Method for determining equivalent hydraulic seam width of cement sheath interface of CO2 injection well

Abstract

The invention provides a method for determining equivalent hydraulic seam width of a cement sheath interface of a CO2 injection well. Comprising the following steps: S1, manufacturing a cement sheath test piece; s2, pressing and channeling a cement sheath; s3, monitoring the gas flow at the top of the cement sheath, and recording the pressure of the gas passing through the cement sheath under different CO2 gas flows by adjusting the injected CO2 flow; the flow meter is used for recording the gas flow passing through the cement sheath under different gas injection pressure conditions; s4, calculating the supercritical CO2 density; s5, obtaining the gas flow at the top of the cement sheath under different CO2 viscosities and well cementation qualities; and S6, the equivalent hydraulic seam width of the supercritical CO2 in the cement sheath interface is obtained through calculation. According to the method, experimental data are processed and analyzed to obtain the equivalent seam width of the cement sheath interface; the method is used for evaluating the viscosity and flow of supercritical CO2 and the influence of different well cementation qualities on a cement sheath interface annular gap, and evaluating the anti-channeling capability of a cement sheath under different CO2 injection working conditions.

Description

Technical Field

[0001] The invention relates to the technical field of oil production engineering, and in particular to a method for determining an equivalent hydraulic fracture width of a cement sheath interface of a CO2 injection well. Background Art

[0002] As the oil wells in many oil fields in my country enter the middle and late stages, the oil field recovery rate has dropped significantly. In order to improve the recovery rate and output of low permeability oil fields, it is urgent to study new oil recovery technologies. A large number of research results at home and abroad show that CO2 flooding can significantly increase the oil and gas recovery rate and bury CO2 underground. Therefore, the use of CO2 flooding to develop low permeability oil fields has broad prospects. However, CO2 injection wells are generally completed early, and the current wellbore safety status is unclear. In addition, the downhole conditions after the conversion to CO2 injection wells are more complicated. The casing-cement sheath interface has the risk of sealing failure under the harsh service conditions of high-pressure injection, temperature and pressure alternating loads, and supercritical CO2 corrosion. The injected gas will channel into the layer or channel to the ground, affecting the CO2 injection effect and also causing safety hazards. Therefore, it is necessary to analyze the annular gap size of the casing-cement sheath interface under different injection conditions of CO2 injection wells and evaluate the anti-channeling ability of the cement sheath interface to ensure safe and efficient production of CO2 injection wells.

[0003] Although relevant research on the evaluation of cement sheath interface anti-channeling ability has been carried out in China, there are still deficiencies in the evaluation of cement sheath interface anti-channeling ability under CO2 injection conditions. The current research methods for evaluating the anti-channeling ability of cement sheath interface mainly include experimental and numerical simulation methods:

[0004] (1) In terms of experimental methods, the high-temperature and high-pressure gas well cement ring sealing integrity evaluation system (CN 109681190 A) mainly uses N2 as a fluid medium to pressurize the cement ring interface, and obtains the pressure of the pressed cement ring to evaluate the cement ring isolation capacity. However, this method cannot simulate the injection of CO2 under supercritical conditions, nor can it obtain the size of the annular gap at the casing-cement ring interface. A method for measuring the size of the micro-annular gap at the first interface of cementing (CN 110424947B) calculates the cement ring interface gap by passing gas into the bottom of the cement ring and detecting the pressure and flow rate at the upper and lower ends of the cement ring. However, the device does not have a supercritical CO2 generator and cannot simulate supercritical CO2 injection conditions. Therefore, it cannot accurately characterize the cement ring's ability to isolate supercritical CO2. At the same time, the device does not have a cementing quality detection device and cannot analyze the influence of the cement ring interface under different cementing quality conditions. The cementing quality of old wells on site varies greatly, so this evaluation method still has limitations in the field application of CO2 injection wells. A non-contact high-temperature and high-pressure well cement ring micro-annulus generating device (CN CN115680621A) performs cyclic loading and unloading in the casing until the cement ring seal fails, and uses an image acquisition device to capture digital images and track the motion state of image points to analyze the size of the cement ring annulus. Although the device can monitor the annular gap changes after the cement ring interface is damaged, it also does not have a supercritical CO2 generating device and cannot analyze the size of the cement ring interface annular gap under different CO2 injection conditions; and the device does not have a built-in cementing quality detection instrument and cannot analyze the change law of the cement ring interface under different cementing bonding index conditions under field CO2 injection conditions. Therefore, this method also has limitations in field application in CO2 injection wells.

[0005] (2) In terms of numerical simulation, a numerical simulation method, system and storage medium for oil and gas crossflow in the cementing annulus of a deepwater high-temperature and high-pressure well (CN113898312A), and a numerical simulation method for sealing failure of casing-cement ring-formation system in a deepwater high-temperature and high-pressure well (CN113756744A). The above methods mainly use Cohesive units to simulate the cement ring interface, set two injection units and one injection point, and use the interface stiffness degradation coefficient SDEG to evaluate the state of cement ring breakthrough. When SDEG = 1, the injection pressure is used as an indicator to evaluate the sealing capacity of the cement ring. This numerical simulation method mainly simulates the complete destruction of the cement ring interface, which is significantly different from the situation where the cement ring is partially destroyed on site, that is, the possible sealing failure, and therefore cannot correspond to the actual situation on site.

