A method for determining the optimal length and diameter of a solid bubble rod for critical drop in a continuously producing gas well

Abstract

The present invention provides a method for determining the optimal length and diameter of the critical drop of a solid bubble rod in a continuously produced gas well. First, the gas well production parameters are obtained, a series of bubble rod lengths and diameters are given, and the bubble rod density is determined according to the conditions such as the raw materials for making the bubble rods on site. Then, based on the flow similarity criterion, the field production under high pressure is converted into the corresponding gas-liquid flow rate under normal pressure. The critical drop gas flow rate of multiple groups of solid bubble rods in the continuously produced gas well is calculated by the obtained liquid flow rate, bubble rod density, and a series of bubble rod lengths and diameters. Then, the critical drop gas flow rate is compared with the gas flow rate under normal pressure after conversion, and a value greater than the latter is selected. The corresponding length and diameter are calculated using the volume formula combined with the fracture coefficient to select the maximum value of the result, and the corresponding length and diameter are the optimal. Most of the parameters required by this method can be obtained from field logging data, which is convenient and fast.

Description

Technical Field

[0001] The invention belongs to the field of gas reservoir drainage and gas production, and in particular relates to a method for determining the optimal length and diameter of a solid bubble rod for critical drop in a continuously producing gas well. Technical Background

[0002] Foam drainage gas production is one of the economical and effective production methods for water-producing gas wells. Usually, the foaming agent solution is continuously pumped into the casing annulus from the wellhead, which is suitable for both continuous production gas wells and intermittent production gas wells; but for wells with packers, the casing annulus is not connected, and the foaming agent cannot be added through the casing annulus. The density of the solid foam rod is greater than that of the gas well fluid. It can be dropped from the wellhead wax cleaning gate and fall in the oil pipe. It is fully in contact with the downhole liquid and slowly dissolved and released, which can effectively improve the gas liquid carrying capacity, reduce wellbore liquid accumulation, and extend the gas well self-flowing production time.

[0003] In order to ensure that the solid bubble rod falls in the oil pipe, the well needs to be shut down when the bubble rod is thrown, so that the bubble rod falls in the static fluid to prevent the bubble rod from being carried out of the wellhead by the fluid flowing to the wellhead. However, frequent opening and closing of the well will lead to low production rate of the gas well. Therefore, it is very important to throw the solid bubble rod without shutting down the well and ensure smooth falling to achieve continuous production of the gas well. However, the wellbore of the gas well is a complex gas-liquid two-phase flow. Whether the solid bubble rod can fall in the two-phase flow is the key to whether the process can be implemented. Therefore, it is necessary to propose a method to determine the optimal length and diameter of the critical fall of the solid bubble rod in the continuous production gas well.

[0004] This patent is to solve the above problems and provides a new idea and method to solve the above problems. This method can be accurately applied to determine the optimal length and diameter of the solid bubble rod in the bubble rod process in the continuous production gas well, and provide guidance for the on-site implementation of the bubble rod process. Summary of the invention

[0005] The purpose of the present invention is to solve the problem that it is difficult to determine the critical drop length and diameter of a bubble rod in a continuous production gas well, and to provide a method for determining the optimal critical drop length and diameter of a solid bubble rod in a continuous production gas well.

[0006] A method for determining the optimal length and diameter of a solid bubble rod for critical drop in a continuously producing gas well comprises the following steps:

[0007] Step 1: Obtain the production data of the gas wells that need to be invested in the bubble rod process, including wellhead pressure, wellhead temperature, natural gas relative density, tubing inner diameter, gas production, liquid production and other data; according to the conditions of the on-site bubble rod production raw materials and other conditions, the bubble rod density is given, and a series of bubble rod lengths L1, L2, L3...L N , given a series of bubble rods with diameters of d1, d2, d3…d MSince the longer the foam rod is, the easier it is to break, the fracture coefficient X (0≤X≤1) is introduced, and X is positively correlated with the length and negatively correlated with the diameter.

