basis are used as the reference for the implementation of water injection operations. During the implementation of water injection operations, the actual water injection pressure change and water injection volume change are continuously compared. When the water injection pressure change and water injection volume change are out of sync during the water injection operation, the magnitude of water injection pressure change and the rhythm of water injection volume change are adjusted accordingly based on the correspondence determined in the coordination judgment basis, so that the water injection pressure change and water injection volume change remain coordinated and consistent within the same time period. The adjusted water injection pressure change and water injection volume change are uniformly determined as the coordinated control result.

[0128] S4.3: The results of coordination and control will be continuously applied to the water injection operation process, and the current water injection operation state will be solidified under the condition that the water injection pressure and water injection volume remain in coordination, so as to form a stable water injection state.

[0129] Specifically, the changes in water injection pressure and water injection volume from the coordinated control results are continuously applied to the water injection operation process, ensuring that the water injection operation maintains consistent changes in water injection pressure and water injection volume according to the coordinated control results. During the continuous water injection operation, the changes in water injection pressure and water injection volume are continuously observed. When the changes in water injection pressure and water injection volume remain coordinated over a continuous period of time and no longer show any asynchrony, the current water injection operation status is determined as a stable water injection status.

[0130] S5. Implement water injection operations under stable water injection conditions, regulate the formation damage state generated during the water injection operation, form a formation damage control operation state, and implement water injection capacity release control under stable water injection conditions to form an environmentally friendly water injection operation state.

[0131] S5.1: Based on the stable water injection state, the records of water injection pressure change and water injection volume change are compared and organized to generate the formation damage state quantity;

[0132] Specifically, under stable water injection conditions, continuous monitoring of the water injection operation process is conducted, and records of water injection pressure and volume changes generated by the throttle valve, Christmas tree, and blowout preventer during the water injection operation are collected simultaneously. The water injection pressure and volume change records within the same water injection operation period are compared and organized to ensure that the water injection operation status remains consistent over time. During the comparison and organization process, the water injection pressure and volume changes under stable water injection conditions are continuously compared. When the water injection operation status deviates continuously from the stable water injection state, the deviation is regarded as a manifestation of changes in the formation under the action of water injection. The water injection pressure and volume change records reflecting the degree of deviation are then collected together to form a formation damage status quantity.

[0133] It should be noted that the water injection tubing, as a structural component of the water injection channel, is not directly monitored. The water injection operation status is indirectly reflected through changes in the operating response at the throttle valve, Christmas tree, and blowout preventer.

[0134] Continuous deviation refers to the fact that, within multiple consecutive operation monitoring cycles, the corresponding relationship between changes in water injection pressure and changes in water injection volume has not recovered to the coordinated relationship corresponding to the stable water injection state.

[0135] S5.2: Based on the formation damage state quantity, constrain and adjust the rate of change of water injection pressure and water injection volume during the water injection operation to form the formation damage control result;

[0136] Specifically, the degree of formation impact from water injection operations in the formation damage state quantity is used as a constraint during the implementation of water injection operations. During continuous water injection operations, the current changes in water injection pressure and the rate of change in water injection volume are compared. When the formation damage state quantity shows that the degree of formation impact is increasing, the magnitude of changes in water injection pressure and the rate of change in water injection volume are reduced, causing the water injection operation to revert to a state with a lower degree of formation damage. When the formation damage state quantity shows that the degree of formation impact remains stable, the current changes in water injection pressure and the rate of change in water injection volume are maintained unchanged. The water injection operation state that can keep the formation damage state quantity under control is uniformly determined as the formation damage control result.

[0137] S5.3: The formation damage control results are continuously applied to the water injection operation process, and the current water injection operation state is solidified while the formation damage state remains under controlled change, forming the formation damage control operation state.

[0138] Specifically, the methods for adjusting water injection pressure and water injection rate from the formation damage control results are continuously applied to the water injection operation process, ensuring that the water injection operation remains in a consistent control state according to the formation damage control results throughout the operation. During the water injection operation, the changes in the formation damage state are continuously recorded. When the formation damage state no longer shows an increasing trend within a continuous time period, the current water injection operation state is determined as the formation damage control operation state.

[0139] S5.4: The formation damage control operation status is used as an operation constraint to continuously monitor the water injection operation process and form operation constraint information;

[0140] Specifically, the changes in water injection pressure and volume during the formation damage control operation are used as operational constraints during the water injection process. As the water injection operation continues, changes in water injection pressure, volume, and formation damage status are recorded synchronously. The actual operational status is compared with the water injection pressure and volume changes corresponding to the formation damage control operation status to confirm whether the water injection operation remains consistent with the formation damage control operation status. Records of consistency and deviations between the water injection operation and the formation damage control operation status are then compiled to form operational constraint information.

