SU1730439A1 - Method of operating geothermal circulation systems - Google Patents

Abstract

The invention relates to a technology for extracting and using the Earth's deep heat, namely, to prevent the deposition of CaCO3 in the underground reservoir of thermal thermal circulation systems containing carbonate rocks. The purpose of the invention is to eliminate the use of chemical agents in restoring the filtration characteristics of a carbonate-containing formation. For this purpose, geothermal water is extracted from the reservoir by production wells. Heat is taken by unearthly heat equipment and chilled water is pumped through injection wells. When the filtration properties of the reservoir deteriorate, injection wells are transferred to production, and production wells - to injection wells. It is possible to change the functions of the wells repeatedly. The time of the wells in the new mode increases, but not more than twice the time of the wells in the old function. The method allows to select the appropriate temperature and pressure to dissolve the CaCO3 deposits. 1 il. (L

Description

The invention relates to the technology for extracting and using the Earth's deep heat, namely, to restore the filtration properties of underground reservoirs of geothermal circulation systems (GVS) of energy supply containing carbonate rocks.

There is a known method for preventing the deposition of CaCO3 and CaS04 in wells, surface equipment, and also in oil field reservoirs by mixing groundwater with a solution of inorganic polyphosphates, carbon dioxide or inhibited hydrochloric acid,

Due to the large volumes of geothermal water recovery, the use of these

The methods of protecting the GCC are impractical because of the need for a significant consumption of reagent, the creation and operation of reagent assets, and because the contamination of the underground reservoir with a foreign substance is associated with unknown, usually negative consequences.

Closest to the proposed technical essence and the achieved result is a method based on maintaining carbon dioxide equilibrium in water by selecting the appropriate temperature and pressure. The method can be used to protect the ground part of the energy complex from formation

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CaCO3 deposits, where it is possible to influence the parameters of geothermal water. In the underground part, the ability to influence the parameters of geothermal water is limited. Therefore, when injecting cooled geothermal water due to the higher solubility of CaCO3 at low temperatures than at high temperatures, the carbonate component of the rock is leached at the bottom of the injection well. As geothermal water moves along the underground reservoir, as a result of heating, solid CaCO3 phase is released on the pore surface of the rock, reducing its filtration properties, which leads to the need to attract additional power and geothermal water injection.

The purpose of the invention is to increase the efficiency of the system by eliminating chemical reagents to restore the filtration properties of the underground collector of the geothermal circulation system.

The goal is achieved by the fact that in a known method of operating geothermal circulation systems, including the extraction of hot geothermal water from a formation by production wells, heat extraction by surface thermal equipment and injection of cooled water into the formation through injection wells, to restore the carbonate-containing formation’s filtration characteristics when they deteriorate injection wells are put into production wells, and production wells are put into the water injection mode, with the modes of operation of the well n is repeated many times, while the time of the well in the new mode is increased, but not more than two times relative to the time of the well in the previous function. Switching the injection well to the production mode leads to the fact that acidic reservoir waters with an increased partial pressure of carbon dioxide begin to move to its bottom, which dissolve the solid CaCo3 film formed on the surface.

When injecting spent geothermal water into the formation, simultaneous heating of water, dissolution of carbonate-containing substances in it and redeposition of these substances in the formation occur. It has been established that if water is not saturated with carbonates, then in the initial period of water-rock interaction, the rock dissolves rather quickly, then as it dissolves, the dissolution rate decreases, and when a concentration equal to solubility is reached, the dissolution stops. Further heating of the water leads to the release of

solid phase CaCO3. If water is saturated with CaCO3, then heating it immediately leads to crystallization of CaCO3. Studies have shown that the rate of dissolution of carbonates under reservoir conditions is two times lower than the rate of deposition of the solid CaCO3 phase. It follows that, ceteris paribus, the process of dissolving the re-deposited substance lasts two times longer than the process of its deposition. Therefore, when changing the function of the wells, the execution time of each next function should be increased no more than by a factor of only. If we increase the execution time of the new function by more than two times, the well, earlier

0 The former operational, the new function of which is the injection of water into the formation, is slammed more than twice. It will be more difficult to ensure the normal operation of wells.

5 Thus, the need to increase the time for performing the function of wells when switching is dictated by the fact that the rate of dissolution of the redeposited substance is two times less than the speed of its

0 crystallization.

The drawing shows the scheme of the GCC, which implements the proposed method.

Underground collector 1 is connected by wells 2 and 3 to the ground-based energy complex 4, at the outlet of which pumps for heat transfer pumps 5 are installed. Complex 4 and pumps 5 are enclosed by bypass pipelines 6.7 and equipped with valves 8-11,

The geothermal water of increased mineralization through well 2 enters the ground-based energy complex 4. After heat recovery, the cooled water is pumped through pumps 5 by injection

5 well 3 into the underground reservoir 1. The injection pressure has a strictly defined value and depends on the performance of the GCC and the permeability of the reservoir. With the deterioration of permeability due to redeposition of substances, the injection pressure increases. As the injection pressure increases, well 2 is switched to injection mode by means of valves 8-11, and well 3 is switched to production mode.

