Method for regulating formation pressure in offshore oilfield reinjection process based on environmental protection collaboration

Abstract

The application discloses a method for formation pressure regulation in offshore oilfield reinjection based on environmental protection synergy, relates to the technical field of oilfield production water reinjection, and comprises the following steps: collecting the reinjection discharge capacity, reinjection pressure and operation time of a throttling valve, a Christmas tree channel and a reinjection fluid along a water injection string under the working condition of stratum transportation, and performing unified checking and working condition correlation analysis to generate a reinjection basic operation parameter set; performing throttling valve and Christmas tree internal flow characteristic analysis on the reinjection basic operation parameter set, obtaining equivalent throttling characteristic parameters, and correcting wellhead injection pressure according to the equivalent throttling characteristic parameters to obtain effective injection pressure. The application provides unified and continuous pressure correction basis for the determination of a safety constraint boundary and the screening of optimal combinations of reinjection pressure and reinjection discharge capacity, so that reinjection regulation is unified among efficiency, safety and stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oilfield production water reinjection, in particular to a method for regulating formation pressure in offshore oilfield reinjection based on environmental protection synergy. BACKGROUND

[0002] With the development of offshore oilfields entering the middle and late stages, reinjection technology has become an important technical path to maintain formation pressure, improve recovery ratio and achieve injection-production balance. At present, the water treatment capacity of some production facilities at sea has been saturated, and by large-scale reinjection of treated production water into designated formations, the shortage of sewage treatment capacity can be fundamentally solved. This can release the liquid lifting constraints and provide key infrastructure support for stable production of oilfield groups. Existing offshore oilfield reinjection operations usually transport and regulate reinjection fluid through choke valves, Christmas trees and water injection strings, and rely on wellhead pressure and reinjection discharge rate operating parameters to monitor the reinjection state. With the increase of reinjection scale and the popularization of non-returning discharge operation mode, the reinjection process gradually presents the operating characteristics of high discharge rate, long cycle and strong coupling, which puts forward higher requirements for the pressure control accuracy of the reinjection process and the cognition of formation response.

[0003] However, reinjection pressure regulation mainly depends on static design parameters and local monitoring results, which is difficult to fully reflect the flow and pressure-bearing state of choke valves, Christmas trees, water injection strings and sand control strings in the continuous reinjection process, especially under the condition of non-returning discharge, the dynamic correlation between reinjection pressure change and formation pressure response is not clear, which leads to a lack of unified constraint basis for reinjection pressure regulation, and conflicts between ensuring formation safety and reinjection efficiency are easy to occur. Therefore, how to realize the synergistic optimization of reinjection pressure and reinjection discharge rate under the joint action of multi-node flow constraints and formation dynamic response has become a problem to be solved in current offshore oilfield reinjection technology. SUMMARY

[0004] In view of the above existing problems, the present application is proposed.

[0005] Therefore, the present application provides a method for regulating formation pressure in offshore oilfield reinjection based on environmental protection synergy, which solves the problem of lack of unified and synergistic regulation basis between reinjection pressure dynamic change and formation pressure response under non-returning discharge condition and multi-node pressure-bearing constraints in the reinjection process.

[0006] To solve the above technical problems, the present application provides the following technical solutions:

[0007] The application provides a method for regulating formation pressure in offshore oilfield reinjection based on environmental protection synergy, which comprises the following steps: collecting the reinjection discharge, reinjection pressure and operation time of a choke valve, a Christmas tree channel and a reinjection fluid under the working condition of the reinjection fluid column to the formation, and performing unified checking and working condition correlation analysis to generate a reinjection basic operation parameter set; performing choke valve and Christmas tree internal flow characteristic analysis on the reinjection basic operation parameter set to obtain equivalent choke characteristic parameters, and correcting the wellhead injection pressure according to the equivalent choke characteristic parameters to obtain effective injection pressure; performing formation pressure dynamic response analysis based on the effective injection pressure to judge the formation pressure change trend and identify abnormal pressure rise characteristics, and obtaining a pressure response result; performing pressure regulation processing of the reinjection pressure under the current reinjection working condition under the condition of no backflow discharge based on the pressure response result to obtain a reinjection pressure state; under the reinjection pressure state, checking the pressure response result and the pressure bearing state of the choke valve, the Christmas tree and the reinjection fluid column in the reinjection process to obtain a safety constraint boundary, matching the safety constraint boundary with a preset formation allowable pressure interval to obtain an optimal combination of the reinjection pressure and the reinjection discharge, and continuously reinjecting the optimal combination of the reinjection pressure and the reinjection discharge to obtain a new reinjection pressure, and comparing the new reinjection pressure with the pressure response result to generate a pressure regulation parameter set.

[0008] As a preferred scheme of the method for regulating formation pressure in offshore oilfield reinjection based on environmental protection synergy, the generation of the reinjection basic operation parameter set comprises the following steps:

[0009] Perform unified time alignment and consistency checking on the reinjection discharge, the reinjection pressure and the operation time to generate effective reinjection operation data;

[0010] Perform smoothing processing on the effective reinjection operation data to obtain smooth reinjection pressure data and smooth reinjection discharge data;

[0011] According to the smooth reinjection pressure data and the smooth reinjection discharge data, the reinjection pressure change rate and the reinjection discharge stability parameters are calculated, and the reinjection pressure change rate and the reinjection discharge stability parameters are associated with the operation time to obtain working condition characteristic parameters;

[0012] The smooth reinjection pressure data, the smooth reinjection discharge data, the operation time and the working condition characteristic parameters are uniformly packaged to generate the reinjection basic operation parameter set.

[0013] As a preferred scheme of the method for regulating formation pressure in offshore oilfield reinjection based on environmental protection synergy, the generation of the reinjection basic operation parameter set comprises the following steps:

[0014] Based on the reinjection basic operation parameter set, the reinjection working condition of the choke valve and the Christmas tree is digitally twin instantiated to form the internal flow working condition state of the choke valve and the Christmas tree.

