Method for filling and plugging material and expanding safe density window of drilling fluid

Abstract

The invention provides a filling plugging material and a method for expanding a safe density window of drilling fluid, the method comprises the step of forming a filling layer to bear pressure, and the step of forming the filling layer comprises the following substeps: forming the filling layer on defects on the surface of a well wall rock stratum by adopting the filling plugging material in a real drilling process, the filling and plugging material comprises elastic particles, fibers and rigid particles with different particle sizes, and the rigid particles are irregular non-spherical substances and comprise calcium carbonate particles, graphite particles and elastic particles, so that a compact force chain network is formed by bridging in defects on the surface of a well wall rock stratum; the force chain network is filled with the elastic particles, the rebound rate is 60% or above, the temperature resistance is 150 DEG C or above, and the elastic particles comprise emulsified asphalt and graphite particles; the fibers are embedded into the force chain network, and the fibers comprise one or more of plant fibers, flaky mica and organic fiber resin compounds.

Description

Technical Field

[0001] This invention relates to the field of oil and gas technology, specifically to a plugging and sealing material and a method for expanding the safe density window of drilling fluid. Background Technology

[0002] Drilling depths in the Sichuan-Chongqing region are steadily increasing, with efforts now focused on wells reaching depths of 10,000 meters. The Shuangyushi structure in western Sichuan, in particular, continues to break deepest records. Statistics show that by the end of 2023, 24 wells had been completed in the Shuangyushi structure, with an average depth of 7,870 meters and an average drilling cycle of 405.45 days. Of these, 24 wells are over 7,000 meters deep, 7 are over 8,000 meters deep, and 1 is over 9,000 meters deep. The increasing depth design inevitably leads to a growth in the drilling section of large-diameter, multi-pressure systems.

[0003] Currently, the most common method to increase the safe density window of drilling fluid is to plug leaks encountered during actual drilling and to improve the formation's pressure-bearing capacity through specialized pressure-bearing methods. However, this method suffers from problems such as long processing time, high cost, and unsatisfactory results.

[0004] Existing technologies cannot meet the safe density window of drilling fluid in multi-pressure systems, and there is an urgent need for a method to expand the safe density window of drilling fluid in large-bore multi-pressure systems. Summary of the Invention

[0005] The purpose of this invention is to address at least one of the aforementioned deficiencies in the prior art. For example, one objective of this invention is to provide a method for expanding the drilling fluid safety density window in a large-bore multi-pressure system.

[0006] To achieve the above objectives, the present invention provides a method for expanding the safe density window of drilling fluid. The method includes forming a plugging layer to withstand pressure. The forming of the plugging layer includes: during actual drilling, using a plugging and sealing material to form a plugging layer on defects in the wellbore rock surface. The plugging and sealing material includes elastic particles, fibers, and rigid particles of different sizes. The rigid particles are irregular, non-spherical materials, including calcium carbonate particles, graphite particles, and elastic particles, to bridge and form a dense force chain network in the defects on the wellbore rock surface. The elastic particles, filling the force chain network, have a resilience of 60% or more and a temperature resistance of 150°C or more. The elastic particles include emulsified bitumen and graphite particles. The fibers are embedded in the force chain network, and the fibers include one or more of plant fibers, flaky mica, and organic fiber resin composites.

[0007] Optionally, the filling and sealing material may include: granular materials, including calcium carbonate particles, quartz particles, graphite particles, and polyester granular materials with a compressive strength of 50 MPa to 150 MPa and a particle size range of 0.013 mm to 0.125 mm; fibrous materials, including plant fibers with a length of less than 3 mm; sheet-like materials, including sheet-like mica with a surface length of 3 to 5 mm and a thickness of 0.5 ± 0.1 mm; and variable materials, including emulsified asphalt and asphalt-based materials.

[0008] Optionally, by weight percentage, the filling and sealing material may include: 3% to 6% calcium carbonate particles, 4% to 6% graphite particles, 1% to 3% modified plant fibers, 1% to 3% flake material and 4% to 8% emulsified asphalt, wherein the particle size of the calcium carbonate particles is 500 mesh to 1250 mesh, the particle size of the graphite particles is 0.013 mm to 0.125 mm, and the size of the modified plant fibers is <3 mm.

[0009] Optionally, the rigid particles of different sizes may include large rigid particles of 0.0750 mm to 0.125 mm and small rigid particles of 10 μm to 0.0749 mm.

[0010] Optionally, the method may further include measures to prevent wellbore instability in gypsum-salt layers. These measures include: simplifying the drill string structure and using auger collars instead of centralizers; before exposing the salt layer, if the well temperature is below 130°C or the gypsum-salt layer thickness is less than 1000m, converting to undersaturated / saturated brine drilling fluid; and if the well temperature is above 130°C or the gypsum-salt layer thickness exceeds 1000m, converting to oil-based drilling fluid.