5 In the new mode, well 2 is injection, 3 is operational. The re-deposited substance in the bottomhole formation of well 3 will begin to dissolve and be carried with the water to the surface. The operating time on this mode should be more than

operating time on the first mode, but not more than twice, etc.

The existing experience of using GCC in the USSR is extremely small. The clogging of wells and reservoirs has not been studied. The practice of injecting water to maintain pressure in oil-bearing reservoirs can be used only partially, since in the event of an increase in the resistance of the reservoir due to clogging of the reservoir, it is fractured. Such a method is not acceptable for restoring GCC functionality. In connection with the foregoing, we show the possibility of its use in the following example.

In the Stavropol Territory, at the Kasulinskoye field, geothermal water is extracted with a temperature of 160 ° C and salinity above 100 g / l. The collector consists of calcium carbonate and dolomite. It is proposed to pump water with a temperature of 40-50 ° C. The solubility of CaCO3 at this temperature is approximately 200 times higher than at 160 ° C PRsOCO3 (40 ° C) PRsOCO3 (160 ° C) 31.2, 175-10 10 182. Obviously, under these conditions, as far as from the bottom of the well increase in temperature, especially at the initial moment of field operation, when the underground collector is uniformly heated, the deposition of CaCO3 will occur at a small distance from the bottom of the well. When the reservoir potential draws down as it cools, CaCO3 deposition will take place at an ever greater distance from the well. Alternating well functions will eliminate the use of reagents and eliminate the cost of conducting reagent treatments for wells.

The proposed method of operating geothermal circulation systems provides the following advantages compared with existing methods: eliminates the costs of creating a reagent farm, its operation and reagents; environmentally friendly; creates conditions for uniform cooling of the underground reservoir, which reduces the likelihood of geological disasters.

The following economic effect is expected from the use of carbonate prevention in the underground reservoir of geothermal circulation systems.

According to Dagneft, the average cost per acid treatment in the well bottom zone, taking into account the cost of acid, equipment depreciation and staff salaries, is 25,000 rubles.

The basic option is that in order to ensure the performance of the GCC, one acid treatment of the injection well per year is performed. Let us also assume that the cost of 5 new rounding of wells, which allows switching the functions of the wells, is 27,000 rubles. If we assume that the service life must be at least 27 years, then the annual expenditure for the conversion of the GCC is 10 em 1000 rubles. In this case, the annual economic effect from using the proposed technical solution is 24,000 rubles. This value is minimal because the number of acid treatments may be more than one per year. At the same time, the cost of acid for treating a geothermal well must be significantly higher because part of the acid is neutralized when interacting with the rock before it approaches the clogging zone. The depth of geothermal wells and their productivity is much higher than oil wells. Last circumstance requires tubing

5 equipment more power.

The report of the research and production association for the use of the deep heat of the Earth, Soyuzburggeothermi, presents the results of field research

0 at the Mostovskoye field of geothermal waters in the ST and 2T wells, confirming the effectiveness of the use of the proposed technical solution.

An injection with a flow rate of 1500 m / day was produced into the ST well, well. 2T - mining. The content of suspended substances in water is 0.001 g / l, the collector has carbonate cement up to 1 ° / o, the mineralization of water is not higher than 1.5 g / l. After 15 days of operation at a potochnoe injection pressure of 2.5 MPa, the flow rate of the ST well decreased by half. After that, another pump was connected, the pressure was increased to 4.0 MPa and the flow rate was raised to the initial one. Further download, length 15

5 days, was accompanied by the same decrease in the performance of the ST well.

The decrease in well productivity can only be explained by a change in the permeability of the reservoir, in which

Due to the very low content of mechanical impurities, chemical clogging obviously plays a major role. After that, the well ST was transferred to the selection mode. The initial debit, which was

5 3168 m3 / day, within an hour, decreased to 800 m3 / day, which is lower than the flow rate of the well before injection. This once again confirms that the reservoir penetrability decreased. Recovery of well production and even its increase to 1700 m / day occurred

after 3 months of operation of the ST in the selection mode. The latter means that the kinked zone of the reservoir has regained its reservoir properties, moreover, permeability has increased.

Thus, the experiment confirms the possibility of implementing the considered technical solution.

Claims (1)

The invention of the method of operation of geothermal circulation systems, including the selection of hot geothermal water from the reservoir production wells, heat extraction by ground thermal equipment and injection of chilled water into the reservoir through injection wells, characterized in that, in order to eliminate the use of chemical agents for the recovery the filtration characteristics of the carbonate-containing formation, with deterioration of the filtration properties of the formation, injection wells are transferred to production wells, and production wells into water injection mode, the wells operating modes being repeated many times, while the wells operating time in the new mode increase, but not more than than twice the well execution time in the former functions. Dissolution of CaCO3 щщщщг SASO attack