A method for circulating plugging of inert materials in construction of surface drilling in fractured formation

Abstract

The application discloses a kind of fissure development stratum ground drilling construction inert material circulation plugging method, comprising: determining lost well section and obtaining leakage speed, fissure opening and wellbore size;According to the leakage speed, determine the working condition of leakage, according to the fissure opening, determine three grades of particle size, according to the working condition of leakage, determine the type and mass percentage concentration of inert plugging material, adjust the funnel viscosity of drilling fluid according to the type and mass percentage concentration of inert plugging material, and determine the circulating discharge according to the wellbore size;Three grades of particles are added to drilling fluid to prepare plugging slurry, and circulating pump into the lost well section to form a bridge plug;According to the wellhead return slurry condition, judge the plugging effect, and control to continue or stop circulating plugging.The application can improve the adaptability of plugging material to fissure condition and leakage working condition.

Description

Technical Field

[0001] This invention relates to the field of surface drilling construction technology, specifically to a method for circulating and plugging leaks with inert materials in surface drilling construction of fractured formations. Background Technology

[0002] Fractured formations include fault fracture zones, coal seam fractures, and rock joints. Because these formations contain fractures of varying degrees of opening and development, drilling fluid can easily enter the formation along these fractures during surface drilling operations, resulting in drilling fluid loss.

[0003] Drilling fluid loss can affect the normal circulation of drilling fluid in the well, thus impacting the drilling fluid's support for the wellbore and its ability to carry drill cuttings. In severe cases, it can even lead to wellbore instability, stuck drill bits, and other construction problems. Therefore, when conducting surface drilling operations in fractured formations, it is usually necessary to plug the lost section of the well.

[0004] In circulating plugging operations, plugging materials enter the lost well section with the drilling fluid and accumulate in the fractures to reduce or prevent further loss of drilling fluid. The plugging effect is related to the fracture conditions, the plugging material, and the circulating operation conditions. When the particle size of the plugging material is not compatible with the degree of fracture opening, the plugging material is not easy to form an effective seal at the fracture entrance, which may affect the plugging effect.

[0005] In addition, the leakage situation, fracture conditions and wellbore conditions vary in different leakage sections; if the plugging material and circulation construction parameters are not compatible with the actual leakage situation, it may affect the suspension, transportation and sealing process of the plugging material; at the same time, during the circulation plugging process, it is also necessary to judge the transportation and sealing status of the plugging material based on the wellhead slurry return situation in order to determine the subsequent circulation operation.

[0006] Therefore, improving the compatibility between plugging materials and fracture conditions and leakage situations, and enhancing the pertinence and controllability of the cyclic plugging construction process are technical problems that need to be further solved in surface drilling operations in fractured formations. Summary of the Invention

[0007] The purpose of this invention is to provide a method for inert material circulation plugging in surface drilling operations in fractured formations, in order to solve the problems mentioned in the background art regarding the insufficient adaptability of plugging materials to fracture conditions and leakage, and the poor targeting and process controllability of plugging operations.

[0008] To achieve the above objectives, the present invention provides the following technical solution: a method for inert material circulation plugging in surface drilling operations in fractured formations, comprising:

[0009] Identify the lost well sections during surface drilling operations and obtain the loss velocity, fracture opening, and wellbore size of the lost well sections;

[0010] The leakage condition of the leakage section is determined based on the leakage rate.

[0011] The particle sizes of the largest, medium, and small particles in the inert plugging material are determined according to the fracture opening. The type and mass percentage concentration of the inert plugging material are determined according to the leakage conditions. The drilling fluid funnel viscosity is adjusted according to the type and mass percentage concentration of the inert plugging material. The circulation discharge rate is determined according to the wellbore size.

[0012] The largest, medium, and small particles with the determined particle size are added together to the drilling fluid after viscosity adjustment in the funnel and stirred to prepare the plugging slurry.

[0013] The drill string is lowered above the lost well section, and the plugging slurry is pumped into the well according to the circulation rate, so that the inert plugging material enters the fracture of the lost well section along with the plugging slurry and forms a bridge plug at the entrance of the fracture.

