A controlled pressure drilling method based on a controlled pressure window for formations with spillage and leakage

Abstract

The present invention relates to the technical field of pressure-controlled drilling for oil and gas development, and in particular to a pressure-controlled drilling method for a formation with coexisting leakage and spillage based on a controllable pressure window. The technical solution comprises the following steps: determining the formation pressure coefficient and pressure window; judging whether the pressure window is safe based on monitoring data and the density of the drilling fluid used on site; if the pressure window is within the safe pressure window, maintaining normal drilling; otherwise, entering the controllable safety window calculation process; determining the maximum controllable leakage rate based on the actual leakage volume and the on-site drilling fluid mud supply capacity; determining the maximum controllable overflow rate based on the on-site wellhead back pressure control capacity; forming a controllable safety density window; after obtaining the controllable drilling fluid safety density window and the bottomhole pressure range, updating the safety density window, and drilling under the condition of maintaining micro-leakage and micro-overflow in the coexisting leakage formation. The present invention implements a pressure-controlled drilling method within the controllable pressure window, thereby ensuring operational safety.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas development pressure-controlled drilling, and in particular to a pressure-controlled drilling method based on a formation with coexisting spillage and controllable pressure windows. Background Art

[0002] As oil and gas development expands into deepwater and deep sea, the geological conditions encountered during drilling and completion are becoming increasingly complex. The narrow safe pressure window is particularly problematic during drilling, making it difficult to precisely control wellbore pressure within this window, compromising operational safety. This is particularly true in specialized formations like sandstone oil and gas, where complex conditions prone to both spills and leaks are common. Simply adjusting drilling fluid density or using traditional pressure control methods is insufficient to meet operational requirements.

[0003] like Figure 1 As shown in the figure, under extreme conditions such as the negative pressure window under the formation where leakage coexists, the mud pressure may exceed the pressure safety window when the pump is normally started or stopped, causing downhole leakage or fluid invasion.

[0004] The Chinese patent number is CN202110398750.9, and the patent name is "Operation method, operation system, medium and equipment for establishing a safe density window". The operation method includes the following steps: S1. Determine the formation parameters and operation parameters. S2. Collect the outlet flow rate and real-time formation pressure P during the circulation drilling operation. p2 S3, according to the formation parameters, operation parameters and real-time formation pressure P p2 , solve for the leakage pressure coefficient ρ L , drilling fluid density ρ1, real-time formation pressure coefficient ρ p2 and the leakage pressure coefficient ρ L and real-time formation pressure coefficient ρ p2 The difference △ between them. S4. Determine the safe density window based on the outlet flow rate and the difference △. The operating method for establishing a safe density window disclosed in the present invention can release formation energy, reduce formation pressure, and avoid the risk of alternating leakage in the drilled section due to abnormal high-pressure well drilling. However, the problems it has are: 1. This method relies on the gradual adjustment of the on-site drilling fluid density to achieve the expansion of the safe density window. The technology mentions the specific steps of "continue to reduce the drilling fluid density ρ1 to increase the outlet flow rate, thereby continuing to reduce the real-time formation pressure coefficient ρ p2 , and repeatedly determines whether the outlet flow rate exceeds the threshold until the obtained safe density window meets the drilling operation requirements. This is an adjustment measure that relies on passive response. This process is highly dependent on passive feedback from field monitoring data and requires multiple rounds of adjustments and real-time observation of the outlet flow rate. This results in cumbersome operation procedures, delayed response, low implementation efficiency, and a significant lag risk when underground conditions change frequently.

[0005] 2. This technology adjusts the real-time formation pressure coefficient ρ p2 The lower limit of the safety density window is lowered, but the loss pressure coefficient is not corrected or adaptively predicted, resulting in limited window expansion capabilities. When the formation loss pressure is close to the formation pressure, simply lowering the lower limit is difficult to meet the operational requirements under extremely narrow window conditions. The window control strategy lacks systematic and two-way adjustment capabilities.

[0006] 3. In complex downhole environments, wellbore pressure is susceptible to factors such as formation heterogeneity, encountering unusual formations, or sudden geological changes, potentially leading to unsteady-state events such as sudden overflows or leaks. However, this technology lacks a dynamic pressure regulation mechanism and cannot support real-time pressure control and emergency response during operations, thus lacking the supporting managed pressure drilling capabilities. Summary of the Invention

[0007] The purpose of the present invention is to address the above-mentioned defects of the existing technology and provide a pressure-controlled drilling method for formations with co-existing overflows and leakages based on a controllable pressure window. In formations with a narrow safety window, facing the co-existing overflow and leakage conditions, the limit value of the bottom hole pressure is calculated by judging the traditional pressure window and predicting the degree of controllable micro-leakage and micro-overflow, and the safety pressure window is expanded to realize a pressure-controlled drilling method within the controllable pressure window, thereby ensuring operation safety.

