RU2150721C1 - Method of control over stressed state of seismic region - Google Patents

Abstract

FIELD: mining industry, removal of stressed state over territories having plants producing soda and potash fertilizers. SUBSTANCE: liquid is pumped into deep water-bearing horizons. Excessive brines of potash production and chlorine-calcium sewage of soda production specially prepared and separated from suspended solid phase are used as pumped liquid. Value of seam pressure is measured after start of pumping. Underground tremors are recorded, pressure on well-head is being reduced after their appearance till tremors stop. Then pressure on well-head is raised again till tremors start and so on. EFFECT: enhanced functionality of wells by their usage for utilization of industrial sewage.

Description

 The present invention relates to mining and can be used to relieve the stress of seismic regions in the territory of which there are enterprises for the production of potash fertilizers and soda.

 In recent years, earthquakes have become more frequent in the Bereznikovsk-Solikamsk industrial region. On January 5, 1995, an earthquake of up to 5 points on the Richter scale in Solikamsk occurred, which resulted in the destruction of part of underground mining and surface structures. On October 9, 1997, an earthquake occurred at the epicenter of up to 4 points in the city of Berezniki. Due to the fact that under the residential development of these cities there are voids formed as a result of underground mining, it is advisable to conduct earthquake management in this area by artificially removing deep stresses.

 The noted earthquakes must be classified as excited as a result of the integrated impact on the subsoil of the Kama reservoir, the work of the Usolsky, Bygelsky and Solikamsky water intakes, the exploitation of the Yurchuk, Belsky, Chashkinsky, Siberian and Unvinsky oil fields, and the development of the Verkhnekamsk potash salt field.

 The increase in groundwater pressure in the reservoir zone depends on the rise in the level of surface water, the filtration characteristics of the rocks and hydrogeological conditions. Of particular importance is the spread of groundwater backwater. When filling a reservoir, the most significant increase in reservoir pressure in deep aquifers occurs when they are hydraulically connected to surface and ground waters. In the absence of such a relationship, reservoir pressures will increase to a lesser extent only due to an increase in the load on the aquifer.

 The fact that the most significant earthquakes occur in the areas of reservoirs, where the water level reached 100 m or more, indicates the significant role of the increase in groundwater pressure in the mechanism of such earthquakes.

 The increase in seismic activity in the Denver area (Colorado, USA), which began after the injection of sewage into the absorbing well, gave an impetus to the study of excited earthquakes associated with direct impact on deep aquifers [1].

 A well with a depth of 3671 m uncovered in the interval 3638-3671 m fissured Precambrian gneisses, where sewage was discharged. Water injection was started on March 8, 1962, and from the end of April, seismic stations began to record weak tremors. Subsequently, the dependence of the frequency of earthquakes on the amount of injected water was established. With a temporary cessation of injection, the number of shocks decreased sharply. A correspondence was also observed between seismic activity and water pressure at the bottom of the well. The centers of earthquakes determined by instrumental data were localized in a small zone and had a depth of 4.5 - 5.5 km.

 Excited earthquakes associated with the exploitation of oil fields were recorded at the Rangeli fields (Colorado, USA), Grozny (Russia), etc. The mechanism of such earthquakes is primarily associated with a decrease in reservoir pressure during oil production and its subsequent recovery in the event of water injection during outflow waterflooding. Such a change in the hydrogeological situation affects the frictional resistance in seismogenic faults [2].

 To regulate earthquakes in the USA at the Rangely oil field in 1969-1973 water was injected into the formation and drainage of the formation. For this purpose, four wells were used with a depth of about 2 km. The dependence of the monthly number of tremors on the mode of operation of the wells was established. The number of shocks decreased after the injection of water was replaced by pumping. The foci were concentrated near the existing fault in the zone of the highest reservoir pressure. The critical value of reservoir pressure at which shocks were excited was 257 bar. The experiments in the Range showed that the stress state in the centers of earthquakes under the influence of water pressure is gradually removed - there is a discharge of stresses. Similar experiments were conducted in Japan, in the seismic region of Matsushiro, where water was pumped into a 1800 m deep well.

 A known method of controlling the stress state of a seismic region, including pumping fluid into deep aquifers located in this region [1, p. 64]. This technical solution is taken as a prototype.

