A method for determining a gas lift fluid discharge mode of gas drilling

Abstract

The present application relates to the technical field of underbalanced drilling of oil drilling, and discloses a method for determining a gas lifting liquid discharge mode in gas drilling, which comprises the following steps: determining whether one-time gas lifting liquid discharge can be adopted according to calculation; calculating the time t required for one-time gas lifting liquid discharge; determining whether gas-charged gas lifting liquid discharge can be adopted according to calculation; determining whether alternating gas lifting liquid discharge can be adopted according to calculation; adopting a segmented gas lifting liquid discharge mode to perform gas lifting, and calculating the drilling depth of each segment. The method provides a decision for selection of a gas lifting liquid discharge mode before gas drilling by using an optimized method, which comprehensively considers the performance of well site equipment and a gas lifting predicted time factor, and gives a suitable gas lifting liquid discharge mode through calculation and analysis. The method for determining a gas lifting liquid discharge mode in gas drilling is layer-by-layer optimized, has clear logic, simple thinking, and a simple calculation process, and is suitable for decision-making by field personnel.

Description

Technical Field

[0001] This invention relates to the field of underbalanced drilling technology in oil drilling, and particularly to a method for determining the gas lift fluid removal method before the start of gas drilling. Background Technology

[0002] Currently, oil drilling primarily uses liquid-phase drilling fluids, typically maintaining a bottomhole pressure higher than the formation pressure. This results in a significant bottomhole pressure holding effect and low mechanical drilling rate. The bottomhole pressure differential can easily damage the producing formation, affecting subsequent oil (gas) production and hindering the discovery of new producing formations. Furthermore, encountering caverns or fractured formations greatly increases the risk of complex well leakage. Therefore, conventional drilling can lead to low drilling speed, low efficiency, low well production, and low-quality completion when drilling complex and difficult-to-develop blocks. Gas drilling technology effectively addresses the shortcomings of conventional liquid-phase drilling fluids. It uses gas (air, nitrogen, natural gas) as the circulating medium, creating a negative pressure differential at the bottom of the well. This technology eliminates the bottomhole pressure holding effect, increasing the mechanical drilling rate while achieving zero reservoir contamination. It maximizes the discovery of new reservoirs and effectively avoids complex well leakage. Therefore, gas drilling is a low-cost, high-efficiency, and safe drilling method with excellent application results in drilling complex reservoirs.

[0003] Before gas drilling, high-pressure gas is used to lift the liquid (drilling fluid or water, hereinafter referred to as water) out of the wellbore. This process is commonly known as gas lift drainage. Common gas lift drainage methods include single-stage gas lift drainage, staged gas lift drainage, alternating gas lift drainage, and aeration gas lift drainage. Single-stage gas lift refers to lowering the drill bit near the bottom of the well and injecting gas into the drilling tools to lift all the liquid in the well in one go. Staged gas lift involves lowering the drill bit to a certain depth, lifting the liquid, lowering the drill bit again to lift the second stage, and so on, until the entire wellbore is lifted. Alternating gas lift involves first injecting high-pressure gas into the drilling tools, then stopping the gas injection and pumping in clean water once the injection pressure reaches the pump's allowable value. Gas injection is then resumed after the pump pressure decreases, and this process is repeated until all the gas is returned to the wellbore. Aeration gas lift involves simultaneously injecting clean water and gas into the drilling tools. As the pump pressure decreases, the water injection rate is gradually reduced while the gas injection rate is increased (or the gas injection rate remains constant), gradually reducing the volume fraction of the liquid phase in the well until it is completely lifted by the gas. For shallow wells, the maximum pressure of the booster pump is generally higher than the bottom hole pressure, allowing for direct single-stage gas lift. However, for deep wells, due to limitations in the gas supply capacity and maximum supply pressure of the surface gas supply equipment, only the latter three methods can be used. For the latter three methods, the choice is usually made based on experience during on-site construction, without mature theoretical guidance, resulting in a high degree of uncertainty.

[0004] The above analysis shows that gas lift fluid removal before gas drilling is a relatively complex multiphase flow process within the well. Currently, there is a lack of research on the applicable conditions for each gas lift method, especially how to optimize a suitable gas lift fluid removal method under deep well conditions. Therefore, it is urgent to propose a method for determining the gas lift fluid removal method in gas drilling, ensuring that the gas lift process does not exceed the performance range of the on-site equipment while minimizing construction time. This is also a challenge in the field of gas drilling technology. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for determining the gas lift fluid discharge method in gas drilling.

