Vertical or horizontal well fracturing sand plugging and spraying method

Abstract

The present invention relates to the technical field of fracturing sand plugging and blowout methods, and is a method for fracturing sand plugging and blowout in a vertical well or horizontal well, which includes calculating the pump stop pressure according to the construction pressure curve before sand plugging to obtain a predicted value of the pump stop pressure; selecting the blowout timing according to the nozzle outlet flow rate corresponding to different predicted values ​​of the pump stop pressure; determining the corresponding blowout flow rate through a blowout flow chart based on the inner diameter of the tubing string of the horizontal well or the vertical well, and then determining the nozzle specifications selected for the blowout through blowout flow charts of different nozzles with different pressures based on the blowout flow rate and the predicted value of the pump stop pressure; after the blowout conditions are met, the blowout is performed with the selected nozzle specifications. The method of the present invention is simple to operate, and a reasonable and optimized blowout system is determined by calculation, so as to avoid subjective assumptions and reduce operational errors. It has the advantages of improving the success rate of sand plugging and blowout, reducing the economic losses of sand plugging, and effectively reducing the well control safety risks such as wellhead and pipeline leakage; and is particularly suitable for wells with sufficient reservoir energy.

Description

Technical Field

[0001] The invention relates to the technical field of fracturing sand plugging and gushing methods, in particular to a fracturing sand plugging and gushing method for a vertical well or a horizontal well. Background Art

[0002] At present, with the exploration and development of various oil fields, the exploration and development targets have gradually evolved from conventional sandstone reservoirs to unconventional reservoirs such as low-grade tight oil and shale oil, and the reservoir properties have gradually deteriorated. In order to achieve economical development of low-grade oil layers, fracturing has become the main technical means for stabilizing and increasing production in various oil fields. Due to the influence of factors such as reservoir properties, ground stress, sand-carrying performance of slick water (fracturing fluid) and equipment capacity, abnormal situations such as sand plugging often occur during the fracturing process. According to relevant fracturing construction statistics, sand-blocked wells (layers) account for about 1% to 3%. In recent years, the annual average fracturing of unconventional oil reservoirs in China has exceeded 10,000 layers, and the number of fracturing wells (layers) has increased year by year, and the number of sand-blocked wells has also increased. If sand blockage occurs, the timing of release and the selection of nozzles are extremely important. If the nozzle is too small, the sand in the well cannot be released out of the wellhead. For vertical well fracturing, it is very easy to cause sand burial and overhaul of the fracturing column. For horizontal well staged fracturing, it will affect the subsequent layer fracturing and cause economic losses. At the same time, if the timing of release or the nozzle selection is unreasonable, it may also cause leakage at the wellhead and the release pipe line, causing well control safety risks. At this stage, at each fracturing construction site, if sand blockage occurs, release and release are mostly carried out based on field experience, and a set of effective sand plugging and release methods have not yet been formed. Summary of the invention

[0003] The present invention provides a method for fracturing sand plugging and blowing out in a vertical well or a horizontal well, which overcomes the shortcomings of the above-mentioned prior art. When a vertical well or a horizontal well encounters fracturing sand plugging, the method has the characteristics of fast decision-making in abnormal sand plugging situations and simple operation. By quantitative calculation and avoiding subjective conjecture, the economic losses and well control safety risks caused by fracturing sand plugging can be effectively reduced, and the abnormal sand plugging situation can be correctly and quickly handled.

[0004] The technical scheme of the present invention is achieved through the following measures: a method for sand plugging and blowout in a vertical well or horizontal well fracturing, comprising calculating the pump-off pressure according to the construction pressure curve before sand plugging to obtain a predicted value of the pump-off pressure; selecting the blowout timing according to the nozzle outlet flow rate corresponding to different predicted values ​​of the pump-off pressure; determining the corresponding blowout flow rate through a blowout flow chart based on the inner diameter of the tubing of the horizontal well or the vertical well, and then determining the nozzle specification selected for the blowout through blowout flow charts of different nozzles with different pressures based on the blowout flow rate and the predicted value of the pump-off pressure; and after the blowout conditions are met, blowing is performed with the selected nozzle specification.