 The disadvantage of this method is the low functionality of the wells. Deep expensive wells are used only to relieve the stress state of a seismic area.

 The aim of the invention is to increase the functionality of the wells by using them for the disposal of industrial effluents.

 The goal is achieved in that as the injected liquid, specially prepared, excess brines of potash production and calcium chloride wastewater from soda production are separated from the suspended solid phase.

 The method is as follows.

 On a site free of housing and industrial enterprises, located in a seismic area, wells are drilled to deep aquifers that lie at depths of about 2 km. The use of aquifers lying at depths of more than 2 km is technically difficult, and less than 2 km may not lead to a change in the stress state of the mountain range. After casing the wells with pipes and perforating them at the level of these horizons, fluid injection begins in them.

 As the injected liquid, specially prepared excess brines of potash production and (or) calcium chloride wastewater from soda production are used. Special preparation consists in separating brines, wastewater from soda production from suspended solids and adding well-known corrosion inhibitors, such as AKS-1, Kameliks 1116x and others, to prevent casing corrosion.

 After the start of sewage injection, the reservoir pressure is constantly recorded. Immediately after the initiation of tremors, the pressure at the mouth of the injection wells is gradually reduced until the tremors are completely stopped. Then, the pressure at the wellhead is again increased before the start of the tremors and, thus, the stress state in the seismic region is gradually relieved under the influence of wastewater pressure by stress relief.

 The change in rock permeability when passing through samples of the Yasnaya Polyana horizon, taken from a depth of about 2 km, of soda wastewater was studied at the PermNIPIneft Institute. The data obtained indicate a significant decrease in the water permeability of the samples both when filtering fresh water through them and industrial waste water. When pumping wastewater from the soda production sludge storage facility, a lower attenuation rate and a higher relative water permeability are observed than in experiments with fresh water. Similar results were obtained by filtering excess brines of potash production. The increase in water permeability is caused by coagulation of the clay fraction of sandstones when mineralized solutions are passed through them.

 An example implementation of the method. Wells NN 1-OP and 2-OP were drilled in the Durinsky trough near the deep-seated sub-latitudinal strike fault. Filters in the wells were installed in the interval of occurrence of the Franco-Famennian aquifer at a depth of 2.1-2.5 km.

 Experimental hydrogeological work carried out at these wells included trial and experimental pumping of produced water and experimental pumping of these waters, temporarily stored during pumping into sedimentation tanks.

 As a result of pilot injections, an aquifer capacity of 211 thousand cubic meters was established. m per year. Due to the fact that the required productivity of 900 thousand cubic meters. m per year was not achieved, the wells were mothballed.

 To regulate the stress state of the seismic region, the wells are re-mothballed and their productivity increased by hydraulic fracturing. Then they start pumping excess brines from the sludge storage facility of the Fourth Bereznikovsky Potash Mine Administration. After the start of injection, the reservoir pressure is constantly recorded. Immediately after the initiation of tremors of 1-2 points on the Richter scale, the pressure at the wellhead is gradually reduced until the tremors cease. Then, the pressure at the wellhead is raised again before the start of the tremors and so on.

 Literature.

 1. Kissin I.G. and others. Underground hydrosphere and seismic processes. Sat: Fundamentals of hydrogeology. Geological activity and history of water in the bowels of the earth. - Novosibirsk: Nauka, 1982, p. 57-64.

 2. Smirnova M.N. Excited earthquakes in connection with the development of oil fields (on the example of the Starogroznensky earthquake). Sat: The influence of engineering activity on the seismic regime. - M .: Nauka, 1977, p. 128-141.

Claims (1)

 A method for controlling the stress state of a seismic region, including pumping liquid into deep aquifers lying at depths of about 2 km, located in a seismic region, characterized in that specially prepared, that is, separated from the suspended solid phase with the addition of corrosion inhibitors, are used as the injected liquid , excess brines of potash production and calcium chloride wastewater from soda production, after the start of injection, the formation pressure is constantly measured eniya tremors and registration immediately after the excitation force tremors 1 - 2 on the Richter scale pressure at the mouth of wells is gradually reduced until the termination shock, then the pressure on the mouth of the wells again increased prior to the shock and so on.