A high-efficiency cavity measurement method for underground cavities

Abstract

The present invention discloses an efficient cavity measurement method for old underground cavities, and relates to the technical field of underground reservoir evaluation, construction and development in the field of engineering construction. The present invention includes a gas injection volume measurement method and a high-precision microgravity cavity measurement method. The gas injection volume measurement method is to inject a certain amount of air into the salt cavern by a ground compressor, measure the corresponding gas injection volume and the average pressure before and after the gas injection of the old cavity of the salt cavern, and judge the connectivity and air tightness between the cavities; the gas injection volume measurement includes the following steps: improvement of the wellbore and wellhead of the old well; connection of the compressor and the gas injection pipeline of the well site; and monitoring of the gas injection and adjacent well pressures. The high-precision microgravity cavity measurement method includes the following steps: work arrangement; gravity measurement; interpretation of gravity anomalies. The present invention overcomes the problems existing in poor wellbore conditions, large diameter of salt caverns, and the overall detection of the remaining space volume of the cavity group, and can accurately analyze the closure of single cavities, combined cavities, and cavity groups.

Description

Technical Field

[0001] The present invention belongs to the field of underground reservoir evaluation, construction and development technology in the field of engineering construction, and specifically relates to an efficient cavity measurement method for underground cavities. Background Art

[0002] Underground storage is mainly divided into underground gas storage, salt cavern oil storage, compressed air / hydrogen energy storage, underground CO 2 Storage and waste slag / waste storage, etc. Underground gas storage is one of the five links in the natural gas "production, transportation, storage, sales, and use" business chain, and is an important part of the natural gas industry. There are four main types: depleted oil and gas reservoir type, aquifer type, salt cavern type, and abandoned mine pit type. The underground storage in the present invention is mainly a salt cavern type storage, which can be converted into an underground oil depot, gas storage, energy storage, waste storage, etc.

[0003] The idea of ​​building a salt cavern gas storage was first proposed by the Germans in 1916. In 1959, the Soviet Union built the world's first salt cavern underground gas storage. Compared with other types of underground gas storage, salt cavern gas storage has the advantages of high gas injection and production efficiency, high gas storage utilization, low gas volume and complete extraction of gas when needed. In addition, salt rock deposits have good creep characteristics and low permeability. Therefore, salt cavern gas storage is relatively less prone to gas leakage accidents, has high safety, and has broad application prospects.

[0004] Due to the fact that many old cavities in China have been mined for a long time and salt mining enterprises are pursuing the maximum utilization of resources, many old cavities have been connected or even connected. Some are connected by several single wells and single cavities, some are connected by fracturing, and some are connected by horizontal docking and then connected with other wells during the mining process. However, they are generally closed within a certain area. The difference is that the gas storage reservoir is converted from the oil and gas reservoir. Before the reconstruction, the sealing properties of the cap rock, faults or lithology have been analyzed, and the gas-tight conditions have been basically implemented. Although the connected cavity group has good sealing performance when it is still an independent single well or docking well at the beginning, it has changed in the subsequent dissolution process and needs further research and exploration. As long as there are no large faults or cracks in the area, it has great availability. Therefore, the utilization of old cavities in China not only needs to implement the size, shape and sealing of the remaining space of a single well and a single cavity, but also needs to further develop in the direction of the overall utilization of the cavity group, and implement the existing remaining space size and sealing of the single cavity and cavity group.

[0005] At present, the detection of salt caverns mainly relies on sonar detection technology, with a maximum detection distance of only about 100m, and sonar signals cannot penetrate the sediment bulk detection. Sonar cavity detection technology can only detect the shape of the salt cavity at the top of the vertical well or inclined well, and it is difficult to detect the overall shape of the brine dissolution cavity of the docking well, and it is even more difficult to detect the shape and size of large-diameter salt caverns and cavity groups, which brings great difficulties to the design and construction of the reconstruction of the existing dissolution cavity of the docking well and the overall utilization of the cavity group. Therefore, it is necessary to propose a new detection technology. Summary of the invention