[0005] After more than one volume of liquid in the wellbore has been released and there is basically no sand at the nozzle outlet, reorganize the displacement and construction.

[0006] The following are further optimizations and / or improvements to the above technical solutions:

[0007] The above pump stop pressure is calculated according to the following formula:

[0008] P y =P+P H -P f -P J (1)

[0009] P 停 =P y -P H (2)

[0010] In formulas (1) to (2), P y is the extension pressure, P is the construction pressure, P H is the liquid column pressure, P f is the string friction, P J is the throttling pressure difference of the string hole, P 停 is the pump stop pressure (i.e. the predicted value of the pump stop pressure).

[0011] The above construction pressure P is the normal pumping pressure before sand plugging and can be directly read by the fracturing instrument vehicle.

[0012] The above string friction P f In order to combine the actual liquid used on site, the friction resistance (pipe friction resistance) value is calculated by the drag reduction ratio:

[0013]

[0014] In formula (3), σ is the ratio of fracturing fluid to water friction, D is the borehole diameter, Q is the displacement, Cg is the thickener concentration, and Cs is the sand-carrying fluid concentration. The water friction is a known value, and its combination with σ can be used to obtain the string friction P f value.

[0015] The throttling pressure difference P of the above-mentioned string hole J Calculate as follows:

[0016] P J =225.16ρQ 2 / (C d 2 *n 2 *d1 4 ) (4)

[0017] In formula (4), P J is the throttling pressure difference of the string hole, ρ is the liquid density, Q is the displacement, C d is the flow coefficient, n is the number of holes, and d1 is the hole diameter.

[0018] For the vertical well, the blowout flow chart is a chart drawn with different pipe string inner diameters and the minimum blowout flow, and the minimum blowout flow of the vertical well is twice the natural settling flow of the proppant; the natural settling flow of the proppant is calculated by combining the free settling velocity of the proppant in the vertical well section with the flow formula;

[0019] The free settling velocity of the proppant in the vertical well section is calculated using the following formula:

[0020] Vs=a*d k (ρ p g-ρg) m / (b*μ f ) (5)

[0021] In formula (5), Vs is the natural settling velocity of the proppant, a, b, k, m, f are constants, and ρ P is the proppant density, ρ is the liquid density, and μ is the liquid viscosity.

[0022] For horizontal wells, the blowout flow chart is a chart drawn with different sand ratios, different string inner diameters and proppant critical resuspension flow rates. The proppant critical resuspension flow rate is the proppant resuspension velocity in the horizontal section calculated using the flow formula.

[0023] The proppant resuspension velocity in the horizontal section is calculated using the following formula:

[0024]

[0025] In formula (6), Vsc is the proppant resuspension velocity, a is a constant, and d p is the proppant diameter, d is the column diameter, C1 is the sand ratio, ρ P is the proppant density, ρ is the liquid density, N Re is the Reynolds number and g is the acceleration due to gravity.

[0026] The above flow formula is Q=V*S, where Q is the flow rate, V is the liquid flow rate in the wellbore (the free settling velocity of the proppant in the vertical well section or the resuspension velocity of the proppant in the horizontal section), and S is the cross-sectional area of ​​the wellbore (it can also be the cross-sectional area of ​​the tubing).

[0027] The nozzle outlet flow rate corresponding to the above different pump stop pressure prediction values ​​is calculated by Bernoulli equation:

[0028]

[0029] In formula (7), P 停 is the predicted value of the pump stop pressure, ρ is the liquid density, υ is the nozzle outlet flow rate, g is the gravity acceleration, h is the height of the liquid column, and C is a constant; the nozzle outlet flow rate calculated by formula (7) is 流 =υ*πd z2 / 4 Calculate the corresponding flow value, and draw a chart of different pressures and different nozzle release flow rates with different pump stop pressures, different nozzle specifications and nozzle release flow rates, where Q 流 is the flow rate, υ is the nozzle outlet flow rate, d z is the inner diameter of the oil nozzle, and the pump stop pressure is the predicted value of the pump stop pressure.