[0008] The present invention provides a method for pressure-controlled drilling based on a controlled pressure window with leakage coexisting in a formation, and the technical solution includes the following steps:

[0009] 1. Determine the formation pressure coefficient and pressure window based on the formation pore pressure data and lost circulation pressure data, as well as the acquired wellbore trajectory and downhole vertical depth data;

[0010] 2. Use monitoring equipment: inlet flow meter, casing pressure sensor, outlet flow meter to obtain wellhead casing pressure data and drilling fluid flow;

[0011] 3. Determine whether the pressure window is safe based on monitoring data and the density of the drilling fluid used on site;

[0012] If the drilling fluid density is within the safe pressure window, normal drilling is maintained; if it is not within the safe pressure window, the controllable safety window calculation process is entered;

[0013] 4. Determine the maximum controllable loss rate based on the actual loss volume and the on-site drilling fluid and mud supply capacity; determine the maximum controllable overflow rate based on the on-site wellhead back pressure control capacity;

[0014] The expansion range of drilling fluid density under controllable micro-overflow and micro-leakage is obtained, which constitutes a controllable safety density window.

[0015] 5. After obtaining the safe density window and bottom hole pressure range of the controllable drilling fluid, update the safe density window and drill under the condition of micro-leakage and micro-overflow in the formation while overflow and leakage coexist;

[0016] During the drilling process, the wellbore flow rate is monitored in real time and the current annular pressure loss P is calculated. f ;

[0017] The bottom hole pressure P during normal circulation is calculated according to the following formula b :

[0018] (V),

[0019] Among them, P f is the calculated current annular pressure loss; P a The wellhead back pressure value set on site;

[0020] 6. Using real-time bottom hole pressure P b and bottom hole pressure P under leakage b1 and overflow bottom hole flow pressure P b2 Compare and judge whether it exceeds the range of controllable micro overflow or micro leakage;

[0021] When P b >P b1 , beyond the controllable micro-leakage range, it is necessary to reduce the wellhead back pressure and return to the fifth step for real-time monitoring and calculation;

[0022] When P b <P b2 , beyond the range of controllable micro-overflow, it is necessary to increase the wellhead back pressure and return to the fifth step for real-time monitoring and calculation;

[0023] When P b If the bottom hole pressure is within the range of controllable micro-overflow or micro-leakage, return to step 5 for real-time monitoring and calculation;

[0024] 7. After reaching the target well section, perform cementing operations.

[0025] Preferably, the specific method of step 4 is as follows:

[0026] (1) Calculate the bottom hole pressure P under micro leakage according to the following formula b1 :

[0027] (I),

[0028] Where Q1 is the loss rate, m³ / h; P is the formation pressure; α is the loss calculation coefficient; n is the loss calculation index related to the flow properties of the drilling fluid;

[0029] (2) Calculate the bottom hole flow pressure P under micro overflow according to the following formula: b2:

[0030] (II),

[0031] Among them, Q k is the overflow gas production rate, m³ / h; P is the formation pressure; β is the gas production flow coefficient; m is the gas production index;

[0032] (3) Calculate the annular pressure loss P according to the following formula: f :

[0033] (III),

[0034] Where L is the length of the annulus, Q is the flow rate of the drilling fluid, ρ is the density of the drilling fluid obtained from field data, D is the equivalent diameter of the annulus, and f is the friction coefficient;

[0035] (4) Calculate the drilling fluid density under micro-overflow or micro-leakage according to the following formula, where P b For micro leakage and micro overflow, P is introduced respectively. b1 and P b2 :

[0036] (IV),

[0037] Where H is the well depth, P 井口 is the wellhead casing pressure, P f is the annular pressure loss.

