RU2557371C1 - Method determining size of depletion of saline domes during construction of underground gas storages - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: method includes use of two feeding electrodes. The first electrode is lowered in the work well. The second electrode is located on surface as per infinity circuit. Using two surface sensing electrodes installed in the vicinity of the first feeding electrode the potentials difference is measured in the vicinity of the first feed electrode, the feeding electrode is lowered on the salt chamber bottom, and after current supply the potentials are measured using the movable sensing electrode along at least four straight profiles uniformly distributed along the azimuth, each profile length is 50 m, spacing along profile is 2 m maximum. Abrupt increasing of the measured potential upon crossing the border between non-homogeneous mediums of the salt chamber walls is recorded. Length of the chamber projection on the day surface as per the appropriate profile is determined according to points of potential separation (abrupt increasing) measure for this profile, and characterising border of crossing of the non-homogeneous mediums in the saline dome.

EFFECT: possibility to determine size of the salt chamber in the saline dome using the charge method.

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Description

The invention relates to the field of field electrical exploration and is used to estimate the size of the chamber in a salt dome formed during the construction of underground gas storages (UGS), due to the dissolution of salt by water supplied through tubing to the chamber.

During the construction of underground gas storage in a salt dome through a special working well (PC), a continuous supply of water to the walls of the salt dome is ensured, whereby it dissolves with the creation of a saturated salt solution (brine).

Currently, to locate the shape of the chamber, on the basis of which its dimensions are determined, the acoustic method is applied, which requires extraction of the tubing from the working well. This method of location, in principle, is not able to provide an operational assessment of the size of the camera.

The inventive method provides that the location of the camera is carried out by the charged body method (charge method in a modification of the charged body method) (MZT) (Instructions for electrical exploration. - L .: Nedra, 1984, S. 19-26).

It is known that the charge method is used in hydrogeology to determine the direction and speed of groundwater movement in the modification of isolines of measured potentials. In accordance with the methodological recommendations, the feed electrode is immersed in the well to the middle of the aquifer, the second grounding is carried at a distance of about 10-15 times the immersion depth of the current electrode, and sodium chloride is used as the electrolyte.

The processing of the results consists in constructing the isolines of the potential, determining the maximum displacements of the isolines, the directions of their displacements, as well as constructing graphs for determining the speed in accordance with the methodology (Instructions for electrical exploration. - L .: Nedra, 1984, p.19-26).

The known method is intended to determine the direction and actual speed of groundwater movement and is not intended to calculate the size of underground salt chambers filled with brine, the resistivity of which varies from a high of 10 ⁷ Ohm · m to a value of about 0.01 Ohm · m s the increase in the size of the chamber due to its filling with brine.

In this case, the chambers have the boundaries of the transition from the liquid to the dome walls (medium heterogeneity), when measuring the potential of which there is a “separation” of the potential — a sharp increase in resistivity.

There is a method of electroprofiling surface inhomogeneities by the charge method, based on recording distortions of the charge field when crossing the boundary of these inhomogeneities (Instructions for electrical exploration. - L .: Nedra, 1984, p.24).

The known technique is designed to determine surface inhomogeneities on a plane and does not provide a determination of the spatial dimensions of underground salt chambers.

There is a known method of electrical exploration, which includes the use of two supply electrodes, the first supply electrode immersed in the ground and the second supply electrode placed on the ground at a sufficient distance (practical infinity), and two measuring electrodes placed on the ground in the vicinity of the first supply electrode, with the help of which the potential difference is measured in the vicinity of the first supply electrode, while the supply electrode is made in the form of a rod, which is immersed in the ground while the measuring electrodes are kept stationary, as the rod is immersed, the ratio of the potential difference on the measuring electrodes and the current in the supply electrode circuit is measured, and the depth of immersion of the rod, according to the potential difference on the measuring electrodes and the current in the first supply electrode, is determined taking into account the immersion depth rod resistivity of rocks crossed by the rod (RF Patent No. 2466430, prior. 12.01.2011, publ. 11/10/2012).

The method is as follows. As the first feed electrode, a penetrator rod is used, which is a composite rod, while it plays the role of a feed electrode in a three-electrode installation, similar to the installation for ground-based electrical profiling with a three-electrode installation. The measuring electrodes are located at a distance comparable to the penetration depth of the penetrator. As the composite rod immerses, it will cross the rock with different electrical resistivity, which will affect the value of the potential difference between the measuring electrodes. As a result, the curve of the relationship between the potential difference on the measuring electrodes and the immersion depth of the composite rod will carry information on the electrical conductivity of the rocks crossed by the composite rod. At the same time, there is no influence of equivalence, that is, an unambiguous interpretation of the measurement data is possible, since, in contrast to traditional ground-based methods of electrical exploration, there is an additional independently measurable quantity - the immersion depth of the rod.

Thus, the known method, using the method of ground-based electrical profiling with a three-electrode installation, solves the problem of measuring the electrical conductivity of rocks crossed by a composite rod along the depth of the rod in the well.

It is not possible to apply the known method to solving the problem of determining the size of the salt chamber, since it provides for obtaining information on the vertical component of the intersected rocks and does not provide a determination of the spatial dimensions of underground salt chambers.

The objective of the proposed method is to expand the scope of electrical exploration methods using the charge method by applying it to calculate the size of an underground salt chamber in a salt dome formed during the construction of underground gas storages (UGS), due to the dissolution of salt by water supplied through tubing (tubing) into the chamber, without lifting them to the surface, thereby increasing efficiency and reducing the complexity of research.

