A method of underbalanced well drilling

Abstract

A method for tripping out of an underbalanced well, the method comprising: determining the drilling fluid balance density and the annular pressure loss outside the drill pipe; determining the time for oil and gas to surge to the wellhead and the tripping time to the depth of the first injected gas plug, and comparing them to determine whether the conditions for safe operation are met; if the conditions for safe operation are met, determining the density and volume of the first gas plug based on the drilling fluid balance density and the annular pressure loss outside the drill pipe; tripping out of the well based on the density and volume of the first gas plug, completing the tripping out of the first gas plug; determining the density and volume of the gas plug at the depth near the wellhead using a preset method based on the depth after the tripping out of the first gas plug; and completing the tripping out of the gas plug near the wellhead based on the determined density and volume of the gas plug at the depth near the wellhead.

Description

Technical Field

[0001] This article relates to the field of oil and gas well drilling and completion technology, and in particular to a tripping method for underbalanced wells. Background Technology

[0002] With the increasing development of unconventional oil and gas resources such as shale gas and shale oil, the drilling process is characterized by active oil and gas reservoirs, narrow safety windows, and difficulty in maintaining balance due to formation properties, fault and fracture development, and other factors. Increasing drilling fluid density may lead to lost circulation, reduced drilling speed, increased drilling costs, and may also clog the pore throat, destroying the original reservoir properties and preventing the production of oil and gas during oil testing.

[0003] Therefore, for underbalanced uncontrolled wells, the urgent problem to be solved is how to achieve a tripping method that can protect the oil and gas reservoir and meet well control safety requirements without controlling the well. This method involves low-density underbalanced drilling and tripping. Summary of the Invention

[0004] This application provides a tripping method for underbalanced, uncontrolled wells. This method uses low-density underbalanced drilling fluid to inject gas plugs in stages and multiple times, thereby saving economic costs during tripping while protecting oil and gas reservoirs, reducing reservoir pollution, and increasing production capacity, all while ensuring safe tripping operations.

[0005] This application provides a method for tripping out an underbalanced well, the method comprising:

[0006] Determine the drilling fluid equilibrium density and drill pipe annular pressure loss for underbalanced wells;

[0007] Determine the time when oil and gas surge to the wellhead location and the time when the drill string is pulled out to the depth of the first gas plug injection, and compare them to determine whether the conditions for safe operation are met.

[0008] If the conditions for safe operation are met, the density and volume of the first gas stagnation plug are determined based on the drilling fluid balance density and the annular pressure loss of the drill pipe.

[0009] The drilling is initiated based on the density and volume of the first air plug, thus completing the first air plug drilling.

[0010] Based on the depth after the first tripping of the gas plug, the density and volume of the gas plug at the depth near the wellhead are determined using a preset method.

[0011] The near-wellhead gas plug tripping is completed based on the determined gas plug density and volume at the near-wellhead depth.

[0012] Optionally, the process for determining the equilibrium density of the drilling fluid in an underbalanced well is as follows:

[0013] Obtain formation pore pressure and fracture pressure in underbalanced wells;

[0014] Determine the safety bonus based on the type of underbalanced well;

[0015] The drilling fluid density is determined based on the formation pore pressure and the safety margin.

[0016] If the drilling fluid density is less than the fracture pressure, then the drilling fluid density is determined to be the drilling fluid equilibrium density.

[0017] Optionally, the drilling fluid density ρ0 is:

[0018] ρ0=ρ 孔 +Δρ0;

[0019] Where ρ0 is the drilling fluid density, ρ 孔 Δρ0 represents the formation pore pressure, and Δρ0 represents the safety margin.

[0020] Optionally, the process for determining the annular pressure loss of the drill pipe is as follows:

[0021] Calculate the drill pipe external circulation pressure coefficient based on the actual drilling fluid density of the underbalanced well;

[0022] The external annular pressure loss of the drill pipe is determined based on the external circulation pressure coefficient of the drill pipe.

[0023] Optionally, the external circulation pressure coefficient of the drill pipe is:

[0024]

[0025] The annular pressure loss of the drill pipe is:

[0026] Δp pi =k pi ×L p ×Q 1.8 ;

[0027] In the above formula, k pi ρ is the external circulation pressure coefficient of the drill pipe. d The actual drilling fluid density is expressed in μ. pi For plastic viscosity, d h d is the wellbore diameter. p Let Δp be the outer diameter of the drill pipe. pi For the annular air pressure loss of the drill pipe, L p This is the length of the drill pipe.

[0028] Optionally, the process of determining the time it takes for oil and gas to rise to the wellhead location is as follows:

[0029] Raise the drill string to the first depth and measure the rate of oil and gas rise.

[0030] The time it takes for oil and gas to reach the wellhead position without gas blockage is determined based on the oil and gas upflow rate.

[0031] The time t1 during which the oil and gas rise to the wellhead is:

[0032]

[0033] In the above formula, t1 is the time it takes for oil and gas to rise to the wellhead, h is the well depth, and V is the depth of the well. a This refers to the rate at which oil and gas rise.

[0034] The tripping time from the start of drilling to the depth of the first gas injection plug is:

[0035]

[0036] Where t2 is the tripping time from the first injection of gas plug to the well depth, h is the well depth, h1 is the depth of the first tripping, and V b This refers to the drilling speed.