[0014] During the process of circulating and pumping the plugging slurry, the return slurry at the wellhead is obtained, the plugging effect is judged based on the return slurry at the wellhead, and the circulation and pumping of the plugging slurry is controlled based on the judgment result.

[0015] As a further technical solution of the present invention, the particle size of the largest particle is taken as the target particle size based on the estimated crack opening.

[0016] The particle size of the medium-sized particles is 1 / 3 to 1 / 2 of the estimated crack opening.

[0017] The particle size of the small particles is 1 / 5 to 1 / 10 of the estimated crack opening.

[0018] As a further technical solution of the present invention, the inert sealing material is selected from at least one of walnut shells, sawdust, mica flakes, vermiculite and cottonseed hulls, and the largest particles, the medium particles and the small particles are respectively composed of the selected inert sealing material.

[0019] As a further technical solution of the present invention, when the leakage rate is less than 15 m 3 When / h, the leakage condition is determined to be a minor leakage condition, and the inert plugging material is sawdust;

[0020] When the leakage rate is greater than or equal to 15 m 3 / h and less than 30 m 3When / h, the leakage condition is determined to be a medium leakage condition. The inert plugging material includes sawdust and walnut shells used together, and the sawdust and the walnut shells respectively include the largest particles, the medium particles and the small particles.

[0021] When the leakage rate is greater than or equal to 30 m 3 When the leakage condition is determined to be a continuous leakage condition, the inert plugging material is sawdust, and thick mud is used as the drilling fluid for preparing the plugging slurry.

[0022] As a further technical solution of the present invention, under the condition of slight leakage, the mass percentage concentration of the sawdust is 2% to 5%, the viscosity of the drilling fluid funnel is 30 to 35 s, and the circulation discharge rate determined according to the wellbore size is 30 to 40 m³. 3 / h, the time for circulating the plugging slurry is 2 to 3 hours.

[0023] As a further technical solution of the present invention, under the medium leakage condition, the total mass percentage concentration of the sawdust and the walnut shell is 5% to 10%, the drilling fluid funnel viscosity is 35 to 40 s, and the circulation discharge rate determined according to the wellbore size is 40 to 50 m³ / s. 3 / h, the time for circulating the plugging slurry is 3 to 4 hours.

[0024] As a further technical solution of the present invention, under the continuous leakage condition, the sawdust mass percentage concentration is 5% to 10%, the drilling fluid funnel viscosity is 40 to 50 s, and the circulation discharge rate determined according to the wellbore size is 40 to 50 m³ / s. 3 / h, the time for circulating the plugging slurry is 3-4 h;

[0025] The sawdust is dispersed in the thick mud, which suspends and carries the sawdust.

[0026] As a further technical solution of the present invention, the preparation of the sealing slurry includes:

[0027] The funnel viscosity of the drilling fluid is adjusted according to the type and mass percentage concentration of the inert plugging material;

[0028] During the stirring of the drilling fluid, the largest particles, the medium particles, and the small particles are all added to the drilling fluid;

[0029] Continue stirring the drilling fluid to disperse the largest, medium, and small particles in the drilling fluid, thereby obtaining the plugging slurry.

[0030] As a further technical solution of the present invention, when the amount of slurry returned from the wellhead increases compared to before the slurry was pumped in, and has not yet returned to the normal amount of slurry returned, the current circulatory plugging is determined to be effective, and the slurry is pumped in again.

[0031] When the wellhead slurry return rate returns to normal, it is determined that the fracture has been completely sealed, and the circulation pumping of the plugging slurry is stopped.

[0032] As a further technical solution of the present invention, if the amount of slurry returned from the wellhead has not increased compared to before the slurry was pumped in before the corresponding circulation time has been reached, the slurry is pumped in again; if the amount of slurry returned from the wellhead has not increased compared to before the slurry was pumped in after the corresponding circulation time has been reached, the current slurry pumping is deemed invalid and the current slurry pumping is terminated.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] Based on the estimated fracture opening of the lost well section, this invention determines the particle size of the largest, medium, and small particles in the inert plugging material, and uses all three particle sizes together to prepare the plugging slurry, so that the particle size of the inert plugging material is adapted to the fracture opening. As a result, inert plugging materials of different particle sizes can enter the fracture with the plugging slurry and accumulate at the fracture entrance to form a bridge plug, providing conditions to prevent drilling fluid from continuing to enter the fracture.