[0006] In order to solve the problems existing in detecting the remaining space volume of the whole cavity group when the wellbore condition is poor, the diameter of the salt cavern is large, and the sealing of the single cavity, the combined cavity and the cavity group is analyzed, and the present invention proposes: an efficient cavity measurement method for the old cavity of the underground cavity, including a gas injection volume measurement method and a high-precision microgravity cavity measurement method, wherein the gas injection volume measurement method is to inject a certain amount of air into the salt cavern by a ground compressor, measure the corresponding gas injection volume and the average pressure of the old cavity of the salt cavern before and after gas injection, and judge the connectivity and air tightness between the cavities;

[0007] Furthermore, the gas injection capacity measurement comprises the following steps:

[0008] S1. Improvement of the wellbore and wellhead of the old well;

[0009] S2, compressor and well site gas injection pipeline connection;

[0010] S3. Gas injection and adjacent well pressure monitoring.

[0011] Furthermore, the high-precision microgravity cavity measurement method comprises the following steps:

[0012] S1. Work arrangement;

[0013] S2, gravity measurement;

[0014] S3. Explanation of gravity anomaly.

[0015] Furthermore, the gas injection capacity measurement method is to determine the residual space volume of the old cavity by the following formula, Vu = (PaVa / (Pu'-Pu))(Tu / Ta);

[0016] Where: Pu is the old cavern formation pressure before gas injection, Pu' is the old cavern formation pressure after gas injection balance, Pa is the atmospheric pressure at the compressor inlet, in MPa, Tu is the formation temperature in the middle of the salt cavern, Ta is the atmospheric temperature at the compressor inlet, in K; Va is the volume of air at atmospheric temperature and pressure injected by the compressor, in m 3 .

[0017] Furthermore, the formation pressure value of the old cavity in the balance section is read; the air tightness of the salt cavern is determined based on the large slope and pressure drop rate of the pressure drop section; the leakage location and cause are determined based on the pressure changes in each pressure monitoring well; in the implementation of the gas injection volume measurement technology, the pressure changes in different old cavities and old wells are measured, and the pressures of the wells are compared with each other, that is, the connectivity between the cavities is determined, and the size of the connected section is semi-quantitatively determined.

[0018] Furthermore, the maximum value of gravity anomaly of the high-precision microgravity cavity measurement method is calculated by the following formula, the gravity anomaly value is proportional to the target mass, and the gravity anomaly value is inversely proportional to the square of the central burial depth:

[0019] ΔgMax=G*M / D 2

[0020] Where ΔgMax is the gravity anomaly value, G is the gravity acceleration, M is the mass of the detection target, in kg; D is the burial depth of the target center, in km;

[0021] Furthermore, the location, geometric characteristics and physical properties of the remaining space in the old salt cavern were obtained by forward calculation of the gravity anomaly model.

[0022] Further, step S1 includes the following:

[0023] The high-precision microgravity cavity measurement method adopts the static method to achieve detailed measurement of gravity area, and its working arrangement process is as follows:

[0024] S1. Carry out work at a large scale of 1:50;

[0025] S2. Cover the survey area, survey line and survey point in the distribution area of ​​the old salt cavern predicted by geological analysis;

[0026] S3. Through planning and additional measurement, each gravity anomaly area should have at least 4 measurement points;

[0027] S4. The line spacing of the survey lines shall not be greater than 1 / 3 of the predicted old cavity diameter; 1:50 area measurement shall be carried out on a regular survey network / free survey network with a line spacing of 10m and a point spacing of 5m, and the point spacing in abnormal areas shall be increased to 2.5m.

[0028] Furthermore, in the high-precision microgravity cavity measurement method, after the gravity measurement is completed through field measurement, 1-2 base points are selected in the work area according to the size of the measurement area to ensure the quality of observation. Each instrument repeats the observation at the base points on time at least three times a day to check the zero point displacement of the instrument.

[0029] Furthermore, in the high-precision microgravity cavity measurement method: the gravity anomaly interpretation processes and inverts the original gravity anomaly to form a gravity anomaly analytical profile, and a high-pass filtering processing method is selected to process and calculate the original gravity anomaly to obtain a gravity anomaly contour map, showing the old cavity gravity anomaly, and the old cavity of the salt cavern exhibits a negative gravity anomaly.