[0030] The above-mentioned release timing is to control the nozzle release flow rate to be below 200m / s or the predicted value of the pump stop pressure ≤50MPa.

[0031] The method of the present invention is simple to operate, and a reasonable and optimized blowout system is determined by calculation, thereby avoiding subjective assumptions and reducing operational errors. It has the advantages of improving the success rate of sand plugging and blowout, reducing economic losses from sand plugging, and effectively reducing well control safety risks such as wellhead and pipeline leakage; and is particularly suitable for wells with sufficient reservoir energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Attached Figure 1 The nozzle outlet flow rate curve corresponding to different pump stop pressures.

[0033] Attached Figure 2 This is the critical resuspension flow curve for horizontal wells with different sand ratios and casings.

[0034] Attached Figure 3 It is the minimum blowdown flow rate corresponding to different inner diameters of tubing strings in vertical wells.

[0035] Attached Figure 4 This is a chart showing the spray flow rate corresponding to different pressures and different oil nozzles.

[0036] Attached Figure 1 In the figure, the horizontal axis is the pump stop pressure, in MPa; the vertical axis is the nozzle flow rate, in m / s.

[0037] Attached Figure 2 In the figure, the horizontal axis is the sand ratio, the unit is percentage; the vertical axis is the flow rate, the unit is liter / minute.

[0038] Attached Figure 3 In the figure, the horizontal axis is the inner diameter of the column, in millimeters; the vertical axis is the flow rate, in liters per minute.

[0039] Attached Figure 4 In the figure, the horizontal axis is the predicted pump stop pressure, in MPa; the vertical axis is the flow rate, in liters / minute; each curve is the spray flow rate of different nozzles at different pressures; in each curve, from top to bottom, they are the spray flow rate curves corresponding to 12mm nozzles, 11mm nozzles, 10mm nozzles, 9mm nozzles, 8mm nozzles, 7mm nozzles, 6mm nozzles, 5mm nozzles, 4mm nozzles, 3mm nozzles, and 2mm nozzles. DETAILED DESCRIPTION

[0040] The present invention is not limited by the following embodiments, and specific implementation methods can be determined based on the technical solution of the present invention and actual conditions.

[0041] The relevant figures in the present invention may vary due to different liquid properties and sand plugging conditions. The inner diameter of the pipe column in the present invention is in millimeters unless otherwise specified; the pressure in the present invention is in megapascals unless otherwise specified; the blowdown flow rate in the present invention is in liters per minute unless otherwise specified.

[0042] The present invention will be further described below in conjunction with embodiments:

[0043] Embodiment 1: A method for fracturing sand plugging and blowout in a vertical well or horizontal well, comprising calculating the pump-off pressure according to the construction pressure curve before sand plugging to obtain a predicted pump-off pressure value; selecting a blowout timing according to the nozzle outlet flow rate corresponding to different predicted pump-off pressure values ​​(the blowout timing is to control the nozzle blowout flow rate to be below 200 m / s or the predicted pump-off pressure value ≤ 50 MPa); determining the corresponding blowout flow rate through a blowout flow chart based on the inner diameter of the tubing of the horizontal well or the vertical well, and then determining the nozzle specification selected for blowout through blowout flow charts of different nozzles with different pressures based on the blowout flow rate and the predicted pump-off pressure; after the blowout conditions are met, blowout is performed with the selected nozzle specification; after blowout of more than one wellbore volume of liquid and the nozzle outlet is substantially free of sand, reorganizing displacement and construction.

[0044] The pump stop pressure is calculated as follows:

[0045] P y =P+P H -P f -P J (1)

[0046] P 停 =P y -P H (2)

[0047] In formulas (1) to (2), P y is the extension pressure, P is the construction pressure, P H is the liquid column pressure, P f is the string friction, P J is the throttling pressure difference of the string hole, P 停 is the pump stop pressure (i.e. the predicted value of the pump stop pressure).

[0048] The construction pressure P is the normal pumping pressure before sand plugging and can be directly read by the fracturing instrument vehicle.

