RU2813580C1 - Method of determining location of magnetic observatory on territory of investigated deposit - Google Patents

Abstract

FIELD: physics; measurement.

SUBSTANCE: invention relates to the field of magnetometric exploration, in particular to the combined, namely aeromagnetic and ground, magnetic gradient survey of large areas to search for the optimal installation location of the absolute and variometric pavilions of the magnetic observatory. Method for determining the location of the magnetic observatory on the territory of the investigated deposit, according to which aerial photography of the selected area is carried out, two-stage aeromagnetic survey is carried out and a site is selected for further two-stage ground magnetic survey, according to the results of which the optimal places for construction of the absolute and variometric pavilions of the magnetic observatory are determined.

EFFECT: increased accuracy of combined magnetometric survey, as well as reduced time for combined survey due to use of UAV.

8 cl, 6 dwg

Description

Field of technology

The invention relates to the field of magnetometric reconnaissance, in particular to combined, namely aeromagnetic and ground-based, magnetogradientometric survey of large areas to find the optimal location for installing the absolute and variometric pavilions of a magnetic observatory.

State of the art

The level of technology widely discloses the conduct of various types of magnetic reconnaissance from simple ground-based magnetic reconnaissance to promising types of aeromagnetic and aerogradientometric reconnaissance using various types of unmanned aerial vehicles (hereinafter referred to as UAVs), for example, such as a “wing” or “copter” with a different number of propellers .

An article [1] is known from the prior art, which describes the methodology for choosing a location for deploying a geomagnetic observatory. According to this methodology, in the process of choosing the location for installing a magnetic observatory, 11 factors are taken into account, among which the main one is taking into account the distribution of the Earth’s magnetic field. Variations in the Earth's magnetic field are mapped and a location with minimal variations is selected. Thus, in the example given in this article, seven areas were identified where magnetic observatories could be deployed.

However, the methodology disclosed in this article does not have sufficient accuracy; it also lacks information about the search and selection of a deposit for the subsequent selection of a specific location for a magnetic observatory on the territory of the selected deposit.

There is a known patent source of information [2], which discloses a combined method for determining the distribution of the Earth’s magnetic field, implemented in three stages. At the first stage, a ground-based magnetometric survey is carried out on the terrain of the exploration area along the baseline measurement line. At the second stage, aerial photogrammetry is carried out using a UAV, directing it along the measurement baseline. In this case, a multi-level assessment of the distribution of magnetic field lines is obtained. After correcting the measurement results, a quick scan of the study area is performed and a circular area is determined to confirm the preliminary target production area. In the third stage, a final magnetic survey is carried out in front of the target zone of the proposed mining mine. This solution makes it possible to determine with high accuracy, based on the results of a magnetic field study, locations for subsequent deployment of drilling equipment.

The methodology disclosed in this source of information, although it is aimed at increasing the accuracy of measurements, nevertheless, it does not contain information about the search and selection of a specific location for a magnetic observatory on the territory of the developed field.

Known from the prior art is the book [3], which we accepted as a prototype, in which, on pages 15–16, recommendations are shown for selecting promising locations for the location of a magnetic observatory and a more thorough examination of each promising location to select a specific location for the magnetic observatory for its further construction.

So, first an area geomagnetic survey is carried out. It is enough to ensure that at least one element has a normal distribution over the area surrounding the observatory. If a detailed survey of the area has not previously been carried out, a profile of 30 kilometers should be surveyed to the north and south of the promising site with a distance between stations of three kilometers. Usually vertical or total intensity is measured. The observed values, plotted against distance, should produce an approximately straight, albeit sloping, line. The traverse from east to west should be examined in the same way. Results plotted against distance will give the vertical and overall intensity of either a horizontal or slightly slanted line. The site will be excellent if the anomalies (deviations from the straight line) are less than 50 gamma. Anomalies greater than 200 gamma should be avoided. Two short profiles can be added from northwest to southeast and from northeast to southwest at a distance of up to 10 kilometers in each direction from the observatory.

The area magnetic survey is followed by a more detailed magnetic survey of the potential observatory site. An area of 100 by 100 meters is marked with pegs from 10 to 10 meters and then surveyed. Diurnal variations can be accounted for by observing a central point every thirty minutes. Based on the results of a more detailed survey, a specific location for installing the magnetic observatory is selected.

Also, if necessary, reconnaissance surveys are carried out either using a vertical field strength balance or, preferably, using a proton magnetometer. A proton magnetometer will be very useful, especially when shooting at close range.