[0038] The specific method of step three is as follows:

[0039] (1) Drilling fluid density needs to be converted into drilling fluid pressure;

[0040] (2) Calculate the drilling fluid pressure P in the wellbore 钻井液 =0.0098ρH+P f +P a ,

[0041] P 钻井液 is the drilling fluid pressure in the wellbore, MPa; ρ is the drilling fluid density, g / cm 3 ; H is the height of the liquid column, m; P f is the annular pressure loss; P a The wellhead back pressure value set on site;

[0042] (3) Calculation of drilling fluid pressure coefficient P 钻井液系数 =P 钻井液 / P0;

[0043] (4) If P is satisfied 地层系数 ≤P 钻井液系数 ≤P 漏失系数 , it is within the safe pressure window.

[0044] Preferably, in step six, the pressure regulation operation method after exceeding the controllable micro-overflow or micro-leakage range is as follows:

[0045] (1) When the micro-leakage exceeds the controllable range, the wellhead back pressure needs to be reduced. Specifically:

[0046] ① Inform the throttle manifold operator on duty to slowly open the throttle valve. The adjustment range each time should not exceed 3-5% of the full stroke of the throttle valve.

[0047] ②After each adjustment, observe the trend of data changes for one minute to determine whether the leakage has been reduced;

[0048] (2) When the flow exceeds the controllable micro-overflow range, it is necessary to increase the wellhead back pressure, specifically:

[0049] ① Inform the throttle manifold operator on duty to slowly close the throttle valve. The adjustment range each time should not exceed 3-5% of the full stroke of the throttle valve.

[0050] ②After each adjustment, observe the data change trend for one minute to determine whether the overflow is slowed down;

[0051] ③ If overflow continues, increase the monitoring frequency and prepare the well killing procedure in advance if necessary.

[0052] Preferably, the specific method of step one is as follows:

[0053] (1) Prepare the original data and unify the units: pressure is unified into MPa and depth is unified into m;

[0054] (2) Calculate the hydrostatic pressure P0=0.0098ρ0H,

[0055] P0 is the hydrostatic pressure, MPa; ρ0 is the hydrostatic density, g / cm 3 ; H is the height of the liquid column, m;

[0056] (3) Calculation of formation pressure coefficient P 地层系数 =P 地层 / P0;

[0057] (4) Calculate the leakage pressure coefficient P 漏失系数 =P 漏失 / P0;

[0058] (5) Draw a graph of the pressure coefficient versus well depth.

[0059] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0060] This invention addresses the coexistence of overflow and leakage in formations with a narrow safety density window and proposes a controlled pressure drilling method based on a controllable pressure window to address the problem that the traditional safety pressure window range cannot meet the needs of field operations. In the face of the simultaneous existence of overflow and leakage risks, this invention, based on a thorough analysis of traditional safety window boundary determination methods, introduces an active prediction mechanism for the degree of controllable micro-leakage and micro-overflow. By predicting the extreme values ​​of bottomhole pressure under different working conditions, the upper and lower limits of the safety window are further expanded, thereby achieving more adaptable controlled pressure drilling operations.

[0061] Unlike existing passive response control methods that primarily adjust the lower limit of the safety window based on real-time formation pressure, the present invention pre-models and quantitatively predicts pressure changes under controllable micro-leakage or micro-overflow conditions downhole, calculating an expanded safe density window range in one go to guide reasonable drilling fluid density selection. This ensures that the wellbore pressure is always controlled within the predicted window during operation and maintained at an acceptable micro-leakage or micro-gas intrusion state, thereby ensuring operational safety and improving drilling efficiency.

[0062] Furthermore, considering the ongoing risk of overflow and leakage coexisting under narrow window overflow and leakage conditions, the present invention further introduces real-time bottomhole pressure monitoring and continuous calculation mechanisms after obtaining an expanded safety density window to dynamically assess whether the pressure deviates from the controllable range during the operation. Once the pressure is detected to be outside the predicted window range, the pressure control operation strategy that matches the window expansion result can be immediately triggered, making the pressure control response more accurate and timely, ensuring that the safety management process is highly consistent with the field operation, and significantly improving the guidance, predictability, and adaptability of the field pressure control operation.