[0049] The pipe friction P fIn order to combine the actual liquid used on site, the friction resistance (pipe friction resistance) value is calculated by the drag reduction ratio:

[0050]

[0051] In formula (3), σ is the ratio of fracturing fluid to water friction, D is the borehole diameter, Q is the displacement, Cg is the thickener concentration, and Cs is the sand-carrying fluid concentration. The water friction is a known value, and its combination with σ can be used to obtain the string friction P f value.

[0052] The throttling pressure difference P of the pipe string hole J Calculate as follows:

[0053] P J =225.16ρQ 2 / (C d 2 *n 2 *d1 4 ) (4)

[0054] In formula (4), P J is the throttling pressure difference of the string hole, ρ is the liquid density, Q is the displacement, C d is the flow coefficient, n is the number of holes, and d1 is the hole diameter.

[0055] For vertical wells, the blowout flow chart is a chart drawn with different pipe string inner diameters and the lowest blowout flow (see attached Figure 3 ), the minimum blowdown flow rate of the vertical well is twice the natural settling flow rate of the proppant; the natural settling flow rate of the proppant is calculated by combining the free settling velocity of the vertical well section of the proppant with the flow formula;

[0056] The free settling velocity of the proppant in the vertical well section is calculated using the following formula:

[0057] Vs=a*d k (ρ p g-ρg) m / (b*μ f ) (5)

[0058] In formula (5), Vs is the natural settling velocity of the proppant, a, b, k, m, f are constants, and ρ P is the proppant density, ρ is the liquid density, and μ is the liquid viscosity.

[0059] For horizontal wells, the blowdown flow chart is a chart drawn with different sand ratios, different pipe string inner diameters and proppant critical resuspension flow rates (see attached Figure 2 ), the critical resuspension flow rate of proppant is the resuspension velocity of proppant in the horizontal section calculated by the flow formula;

[0060] The proppant resuspension velocity in the horizontal section is calculated using the following formula:

[0061]

[0062] In formula (6), Vsc is the proppant resuspension velocity, a is a constant, and d p is the proppant diameter, d is the column diameter, C1 is the sand ratio, ρ P is the proppant density, ρ is the liquid density, N Re is the Reynolds number and g is the acceleration due to gravity.

[0063] The flow formula is Q 流 =V*S, where Q 流 is the flow rate, V is the liquid flow rate in the wellbore (the free settling velocity of the proppant in the vertical well section or the resuspension velocity of the proppant in the horizontal section), and S is the cross-sectional area of ​​the wellbore (the cross-sectional area of ​​the tubing string).

[0064] The nozzle outlet flow rate corresponding to the different pump stop pressure prediction values ​​is calculated by the Bernoulli equation:

[0065]

[0066] In formula (7), P 停 is the predicted value of pump stop pressure, ρ is the liquid density, υ is the nozzle outlet flow rate, g is the gravity acceleration, h is the height of the liquid column, and C is a constant; the nozzle outlet flow rate corresponding to different pump stop pressure predicted values ​​is calculated according to formula (7) and the nozzle outlet flow rate curve corresponding to different pump stop pressures is plotted (see attached). Figure 1 ); The nozzle outlet flow rate calculated by formula (7) is 流 =υ*πd z 2 / 4 calculates the corresponding flow value, where Q 流 is the flow rate, υ is the nozzle outlet flow rate, d z is the inner diameter of the nozzle, the pump stop pressure is the predicted value of the pump stop pressure, and a chart of the discharge flow rate of different nozzles at different pressures is drawn (see the attached figure). Figure 4 ).

[0067] When fracturing sand plugging occurs in a vertical well or a horizontal well, when the vertical well or horizontal well fracturing sand plugging and blowout method described in the present invention is used on-site, the pump stop pressure and the nozzle blowout flow rate are first calculated to determine whether the blowout conditions are met (the nozzle blowout flow rate is below 200m / s or the pump stop pressure prediction value is ≤50MPa), and then, the blowout flow rate is determined according to the corresponding blowout flow rate chart (vertical well minimum blowout flow rate chart or horizontal well critical resuspension flow rate curve chart) based on the inner diameter of the tubing string of the vertical well or the horizontal well, and then, the nozzle specifications are determined according to the predicted value of the pump stop pressure and the blowout flow rate. After the blowout conditions are met, the selected nozzle is used for blowout.