[0006] This method uses theoretical analysis to determine the drainage method for gas drilling under different equipment conditions, ultimately aiming to shorten the gas lift time, shorten the well construction cycle, and reduce drilling costs.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A method for determining the gas lift drainage method in gas drilling, wherein the gas lift drainage method is selected from four methods—single gas lift drainage, gas-filled gas lift drainage, alternating gas lift drainage, and segmented gas lift drainage—through a condition judgment method, and a reasonable gas lift drainage method is selected once or multiple times.

[0009] In the preferred method of implementation, the process of determining the air-lift discharge method includes the following steps:

[0010] (1) Determine whether a single air lift can be used for liquid drainage based on calculations;

[0011] (2) Calculate the minimum time t required for one airlift discharge;

[0012] (3) Determine whether air-lift drainage can be used based on calculations;

[0013] (4) Determine whether alternating air lift drainage can be used based on calculations;

[0014] (5) Use segmented air lift for liquid removal.

[0015] In the implementation method, step (1) of the method for determining the air lift drainage method specifically involves calculating and determining whether a single air lift drainage method can be used based on a formula.

[0016] In the implementation method, step (2) of the method for determining the air-lift drainage method specifically involves calculating the minimum time t required for one air-lift drainage, which is the time it takes for the gas in the drill bit to press all the liquid in the drill bit into the annulus.

[0017] In the implementation method, step (3) of the method for determining the air-lift drainage method specifically involves calculating and determining whether air-lift drainage can be used based on the formula.

[0018] In the implementation method, the maximum casing pressure P that appears at the wellhead during the gas lift drainage process in step (3) of the gas lift drainage method determination method is... amax The value should be determined using a formula.

[0019] In the implementation method, step (4) of the method for determining the air lift drainage method specifically involves determining whether alternating air lift drainage can be used based on calculations.

[0020] In the implementation method, step (5) of the method for determining the air lift drainage method is to perform air lift by adopting a segmented air lift drainage method.

[0021] In the implementation method, the entry depth of the first stage of the air-lifted drill string should be calculated first, and then the entry depth of the drill string for the second to Nth stages of air-lifted drill string should be calculated separately for the cases of drill string without a check valve and drill string with a check valve.

[0022] The beneficial effects of this invention are:

[0023] (1) The logic is clear, the selection is optimized at each level, and there is a theoretical basis, which avoids the shortcomings of the general practice of selecting the air lift method based on experience.

[0024] (2) By using this method, the best gas lift liquid discharge method can be selected, the gas lift time can be shortened, and the lift efficiency can be improved.

[0025] (3) The theoretical calculation process has been reasonably simplified for complex multiphase flow in wells, making the calculation method simpler and suitable for field use and promotion. Attached Figure Description

[0026] Figure 1 This is a schematic diagram illustrating the preferred process of determining a gas lift fluid discharge method for gas drilling according to the present invention; Detailed Implementation

[0027] The present invention will now be further described with reference to the accompanying drawings.

[0028] Please refer to the appendix. Figure 1 The diamond-shaped box in the figure shows the judgment conditions for selecting a certain airlift method, and the rectangle shows the results of each layer of selection.

[0029] The method for determining the gas lift fluid removal method before gas drilling includes the following steps:

[0030] 1. Determine whether a single airlift drainage method can be used based on calculations;

[0031] When using gas injection equipment to lift fluid from the well, the following formula should be used to determine whether a single gas lift method can be used to remove the fluid:

[0032] P zmax >P b (1)

[0033] P b =0.00981ρ m H t (2)

[0034] In the formula: P zmax P represents the maximum allowable pressure of the booster compressor, measured in MPa. b ρ is the bottom hole pressure before gas lift, in MPa. m The density of the fluid in the well is expressed in g / cm³. 3 H t The vertical depth of the gas lift well is expressed in meters (m).

[0035] If equation (1) satisfies the condition, proceed to step 2; otherwise, proceed to step 3.

[0036] 2. Calculate the minimum time t required for one air lift to discharge the liquid;

[0037] The minimum time required for a single gas lift, i.e. the time it takes for the gas in the drill string to completely force the fluid in the drill string into the annulus, is determined as follows:

[0038]

[0039]

[0040]

[0041] Where: t is the minimum time required for one air lift, in min; ρ g To lift the gas at the bottom hole pressure P b Density in numerical form, g / cm³ 3 ;ρ g0 The density of the lifted gas at standard atmospheric pressure is expressed in g / cm³. 3 V pipe The internal volume of the drilling tools in the well is m. 3 Q zmax The rated gas displacement of the booster compressor is in meters. 3 / min; M g The relative molecular weight of the lifted gas is dimensionless; R is the universal gas constant, J / (mol·K); D pipe and D collar Here, H represents the inner diameter of the drill pipe and drill collar, respectively, in meters (m); pipe and H collar, respectively, represent the lengths of the drill pipe and drill collar inside the well, in meters (m). T is the formation temperature at half the well depth, in kilometer (K).