[0006] In summary, the current existing technology cannot accurately and quantitatively evaluate the annular gap between casing and cement sheath under different CO2 injection conditions, and thus guide the feasibility analysis of gas well conversion. Summary of the invention

[0007] The technical problem to be solved by the present invention is to overcome the problem in the background technology that the variation law of the casing-cement sheath interface anti-channeling ability under different CO2 injection conditions cannot be precisely quantified, and a method for determining the equivalent hydraulic fracture width of the cement sheath interface of a CO2 injection well is provided. The method for determining the equivalent hydraulic fracture width of the cement sheath interface of a CO2 injection well obtains the equivalent fracture width of the cement sheath interface by processing and analyzing experimental data; the viscosity and flow rate of supercritical CO2 and the influence of different cementing qualities on the annular gap of the cement sheath interface are evaluated by the equivalent fracture width, and then the anti-channeling ability of the cement sheath under different CO2 injection conditions is evaluated.

[0008] The present invention solves the problem through the following technical solution: The method for determining the equivalent hydraulic fracture width of the cement sheath interface of the CO2 injection well comprises the following steps:

[0009] S1. Prepare the test cement ring required for the experiment, wherein the test cement ring comprises:

[0010] Cement ring test piece A used to test the gas flow Q at the top of the cement ring under different CO2 viscosity conditions;

[0011] Cement ring test piece B is used to test the gas flow Q at the top of the cement ring under different cementing quality conditions;

[0012] S2. Inject supercritical CO2 produced under certain working conditions into the bottom of the cement ring installed at the casing to pressurize the cement ring;

[0013] S3. After gas leakage from the cement ring, monitor the gas flow rate Q at the top of the cement ring, adjust the injected CO2 flow rate, and record the pressure of gas passing through the cement ring under different CO2 gas flow rates; and use a flow meter to record the gas flow through the cement ring under different gas injection pressure conditions;

[0014] S4. Calculate the density of supercritical CO2;

[0015] S5. For cement sheath test piece A, obtain supercritical CO2 with different viscosities by adjusting the temperature and pressure of the supercritical CO2 generator, calculate the supercritical CO2 viscosity, and record the pressure of gas passing through the cement sheath under different CO2 viscosities; repeat step 3 under different CO2 viscosities, adjust the gas injection pressure at the bottom of the cement sheath, and record the gas flow rate Q at the top of the cement sheath under different CO2 viscosities;

[0016] For cement sheath test piece B, after obtaining the cement sheath test piece of the cementing quality required for the experiment, repeat steps 2 to 3, and record the gas flow Q at the top of the cement sheath under the different cementing quality conditions;

[0017] S6. Based on the gas flow rate Q at the top of the cement sheath under different CO2 viscosity conditions in step S5, and the gas flow rate Q at the top of the cement sheath under different cementing quality conditions; as well as the experimental data for evaluating the sealing performance of the cement sheath, the equivalent hydraulic fracture width of supercritical CO2 at the cement sheath interface is calculated using the nonlinear Darcy seepage formula combined with the gas state equation.

[0018] Preferably, the cement ring test piece A in step S1 is the original test piece after curing, and the cement ring acoustic amplitude is tested on the original test piece after curing, and the initial bonding index and bonding strength of the cement ring after curing are calculated;

[0019] The cement ring test piece B is a test piece after the curing is completed, and the cement ring acoustic amplitude is tested; after calculating the initial bonding index and bonding strength of the cured cement ring, a certain internal pressure load is applied in the casing, and the bonding index is measured again after unloading, and this operation is repeated until a cement ring test piece with the cementing quality required for the experiment is obtained;

[0020] and / or,

[0021] The method of preparing the test piece cement ring and completing the curing of the test piece cement ring in step S1 is:

[0022] The experiment was conducted using a full-size cement ring seal integrity evaluation device. A formation rock ring of corresponding size was prepared based on the device inner diameter and the field casing outer diameter and placed in the device.

[0023] Prepare cement slurry with cement used in the field, fill the annulus between the casing and the formation ring with the prepared cement slurry, and place the cementing quality detector in the casing;

[0024] The poured cement ring is cured for 48 hours according to the on-site temperature and pressure.

[0025] Preferably, the method for calculating the initial bonding index and bonding strength of the cement sheath after curing in step S1 is specifically as follows:

[0026] The cementing quality detector is used to collect acoustic logging data for testing the acoustic amplitude; the cement sheath bonding index BI is calculated according to the bonding index formula; the cement sheath bonding strength S is calculated according to the cement sheath bonding strength formula to evaluate the initial cement sheath bonding quality;

[0027] The cementation index formula is:

[0028]

[0029] Where: BI is the cementation index; A Max A is the maximum amplitude of the first wave obtained by high engraving; E A is the amplitude of the first wave at the measuring point; minis the amplitude value of the first wave obtained by low engraving; the above parameters are all measured by cementing quality tester;

[0030] The cement sheath bonding strength formula is:

[0031]

[0032] in:

[0033] p=-0.00434T 2 -0.0622T+4.44 (3)

[0034] α=-21.8723×logU-0.0137×d+49.62 (4)

[0035] Where: S is cement bonding strength, MPa; T is casing wall thickness, mm; p is dimensionless index; α is acoustic wave attenuation rate, dB / m;

[0036] d is the outer diameter of the casing, mm; U is the relative acoustic amplitude, %, which is measured by the cementing quality detector; k is a coefficient related to the source distance l, and the value of k is given by the source distance, which is the distance between the transmitting transducer and the receiving transducer in the cementing quality detector.

[0037] Preferably, the method for compressing the cement ring in step S2 is: using a full-size cement ring sealing evaluation device and a supercritical CO2 generating device, injecting supercritical CO2 generated under certain working conditions into the bottom of the casing cement ring, continuously increasing the pressure, and compressing the cement ring until gas leakage occurs in the cement ring.