[0011] Optionally, the method may also include measures to prevent wellbore instability in gypsum-salt formations. Measures to prevent wellbore instability in gypsum-salt formations include: when drilling through gypsum-salt formations, adopting a one-forward-two-backward method, pulling up once every 1m or half an hour of drilling, with a pull-up distance of not less than 3m; closely monitoring changes in rotary table torque, pump pressure, pump flush, and returned cuttings during drilling, and immediately pulling up the drill string if the torque increase rate exceeds 10%; when drilling through salt formations, minimizing the time the drill string remains stationary, with each stationary time not exceeding 2 minutes, and if maintenance is required, the drill string must be pulled up to a safe section of the well.

[0012] Optionally, the method may further include measures to prevent wellbore instability in gypsum-salt layers. These measures include: reaming the borehole 2-3 times before connecting a single rod; after the angular drill pipe is pulled out, stopping the pump and clearing the borehole; only if no obstruction is encountered can a single rod be connected; otherwise, reaming should be repeated; drilling 200m-300m or 48 hours later, short-tripping the drill string to verify the borehole stress release time and to determine the diameter reduction cycle of the gypsum-salt layer.

[0013] Optionally, chloride ion monitoring can be strengthened to prevent the salt layer from dissolving and forming a large belly.

[0014] Optionally, the method can extend the drilling fluid density range to 1.2 g / cm³. 3 ~2.1g / cm 3 .

[0015] In another aspect, the present invention provides a filling and sealing material, the filling and sealing material comprising: granular material, the granular material comprising calcium carbonate particles, quartz particles, graphite particles, and polyester granular material with a compressive strength of 50 MPa to 150 MPa and a particle size range of 0.013 mm to 0.125 mm; fibrous material, the fibrous material comprising one or more of plant fibers with a length less than 3 mm, flake mica, and organic fiber resin composites; flake material, the flake material being flake mica with a surface length of 3 mm to 5 mm and a thickness of 0.5 ± 0.1 mm; and variable material, the variable material comprising emulsified asphalt and asphalt-based materials. Attached Figure Description

[0016] The above and other objects and features of the present invention will become clearer from the following description taken in conjunction with the accompanying drawings, in which:

[0017] Figure 1A The diagram shows the drilling process of a well in the fourth stage, including schematic diagrams of each layer in the well design.

[0018] Figure 1B The drilling fluid density range for each layer in the drilling design during the fourth stage of drilling of a certain well is shown.

[0019] Figure 1C The wellbore design for the fourth stage of a certain well is shown.

[0020] Figure 2 A schematic diagram of creep failure in each layer of gypsum-salt rock is shown.

[0021] Figure 3A and Figure 3B A schematic diagram of particle bridging in a fracture is shown, illustrating a method for expanding the drilling fluid safety density window according to an exemplary embodiment of the present invention.

[0022] Figure 4A and Figure 4B A diagram illustrating the fracture-filling layer formation process of a method for expanding the drilling fluid safety density window according to an exemplary embodiment of the present invention is shown.

[0023] Explanation of reference numerals in the attached figures:

[0024] 1-Three-section casing, 2-Four-section casing, 3-Five-section casing, 4-Six-section casing, 5-NaCl salt layer, 6-High-salt mudstone interlayer, 7-Bridge. Detailed Implementation

[0025] In the following description, a plugging and sealing material and a method for expanding the safe density window of drilling fluid according to the present invention will be described in detail with reference to the accompanying drawings and exemplary embodiments.

[0026] In the description of this application, it should be understood that the terms "first," "second," etc., are used merely for convenience of description and distinction, and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0027] In this application, the drilling fluid safety density window refers to the following: when the density is higher than a certain value, i.e., the upper limit, formation leakage occurs; when the density is lower than a certain value, the wellbore becomes unstable and collapses. Expanding the safety density window means expanding the lower and upper limits of drilling fluid density to ensure wellbore stability and prevent complex situations such as well leakage and wellbore collapse when using different drilling fluid densities.

[0028] Exemplary Example 1

[0029] This exemplary embodiment provides a method for extending the safety density window of drilling fluid. The method includes forming a plugging layer to withstand pressure, wherein forming the plugging layer includes: during actual drilling, using a plugging and sealing material to form a plugging layer on defects in the wellbore rock surface, the plugging and sealing material including elastic particles, fibers, and rigid particles of different particle sizes, the rigid particles being irregular non-spherical materials including calcium carbonate particles, graphite particles, and elastic particles to bridge and form a dense force chain network in the defects in the wellbore rock surface; the elastic particles, filling the force chain network, having a high rebound rate (rebound rate above 60%, rebound rate = 100 × (rebound height / initial height)) and temperature resistance (above 150°C), the elastic particles including emulsified bitumen and graphite particles; and fibers embedded in the force chain network, the fibers including one or more of plant fibers, flaky mica, and organic fiber resin composites.