[0030] The beneficial effects of the present invention are:

[0031] The contour map of Bouguer gravity anomaly field in the survey area can clearly and accurately obtain the location and shape of the old salt cavern, and verify it with the gas injection volume measurement. It overcomes the problems of poor wellbore conditions, large diameter of salt caverns and the remaining space volume of the cavity group as a whole, and can accurately analyze the closure of single cavity, combined cavity and cavity group. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the cavity pressure change curve of the present invention. DETAILED DESCRIPTION

[0033] Example 1

[0034] It includes a gas injection volume measurement method and a high-precision microgravity cavity measurement method. The gas injection volume measurement method is to inject a certain amount of air into the salt cavern by a ground compressor, measure the corresponding gas injection volume and the average pressure of the old cavity of the salt cavern before and after gas injection, and judge the connectivity and air tightness between the cavities;

[0035] Wherein, the gas injection capacity measurement comprises the following steps:

[0036] S1. Improvement of the wellbore and wellhead of the old well;

[0037] S2, compressor and well site gas injection pipeline connection;

[0038] S3. Gas injection and adjacent well pressure monitoring.

[0039] Wherein, the gas injection capacity measurement method is to determine the residual space volume of the old cavity by the following formula, Vu = (PaVa / (Pu'-Pu))(Tu / Ta);

[0040] Where: Pu is the old cavern formation pressure before gas injection, Pu' is the old cavern formation pressure after gas injection balance, Pa is the atmospheric pressure at the compressor inlet, in MPa, Tu is the formation temperature in the middle of the salt cavern, Ta is the atmospheric temperature at the compressor inlet, in K; Va is the volume of air at atmospheric temperature and pressure injected by the compressor, in m 3 .

[0041] Among them, the formation pressure value of the old cavity in the balance section is read; the air tightness of the salt cavern is judged according to the large slope and pressure drop rate of the pressure drop section; the leakage location and cause are judged according to the pressure changes of each pressure monitoring well; in the implementation of the gas injection volume measurement technology, by measuring the pressure changes of different old cavities and old wells, the pressure sizes of each well are compared, that is, the connectivity between the cavities is judged, and the size of the connected section is semi-quantitatively judged.

[0042] It should be pointed out that the initial stage of gas injection in salt caverns will not reach equilibrium immediately due to the influence of gas transmission and diffusion. After stopping gas injection, even if the old cavity is geologically and engineering sealed, the pressure of the injected gas will slowly decrease due to the dissolution of residual brine, the adsorption of gas on the liquid and solid interface, and oxidation consumption. The formation pressure will show the following Figure 1 As shown in the three-stage rise, balance, and decline, the wellhead pressure will also be "three-stage", so Pu' needs to read the pressure of the balance stage. At the same time, the gas tightness of the salt cavern can also be judged according to the large slope and pressure drop speed of the pressure drop stage. According to the pressure changes of each pressure monitoring well, the leakage location and cause can be further judged.

[0043] In the implementation of gas injection capacity measurement technology, by measuring the pressure changes in different old cavities and old wells and comparing the pressures between the wells, the connectivity between the cavities can be determined and the size of the connected section can be semi-quantitatively determined.

[0044] Since the gas injection volume measurement method can only determine the current remaining space size of the old cavity, but cannot detect the specific position and shape of the space, it is necessary to combine the microgravity measurement results of various nodes and measurement lines on the ground.

[0045] The maximum value of gravity anomaly in the high-precision microgravity cavity measurement method is calculated by the following formula. The gravity anomaly value is proportional to the target mass, and the gravity anomaly value is inversely proportional to the square of the central burial depth:

[0046] ΔgMax=G*M / D 2

[0047] Where ΔgMax is the gravity anomaly value, G is the gravity acceleration, M is the mass of the detection target, in kg; D is the burial depth of the target center, in km;

[0048] Among them, the position, geometric characteristics and physical properties of the remaining space of the old salt caverns are obtained by forward calculation of the gravity anomaly model. With the cooperation of fine terrain measurement, the microgravity cavity measurement and the interpretation of the results are not affected by the terrain, access, visibility and narrow site range. It is suitable for shallow salt cavern old cavity measurement with a certain size in various terrains and covering layer types.