[0015] Under the constraints of the throttle valve and the internal flow condition of the Christmas tree, the operator mapping reasoning is performed on the throttle valve and the internal flow area of the Christmas tree, and the pressure change and flow rate change state of each flow area are obtained;

[0016] The pressure change and flow rate change state of each flow area are corrected for physical consistency, and the rotational dominant flow characteristics of the throttle part, the Christmas tree corner and the valve cavity area are identified synchronously;

[0017] The rotational dominant flow characteristics are time-correlated and scaled with the local pressure change characteristics in the Christmas tree, and the equivalent throttling characteristic parameters are obtained.

[0018] As a preferred scheme of the method for regulating formation pressure in the offshore oilfield reinjection process based on environmental protection collaboration, wherein, the effective injection pressure is obtained by the following steps,

[0019] The wellhead injection pressure in the reinjection basic operation parameter set is time-correlated with the equivalent throttling characteristic parameters to establish a throttling correction relationship;

[0020] According to the throttling correction relationship, the wellhead injection pressure change in the reinjection process is corrected to form a wellhead pressure evolution state;

[0021] The wellhead pressure evolution state is used as a correction basis to uniformly correct the wellhead injection pressure to obtain the effective injection pressure.

[0022] As a preferred scheme of the method for regulating formation pressure in the offshore oilfield reinjection process based on environmental protection collaboration, wherein, the pressure response result is obtained by the following steps,

[0023] The action process of the effective injection pressure changing with time is arranged and sequenced to construct an injection pressure change sequence;

[0024] Based on the injection pressure change sequence, the dynamic response analysis of the formation pressure changing with time is performed to obtain the pressure response result.

[0025] As a preferred scheme of the method for regulating formation pressure in the offshore oilfield reinjection process based on environmental protection collaboration, wherein, the reinjection pressure state is obtained by the following steps,

[0026] According to the pressure response result, the pressure change range that can be borne by the formation under the current reinjection condition is determined;

[0027] Under the constraint of the pressure change range, the change process of the reinjection pressure is planned under the non-flowback condition to obtain the reinjection pressure change process;

[0028] According to the change process of the reinjection pressure, the reinjection pressure is uniformly regulated to form a reinjection pressure state.

[0029] As a preferred scheme of the method for regulating the formation pressure in the reinjection process of the offshore oilfield based on the environmental protection synergy, the safe constraint boundary is obtained by the following steps,

[0030] The formation pressure response and the formation pressure change state are evaluated for safety based on the reinjection pressure state as a unified working condition, to form a formation side safety evaluation result.

[0031] The pressure bearing states of the choke valve, the Christmas tree and the water injection string are checked, and the pressure consumption state of the sand control string in the reinjection process is inferred to form an equipment side safety evaluation result.

[0032] The formation side safety evaluation result and the equipment side safety evaluation result are uniformly aligned and associated analyzed to identify the synergy constraint relationship between the formation safety requirement and the equipment bearing capacity.

[0033] According to the synergy constraint relationship, a pressure allowable range that meets the formation side safety evaluation result and the equipment side safety evaluation result is determined to obtain a safe constraint boundary.

[0034] As a preferred scheme of the method for regulating the formation pressure in the reinjection process of the offshore oilfield based on the environmental protection synergy, the optimal combination of the reinjection pressure and the reinjection flow rate is obtained by the following steps,

[0035] The safe constraint boundary and a preset formation allowable pressure interval are uniformly aligned to determine a feasible pressure range that can be used for reinjection regulation under the current reinjection working condition.

[0036] The reinjection pressure and the corresponding reinjection flow rate are screened and constrained in the feasible pressure range to form a candidate combination interval that meets the safety condition.

[0037] The reinjection pressure and the reinjection flow rate combination that can achieve the optimal reinjection capacity without breaking through the feasible pressure range are selected from the candidate combination interval to obtain the optimal combination of the reinjection pressure and the reinjection flow rate.

[0038] As a preferred scheme of the method for regulating the formation pressure in the reinjection process of the offshore oilfield based on the environmental protection synergy, the new reinjection pressure is obtained by the following steps,

[0039] The optimal combination of the reinjection pressure and the reinjection flow rate is set as the regulation reference of the current reinjection working condition, and the reinjection process is continuously adjusted under the constraint of the regulation reference to form a stable reinjection operation state.

[0040] The change process of the reinjection pressure over time is continuously recorded under the stable reinjection operation state to obtain the new reinjection pressure.

[0041] As a preferred scheme of the method for regulating formation pressure in offshore oilfield reinjection process based on environmental protection synergy, wherein: the step of generating the pressure regulation parameter set is as follows,

[0042] The new reinjection pressure is uniformly time-aligned with the pressure response result of the corresponding period to form a pressure alignment sequence.

[0043] Based on the pressure alignment sequence, the difference between the new reinjection pressure and the pressure response result is quantitatively analyzed to form a pressure deviation feature.

[0044] According to the pressure deviation feature, the reinjection pressure level in the stable reinjection operation state is characterized and summarized to form the pressure regulation parameter set.

[0045] The beneficial effects of the present application are: by characterizing the flow characteristics of the throttle valve and the Christmas tree and extracting the equivalent throttle feature parameters, the wellhead injection pressure can be corrected in the reinjection process, the effective injection pressure that can reflect the actual reinjection working condition is obtained, the representation of the reinjection pressure is no longer limited to the surface monitoring value, but can reflect the influence of the flow state of the throttle valve and the Christmas tree on the pressure transmission, so that the identification of the formation pressure dynamic response has a more reliable basis; the reinjection pressure regulation can closely match the real pressure change process of the formation, effectively support the pressure regulation decision under the condition of no return, avoid the accumulation of deviation of the reinjection pressure in the running process and the mismatch with the formation response; at the same time, a unified and continuous pressure correction basis is provided for the determination of the safety constraint boundary and the selection of the optimal combination of the reinjection pressure and the reinjection flow rate, so that the reinjection regulation realizes the unity among efficiency, safety and stability. BRIEF DESCRIPTION OF DRAWINGS

[0046] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0047] Fig. 1 The flow chart of the method for regulating formation pressure in offshore oilfield reinjection process based on environmental protection synergy.