[0037] Optionally, determining the density and volume of the first gas stagnation plug based on the drilling fluid equilibrium density and the annular pressure loss of the drill pipe includes:

[0038] The length of the first gas plug is determined based on the oil and gas upwelling speed and the tripping time to the well depth of the first gas plug injection.

[0039] The density of the first air stagnation plug is determined based on the length of the first air stagnation plug and the pressure loss of the outer annulus of the drill pipe;

[0040] The volume of the first gas block is determined based on the length of the first gas block and the wellbore diameter.

[0041] Optionally, the length l1 of the first stagnation plug is:

[0042] l1 = V a ×t2;

[0043] The density ρ1 of the first air stagnation plug is:

[0044] ρ1=ρ0+Δρ1;

[0045] in,

[0046] The volume V1 of the first air stagnation plug is:

[0047] V1=π / 4·d h 2 ·l1;

[0048] In the above formula, l1 is the length of the first gas block, ρ1 is the density of the first gas block, V1 is the volume of the first gas block, and V a t2 is the drilling time from tripping the drill string to the depth of the first gas plug injection, ρ0 is the drilling fluid density, Δρ1 is the safety margin, and Δp is the drilling fluid density. pi1 The pressure loss is the air pressure loss in the outer annulus of the drill pipe, g is the acceleration due to gravity, and d is the pressure loss due to gravity. h This refers to the diameter of the wellbore.

[0049] Optionally, the drilling is initiated based on the density and volume of the first gas plug, completing the first gas plug initiation, including:

[0050] Configure the air plug according to the density of the first air plug, and inject the air plug according to the preset pump discharge rate to start drilling;

[0051] During the tripping process, the pressure value P of the rotary blowout preventer was acquired in real time. 环 ;

[0052] If the pressure value P of the rotary blowout preventer 环 If the pressure is greater than or equal to 3 MPa, stop the tripping operation, circulate the air to remove air, adjust the drilling fluid balance density, and perform the second plugging operation.

[0053] If the pressure value P of the rotary blowout preventer 环 If the pressure is less than 3 MPa, then start drilling to the preset first drilling depth.

[0054] Optionally, the process of determining the density and volume of the gas plug at the depth near the wellhead during drilling is as follows:

[0055] Calculate the safe time for starting drilling based on the first drilling depth;

[0056] The length of the gas plug at the depth near the wellhead is determined based on the operation time for replacing the bridge plug accessory and the aforementioned safe tripping time.

[0057] Calculate the near-wellhead annular circulation pressure loss based on the first drilling depth, and determine the near-wellhead stagnant gas plug density based on the near-wellhead annular circulation pressure loss;

[0058] The volume of the near-wellhead gas plug is determined based on the length of the gas plug at the near-wellhead depth.

[0059] Optionally, the length of the gas plug from the start-up point to the depth near the wellhead is:

[0060] l2=V a ×(t3+t4);

[0061] The density of the gas plug near the wellhead depth is:

[0062] ρ' = ρ0 + Δρ2;

[0063] The volume of the gas plug at the depth near the wellhead is:

[0064] V2=π / 4·d h 2 ·l2

[0065] In the above formula, l2 is the length of the gas plug from the start of drilling to the depth near the wellhead. h1 is the initial drilling depth, V b t4 is the tripping speed; t4 is the time required to replace the bridge plug accessories; ρ' is the density of the gas plug near the wellhead depth; and ρ0 is the drilling fluid density. Δp pi2 V1 represents the annular pressure loss of the drill pipe at depths near the wellhead, g represents the acceleration due to gravity, and V2 represents the volume of the stagnant gas plug at depths near the wellhead.

[0066] Compared with related technologies, this application provides a method for tripping out of an underbalanced well. The method includes: determining the drilling fluid balance density and the annular pressure loss of the drill pipe in the underbalanced well; determining the time for oil and gas to surge to the wellhead and the tripping time to the depth of the first injected gas plug, and comparing them to determine whether the conditions for safe operation are met; if the conditions for safe operation are met, determining the density and volume of the first gas plug based on the drilling fluid balance density and the annular pressure loss of the drill pipe; tripping out of the well based on the density and volume of the first gas plug to complete the tripping out of the first gas plug; determining the density and volume of the gas plug at the depth near the wellhead using a preset method based on the depth after the first gas plug tripping out; and completing the tripping out of the gas plug near the wellhead based on the determined density and volume of the gas plug at the depth near the wellhead. This application uses low-density underbalanced drilling fluid to inject gas plugs in stages and multiple times, so as to save economic costs of tripping out of the drilling while protecting the oil and gas reservoir, reducing gas reservoir pollution, and increasing production capacity under safe tripping out operations.

[0067] Other features and advantages of this application will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the application. Other advantages of this application can be realized and obtained by means of the solutions described in the description and the accompanying drawings. Attached Figure Description

[0068] The accompanying drawings are used to provide an understanding of the technical solutions of this application and constitute a part of the specification. They are used together with the embodiments of this application to explain the technical solutions of this application and do not constitute a limitation on the technical solutions of this application.

[0069] Figure 1 This is a flowchart of the tripping method for an underbalanced well according to an embodiment of this application;

[0070] Figure 2 A flowchart illustrating the tripping method for an underbalanced well in some exemplary embodiments;

[0071] Figure 3 This is a schematic diagram of the wellhead apparatus for an underbalanced well in some exemplary embodiments. Detailed Implementation

[0072] This application describes several embodiments, but these descriptions are exemplary and not restrictive, and it will be apparent to those skilled in the art that many more embodiments and implementations are possible within the scope of the embodiments described herein. Although many possible combinations of features are shown in the drawings and discussed in the detailed description, many other combinations of the disclosed features are also possible. Unless specifically limited, any feature or element of any embodiment may be used in combination with, or may replace, any feature or element of any other embodiment.