[0030] The filling and sealing materials can include granular materials, fibrous materials, sheet materials, and variable materials.

[0031] The particulate materials may include calcium carbonate particles, quartz particles, graphite particles, and high-strength (compressive strength 50 MPa to 150 MPa) polyester particulate materials with a particle size range of 0.013 mm to 0.125 mm.

[0032] Fiber materials may include plant fibers with a length of less than 3 mm.

[0033] The sheet material can be sheet mica, with a surface length of 3mm to 5mm and a thickness of 0.5±0.1mm;

[0034] Variable materials can include emulsified asphalt and asphalt-based materials.

[0035] In an embodiment, the filling and sealing material may include, by mass percentage: 3%–6% calcium carbonate particles, 4%–6% graphite particles, 1%–3% modified plant fibers, 1%–3% flake material and 4%–8% emulsified bitumen, wherein the calcium carbonate particles have a particle size of 500 mesh to 1250 mesh, the graphite particles have a particle size of 0.013 mm to 0.125 mm, and the plant fiber size (longest end) is <3 mm.

[0036] In this embodiment, the plugging and sealing material, by weight percentage, may include: 3%–6% calcium carbonate particles, 4%–6% graphite particles (HR-2), 1%–3% modified plant fiber (WNSX), 1%–3% flake material (WNDK), and 4%–8% emulsified bitumen (FRH). The calcium carbonate particles have a particle size of 500–1250 mesh, the graphite particles have a particle size of 0.013 mm–0.125 mm, and the modified plant fiber has a length (longest end) <3 mm. All reagents WNSX, WNDK, and FRH used in the plugging and sealing material are from Chongqing Weineng Drilling Additives Co., Ltd.

[0037] Here, rigid particles of different sizes include large rigid particles with a particle size range of 0.0750 mm to 0.125 mm and small rigid particles with a particle size range of 10 μm to 0.0749 mm.

[0038] Furthermore, the method may also include measures to prevent wellbore instability in gypsum-salt formations, and these measures may include:

[0039] Simplify the drill string structure and use auger collars to replace centralizers;

[0040] Before exposing the salt layer, if the well temperature is below 130℃ or the salt-gypsum layer thickness is less than 1000m, convert to undersaturated / saturated brine drilling fluid; if the well temperature is above 130℃ or the salt-gypsum layer thickness exceeds 1000m, convert to oil-based drilling fluid.

[0041] When drilling through the salt-gypsum layer, the method of advancing one step and retreating two steps should be adopted. The drill must be lifted once every 1 meter or half an hour, and the lifting distance should be no less than 3 meters.

[0042] During drilling, pay close attention to changes in rotary table torque, pump pressure, pump flush, and returned cuttings. If an increase in torque is detected (the rate of change exceeds 10%), the drill hole should be lifted immediately.

[0043] When drilling through salt layers, minimize the time the drill string remains stationary. Each stationary period should not exceed 2 minutes. If maintenance is required, the drill string must be pulled up to a safe section of the well.

[0044] Before connecting a single rod, ream the hole 2-3 times. After pulling out the square drill pipe, stop the pump and clear the wellbore. Only connect a single rod if there is no obstruction. Otherwise, ream the hole again.

[0045] Drill 200m to 300m at an appropriate time or shortly pull up after 48 hours of drilling to verify the wellbore stress release time and to determine the diameter reduction cycle of the salt-gypsum layer.

[0046] Strengthen chloride ion monitoring to prevent the formation of "bulging" wellbores due to salt dissolution. In drilling engineering, a "bulging" wellbore refers to a phenomenon where the wellbore diameter suddenly increases at a certain point. This is usually caused by technical or geological problems encountered during the drilling process. In particular, wells with formations containing large amounts of salt rock will form "bulging" wellbores after dissolving in water. To prevent this phenomenon, it is common practice to add salts such as NaCl and KCl to the drilling fluid in advance to prevent the salt layer from dissolving into the drilling fluid and forming a "bulging" wellbore.

[0047] The method according to an exemplary embodiment of the present invention can extend the drilling fluid density range to 1.2 g / cm³. 3 ~2.1g / cm 3 .

[0048] Exemplary Example 2

[0049] This exemplary embodiment provides a plugging and sealing material, comprising: granular materials, including calcium carbonate particles, quartz particles, graphite particles, and high-strength (compressive strength 50 MPa to 150 MPa) polyester granular materials, wherein the polyester granular materials are a drilling fluid plugging agent deformable resin composite (WNSOL) made from modified polymers, deformable resins, etc., with a particle size range of 0.013 mm to 0.125 mm; fibrous materials, including plant fibers with a length of less than 3 mm; sheet-like materials, wherein the sheet-like materials are sheet-like mica with a surface length of 3 mm to 5 mm and a thickness of 0.5 ± 0.1 mm; and variable materials, including emulsified asphalt and asphalt-based materials.