[0068] Embodiment 2:

[0069] If sand plugging occurs during fracturing of a vertical well, the fracture extension pressure and predicted pump stop pressure are calculated based on the fracturing operation pressure before sand plugging. If the predicted pump stop pressure is > 50MPa or the nozzle velocity is > 200m / s, blowout is prohibited. The subsequent blowout procedure is performed after the pressure drops to ≤50MPa. The minimum blowout flow rate of different tubing diameters in vertical wells is calculated (based on the attached Figure 3 query); according to the pump stop pressure, combined with different pressures and different nozzles corresponding to the spray flow chart ( Figure 4 ) Select a reasonable oil nozzle to organize the blowdown; after blowing out more than one volume of liquid in the wellbore and the outlet is basically free of sand, re-organize the displacement and construction.

[0070] The minimum discharge flow rate is Figure 3 Read.

[0071] The reasonable oil nozzle is a combination of the pump stop pressure and the Figure 4 Select from the spray flow chart.

[0072] Specific implementation case: Taking a vertical well fracturing oil pipe with an inner diameter of 76mm as an example, the construction pressure before sand plugging is 50MPa. The expected pump stop pressure is 30MPa calculated by formulas (1) to (2). The flow rate of the oil nozzle is <200m / s, which meets the conditions for organizing the spraying. The minimum spraying flow rate is determined to be 408L / min according to the inner diameter of the oil pipe (based on Figure 3 Select), then follow the Figure 4 Select an 8mm oil nozzle for spraying, and adjust it at any time according to the pressure changes. After spraying more than one wellbore volume of liquid and the outlet is basically free of sand, re-organize the displacement and construction.

[0073] Embodiment 3:

[0074] When sand plugging occurs during fracturing of horizontal wells, the fracture extension pressure and predicted pump-off pressure are calculated based on the fracturing operation pressure before sand plugging. If the predicted pump-off pressure is greater than 50MPa or the nozzle velocity is greater than 200m / s, blowout is prohibited. After the pressure drops to ≤50MPa, the subsequent blowout procedure is performed. The critical resuspension flow rate of horizontal wells with different sand ratios and casings is calculated (it can be calculated based on the attached Figure 2 query); select a reasonable nozzle to organize the blowdown according to the pump stop pressure and the blowdown flow chart; after the wellbore volume of liquid is blown out and the outlet is basically free of sand, re-organize the displacement and construction.

[0075] The minimum discharge flow rate is Figure 2 Read.

[0076] The reasonable oil nozzle is a combination of the pump stop pressure and the Figure 4 Select from the spray flow chart.

[0077] Specific implementation case: Taking the casing inner diameter of a horizontal well fracturing horizontal section as an example, the construction pressure before sand plugging is 45MPa. The estimated pump stop pressure is 32MPa calculated by formulas (1) to (2). The flow rate of the oil nozzle is <200m / s, which meets the conditions for organizing the blowout. The minimum blowout flow rate is determined to be 1100L / min according to the casing inner diameter (based on Figure 2 Select), then follow the Figure 4 Select a 12mm oil nozzle to organize the blowdown until more than one volume of wellbore liquid is blown out and the outlet is basically free of sand, then re-organize the displacement and construction.

[0078] In summary, the method for fracturing sand plugging and blowing out of a vertical well or horizontal well described in the present invention has the characteristics of fast decision-making and simple operation for abnormal sand plugging conditions in vertical wells or horizontal wells. It can effectively reduce the economic losses and well control safety risks caused by fracturing sand plugging through quantitative calculation and avoid subjective conjecture, and realize correct and rapid handling of abnormal sand plugging conditions.

[0079] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effect. Non-essential technical features can be added or reduced according to actual needs to meet the requirements of different situations.