[0063] The core advantage of the present invention lies in: through the active prediction, one-time calculation and real-time monitoring linkage mechanism, it realizes the maximum expansion of the safety density window and intelligent pressure control response, effectively making up for the shortcomings of the traditional safety window establishment method under extremely narrow safety window conditions, such as delayed response and frequent adjustments, and provides a more forward-looking and practical solution for pressure control drilling under complex formation conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 This is a schematic diagram of the narrow safety window of the present invention;

[0065] Figure 2 This is a schematic diagram of the controllable safety window of the present invention;

[0066] Figure 3 This is a flow chart of the controllable safety window determination calculation process and downhole pressure regulation determination process of the present invention;

[0067] Figure 4 This is a layout diagram of the controllable safety window managed pressure drilling system of the present invention;

[0068] In the above figure: 1. Drilling fluid tank; 2. Drilling pump; 3. Inlet flow meter; 4. BOP; 5. Casing pressure sensor; 6. Outlet flow meter; 7. Automatic pressure regulating device; 8. Mud pool. DETAILED DESCRIPTION

[0069] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0070] Example 1, the present invention provides a method for pressure-controlled drilling based on a controllable pressure window for leaking and spilling formations, comprising the following steps:

[0071] 1. Determine the formation pressure coefficient and pressure window based on the formation pore pressure data and lost circulation pressure data, as well as the acquired wellbore trajectory and downhole vertical depth data;

[0072] (1) Prepare the original data and unify the units: pressure is unified into MPa and depth is unified into m;

[0073] (2) Calculate the hydrostatic pressure P0=0.0098ρ0H,

[0074] P0 is the hydrostatic pressure, MPa; ρ0 is the hydrostatic density, g / cm 3 ; H is the height of the liquid column, m;

[0075] (3) Calculation of formation pressure coefficient P 地层系数 =P 地层 / P0;

[0076] (4) Calculate the leakage pressure coefficient P 漏失系数 =P 漏失 / P0;

[0077] (5) Draw a graph of the pressure coefficient versus well depth;

[0078] 2. Utilize monitoring equipment: an inlet flowmeter 3, a casing pressure sensor 5, and an outlet flowmeter 6 to obtain wellhead casing pressure data and drilling fluid flow rate. The inlet flowmeter 3 is located between the drilling pump 2 and the blowout preventer 4, and the inlet of the drilling pump 2 is connected to the drilling fluid tank 1. The casing pressure sensor 5 is installed between the oil pipe and the casing, and the outlet flowmeter 6 is installed on the pipeline connected to the outlet end of the wellhead assembly. The pipeline is then connected to the mud tank 8 via an automatic pressure regulating device 7.

[0079] 3. Determine whether the pressure window is safe based on monitoring data and the density of the drilling fluid used on site;

[0080] If the drilling fluid density is within the safe pressure window, maintain normal drilling; if it is not within the safe pressure window, enter the controllable safety window calculation process; the specific method is as follows:

[0081] (1) Drilling fluid density needs to be converted into drilling fluid pressure;

[0082] (2) Calculate the drilling fluid pressure P in the wellbore 钻井液 =0.0098ρH+P f +P a ,

[0083] P 钻井液 is the drilling fluid pressure in the wellbore, MPa; ρ is the drilling fluid density, g / cm 3 ; H is the height of the liquid column, m; P f is the annular pressure loss; P a The wellhead back pressure value set on site;

[0084] (3) Calculation of drilling fluid pressure coefficient P 钻井液系数 =P 钻井液 / P0;

[0085] (4) If P is satisfied 地层系数 ≤P 钻井液系数 ≤P 漏失系数 , it is within the safe pressure window;

[0086] 4. Determine the maximum controllable loss rate based on the actual loss volume and the on-site drilling fluid and mud supply capacity; determine the maximum controllable overflow rate based on the on-site wellhead back pressure control capacity;

[0087] The bottom hole pressure P under micro leakage is calculated according to the following formula b1 :

[0088] (I),

[0089] Where Q1 is the loss rate, m³ / h; P is the formation pressure; α is the loss calculation coefficient; n is the loss calculation index related to the flow properties of the drilling fluid;

[0090] The bottom hole flow pressure P under micro overflow is calculated according to the following formula b2 :

[0091] (II),

[0092] Among them, Q k is the overflow gas production rate, m³ / h; P is the formation pressure; β is the gas production flow coefficient; m is the gas production index;

[0093] Calculate the annular pressure loss P according to the following formula f :

[0094] (III),

[0095] Where L is the length of the annulus, Q is the flow rate of the drilling fluid, ρ is the density of the drilling fluid obtained from field data, D is the equivalent diameter of the annulus, and f is the friction coefficient;

[0096] The drilling fluid density under micro overflow or micro leakage is calculated according to the following formula: b For micro leakage and micro overflow, P is introduced respectively. b1 and P b2 :