[0035] This invention determines the leakage conditions based on the leakage rate, and determines the type and mass percentage concentration of the inert plugging material based on the leakage conditions, so that the slight leakage conditions, moderate leakage conditions and continuous leakage conditions correspond to the corresponding plugging material systems, thereby enabling the formulation of plugging slurry for different leakage conditions and improving the adaptability of the circulating plugging method to different leakage conditions.

[0036] This invention adjusts the viscosity of the drilling fluid funnel according to the type and mass percentage concentration of the inert plugging material, so that the suspension and carrying capacity of the drilling fluid is adapted to the inert plugging material. In particular, under continuous loss conditions, using thick mud as the drilling fluid for preparing the plugging slurry can improve the suspension capacity of sawdust in the plugging slurry, reduce the possibility of sawdust settling during slurry preparation and circulation, and facilitate the delivery of sawdust to the lost well section.

[0037] The present invention determines the circulation discharge rate based on the wellbore size of the lost well section, so that the circulation and transportation conditions of the plugging slurry are adapted to the wellbore conditions. This is beneficial for the inert plugging material to reach the lost well section and enter the fracture along with the plugging slurry, and avoids the circulation discharge rate being incompatible with the wellbore conditions, which would affect the delivery of the plugging slurry.

[0038] This invention obtains the wellhead return volume during the circulation pumping of plugging slurry and uses the wellhead return volume before the circulation pumping of plugging slurry as a comparison benchmark; the plugging effect is judged based on whether the wellhead return volume increases or returns to the normal return volume, providing a basis for controlling the continued circulation or stopping the circulation of plugging slurry;

[0039] This invention controls the actual circulation process of the plugging slurry based on the change in the amount of slurry returning from the wellhead. When the amount of slurry returning from the wellhead increases but has not yet returned to normal, the slurry continues to be pumped in. When the amount of slurry returning from the wellhead returns to normal, the pumping stops. The current plugging cycle ends when the amount of slurry returning from the wellhead has not increased after the corresponding circulation time has elapsed. Therefore, the plugging operation can be adapted to the actual plugging condition, improving the controllability of the plugging process and helping to avoid unnecessary circulation after the plugging has been completed.

[0040] This invention sequentially connects the determination of leakage conditions, particle size matching, selection of plugging materials, adjustment of drilling fluid funnel viscosity, determination of circulation discharge rate, preparation of plugging slurry, circulation pumping, and judgment of slurry return, forming a complete construction process from determining the plugging scheme to judging the plugging effect. This is conducive to improving the standardization and pertinence of circulation plugging construction in fractured formations. Attached Figure Description

[0041] Figure 1 This is a schematic diagram of the method flow of the present invention. Detailed Implementation

[0042] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0043] Please see Figure 1 Example 1 provides a method for plugging leaks in surface drilling operations using inert materials in fractured formations, comprising:

[0044] Identify the lost well sections during surface drilling operations and obtain the loss velocity, fracture opening, and wellbore size of the lost well sections;

[0045] The fracture opening is estimated based on logging data from the lost circulation section. For example, logging data for estimating the fracture opening can be obtained using methods such as dual-lateral logging or imaging logging, or other logging data capable of providing fracture opening estimation results can be used.

[0046] The leakage condition of the leakage section is determined based on the leakage rate.

[0047] The particle sizes of the largest, medium, and small particles in the inert plugging material are determined according to the fracture opening. The type and mass percentage concentration of the inert plugging material are determined according to the leakage conditions. The drilling fluid funnel viscosity is adjusted according to the type and mass percentage concentration of the inert plugging material. The circulation discharge rate is determined according to the wellbore size.

[0048] The largest, medium, and small particles with the determined particle size are added together to the drilling fluid after viscosity adjustment in the funnel and stirred to prepare the plugging slurry.

