A construction method for cement plugging for leaking backfill of fractured and cave-type ultra-deep wells in oil fields

Abstract

The present invention relates to the technical field of oilfield exploitation, and in particular to a construction method for cement plugging for leaking backfill of ultra-deep wells with fractured karst caves in oilfields. The method comprises designing the side drilling point position according to the leaking point position of the historical side drilling well, and designing the positions of the cement upper plug surface and the cement lower plug surface according to the side drilling point position, and obtaining the design depth H of the cement upper plug surface. 上塞面 and the design depth H of the cement plug surface 下塞面 ; Calculate the depth H of the bare drill pipe cement plug 光钻杆 According to H 光钻杆 and H 上塞面 Calculate the maximum leakage M max =(H 上塞面 ‑H 光钻杆 )×L 井眼 , the allowable leakage range is Q0~M max ; Lower the drill rod to depth H 光钻杆 , grouting is carried out according to the displacement volume of the drill pipe, and the total amount of leakage is calculated in real time to ensure that the total amount of leakage is within the leakage range. The position of the plug surface of the backfill cement plug can be controlled more accurately, which greatly improves the success rate of cement plug injection and ensures underground safety.

Description

Technical Field

[0001] The invention relates to the technical field of oilfield exploitation, and in particular to a construction method for backfilling cement plugs for leakage in fractured cavernous ultra-deep wells in oilfields. Background Art

[0002] With the advancement of the implementation plan for stabilizing oil production, increasing gas production and reducing costs in Northwest Oilfield, the continuous requirements for improving quality, speed, efficiency and production have been met. In order to achieve the goal of increasing oil storage and production, Northwest Oilfield continued to increase the transformation of old well reservoirs in the main block and Shunbei work area in 2020, and the deployment of side drilling wells has further increased. When constructing side drilling wellbore operations, whether it is open-hole side drilling or casing window side drilling, cement plugs will inevitably be injected to prepare for backfilling side drilling.

[0003] In the prior art, side-drilling wells need to achieve the purpose of cementing by backfilling cement plugs during side drilling. After cementing injection and slurry replacement are completed, the cement plugs achieve the cementing effect in the well, which is convenient for side drilling and achieves the success rate of backfilling cement plugs. However, in the prior art, backfilling cement plugs are only controlled by experience for grouting. Since the wellbore is in a dynamic process of leakage and overflow coexisting before cement plug injection, operation based on experience alone can easily lead to the plug surface position of the backfilling cement plug being too high or too low, resulting in the cement plug strength not meeting the side drilling requirements, and even complex failures such as "flagpole insertion" may occur, resulting in failure of backfilling cement plugs. At present, the one-time success rate of backfilling cement plugs in leakage wells in the work area is about 30%, which seriously affects production timeliness and increases downhole risks. Summary of the invention

[0004] The purpose of the present invention is to address the defects of the prior art and provide a construction method for backfilling cement plugs for ultra-deep wells with fractured caves in oil fields, which can more accurately control the plug surface position of the backfill cement plug, greatly improve the success rate of cement plug injection, and ensure underground safety.

[0005] The present invention provides a construction method for cement plugging for leaking backfill of fractured and cave-type ultra-deep wells in oil fields, and the technical scheme thereof is as follows:

[0006] According to the location of the leakage point of the historical side drilling well, the side drilling point location is designed, and the cement upper plug surface and cement lower plug surface locations are designed according to the side drilling point location, and the design depth H of the cement upper plug surface is obtained. 上塞面 and the design depth H of the cement plug surface 下塞面 ;

[0007] Calculate the penetration depth H of the bare drill pipe cement plug 光钻杆 ;

[0008] According to H 光钻杆 and H 上塞面 Calculate the maximum leakage M max =(H 上塞面 -H 光钻杆)×L 井眼 , the allowable leakage range is Q0~M max , where L 井眼 is the unit volume of the wellbore, Q0 is the amount of pre-fluid and post-fluid;

[0009] Lower the drill rod to depth H 光钻杆 , grouting is carried out according to the displacement volume of the drill pipe, and the total leakage is calculated in real time to ensure that the total leakage is within the leakage range.