[0038] Preferably, the method for obtaining the supercritical CO2 density in step S4 is:

[0039] Based on the Peng-Robinson theory, the density ρ of supercritical CO2 under certain temperature and pressure conditions is obtained using the supercritical CO2 state equation and density formula:

[0040] The supercritical CO2 state equation is:

[0041]

[0042] The density formula is:

[0043]

[0044] Where: P is the fluid pressure in equilibrium state; T is the fluid temperature in equilibrium state;

[0045]

[0046] V mis the molar volume of supercritical CO2 under the temperature and pressure conditions, which can be calculated by formula (5).

[0047] Preferably, the method for calculating the viscosity of supercritical CO2 under certain temperature and pressure conditions in step S5 is:

[0048] Chung's viscosity calculation method is used to calculate the viscosity μ of supercritical CO2 under certain temperature and pressure conditions. Chung's viscosity calculation formula is as follows:

[0049]

[0050] in:

[0051]

[0052] T * =1.2593T r (9)

[0053]

[0054]

[0055]

[0056]

[0057]

[0058] Where: A1 = 1.16145; B1 = 0.14874; C1 = 0.52487; D1 = 0.7732; E = 2.16178; F1 = 2.43787; F c =1-0.2756ω;

[0059] The critical parameter for CO2 to transform from gas phase to supercritical state is: T c =304.13K, P c =7.38MPa, V c =93.8cm 3 / mol, for CO2, ω=0.2249, M=44g / mol, E1~E 10 The values ​​are as follows: E1 = 17.662, E2 = 9.5 × 10-4, E3 = 62.455, E4 = 15.200, E5 = 21.461, E6 = -4.720, E7 = 25.051, E8 = 1.048, E9 = -0.223, E 10 =0.147.

[0060] Preferably, the method for calculating the equivalent hydraulic joint width of supercritical CO2 in the cement sheath interface in step S6 specifically includes:

[0061] 1) The seepage of supercritical CO2 gas in the cement sheath interface satisfies the supercritical CO2 state equation (5) and the nonlinear Darcy seepage formula (15);

[0062] 2) Obtain the permeability k of supercritical CO2 gas in the cement sheath interface;

[0063] 3) Based on the permeability k, according to the cubic law formula, the expression of the equivalent seam width h can be determined; based on the determined equivalent seam width expression, the value of the equivalent seam width is obtained.

[0064] Preferably, the method for obtaining the permeability k of supercritical CO2 gas in the cement sheath interface comprises:

[0065] The seepage of supercritical CO2 gas in the cement sheath interface satisfies the supercritical CO2 state equation (5) and the nonlinear Darcy seepage formula (15), and the formula (5) is transformed according to the isothermal steady-state flow condition to obtain the formula (16);

[0066] Establish the average pressure formula (17), substitute the formula (17) into the formula (16), and obtain the average pressure conversion formula (18);

[0067] Then, formula (18) is substituted into the nonlinear Darcy formula (15) to obtain the pressure gradient transformation formula (19);

[0068] Finally, the CO2 gas permeation formula (20) can be obtained by transforming the formula (19);

[0069] Wherein, the nonlinear Darcy seepage formula (15) is:

[0070]

[0071] Where: △P is the pressure gradient, Q is the annular supercritical CO2 volume flow rate, μ is the supercritical CO2 viscosity, k is the permeability, is the cross-sectional area of ​​supercritical CO2 flow in the annulus, D is the cement annulus diameter, d is the casing diameter, β is the inertia coefficient, and ρ is the supercritical CO2 density;

[0072] The gas state equation (5) is transformed according to the isothermal steady-state flow condition of the gas to obtain formula (16):

[0073]

[0074] Where: is the average pressure; V mis the molar volume of supercritical CO2 under the temperature and pressure conditions, T is the supercritical CO2 temperature,;

[0075] And the average pressure The expression can also be expressed as:

[0076]

[0077] Where: P u , P d Respectively represent the pressure of CO2 injection and discharge of cement sheath; the cementing strength S in step 2 = P u -P d , if P d = 0, then S and the injection end pressure P u The same; then:

[0078]

[0079]

[0080]

[0081] Where: L is the cement sheath interface length;

[0082] Rewrite equation (20) as:

[0083]

[0084] Where:

[0085] The data obtained from the experiment and the results calculated based on the experimental data are substituted into formula (21) to obtain the coordinates (x, y) of different points. The point coordinates (x, y) are plotted as a straight line, whose slope is a function of the inertia coefficient β, and the intercept is inversely proportional to the permeability k. The permeability k can be obtained by plotting.

[0086] Preferably, the method for obtaining the equivalent seam width specifically includes:

[0087] Based on the permeability k, the expression of the equivalent seam width h can be determined according to the following cubic law formula, as shown in formula (22):

[0088]

[0089] Where, ω = πd is the hydraulic circumference; A = πdL is the surface area of ​​the cement sheath interface; h is the equivalent hydraulic joint width; k is the permeability.

[0090] Preferably, the equivalent hydraulic fracture width of supercritical CO2 at the cement sheath interface obtained through steps S1-S6 can be used to evaluate the influence of different CO2 viscosities and gas flow rates on the hydraulic fracture width of the cement sheath interface; or to evaluate the influence of different cementing qualities on the hydraulic fracture width of the cement sheath interface.