[0049] The drill string is lowered above the lost well section, and the plugging slurry is pumped into the well according to the circulation rate, so that the inert plugging material enters the fracture of the lost well section along with the plugging slurry and forms a bridge plug at the entrance of the fracture.

[0050] During the process of circulating and pumping the plugging slurry, the wellhead slurry return situation is obtained, the plugging effect is judged based on the wellhead slurry return situation, and the circulation and pumping of the plugging slurry is controlled based on the judgment result.

[0051] Furthermore, the particle size of the largest particle is taken as the target particle size based on the estimated crack opening.

[0052] The particle size of the medium-sized particles is 1 / 3 to 1 / 2 of the estimated crack opening.

[0053] The particle size of the small particles is 1 / 5 to 1 / 10 of the estimated crack opening.

[0054] Furthermore, the inert sealing material is selected from at least one of walnut shells, sawdust, mica flakes, vermiculite, and cottonseed hulls, and the largest particles, the medium particles, and the small particles are each composed of the selected inert sealing material.

[0055] Furthermore, when the leakage rate is less than 15 m 3 When / h, the leakage condition is determined to be a minor leakage condition, and the inert plugging material is sawdust;

[0056] When the leakage rate is greater than or equal to 15 m 3 / h and less than 30 m 3 When / h, the leakage condition is determined to be a medium leakage condition. The inert plugging material includes sawdust and walnut shells used together, and the sawdust and the walnut shells respectively include the largest particles, the medium particles and the small particles.

[0057] When the leakage rate is greater than or equal to 30 m 3When / h, the leakage condition is determined to be a continuous leakage condition, the inert plugging material is sawdust, and thick mud is used as the drilling fluid for preparing the plugging slurry;

[0058] Furthermore, under the aforementioned slight leakage condition, the sawdust concentration is 2%–5% by mass, the drilling fluid funnel viscosity is 30–35 s, and the circulation rate determined based on the wellbore size is 30–40 m³ / s. 3 / h, the time for circulating the plugging slurry is 2-3 h;

[0059] Furthermore, under the aforementioned moderate leakage conditions, the total mass percentage concentration of the sawdust and walnut shells is 5%–10%, the funnel viscosity of the drilling fluid is 35–40 s, and the circulation rate determined based on the wellbore size is 40–50 m³ / s. 3 / h, the time for circulating the plugging slurry is 3-4 h;

[0060] Furthermore, under the continuous leakage condition, the sawdust concentration is 5%–10% by mass, the drilling fluid funnel viscosity is 40–50 s, and the circulation rate determined according to the wellbore size is 40–50 m³ / s. 3 / h, the time for circulating the plugging slurry is 3-4 h;

[0061] The sawdust is dispersed in the thick mud slurry, which is used to suspend and carry the sawdust.

[0062] Furthermore, the preparation of the sealing slurry includes:

[0063] The funnel viscosity of the drilling fluid is adjusted according to the type and mass percentage concentration of the inert plugging material;

[0064] During the stirring of the drilling fluid, the largest particles, the medium particles, and the small particles are all added to the drilling fluid;

[0065] Continue stirring the drilling fluid to disperse the largest, medium, and small particles in the drilling fluid, thereby obtaining the plugging slurry;

[0066] Furthermore, when the amount of slurry returned from the wellhead increases compared to before the plugging slurry was pumped in, and has not yet returned to the normal amount of slurry returned, the current plugging process is deemed effective, and the plugging slurry is pumped in again.

[0067] When the wellhead slurry return rate returns to normal, it is determined that the fracture has been completely sealed, and the circulation pumping of the plugging slurry is stopped.

[0068] Furthermore, if the amount of slurry returned from the wellhead has not increased compared to before the slurry was pumped in before the corresponding circulation time has been reached, the slurry will continue to be pumped in. If the amount of slurry returned from the wellhead has not increased compared to before the slurry was pumped in after the corresponding circulation time has been reached, the current slurry pumping is deemed invalid and the current slurry pumping is terminated.

