A method for monitoring geological safety of oil and gas reinjection

Abstract

The present invention discloses a method for monitoring geological safety of oil and gas reinjection. The method is supported by geological and geophysical data, and classifies the seismic activity in the oil and gas reinjection well area into dangerous levels based on the historical seismic activity in the target area, so as to obtain a quantitative seismic hazard classification map. The reinjection well plan is reasonably set on the basis of the quantitative seismic hazard classification map, and the relevant active structures of the reinjection well and the hazard level of the well field are determined. The real-time seismic monitoring and other technical means are used to reflect the seismic activity intensity of the reinjection well and the surrounding active faults in real time, so as to form a set of geological safety monitoring methods for oil and gas reinjection wells as a whole, which can monitor the geological safety of oil and gas reinjection in real time and reduce the risk of safety accidents in the reinjection wells.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas field development, and in particular to a method for monitoring geological safety of oil and gas reinjection. Background Art

[0002] Reinjection wells are an environmental protection measure that injects produced water from oil and gas fields back into the formation to replenish formation energy, maintain formation pressure, and reduce environmental pollution. However, the reinjection work will be affected by geological safety. When the geology changes, if reinjection is continued, production safety accidents may occur. Therefore, realizing geological safety monitoring of oil and gas reinjection and formulating reasonable reinjection plans can reduce the risk of safety accidents in reinjection wells. Summary of the invention

[0003] In view of the above-mentioned deficiencies in the prior art, the present invention provides a method for monitoring geological safety of oil and gas reinjection, which can monitor the geological safety of oil and gas reinjection in real time and reduce the risk of safety accidents in reinjection wells.

[0004] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is:

[0005] A method for monitoring geological safety of oil and gas reinjection is provided, which comprises the following steps:

[0006] S1. Obtain the uplift rate of active faults in the target area; select the horizontal distance between the surface position of the active fault and the position of the target layer for shale gas extraction as the interpolation radius, obtain the fault movement rate contour network in the target area, and use the smallest negative value in the interpolation result as the default value of the fault movement rate;

[0007] S2. Perform seismic geological interpretation on the seismic exploration data accumulated during the oil and gas field exploration process to obtain the reinjection operation layer faults and their fault distances; select the horizontal and vertical distances between the reinjection operation layer faults and the oil and gas well reinjection target layer as the interpolation radius, obtain the fracture fault distance contour line grid in the target area, and use the smallest negative value in the interpolation result as the default value of the fracture fault distance;

[0008] S3, obtaining historical earthquake activity data of the target area, using the middle value of two known earthquake magnitudes as the interpolation radius, obtaining the earthquake magnitude contour grid of the target area, and using the smallest negative value in the interpolation result as the default value of the earthquake magnitude;

[0009] S4. Perform grid calculation based on the uplift rate, fault throw, magnitude of active faults in the target area and corresponding default values ​​to obtain a quantitative earthquake hazard classification map;

[0010] S5, performing low-pass filtering on the quantitative earthquake hazard classification map to obtain a filtered earthquake hazard classification map;

[0011] S6. Based on the filtered seismic hazard classification map, the maximum hazard level within n meters of the target well site is selected as the risk level of the well site, and the active structure corresponding to the maximum hazard level is selected as the key monitoring fault zone;

[0012] S7. Determine whether an earthquake with a magnitude greater than or equal to k occurs in the fault zone during the target oil and gas well reinjection process and within the next m days. If so, reduce or suspend the reinjection operation intensity; otherwise, carry out the reinjection operation normally.

[0013] Furthermore, the uplift rate of an active fault is calculated by dividing the total displacement of the same geological or geomorphic unit caused by fault dislocation in a certain period by the corresponding period of time as the result of the active fault uplift rate.

[0014] Furthermore, the expression for grid calculation is:

[0015] R=sqrt((U+U default )×(T+T default )*(M+M default ))

[0016] Where R is the quantitative earthquake hazard value calculated for a single grid; sqrt is the square root function; U is the uplift rate of the active fault in a single grid; U default is the default value of the fracture movement rate in a single grid; T is the fracture distance in a single grid; T default is the default value of the fault distance; M is the magnitude; M default The default value for earthquake magnitude.

[0017] Furthermore, the method for low-pass filtering is: using a low-pass filter matrix The quantitative earthquake hazard classification map was Gaussian filtered four times to obtain the filtered earthquake hazard classification map.

[0018] Further, the value of n is 500.

[0019] Furthermore, the value of m is 2.

[0020] Furthermore, the value of k is 3.