[0042] 3. Determine whether air-lift drainage can be used based on calculations;

[0043] The following formula should be used to determine whether airlift drainage is appropriate:

[0044] P zmax >P amax (6)

[0045] Among them, P amax The calculation of the maximum casing pressure at the wellhead during gas lift drainage is complex and can be estimated using the following simplified method. The volume fraction of the multiphase flow gas components in the drill pipe is highest at the wellhead and lowest at the bottom. A simplified approach is to use the gas volume fraction at the midpoint between the wellhead and the bottom to represent the average gas volume fraction of the two-phase flow throughout the drill pipe. This allows for the calculation of the hydrostatic column pressure within the drill pipe. P amax The solution is obtained from the following system of equations:

[0046]

[0047]

[0048]

[0049] In the formula: P amax P represents the maximum pump pressure at the wellhead during the air-lift fluid discharge process, in MPa. zmax The maximum permissible pressure of the booster compressor is in MPa; α0 and α t Q represents the gas volume fraction at the wellhead and bottom of the well, respectively, under the maximum wellhead pump pressure of gas lift, and is dimensionless; g and Q m These represent the injection displacement of gas and liquid under airlift conditions, respectively, in m. 3 / min.

[0050] The method for obtaining the value is as follows: First, a value Q that conforms to the on-site construction is given. g and Q m Numerical value. Substituting equations (8) and (9) into equation (7), we can obtain a value with P. amax Q is an implicit function of the independent variable, and can be obtained through numerical iteration. g and Q m The maximum pump pressure P at the wellhead when the construction parameters are specified. amax .

[0051] If equation (6) is satisfied, then the air-lift drainage method is implemented, and the air injection volume and liquid injection volume of the construction parameters are Q, respectively. g and Qm Otherwise, proceed to step 4.

[0052] 4. Determine whether alternating air lift drainage can be used based on calculations;

[0053] The following formula should be used to determine whether alternating air lift drainage is appropriate:

[0054] P zmax ≥P b / 3 (10)

[0055] If equation (10) is satisfied, then the alternating gas lift method is adopted. The steps are as follows: first, use a booster to inject gas into the drill string at maximum displacement; wait until the booster pressure reaches P zmax After stopping gas injection, turn on the drilling pump or fracturing pump and inject fluid into the drill string; after fluid injection, the pump pressure will begin to drop, wait until the pump pressure drops to P zmax / 2 Stop injecting liquid; turn on the booster to inject gas again, and repeat this cycle.

[0056] If equation (10) does not meet the conditions, proceed to step 5.

[0057] 5. Use a segmented air lift method for liquid removal;

[0058] The key construction point of the segmented air-lift fluid removal method is to determine the depth to which the drill string needs to be lowered before each air lift. Depending on the drill string assembly, this can be divided into two cases: drill string without a check valve and drill string with a check valve. For both cases, the lowering depth H of the first segment of the air-lift drill string is determined by the following formula:

[0059]

[0060] For drill strings without check valves, since the drill string and annulus are connected, annular fluid can enter the drill string, and their fluid levels are always the same. The depth of the drill string from the 2nd to the Nth section is affected by the drill string volume and is determined by the following formula:

[0061]

[0062] When the drill string contains a check valve, since the fluid in the annulus cannot flow into the drill string, grouting is required during the drilling process to ensure that the fluid level inside the drill string and the fluid level in the annulus are aligned. Therefore, the drilling depth from the 2nd to the Nth section is determined by the following formula:

[0063]

[0064] In the formula: H2 and H′2 are the drilling depths from the 2nd to the Nth drilling operations, respectively, when there is no check valve in the drill string and when there is a check valve in the drill string; D h D is the inner diameter of the last casing section, in meters (m). p1 D is the outer diameter of the drill bit, in meters (m).p2 H is the inner diameter of the drill string, in meters; H is the depth of the drill string during the first stage of air lift, in meters.

[0065] The present invention provides a method for determining the gas lift drainage method in gas drilling. Based on the performance of the on-site gas supply equipment and the well structure, a suitable gas lift drainage method is selected by comprehensively considering various factors. This ensures that the gas lift process is carried out quickly and efficiently, thereby providing conditions for subsequent gas drilling and enabling gas drilling technology to provide technical support for accelerating, improving efficiency, enhancing quality, and increasing production in oil drilling.