[0048] Fig. 2 The flow chart of generating the reinjection basic operation parameter set.

[0049] Fig. 3 The flow chart of obtaining the safety constraint boundary.

[0050] Fig. 4 The flow chart of generating the equivalent throttle feature parameters. Detailed Implementation

[0051] 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.

[0052] 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.

[0053] 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.

[0054] Reference Figs. 1-4 This is one embodiment of the present invention, which provides a method for regulating formation pressure during offshore oilfield reinjection based on environmental protection synergy, comprising the following steps:

[0055] S1. Collect the reinjection discharge rate, reinjection pressure, and operating time under the operating conditions of the throttle valve, the tree channel, and the reinjection fluid being transported to the formation along the water injection string. Perform unified verification and operating condition correlation analysis to generate a set of basic reinjection operating parameters.

[0056] S1.1: Perform unified time alignment and consistency verification on reinjection displacement, reinjection pressure and running time to generate valid reinjection operation data;

[0057] Specifically, the reinjection volume, reinjection pressure, and operating time are organized according to a unified time identifier, so that the reinjection volume and reinjection pressure form a one-to-one correspondence in the operating time dimension. According to the operating time sequence, the synchronization and continuity of the reinjection volume change process and the reinjection pressure change process in the corresponding operating time period are compared and verified. It is checked whether the reinjection volume change process and the reinjection pressure change process maintain a synchronous continuity in the corresponding operating time period, and segments with missing records and abrupt changes in the operating time are removed. The verified reinjection volume, reinjection pressure, and corresponding operating time are then integrated and correlated with the operating conditions to generate valid reinjection operating data.

[0058] S1.2: The effective reinjection operation data is stabilized to obtain stable reinjection pressure data and stable reinjection discharge data;

[0059] Specifically, the effective reinjection operation data is continuously organized according to the operation time sequence, so that the reinjection pressure and reinjection discharge are continuously connected on a unified operation time axis. The high-frequency fluctuations in the reinjection process are compressed in time continuity, so that the changes in reinjection pressure and reinjection discharge are smooth and continuous in the operation time, and stable reinjection pressure data and stable reinjection discharge data that reflect the characteristics of stable reinjection conditions are obtained.

[0060] S1.3: Based on the stable reinjection pressure data and stable reinjection discharge data, calculate the reinjection pressure change rate and reinjection discharge stability parameters, and perform correlation analysis between the reinjection pressure change rate and reinjection discharge stability parameters and the running time to obtain the operating condition characteristic parameters;

[0061] Specifically, based on stable reinjection pressure data and stable reinjection discharge data, the reinjection pressure change rate and reinjection discharge stability parameters are calculated. The reinjection pressure change rate and reinjection discharge stability parameters are correlated and compared according to the operating time sequence and the operating conditions are merged. In this way, the differences in operating conditions corresponding to the degree of reinjection pressure change and the stability level of reinjection discharge are clarified in different operating time periods, and the operating condition characteristic parameters are obtained.

[0062] The expressions for calculating the reinjection pressure change rate and the reinjection displacement stability parameters are as follows:

[0063] ;

[0064] The expression for calculating the reinjection displacement stability parameter is:

[0065] ;

[0066] ;

[0067] in, Indicates the first The rate of change of reinjection pressure at each sampling time is expressed in MPa / s. The data indicates that the steady-state reinjection pressure is in the first... Stable reinjection pressure data at each sampling time, in MPa; The data indicates that the steady-state reinjection pressure is in the first... Stable reinjection pressure data at each sampling time, in MPa; Indicates the first The running time at each sampling moment, in seconds; Indicates the first The running time at each sampling moment is expressed in seconds. This represents the sample sequence number index during runtime; This represents the parameter indicating the stability of the reinjection displacement. represents the total number of sampling points contained in the selected continuous running time period; represents the sampling point serial number index in the selected continuous running time period; represents the steady backflow displacement data corresponding to the sampling point in the continuous running time period; represents the average level of the steady backflow displacement data in the selected continuous running time period.

[0068] S1.4: uniformly package the steady backflow pressure data, the steady backflow displacement data, the running time and the operating condition characteristic parameters to generate a backflow basic operating parameter set.

[0069] Specifically, the steady backflow pressure data and the steady backflow displacement data are correspondingly arranged in the order of running time, so that the steady backflow pressure data and the steady backflow displacement data form a stable corresponding relationship in the running time dimension; the operating condition characteristic parameters corresponding to each running time period are synchronously collected with the steady backflow pressure data and the steady backflow displacement data, and are uniformly collected and arranged in the order of running time, so that the running time, the steady backflow pressure data, the steady backflow displacement data and the operating condition characteristic parameters are consistently arranged in the same record structure to generate the backflow basic operating parameter set.

[0070] It should be noted that the steady backflow pressure data is the stable pressure state of the wellhead injection pressure in the running time dimension, which is used to reflect the actual driving pressure formed before the injection fluid enters the wellbore.

[0071] S2, analyze the flow characteristics of the choke valve and the Christmas tree based on the backflow basic operating parameter set to obtain equivalent choke characteristics parameters, and correct the wellhead injection pressure according to the equivalent choke characteristics parameters to obtain the effective injection pressure.

[0072] S2.1: based on the backflow basic operating parameter set, perform digital twin instantiation processing on the backflow operating condition of the choke valve and the Christmas tree to form the internal flow operating condition state of the choke valve and the Christmas tree;

[0073] Specifically, based on the backflow basic operating parameter set, the backflow displacement and the backflow pressure corresponding to the running time are one-to-one mapped according to the actual channel structure of the choke valve and the Christmas tree, so that the backflow displacement and the backflow pressure form a flow distribution relationship corresponding to the actual operating state in the choke valve throttling channel, the Christmas tree main channel and the branch channel, and the mapping results under different running time periods are continuously spliced, so that the flow state of the choke valve and the Christmas tree in the backflow process forms a continuous operating condition mapping with the running time, forming the internal flow operating condition state of the choke valve and the Christmas tree.