[0073] This application includes and contemplates combinations of features and elements known to those skilled in the art. The embodiments, features, and elements disclosed in this application may also be combined with any conventional features or elements to form a unique inventive scheme as defined by the claims. Any feature or element of any embodiment may also be combined with features or elements from other inventive schemes to form another unique inventive scheme as defined by the claims. Therefore, it should be understood that any feature shown and / or discussed in this application may be implemented individually or in any suitable combination. Therefore, the embodiments are not limited except by the limitations imposed by the appended claims and their equivalents. Furthermore, various modifications and changes may be made within the scope of the appended claims.

[0074] Furthermore, in describing representative embodiments, the specification may have presented methods and / or processes as a specific sequence of steps. However, the method or process should not be limited to the specific order of steps described herein, to the extent that it does not depend on such a specific order. As will be understood by those skilled in the art, other sequences of steps are also possible. Therefore, the specific order of steps set forth in the specification should not be construed as a limitation of the claims. Moreover, the claims concerning the method and / or process should not be limited to the steps performed in the written order, and those skilled in the art will readily understand that these orders can be varied and still remain within the spirit and scope of the embodiments of this application.

[0075] For underbalanced drilling operations, some techniques for ensuring safe tripping of the drill string without well pressure are as follows:

[0076] 1. An underbalanced tripping mud compensation system (Zhang Fuxiao, Zhao Shiying, CN 204782867 U).

[0077] This patent describes an underbalanced drilling mud compensation system. A gear-driven mud pump draws mud from the mud tank and injects it into the wellbore. Simultaneously, a sand pump draws mud from an external mud pit and adds it to the mud tank, maintaining a constant mud balance. This system automatically replenishes the drilling team's mud tank and continuously outputs mud, maintaining stable pressure during the tripping process. It saves tripping time and improves the stability and safety of the tripping phase in domestic underbalanced drilling operations.

[0078] 2. A whole-process underbalanced drilling pressure compensation system and method (Yi Ming, Yang Gang, Chen Ruoming et al., CN101929331 A).

[0079] This patented technology connects a downhole casing valve to the upper casing string. A rotary blowout preventer (BOP) is placed on top of the BOP assembly. The rotary BOP is connected to the underbalanced choke manifold via a high-pressure hose. A kill manifold connected to a conventional wellhead control device is linked in parallel with the continuous drilling fluid injection system via a double-connector. Before tripping to the downhole casing valve, the continuous drilling fluid injection system grouts, the underbalanced choke manifold controls the wellbore pressure, and the circulating drilling fluid enters the conventional drilling fluid circulation system. This invention enables continuous drilling fluid injection into the wellbore through a surface pressure compensation system during tripping, while simultaneously dynamically controlling the bottom hole pressure. This effectively controls formation fluid intrusion into the wellbore during tripping, maintaining a stable underbalanced state in the wellbore.

[0080] 3. A method for implementing underbalanced drilling operations (Yang Lingrui, Xiao Xinyu, et al., CN 101042043A)

[0081] This invention employs a controlled drilling operation using drilling fluid at a pressure lower than the formation pressure. The invention includes underbalanced drilling technology, design technology, equipment configuration technology, and a technology for running in-well tubing without pressure. Because drilling fluid at a pressure lower than the formation pressure is used, the drilling fluid does not enter the formation and does not contaminate the drilled formation. After drilling is completed, oil or natural gas can flow smoothly to the surface. This allows many wells that previously did not produce oil or gas due to drilling fluid contamination to obtain industrial oil and gas flow. The reduced drilling fluid density also significantly increases drilling speed. This invention overcomes the problem of heavy mud intrusion into the formation, which can block oil and gas channels and damage the original state of the formation when using overbalanced or near-balanced drilling techniques.

[0082] 4. Application of underbalanced drilling technology throughout the entire process using downhole isolation method (Zhao Jinzhou, Natural Gas Industry, 2006.11).

[0083] The underbalanced drilling technology discussed in this article refers to the underbalanced drilling, drilling tool handling, logging instruments, and completion tools performed without well pressure. Downhole isolation technology utilizes casing valves to isolate downhole oil, gas, and pressure below the valve plate; it is currently the most practical well pressure-free operation technology.

[0084] Regarding underbalanced tripping technology, the following problems exist:

[0085] 1. Continuous grouting is achieved through automatic grouting devices to maintain stable fluid column pressure during the tripping process. However, for solid-free drilling fluid systems, gas slippage is rapid, and simply injecting drilling fluid cannot meet the tripping requirements.

[0086] 2. Design a downhole casing valve connected to the upper casing string, with a rotary blowout preventer installed at the wellhead. Dynamic control of the bottom hole pressure is achieved through a surface pressure compensation system. However, the safety and stability of the casing valve are questionable.

[0087] 3. The technology, design process, equipment configuration process, and in-hole tubing string process for unbalanced drilling were reviewed. For unbalanced drilling tripping devices, they must be removed and cannot be used when the drill string weight is less than 50NK.

[0088] 4. Downhole isolation technology uses casing valves to seal downhole oil, gas and pressure below the valve plate. However, imported casing valves are expensive and have high service costs. Moreover, they are connected to the upper casing after entering the well and cannot be reused.