[0010] Preferably, the H 光钻杆 =H 下塞面 -L 总 -H 下行 , where H 下塞面 is the height of the cement plug surface, L 总 is the total length of the cement plug, H 下行 is the descending height of cement slurry.

[0011] Preferably, the total length L of the cement plug is 总 =L1+H 下塞面 -H 套管 , where H 套管 is the lower depth of the ultra-deep well casing, and L1 is the length of the cement plug above the lower depth of the ultra-deep well casing.

[0012] Preferably, the calculation of L1 includes:

[0013] According to the lowering depth H of ultra-deep well casing 套管 And the cement plug bottom plug surface H 下塞面 Numerical calculation of the lower depth H of ultra-deep well casing 套管 With cement plug bottom plug surface H 下塞面 The amount of cement slurry between them is Q1;

[0014] According to Q1 and the designed total amount of cement slurry Q 总量 Calculate L1, L1 = (Q 总量 -Q1) / L 套管 , where L 套管 is the unit volume of the casing.

[0015] Preferably, the descending height H of the cement slurry is 下行 =Q 钻杆 / L 井眼 , where L 井眼 is the unit volume of the wellbore, Q 钻杆 It is the volume of the bare drill pipe.

[0016] Preferably, the total amount of cement slurry Q 总量 The calculation includes:

[0017] Get the distance between the cement plug surface and the lower depth H of the ultra-deep well casing 套管 The borehole volume between them is Q1;

[0018] Get the lower depth H of ultra-deep well casing 套管 The volume of the wellbore between the well bottom and the borehole is Q2;

[0019] According to the formula: Q 总量 =Q1+Q2 to calculate the total amount of cement slurry Q 总量 .

[0020] Preferably, the real-time calculation of the total amount of leakage makes the total amount of leakage within the leakage range include:

[0021] When the total amount of leakage is less than Q0, increase the grouting amount per hour;

[0022] When the total amount of leakage is greater than the threshold value M1, the hourly grouting amount is reduced;

[0023] Among them, 2 / 3M max ≤M1 <M max .

[0024] Preferably, the calculation of the total amount of leakage includes:

[0025] Monitor the annular liquid level and water hole liquid level to obtain cement slurry leakage out of the drill pipe and the loss of water hole and annular liquid level drop during the drilling process;

[0026] The sum of the annular fluid replenishment volume, the cement slurry loss out of the drill pipe, the water hole loss during the drilling process, and the annular fluid level drop loss is taken as the total loss volume.

[0027] The beneficial effects of the present invention are:

[0028] 1. Before construction, the feasible leakage range is calculated according to the location of the leakage points of the historical side drilling, and the leakage range is used as a reference for grouting to adjust the grouting volume to ensure that the total leakage meets the leakage range, thereby reducing the downhole risk, ensuring construction safety, and improving the success rate of cement plugging.

[0029] 2. Calculate the depth of cement plug driven by bare drill pipe, and calculate the leakage range based on the depth of cement plug driven by bare drill pipe, so as to further realize grouting control. It can take into account the dynamic process of coexistence of leakage and overflow in the wellbore before cement plug injection, and accurately quantify and control the grouting process, so that the final positions of the upper and lower plug surfaces of cement meet the design requirements, thereby ensuring that the strength of cement plug meets the requirements of side drilling. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the process of the present invention. DETAILED DESCRIPTION

[0031] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0032] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element.

[0033] It should be understood that the orientation or position relationship indicated by terms such as "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0034] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0035] Figure 1 The present invention provides a construction method for backfilling cement plugs for oilfield fracture cave ultra-deep wells, and the process is as follows:

[0036] According to the location of the leakage point of the historical side drilling well, the side drilling point location is designed, and the cement upper plug surface and cement lower plug surface locations are designed according to the side drilling point location, and the design depth H of the cement upper plug surface is obtained. 上塞面 and the design depth H of the cement plug surface 下塞面 ;

[0037] Calculate the penetration depth H of the bare drill pipe cement plug 光钻杆 ;

[0038] According to H 光钻杆 and H 上塞面 Calculate the maximum leakage M max =(H 上塞面 -H 光钻杆 )×L 井眼 , the allowable leakage range is Q0~Mmax , where L 井眼 is the unit volume of the wellbore, Q0 is the amount of pre-fluid and post-fluid;

[0039] Lower the drill rod to depth H 光钻杆 , grouting is carried out according to the displacement volume of the drill pipe, and the total leakage is calculated in real time to ensure that the total leakage is within the leakage range.