[0097] (IV),

[0098] Where H is the well depth, P 井口 is the wellhead casing pressure, P f is the annular pressure loss;

[0099] It is concluded that the expansion range of drilling fluid density under micro-overflow and micro-leakage within the controllable range constitutes a controllable safety density window;

[0100] 5. After obtaining the safe density window and bottom hole pressure range of the controllable drilling fluid, update the safe density window and drill under the condition of micro-leakage and micro-overflow in the formation while overflow and leakage coexist;

[0101] During the drilling process, the wellbore flow rate is monitored in real time, and the current annular pressure loss P is calculated according to formula (III) f ;

[0102] The bottom hole pressure P during normal circulation is calculated according to the following formula b :

[0103] (V),

[0104] Among them, P f is the calculated current annular pressure loss; P a The wellhead back pressure value set on site;

[0105] 6. Using real-time bottom hole pressure P b and bottom hole pressure P under leakage b1 and overflow bottom hole flow pressure P b2 Compare and judge whether it exceeds the range of controllable micro overflow or micro leakage;

[0106] When P b >P b1 , beyond the controllable micro-leakage range, it is necessary to reduce the wellhead back pressure and return to the fifth step for real-time monitoring and calculation;

[0107] When P b <P b2 , beyond the range of controllable micro-overflow, it is necessary to increase the wellhead back pressure and return to the fifth step for real-time monitoring and calculation;

[0108] When P b If the bottom hole pressure is within the range of controllable micro-overflow or micro-leakage, return to step 5 for real-time monitoring and calculation;

[0109] The pressure regulation method after exceeding the controllable micro-overflow or micro-leakage range is as follows:

[0110] (1) When the micro-leakage exceeds the controllable range, the wellhead back pressure needs to be reduced. Specifically:

[0111] ① Inform the throttle manifold operator on duty to slowly open the throttle valve. The adjustment range each time should not exceed 3-5% of the full stroke of the throttle valve.

[0112] ②After each adjustment, observe the trend of data changes for one minute to determine whether the leakage has been reduced;

[0113] (2) When the flow exceeds the controllable micro-overflow range, it is necessary to increase the wellhead back pressure, specifically:

[0114] ① Inform the throttle manifold operator on duty to slowly close the throttle valve. The adjustment range each time should not exceed 3-5% of the full stroke of the throttle valve.

[0115] ②After each adjustment, observe the data change trend for one minute to determine whether the overflow is slowed down;

[0116] ③ If overflow continues, increase monitoring frequency and prepare well killing procedures in advance if necessary;

[0117] 7. After reaching the target well section, perform cementing operations.

[0118] The above descriptions are merely some preferred embodiments of the present invention. Anyone skilled in the art may be able to modify the above-described technical solutions or convert them into equivalent technical solutions. Therefore, any corresponding simple modifications or equivalent transformations based on the technical solutions of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A pressure-controlled drilling method for a formation with coexisting spillage based on a controllable pressure window, characterized by: The following steps are involved:

1. Determine the formation pressure coefficient and pressure window based on the formation pore pressure data and lost circulation pressure data, as well as the acquired wellbore trajectory and downhole vertical depth data; 2. Using monitoring equipment: inlet flow meter (3), casing pressure sensor (5), outlet flow meter (6), obtain wellhead casing pressure data and drilling fluid flow rate; 3. Determine whether the pressure window is safe based on monitoring data and the density of the drilling fluid used on site; If the drilling fluid equivalent density is within the safe pressure window, maintain normal drilling; If it is not within the safe pressure window, the controllable safety window calculation process will be entered; 4. Determine the maximum controllable loss rate based on the actual loss volume and the on-site drilling fluid and mud supply capacity; Determine the maximum controllable overflow rate based on the on-site wellhead back pressure control capability; The expansion range of drilling fluid density under controllable micro-overflow and micro-leakage is obtained, which constitutes a controllable safety density window.