[0050] In the embodiments, the filling and sealing material may include, by mass percentage: 3%–6% calcium carbonate particles, 4%–6% graphite particles HR-2, 1%–3% modified plant fiber WNSX, 1%–3% sheet material WNDK, and 4%–8% emulsified asphalt FRH, wherein the particle size of the calcium carbonate particles is 500 mesh–1250 mesh, the particle size of the graphite particles is 0.013 mm–0.125 mm, and the size (longest end) of the modified plant fiber is <3 mm.

[0051] All reagents used in the plugging and sealing materials, including WNSX, WNDK, and FRH, were sourced from Chongqing Weineng Drilling Additives Co., Ltd.

[0052] Exemplary Example 3

[0053] Figure 1A The diagram shows the drilling process of a well in the fourth stage, including schematic diagrams of each layer in the well design. Figure 1B The drilling fluid density range for each layer in the drilling design during the fourth stage of drilling of a certain well is shown. Figure 1C The wellbore design for the fourth stage of a certain well is shown.

[0054] According to the drilling design requirements of a certain well, the fourth drilling stage (i.e., the fourth phase of the drilling process) is designed with a 444.5mm large borehole to a depth of over 7300 meters, with an open-hole section of over 3700 meters. Figure 1C As shown. Among them, Figure 1B The red numbers 1.50, 1.60, 1.75, and 1.80 represent formation pressure coefficients, while the blue numbers 1.57-1.80, 1.67-2.00, 1.82-2.00, and 1.87-2.00 represent drilling fluid densities. The unit for both can be g / cm³. 3 . Figure 1A The geological conditions of the open-hole section, which is over 3,700 meters long, are shown.

[0055] The fourth stage of drilling in a certain well involved a complex pressure system with leaking layers distributed throughout from top to bottom. The pressure system from the Xujiahe Formation to the Maokou Formation was complex, with localized high-pressure water and gas layers existing between the Xujiahe and Changxing Formations. The Maokou Formation exhibited significant lateral pressure differences, with leaks and overflows occurring simultaneously within the same open-hole section. The Leikoupo and Jialingjiang Formations contained gypsum and salt deposits (…). Figure 2 The NaCl salt layer (5) and high-salinity mudstone interlayers (6), due to different creep rates between the layers, caused the strata to collapse. Figure 2 As shown in the diagram. Before entering Changxing, the upper formation needs to be tested according to the design specifications, with a maximum drilling fluid density of 2.10 g / cm³. 3 Under pressure.

[0056] Currently, there are no wells with a diameter of 444.5 mm, a depth of over 7300 meters, and an open-hole section of over 3700 meters. The lithological pressure system ranges from 1.5 g / cm³. 3 ~1.8g / cm 3 Technical methods for expanding the upper and lower limits of drilling fluid density under certain conditions.

[0057] Therefore, this exemplary embodiment provides a method for expanding the drilling fluid safety density window applicable to the above-mentioned large-bore multi-pressure system. This method is based on actual drilling experience in fractured and broken formations. The development of formation fractures and the expansion of weak formation structural surfaces under fluid-induced effects are among the main reasons affecting the narrow drilling fluid safety density window.

[0058] The applicant discovered that to improve the drilling fluid safety density window, one can start by changing the mechanical state of the wellbore and the stability of the gypsum-salt layer, and improve the drilling fluid safety density window by utilizing the pressure bearing of the plug layer and preventing wellbore instability of the gypsum-salt layer.

[0059] During actual drilling, numerous defects such as microcracks were found on the surface of the rock formation in the wellbore. However, the presence of a large number of solid particles in the drilling fluid repaired these defects, giving the formation a high pressure-bearing capacity to meet drilling requirements.

[0060] The calculation model for reducing circumferential stress after filling the gap is as follows: (1)

[0061]

[0062] In equation (1), Δp is the increased bearing capacity after the fracture is filled, MPa; W is the fracture width, m; R is the wellbore radius, i.e., the distance from the sealing layer to the well center, m; E is the Young's modulus of the formation, MPa; and V is the Poisson's ratio of the formation rock.

[0063] The above formula shows that when the crack width increases to 1 mm and the wellbore radius is 0.1 m, the wellbore pressure bearing capacity can be effectively increased to over 6.895 MPa.