[0074] S2.2: under the constraint of the throttle valve and the internal flow condition of the Christmas tree, performing operator mapping reasoning on the throttle valve and the internal flow area of the Christmas tree to obtain the pressure change and flow rate change state of each flow area;

[0075] Specifically, under the constraint of the throttle valve and the internal flow condition of the Christmas tree, the throttle valve and the internal flow path of the Christmas tree are divided into multiple flow areas, and the flow state is mapped to each flow area along the flow path according to the corresponding relationship between the reinjection basic operating parameter set and the reinjection displacement and pressure in each flow area, so that the flow state formed in the previous flow area is naturally extended to the next flow area, thereby gradually obtaining the corresponding pressure change and flow rate change state of each flow area under the continuous structure constraint of the throttle valve and the internal passage of the Christmas tree.

[0076] S2.3: correcting the physical consistency of the pressure change and flow rate change state of each flow area, and simultaneously identifying the rotational dominant flow characteristics of the throttle part, the Christmas tree corner and the valve cavity area;

[0077] Specifically, based on the pressure change and flow rate change state of each flow area, the change connection relationship between adjacent flow areas is uniformly checked, so that the pressure change and flow rate change state remain continuous and consistent on the throttle valve and the internal flow path of the Christmas tree, and the local change that does not conform to the connection relationship is uniformly adjusted, so that the pressure change and flow rate change state of each flow area match the spatial form of the throttle part, the Christmas tree corner and the valve cavity area; according to the throttle part and the marked corner area and valve cavity area position inside the Christmas tree, the change form of the flow rate change state in the turning position and the cavity space is identified synchronously, so that the rotational dominant flow characteristics in the throttle part, the Christmas tree corner and the valve cavity area are identified.

[0078] S2.4: time correlation and scale unification of the rotational dominant flow characteristics and the local pressure change characteristics inside the Christmas tree to obtain equivalent throttling characteristic parameters.

[0079] Specifically, the rotational dominant flow characteristics are aligned and arranged according to the running time sequence and the local pressure change characteristics of the corresponding positions of the throttle valve and the Christmas tree, so that the rotational dominant flow characteristics are consistent with the local pressure change in the time dimension, and the rotational dominant flow characteristics and the local pressure change characteristics in different running time periods are uniformly merged, so that the rotational dominant flow characteristics and the local pressure change characteristics form a stable corresponding relationship on the same scale level, forming equivalent throttling characteristic parameters that can reflect the throttling influence degree inside the Christmas tree.

[0080] S2.5: time correlation of the wellhead injection pressure in the reinjection basic operating parameter set and the equivalent throttling characteristic parameters to establish a throttling correction relationship;

[0081] Specifically, the wellhead injection pressure in the reinjection basic operation parameter set is sorted according to the operation time sequence, and is one-to-one corresponding with the equivalent throttle characteristic parameter under the same operation time identifier, so that the wellhead injection pressure is stably corresponding with the corresponding equivalent throttle characteristic parameter in each operation time period; the corresponding conditions of the wellhead injection pressure change and the equivalent throttle characteristic parameter change in different operation time periods are uniformly merged and sorted, forming a throttle correction relationship capable of reflecting the change of the wellhead injection pressure in different operation time periods affected by the throttle.

[0082] S2.6: According to the throttle correction relationship, the change of the wellhead injection pressure in the reinjection process is corrected to form the wellhead pressure evolution state;

[0083] Specifically, according to the throttle correction relationship, the wellhead injection pressure change corresponding to different operation times in the reinjection process is compared segment by segment, so that the wellhead injection pressure in each operation time period is consistent with the change of the throttle reflected by the throttle correction relationship, and the wellhead injection pressure deviating from the throttle correction relationship is sequentially calibrated. The calibrated wellhead injection pressure is continuously connected and uniformly sorted according to the operation time, so that the change process of the wellhead injection pressure with the operation time is unified and standardized in time continuity and change trend, forming the wellhead pressure evolution state.

[0084] S2.7: The wellhead pressure evolution state is used as a correction basis to uniformly correct the wellhead injection pressure to obtain the effective injection pressure.

[0085] Specifically, the wellhead injection pressure and the pressure change process in the corresponding time period in the wellhead pressure evolution state are compared segment by segment according to the operation time sequence, the change segment of the wellhead injection pressure inconsistent with the wellhead pressure evolution state is uniformly corrected, so that the wellhead injection pressure is consistent with the wellhead pressure evolution state in change amplitude and change continuity, and the corrected wellhead injection pressure is reorganized according to the operation time to form the effective injection pressure capable of truly reflecting the actual injection condition in the reinjection process.

[0086] S3, based on the effective injection pressure, performing formation pressure dynamic response analysis, judging the formation pressure change trend and identifying abnormal pressure rise characteristics, obtaining pressure response results.

[0087] S3.1: The change process of the effective injection pressure with time is sorted and sequenced to construct an injection pressure change sequence;

[0088] Specifically, the effective injection pressure is arranged in order of corresponding operation time, so that the effective injection pressure forms a continuous corresponding relationship in the operation time dimension, and the change of the effective injection pressure in each operation time period is arranged in turn, the change relationship of the effective injection pressure is arranged through the unified operation time mark, so that the change process of the effective injection pressure with the operation time has continuity and integrity, and the injection pressure change sequence is formed.

[0089] S3.2: Based on the injection pressure change sequence, the dynamic response analysis of the change of the formation pressure with time is carried out, and the pressure response result is obtained.

[0090] Specifically, the injection pressure change sequence is compared with the corresponding operation time in sections, so that the injection pressure change sequence is consistent with the formation stress process in the operation time dimension; according to the change of the injection pressure change sequence, the change process of the formation pressure with time is continuously mapped, the change of the formation pressure in different operation time periods is obtained, and the overall change trend of the formation pressure with time and the abnormal pressure rise form in the operation process are summarized in the change process, and the pressure response result containing the formation pressure dynamic response, the formation pressure change trend and the abnormal pressure rise form is formed.

[0091] S4, based on the pressure response result, the injection pressure under the condition of no flowback is executed for the injection pressure under the current injection condition, and the injection pressure state is obtained.