[0089] By addressing the problems encountered in underbalanced drilling operations, the inventors conducted research on the tripping process of underbalanced wells without well control, and developed a method using segmented injection of gas plugs to control natural gas slippage within the wellbore, delay the time for oil and gas to reach the wellhead, maintain the rotating blowout preventer within the pressure control range, achieve safe, pressurized tripping operations, avoid a series of negative impacts caused by increasing drilling fluid density, thereby protecting formation occurrence and ensuring oil and gas recovery.

[0090] This invention provides a method for tripping out an underbalanced well, such as... Figure 1 As shown, the method includes steps S100-S150:

[0091] S100: Determine the drilling fluid balance density and drill pipe annular pressure loss for underbalanced wells, respectively;

[0092] S110: Determine the time when oil and gas surge to the wellhead position and the time when the drill string is pulled out to the depth of the first gas plug injection, and compare them to determine whether the conditions for safe operation are met.

[0093] S120: If the conditions for safe operation are met, the density and volume of the first gas stagnation plug are determined based on the drilling fluid balance density and the annular pressure loss of the drill pipe.

[0094] S130: Based on the density and volume of the first air slug, start drilling to complete the first air slug start-up;

[0095] S140: Based on the depth after the first tripping of the gas plug, determine the density and volume of the gas plug at the depth near the wellhead using a preset method;

[0096] S150: Based on the determined gas plug density and volume at the near-wellhead depth, complete the near-wellhead gas plug tripping.

[0097] In one exemplary embodiment, determining the drilling fluid equilibrium density of an underbalanced well includes:

[0098] Step 1: Obtain the formation pore pressure ρ of the underbalanced well. 孔 and rupture pressure ρ 破 ;

[0099] Based on the formation pore pressure ρ obtained from actual drilling 孔 and rupture pressure ρ 破 value.

[0100] Step 2: Determine the type of the underbalanced well and determine the safety margin Δρ0 based on the determined type;

[0101] The safety bonus Δρ0 varies in range depending on the type of well.

[0102] For oil and water wells, the safety margin Δρ0 ranges from 0.05 g / cm³. 3 ~0.10g / cm 3 ;

[0103] In the case of gas wells, the safety margin Δρ0 ranges from 0.07 g / cm³. 3 ~0.15g / cm 3 .

[0104] Step 3: Based on the formation pore pressure ρ 孔 The drilling fluid density is determined by the aforementioned safety margin Δρ0; the drilling fluid density ρ0 is:

[0105] ρ0=ρ 孔 +Δρ0,

[0106] Where ρ0 is the drilling fluid density and Δρ0 is the safety margin.

[0107] Step 4: Determine whether the drilling fluid density is less than the fracturing pressure ρ.破 ;

[0108] If the drilling fluid density is less than the fracturing pressure ρ 破 If so, the drilling fluid balance density is determined to be the drilling fluid balance density that meets the safety conditions for tripping out of the well.

[0109] If the drilling fluid density is greater than or equal to the fracturing pressure ρ 破 Otherwise, well leakage is likely to occur. In this case, the drilling fluid density can be adjusted or other measures can be taken. There are no specific limitations on this. The tripping condition in this application is that the drilling fluid density is less than the fracturing pressure ρ. 破 Execute under the following circumstances.

[0110] In one exemplary embodiment, calculating the annular pressure loss of the drill pipe based on the drilling fluid equilibrium density includes:

[0111] Step 1: Calculate the external circulation pressure coefficient of the drill pipe based on the determined drilling fluid equilibrium density;

[0112] The external circulation pressure coefficient of the drill pipe:

[0113]

[0114] Step 2: Determine the annular pressure loss of the drill pipe based on the external circulation pressure coefficient of the drill pipe.

[0115] The annular pressure loss of the drill pipe is:

[0116] Δp pi =k pi ×L p ×Q 1.8 …………………………(1)

[0117] In formulas (1) and (2) above, Δp pi The external circulation pressure loss of the drill pipe is expressed in MPa and kJ. pi L is the external circulation pressure coefficient of the drill pipe, a dimensionless quantity. p ρ is the drill pipe length, in meters; the drill pipe length equals the well depth; Q is the flow rate, in liters per second (L / s); ρ d Density of drilling fluid, g / cm³ 3 μ pi The viscosity is plastic, in mPa·s; d h d represents the wellbore diameter in mm. p The outer diameter of the drill pipe is in mm.

[0118] In one exemplary embodiment, the time it takes for oil and gas to surge to the wellhead is compared with the time it takes to pull out of the well to the depth of the first gas plug injection to determine whether the conditions for safe operation are met, including:

[0119] Step 1, measure the upward migration velocity V of oil and gas a ;

[0120] At the first depth of the drill pipe being pulled out, measure the upward migration velocity V of oil and gas a ; The first depth here can be 100 - 500 m from the top of the oil layer or 10 - 30 m below the upper technical casing shoe, which is also the expected well depth for the first injection of the stagnant gas plug.

[0121] Step 2, determine the time for the oil and gas to migrate upward to the wellhead position:

[0122] Determine the time for the oil and gas to migrate upward to the wellhead position without a stagnant gas plug according to the upward migration velocity of the oil and gas;

[0123] Among them, the time t1 for the oil and gas to migrate upward to the wellhead position is:

[0124]

[0125] In the above formula, h is the well depth, and Va is the upward migration velocity of the oil and gas.