Despite the good accuracy of two-stage magnetic surveying, it is nevertheless very labor-intensive due to the involvement of specially trained personnel to carry out two stages of surveying, and is also time-consuming, since it is necessary to conduct an areal ground survey of several directions with a length of several kilometers in a short time in the presence of impassable terrain. territories is impossible. At the same time, the prototype does not contain information about conducting preliminary aerogradientometric survey using a UAV, which can significantly reduce the time for conducting area surveys, as well as significantly increase the accuracy of measurements due to the elimination of the human factor.

Thus, there is a need for methods to eliminate, reduce or overcome the disadvantages of prior art solutions.

Disclosure of the invention

Based on the above disadvantages, the technical result to which the present invention is aimed is to increase the accuracy of combined magnetometric surveys to determine the installation location of a magnetic observatory in the territory of the field under study, as well as to reduce the time for conducting combined surveys through the use of UAVs.

To achieve the specified technical result, a method is presented for determining the installation location of a magnetic observatory on the territory of the field under study, according to which aerial photography of the selected area is carried out using a UAV, based on the results of which a digital map of the area is constructed. Then, an areal aeromagnetic survey is carried out using a UAV with an overhead magnetometer, and a detailed areal aeromagnetic survey of the area is carried out using a UAV with an overhead magnetometer. Based on the results of aeromagnetic surveys, a digital map of the anomalous component of the Earth’s magnetic field of the area is constructed, then the areas where the magnetic component of the Earth’s field changes most smoothly in a given direction are determined. A detailed ground-based magnetogradiometric survey of selected areas is carried out; based on the results of the ground-based detailed magnetic survey, two areas are determined where there are no significant magnetic anomalies, after which a ground-based micromagnetic survey is carried out in relation to the selected areas to determine the specific construction site of the absolute and variometric pavilions of the magnetic observatory.

In another aspect of the claimed invention, an aircraft-type UAV is used to conduct aeromagnetic magnetic surveys.

In another aspect of the claimed invention, a multi-rotor UAV is used to conduct aeromagnetic magnetic surveys, which can be made in the form of a quadcopter, hexacopter or octocopter.

In another aspect of the claimed invention, a proton Overhauser magnetometer is used when conducting ground-based magnetic gradientometric and micromagnetic surveys.

In another aspect of the claimed invention, before conducting a ground magnetic survey, areas measuring 100 by 100 meters are selected.

In another aspect of the claimed invention, a detailed ground-based magnetic gradient survey of selected areas is carried out with a step of 10 by 10 meters.

In another aspect of the claimed invention, terrestrial micromagnetic survey is carried out with a step of 1 by 1 meter.

Brief description of drawings

In fig. Figure 1 shows an example of a flight mission for an aircraft-type UAV when conducting aerial photography.

In fig. Figure 2 shows an example of a digital map of the area constructed based on the results of aerial photography.

In fig. Figure 3 shows an example of a flight mission for a multi-rotor UAV when conducting aeromagnetic surveys.

In fig. Figure 4 shows an example of a constructed map of the Earth's magnetic field of an area based on the results of ground-based magnetogradimetric surveys, with the anomalous component shown on the left and the vertical gradient of the Earth's magnetic field on the right.

In fig. Figure 5 shows an example of a map of the anomalous component (top) and vertical gradient (bottom) of the Earth’s magnetic field for a site of ground-based magnetogradiometric survey. Areas for micromagnetic surveys for future observatory pavilions are indicated in red on the map: A – absolute pavilion, B – variometric pavilion.

In fig. Figure 6 shows an example of a map of the anomalous component (top) and vertical gradient (bottom) of the Earth’s magnetic field based on the results of a micromagnetogradientometric survey, indicating the optimal locations for installing the pedestals of the absolute and variometric pavilions of the magnetic observatory in the area of the developed field.

Carrying out the invention

When drilling production wells in the field, the most modern high-tech directional drilling methods are used, which require detailed operational information about the dynamics of the Earth's magnetic field. To do this, it is necessary to use data from continuous high-precision geomagnetic measurements carried out near the field development site. To carry out high-tech work on the development of the field, it is advisable to build a new full-scale domestic magnetic observatory on the territory of the field itself.

Taking into account magnetic field variations in real time by monitoring them in the drilling area using high-precision magnetometric equipment is an integral element in high-tech hydrocarbon production.