[0092] S4.1: According to the pressure response result, the pressure change range that the formation can withstand under the current injection condition is determined;

[0093] Specifically, according to the formation pressure dynamic response, the formation pressure change trend and the abnormal pressure rise form in the pressure response result, the overall trend and local fluctuation of the formation pressure change in different operation time periods are compared and sorted, the change interval of the formation pressure that keeps stable change and does not trigger the abnormal pressure rise form under the continuous injection condition is determined, and the change interval is taken as the pressure change range that the formation can continuously withstand under the current injection condition.

[0094] S4.2: Under the constraint of the pressure change range, the change process of the injection pressure is regulated and planned under the condition of no flowback, and the injection pressure change process is obtained.

[0095] Specifically, under the constraint of the pressure change range, the operation state in which the medium does not flow back under the current reinjection working condition is taken as a premise condition, the change process of the reinjection pressure with the operation time is sequentially combed, the pressure increase stage, the pressure stabilization stage and the adjustment stage of the reinjection pressure are all limited within the pressure change range, and according to the risk characteristics reflected by the abnormal pressure increase mode in the pressure response result, the change sequence and the change amplitude of the reinjection pressure are coordinated and arranged, so that the reinjection pressure remains continuous transition without being higher than the pressure change range in the operation process, and the reinjection pressure change process is obtained.

[0096] S4.3: uniformly regulating the reinjection pressure according to the reinjection pressure change process to form a reinjection pressure state.

[0097] Specifically, according to the reinjection pressure change process, the change sequence and the change amplitude of the reinjection pressure with the operation time are uniformly regulated, so that the reinjection pressure in the pressure increase stage, the pressure stabilization stage and the adjustment stage is strictly consistent with the operation state defined by the reinjection pressure change process, and the change rhythm of the reinjection pressure is consistent with the reinjection pressure change process in the continuous reinjection process, so that the reinjection pressure is continuously in a stable and controllable operation mode in the entire operation time range, and the reinjection pressure state is formed.

[0098] S5, under the reinjection pressure state, the pressure response result and the pressure bearing state of the choke valve, the Christmas tree and the injection string in the reinjection process are verified to obtain a safety constraint boundary, the safety constraint boundary is matched with a preset formation allowable pressure interval to obtain an optimal combination of the reinjection pressure and the reinjection flow rate.

[0099] S5.1: taking the reinjection pressure state as a unified working condition basis, the safety of the formation pressure response and the formation pressure change state is evaluated to form a formation side safety evaluation result;

[0100] Specifically, the reinjection pressure state is taken as a unified working condition basis, the operation time period corresponding to the reinjection pressure state and the formation pressure response are aligned and arranged, so that the formation pressure response forms a checkable formation pressure change state under the constraint of the reinjection pressure state; the formation pressure change state is consistently checked with the abnormal pressure increase mode in the formation pressure response, and it is determined whether the formation pressure change state exceeds the preset formation allowable pressure interval under the reinjection pressure state; when there is an exceeding case, the corresponding operation time period is identified as a pressure risk section, and when there is no exceeding case, the corresponding operation time period is identified as a pressure safe section; the formation pressure safe section and the pressure risk section of each operation time period are uniformly merged to form a formation side safety evaluation result.

[0101] It should be noted that the allowable formation pressure range is set based on the dynamic response of formation pressure, the trend of formation pressure change, and the constraints on formation integrity and long-term stability caused by abnormal pressure rise patterns. The specific setting steps include: under reinjection conditions, summarizing the changes in formation pressure over time according to the injection pressure change sequence, identifying pressure ranges where the formation can maintain stable pressure and without abnormal pressure rise patterns during continuous reinjection; comparing and screening pressure sections that have not experienced formation anomalies, have not significantly deteriorated seepage capacity, and have remained stable during the reinjection process in historical reinjection phases, selecting pressure ranges that maintain stable performance across multiple operating time periods as the allowable formation pressure range; the exemplary range is 6.36 MPa to 8.99 MPa. The allowable wellhead injection pressure range of 6.36 MPa to 6.74 MPa corresponds to the scenario of "two wells injecting water simultaneously, with a single well injection rate of 15,000 m³ / d". Under the reinjection condition of a single well injecting water at a rate of 30,000 m³ / d, the corresponding allowable wellhead injection pressure range is 8.61 MPa to 8.99 MPa. When the wellhead injection pressure is below 6.36 MPa, the dynamic response amplitude of the formation pressure is relatively small, and the pressure change during reinjection is difficult to form a continuous and stable response characteristic, and the reinjection discharge is prone to significant fluctuations over time. When the wellhead injection pressure is above 8.99 MPa, the abnormal pressure rise characteristics in the dynamic response of the formation pressure are significantly enhanced, the formation pressure change trend deviates from the stable zone, and the formation integrity risk accumulates with the increase of operating time.

[0102] S5.2: Verify the pressure-bearing status of the throttle valve, the wellhead, and the water injection tubing, and estimate the pressure loss status of the sand control tubing during the reinjection process to form the equipment-side safety assessment results.

[0103] Specifically, under the reinjection pressure condition, the reinjection pressure condition within the corresponding operating time period is aligned with the channel positions of the throttle valve, Christmas tree, and water injection tubing. This ensures that the reinjection pressure condition forms a verifiable pressure condition record at the actual pressure-bearing locations of the throttle valve, Christmas tree, and water injection tubing. The pressure condition record is then compared segment by segment with the preset equipment pressure tolerance range to determine whether the pressure levels of the throttle valve, Christmas tree, and water injection tubing are within the equipment pressure tolerance range for each operating time period. Combining the reinjection pressure condition at the end of the water injection tubing, the reinjection discharge rate, and the structural dimensions and layout information of the sand control tubing, the pressure loss of the reinjected fluid within the sand control tubing is estimated, resulting in the pressure loss state of the sand control tubing during the reinjection process. Finally, the pressure verification results of the throttle valve, Christmas tree, and water injection tubing are unified and merged with the pressure loss state of the sand control tubing to form the equipment-side safety assessment result.