[0091] Compared with the above background technology, the present invention has the following beneficial effects:

[0092] The present invention proposes a method for determining the equivalent hydraulic fracture width of the cement sheath interface of a CO2 injection well. The experimental method of the present invention can truly simulate the CO2 injection viscosity, injection gas volume, different cement sheath bonding strengths, and cement sheath CO2 gas channeling process under different injection conditions of the CO2 injection well. At the same time, a calculation method for the equivalent fracture width of the cement sheath interface is proposed, which can accurately characterize the influence of different CO2 viscosities, gas flow rates, and different cementing qualities on the anti-channeling ability of the cement sheath interface, thereby realizing the quantitative evaluation of the anti-channeling ability of the cement sheath interface under different injection conditions of the CO2 injection well. BRIEF DESCRIPTION OF THE DRAWINGS

[0093] Figure 1 This is a flowchart of a method for determining an equivalent hydraulic fracture width of a cement sheath interface of a CO2 injection well according to the present invention;

[0094] Figure 2 The curve showing the influence of CO2 viscosity on the equivalent hydraulic joint width of the cement sheath interface in the embodiment of the present invention;

[0095] Figure 3 The curve showing the effect of gas flow rate on the equivalent hydraulic joint width of the cement sheath interface in the embodiment of the present invention;

[0096] Figure 4 This is a curve showing the influence of cementing quality on the equivalent hydraulic fracture width of the cement sheath interface according to an embodiment of the present invention. DETAILED DESCRIPTION

[0097] The present invention will be further described below in conjunction with the accompanying drawings and embodiments:

[0098] In order to more clearly illustrate the implementation of the method, the technical solution of the present invention will be described by way of example in conjunction with the accompanying drawings. Figure 1 As shown, a method for determining the equivalent hydraulic fracture width of the cement sheath interface of a CO2 injection well comprises the following steps:

[0099] Step 1: Conduct experiments based on the full-size cement ring seal integrity evaluation device. Prepare a formation rock ring of corresponding size according to the inner diameter of the device and the outer diameter of the on-site casing, and place it in the device. Prepare cement slurry with on-site cementing cement, fill the annulus between the casing and the formation ring with the prepared cement slurry, and place the cementing quality detector in the casing.

[0100] Step 2: After the cement ring is poured, the cement ring is cured for 48 hours according to the on-site temperature and pressure. The cementing quality detector is used to collect the acoustic logging data, and the cement ring bonding index BI is calculated according to formula (1), and the cement ring bonding strength S is calculated according to formula (2) to evaluate the initial cement ring bonding quality;

[0101]

[0102] Where: BI is the cementation index; A Max A is the maximum amplitude of the first wave obtained by high engraving; E A is the amplitude of the first wave at the measuring point; min is the amplitude value of the first wave obtained at the low engraving.

[0103]

[0104] Where: S is the cement bonding strength, MPa; T is the casing wall thickness, mm; p is the dimensionless index, given by formula (3); α is the sound wave attenuation rate, dB / m, given by formula (4):

[0105] p=-0.00434T 2 -0.0622T+4.44 (3)

[0106] α=-21.8723×logU-0.0137×d+49.62 (4)

[0107] In the formula: d is the outer diameter of the casing, mm; U is the relative acoustic amplitude, %, which is measured by the cementing quality detector; k is a coefficient related to the source distance l, and the value of k is given by the source distance, which is the distance between the transmitting transducer and the receiving transducer in the cementing quality detector. Table 1 shows the applicable range of the selected k value, the source distance and the corresponding k value.

[0108] Table 1

[0109]

[0110] Step 3: Using a full-size cement ring sealing evaluation device, supercritical CO2 produced under certain working conditions is injected into the bottom of the cement ring, and the pressure is continuously increased until gas breakthrough occurs in the cement ring.

[0111] Step 4: After gas leakage through the cement ring, a soap film flowmeter is used at the top of the cement ring to monitor the gas flow rate Q on the upper end surface of the cement ring. The test of the gas flow rate Q is measured by a soap film flowmeter in accordance with the standard GB / T 22133-2008. After gas leakage through the cement ring, the gas injection pressure at the bottom of the cement ring is adjusted according to the experimental requirements, and the gas flow through the cement ring under different gas injection pressure conditions is recorded by the flowmeter.

[0112] Step 5, calculate the density of supercritical CO2. Based on the Peng-Robinson theory, the density ρ of supercritical CO2 under the temperature and pressure conditions is obtained using the supercritical CO2 state equation (5) and equation (6):

[0113] Supercritical CO2 state equation (5):

[0114]

[0115]

[0116] Where: V m is the molar volume of supercritical CO2 under the temperature and pressure conditions, which can be calculated by formula (6).

[0117] Step 6, obtain CO2 with different viscosities by changing the temperature and pressure of the supercritical CO2 generator, repeat step 4 under different CO2 viscosity conditions, adjust the gas injection pressure at the bottom of the cement sheath, and record the leakage gas flow Q at the top of the cement sheath under different injection pressures.

[0118] The method for calculating the viscosity of supercritical CO2 is specifically as follows: the viscosity μ of supercritical CO2 under the temperature and pressure conditions is calculated using the Chung method, as shown in equations (7) to (14):

[0119]

[0120] in:

[0121]

[0122] T * =1.25 r 9 (9)

[0123]

[0124] Where: A1 = 1.16145, B1 = 0.14874, C1 = 0.52487, D1 = 0.7732, E = 2.16178, F1 = 2.43787, F c =1-0.2756ω

[0125]

[0126]

[0127]

[0128]

[0129] For CO2, ω = 0.2249, M = 44 g / mol, E1 ~ E 10 The values ​​are as follows:

[0130] E1=17.662, E2=9.5×10-4, E3=62.455, E4=15.200, E5=21.461, E6=-4.720, E7=25.051, E8=1.048, E9=-0.223, E 10 =0.147.