To deploy a geomagnetic observatory, it is necessary to study the place in which it will be located using areal magnetic surveys on several scales. First, a small-scale magnetic survey is carried out, then a detailed survey is carried out, which is necessary to accurately determine the locations of future observatory buildings where functioning magnetometric equipment will be located. Observatory pavilions are located in areas characterized by the most uniform anomalous magnetic field and the minimum values of its gradient.

To determine the optimal location for installing a magnetic observatory on the territory of the field under study, it is necessary:

- conduct aerial photography of the selected area;

- build a digital map of the area based on the results of aerial photography;

- conduct an area aeromagnetic survey using a UAV with an overhead magnetometer;

- conduct a detailed areal aeromagnetic survey of the site using a UAV with an overhead magnetometer;

- construct a digital map of the anomalous component of the Earth’s magnetic field of the surveyed area based on the results of aeromagnetic surveys;

- determine areas (mainly 100x100 meters in size) where the magnetic component of the Earth’s field changes most smoothly in a given direction;

- carry out a detailed ground-based magnetic gradientometric survey of the areas selected at the previous stage (mainly with a step of 10x10 meters);

- to determine, based on the results of the detailed ground survey, two areas where there are no significant magnetic anomalies;

- carry out ground-based micromagnetic survey of selected areas (mainly with a step of 1×1 meter) to determine the specific construction site of the absolute and variometric pavilions of the magnetic observatory.

To carry out aerial photography and subsequent aeromagnetic survey, wing-type UAVs, for example Geoscan-101, and multi-rotor type, for example Geoscan-401 octocopter, can be used, but other quad- or hexacopter UAVs can also be used.

To process aerial photography materials carried out using a wing-type UAV, the use of an operating GNSS receiver base station operating in static mode with a recording resolution of 10 Hz is required. At the same time, to process the obtained aerial photography data, the UAV was used in combination with an existing GNSS receiver base station, which made it possible to accurately determine the coordinates and orientation of the received images.

The flight of the UAV, in this case Geoscan-101, was carried out in accordance with a pre-prepared flight mission. The flight mission was developed in advance and then adjusted on site taking into account the terrain features (see Fig. 1). The flight altitude was up to 390 meters above the surface of the earth (true height). The flight duration was up to 8 hours.

After the flights were completed, a digital map of the area was created (see Fig. 2). Image processing and creation of a map of the area were carried out on a portable workstation. Processing time was a little over 10 hours.

Based on the resulting digital map of the area, the UAV flight was planned; in this case, Geoscan-401 was used, with an overhead magnetometer (see Fig. 3). The flight, according to the flight instructions, took two days.

The anomalous component of the magnetic field is a time-constant magnetic effect from natural sources (geological bodies) or sources of artificial origin. The anomalous component of the magnetic field is calculated as the difference between the field modulus value measured by the operator at the shooting point and the field modulus value measured by the base magnetometer at the same or close time. Since the period of automatic measurements of the scalar magnetometer on the Geoscan-401 UAV was 0.1 s, and the period of the base magnetometer was 3 s, to correctly account for the daily cycle, the record from the base magnetometer was interpolated with the same step.

Next, the problem of sequential detailing of the location of the observatory was solved, consisting of the following two stages:

1. Detailed survey (mainly with a step of 10×10 m, i.e. the profile step and the step between profiles are 10 m) to study magnetic anomalies comparable to the size of the territory of the future observatory;

2. Micromagnetic survey (mainly with a step of 1×1 m) to study the areas selected based on the results of the previous survey for the construction of measuring pavilions.

Magnetogradientometry was performed with a MMPOS-2 proton Overhauser magnetometer. The vertical gradient of the magnetic field was measured at a height of approximately 2 meters above the ground, the distance between the sensors was chosen to be 50 cm. The height of the vertical gradient measurement was chosen to assess the gradient values in the immediate location of the instrument pedestals of the absolute and variometric pavilions, taking into account the future foundation.

In the area of ground-based magnetograditometric survey (mainly 100×100 m with a step of 10×10 m), the total number of magnetograditometry points was 11×11 = 121. Control measurements were performed for 6 points (according to the last profile), which amounted to 5% of the total volume and satisfied the general requirements for shooting (see Fig. 4).

The accuracy values for the anomalous component and vertical gradient of the magnetic field calculated from control measurements are 0.12 nT and 0.1 nT/m, respectively. This makes it possible to construct maps of the indicated characteristics with the most optimal section of isolines, respectively, 0.3 nT and 0.3 nT/m. It can be seen that at the control points the values of the anomalous component of the magnetic field are closer to each other than the values of the vertical gradient of the magnetic field; the latter do not exceed the first units of nT/m in absolute value, but have noticeable variability within this range.