[0104] It should be noted that the device pressure allowable range is set based on the balance requirements of the actual pressure bearing condition and the structural bearing safety demand of the choke valve, the Christmas tree, the water injection string and the sand control string in the back injection process under the back injection pressure state. The specific setting steps include: in the back injection operation process, combining the back injection basic operation parameter set and the pressure response result, the change situation of the pressure bearing level formed by the back injection pressure acting on the choke valve, the Christmas tree, the water injection string and the sand control string in different operation time periods is determined, and the pressure bearing condition required for the device to maintain structural stability and bearing reliability under long-term back injection condition is compared, and the pressure interval that can meet the back injection continuity and structural safety at the same time is selected as the device pressure allowable range; the exemplary value range is 6.36MPa to 15.00MPa, the lower limit 6.36MPa is taken from the lower limit of the allowable wellhead injection pressure under the condition of simultaneous water injection of two wells, which is used to ensure that the choke valve, the Christmas tree, the water injection string and the sand control string have the basic pressure difference driving required for continuous back injection; the upper limit 15.00MPa is taken from the injection pressure grade 15MPa on the device platform side, which is used to limit the device side from entering the abnormal section; when the pressure level is lower than 6.36MPa, the back injection displacement adjustment space is limited and the stability decreases; when the pressure level is higher than 15.00MPa, the erosion of the throttle part is aggravated, the stress of the Christmas tree connection part is abnormal, and the long-term bearing reliability of the water injection string and the sand control string decreases.

[0105] S5.3: The formation side safety evaluation result and the device side safety evaluation result are uniformly aligned and associated analyzed, and the cooperative constraint relationship between the formation safety requirement and the device bearing capacity is identified;

[0106] Specifically, the formation side safety evaluation result and the device side safety evaluation result are uniformly aligned according to the operation time period corresponding to the back injection pressure state, so that the formation pressure safety level in each operation time period and the pressure safety level of the choke valve, the Christmas tree, the water injection string and the sand control string in the back injection process form a one-to-one correspondence; the formation side safety evaluation result and the device side safety evaluation result in the same operation time period are compared and checked to determine whether the formation safety requirement and the device bearing capacity meet the preset formation allowable pressure interval and device pressure allowable range at the same time under different back injection pressure states; when both are in the cooperative satisfaction section, it is identified as the cooperative satisfaction section, when any one is in the risk section, it is identified as the cooperative limitation section, and the cooperative satisfaction section and the cooperative limitation section are uniformly merged to identify the cooperative constraint relationship between the formation safety requirement and the device bearing capacity.

[0107] S5.4: According to the cooperative constraint relationship, the pressure allowable range that meets the formation side safety evaluation result and the device side safety evaluation result at the same time is determined, and the safety constraint boundary is obtained.

[0108] Specifically, according to the cooperative constraint relationship, the reinjection pressure states identified as the cooperative satisfaction section in each operation time period are centrally arranged, the reinjection pressure states that simultaneously satisfy the formation side safety evaluation result and the equipment side safety evaluation result form a continuous available pressure section, and the upper and lower boundaries of the pressure section in the operation time dimension are uniformly summarized to determine the pressure allowable range that neither exceeds the preset formation allowable pressure interval nor exceeds the preset equipment pressure-bearing allowable range under the current reinjection working condition, and the pressure allowable range is taken as the safety constraint boundary.

[0109] It should be noted that the pressure allowable range is set based on the requirement that the formation side safety evaluation result and the equipment side safety evaluation result are simultaneously satisfied according to the cooperative constraint relationship; an exemplary value range is 6.36 MPa to 8.99 MPa, when the reinjection pressure is lower than 6.36 MPa, the reinjection driving force is insufficient, the reinjection discharge capacity improvement space is limited, and the reinjection process fluctuation and the reinjection stability are prone to decline; when the reinjection pressure is higher than 8.99 MPa, the reinjection pressure will exceed the controllable pressure section corresponding to the formation side safety evaluation result, and the pressure-bearing level of the choke valve and the pipe string will be significantly increased, which is prone to cause abnormal pressure rise characteristics and increase the safety risk in the reinjection process.

[0110] S5.5: The safety constraint boundary is uniformly aligned with the preset formation allowable pressure interval to determine the feasible pressure range available for reinjection control under the current reinjection working condition;

[0111] Specifically, the safety constraint boundary and the preset formation allowable pressure interval are uniformly aligned according to the operation time period corresponding to the reinjection pressure state, so that the safety constraint boundary and the preset formation allowable pressure interval form a pressure range that can be directly compared in the time dimension, and the pressure section that simultaneously falls into the safety constraint boundary and the preset formation allowable pressure interval is identified in each operation time period. The pressure section is continuously arranged and merged to determine the feasible pressure range.

[0112] S5.6: In the feasible pressure range, the reinjection pressure and the corresponding reinjection discharge capacity are screened and constrained to form a candidate combination interval that satisfies the safety condition;

[0113] Specifically, in the feasible pressure range, the reinjection pressure and the corresponding reinjection discharge capacity are compared and arranged according to the operation time period corresponding to the reinjection pressure state, so that each reinjection pressure level corresponds to a clear reinjection discharge capacity change section, and the combination section that simultaneously falls into the feasible pressure range is identified. The reinjection discharge capacity section that does not fall into the feasible pressure range and does not match the reinjection pressure state is excluded, the reinjection pressure and reinjection discharge capacity combination section that simultaneously satisfies the feasible pressure range and has continuous availability under the current reinjection working condition is retained, and the candidate combination interval is formed.

[0114] S5.7: Select the injection pressure and injection flow rate combination that can achieve the optimal injection capacity without breaking the feasible pressure range from the candidate combination interval, to obtain the optimal injection pressure and injection flow rate combination.

[0115] Specifically, in the candidate combination interval, the injection pressure and injection flow rate combinations are sequentially compared according to the operating time period corresponding to the injection pressure state, and the combination section that continuously falls within the feasible pressure range and maintains stable and continuous injection flow rate level throughout the operating time period is preferentially selected. When there are multiple combination sections that meet the conditions, the injection flow rates corresponding to the same injection pressure level of each combination section are compared, and the injection pressure and injection flow rate combination with a higher overall injection flow rate level and a consistent and continuous operating process is selected as the optimal injection pressure and injection flow rate combination.