[0069] Example 2: Determination of process parameters for circulating plugging:

[0070] In this embodiment, the leakage condition corresponding to the leakage section is determined according to the leakage rate, and the type and mass percentage concentration of the inert plugging material are determined according to different leakage conditions. The drilling fluid funnel viscosity is adjusted according to the type and mass percentage concentration of the inert plugging material, the circulation discharge rate is determined according to the wellbore size, and the corresponding circulation time is selected.

[0071] The relationship between leakage rate and leakage conditions is shown in Table 1.

[0072] Table 1 Classification of Leakage Conditions

[0073]

[0074] In order to correspond with the three types of leak sealing solutions in this application, this embodiment classifies micro-leakage and small leaks into slight leakage conditions, medium leaks into moderate leakage conditions, and large leaks and total leaks into continuous leakage conditions.

[0075] The process parameters for cyclic plugging corresponding to different leakage conditions are shown in Table 2.

[0076] Table 2 Circulation Leakage Plugging Process Parameters

[0077]

[0078] In Table 2, under slight leakage conditions, the mass percentage concentration of the inert plugging material is the same as the mass percentage concentration of sawdust; under moderate leakage conditions, the mass percentage concentration of the inert plugging material is the same as the total mass percentage concentration of sawdust and walnut shells; and under continuous leakage conditions, the mass percentage concentration of the inert plugging material is the same as the mass percentage concentration of sawdust.

[0079] The concentration of the inert plugging material in this application is expressed as a mass percentage concentration; under moderate leakage conditions, the total mass percentage concentration is the combined mass percentage concentration of sawdust and walnut shells.

[0080] The drilling fluid viscosity in this application is the drilling fluid funnel viscosity, which is measured in seconds (s). It is used to represent the time required for a fixed volume of drilling fluid to flow out of the funnel and is a conditional viscosity.

[0081] The type and mass percentage concentration of the inert plugging material are determined based on the leakage conditions. The viscosity of the drilling fluid funnel is adjusted to the corresponding range shown in Table 2 based on the type and mass percentage concentration of the inert plugging material. The circulation discharge rate is determined within the corresponding range shown in Table 2 based on the wellbore size of the leakage section, and the circulation time corresponding to the leakage conditions is adopted. During the circulation pumping of the plugging slurry, the plugging effect is judged based on the wellhead return slurry situation, and the circulation pumping of the plugging slurry is controlled to continue or stop based on the judgment result.

[0082] Example 3: Circulatory leak sealing under slight leakage conditions:

[0083] In this embodiment, when the leakage velocity of the lost section is less than 15 m 3 When / h, it is determined that the lost well section is in a slight loss condition;

[0084] Obtain the estimated fracture opening of the lost well section, and screen the sawdust according to the fracture opening so that the screened sawdust includes the largest particles, medium particles and small particles.

[0085] Wherein, the particle size of the largest particle is the target particle size based on the estimated crack opening, the particle size of the medium particle is 1 / 3 to 1 / 2 of the estimated crack opening, and the particle size of the small particle is 1 / 5 to 1 / 10 of the estimated crack opening.

[0086] The sawdust mass percentage concentration is controlled at 2% to 5%, and the drilling fluid funnel viscosity is adjusted to 30 to 35 s according to the sawdust mass percentage concentration.

[0087] During the process of adjusting the viscosity of the drilling fluid funnel, the drilling fluid is stirred; while maintaining the stirring state, sawdust with the largest, medium and small particles is added to the drilling fluid; stirring continues to disperse sawdust of different particle sizes in the drilling fluid to obtain the plugging slurry.

[0088] Obtain the wellbore size of the lost well section, and based on the wellbore size, within 30–40 m... 3 Determine the circulating displacement within the range of / h;

[0089] The drill string is lowered above the lost section of the well, and the plugging slurry is pumped into the well according to the determined circulation rate. After the plugging slurry reaches the lost section of the well, sawdust of different particle sizes enters the fracture with the plugging slurry and accumulates at the fracture entrance to form a bridge plug.