Maps of the anomalous component of the Earth's magnetic field and the vertical gradient over the area of the ground survey stage are shown in Fig. 5.

For ease of interpretation, the map of the anomalous component is presented in a blue-white-red color scale with a transition in the area of average values. In the southwestern part of the area there is an area of relatively high values. However, the amplitudes of magnetic anomalies are small, and the horizontal gradient over almost the entire area does not exceed 0.5–1 nT/m. The values of the vertical gradient in some places exceed 1 nT/m. However, we can draw a general conclusion that this area fully satisfies the IAGA recommendations for choosing a location for deploying a geomagnetic observatory, according to which, in the area where observatory buildings are located, the values of horizontal and vertical gradients should, if possible, not exceed 2 nT/m in absolute value, and in a location where pedestals for absolute measurements and observatories of horizontal and vertical gradients will be located - 1 nT/m.

Thus, based on the results of the ground survey stage, two areas with an area of 10x10 m were selected to perform micromagnetogradietometry and make a final conclusion about the suitability of the areas for placing observatory pavilions (see Fig. 5).

Finally, the final stage of micromagnetogradientometric survey (mainly with a step of 1 × 1 m) in selected areas 30 m from each other made it possible to verify their suitability for the placement of future pavilions A and B of the magnetic observatory. The maps show no significant magnetic anomalies. Within the areas in the zones of the most undisturbed anomalous field, places were chosen for two pedestals of the absolute pavilion and one pedestal of the variometric pavilion, as shown in Fig. 6.

Thus, the goals set to significantly increase the accuracy for determining the optimal location for installing the absolute and variometric pavilions of the magnetic observatory on the territory of the field under study, as well as reducing the time of surveys through the use of different types of promising UAVs, were achieved in full.

The examples presented here are intended to provide a better understanding of the principles of the present method for determining the location of a magnetic observatory in the territory of the field under study, and not to limit its scope to such specifically given examples.

List of sources used:

1. Marjan Izadi et al. “A GIS-based site selection experience for the construction of a geomagnetic observatory in Kerman Province, Iran” // Geophysical Prospecting, 2017, 65 (S1), 237–245 doi: 10.1111/1365-2478.12568

2. Application CN 109901225 A, publ. 06/18/2019, Beijing Chuang Chuang Resources Technology Co Ltd.

3. Book by the author Karl A. Wienert “Notes on geomagnetic observatory and survey practice” UNESCO, Paris 1970

Claims (8)

1. A method for determining the installation location of a magnetic observatory on the territory of the field under study, characterized by the fact that aerial photography of the selected area is carried out using an unmanned aerial vehicle (UAV), based on the results of which a digital map of the area is constructed, then an area aeromagnetic survey is carried out using a UAV with an overhead magnetometer, carry out a detailed areal aeromagnetic survey of the site using a UAV with an overhead magnetometer, based on the results of aeromagnetic surveys, build a digital map of the anomalous component of the Earth's magnetic field of the site, then determine the areas where the magnetic component of the Earth's field changes most smoothly in a given direction, conduct a detailed ground-based magnetogradiometric survey of the selected areas , based on the results of a ground-based detailed magnetic survey, two areas are identified where there are no significant magnetic anomalies, after which a ground-based micromagnetic survey is carried out in relation to the selected areas to determine the specific construction site of the absolute and variometric pavilions of the magnetic observatory. 2. The method according to claim 1, characterized in that an aircraft-type UAV is used to conduct aeromagnetic magnetic surveys. 3. The method according to claim 1, characterized in that a multi-rotor UAV is used to conduct aeromagnetic magnetic surveys. 4. The method according to claim 3, characterized in that the multi-rotor UAV is made in the form of a quadcopter, hexacopter or octocopter. 5. The method according to claim 1, characterized in that when carrying out ground-based magnetic surveys, a proton Overhauser magnetometer is used. 6. The method according to claim 1, characterized in that before carrying out ground magnetic survey, areas measuring 100 by 100 meters are selected. 7. The method according to claim 1, characterized in that a detailed ground-based magnetic gradient survey of selected areas is carried out with a step of 10 by 10 meters. 8. The method according to claim 1, characterized in that ground-based micromagnetic survey is carried out with a step of 1 by 1 meter.