[0116] S6, continuously inject the optimal injection pressure and injection flow rate combination to obtain a new injection pressure, compare the new injection pressure with the pressure response result, and generate a pressure control parameter set.

[0117] S6.1: Set the optimal injection pressure and injection flow rate combination as the control reference of the current injection operating condition, and continuously adjust the injection process under the constraint of the control reference to form a stable injection operating state;

[0118] Specifically, the optimal injection pressure and injection flow rate combination is set as the control reference of the current injection operating condition, and the control reference is aligned with the corresponding operating time period, so that the injection pressure and injection flow rate have a unified reference standard during the operating process. Under the constraint of the control reference, the injection pressure and injection flow rate in the injection process are continuously coordinated according to the change order corresponding to the optimal injection pressure and injection flow rate combination, so that the actual injection process gradually conforms to the control reference and maintains a continuous change process, thereby maintaining the injection pressure and injection flow rate within the control reference range throughout the operating time period, forming a stable injection operating state.

[0119] S6.2: Continuously record the change process of the injection pressure over time under the stable injection operating state to obtain a new injection pressure.

[0120] Specifically, the injection pressure is aligned with the corresponding operating time, and the change of the injection pressure is continuously collected and sequentially arranged according to the operating time order, so that the injection pressure forms a continuous and complete time corresponding record in each operating time period, and the injection pressure state of each time period under the stable injection operating state is retained, to obtain a new injection pressure that can reflect the change of the injection pressure over time under the stable injection operating state.

[0121] S6.3: Align the new injection pressure with the pressure response result of the corresponding time period in time to form a pressure alignment sequence;

[0122] Specifically, in the stable reinjection operation state, the operation time period corresponding to the new reinjection pressure is aligned with the time identifiers of the formation pressure dynamic response, the formation pressure change trend and the abnormal pressure rise pattern in the pressure response result, so that the new reinjection pressure and the corresponding pressure response result form a one-to-one correspondence in each operation time period, and the corresponding relationship is continuously arranged in the order of operation time. The new reinjection pressure and the pressure response result of the corresponding time period are unified and arranged into a pressure alignment sequence with time continuity.

[0123] S6.4: Based on the pressure alignment sequence, the difference between the new reinjection pressure and the pressure response result is quantitatively analyzed to form a pressure deviation feature;

[0124] Specifically, based on the pressure alignment sequence, the formation pressure dynamic response, the formation pressure change trend and the abnormal pressure rise pattern in the new reinjection pressure and the corresponding pressure response result are compared in each operation time period, the difference between the new reinjection pressure and the pressure response result in each operation time period is summarized and arranged, and the difference in each operation time period is unified and collected in the dimensions of time continuity and change trend to form a pressure deviation feature that can reflect the difference degree and change law between the new reinjection pressure and the pressure response result.

[0125] S6.5: According to the pressure deviation feature, the reinjection pressure level in the stable reinjection operation state is characterized and summarized to form a pressure control parameter set.

[0126] Specifically, according to the pressure deviation feature, the operation time period corresponding to the pressure deviation feature is aligned with the reinjection pressure level in the stable reinjection operation state, the change of the reinjection pressure level in each operation time period relative to the change reflected by the pressure deviation feature is merged, the reinjection pressure levels with similar pressure deviation features form a clear corresponding relationship in the operation time dimension, and the reinjection pressure levels corresponding to different pressure deviation features in the stable reinjection operation state are unified and summarized, so as to extract a pressure control parameter set that can reflect the reinjection pressure control demand and control direction.

[0127] To sum up, by characterizing the flow characteristics of the choke valve and the internal flow characteristics of the Christmas tree and extracting equivalent choke characteristic parameters, the wellhead injection pressure can be corrected in the reinjection process, the effective injection pressure that can reflect the actual reinjection working condition is obtained, the representation of the reinjection pressure is no longer limited to the surface monitoring value, but can reflect the influence of the flow state of the choke valve and the internal flow of the Christmas tree on the pressure transmission, and the identification of the formation pressure dynamic response has a more reliable basis; the reinjection pressure regulation can closely match the real pressure change process of the formation, effectively support the pressure regulation decision under the condition of no return, and avoid the accumulation of deviation of the reinjection pressure from the formation response in the operation process; at the same time, a unified and continuous pressure correction basis is provided for the determination of the safety constraint boundary and the selection of the optimal combination of the reinjection pressure and the reinjection rate, so that the reinjection regulation realizes the unity among the efficiency, safety and stability.

[0128] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present application and not to limit the present application. Although the present application has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application, which should be covered in the scope of the claims of the present application.

Claims

1. A method for regulating formation pressure during offshore oilfield reinjection based on environmental protection synergy, characterized by: include, The data on reinjection discharge rate, reinjection pressure, and operating time under the conditions of throttle valve, tree channel, and reinjection fluid being transported to the formation along the water injection string are collected, and unified verification and operating condition correlation analysis are performed to generate a set of basic reinjection operating parameters. The flow characteristics inside the throttling valve and the wellhead are analyzed based on the basic operating parameter set of the reinjection system to obtain the equivalent throttling characteristic parameters. The wellhead injection pressure is then corrected based on the equivalent throttling characteristic parameters to obtain the effective injection pressure. Based on the effective injection pressure, dynamic response analysis of formation pressure is performed to determine the trend of formation pressure change and identify abnormal pressure rise characteristics, and to obtain pressure response results; Based on the pressure response results, pressure regulation is performed on the reinjection pressure under the current reinjection conditions without backflow to obtain the reinjection pressure status. Under the reinjection pressure condition, the pressure response results are verified and compared with the pressure bearing state of the throttle valve, the wellhead, and the water injection string during the reinjection process to obtain the safety constraint boundary. The safety constraint boundary is then matched with the preset formation allowable pressure range to obtain the optimal combination of reinjection pressure and reinjection discharge rate. The optimal combination of reinjection pressure and reinjection displacement is continuously reinjected to obtain a new reinjection pressure. The new reinjection pressure is then compared with the pressure response results to generate a pressure control parameter set.