[0021] The beneficial effects of the present invention are as follows: the method is supported by geological and geophysical data, and the historical seismic activity in the target area is comprehensively considered to classify the seismic activity in the oil and gas reinjection well area into dangerous levels, thereby obtaining a quantitative seismic hazard classification map; and based on the quantitative seismic hazard classification map, the reinjection well plan is reasonably set, the active structures related to the reinjection well and the hazard level of the well field are determined, and technical means such as real-time seismic monitoring are used to reflect the intensity of seismic activity of the reinjection well and the surrounding active faults in real time, thereby forming a set of geological safety monitoring methods for oil and gas reinjection wells as a whole, which can monitor the geological safety of oil and gas reinjection in real time and reduce the risk of safety accidents in the reinjection wells. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the process of this method. DETAILED DESCRIPTION

[0023] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0024] like Figure 1 As shown, the oil and gas reinjection geological safety monitoring method includes the following steps:

[0025] S1. Obtain the uplift rate of active faults in the target area; select the horizontal distance between the surface position of the active fault and the position of the target layer for shale gas extraction as the interpolation radius, obtain the fault movement rate contour network in the target area, and use the smallest negative value in the interpolation result as the default value of the fault movement rate;

[0026] S2. Perform seismic geological interpretation on the seismic exploration data accumulated during the oil and gas field exploration process to obtain the reinjection operation layer faults and their fault distances; select the horizontal and vertical distances between the reinjection operation layer faults and the oil and gas well reinjection target layer as the interpolation radius, obtain the fracture fault distance contour line grid in the target area, and use the smallest negative value in the interpolation result as the default value of the fracture fault distance;

[0027] S3, obtaining historical earthquake activity data of the target area, using the middle value of two known earthquake magnitudes as the interpolation radius, obtaining the earthquake magnitude contour grid of the target area, and using the smallest negative value in the interpolation result as the default value of the earthquake magnitude;

[0028] S4. Perform grid calculation based on the uplift rate, fault throw, magnitude of active faults in the target area and corresponding default values ​​to obtain a quantitative earthquake hazard classification map;

[0029] S5, performing low-pass filtering on the quantitative earthquake hazard classification map to obtain a filtered earthquake hazard classification map;

[0030] S6. Based on the filtered seismic hazard classification map, the maximum hazard level within n meters of the target well site is selected as the risk level of the well site, and the active structure corresponding to the maximum hazard level is selected as the key monitoring fault zone;

[0031] S7. Determine whether an earthquake with a magnitude greater than or equal to k occurs in the fault zone during the target oil and gas well reinjection process and within the next m days. If so, reduce or suspend the reinjection operation intensity; otherwise, carry out the reinjection operation normally.

[0032] The calculation method of active fault uplift rate is: the total displacement of the same geological or geomorphic unit caused by fault dislocation in a certain period of time is divided by the corresponding period of time as the result of active fault uplift rate. This parameter is sometimes also used as a regional empirical value, which is generally 3-5 mm / year in Sichuan and Chongqing.

[0033] The expression for grid calculation is:

[0034] R=sqrt((U+U default )×(T+T default )*(M+M default ))

[0035] Where R is the quantitative earthquake hazard value calculated for a single grid; sqrt is the square root function; U is the uplift rate of the active fault in a single grid; U default is the default value of the fracture movement rate in a single grid; T is the fracture distance in a single grid; T default is the default value of the fault distance; M is the magnitude; M default The default value for earthquake magnitude.

[0036] Using low-pass filter matrix The quantitative earthquake hazard classification map was Gaussian filtered four times to obtain the filtered earthquake hazard classification map.

[0037] In a specific implementation process, the value of n is 500, the value of m is 2, and the value of k is 3.

[0038] In one embodiment of the present invention, take the H1 well in area A as an example: the well is located at the high point of the anticline, is a depletion type reinjection well, the gas reservoir type is fracture type, and the depth of the water injection target layer is 2418 meters. There are 17 third-level faults within 10 kilometers of the area, with a vertical distance of 7-219 meters, and the uplift (or sliding) rate of the faults in the extraction area is 3.7 mm / year. The historical earthquake magnitude is 0.3-3.7. According to the determined regional fault movement rate U value of 3.7 mm / year, and the smallest negative value Udefault in the interpolation result of -0.4 mm / year, the median vertical fault distance T of 91 meters, the corresponding minimum interpolation Tdefault of -13 meters, the median magnitude M of 1.6, and the corresponding minimum interpolation Mdefault of -0.3, the software is used for grid calculation, and the quantitative earthquake hazard classification parameters obtained by calculation are Gaussian filtered 4 times using a low-pass filter matrix. The median of the regional earthquake hazard level quantitative division parameter R = Sqrt((3.7-0.4)*(91-13)*(1.6-0.3)) = 18.3. The earthquake hazard classification within the region after filtering is 2-26. The determined earthquake hazard level quantitative division parameter R is used to evaluate the regional geological safety level.