[0126] Step 3, close the rotating blowout preventer and set the average pulling-out speed V b , and calculate the time required for pulling out the drill pipe.

[0127] According to the operating procedures of the blowout preventer, the pulling-out speed is generally 150 - 300 m / h, and the pulling-out time from the start of pulling out the drill pipe to the well depth for the first injection of the stagnant gas plug is:

[0128]

[0129] Among them, h is the well depth, h1 is the depth of the first pulling out of the drill pipe, and V b is the pulling-out speed; h1 can be set according to specific circumstances, and can be 1500 m or 1000 m.

[0130] Step 4, determine whether the conditions for safe operation are met

[0131] If t1 > t2, the conditions for safe operation are met, and the drill pipe can be pulled out normally;

[0132] If t1 < t2, the length l1 - 2l1 of the stagnant gas plug section can be increased, and at the same time, the density of the stagnant gas plug is adjusted to (ρ0 + Δρ1 + Δρ0); increase the safety additional value Δρ0 according to the requirements of the well control implementation rules.

[0133] In an exemplary embodiment, the determination of the density and volume of the first stagnant gas plug according to the pressure loss in the annulus outside the drill pipe includes:

[0134] Step 1, determine the length l1 of the first stagnant gas plug according to the upward migration velocity V a of the oil and gas and the pulling-out time from the start of pulling out the drill pipe to the well depth for the first injection of the stagnant gas plug

[0135] The length l1 of the first slack plug is:

[0136] l1 = V a ×t2;

[0137] Step 2: Determine the density of the first air stagnation plug based on the length l1 of the first air stagnation plug and the pressure loss of the outer annulus of the drill pipe;

[0138] The density ρ1 of the first airlock is:

[0139] ρ1=ρ0+Δρ1

[0140] in,

[0141] In the above formula, g is the acceleration due to gravity, and g = 9.8 m / s². 2 .

[0142] Step 3: Determine the volume of the first gas stagnation plug based on the length l1 of the first gas stagnation plug and the wellbore diameter.

[0143] The volume V1 of the first slack plug is:

[0144] V1=π / 4·d h 2 ·l1.

[0145] Based on the calculation results, prepare the airlock plug; the airlock plug can be prepared using conventional methods in this field.

[0146] In one exemplary embodiment, the first gas plug tripping is performed based on the determined density and volume of the first gas plug, completing the first gas plug tripping, including:

[0147] Step 1: Inject the first gas block into the gas block according to the predetermined pump displacement based on the determined density of the first gas block.

[0148] Use drilling pumps or cement trucks with a pump displacement of 0.5-1.8m³. 3 / min of the gas stagnation plug is injected, replacing the gas in the annulus, and the length of the gas stagnation plug satisfies l1.

[0149] Step 2: During the drilling process, obtain the real-time pressure value P of the rotary blowout preventer. 环 ;

[0150] Step 3, if P 环 If the pressure is greater than or equal to 3 MPa, stop the tripping operation, circulate the air to remove air, adjust the drilling fluid balance density, and perform the second plugging operation.

[0151] If P 环 If the pressure is less than 3 MPa, then start drilling to the preset first drilling depth.

[0152] Specifically, to reduce the risk of drilling, if P 环 When the pressure is greater than or equal to 3 MPa, after circulating the vent, prepare for the second plugging operation. If P 环 When the pressure is less than 3 MPa, pull the drill string to a depth of 1000-1500 m and prepare for the final plugging operation near the wellhead.

[0153] In one exemplary embodiment, the process of determining the density and volume of the near-wellhead gas plug is as follows:

[0154] Step 1: Calculate the safe time for starting the drill string based on the initial drilling depth;

[0155] The time required for drilling is t3;

[0156]

[0157] Where h1 is the depth of the last gas plugging well, in meters;

[0158] Step 2: Determine the length l2 of the near-wellhead gas plug based on the time required for the additional bridge plug replacement operation and the aforementioned tripping safety time;

[0159] Based on the workflow and experience, the operation time for replacing bridge plug accessories is generally 2-4 hours (t4).

[0160] Length l2 of the gas plug near the wellhead:

[0161] l2=V a ×(t3+t4).

[0162] Step 3: Calculate the near-wellhead annular circulation pressure loss based on the first drilling depth, and determine the near-wellhead sludge density based on the near-wellhead annular circulation pressure loss.

[0163] ρ' = ρ0 + Δρ2;

[0164] In the above formula, ρ' is the density of the gas plug near the wellhead; Δρ2 is the safety margin. l2 is the length of the gas block near the wellhead;

[0165] Δp pi2 Pressure loss in the external circulation near the wellhead drill pipe: Δp pi2 =k pi ×L p2 ×ρ 1.8 ;

[0166] In the above formula: Δp pi2 The external circulation pressure loss of the drill pipe is expressed in MPa and kJ. pi L is the external circulation pressure coefficient of the drill pipe, a dimensionless quantity. p2 is the drill pipe length, in meters; Q is the flow rate, in liters (L / s).

[0167] Step 4: Determine the volume of the near-wellhead gas stagnation plug based on the near-wellhead gas stagnation plug length l2;

[0168] Near-wellhead gas plug volume V2=π / 4·d h 2 ·l2.