[0064] Figure 3A and Figure 3B A schematic diagram of particle bridging in a fracture is shown, illustrating a method for expanding the drilling fluid safety density window according to an exemplary embodiment of the present invention. Figure 3A This diagram illustrates how the filling and sealing material quickly adheres to the crack, initiating bridging (7). Figure 3B The extrusion bridge 7 is shown, forming a fill, which reduces the drilling fluid filtration pressure at point A.

[0065] Figure 4A and Figure 4B A diagram illustrating the fracture-filling layer formation process of a method for expanding the drilling fluid safety density window according to an exemplary embodiment of the present invention is shown.

[0066] The selected plugging and sealing material must rapidly form a plugging layer, quickly attaching, bridging, filling, and forming a structure within the crack. After bridging with rigid particles of different sizes, a dense force chain network will form. The space within this force chain network requires the filling of elastic particles and the embedding of fibers to create a dense structural seal. Therefore, the plugging and sealing material must contain three types of materials: rigid particles, elastic particles, and fibers.

[0067] The rigid granular material used for bridging must be irregular, non-spherical, as it easily traps and hinders bridging within cracks due to edge effects. Furthermore, a mixture of large and small particles is required: large particles (0.0750mm–0.125mm) for bridging, and small particles (10μm–0.0749mm) for filling. The elastic particles used to fill the force chain network must possess high resilience and temperature resistance. The structural fibers should combine rigidity and flexibility. Only the coexistence of these three materials can rapidly form the filling layer.

[0068] The recommended materials are as follows: (1) Particle materials: calcium carbonate particles, quartz particles, graphite particles and high-strength polyester particles, etc., with a particle size range of 0.013mm to 0.125mm.

[0069] (2) Fiber material: Modified plant fiber with a length of less than 3 mm. It has stable physical and chemical properties. The fiber material helps the agglomeration of particulate materials, fills micropores, and helps to enhance the integrity and density of the sealing wall.

[0070] (3) Sheet material: A sheet-like high-friction material with high strength, an uneven surface, and fibrous edges. The sheet material can be sheet-like mica with a surface length of 3mm to 5mm and a thickness of 0.5±0.1mm. This sheet material has a wrapping effect on granular materials and enhances the frictional resistance between the sealing partition and the crack wall, which is beneficial to the formation and stability of the seal.

[0071] (4) Deformable materials: Emulsified asphalt and asphalt-based materials are deformable materials. Under the action of temperature and pressure, the materials deform and fill various pores and cracks, improve the sealing performance of drilling fluid, and form a denser filter cake.

[0072] In the example process, the above materials were added in a composite ratio to achieve good results, namely: calcium carbonate particles (500 mesh to 1250 mesh) 3% to 6% + graphite particles (0.013 mm to 0.125 mm) 4% to 6% + modified plant fiber (<3 mm) 1% to 3% + flake material (flake mica) 1% to 3% + emulsified asphalt 4% to 8%. Here, the percentages mentioned refer to the mass percentage.

[0073] In well SDCK1, a large wellbore of 444.5 mm was drilled, with an open hole section exceeding 3700 meters. The lithological pressure system ranged from 1.5 g / cm³. 3 ~1.8g / cm 3 Under these conditions, the drilling fluid density range was extended to 1.2 g / cm³. 3 ~2.1g / cm 3 .

[0074] Determining the safe density of drilling fluid in gypsum-salt formations. Most stuck pipe and complex situations in gypsum-salt formations can be attributed to inappropriate drilling fluid density. Given the temperature and stress conditions of the surrounding rock, the rheological mechanism of gypsum-salt formations falls under the category of dislocation slip, and its creep equation can be described by the following equation (2):

[0075]

[0076] In equation (2), ε is the steady-state creep rate; A and B are creep parameters; Q is the activation energy; R is an ideal gas constant; T is the absolute temperature; sinh() is a hyperbolic sine function; and σ is the differential stress.

[0077] During drilling through gypsum-salt rock formations, excessively low drilling fluid density often leads to borehole narrowing and stuck pipe; excessively high drilling fluid density can easily cause lost circulation, resulting in complex situations such as differential pressure stuck pipe. Therefore, rationally designing the drilling fluid density when encountering gypsum-salt formations is crucial. The impact of drilling fluid density on borehole narrowing in gypsum-salt formations under uniform geostress conditions can be calculated and analyzed using the aforementioned mathematical model. This can be combined with the previously described plugging methods to address the issue.

[0078] Engineering measures for maintaining the safe density of drilling fluid in gypsum-salt formations:

[0079] (1) Simplify the drill string structure, get rid of the centralizer, and select the auger drill collar. This can reduce the rigidity of the drill string and reduce the contact area between the drill string and the well wall. This can reduce the friction between the drill string and the well wall, avoid damaging the stability of the well wall, and contribute to the lower limit of the safe density window.