[0040] Preferably, the H 光钻杆 =H 下塞面 -L 总 -H 下行 , where H 下塞面 is the height of the cement plug surface, L 总 is the total length of the cement plug, H 下行 is the descending height of cement slurry.

[0041] Preferably, the total length L of the cement plug is 总 =L1+H 下塞面 -H 套管 , where H 套管 is the lower depth of the ultra-deep well casing, and L1 is the length of the cement plug above the lower depth of the ultra-deep well casing.

[0042] Preferably, the calculation of L1 includes:

[0043] According to the lowering depth H of ultra-deep well casing 套管 And the cement plug bottom plug surface H 下塞面 Numerical calculation of the lower depth H of ultra-deep well casing 套管 With cement plug bottom plug surface H 下塞面 The amount of cement slurry between them is Q1;

[0044] According to Q1 and the designed total amount of cement slurry Q 总量 Calculate L1, L1 = (Q 总量 -Q1) / L 套管 , where L 套管 is the unit volume of the casing.

[0045] Preferably, the descending height H of the cement slurry is 下行 =Q 钻杆 / L 井眼 , where L 井眼 is the unit volume of the wellbore, Q 钻杆 It is the volume of the bare drill pipe.

[0046] Preferably, the total amount of cement slurry Q 总量 The calculation includes:

[0047] Get the distance between the cement plug surface and the lower depth H of the ultra-deep well casing 套管 The borehole volume between them is Q1;

[0048] Get the lower depth H of ultra-deep well casing 套管 The volume of the wellbore between the well bottom and the borehole is Q2;

[0049] According to the formula: Q 总量 =Q1+Q2 to calculate the total amount of cement slurry Q 总量 .

[0050] Preferably, the real-time calculation of the total amount of leakage makes the total amount of leakage within the leakage range include:

[0051] When the total amount of leakage is less than Q0, increase the grouting amount per hour;

[0052] When the total amount of leakage is greater than the threshold value M1, the hourly grouting amount is reduced;

[0053] Among them, 2 / 3M max ≤M1 <M max The threshold M1 can be selected according to the actual construction requirements, Q0 and M max A certain value, which is not limited to 2 / 3M max .

[0054] Preferably, the calculation of the total amount of leakage includes:

[0055] Monitor the annular liquid level and water hole liquid level to obtain cement slurry leakage out of the drill pipe and the loss of water hole and annular liquid level drop during the drilling process;

[0056] The sum of the annular fluid replenishment volume, the cement slurry loss out of the drill pipe, the water hole loss during the drilling process, and the annular fluid level drop loss is taken as the total loss volume.

[0057] In order to ensure the acquisition and control of various parameters during construction, it is necessary to collect data on ultra-deep wells before construction to obtain basic data of ultra-deep wells and parameters of ultra-deep well casings. The basic data of ultra-deep wells include the liquid level height H in the well. 液面 , the density of drilling fluid ρ 钻井液 , bottom depth H 深度 And the design side drilling point position H 侧钻 The parameters of ultra-deep well casing include the length L of a single ultra-deep well casing, the depth H of the ultra-deep well casing, 套管 And the inner diameter of the casing Φ. In addition, the upper plug surface H of the cement plug is designed in advance. 上塞面 Position value, lower plug surface H 下塞面 The numerical value of .

[0058] The bottom hole pressure P 井底压力 According to the liquid level height H in the well 液面 , the density of drilling fluid ρ 钻井液, bottom depth H 深度 Calculate, specifically:

[0059] P 井底压力 =ρ 钻井液 ×g×(H 深度 -H 液面 ).

[0060] Embodiment 2

[0061] In order to further illustrate the technical solution of the present invention, in this embodiment, data from a well (TP278CH) in the Northwest Oilfield is used as an example for specific explanation.