Claims

1. A method for determining the gas lift fluid discharge method in gas drilling, characterized in that: The air-lift drainage method is selected from four methods—single air-lift drainage, gas-filled air-lift drainage, alternating air-lift drainage, and segmented air-lift drainage—through a conditional judgment method, either once or multiple times, to determine a reasonable air-lift drainage method. The process of determining the air-lift drainage method includes the following steps: (1) Determine whether single air-lift drainage can be used based on calculations. If so, use single air-lift drainage; otherwise, proceed to step (3); (2) Calculate the minimum time t required for single air-lift drainage; (3) Determine whether gas-filled air-lift drainage can be used based on calculations. If so, use gas-filled air-lift drainage; otherwise, proceed to step (4); (4) Determine whether alternating air-lift drainage can be used based on calculations. If so, use alternating air-lift drainage; otherwise, proceed to step (5); (5) Perform air-lift drainage using the segmented air-lift drainage method. Specifically, step (1) involves determining whether single air-lift drainage can be used based on calculations: The calculation uses the following formula: In the formula: This is the maximum allowable pressure of the booster compressor. This refers to the bottom hole pressure before gas lift. The density of the fluid inside the well. Let m be the vertical depth of the gas lift well. Step (2) specifically involves calculating the minimum time t required for one gas lift to discharge fluid, which is the time it takes for the gas in the drill string to completely force the fluid in the drill string into the annulus. The determination method is as follows: ； Where: t is the minimum time required for one air lift, in minutes; To increase the pressure of the gas at the bottom of the well Density in numerical form, g / cm³ 3 ; The density of the lifted gas at standard atmospheric pressure is expressed in g / cm³. 3 ; The internal volume of the drilling tools in the well is m. 3 ; The rated gas displacement of the booster compressor is in meters. 3 / min; The relative molecular weight of the lifted gas is dimensionless; R is the universal gas constant. These are the inner diameters of the drill pipe and drill collar, respectively, in meters (m). These are the lengths of the drill pipe and drill collar inside the well, respectively, in meters (m). T is the formation temperature at half the well depth, in K; step (3) specifically involves determining whether gas lift drainage can be used based on calculations. The following formula should be used to determine whether gas lift drainage can be used: (6) Among them, This refers to the maximum casing pressure that occurs at the wellhead when using pneumatic lift for fluid removal. Step (5) specifically involves using a segmented air lift method for liquid removal. The air lift height H of the first segment of the segmented air lift liquid removal is determined using the following formula: The determination of the airlift height from the second to the Nth time in step (5) is made by the following formula: For drill strings that do not contain check valves, the drilling depth from the 2nd to the Nth drilling depth is determined by the following formula: ； For drill strings containing check valves, the drilling depth from the 2nd to the Nth drill bit is determined by the following formula: ； In the formula: The drilling depths from the 2nd to the Nth drilling operations are respectively the drilling depths with and without check valves in the drill string. Let m be the inner diameter of the last casing section. Let be the outer diameter of the drill bit, in meters (m). H is the inner diameter of the drill string, in meters; H is the depth of the drill string during the first stage of air lift, in meters.

2. The method for determining the gas lift fluid discharge method in gas drilling according to claim 1, characterized in that: The maximum casing pressure that occurs at the wellhead during the gas lift and fluid discharge process in step (3) The determination is made using the following method: The volume fraction of the multiphase flow component gas in the drill pipe is the largest at the wellhead and the smallest at the bottom of the well. The simplified treatment is to use the gas volume fraction at the middle of the wellhead and the bottom of the well to represent the average gas volume fraction of the two-phase flow gas in the entire drill pipe, and then the hydrostatic column pressure in the drill pipe can be calculated. The solution is obtained from the following system of equations: In the formula: The maximum casing pressure at the wellhead when using air lift for fluid removal, in MPa; These are the gas volume fractions at the wellhead and bottom of the well, respectively, under the maximum wellhead pump pressure of gas lift, and are dimensionless. These represent the injection displacement of gas and liquid under airlift conditions, respectively, in m. 3 / min; the method for obtaining this value is as follows: first, a value suitable for on-site construction is given. Numerical value; Substituting equations (8) and (9) into equation (7), we can obtain a value based on For an implicit function of the independent variable, it can be obtained through numerical iteration. The maximum casing pressure at the wellhead when the construction parameters are specified. .

3. The method for determining the gas lift fluid discharge method in gas drilling according to claim 2, characterized in that: Step (4) specifically involves determining, based on calculations, whether alternating air lift drainage can be used, and the following formula should be adopted: (10) The maximum allowable pressure of the booster is MPa; if equation (10) is satisfied, then the alternating air lift drainage method is adopted; The steps are as follows: First, use a booster to inject gas into the drill bit at maximum displacement; wait until the booster pressure reaches... After stopping gas injection, turn on the drilling pump or fracturing pump and inject fluid into the drill string; after the fluid is injected, the pump pressure will begin to drop, and wait until the pump pressure drops to a certain level. Stop injecting liquid; turn on the booster pump to inject gas again, and repeat this cycle.

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