[0141] S5.5: Under stable water injection conditions, the rate of change of water injection volume during the water injection operation is gradually relaxed based on the operational constraint information to form the water injection capacity release regulation result;

[0142] Specifically, under stable water injection conditions, operational constraint information is used as the control basis for the water injection operation. During the water injection operation, the current rate of change of water injection volume is compared with the stable water injection state and formation damage control operation state in the operational constraint information. Provided that the water injection pressure remains stable and the formation damage state does not deviate, the rate of change of water injection volume during the water injection operation is relaxed once, and the stable water injection state and formation damage control operation state are reconfirmed after relaxation. When the stable water injection state and formation damage control operation state remain consistent throughout the continuous relaxation process, the current rate of change of water injection volume is determined as the effective implementation state and used as the basis for the next relaxation. The relaxation control operation is gradually repeated, forming the water injection capacity release regulation result without disrupting the stable water injection state and formation damage control operation state.

[0143] S5.6: The results of water injection capacity release regulation will be continuously applied to the water injection operation process. Under the condition of meeting the operational constraints, the current water injection operation state will be solidified to form an environmentally friendly water injection operation state.

[0144] Specifically, under stable water injection conditions, the water injection capacity release control results are directly applied to the water injection operation process, ensuring that the water injection operation operates according to the water injection volume change rate corresponding to the water injection capacity release control results. During the continuous water injection operation, the actual changes in water injection pressure, the actual change rate of water injection volume, and the corresponding formation damage status are continuously monitored, and the monitoring results are compared item by item with the formation damage control operation status. When the changes in water injection pressure and the change rate of water injection volume do not cause abnormal changes in the formation damage status during operation, and the formation damage status remains consistent with the formation damage control operation status, the relaxation of the water injection volume change rate is stopped, and the current water injection operation mode is maintained, confirming the current water injection operation mode as an environmentally friendly water injection operation status.

[0145] In summary, this invention, by combining the wellhead, water injection string, sand control string, and completion string, solidifies the coordinated operation of water injection pressure and volume into a stable water injection foundation. Based on this stable water injection, it introduces a water injection capacity release mechanism constrained by formation damage conditions. This ensures that the increase in water injection capacity is controlled by formation stability requirements, achieving an orderly release of water volume. While guaranteeing the safe operation of the entire wellhead assembly and completion string, it continuously improves the effectiveness of the water injection channel under non-backflow conditions, reduces formation damage risks, and meets the stringent environmental requirements of water injection operations. This provides reliable support for the long-term stable operation of the entire wellhead assembly and completion string, significantly improving the overall operational quality and sustainability of oilfield water injection operations.

[0146] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for environmentally friendly water injection and formation damage control in offshore oilfields, characterized in that: include, Collect geological condition data and basic state data of water injection medium of the target offshore oilfield water injection layer, and make unified judgments to obtain a set of basic formation state information. Based on the set of basic formation state information, an acidizing and plugging fluid system under non-flowback working conditions is constructed, and the function state of the acidizing and plugging fluid system in the formation is controlled to form the final state control parameters of the non-flowback acidizing reaction. The initial water injection conditions are set according to the final state control parameters of the non-backflow acidification reaction, and water injection operations are carried out under the initial water injection conditions to generate initial water injection state information. Based on the initial water injection status information, the implementation process of the water injection operation is adjusted to ensure that the water injection pressure and water injection volume change in a coordinated manner during the water injection operation, thereby forming a stable water injection state. Water injection operations are carried out under stable water injection conditions. The formation damage state generated during the water injection operation is regulated to form a formation damage control operation state. Water injection capacity release is controlled under stable water injection conditions to form an environmentally friendly water injection operation state.

2. The offshore oilfield environmental-friendly water injection and formation damage control governing method according to claim 1, characterized in that: The geological condition data includes stratigraphic lithology, stratigraphic pore structure characteristics, original permeability of the stratigraphy, and stratigraphic mineral composition characteristics; The basic state data of the water injection medium includes the salinity composition of the water injection medium, the content of reactive ions in the water injection medium, and the content of suspended solids in the water injection medium.

3. The offshore oilfield environmental-friendly water injection and formation damage control governing method according to claim 2, characterized in that: The steps to obtain the set of basic geological state information are as follows: The geological condition data and basic state data of the injection medium of the target offshore oilfield water injection layer are uniformly quantified to form a formation structure state vector and a water injection medium reaction potential vector. A unified scale mapping and coupling determination are performed on the formation structure state vector and the water injection medium response potential vector to generate a formation-medium coupling state index. The formation structure state vector, the water injection medium reaction potential vector, and the formation-medium coupling state index are integrated into a set of basic formation state information.