[0080] (2) Before exposing the salt layer, if the well temperature is below 130°C or the salt-gypsum layer thickness is less than 1000m, convert to undersaturated / saturated brine drilling fluid; if the well temperature is above 130°C or the salt-gypsum layer thickness exceeds 1000m, convert to oil-based drilling fluid. The drilling fluid density is controlled based on the salt-gypsum layer depth, temperature, and the drilling fluid used to control salt-gypsum creep. If a high-pressure brine layer exists in the salt-gypsum section, it must be based on its pore pressure coefficient. This technique has a similar effect to addressing the formation of a "bulging belly" from salt-gypsum dissolution. If the salt-gypsum layer thickness is less than 1000mm and the temperature is below 130°C, inorganic salts such as KCl and NaCl can be added to form an undersaturated / saturated brine drilling fluid to prevent the salt-gypsum from dissolving into the drilling fluid. If the salt-gypsum layer is too thick or the temperature is above 130°C, the above methods cannot effectively solve the problem of salt-gypsum dissolution because the solubility of salt increases with temperature. Converting to oil-based drilling fluid can effectively prevent salt dissolution because salt cannot dissolve into oil. This can mitigate the negative effects of salt paste dissolution and contribute to the lower limit of the safe density window and prevention of stuck drill bits.

[0081] (3) When drilling through salt-salt layers, the "one-forward, two-backward" method must be adopted, that is, the wellhead must be pulled up once every 1m or half an hour of drilling, and the distance of the pull-up must be no less than 3m. In addition to the dissolution of salt, salt-salt layers are also prone to deformation. After drilling through the salt-salt layer, the formation pressure is released, and the salt-salt layer is very easy to deform, which leads to the wellbore narrowing. This technique can keep the wellbore open and avoid the problem of drill string getting stuck due to wellbore narrowing.

[0082] (4) During drilling, pay close attention to changes in rotary table torque, pump pressure, pump flush, and returned cuttings. If an increase in torque is detected (change rate exceeding 10%), the reamer should be pulled up immediately. Parameter changes can reflect whether the bottom of the well is unobstructed. Increased torque, pump pressure, etc., indicate that there are obstructions at the bottom of the well, requiring the reamer to be pulled up to remove the obstructions. This operation can ensure a clear wellbore and stable wellbore, and also contributes to preventing stuck drill pipe.

[0083] (5) Before connecting a single pipe, ream the hole 2 to 3 times. After the square drill pipe is pulled out, stop the pump and clear the wellbore. Only if there is no obstruction can a single pipe be connected. Otherwise, ream the hole again (this operation is for the same purpose as above, which can make the wellbore clear and the well wall stable, and also contribute to preventing stuck drill).

[0084] (6) Short-term tripping in time to verify the wellbore stress release time and grasp the diameter reduction cycle of the salt gypsum layer (same as (3). This technique can deal with the negative effects of salt gypsum creep and contribute to the lower limit of the safe density window and the prevention of stuck drill bit).

[0085] (7) Strengthen chloride ion monitoring to prevent the formation of "bulging" wellbores from salt dissolution. In drilling engineering, a "bulging" wellbore refers to the phenomenon where the diameter of the wellbore suddenly increases in a certain section. This is usually caused by some technical or geological problems encountered during the drilling process. In particular, when the formation contains a large amount of salt rock, it will form a "bulging" wellbore after dissolving in water. To prevent this phenomenon, it is common practice to add salts such as NaCl and KCl to the drilling fluid in advance to prevent the salt layer from dissolving into the drilling fluid and forming a "bulging" wellbore.

[0086] (8) When drilling through salt formations, minimize the time the drill string remains stationary. Each stationary period should not exceed 2 minutes. If maintenance is required, the drill string must be pulled to a safe section of the well. This prevents the drill string from remaining stationary in the salt formation for extended periods, which can lead to stuck drill string. This operation contributes to preventing stuck drill string.

[0087] In a certain well, a large borehole diameter of 444.5 mm was constructed, with an open-hole section exceeding 3700 meters in length. The lithological pressure coefficient was 1.5 g / cm³. 3 ~1.8g / cm 3 Under these conditions, the drilling fluid density range was extended to 1.2 g / cm³. 3 ~2.1g / cm 3 This also ensured normal drilling in the gypsum-salt layer well section, guaranteeing smooth tripping in and out of the well and preventing various accidents and complex situations such as hole reaming.

[0088] Based on the above-mentioned method for expanding the drilling fluid safety density window in a large-bore, long-open-hole, multi-pressure system, the drilling fluid safety density window can be expanded during the drilling process, changing the past practice of stopping drilling and plugging leaks to improve pressure resistance when encountering complex situations.

[0089] To better understand the exemplary embodiments of the present invention described above, the following specific examples illustrate the method of filling and sealing materials and expanding the safe density window of drilling fluid.