[0008] Step 2: Based on the flow similarity criterion, use the dimensionless criterion to convert the field production under high pressure into the corresponding gas-liquid flow rate under normal pressure. The corresponding calculation formula is as follows:

[0009] Calculate the gas superficial velocity v under high pressure SG高压 :

[0010]

[0011] where v SG高压 is the apparent gas velocity under high pressure, m / s; Q g Gas phase flow rate, m 3 / d, A is the cross-sectional area of ​​the pipe, m 2 ,and

[0012]

[0013] Calculate the gas density at a given wellbore location under pressure and temperature conditions:

[0014]

[0015] Where ρ is the gas density at a given temperature and pressure, kg / m 3 ; γ g is the relative density of gas, dimensionless; Z is the gas compressibility factor, dimensionless; P is the pressure, MPa; T is the temperature, K;

[0016]

[0017] After transformation, there is a relationship:

[0018]

[0019] In the formula, F r is the Froude dimensionless number, dimensionless; ρ G高压 , L高压 is the density of gas or liquid under high pressure, kg / m 3 ;v SG标况 is the apparent gas velocity under standard conditions (0.1MPa, 20℃), m / s;

[0020] Calculate the apparent velocity v of the liquid phase under standard conditions sl :

[0021]

[0022] Its sl is the apparent liquid velocity under standard conditions, m / s;l is the liquid phase flow rate, m 3 / d.

[0023] Step 3: The critical falling gas velocity of the solid bubble rod in the continuous production gas well is determined by the calculation formula established based on the experimental test results:

[0024] v sg =(a1×v sl +a2)(a3×L * +a4)(a5×D *3 +a6×D *2 +a7×D * +a8)(a9×ρ+a 10 ) (7)

[0025] Among them, v sg Indicates the calculated superficial gas velocity, m / s; L * Indicates the ratio of the length to the diameter of the foam rod; D * It represents the ratio of the diameter of the foam rod to the tube diameter; ρ represents the density of the foam rod, g / cm 3 .

[0026] The constants of the above formula are shown in Table 1:

[0027] Table 1 Constants of calculation formula for critical drop specifications of bubble rods in continuous production gas wells

[0028] <![CDATA[a1]]> -2.2555 <![CDATA[a2]]> 1.2708 <![CDATA[a3]]> 2.5514 <![CDATA[a4]]> 49.8951 <![CDATA[a5]]> 1.3449 <![CDATA[a6]]> -2.1916 <![CDATA[a7]]> 1.1652 <![CDATA[a8]]> -0.1799 <![CDATA[a9]]> 2.4524 <![CDATA[a 10 ]]> 4.9591

[0029] Then, the determined parameters, liquid flow rate, bubble rod density, length, and diameter are substituted into formula (7) to calculate a series of critical falling air velocities of the bubble rod, which are then compared with the v calculated in step 2. SG标况 Compare and select the value greater than v SG标况 The critical falling air velocity of the bubble rod.

[0030] Step 4: Here is the calculation formula for the fracture coefficient:

[0031]

[0032] Where L0 and d0 are the reference values ​​of length and diameter that are not easy to break, L0 = 30cm, d0 = 3cm; coefficient A = 0.01; L is the length of the bubble rod; d is the diameter of the bubble rod, cm, and when L≤L0 or d≥d0, X=0;

[0033] Using the volume formula and introducing the fracture coefficient, the calculation formula can be obtained:

[0034]

[0035] This method can ensure that the foam rod is not easy to break and the foam agent volume is the largest;

[0036] Finally, substitute the length and diameter of the bubble rod corresponding to the values ​​selected in step 3 into equations (7) and (8), and take the set of values ​​that maximize ΔV as the optimal length and diameter.

[0037] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The following examples further illustrate the technology of the present invention:

[0039] The wellhead pressure of a gas well is 16Mpa, the wellhead temperature is 42℃, the relative density of natural gas is 0.68, the inner diameter of the oil pipe is 70mm, and the gas production is 10×10 4 m 3 / d, liquid production 20m 3 / d. The optimal density is determined by on-site process to be 1.5g / cm 3 , the given bubble rod length is 40 / 50 / 60, and the given bubble rod diameter is 4 / 4.5 / 5.