[0169] In one exemplary embodiment, after determining the density and volume of the near-wellhead gas plug, a drilling pump or cement truck is used to pump it at a displacement of 0.5-1.8 m³ / h. 3 Inject the gas plug at a rate of / min to displace it into the annulus, ensuring the gas plug length meets l2. After injecting the gas plug, do not use the rotating blowout preventer; open the well, pull out the drill string directly, and complete the installation of the plugging bridge plug.

[0170] Example 1

[0171] This example combines the X-well with a four-section wellbore structure, such as... Figure 3 The diagram shows the wellhead assembly. The relevant parameters of this well are as follows:

[0172] The outer diameter of the surface sleeve, D1, is 339.7 mm.

[0173] Depth H1 = 502m

[0174] The outer diameter of the technical sleeve, D2, is 244.5 mm.

[0175] The depth H2 = 2235m

[0176] The outer diameter of the oil layer casing, D2, is 177.8 mm.

[0177] Wall thickness 11.51mm,

[0178] From the wellhead down to a depth of H2 = 4552m,

[0179] Four-section drill bit diameter D 钻头 =149.2mm,

[0180] Well depth H3=4688m;

[0181] The drilling fluid system is a potassium salt polysolid-free drilling fluid with a density of 1.10 g / cm³. 3 ;

[0182] The following describes the process of pulling out the drill string for this underbalanced well without controlling the well, as follows: Figure 2 As shown:

[0183] Step 1: Determine the equilibrium density of the drilling fluid during drilling;

[0184] The drilling fluid equilibrium density of this well is determined based on the formation pore pressure and the predetermined safety margin for oil and gas wells Δρ0:

[0185] ρ0=ρ 孔 +Δρ0=1.05+(0.05~0.10)=1.10~1.15g / cm 3 ;

[0186] Where ρ0 is the drilling fluid density, ρ 孔 The value is 1.05, and Δρ0 is the safety margin for oil and gas wells. This safety margin is determined based on the well type, with a range of values ​​of 0.05 g / cm³ for oil and water wells. 3 ~

[0187] 0.10g / cm 3 .

[0188] ρ0 is less than the fracture pressure of this well (ρ 破 =2.05), ρ0 is the drilling fluid equilibrium density, which can be used to execute subsequent processes.

[0189] Step 2: Preparations before drilling

[0190] According to the well drilling engineering design requirements, a reserve of 60m is required. 3 Density 1.40 g / cm³ 3 Heavy drilling fluid.

[0191] Step 3: Turn off the rotary blowout preventer, pull up the drill string under pressure, and determine the rate of oil and gas surge.

[0192] Close the rotary blowout preventer, dynamic pressure 2 MPa. Raise the drill string to a depth of 4562-4582 m above the casing opening in the oil layer. After standing for 2 hours, circulate the vent and measure the oil and gas rise velocity V. a It is 50.2 m / h.

[0193] Step 4: Calculation of annular pressure loss and pressure coefficient of drilling fluid

[0194] Calculate the external circulation pressure coefficient of the drill pipe according to formula (2):

[0195]

[0196] Because the oil layer casing is connected to the wellhead, therefore k pi With the value remaining constant, calculate the bottom hole annulus circulation pressure loss according to formula (1):

[0197] Δp pi =k pi ×L p ×Q 1.8

[0198] =7.19×10 -6 ×4688×17 1.8 =7.19×10 -6×4688×163.99=5.53MPa;

[0199] The calculated bottom hole annular circulation pressure loss was verified to be consistent with actual drilling data; therefore, the calculation method was deemed reasonable.

[0200] Step 5: Determine the length, density, and volume of the first airlock.

[0201] Step 51: Determine if the drilling is started normally.

[0202] The initial plan is to pull the drill string to a position 1500m from the wellhead. Assuming no gas blockage, calculate the time t1 for oil and gas to rise to the wellhead, where the well depth H3 = 4688m.

[0203]

[0204] When using a rotary blowout preventer at a pull-up speed of 300 m / h, the normal tripping time t2 to the depth of the first gas plug injection is:

[0205]

[0206] Where h is the well depth, and h1 is the initial drilling depth. In this well, the initial plan is to pull the drill string to a position 1500m from the wellhead, i.e., h1 = 1500m.

[0207]

[0208] Determine the relationship between the time it takes for oil and gas to rise to the wellhead and the time required for normal tripping. If t1 > t2, then it is determined that the operation is within the safe range and normal tripping can proceed. Continue to step 52.

[0209] Step 52: Calculate the first stagnation plug length l1

[0210] l1 = V a ×t2=50.2×12.29=617m.

[0211] Step 53: Calculate the density of the airlock.

[0212] First, calculate the annular circulation pressure loss:

[0213] Δp pi1 =k pi ×L p1 ×Q 1.8 =7.19×10 -6 ×4582×17 1.8 =7.19×10 -6 ×4582×163.99=5.33MPa.

[0214] The increase in annular pressure loss density Δρ1 is calculated based on the annular circulation pressure loss:

[0215]

[0216] The density of the sludge block is calculated based on the determined increase in annular pressure loss: (ρ0 + Δρ1)

[0217] =1.10 + 0.0008 ≈ 1.10 g / cm³ 3 .

[0218] Step 53: Calculate the volume V1 of the slack plug.

[0219]

[0220] Based on the above calculations, a 17m airlock plug was prepared. 3 Ensure effective injection of 12m 3 .

[0221] Step 6: Inject the first air plug and perform the first tripping drill bit.