[0090] The time for circulating the plugging slurry is 2-3 hours. During the circulation pumping process, the wellhead slurry return data is continuously monitored. The plugging effect is judged based on the wellhead slurry return data, and the circulation pumping of the plugging slurry is controlled to continue or stop based on the judgment result.

[0091] Example 4: Circulatory plugging under moderate leakage conditions:

[0092] In this embodiment, when the leakage velocity of the lost well section is greater than or equal to 15 m 3 / h and less than 30 m 3 When / h, it is determined that the lost well section is under medium loss conditions;

[0093] The estimated fracture opening of the lost well section is obtained, and the sawdust and walnut shells are screened to ensure that the screened sawdust and walnut shells include the largest, medium and small particles.

[0094] Wherein, the particle size of the largest particle is the target particle size based on the estimated crack opening, the particle size of the medium particle is 1 / 3 to 1 / 2 of the estimated crack opening, and the particle size of the small particle is 1 / 5 to 1 / 10 of the estimated crack opening.

[0095] Sawdust and walnut shells are used together to prepare the sealing grout, with a total mass percentage concentration of 5% to 10%; this embodiment does not limit the specific ratio between sawdust and walnut shells.

[0096] Adjust the viscosity of the drilling fluid funnel to 35–40 s based on the type and total mass percentage concentration of sawdust and walnut shells.

[0097] While keeping the drilling fluid agitated, sawdust and walnut shells, which respectively contain the largest, medium, and small particles, are added to the drilling fluid; stirring is continued to disperse the sawdust and walnut shells in the drilling fluid, thus obtaining a plugging slurry.

[0098] Obtain the wellbore size of the lost well section, and based on the wellbore size, within 40–50 m... 3 Determine the circulating displacement within the range of / h;

[0099] The drill string is lowered above the lost section of the well. The plugging slurry is pumped into the well according to the determined circulation rate, so that sawdust and walnut shells enter the fractures of the lost section along with the plugging slurry and form a bridge plug at the fracture entrance.

[0100] The time for circulating the plugging slurry is 3 to 4 hours. During the circulation of the plugging slurry, the amount of slurry returning to the wellhead is continuously measured; when the amount of slurry returning to the wellhead increases compared to before the circulation of the plugging slurry, and has not yet returned to the normal amount of slurry, the circulation of the plugging slurry continues; when the amount of slurry returning to the normal amount of slurry returns to the normal amount of slurry, the circulation of the plugging slurry is stopped.

[0101] Example 5: Circulatory leak sealing under continuous leakage conditions:

[0102] In this embodiment, when the leakage velocity of the lost well section is greater than or equal to 30 m... 3 When / h, it is determined that the lost well section is in a continuous loss condition;

[0103] Obtain the estimated fracture opening of the lost well section, and screen the sawdust according to the fracture opening so that the screened sawdust includes the largest particles, medium particles and small particles.

[0104] Wherein, the particle size of the largest particle is the target particle size based on the estimated crack opening, the particle size of the medium particle is 1 / 3 to 1 / 2 of the estimated crack opening, and the particle size of the small particle is 1 / 5 to 1 / 10 of the estimated crack opening.

[0105] In this embodiment, thick mud is used as the drilling fluid for preparing the plugging slurry, and sawdust is used as the inert plugging material; the mass percentage concentration of sawdust is 5% to 10%, and the funnel viscosity of the drilling fluid is 40 to 50 s;

[0106] The thick slurry is used to suspend and carry sawdust, thereby reducing the possibility of sawdust settling during slurry preparation and circulation.

[0107] When preparing the sealing slurry, first stir the thick mud slurry and adjust the funnel viscosity of the thick mud slurry to 40-50s; while keeping stirring, add sawdust with the largest, medium and small particles to the thick mud slurry; continue stirring to disperse the sawdust of the three particle sizes in the thick mud slurry to obtain the sealing slurry.

[0108] Obtain the wellbore size of the lost well section, and based on the wellbore size, within 40–50 m... 3 Determine the circulating displacement within the range of / h;

[0109] The drill string is lowered above the lost section of the well. The plugging slurry is pumped into the well according to the determined circulation rate, so that sawdust of different particle sizes enters the fractures of the lost section along with the thick mud and forms a bridge plug at the fracture entrance.