Claims

1. A method for fracturing sand plugging and spraying in a vertical well or horizontal well, characterized in that According to the construction pressure curve before sand plugging, the pump stop pressure is calculated to obtain the pump stop pressure prediction value; according to the nozzle outlet flow rate corresponding to different pump stop pressure prediction values, the timing of spraying is selected; the corresponding spraying flow rate is determined by the inner diameter of the pipe string of the horizontal well or vertical well through the spraying flow chart, and then the nozzle specifications selected for spraying are determined by the spraying flow rate and the pump stop pressure prediction value through the spraying flow chart of different nozzles with different pressures; after the spraying conditions are met, spraying is carried out with the selected nozzle specifications; Among them, the pump stop pressure is calculated as follows: P y =P+P H -P f -P J (1) P 停 =P y -P H (2) In formulas (1) to (2), P y is the extension pressure, P is the construction pressure, P H is the liquid column pressure, P f is the string friction, P J is the throttling pressure difference of the string hole, P 停 The pump stop pressure; The pipe string friction resistance is the pipe string friction resistance value calculated by the drag reduction ratio based on the actual liquid used on site: In formula (3), σ is the ratio of fracturing fluid to clean water friction, D is the borehole diameter, Q is the displacement, Cg is the thickener concentration, Cs is the sand-carrying fluid concentration, and the string friction is calculated by combining σ; The throttling pressure difference P of the pipe string hole J Calculate as follows: P J =225.16ρQ 2 / (C d 2 *n 2 *d1 4 ) (4) In formula (4), P J is the throttling pressure difference of the string hole, ρ is the liquid density, Q is the displacement, C d is the flow coefficient, n is the number of holes, and d1 is the hole diameter; For vertical wells, the blowout flow chart is a chart drawn with different pipe string inner diameters and the minimum blowout flow, wherein the minimum blowout flow of a vertical well is twice the natural settling flow of the proppant; the natural settling flow of the proppant is calculated by combining the free settling velocity of the proppant in the vertical well section with the flow formula; The free settling velocity of the proppant in the vertical well section is calculated using the following formula: Vs=a*d k (r p g-ρg) m / (b*μ f ) (5) In formula (5), Vs is the natural settling velocity of the proppant, a, b, k, m, f are constants, and ρ P is the proppant density, ρ is the liquid density, and μ is the liquid viscosity; For horizontal wells, the blowout flow rate chart is a chart drawn with different sand ratios, different string inner diameters and proppant critical resuspension flow rates. The proppant critical resuspension flow rate is the proppant resuspension velocity in the horizontal section calculated using the flow formula. The proppant resuspension velocity in the horizontal section is calculated using the following formula: In formula (6), Vsc is the proppant resuspension velocity, a is a constant, and d p is the proppant diameter, d is the column diameter, C1 is the sand ratio, ρ P is the proppant density, ρ is the liquid density, N Re is the Reynolds number and g is the acceleration due to gravity.

2. The vertical well or horizontal well fracturing sand plugging and spraying method according to claim 1, characterized in that The nozzle outlet flow rate corresponding to different pump stop pressure prediction values ​​is calculated by the Bernoulli equation: In formula (7), P 停 is the predicted value of the pump stop pressure, ρ is the liquid density, υ is the nozzle outlet flow rate, g is the gravity acceleration, h is the height of the liquid column, and C is a constant; the nozzle outlet flow rate calculated by formula (7) is 流 =υ*πd z 2 / 4 Calculate the corresponding flow value, and draw a chart of different pressures and different nozzle release flow rates with different pump stop pressures, different nozzle specifications and nozzle release flow rates, where Q 流 is the flow rate, υ is the nozzle outlet flow rate, d z is the inner diameter of the oil nozzle, and the pump stop pressure is the predicted value of the pump stop pressure.

3. The vertical well or horizontal well fracturing sand plugging and spraying method according to claim 1 or 2, characterized in that The timing of spraying is to control the nozzle spraying flow rate to be below 200m / s or the predicted value of pump stop pressure ≤50MPa.

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