[0090] Example 1

[0091] The formula for the third pressurized plugging of oil-based mud during the third stage of drilling of Well No. 1, by mass percentage, is as follows: well mud + 5% fine walnut shells + 3% flaky mica + 1% cottonseed hulls + 3% 5000-mesh ultrafine calcium + 5% 3000-mesh ultrafine calcium + 5% calcium carbonate (1200 mesh) + 5% ultrafine calcium (800 mesh) + 2% dry powder asphalt + 5% paste asphalt + 3% modified plant fiber (<3mm).

[0092] After construction, the on-site density ranged from 1.2 g / cm³. 3 ~1.3g / cm 3 Increased to 1.2 g / cm³ 3 ~1.6g / cm 3 Test method: With the semi-sealing device closed at the wellhead, the well is in a sealed state. Pressure is applied to the well through the wellhead and held steady for 10 minutes. If the pressure does not drop, the increase in bottom hole pressure can be calculated and converted into drilling fluid density. Failure to hold steady pressure indicates that the drilling fluid's safe density window has not been extended.

[0093] Example 2

[0094] The formula for pressure-bearing plugging slurry of well No. 2, by mass percentage, is: well slurry + 5% modified plant fiber + 2% calcium carbonate (800 mesh) + 5% calcium carbonate (1200 mesh) + 2% dry powder asphalt + 5% paste asphalt.

[0095] After construction, the on-site density ranged from 1.6 g / cm³. 3 ~1.7g / cm 3 Increased to 1.6 g / cm³ 3 ~2.0g / cm 3 The testing method is the same as in Example 1.

[0096] Example 3

[0097] In the Xujiahe and Lei-1-2 sections of well LJ21, the aforementioned method was used for pressure-bearing plugging, achieving a 100% success rate. The drilling cycle was also significantly shortened, demonstrating remarkable effectiveness in the plugging operation. Ultimately, the well completed its third drilling phase ahead of schedule in 25.9 days, 6.1 days ahead of the planned timeframe, and 19.74 days faster than well Luojia-22, representing a 43% acceleration.

[0098] Comparative Example

[0099] In the LJ21 well, section 4 (2363.6-2639 meters), drilling reached a depth of 2412.35 meters when well leakage was detected. Further drilling continued to a depth of 2413.00 meters, and leakage velocity was measured during circulation; the maximum leakage velocity was 19.2 m / s². 3 / h, minimum leakage velocity 4.8m 3 / h, average leakage velocity 10.5m 3 / h. 38 tons of cement were used to successfully plug the leak, with no leakage during circulation. Leakage recurred after drilling and plugging, with an average leakage rate of 4.4m / h. 3 / h, 23% bridging slurry plugging was ineffective. Drilling to a depth of 2414.98m revealed a leakage velocity increased to 36.0m. 3 At a drilling depth of 2421.01m, the average leakage rate decreased to 18.5m / h. 3 / h, as drilling reached a depth of 2441.35m, the leakage rate increased, with an average leakage rate of 25.3m / h. 3 / h, 60 tons of cement were used to successfully plug the leak, with no leakage during circulation. Drilling to 2360 meters resulted in a recurrence of the leak; strong drilling with clean water was then conducted to 2479.87 meters, where 59% of the bridging slurry was successfully used to plug the leak. Drilling with clean water to a depth of 2513.95 meters revealed a well leak; observation continued until 2516 meters, with an average leakage rate of 18.5 m / s. 3 / h, observed drilling to 2568.45 meters, average leakage velocity 20m / h. 3 Drilling speed: 2601 meters, leakage velocity: 21 m / h 3 Drilling rate: 18 m / h, reaching a depth of 2729.5 meters, with an average leakage velocity of 18 m / s². 3 / h. Successful sealing was achieved using 48% and 62% bridging grout.

[0100] As can be seen from the comparative examples, although using cement slurry to plug leaks and increase the drilling fluid density window can achieve a temporary solidification and sealing effect, it still cannot effectively seal formation pores and fissures. Only by using bridge plugs to plug leaks can the final on-site effect be achieved.

[0101] In summary, the advantages proposed by this invention include: enabling an extended drilling fluid safety density window during the drilling process, thus changing the past practice of stopping drilling and plugging leaks when encountering complex situations to improve pressure resistance.

[0102] Although a plugging and sealing material and a method for expanding the safe density window of drilling fluid have been described above in conjunction with exemplary embodiments, those skilled in the art should understand that various modifications and changes can be made to the exemplary embodiments of the present invention without departing from the spirit and scope defined by the claims.