[0131] T c =304.13K, P c =7.38MPa, V c =93.8cm 3 / mol, is the critical parameter for CO2 to transform from gas phase to supercritical state. Substituting temperature T and supercritical CO2 density ρ into equation (7) to equation (14), the supercritical CO2 viscosity under the temperature and pressure conditions can be obtained.

[0132] Step 7, calculate the hydraulic crack width h of supercritical CO2 in the cement sheath interface according to the supercritical CO2 gas seepage formula and the cubic formula.

[0133] The seepage of supercritical CO2 gas in the cement sheath interface satisfies the supercritical CO2 state equation (5) and the nonlinear Darcy seepage formula (15), and (5) is deformed according to the isothermal steady-state flow condition to obtain formula (16), and the formula (17) is substituted into formula (16) to obtain formula (18); then, formula (18) is substituted into the nonlinear Darcy formula (15) to obtain formula (19), and finally, the CO2 gas seepage formula (20) can be obtained after the formula (19) is deformed, as shown below:

[0134] Nonlinear Darcy flow formula (15):

[0135]

[0136] Where △P is the pressure gradient, Q is the annular supercritical CO2 volume flow rate, μ is the supercritical CO2 viscosity, k is the permeability, is the cross-sectional area of ​​supercritical CO2 flow in the annulus, β is the inertia coefficient, and ρ is the supercritical CO2 density;

[0137] The gas state equation (5) is transformed according to the isothermal steady-state flow condition of the gas to obtain formula (16):

[0138]

[0139] In the formula, is the average pressure, and the average pressure The expression is:

[0140]

[0141] Where P u , P d represents the pressure of CO2 injection and discharge in the cement sheath, respectively. The cementing strength S in step 2 is P u -P d , if P d = 0, then S and the injection end pressure P u same.

[0142]

[0143]

[0144]

[0145] Where L is the cement sheath interface length.

[0146] Rewrite equation (20) as:

[0147]

[0148] In the formula,

[0149] The data obtained from the above experiments and the results calculated based on the experimental data are substituted into formula (21) to obtain the coordinates (x, y) of different points. The point coordinates (x, y) are plotted as a straight line, whose slope is a function of the inertia coefficient β, and the intercept is inversely proportional to the permeability k. The permeability k can be obtained by plotting.

[0150] The permeability k calculation method can determine the expression of the equivalent seam width h according to the following cubic law formula, as shown in formula (22):

[0151]

[0152] Where ω = πd is the hydraulic circumference, A = πdL is the surface area of ​​the cement sheath interface, h is the equivalent hydraulic joint width, and k is the permeability.

[0153] Step 8, repeat step 1 and step 2, then apply the internal pressure load required by the experiment in the casing, stabilize the pressure for 5 minutes and then unload, then perform acoustic logging again after unloading, and calculate the corresponding cementing bond strength; after repeated loading, the cement sheath bond strength required by the experiment is obtained, which is used for simulation experiments under different cementing quality conditions. After completing a round of experiments, repeat the cement sheath test piece, then destroy the cementing quality, and then do the experiment again.

[0154] Step 9, as in steps 3 to 8, can obtain the influence of different CO2 viscosities, different gas flow rates and different cementing bond strengths on the equivalent fracture width h, thereby achieving a quantitative evaluation of the anti-channeling capability of the cement sheath interface of the CO2 injection well under different injection conditions and different cementing quality conditions.

[0155] Example 1

[0156] The present invention provides a method for calculating the equivalent hydraulic fracture width of the cement sheath interface of a CO2 injection well. The present invention proposes a calculation formula based on the equivalent hydraulic fracture width and uses experimental data to obtain the influence of different CO2 viscosities, different gas flow rates and different cementing bond strengths on the cement sheath isolation capacity. The specific method is as follows:

[0157] Step 1, taking the case of the gas injection field casing outer diameter of 139.7mm, cement ring thickness of 38.1mm, and full-size cement ring sealing integrity evaluation device inner diameter of 400mm as an example; prepare a formation rock ring with an outer diameter of 400mm and an inner diameter of 215.9mm and place it in the device. Use the G-grade cement used on site to prepare cement slurry, pour cement slurry in the annulus formed by the casing and the formation, and pre-place the 8-sector cementing quality logging instrument in the casing.

[0158] Step 2: The cement ring is cured for 48 hours according to the downhole temperature and pressure of the CO2 injection well, and then the sound amplitude curve is detected by the cementing quality logging instrument. The maximum sound amplitude detected is 159.872mv; the minimum sound amplitude is 14.763mv; the ratio of the first wave sound amplitude to the free casing section sound amplitude is 38.39%; the cementation index of the cement ring is calculated by formula (1) to be 0.402. The cementation strength is calculated by formula (2) based on the outer diameter of the casing of 5.5in; the wall thickness of the casing is 0.304in; and the source distance is 1.5m.

[0159] p = -0.00434 × 7.72 2 -0.0622×7.72+4.44=3.7

[0160] α=-21.8723×log38.39-0.0137×139.7+49.62=13.06dB / m

[0161]

[0162] Step 3: Use a full-size cement ring sealing evaluation device and a supercritical CO2 generator to inject supercritical CO2 into the bottom of the cement ring and continuously increase the pressure until gas leakage occurs in the cement ring.

[0163] Step 4: After the cement ring gas is generated, a soap film flowmeter is used at the top of the cement ring to monitor the gas flow rate Q on the upper end face of the cement ring. The test method of the gas flow rate Q is measured by a soap film flowmeter in accordance with the standard GB / T 22133-2008. After the gas is generated, the gas injection pressure at the bottom of the cement ring is adjusted according to the experimental requirements, and the gas flow through the cement ring under different gas injection pressures is recorded by a flowmeter. The experimental results of the cement ring sealing performance evaluation are shown in Table 2. This example takes the experimental results corresponding to the experimental serial number 3 in Table 2 as an example. The injection pressures are 1.34 to 2.73 MPa, and the corresponding CO2 flow rates are 37 to 111 cm 3 / s.