[0049] The high-precision microgravity cavity measurement method adopts the static method to achieve detailed measurement of gravity area.

[0050] The high-precision microgravity cavity measurement method comprises the following steps:

[0051] S1. Work arrangement; the work arrangement process is as follows:

[0052] (1) Carry out work at a large scale of 1:50;

[0053] (2) Cover the survey area, survey lines and survey points in the distribution area of ​​the old salt caverns predicted by geological analysis;

[0054] (3) Through planning and additional measurements, each gravity anomaly area should have at least four measuring points;

[0055] (4) The line spacing of the survey line shall not be greater than 1 / 3 of the predicted old cavity diameter; 1:50 area measurement shall be carried out on a regular survey network / free survey network with a line spacing of 10m and a point spacing of 5m, and the point spacing in abnormal areas shall be increased to 2.5m.

[0056] S2. Gravity measurement: After the gravity measurement is completed, 1-2 base points are selected in the work area according to the size of the measurement area to ensure the observation quality. Each instrument repeats the observation at the base point at least three times a day to check the zero point displacement of the instrument. Two gravimeters are used, which are LaCoste&Rom berg micro-Gal gravimeters with a resolution of 5Gal and a measurement range of 300mGal.

[0057] S3. Interpretation of gravity anomaly: The original gravity anomaly is processed and inverted to form a gravity anomaly analysis profile. The high-pass filtering method is used to process and calculate the original gravity anomaly to obtain a gravity anomaly contour map, which shows the old cavity gravity anomaly. The old cavity of the salt cavern shows a negative gravity anomaly.

[0058] Example 2

[0059] XHYH Second Mining Area (S) was put into production in 1991 and completed production in 2008. It uses 26 single-well convection mining and 1 group of 4 double-well directional convection production. In order to measure the size of the current remaining space in the solution cavity, sonar detection was used before, but due to the limitations of subjective and objective factors such as instrument performance and wellbore conditions, the maximum detection distance was less than 20m, and the effect was not good. For this reason, a vertical well with a central bottom plane position and good cementing quality was selected as the injection well, and the other wells were used as pressure monitoring wells to ensure that at least one well in each salt cavity can measure the wellhead pressure. In the case where the bottomhole pressure cannot be measured directly, the bottomhole pressure can also be converted from the wellhead pressure.

[0060] The roof burial depth of XHYH No. 2 mining area (S) is 350m–400m, the salt layer thickness is 400m, the main mining section thickness is 130m, and the average salt layer temperature is 36.6℃.

[0061] For gas injection, two compressors with an outlet pressure of 10 MPa and a gas injection rate of 45,000 cubic meters / 24 hours are selected, and the gas injection is continuous for 240 hours (10 days). Other data are:

[0062] Compressor inlet pressure Pa = 0.1 MPa;

[0063] The average bottom hole pressure Pu before gas injection recorded by 12 monitoring wells (connected wells) with pressure changes was 0.4 MPa;

[0064] Average bottom hole pressure after gas injection Pu'=0.7MPa;

[0065] Compressor inlet temperature Ta = 25 ° C = 298.15 K;

[0066] The average temperature of the salt layer Tu = 36.55 ° C = 309.7 K;

[0067] Gas injection volume under ground conditions Va=90×104m 3 .

[0068] From the above formula, we can calculate that the remaining space Vu of the old cavern in the current second mining area (S) is 124.6×104m 3 .

[0069] According to the actual production data, the cumulative salt production in the second mining area (S) is 287.6×104m 3 The total mined material is 604×104t, and the average density of the mined material is 1.24g / m 3 Calculated, the volume of produced material is 487×104m 3 The salt cavities where the 12 pressure-changing wells, including the injection well, are located have been connected according to production experience analysis, and the gas injection test has also confirmed that they are connected. The volume of the produced material is 147×104m 3 The results of gas injection cavity measurement are reasonable. It is estimated that the residual mud in the cavity is 22.35×104m 3 .