[0040] Using formula (5) and formula (6), the liquid production is converted into the liquid flow rate at normal temperature and pressure, that is, 0.06 m / s, and the gas production is converted into the gas flow rate at normal temperature and pressure, that is, 17.1 m / s. Then, the liquid flow rate, the density, length, and diameter of the bubble rod are substituted into formula (7), and Table 2 can be calculated:

[0041] Table 2 Calculation results of critical falling air velocity

[0042]

[0043] Select the critical falling air velocity greater than the conversion value of 17.1m / s, namely group 6, group 7, and group 9. Substitute the length and diameter of the bubble rod corresponding to each group into formula (8) and formula (9), and calculate to obtain Table 3:

[0044] Table 3 ΔV calculation results

[0045] Group No. Length of bubble rod, cm Diameter of bubble rod, cm Fracture coefficient ΔV 1 50 5 0.1 883.57 2 60 4 0.3 527.79 3 60 5 0.15 1001.38

[0046] Among them, the calculation result of group 3 is the largest, so the optimal critical drop length and diameter of the bubble rod in this well can be finally determined: length 60cm, diameter 5cm.

Claims

1. A method for determining the optimal length and diameter of a solid bubble rod for critical drop in a continuously producing gas well, comprising the following steps: Step 1: Obtain the production data of the gas wells that need to be invested in the bubble rod process, including wellhead pressure, wellhead temperature, natural gas relative density, tubing inner diameter, gas production, liquid production and other data; according to the conditions of the on-site bubble rod production raw materials and other conditions, the bubble rod density is given, and a series of bubble rod lengths L1, L2, L3...L N , given a series of bubble rods with diameters of d1, d2, d3…d M ; Since the longer the foam rod is, the easier it is to break, the fracture coefficient X (0≤X≤1) is introduced. X is positively correlated with the length and negatively correlated with the diameter; Step 2: Based on the flow similarity criterion, the dimensionless criterion is used to convert the field production under high pressure into the corresponding gas-liquid flow rate under normal pressure; Step 3: Use the experimental test results to fit the established formula for calculating the critical falling gas velocity of the solid bubble rod in the continuous production gas well, substitute the determined parameters, liquid flow rate, bubble rod density, length, and diameter, calculate a series of critical falling gas velocities of the bubble rod, and then compare it with the gas velocity under normal pressure calculated in step 2, and select the value greater than the latter; Step 4: Calculate the length and diameter of the foam rod corresponding to the value selected in step 3 using the volume formula combined with the fracture coefficient to obtain the maximum value. The corresponding length and diameter are the optimal ones.

2. A method for determining the optimal length and diameter of a solid bubble rod in a continuous production gas well according to claim 1, wherein the critical falling gas velocity calculation formula of the solid bubble rod in the continuous production gas well in step 3 is specifically: <h2 style=";text-align:left;direction:ltr">v<h2 style=";text-align:left;direction:ltr"> sg <h2 style=";text-align:left;direction:ltr"> (a1×v)<h2 style=";text-align:left;direction:ltr"> sl <h2 style=";text-align:left;direction:ltr"> +a2)(a3×L<h2 style=";text-align:left;direction:ltr"> * <h2 style=";text-align:left;direction:ltr"> +a4)(a5×D<h2 style=";text-align:left;direction:ltr"> *3 <h2 style=";text-align:left;direction:ltr"> +a6×D<h2 style=";text-align:left;direction:ltr"> *2 <h2 style=";text-align:left;direction:ltr"> +a7×D<h2 style=";text-align:left;direction:ltr"> * <h2 style=";text-align:left;direction:ltr"> +a8)(a9×ρ+a<h2 style=";text-align:left;direction:ltr"> 10 <h2 style=";text-align:left;direction:ltr"> ) (1) The constants of the above formula are shown in Table 1: Table 1 Constants of calculation formula for critical drop specifications of bubble rods in continuous production gas wells in, v sg Indicates the superficial gas velocity, m / s; v sl Indicates the apparent liquid velocity, m / s; L * Indicates the ratio of the length to the diameter of the foam rod; D * It represents the ratio of the diameter of the foam rod to the tube diameter; ρ represents the density of the foam rod, g / cm 3 .

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