[0110] The time for circulating the plugging slurry is 3-4 hours. During the circulation of the plugging slurry, the amount of slurry returning to the wellhead is continuously measured; when the amount of slurry returning to the wellhead increases compared to before the circulation of the plugging slurry, but has not yet returned to the normal amount, the circulation of the plugging slurry continues; when the amount of slurry returning to the wellhead returns to the normal amount, the circulation of the plugging slurry is stopped; when the amount of slurry returning to the wellhead still does not increase after the circulation time has been reached, the current circulation plugging is terminated.

[0111] Example 6: Judging the effectiveness of leak sealing:

[0112] This embodiment applies to any of the leakage conditions in Embodiments 3 to 5;

[0113] Before the plugging slurry is pumped in, the amount of slurry returned from the wellhead is recorded and used as a benchmark for judging the plugging effect.

[0114] During the process of circulating and pumping the plugging slurry, the amount of slurry returned to the wellhead is continuously obtained; the color of the returned slurry and whether it contains inert plugging material can also be observed to help determine the circulation status of the plugging slurry in the well.

[0115] When the amount of slurry returned from the wellhead increases compared to before the plugging slurry was pumped in, and has not yet returned to the normal amount of slurry returned, it indicates that the leakage has decreased, and the current plugging is deemed effective. The plugging slurry should then continue to be pumped in.

[0116] When the slurry return rate at the wellhead returns to normal, it is determined that the fracture has been completely sealed, and the circulation pumping of plugging slurry is stopped; drilling can continue after confirming that the slurry return rate at the wellhead remains normal.

[0117] If the corresponding circulation time has not been reached and the amount of slurry returned from the wellhead has not increased compared to before the slurry was pumped in, continue pumping the slurry in circulation; if the amount of slurry returned from the wellhead still has not increased after the corresponding circulation time has been reached, the current slurry pumping is deemed ineffective and the current slurry pumping is terminated.

[0118] After completing this cycle of leak sealing, other leak sealing methods can be adopted according to the on-site construction conditions.

[0119] Alternative implementation methods:

[0120] In addition to satisfying the size relationship between the largest, medium and small particles and the estimated fracture opening, and being able to enter the fracture with the plugging grout to form a bridge plug, the inert plugging material can also be selected from at least one of mica flakes, vermiculite and cottonseed hulls.

[0121] When using mica flakes, vermiculite, or cottonseed hulls, determine the appropriate particle size according to their particle morphology, and ensure that the selected material includes the largest, medium, and small particles simultaneously.

[0122] The largest, medium, and small particles can be composed of the same inert sealing material or different types of inert sealing materials. When using two or more inert sealing materials, the specific proportions between the different materials are determined according to the actual sealing construction needs.

[0123] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for plugging leaks in surface drilling operations using inert materials in fractured formations, characterized in that, include: Identify the lost well sections during surface drilling operations and obtain the loss velocity, fracture opening, and wellbore size of the lost well sections; The leakage condition of the leakage section is determined based on the leakage rate. The particle sizes of the largest, medium, and small particles in the inert plugging material are determined according to the fracture opening. The type and mass percentage concentration of the inert plugging material are determined according to the leakage conditions. The drilling fluid funnel viscosity is adjusted according to the type and mass percentage concentration of the inert plugging material. The circulation discharge rate is determined according to the wellbore size. The largest, medium, and small particles with the determined particle size are added together to the drilling fluid after viscosity adjustment in the funnel and stirred to prepare the plugging slurry. The drill string is lowered above the lost well section, and the plugging slurry is pumped into the well according to the circulation rate, so that the inert plugging material enters the fracture of the lost well section along with the plugging slurry and forms a bridge plug at the entrance of the fracture. During the process of circulating and pumping the plugging slurry, the return slurry at the wellhead is obtained, the plugging effect is judged based on the return slurry at the wellhead, and the circulation and pumping of the plugging slurry is controlled based on the judgment result.