[0222] Using a drilling mud pump, at a depth of 1.0m 3 / min pump displacement is injected into the stagnation plug and replaces it in the annulus.

[0223] Pulling out the drill string, observing and recording the rotary blowout preventer pressure value P 环 According to the real-time recorded rotary blowout preventer pressure value P 环 Determine whether it falls within a safe range;

[0224] Measure P 环 If the pressure is 0 MPa or less than 3 MPa, the drill can be pulled up directly to 1500m.

[0225] Step 7: Calculate the length, density, and volume of the near-wellhead gas plug.

[0226] After pulling the drill string to a depth of 1500m, vent the air, calculate the safe time for pulling the string, the additional time for replacing the bridge plug accessories, and the length, density, and volume of the last air stagnation plug.

[0227] The normal drilling time t3:

[0228]

[0229] Based on the drilling speed of this well team, the operation time for replacing the bridge plug accessories is t4, where t4 = 2 hours.

[0230] Length l2 of the gas plug near the wellhead:

[0231] l2=V a ×(t3+t4)=50.2×(5+2)=351m.

[0232] Near-wellhead annular circulation pressure loss Δp pi2 :

[0233] Δp pi2 =k pi ×L p2 ×Q 1.8 =7.19×10 -6 ×1500×17 1.8 =7.19×10 -6 ×1500×163.99=1.76MPa

[0234] Near the wellhead, annular pressure loss increases density Δρ2:

[0235]

[0236] Density of stagnant gas near the wellhead = (ρ0 + Δρ2) = 1.10 + 0.0005 ≈ 1.10 g / cm³ 3 .

[0237] Near-wellhead gas plug volume V2:

[0238]

[0239] Based on the calculated near-wellhead gas plug volume, prepare a 12m gas plug. 3 Ensure effective injection of 7m 3 .

[0240] Step 8: Inject near-wellhead gas plug, pull out the drill string, connect the sealing bridge plug, and run in the drill string.

[0241] Use a drilling mud pump with a pump displacement of 1.2m³. 3 Injecting gas into the stagnation plug at a rate of / min, displacing it and entering the annulus, approximately 500m.

[0242] The well was pulled out directly into the open well, and the plug bridge was connected and successfully lowered.

[0243] Practical verification has shown that the tripping method implemented in this application is feasible in underbalanced wells.

[0244] In this example, well X uses a segmented injection of gas-stagnation plugs to control the slippage of natural gas in the wellbore, delaying the time for oil and gas to reach the wellhead. This maintains the rotating blowout preventer within the pressure control range, achieving a safe, pressurized tripping operation. This tripping method avoids a series of negative impacts caused by increasing drilling fluid density, thereby protecting the formation and ensuring oil and gas recovery.

[0245] It will be understood by those skilled in the art that all or some of the steps, systems, or apparatuses disclosed above, and their functional modules / units, can be implemented as software, firmware, hardware, or suitable combinations thereof. In hardware implementations, the division between functional modules / units mentioned above does not necessarily correspond to the division of physical components; for example, a physical component may have multiple functions, or a function or step may be performed collaboratively by several physical components. Some or all components may be implemented as software executed by a processor, such as a digital signal processor or microprocessor, or as hardware, or as an integrated circuit, such as an application-specific integrated circuit (ASIC). Such software may be distributed on a computer-readable medium, which may include computer storage media (or non-transitory media) and communication media (or transient media). As is known to those skilled in the art, the term computer storage media includes volatile and non-volatile, removable and non-removable media implemented in any method or technology for storing information (such as computer-readable instructions, data structures, program modules, or other data). Computer storage media include, but are not limited to, RAM, ROM, EEPROM, flash memory or other memory technologies, CD-ROM, digital versatile disc (DVD) or other optical disc storage, magnetic cartridges, magnetic tape, disk storage or other magnetic storage devices, or any other medium that can be used to store desired information and can be accessed by a computer. Furthermore, it is well known to those skilled in the art that communication media typically contain computer-readable instructions, data structures, program modules, or other data in modulated data signals such as carrier waves or other transmission mechanisms, and may include any information delivery medium.

Claims

1. A method for tripping out an underbalanced well, characterized in that, The method includes: Determine the drilling fluid equilibrium density and drill pipe annular pressure loss for underbalanced wells; Determine the time when oil and gas surge to the wellhead location and the time when the drill string is pulled out to the depth of the first gas plug injection, and compare them to determine whether the conditions for safe operation are met. If the conditions for safe operation are met, the density and volume of the first gas stagnation plug are determined based on the drilling fluid balance density and the annular pressure loss of the drill pipe. The drilling is initiated based on the density and volume of the first air plug, thus completing the first air plug drilling. Based on the depth after the first tripping of the gas plug, the density and volume of the gas plug at the depth near the wellhead are determined using a preset method. The near-wellhead gas plug tripping is completed based on the determined gas plug density and volume at the near-wellhead depth.

2. The tripping method for underbalanced wells according to claim 1, characterized in that, The process of determining the equilibrium density of drilling fluid in an underbalanced well is as follows: Obtain formation pore pressure and fracture pressure in underbalanced wells; Determine the safety bonus based on the type of underbalanced well; The drilling fluid density is determined based on the formation pore pressure and the safety margin. If the drilling fluid density is less than the fracture pressure, then the drilling fluid density is determined to be the drilling fluid equilibrium density.