5. After obtaining the safe density window and bottom hole pressure range of the controllable drilling fluid, update the safe density window and drill under the condition of micro-leakage and micro-overflow in the formation while overflow and leakage coexist; During the drilling process, the wellbore flow rate is monitored in real time and the current annular pressure loss P is calculated. f ; The bottom hole pressure P during normal circulation is calculated according to the following formula b : （Ⅴ）， Among them, P f is the calculated current annular pressure loss; P a The wellhead back pressure value set on site; 6. Using real-time bottom hole pressure P b and bottom hole pressure P under leakage b1 and overflow bottom hole flow pressure P b2 Compare and judge whether it exceeds the range of controllable micro overflow or micro leakage; When P b >P b1 , beyond the controllable micro-leakage range, it is necessary to reduce the wellhead back pressure and return to the fifth step for real-time monitoring and calculation; When P b <P b2 , beyond the range of controllable micro-overflow, it is necessary to increase the wellhead back pressure and return to the fifth step for real-time monitoring and calculation; When P b If the bottom hole pressure is within the range of controllable micro-overflow or micro-leakage, return to step 5 for real-time monitoring and calculation; 7. After reaching the target well section, perform cementing operations.

2. The method for controlled pressure drilling based on a controlled pressure window for coexisting spillage and leakage according to claim 1, characterized in that: The specific method of step four is as follows: (1) Calculate the bottom hole pressure P under micro leakage according to the following formula b1 : （Ⅰ）， Where Q1 is the loss rate, m³ / h; P is the formation pressure; α is the loss calculation coefficient; n is the loss calculation index related to the flow properties of the drilling fluid; (2) Calculate the bottom hole flow pressure P under micro overflow according to the following formula: b2 : （Ⅱ）， Among them, Q k is the overflow gas production rate, m³ / h; P is the formation pressure; β is the gas production flow coefficient; m is the gas production index; (3) Calculate the annular pressure loss P according to the following formula: f : （Ⅲ）， Where L is the length of the annulus, Q is the flow rate of the drilling fluid, ρ is the density of the drilling fluid obtained from field data, D is the equivalent diameter of the annulus, and f is the friction coefficient; (4) Calculate the drilling fluid density under micro-overflow or micro-leakage according to the following formula, where P b For micro leakage and micro overflow, P is introduced respectively. b1 and P b2 : （Ⅳ）， Where H is the well depth, P 井口 is the wellhead casing pressure, P f is the annular pressure loss.

3. The method for controlled pressure drilling based on a controlled pressure window for coexisting spillage and leakage according to claim 1, characterized in that: The specific method of step three is as follows: (1) The drilling fluid density needs to be converted into drilling fluid pressure; (2) Calculate the drilling fluid pressure P in the wellbore 钻井液 =0.0098ρH+P f +P a , P 钻井液 is the drilling fluid pressure in the wellbore, MPa; ρ is the drilling fluid density, g / cm 3 ; H is the height of the liquid column, m; P f is the annular pressure loss; P a The wellhead back pressure value set on site; (3) Calculation of drilling fluid pressure coefficient P 钻井液系数 =P 钻井液 / P0; (4) If P is satisfied 地层系数 ≤P 钻井液系数 ≤P 漏失系数 , it is within the safe pressure window.

4. The method for controlled pressure drilling based on a controlled pressure window for coexisting spillage and leakage according to claim 1, characterized in that: In step 6, the pressure regulation method after exceeding the controllable micro-overflow or micro-leakage range is as follows: (1) When the micro-leakage exceeds the controllable range, the wellhead back pressure needs to be reduced. Specifically: ① Inform the throttle manifold operator on duty to slowly open the throttle valve. The adjustment range each time should not exceed 3-5% of the full stroke of the throttle valve. ②After each adjustment, observe the trend of data changes for one minute to determine whether the leakage has been reduced; (2) When the flow exceeds the controllable micro-overflow range, it is necessary to increase the wellhead back pressure, specifically: ① Inform the throttle manifold operator on duty to slowly close the throttle valve. The adjustment range each time should not exceed 3-5% of the full stroke of the throttle valve. ②After each adjustment, observe the data change trend for one minute to determine whether the overflow is slowed down; ③ If overflow continues, increase the monitoring frequency and prepare the well killing procedure in advance if necessary.

5. The method for controlled pressure drilling based on a controlled pressure window for coexistence of spillage and leakage in a formation according to claim 1, characterized in that: step The specific method is as follows: (1) Prepare the original data and unify the units: pressure is in MPa and depth is in m; (2) Calculate the hydrostatic pressure P0=0.0098ρ0H, P0 is the hydrostatic pressure, MPa; ρ0 is the hydrostatic density, g / cm 3 ; H is the height of the liquid column, m; (3) Calculation of formation pressure coefficient P 地层系数 =P 地层 / P0; (4) Calculate the leakage pressure coefficient P 漏失系数 =P 漏失 / P0; (5) Draw a graph of the pressure coefficient versus well depth.

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