[0062] The original well TP278H was started on April 21, 2017 and completed on July 15. The completed well depth was 6943m oblique / 6459.78m vertical. The completed formation was the Yijianfang Formation of the Ordovician. During the three drillings, the target layer was 1.17g / cm 3 When the density drilling reached 6926.50m, the well section 6926.5-6926.89m was emptied. Afterwards, the well section was drilled to 6943m and the total leakage during the drilling and completion process was 1.17g / cm 3 376.05m3 of drilling fluid 3 .

[0063] TP278CH Well pulled up 110 oil pipes at 09:00 on October 26, 2020. Before pulling up the oil pipes, the whole well was pushed and pressed. The mud density in the wellbore was 1.25g / cm 3 , the well has been in a leakage condition, and the annulus and water hole liquid level positions before cementing are: 1000m.

[0064] 1. Side drilling point design

[0065] The designed side drilling point is 6373m, in preparation for the next step of casing window side drilling construction.

[0066] 1. Design of cementing construction plan

[0067] 1.1 Basic Situation Analysis

[0068] The leakage point of this side drilling is at the bottom of the well at 6925m, and the designed side drilling point is 6373m. Because the 193.7mm casing is 6400.43m deep, the risk of lower bridge plug isolation is high, so the horizontal push method is used to drive the suspended cement plug for cementing and prepare for window side drilling. In order to ensure the quality of the cement plug, the lowest position of the upper cement plug surface is designed to be 6320m, and the lowest position of the lower plug surface is 6500m.

[0069] 1.2 Basic Data

[0070] (1) Borehole volume data (open hole section has not measured wellbore diameter, calculated at 3% expansion rate)

[0071] Well section (m) Section length (m) Casing inner diameter (mm) Wellbore unit volume (l / m) <![CDATA[Wellbore volume (m 3 )]]> 0-6320 6320 168.3-174.63 22.23-23.94 145.36 6320-6400 80 168.3 22.23 1.78 Naked eye 6400-6925 525 18.54 9.73

[0072] (2) Drilling tool displacement volume

[0073] 3.5″ drill pipe wall thickness 9.35mm, internal volume: 3.87L / m, closed row: 6.20L / m, open row: 2.34L / m.

[0074] 4.5″ drill pipe wall thickness 12.7mm, internal volume: 6.20L / m, closed row: 10.26L / m, open row: 4.06L / m.

[0075] (3) Cement slurry thickening test schedule

[0076]

[0077] 2. Calculation of cementing related data and construction design quantity

[0078] (1) Calculation of bottom hole pressure and equivalent density

[0079] Given: Liquid level height 1000m, well bottom 6925m corresponds to vertical depth 6900m, drilling fluid density 1.25g / cm 3 .

[0080] Bottom hole pressure P = ρ*g*H = 1.25*0.0098*(6900-1000) = 72.275MPa.

[0081] Wellbore equivalent density = bottom hole pressure / vertical depth / g = 72.275 / 6900 / 0.0098 = 1.07 g / cm 3 .

[0082] (2) Design of cement slurry quantity

[0083] The side drilling point is at 6373m, the lowest plug surface is reserved at 6320m, and the total mud volume of the 6320-6925m section is 1.78+9.73=11.51m 3 Assuming that all mud in the well section below 6320m is lost, cement slurry can also completely seal the well section 6320-6925m to meet the sidetracking requirements. Therefore, the designed cement slurry volume is 11.5m 3 .

[0084] Calculation of the depth of cement plug inserted into bare drill pipe

[0085] ① Calculate the cement plug section above 6500m below the lowest plug surface based on the amount of cement slurry.

[0086] Known: 6400-6500m open hole section cement slurry 1.85m 3, the casing volume above 6500m is 22.23l / m.

[0087] Length of cement plug above 6400m = (11.5-1.85) / 22.23*10 3 =434m.

[0088] That is, the total height of the cement plug section is 434+(6500-6400)=534m.

[0089] ② The height of cement slurry descending after cementing and slurry replacement is completed.