3. The tripping method for underbalanced wells according to claim 2, characterized in that, The drilling fluid density ρ0 is: p0=p 孔 +Δρ0; Where ρ0 is the drilling fluid density, ρ 孔 Δρ0 represents the formation pore pressure, and Δρ0 represents the safety margin.

4. The tripping method for underbalanced wells according to claim 1, characterized in that, The process for determining the annular pressure loss of the drill pipe is as follows: Calculate the drill pipe external circulation pressure coefficient based on the actual drilling fluid density of the underbalanced well; The external annular pressure loss of the drill pipe is determined based on the external circulation pressure coefficient of the drill pipe.

5. The tripping method for underbalanced wells according to claim 4, characterized in that, The external circulation pressure coefficient of the drill pipe: The annular pressure loss of the drill pipe is: Δp pi =k pi ×L p ×Q 1.8 ; In the above formula, k pi ρ is the external circulation pressure coefficient of the drill pipe. d The actual drilling fluid density is expressed in μ. pi For plastic viscosity, d h d is the wellbore diameter. p Let Δp be the outer diameter of the drill pipe. pi For the annular air pressure loss of the drill pipe, L p This is the length of the drill pipe.

6. The tripping method for underbalanced wells according to claim 5, characterized in that, The process of determining the time it takes for oil and gas to rise to the wellhead is as follows: Raise the drill string to the first depth and measure the rate of oil and gas rise. The time it takes for oil and gas to reach the wellhead position without gas blockage is determined based on the oil and gas upflow rate. The time t1 during which the oil and gas rise to the wellhead is: In the above formula, t1 is the time it takes for oil and gas to rise to the wellhead, h is the well depth, and V is the depth of the well. a This refers to the rate at which oil and gas rise. The tripping time from the start of drilling to the depth of the first gas injection plug is: Where t2 is the tripping time from the first injection of gas plug to the well depth, h is the well depth, h1 is the depth of the first tripping, and V b This refers to the drilling speed.

7. The tripping method for underbalanced wells according to claim 6, characterized in that, The determination of the density and volume of the first gas stagnation plug based on the drilling fluid equilibrium density and the annular pressure loss of the drill pipe includes: The length of the first gas plug is determined based on the oil and gas upwelling speed and the tripping time to the well depth of the first gas plug injection. The density of the first air stagnation plug is determined based on the length of the first air stagnation plug and the annular pressure loss of the drill pipe. The volume of the first gas block is determined based on the length of the first gas block and the wellbore diameter.

8. The tripping method for underbalanced wells according to claim 7, characterized in that, The length l1 of the first stagnation plug is: l1=V a ×t2; The density ρ1 of the first air stagnation plug is: ρ1=ρ0+Δρ1; in, The volume V1 of the first air stagnation plug is: V1=π / 4·d h 2 ·l1; In the above formula, l1 is the length of the first gas block, ρ1 is the density of the first gas block, V1 is the volume of the first gas block, and V a t2 is the drilling time from tripping the drill string to the depth of the first gas plug injection, ρ0 is the drilling fluid density, Δρ1 is the safety margin, and Δp is the drilling fluid density. pi1 The pressure loss is the air pressure loss in the outer annulus of the drill pipe, g is the acceleration due to gravity, and d is the pressure loss due to gravity. h This refers to the diameter of the wellbore.

9. The tripping method for an underbalanced well according to claim 8, characterized in that, Based on the density and volume of the first gas plug, the drilling is initiated, completing the first gas plug initiation, including: Configure the air plug according to the density of the first air plug, and inject the air plug according to the preset pump discharge rate to start drilling; During the tripping process, the pressure value P of the rotary blowout preventer was acquired in real time. 环 ; If the pressure value P of the rotary blowout preventer 环 If the pressure is greater than or equal to 3 MPa, stop the tripping operation, circulate the air to remove air, adjust the drilling fluid balance density, and perform the second plugging operation. If the pressure value P of the rotary blowout preventer 环 If the pressure is less than 3 MPa, then start drilling to the preset first drilling depth.

10. The tripping method for an underbalanced well according to claim 9, characterized in that, The process of determining the density and volume of the gas plug at the depth near the wellhead from the start of drilling is as follows: Calculate the safe time for starting drilling based on the first drilling depth; The length of the gas plug at the depth near the wellhead is determined based on the operation time for replacing the bridge plug accessory and the aforementioned safe tripping time. Calculate the near-wellhead annular circulation pressure loss based on the first drilling depth, and determine the near-wellhead stagnant gas plug density based on the near-wellhead annular circulation pressure loss; The volume of the near-wellhead gas plug is determined based on the length of the gas plug at the near-wellhead depth.

11. The tripping method for an underbalanced well according to claim 10, characterized in that, The length of the gas plug from the start-up point to the depth near the wellhead is: l2=V a ×(t3+t4); The density of the gas plug near the wellhead depth is: ρ'=ρ0+Δρ2; The volume of the gas plug at the depth near the wellhead is: V2=π / 4·d h 2 ·l2 In the above formula, l2 is the length of the gas plug from the start of drilling to the depth near the wellhead. h1 is the initial drilling depth, V b t4 is the drilling speed; t4 is the time for changing bridge plug accessories. ρ' is the density of the gas plug near the wellhead depth, and ρ0 is the drilling fluid density. Δp pi2 V1 represents the annular pressure loss of the drill pipe at depths near the wellhead, g represents the acceleration due to gravity, and V2 represents the volume of the stagnant gas plug at depths near the wellhead.

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