2. The method for formation pressure control during offshore oilfield reinjection based on environmental protection synergy as described in claim 1, characterized in that: The steps for generating the basic operating parameter set for reinjection are as follows: Perform unified time alignment and consistency verification on reinjection displacement, reinjection pressure, and running time to generate valid reinjection operation data; The effective reinjection operation data is stabilized to obtain stable reinjection pressure data and stable reinjection discharge data; Based on stable reinjection pressure data and stable reinjection discharge data, the reinjection pressure change rate and reinjection discharge stability parameters are calculated, and the reinjection pressure change rate and reinjection discharge stability parameters are correlated with the running time to obtain the operating condition characteristic parameters. The stable reinjection pressure data, stable reinjection displacement data, operating time, and operating condition characteristic parameters are uniformly packaged to generate a set of basic reinjection operating parameters.

3. The method for formation pressure control during offshore oilfield reinjection based on environmental protection synergy as described in claim 2, characterized in that: The steps to obtain the equivalent throttling characteristic parameters are as follows: Based on the basic operating parameter set of reinjection, the reinjection conditions of the throttle valve and the wellhead are digitally twinned and instantiated to form the internal flow conditions of the throttle valve and the wellhead. Under the constraints of the flow conditions inside the throttle valve and the tree, operator mapping reasoning is performed on the flow regions inside the throttle valve and the tree to obtain the pressure and velocity changes in each flow region. Physical consistency correction is performed on the pressure and velocity changes in each flow region, and the rotation-dominant flow characteristics of the throttling part of the throttling valve, the tree angle, and the valve cavity region are identified simultaneously. By correlating the rotationally dominant flow characteristics with the local pressure change characteristics inside the throttling valve and the wellhead, and unifying the scale, equivalent throttling characteristic parameters are obtained.

4. The method for formation pressure control during offshore oilfield reinjection based on environmental protection synergy as described in claim 1, characterized in that: The steps to obtain effective injection pressure are as follows: By correlating the wellhead injection pressure with the equivalent throttling characteristic parameters in the basic reinjection operating parameter set over time, a throttling correction relationship is established. Based on the throttling correction relationship, the changes in wellhead injection pressure during the reinjection process are corrected to form the wellhead pressure evolution state; By using the wellhead pressure evolution state as the basis for correction, the wellhead injection pressure is uniformly corrected to obtain the effective injection pressure.

5. The method for formation pressure control during offshore oilfield reinjection based on environmental protection synergy as described in claim 4, characterized in that: The steps for obtaining the pressure response results are as follows: The process of effective injection pressure changing over time is organized and serialized to construct an injection pressure change sequence. Based on the injection pressure change sequence, dynamic response analysis is performed on the formation pressure change over time to obtain pressure response results.

6. The method for formation pressure control during offshore oilfield reinjection based on environmental protection synergy as described in claim 5, characterized in that: The steps to obtain the reinjection pressure state are as follows: Based on the pressure response results, determine the range of pressure variations that the formation can withstand under the current reinjection conditions; Under the constraint of pressure variation range, the control and planning of the reinjection pressure variation process under the condition of no backflow is carried out to obtain the reinjection pressure variation process; The reinjection pressure is uniformly regulated according to the change process of the reinjection pressure to form a reinjection pressure state.

7. The method for formation pressure control during offshore oilfield reinjection based on environmental protection synergy as described in claim 6, characterized in that: The steps to obtain the safety constraint boundary are as follows: Using the reinjection pressure state as a unified operating condition basis, a safety assessment is conducted on the formation pressure response and formation pressure change state to form a formation-side safety assessment result. The pressure-bearing status of the throttle valve, the wellhead, and the water injection tubing is checked, and the pressure loss status of the sand control tubing during the reinjection process is estimated to form the equipment-side safety assessment results. By unifying and correlating the results of the formation-side safety assessment with the results of the equipment-side safety assessment, we can identify the synergistic constraint relationship between formation safety requirements and equipment bearing capacity. Based on the collaborative constraint relationship, the allowable pressure range that simultaneously satisfies the safety assessment results on the formation side and the equipment side is determined, thus obtaining the safety constraint boundary.

8. The method for formation pressure control during offshore oilfield reinjection based on environmental protection synergy as described in claim 1, characterized in that: The steps to obtain the optimal combination of reinjection pressure and reinjection displacement are as follows: Align the safety constraint boundary with the preset formation allowable pressure range to determine the feasible pressure range that can be used for reinjection control under the current reinjection conditions. Within the feasible pressure range, the reinjection pressure and corresponding reinjection discharge are screened and constrained to form a candidate combination range that meets the safety conditions; The optimal combination of reinjection pressure and reinjection displacement is obtained by selecting the combination of reinjection pressure and reinjection displacement from the candidate combination range that can achieve the best reinjection capacity without exceeding the feasible pressure range.

9. The method for formation pressure regulation during offshore oilfield reinjection based on environmental protection synergy as described in claim 8, characterized in that: The steps to obtain the new reinjection pressure are as follows: The optimal combination of reinjection pressure and reinjection displacement is set as the control benchmark for the current reinjection operating condition. Under the constraint of the control benchmark, the reinjection process is continuously adjusted to form a stable reinjection operating state. Under stable reinjection operation, the change process of reinjection pressure over time is continuously recorded to obtain the new reinjection pressure.

10. The method for formation pressure control during offshore oilfield reinjection based on environmental protection synergy as described in claim 1, characterized in that: The steps for generating the pressure control parameter set are as follows: The new reinjection pressure is aligned with the pressure response results of the corresponding time period to form a pressure alignment sequence. Based on the pressure alignment sequence, the difference between the new reinjection pressure and the pressure response result is quantitatively analyzed to form pressure deviation characteristics; Based on the pressure deviation characteristics, the reinjection pressure level under stable reinjection operation is characterized and summarized to form a pressure control parameter set.

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