Claims

1. A method of expanding the safe density window of a drilling fluid, characterized by, The method comprises forming a packing layer to bear pressure, wherein the forming of the packing layer comprises: In the actual drilling process, a packing layer is formed on the defect of the well wall rock surface by using a packing plugging material, the packing plugging material comprises elastic particles, fibers and rigid particles of different particle sizes, the rigid particles are irregular non-spherical substances, and the rigid particles comprise calcium carbonate particles, graphite particles and elastic particles, so as to bridge and form a dense force chain network in the defect of the well wall rock surface; The elastic particles fill the force chain network, have a resilience of 60% or more and a temperature resistance of 150℃ or more, and the elastic particles comprise emulsified asphalt and graphite particles; The fibers are embedded in the force chain network, and the fibers comprise one or more of plant fibers, sheet mica and organic fiber resin composites.

2. The method of expanding the safe density window of a drilling fluid of claim 1, wherein, The packing plugging material comprises: The particle material comprises calcium carbonate particles, quartz particles, graphite particles and polyester particle material with a compressive strength of 50Mpa-150Mpa, and the particle size range is 0.013mm-0.125mm; The fiber material comprises plant fibers with a length of less than 3mm; The sheet material is sheet mica, the surface length is 3-5mm, and the thickness is 0.5±0.1mm; and The variability material comprises emulsified asphalt and asphalt-based materials.

3. The method of expanding the safe density window of a drilling fluid of claim 2, wherein, The packing plugging material comprises, in terms of mass percentage: 3%-6% of calcium carbonate particles, 4%-6% of graphite particles, 1%-3% of modified plant fibers, 1%-3% of sheet material and 4%-8% of emulsified asphalt, wherein the particle size of the calcium carbonate particles is 500-1250 meshes, the particle size of the graphite particles is 0.013mm-0.125mm, and the size of the modified plant fibers is less than 3mm.

4. The method of expanding the safe density window of a drilling fluid of claim 1, wherein, The rigid particles of different particle sizes comprise large particle rigid particles of 0.0750mm-0.125mm and small particle rigid particles of 10μm-0.0749mm.

5. The method of expanding the safe density window of a drilling fluid of claim 1, wherein, The method further comprises preventing the instability of the well wall of the gypsolayer, and the measures for preventing the instability of the well wall of the gypsolayer comprise: Simplify the structure of the drilling tool, and replace the centralizer with a spiral drill collar; Before uncovering the salt layer, when the well temperature is lower than 130℃ or the thickness of the salt and gypsum layer is less than 1000m, convert the undersaturated / saturated salt water drilling fluid, and when the well temperature is higher than 130℃ or the thickness of the salt and gypsum layer exceeds 1000m, convert the oil-based drilling fluid.

6. The method of expanding the safe density window of a drilling fluid of claim 1, wherein, The method further comprises preventing the instability of the well wall of the gypsolayer, and the measures for preventing the instability of the well wall of the gypsolayer comprise: When drilling in the salt and gypsum layer, adopt the method of advancing one step and retreating two steps, and the drilling tool must be lifted once every 1m or half an hour, and the lifting distance is not less than 3m; During drilling, pay close attention to the changes of the rotary table torque, pump pressure, pump stroke and returned cuttings, and if the change rate of the torque increase exceeds 10%, the drilling tool should be lifted immediately to reperforate; During drilling in the salt layer, reduce the static time of the drilling tool, and the static time of the drilling tool should not exceed 2min each time, and the drilling tool must be lifted to a safe well section for maintenance.

7. The method of expanding the safe density window of a drilling fluid of claim 1, wherein, The method further comprises preventing the instability of the well wall of the gypsolayer, and the measures for preventing the instability of the well wall of the gypsolayer comprise: Perforate 2-3 times before connecting the single joint, after lifting the kelly bar, stop the pump to pass through the wellbore, and if no resistance or blockage is encountered, the single joint can be connected, otherwise, the wellbore should be reperforated; Drilling into 200m-300m or short trip after drilling for 48 hours to verify the wellbore stress release time and master the shrinkage period of salt and gypsum layer.

8. The method of expanding the safe density window of a drilling fluid of claim 1, wherein, Strengthening chloride ion monitoring to prevent salt layer dissolution to form a big belly.

9. The method of expanding the safe density window of a drilling fluid of claim 1, wherein, The method can expand the drilling fluid density range to 1.2g / cm 3 ~2.1g / cm 3 .

10. A tamponade occlusive material, characterized in that, The plugging material comprises: Granular material, which comprises calcium carbonate particles, quartz particles, graphite particles and polyester particle material with a compressive strength of 50Mpa-150Mpa, and a particle size range of 0.013mm-0.125mm; Fiber material, which comprises one or more of plant fibers with a length of less than 3mm, sheet mica and organic fiber resin composite; Sheet material, which is sheet mica with a surface length of 3-5mm and a thickness of 0.5±0.1mm; Variable material, which comprises emulsified asphalt and asphalt-based material.

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