[0164] Step 5: Use formula (5) and formula (6) to calculate the corresponding density of CO2 under different temperature and pressure conditions. This example takes the experimental results corresponding to experiment number 1 in Table 2 as an example. The injected CO2 density is 0.08-0.96 g / cm 3 .

[0165] Step 6, by changing the temperature and pressure of the supercritical CO2 generator, obtain CO2 with different viscosities, repeat step 4 under different CO2 viscosity conditions, adjust the gas injection pressure at the bottom of the cement ring, and record the gas flow Q at the top of the cement ring under different injection pressures. The results of the cement ring sealing performance evaluation experiment are shown in No. 1 in Table 2. This example takes the experimental results corresponding to Experiment No. 1 in Table 2 as an example. The injected CO2 viscosity is 0.02-0.1 mPa·s, and the corresponding pressures are 1.68-3.37 MPa.

[0166] Step 7: Use formula (20) to calculate the injection end pressure corresponding to CO2 with different viscosities and different CO2 flow rates, obtain the permeability of the specimens under different experimental conditions, and calculate the equivalent hydraulic fracture width of each specimen according to formula (22).

[0167] Step 8, repeat step 1, step 2, and then apply the internal pressure load required by the experiment in the casing. This time, take the application of internal pressure of 40MPa as an example, unload after stabilizing the pressure for 5 minutes, and perform sonic logging again after unloading to calculate the corresponding bonding index and bonding strength. This time, take the bonding index of 0.4 as an example, and obtain the injection end pressure of 1.39MPa under the condition of bonding index of 0.4. The equivalent hydraulic fracture width is 17.518μm. Repeat the above steps, but apply different loads and repetitions in the casing each time to obtain the cement sheath bonding index required by different experiments. This example takes the experimental results corresponding to experimental number 2 in Table 2 as an example. The cement sheath bonding index is 0.2~0.8, and the corresponding injection pressure is 0.59~2.73MPa.

[0168] Step 9, repeat steps 3 to 8, record the experimental data such as CO2 gas flow rate, CO2 injection end pressure, CO2 discharge end pressure under different CO2 viscosity and different cementing bonding strength experimental conditions, and CO2 injection end pressure, CO2 discharge end pressure under different gas flow rates, and the experimental results of cement sheath sealing performance evaluation are shown in Table 2; according to Table 2, calculate the equivalent hydraulic fracture width of the cement sheath interface under different experimental conditions, and analyze the influence of CO2 viscosity, injection amount, and cementing quality on the equivalent hydraulic fracture width, see Figure 2 , Figure 3 , Figure 4 Combined with the downhole temperature, pressure, and cementing quality of the CO2 injection well, the hydraulic fracture width h calculated according to the above method can be used to quantitatively evaluate the cement sheath isolation capacity of the CO2 injection well under different injection conditions and different cementing quality conditions.

[0169] Table 2 Cement ring isolation performance evaluation test results

[0170]

[0171] Based on the experimental data in Table 2, combined with the following basic parameters: β = 3.09 × 10 4 , D = 139.7 mm, L = 1000 mm, M = 44 g / mol, R = 8.314 J / (mol·K), using the permeability k and equivalent hydraulic fracture width h calculation formula, the effects of CO2 viscosity, gas flow rate and cementing strength on the equivalent hydraulic fracture width h are calculated as follows: Figure 2 to Figure 4 The following is an example of the calculation process of the equivalent hydraulic fracture width under experimental conditions of a temperature of 360K, a pressure of 40MPa, and a cementation index of 0.4:

[0172] Substituting the parameters T = 360K and P = 40MPa into formula (13), we can obtain the result of CO2 density ρ:

[0173]

[0174]

[0175]

[0176] V m =55cm 3 / mol

[0177] ρ=44 / V m =0.8g / cm 3

[0178] The parameters T = 360K, P = 40Mpa, ρ = 0.8g / cm 3Substituting into formula (5) to formula (12), we get the result of CO2 viscosity μ:

[0179]

[0180] y=ρV c / 6=0.893.8 / 6 / =12.5

[0181]

[0182]

[0183]

[0184] Ω V =1.16145×(1.49) (-0.14874) +0.52487e (-0.77320×1.49) +2.16178e (-2.43787×1.49) =1.318

[0185]

[0186]

[0187] Set the parameters T = 360K, P u =1.39MPa, P d =0, Q = 111cm 3 / s、V m =55cm 3 / mol, β = 3.09 × 10 4 , D=139.7mm, L=1000mm, ρ=0.8g / cm 3 , μ=72μPa·s, a=348444.82 are substituted into formula (20) to obtain the result of permeability k:

[0188]

[0189]

[0190] k = 4.48 × 10 -10 mm 2

[0191] Set the parameter k = 4.48 × 10 -10 Substituting into formula (22), we can obtain the hydraulic joint width h:

[0192]

[0193] Repeat the above steps to obtain the hydraulic joint width under different experimental conditions.

[0194] By evaluating the effects of different CO2 viscosities and gas flow rates on the hydraulic joint width of the cement sheath interface, the specific rules obtained are: with the increase of CO2 viscosity and gas flow rate, the hydraulic joint width of the cement sheath interface decreases rapidly in the initial stage and then the decrease rate gradually decreases. The influence of gas flow rate changes is much smaller than that of CO2 viscosity.