[0090] The designed injection density is 1.88g / cm 3 Cement slurry 11.5m 3 ; Density is 1.02g / cm 3 Pre-fill and post-fill 6m each 3 ; According to the borehole pressure, the length of the bare drill pipe and drill string assembly is calculated after the cementing and slurry replacement is completed. By calculating that when the cement slurry is completely replaced by the bare drill pipe, the equivalent density of 1000m-6925m is basically the same as the equivalent density of the well section before cementing. The main reason for the downward movement of cement slurry is that the volume of the 4 1 / 2″ drill pipe (6.2m 3 ) is caused by the liquid column pressure generated by this part of mud.

[0091] Therefore, the cement slurry descending height = 6.2 / 22.23*10 3 =279m.

[0092] Through points ① and ②, the depth of the bare drill pipe is determined to be 6500-534-279=5687m.

[0093] (4) Calculate the allowable leakage range

[0094] ①Inject cement 11.5m at 5687m 3 The initial cement plugging section is when all the cement slurry comes out of the drill pipe.

[0095] Cement plug surface position: 5687+11.5 / 22.23*10 3 =5687+517=6204m

[0096] The initial cement slurry distribution section is 5687-6204m.

[0097] ② When the upper plug surface of the bottom hole leakage cement slurry descends to 6320m, calculate the maximum allowable leakage.

[0098] Maximum allowable mud loss = (6320-5687)*22.23 / 10 3 =14.07m3.

[0099] Therefore, when the leakage range is 6-14.07m3, the cement plug section can seal the 6320-6500m well section and meet the requirements of cement plugging in side drilling.

[0100] 3. Brief introduction to the actual construction of cement plugging and plugging

[0101] (1) Carry out cementing according to the cementing design. Lower the drill pipe to the designed well depth of 5687m and use the horizontal push method to cement: inject 6.0m of pre-fluid 3 , 11.5m3 of cement slurry was injected, 6m of post-injection fluid was injected 3 , density 1.25g / cm 3 Well slurry 30m 3 , construction displacement 0.7m 3 / min. The cementing and injection process is completed.

[0102] (2) The well was opened for drilling operations, and the wellbore pressure was carefully controlled during the drilling process. Grouting was carried out according to the displacement volume of the drill pipe during the drilling process. After drilling, the annular liquid level was measured at 1050m and the water hole liquid level was 900m after 2 hours. The leakage loss of the drilling tool water hole was calculated to be 6.51m 3 , the annulus rose by 0.6m 3 , actual leakage volume 5.91m 3 . The subsequent drilling process grouting will increase by 1m per hour. 3 (In addition to the displacement of drilling tools), the water eye and annulus liquid level are monitored every hour, the leakage is calculated by the drop in liquid level, the bottom hole pressure is controlled, and the grouting volume is adjusted. After 6 hours of drilling, a total of 4m3 more grouting was added. 3 The annulus and drilling tool water hole heights fluctuate around 1000m, that is, the total leakage is 10.2m 3 At the same time, according to the cementing test, the cement slurry initially solidified after 6 hours, and then the grouting was carried out normally according to the displacement volume of the drilling tool. The leakage volume was calculated according to the injection volume, displacement volume, drilling tool water hole and annular liquid level during the subsequent drilling, and there was no continuous leakage.

[0103] The method for calculating the amount of leakage is:

[0104] Total leakage = cement slurry leakage out of drill pipe + annular fluid replenishment (excluding displacement volume) + mud loss due to drop in water hole and annular fluid level during drilling. According to this formula, the total leakage in this embodiment can be calculated to be 10.2m 3 .

[0105] In order to verify this method, the actual plug surface is compared with the theoretical plug surface, proving that the cement plug backfilled by this method can meet the construction requirements, as follows:

[0106] Theoretical cement plug surface = 5687 + 10.2 / 22.23 * 10 3=6146m.

[0107] After backfilling the cement plug in this scheme, the drilling plug was lowered after waiting for 48 hours to set. The actual plug surface was 6100m, which was within the allowable error range with the theoretical cement upper plug surface of 6146m, meeting the construction requirements.