[0039] The maximum danger level within 500 meters of the H1 well is 23, and the corresponding faults are D1, D7, D11, and D3, which are active structures, and are monitored during the reinjection process. A total of 1,437 earthquakes occurred in the area, 136 earthquakes occurred in areas with a risk level of less than 12, accounting for 9.2%; 241 earthquakes occurred in areas with a risk level between 12 and 19, accounting for 16.8%; and 1,060 earthquakes occurred in areas with a risk level greater than 19, accounting for 74.0%. The earthquakes mainly occurred in the maximum danger level of 19 around the H1 well. During the reinjection cycle, due to a maximum earthquake of magnitude 3.4 occurring 4 hours after the start of reinjection, the operation was suspended for safety reasons. After 3 days of observation, the earthquake frequency dropped to the level before the operation and the operation was resumed.

[0040] In summary, this method is supported by geological and geophysical data, and the historical seismic activities in the target area are comprehensively analyzed to classify the seismic activities in the oil and gas reinjection well area into dangerous levels, thus obtaining a quantitative seismic hazard classification map. Based on the quantitative seismic hazard classification map, the reinjection well plan is reasonably set, the active structures related to the reinjection well and the hazard level of the well field are determined, and technical means such as real-time seismic monitoring are used to reflect the intensity of seismic activities of the reinjection well and the surrounding active faults in real time. As a whole, a set of geological safety monitoring methods for oil and gas reinjection wells is formed, which can monitor the geological safety of oil and gas reinjection in real time and reduce the risk of safety accidents in reinjection wells.

Claims

1. A method for monitoring geological safety of oil and gas reinjection, characterized in that: The following steps are involved: S1. Obtain the uplift rate of active faults in the target area; The horizontal distance between the surface position of the active fault and the position of the target layer for shale gas production is selected as the interpolation radius, the fault movement rate contour network of the target area is obtained, and the smallest negative value in the interpolation result is used as the default value of the fault movement rate; S2. Perform seismic geological interpretation on the seismic exploration data accumulated during the oil and gas field exploration process to obtain the reinjection operation layer faults and their fault distances; select the horizontal and vertical distances between the reinjection operation layer faults and the oil and gas well reinjection target layer as the interpolation radius, obtain the fracture fault distance contour line grid in the target area, and use the smallest negative value in the interpolation result as the default value of the fracture fault distance; S3, obtaining historical earthquake activity data of the target area, using the middle value of two known earthquake magnitudes as the interpolation radius, obtaining the earthquake magnitude contour grid of the target area, and using the smallest negative value in the interpolation result as the default value of the earthquake magnitude; S4. Perform grid calculation based on the uplift rate, fault throw, magnitude of active faults in the target area and corresponding default values ​​to obtain a quantitative earthquake hazard classification map; S5, performing low-pass filtering on the quantitative earthquake hazard classification map to obtain a filtered earthquake hazard classification map; S6. Based on the filtered seismic hazard classification map, the maximum hazard level within n meters of the target well site is selected as the risk level of the well site, and the active structure corresponding to the maximum hazard level is selected as the key monitoring fault zone; S7. Determine whether an earthquake with a magnitude greater than or equal to k occurs in the fault zone during the target oil and gas well reinjection process and within the next m days. If so, reduce or suspend the reinjection operation intensity; otherwise, carry out the reinjection operation normally.

2. The method for monitoring geological safety of oil and gas reinjection according to claim 1, characterized in that: The calculation method of active fault uplift rate is: the total displacement of the same geological or geomorphic unit caused by fault dislocation in a certain period of time is divided by the corresponding period of time, and the result is taken as the active fault uplift rate.

3. The method for monitoring geological safety of oil and gas reinjection according to claim 1, characterized in that: The expression for grid calculation is: R=sqrt((U+U default )×(T+T default )*(M+M default )) Where R is the quantitative earthquake hazard value calculated for a single grid; sqrt is the square root function; U is the uplift rate of the active fault in a single grid; U default is the default value of the fracture movement rate in a single grid; T is the fracture distance in a single grid; T default is the default value of the fault distance; M is the magnitude; M default The default value for earthquake magnitude.

4. The method for monitoring geological safety of oil and gas reinjection according to claim 1, characterized in that: The method for low-pass filtering is: using a low-pass filter matrix The quantitative earthquake hazard classification map was Gaussian filtered four times to obtain the filtered earthquake hazard classification map.

5. The method for monitoring geological safety of oil and gas reinjection according to claim 1, characterized in that: The value of n is 500.

6. The method for monitoring geological safety of oil and gas reinjection according to claim 1, characterized in that: The value of m is 2.

7. The method for monitoring geological safety of oil and gas reinjection according to claim 1, characterized in that: The value of k is 3.

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