[0195] Repeat the production of cement sheath test pieces, apply a certain internal pressure load in the casing, measure the bonding index again after unloading, and repeat this operation until the cement sheath test piece with the cementing quality required for the experiment is obtained. Repeat the experiment and calculation again to evaluate the influence of different cementing qualities on the hydraulic fracture width of the cement sheath interface. The evaluation results are as follows: with the increase of cement sheath cementing quality, the hydraulic fracture width of the cement sheath interface decreases rapidly at the beginning, and then the reduction rate gradually decreases. After the bonding index is greater than 0.8, increasing the cementing quality has little effect on the hydraulic fracture width of the interface.

[0196] It should be noted that the embodiments described above are only used to explain the present invention and do not constitute any limitation to the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory words, rather than restrictive words. The present invention may be modified as specified within the scope of the claims of the present invention, and the present invention may be revised without departing from the scope and spirit of the present invention. Therefore, the content of the present invention is not limited to the examples listed, and any equivalent changes taken by ordinary technicians in the field of the present invention by reading the specification of the present invention to the technical solution of the present invention are all covered by the claims of the present invention.

Claims

1. A method for determining the equivalent hydraulic fracture width of the cement sheath interface of a CO2 injection well, characterized in that: Includes the following step: S1. Prepare the test cement ring required for the experiment, wherein the test cement ring comprises: Cement ring test piece A used to test the gas flow Q at the top of the cement ring under different CO2 viscosity conditions; Cement ring test piece B is used to test the gas flow Q at the top of the cement ring under different cementing quality conditions; S2. Inject supercritical CO2 produced under certain working conditions into the bottom of the cement ring installed at the casing to pressurize the cement ring; S3. After gas leakage from the cement ring, monitor the gas flow rate Q at the top of the cement ring, adjust the injected CO2 flow rate, and record the pressure of gas passing through the cement ring under different CO2 gas flow rates; and use a flow meter to record the gas flow through the cement ring under different gas injection pressure conditions; S4. Calculate the density of supercritical CO2; S5. For cement sheath test piece A, obtain supercritical CO2 with different viscosities by adjusting the temperature and pressure of the supercritical CO2 generator, calculate the supercritical CO2 viscosity, and record the pressure of gas passing through the cement sheath under different CO2 viscosities; repeat step 3 under different CO2 viscosities, adjust the gas injection pressure at the bottom of the cement sheath, and record the gas flow rate Q at the top of the cement sheath under different CO2 viscosities; For cement sheath test piece B, after obtaining the cement sheath test piece of the cementing quality required for the experiment, repeat steps 2 to 3, and record the gas flow Q at the top of the cement sheath under the different cementing quality conditions; S6. Based on the gas flow rate Q at the top of the cement sheath under different CO2 viscosity conditions in step S5, and the gas flow rate Q at the top of the cement sheath under different cementing quality conditions; as well as the experimental data for evaluating the sealing performance of the cement sheath, the equivalent hydraulic fracture width of supercritical CO2 at the cement sheath interface is calculated using the nonlinear Darcy seepage formula combined with the gas state equation.

2. The method for determining the equivalent hydraulic fracture width of the cement sheath interface of a CO2 injection well according to claim 1, characterized in that: In step S1, the cement ring test piece A is the original test piece after curing, and the cement ring sound amplitude is tested on the original test piece after curing, and the initial bonding index and bonding strength of the cement ring after curing are calculated; The cement ring test piece B is a test piece after the curing is completed, and the cement ring acoustic amplitude is tested; after calculating the initial bonding index and bonding strength of the cured cement ring, a certain internal pressure load is applied in the casing, and the bonding index is measured again after unloading, and this operation is repeated until a cement ring test piece with the cementing quality required for the experiment is obtained; and / or, The method of preparing the test piece cement ring and completing the curing of the test piece cement ring in step S1 is: The experiment was conducted using a full-size cement ring seal integrity evaluation device. A formation rock ring of corresponding size was prepared based on the device inner diameter and the field casing outer diameter and placed in the device. Prepare cement slurry with cement used in the field, fill the annulus between the casing and the formation ring with the prepared cement slurry, and place the cementing quality detector in the casing; The poured cement ring is cured for 48 hours according to the on-site temperature and pressure.

3. The method for determining the equivalent hydraulic fracture width of the cement sheath interface of a CO2 injection well according to claim 2, characterized in that: The method for calculating the initial bonding index and bonding strength of the cement sheath after curing in step S1 is specifically as follows: The cementing quality detector is used to collect acoustic logging data for testing the acoustic amplitude; The cement sheath bonding index BI is calculated according to the bonding index formula; the cement sheath bonding strength S is calculated according to the cement sheath bonding strength formula, which is used to evaluate the bonding quality of the initial cement sheath; The cementation index formula is: Where: BI is the cementation index; A Max A is the maximum amplitude of the first wave obtained by high engraving; E A is the amplitude of the first wave at the measuring point; min is the amplitude value of the first wave obtained by low engraving; the above parameters are all measured by cementing quality tester; The cement sheath bonding strength formula is: in: p=-0.00434T 2 -0.0622T+4.44 (3) α=-21.8723×logU-0.0137×d+49.62 (4) Where: S is cement bonding strength, MPa; T is the casing wall thickness, mm; p is the dimensionless exponent; α is the sound wave attenuation rate, dB / m; d is the outer diameter of the casing, mm; U is the relative sound amplitude, %, which is measured by the cementing quality detector; k is a coefficient related to the source distance l. The value of k is given by the source distance, which is the distance between the transmitting transducer and the receiving transducer in the cementing quality detector.