2. The method for inert material circulation plugging in surface drilling operations in fractured formations according to claim 1, characterized in that: The particle size of the largest particle is taken as the target particle size based on the estimated crack opening. The particle size of the medium-sized particles is 1 / 3 to 1 / 2 of the estimated crack opening. The particle size of the small particles is 1 / 5 to 1 / 10 of the estimated crack opening.

3. The method for inert material circulation plugging in surface drilling operations in fractured formations according to claim 1 or 2, characterized in that: The inert sealing material is selected from at least one of walnut shells, sawdust, mica flakes, vermiculite, and cottonseed hulls, and the largest particles, the medium particles, and the small particles are each composed of the selected inert sealing material.

4. The method for inert material circulation plugging in surface drilling operations in fractured formations according to any one of claims 1 to 3, characterized in that: When the leakage rate is less than 15 m 3 When / h, the leakage condition is determined to be a minor leakage condition, and the inert plugging material is sawdust; When the leakage rate is greater than or equal to 15 m 3 / h and less than 30 m 3 When / h, the leakage condition is determined to be a medium leakage condition. The inert plugging material includes sawdust and walnut shells used together, and the sawdust and the walnut shells respectively include the largest particles, the medium particles and the small particles. When the leakage rate is greater than or equal to 30 m 3 When the leakage condition is determined to be a continuous leakage condition, the inert plugging material is sawdust, and thick mud is used as the drilling fluid for preparing the plugging slurry.

5. The method for inert material circulation plugging in surface drilling operations in fractured formations according to claim 4, characterized in that: Under the aforementioned slight leakage conditions, the sawdust concentration is 2%–5% by mass, the drilling fluid funnel viscosity is 30–35 s, and the circulation rate determined based on the wellbore size is 30–40 m³ / s. 3 / h, the time for circulating the plugging slurry is 2 to 3 hours.

6. The method for inert material circulation plugging in surface drilling operations in fractured formations according to claim 4, characterized in that: Under the aforementioned moderate leakage conditions, the total mass percentage concentration of the sawdust and walnut shells is 5%–10%, the drilling fluid funnel viscosity is 35–40 s, and the circulation rate determined based on the wellbore size is 40–50 m³ / s. 3 / h, the time for circulating the plugging slurry is 3 to 4 hours.

7. The method for inert material circulation plugging in surface drilling operations in fractured formations according to claim 4, characterized in that: Under the continuous leakage condition, the sawdust concentration is 5%–10% by mass, the drilling fluid funnel viscosity is 40–50 s, and the circulation rate determined according to the wellbore size is 40–50 m³ / s. 3 / h, the time for circulating the plugging slurry is 3-4 h; The sawdust is dispersed in the thick mud, which suspends and carries the sawdust.

8. The method for inert material circulation plugging in surface drilling operations in fractured formations according to any one of claims 1 to 7, characterized in that, The preparation of the sealing grout includes: The funnel viscosity of the drilling fluid is adjusted according to the type and mass percentage concentration of the inert plugging material; During the stirring of the drilling fluid, the largest particles, the medium particles, and the small particles are all added to the drilling fluid; Continue stirring the drilling fluid to disperse the largest, medium, and small particles in the drilling fluid, thereby obtaining the plugging slurry.

9. The method for inert material circulation plugging in surface drilling operations in fractured formations according to any one of claims 1 to 8, characterized in that: When the amount of slurry returned from the wellhead increases compared to before the plugging slurry was pumped in, and has not yet returned to the normal amount of slurry returned, the current plugging process is deemed effective, and the plugging slurry is pumped in again. When the wellhead slurry return rate returns to normal, it is determined that the fracture has been completely sealed, and the circulation pumping of the plugging slurry is stopped.

10. The method for inert material circulation plugging in surface drilling operations for fractured formations according to any one of claims 5 to 7, characterized in that: If the amount of slurry returned from the wellhead has not increased compared to before the slurry was pumped in before the corresponding circulation time has been reached, the slurry will continue to be pumped in. If the amount of slurry returned from the wellhead has not increased compared to before the slurry was pumped in after the corresponding circulation time has been reached, the current slurry pumping is deemed invalid and the current slurry pumping is terminated.

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