This problem is achieved by the fact that in the method for determining the size of the production of salt domes during the construction of underground gas storages, which includes the use of two supply electrodes, the first supply (current) electrode immersed in the PC and the second supply electrode placed at a sufficient distance on the ground (" infinity "), and two measuring electrodes placed on the surface of the earth in the vicinity of the first supply electrode, with which they measure the potential difference in the vicinity of the first unlike the prototype, the first current electrode is lowered onto the sole of the salt chamber and after the current is started, the potentials are measured using a movable measuring electrode along at least four linear profiles uniformly distributed in azimuth, with a length of each profile of 50 m, in increments of a profile of not more than 2 m, while recording a sharp increase in the measured potential when crossing the boundary of inhomogeneous media that make up the walls of the salt chamber formed due to the dissolution of salt by water in salt SG dome, and a saturated salt solution (brine). The projection length of the camera on the day surface by the corresponding profile is determined by the potential separation points (sharp increases), measured by this profile and characterizing the transition boundary of inhomogeneous media in the salt dome.

Figure 1-4 shows the distribution of potentials over four profiles according to the results of electrometry in a PC;

Figure 5 presents the arrangement of profiles on the day surface above the salt chamber.

Figure 6 shows the contour of the projection of the salt chamber on the day surface obtained according to the proposed method.

According to the proposed method, the first current electrode 1 is lowered to the bottom of the salt chamber 2. On the surface of the earth, the second supply electrode 3 is placed at a sufficient distance ("infinity"). One measuring electrode 4 is placed stationary in the vicinity of the current electrode 1. The current electrode 1 is lowered into the PC 6. The second measuring electrode 5 is moved along the surface along the profiles 7 (Fig. 5).

The walls of the salt chamber 8 form a transition of the boundaries of inhomogeneous media. Pos. 9 - tubing in PC 6.

After the electrode 1 is lowered into PC 6, a current is passed through it and on the surface a second measuring electrode 5 measures the potentials of the electric field according to the charge method, at least 4 linear profiles 7 uniformly distributed in azimuth, with a profile length of 50 m, with a step along the profile of not more than 2 m. At the same time, sharp increases in the measured potentials are recorded when the boundary of inhomogeneous media composing the walls of the salt chamber 8 formed as a result of the dissolution of the salt supplied by the tubing 9 to the PC 6 6 in the salt dome is recorded, and saturated salt (brine) solution (Figs. 1-4).

The length of the projection of the camera onto the day surface by the corresponding profile is determined by the separation points (sharp increase) of the potential measured by this profile (Fig.6).

When the current electrode 1 is lowered to the bottom of the salt chamber (PC bottom) with the ground electrode 3 on the earth’s surface is set to “infinity” and the current is turned on, the entire area of the salt chamber becomes charged and acquires an abnormally low potential U, which reflects the almost equipotential nature of the volume distribution camera (Fig.1-4). When crossing the boundary of inhomogeneous media that make up the walls of the salt chamber 8, which is formed due to the dissolution of salt by water supplied via tubing 9 to PC 6 in salt dome 2 and saturated salt solution (brine), anomalous potential Pan will be observed. As mentioned earlier, with the applied technology for the construction of underground gas storage in a salt dome having a high electrical resistivity (resistivity) of 10 ⁷ Ohm · m, a chamber filled with brine appears, the resistivity of which decreases to a value of about 0.01 Ohm · m with increasing size cameras.

Thus on the Earth's surface at the transition boundaries of the brine to the chamber walls will be observed region of _{the An} anomalous building U, whose shape will be determined by the horizontal camera projection onto the Earth's surface (6), wherein the PR-1, Ex-2, Ex-3 , Pr-4 points on the profiles, indicating the boundaries of the contour of the salt chamber, where, according to the measurement results, abnormal values of the potential U _an were observed.

An example of a practical implementation of the method is shown in figures 1-4.

The method is carried out using electrical exploration equipment of the type SVP-74 (Instructions for electrical exploration. - L .: Nedra, 1984, p.20).

The equipment is connected by a wireline cable to the current electrode 1, lowered into the salt dome PC and provides the whole complex of measurements carried out using a standard set of supply and measuring electrodes.

Figure 1-4 shows that the measured anomalous potentials U _en for four profiles were observed at distances along the length of the profiles: 36 m, 8 m, 40 m, 8 m, the points of which on the contour of the projection of the camera onto the day surface marked the boundaries of the salt dome .

Claims (1)

A method for determining the size of the production of salt domes during the construction of underground gas storages, which includes the use of two supply electrodes, a first supply electrode immersed in a PC and a second supply electrode placed at a sufficient distance ("infinity") on the surface of the earth, and two measuring electrodes, one of which is stationary, placed on the surface of the earth in the vicinity of the first supply electrode, with which the potential difference is measured in the vicinity of the first supply electrode, o characterized by the fact that they lower the first supply electrode to the sole of the salt chamber and, after starting the current, measure the potentials with the help of a movable measuring electrode along at least four linear profiles uniformly distributed in azimuth, with a profile length of 50 m, with a profile step of no more than 2 m, while recording a sharp increase in the measured potential when crossing the boundary of inhomogeneous media that make up the walls of the salt chamber formed due to the dissolution of salt by water in the salt dome, and saturated solution of salt (brine), as a result of measurements, the length of the projection of the chamber onto the day surface by the corresponding profile is determined by the potential separation points (sharp increases), measured by this profile and characterizing the transition boundary of inhomogeneous media in the salt dome.

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