[0070] The maximum value of the average gravity anomaly of the high-precision microgravity measurement cavity is 125μGal, and the gravity anomaly is significant. The contour line plane map of the Bouguer gravity anomaly field in the survey area can clearly and accurately obtain the position and shape of the old cavity in the salt cavern, and confirm it with the gas injection volume measurement.

[0071] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solutions and concepts of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for efficiently measuring the old cavity of an underground cavity, characterized in that: It includes a gas injection volume measurement method and a high-precision microgravity cavity measurement method. The gas injection volume measurement method is to inject a certain amount of air into the salt cavern by a ground compressor, measure the corresponding gas injection volume and the average pressure of the old cavity of the salt cavern before and after gas injection, and judge the connectivity and air tightness between the cavities; The gas injection capacity measurement comprises the following steps: The shaft and wellhead of the old well are improved; Compressor and well site gas injection pipeline connection; Gas injection and adjacent well pressure monitoring; The high-precision microgravity cavity measurement method comprises the following steps: Work arrangement; Gravity measurement; Gravity anomaly interpretation; The gas injection capacity measurement method is to determine the residual space volume of the old cavity by the following formula: Vu = (Pa Va / (Pu'-Pu))(Tu / Ta); Where: Pu is the old cavity formation pressure of the salt cavern before gas injection, Pu' is the old cavity formation pressure after gas injection balance, Pa is the atmospheric pressure at the compressor inlet, in MPa, Tu is the formation temperature in the middle of the salt cavern, Ta is the atmospheric temperature at the compressor inlet, in K; Va is the volume of air at atmospheric temperature and pressure injected through the compressor, in m 3 ; Read the formation pressure value of the old cavity in the balance section; judge the gas tightness of the salt cavern according to the slope of the pressure drop section and the pressure drop rate; judge the leakage location and cause according to the pressure changes of each pressure monitoring well; in the implementation of the gas injection volume measurement technology, by measuring the pressure changes of different old cavities and old wells, compare the pressures of each well, that is, judge the connectivity between the cavities, and semi-quantitatively judge the size of the connected section; The maximum value of gravity anomaly in the high-precision microgravity cavity measurement method is calculated by the following formula. The gravity anomaly value is proportional to the target mass and inversely proportional to the square of the center burial depth: ΔgMax=G*M / D 2 Where ΔgMax is the gravity anomaly value, G is the gravity acceleration, M is the mass of the detection target, in kg; D is the burial depth of the target center, in km; The position, geometric characteristics and physical properties of the remaining space in the old salt cavern are obtained by forward calculation of the gravity anomaly model. In the high-precision microgravity cavity measurement method: the gravity anomaly interpretation processes and inverts the original gravity anomaly to form a gravity anomaly analytical profile, and a high-pass filtering processing method is selected to process and calculate the original gravity anomaly to obtain a gravity anomaly contour map, which shows the old cavity gravity anomaly. The old cavity of the salt cavern exhibits a negative gravity anomaly.

2. The underground cavity old cavity efficient cavity measurement method according to claim 1 is characterized in that: The high-precision microgravity cavity measurement method adopts the static method to achieve detailed measurement of gravity area, and its working arrangement process is as follows: Work is carried out on a large scale of 1:50; Cover the survey area, survey line and survey point in the distribution area of ​​the old salt cavern predicted by geological analysis; Through planning and additional measurements, each gravity anomaly area has at least 4 measurement points; The line spacing of the survey lines shall not be greater than 1 / 3 of the predicted old cavity diameter; 1:50 area measurement shall be carried out on a regular survey network / free survey network with a line spacing of 10m and a point spacing of 5m, and the point spacing in abnormal areas shall be increased to 2.5m.

3. The underground cavity old cavity efficient cavity measurement method according to claim 1 is characterized in that: In the high-precision microgravity cavity measurement method, after the gravity measurement is completed through field measurement, 1-2 base points are selected in the work area according to the size of the measurement area to ensure the quality of observation. Each instrument repeats the observation at the base points on time at least three times a day to check the zero point displacement of the instrument.

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