4. The method for environmentally friendly water injection and formation damage control in offshore oilfields as described in claim 3, characterized in that: The steps for constructing an acid-resistant unblocking solution system that operates without backflow are as follows. Coupled analysis was performed on the set of basic formation state information to determine the synergistic relationship between the formation structure state and the reaction potential of the water injection medium, and the coupled analysis results were obtained. Based on the results of the coupling analysis, the composition and synergistic relationship of each functional component in the unblocking fluid are determined, and a construction scheme for the unblocking fluid is formed. By combining the corresponding functional components according to the unblocking fluid construction scheme and completing the configuration, an acid unblocking fluid system suitable for non-backflow conditions is obtained.

5. The method for environmentally friendly water injection and formation damage control in offshore oilfields as described in claim 4, characterized in that: The steps for forming the final state control parameters of the non-backflow acidification reaction are as follows. The acidizing unblocking fluid system is introduced into the formation and an unblocking reaction occurs within the formation. The reaction state information of the acidizing unblocking fluid system in the formation changes with the action time is obtained to form a reaction state sequence. The reaction state sequence is continuously determined to identify the critical state in which the acid unblocking reaction transitions from the enhanced stage to the stable stage, thus forming the final state determination result of the reaction. Based on the final state determination results, the termination timing and intensity boundary of the acid unblocking reaction are determined, forming the final state control parameters for the non-backflow acid unblocking reaction.

6. The method for environmentally friendly water injection and formation damage control in offshore oilfields as described in claim 5, characterized in that: The steps for setting the initial water injection conditions are as follows: The reaction termination timing and action intensity boundary in the final state control parameters of the non-backflow acidification reaction are transformed into constraints for the water injection start-up stage, forming water injection start-up constraint information. Based on the water injection start-up constraint information, the initial value of water injection pressure and the rate of change of water injection volume during the water injection start-up phase are calculated to form candidate initial water injection conditions. The candidate initial water injection conditions are checked for consistency, and the initial water injection pressure and the rate of change of water injection volume that pass the consistency check are determined as the initial water injection conditions.

7. The method for environmentally friendly water injection and formation damage control in offshore oilfields as described in claim 6, characterized in that: The steps for generating the initial water injection state information are as follows: The water injection operation is initiated according to the initial value of the water injection pressure and the rate of change of the water injection volume. The formation is unblocked by the acid unblocking fluid system, and records of water injection pressure change and water injection volume change are generated. The records of changes in water injection pressure and water injection volume are correlated and organized to identify changes in the state of the formation channel during the water injection start-up phase, and to form the water injection start-up response results. The results of the water injection start-up response are summarized to generate water injection initial state information.

8. The method for environmentally friendly water injection and formation damage control in offshore oilfields as described in claim 7, characterized in that: The steps to establish a stable water injection state are as follows: Based on the initial state information of water injection, the characteristics of water injection pressure change and water injection volume change during the water injection operation start-up phase are extracted to form a basis for coordination judgment. Based on the coordination judgment, the relationship between the changes in water injection pressure and water injection volume during the water injection operation is adjusted synchronously to generate a coordinated control result. The results of coordination and control will be continuously applied to the water injection operation process, and the current water injection operation status will be solidified under the condition that the water injection pressure and water injection volume remain in coordinated change, thus forming a stable water injection status.

9. The method for environmentally friendly water injection and formation damage control in offshore oilfields as described in claim 8, characterized in that: The steps for establishing formation damage control operation status are as follows: Based on the stable water injection state, the records of water injection pressure change and water injection volume change are compared and organized to generate the formation damage state quantity. Based on the formation damage state, the rate of change of water injection pressure and water injection volume during the water injection operation is constrained and adjusted to form the formation damage control result. The formation damage control results are continuously applied to the water injection operation process, and the current water injection operation state is solidified while the formation damage state remains under controlled change, thus forming the formation damage control operation state.

10. The method for environmentally friendly water injection and formation damage control in offshore oilfields as described in claim 1, characterized in that: The steps to establish an environmentally friendly water injection operation state are as follows: Using the formation damage control operation status as an operational constraint, the water injection operation process is continuously monitored to generate operational constraint information; Under stable water injection conditions, the rate of change of water injection volume during the water injection operation is gradually relaxed based on the operational constraint information, resulting in the regulation and control of water injection capacity release. The results of water injection capacity release regulation are continuously applied to the water injection operation process, and the current water injection operation status is solidified under the condition of meeting the operational constraints, thus forming an environmentally friendly water injection operation status.

Images