[0108] It should be understood that the size of the serial numbers of the steps in the above embodiments does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0109] The embodiments described above are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. Such modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A construction method for backfilling cement plugs for oilfield fracture cave ultra-deep wells, characterized in that: include: According to the location of the leakage point of the historical sidetracking well, the sidetracking point location is designed, and the cement upper plug surface and cement lower plug surface locations are designed according to the sidetracking point location, and the design depth H of the cement upper plug surface is obtained. 上塞 Design depth H of the surface and cement plug surface 下塞面 ; Calculate the penetration depth H of the bare drill pipe cement plug 光钻杆 ; According to H 光钻杆 and H 上塞面 Calculate the maximum leakage M max =(H 上塞面 -H 光钻杆 )×L 井眼 , the allowable leakage range is Q0~M max , where L 井眼 is the unit volume of the wellbore, Q0 is the amount of pre-fluid and post-fluid; Lower the drill rod to depth H 光钻杆 , grouting is performed according to the displacement volume of the drill pipe, and the total leakage is calculated in real time so that the total leakage is within the leakage range; The H 光钻杆 =H 下塞面 -L 总- H 下行 , where H 下塞面 is the height of the cement plug surface, L 总 is the total length of the cement plug, H 下行 is the descending height of cement slurry; The real-time calculation of the total amount of leakage makes the total amount of leakage within the leakage range include: When the total amount of leakage is less than Q0, increase the grouting amount per hour; When the total amount of leakage is greater than the threshold value M1, the hourly grouting amount is reduced; Among them, 2 / 3M max ≤M1<M max , H 上塞面 , H 下塞面 , H 光钻杆 , H 下行 , L 总 The unit is m, L 井眼 The unit is l / m, Q0, M max The unit is m 3 ; The calculation of the total amount of leakage includes: Monitor the annular liquid level and water hole liquid level to obtain cement slurry leakage out of the drill pipe and the loss of water hole and annular liquid level drop during the drilling process; The sum of the annular fluid replenishment volume, the cement slurry loss out of the drill pipe, the water hole loss during the drilling process, and the annular fluid level drop loss is taken as the total loss volume.

2. The construction method of cement plug for backfilling of ultra-deep wells with fractured karst caves in oil fields according to claim 1, characterized in that: The total length L of the cement plug 总 =L1+H 下塞面 -H 套管 , where H 套管 is the lower depth of the ultra-deep well casing, and L1 is the length of the cement plug above the lower depth of the ultra-deep well casing; Among them, L1, H 套管 The unit is m.

3. The construction method of cement plug for backfilling of ultra-deep wells with fractured karst caves in oil fields according to claim 2, characterized in that: The calculation of L1 includes: According to the lowering depth H of ultra-deep well casing 套管 And the cement plug bottom plug surface H 下塞面 Numerical calculation of the lower depth H of ultra-deep well casing 套管 With cement plug bottom plug surface H 下塞面 The amount of cement slurry between them is Q1; According to Q1 and the designed total amount of cement slurry Q 总量 Calculate L1, L1 = (Q 总量 -Q1) / L 套管 , where L 套管 is the unit volume of the casing; Among them, Q1, Q 总量 The unit is m 3 , L 套管 The unit is l / m.

4. The construction method of cement plug for backfilling of ultra-deep wells with fractured karst caves in oil fields according to claim 1, characterized in that: The descending height H of the cement slurry 下行 =Q 钻杆 / L 井眼 , where L 井眼 is the unit volume of the wellbore, Q 钻杆 is the volume of the drill pipe, Q 钻杆 The unit is m 3 .

5. The construction method of cement plug for backfilling of ultra-deep wells with fractured karst caves in oil fields according to claim 3, characterized in that: The total amount of cement slurry Q 总量 The calculation includes: Get the distance between the cement plug surface and the lower depth H of the ultra-deep well casing 套管 The borehole volume between them is Q1; Get the lower depth H of ultra-deep well casing 套管 The volume of the wellbore between the well bottom and the borehole is Q2; According to the formula: Q 总量 =Q1+Q2 to calculate the total amount of cement slurry Q 总量 ; Among them, the unit of Q2 is m 3 .

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