4. The method for determining the equivalent hydraulic fracture width of the cement sheath interface of a CO2 injection well according to claim 1, characterized in that: The method for compressing the cement ring in step S2 is: using a full-size cement ring sealing evaluation device and a supercritical CO2 generating device, injecting supercritical CO2 generated under certain working conditions into the bottom of the casing cement ring, continuously increasing the pressure, and compressing the cement ring until gas leakage occurs in the cement ring.

5. The method for determining the equivalent hydraulic fracture width of the cement sheath interface of a CO2 injection well according to claim 1, characterized in that: The method for obtaining the supercritical CO2 density in step S4 is: Based on the Peng-Robinson theory, the density ρ of supercritical CO2 under certain temperature and pressure conditions is obtained using the supercritical CO2 state equation and density formula: The supercritical CO2 state equation is: The density formula is: Where: P is the fluid pressure in equilibrium state; T is the fluid temperature in equilibrium state; V m is the molar volume of supercritical CO2 under the temperature and pressure conditions, which can be calculated by formula (5).

6. The method for determining the equivalent hydraulic fracture width of the cement sheath interface of a CO2 injection well according to claim 1, characterized in that: The method for calculating the viscosity of supercritical CO2 under certain temperature and pressure conditions in step S5 is: Chung's viscosity calculation method is used to calculate the viscosity μ of supercritical CO2 under certain temperature and pressure conditions. Chung's viscosity calculation formula is as follows: in: T * =1.2593T r (9) Where: A1 = 1.16145; B1 = 0.14874; C1 = 0.52487; D1 = 0.7732; E = 2.16178; F1 = 2.43787; F c =1-0.2756ω; The critical parameter for CO2 to transform from gas phase to supercritical state is: T c =304.13K, P c =7.38MPa, V c =93.8cm 3 / mol, for CO2, ω=0.2249, M=44g / mol, E1~E 10 The values ​​are as follows: E1 = 17.662, E2 = 9.5 × 10-4, E3 = 62.455, E4 = 15.200, E5 = 21.461, E6 = -4.720, E7 = 25.051, E8 = 1.048, E9 = -0.223, E 10 =0.

147.

7. The method for determining the equivalent hydraulic fracture width of the cement sheath interface of a CO2 injection well according to claim 6, characterized in that: The method for calculating the equivalent hydraulic joint width of supercritical CO2 in the cement sheath interface in step S6 specifically includes: 1) The seepage of supercritical CO2 gas in the cement sheath interface satisfies the supercritical CO2 state equation and the nonlinear Darcy seepage formula; 2) Obtain the permeability k of supercritical CO2 gas in the cement sheath interface; 3) Based on the permeability k, according to the cubic law formula, the expression of the equivalent seam width h can be determined; based on the determined equivalent seam width expression, the value of the equivalent seam width is obtained.

8. The method for determining the equivalent hydraulic fracture width of the cement sheath interface of a CO2 injection well according to claim 7, characterized in that: The method for obtaining the permeability k of supercritical CO2 gas in the cement sheath interface comprises: The seepage of supercritical CO2 gas in the cement sheath interface satisfies the supercritical CO2 state equation (5) and the nonlinear Darcy seepage formula (15), and the formula (5) is transformed according to the isothermal steady-state flow condition to obtain the formula (16); Establish the average pressure formula (17), substitute the formula (17) into the formula (16), and obtain the average pressure conversion formula (18); Then, formula (18) is substituted into the nonlinear Darcy formula (15) to obtain the pressure gradient transformation formula (19); Finally, the CO2 gas permeation formula (20) can be obtained by transforming the formula (19); Furthermore, the nonlinear Darcy flow formula (15) is: Where: △P is the pressure gradient, Q is the annular supercritical CO2 volume flow rate, μ is the supercritical CO2 viscosity, k is the permeability, is the cross-sectional area of ​​supercritical CO2 flow in the annulus, D is the cement annulus diameter, d is the casing diameter, β is the inertia coefficient, and ρ is the supercritical CO2 density; The gas state equation (5) is transformed according to the isothermal steady-state flow condition of the gas, and the obtained formula (16) is: Where: is the average pressure; V m is the molar volume of supercritical CO2 under the temperature and pressure conditions, T is the supercritical CO2 temperature; And the average pressure The expression can also be expressed as: Where: P u , P d Respectively represent the pressure of CO2 injection and discharge of cement sheath; the cementing strength S in step 2 = P u -P d , if P d = 0, then S and the injection end pressure P u The same; then: Where: L is the cement sheath interface length; Rewrite equation (20) as: Where: The data obtained from the experiment and the results calculated based on the experimental data are substituted into formula (21) to obtain the coordinates (x, y) of different points. The point coordinates (x, y) are plotted as a straight line, whose slope is a function of the inertia coefficient β, and the intercept is inversely proportional to the permeability k. The permeability k can be obtained by plotting.

9. The method for determining the equivalent hydraulic fracture width of the cement sheath interface of a CO2 injection well according to claim 8, characterized in that: The method for obtaining the equivalent seam width specifically includes: Based on the permeability k, the expression of the equivalent seam width h can be determined according to the following cubic law formula, as shown in formula (22): Where, ω = πd is the hydraulic circumference; A = πdL is the surface area of ​​the cement sheath interface; h is the equivalent hydraulic joint width; k is the permeability.

10. The method for determining the equivalent hydraulic fracture width of the cement sheath interface of a CO2 injection well according to claim 1, characterized in that: The equivalent hydraulic fracture width of supercritical CO2 at the cement sheath interface obtained by steps S1-S6 can be used to evaluate the influence of different CO2 viscosities and gas flow rates on the hydraulic fracture width of the cement sheath interface; or to evaluate the influence of different cementing qualities on the hydraulic fracture width of the cement sheath interface.

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