Method and system for an environmentally and technically correct decommissioning of a salt rock caves

Abstract

The present invention pertains to the field of methods and systems for filling, sealing and abandoning (decommissioning) caves built in salt rock, especially one located on an inhomogeneous salt structure (with the presence of layers of porous / permeable rock within the salt layer), or close to geological faults, or in which the cave roof has collapsed, which can take place simultaneously and integrated with the decommissioning of the facilities on the site of the venture. The present invention is more particularly used in the decommissioning of civil constructions on sites for production of rock salt, and / or its storage, by the dissolution mining method, in which the cave must be filled by backfilling it with solid material, the recycled solid material being generated by means of the comminution of demolition waste from the decommissioned civil constructions of the facilities of the venture (on site), or from other areas, via a mobile recycling plant (crushing / grinding / sifting) on site or not.. The larger grain size waste (gravel) is placed at the bottom of the salt rock cave and the smaller grain size waste (sand) is placed at the end of the salt rock cave to fill in the voids and gaps.

Description

“ENVIRONMENTALLY AND TECHNICALLY CORRECT METHOD AND SYSTEM FOR DECOMMISSIONING A SALT ROCK CAVE” FIELD OF THE INVENTION

[0001] The present invention finds its field of application among the methods and systems of filling, sealing and abandoning (decommissioning) caverns built in saline rock, especially those located in a non-homogeneous salt structure (with the presence of layers of porous / permeable rocks within the salt layer), or close to geological faults, or even those that have had a cavern ceiling collapse, which can occur simultaneously and integrated with the decommissioning of the facilities at the project location.

[0002] More particularly, the present invention is used in the decommissioning of civil construction in rock salt production and / or storage locations, by the dissolution mining process, where there is a need to fill the cavern with solid material, the recycled solid material being generated through the comminution of demolition waste from the decommissioned civil construction facilities of the project (on-site) or other areas, via a mobile recycling plant (crushing / crushing / screening) on-site or not. The larger-grained waste (gravel) is inserted at the bottom of the CRS and the smaller-grained waste (sand) is inserted at the end of the CRS filling to fill voids and flaws. BACKGROUND OF THE INVENTION

[0003] Rock salt, a rock composed primarily of halite (NaCl), is one of the most versatile raw materials, used in the manufacture of chlorine, caustic soda, hydrochloric acid, and sodium bicarbonate. It is also used in various products in the pharmaceutical, personal hygiene (soap, detergent, and toothpaste), clothing, footwear, and construction pipe industries. Furthermore, it is widely used in the textile, military, paper, pulp, and glass industries, and in water treatment.

[0004] Conventional rock salt extraction can be done in two ways. When the mineral layers are shallow, the rock salt is mined underground using machines. However, when the layers are deep or vertical, the rock salt is extracted through dissolution mining. Thus, it can be summarized as follows: an access well is constructed; water is injected; the rock salt is then dissolved and pumped to the surface for processing. However, these processes have advantages over the process of obtaining rock salt through evaporation and purification of seawater, as they offer a higher degree of purity and concentration (10 times greater).

[0005] It is worth mentioning that the dissolution mining process, which consists of the solubilization or dissolution and removal of the chemical constituents of the saline rock by the action of water (fresh or saturated in NaCl), is called leaching [(PEREIRA JC, Solution Mining Research Institute (SMRI). Research Report RR2012-03. Common Practices – Gas Cavern Site Characterization, Design, Construction, Maintenance, and Operation.2012)], which forms a void in the host rock, called a Saline Rock Cavern (SRC).

[0006] In detail, the process begins with the drilling of one or more access wells, and the rocks are drilled until reaching the region near the top of the cavern, which will be formed by the leaching process. The drill string is then removed to lower a steel pipe (casing), which will be cemented to provide a seal between the rock layers traversed by the drilling.

[0007] Two concentric columns of pipes are lowered near the bottom of the well. One is used for water injection and the other for brine return. The innermost column, with a smaller diameter, is slightly longer (tens of meters) than the outer column to optimize rock salt production.

[0008] The production of rock salt begins, as well as the generation of CRS with the circulation of fresh water or sea water, with the purpose of dissolving the walls of the salt rock. It is important to note that the higher the temperature and flow rate of the injected water, the more efficient the salt dissolution will be. As the injected water becomes saturated, it is replaced by new, unsaturated water. This process of circulating high flows of unsaturated water through the salt dissolves large amounts of it, creating a large space filled with water, which forms the CRS.

[0009] Once the useful life of rock salt extraction from the deposit has been reached, due to the intrinsic characteristics of the saline rock, such as negligible porosity and permeability, and mechanical compressive strength similar to concrete (POIATE Jr E. Rock Mechanics and Computational Mechanics for Oil Well Design in Salt Zones. Doctoral Thesis, Pontifical Catholic University of Rio de Janeiro, PUC-Rio, December 2012), the CRS generated by the leaching process can be used to store, for example, compressed air, hydrocarbons, hydrogen, tailings, and others (CROTOGINO et al. HUNTORF CAES: More than 20 Years of Successful Operation, Solution Mining Research Institute, Spring Meeting, Orlando, Florida, USA, 2001; US ​​DEPARTMENT OF ENERGY, Strategic Petroleum Reserve Storage Sites. Available at: http: / / www.fossil.energy.gov / programs / reserves / spr / spr-sites.html; EVANS DJ, CHADWICK RA (EDS).Underground gas storage: Worldwide experiences and future development in the UK and Europe. The Geological Society, London, Special Publication, 313, 93-128. 2009; LORD, A. S. Overview of geologic storage of natural gas with emphasis on assessing the feasibility of storing hydrogen. SAND2009-5878. Sandia National Laboratories. 2009; MUNSON et al. Approach to first principles model prediction of measured WIPP (Waste Isolation Pilot Plant) in-situ room closure in salt. Tunneling and Underground Space Technology, 5, 135, 1990; VEIL et al. Disposal of NORM-contaminated oil field wastes in Salt Caverns. United States: N. p., 1998. Web.doi:10.2172 / 808431). .

[0010] Todavia, o uso da CRS para a finalidade de armazenamento somente é possível desde que tenham sido realizados previamente estudos e, além disso, It is prudent to verify the dimensions of the CRS via sonar to analyze actual conditions using appropriate global technical standards and recommendations. Otherwise, an abandonment plan for the CRS and access well should be implemented, which should include risk mitigation measures, provide for the removal of equipment, sealing of the well, and monitoring of the region to identify the occurrence of subsidence over time.

[0011] According to API-1114 (American Petroleum Institute (API). Recommended Practice 1114. Recommended Practice for the design of solution-mined underground storage facilities. Second edition, January 2013), in the state of the art, the abandonment of the CRS at the end of its operating cycle must be carried out in accordance with current regulations. In the absence of regulations, the following procedures can serve as guidance.

[0012] First, the stored product must be removed by injecting brine into the cavern, if the CRS that produced rock salt is to be used for storage. Wellhead equipment and all overhead lines should be removed, if possible.

[0013] After removing the equipment and materials, the interior of the production column should be filled in the following positions: place a mechanical plug (bridge plug) near the base of the production column, and a bottom plug (bottom plug) above it. The top plug should be positioned approximately 15 m above the salt layer; in areas with a water table, install bottom and top plugs 30 m below the base and 60 m above the top of the layer, respectively; install top and bottom plugs 2 m below the surface and 30 m below that level, respectively. The spaces between the cemented zones should be filled with saturated brine or non-corrosive drilling fluid of acceptable weight.

[0014] Finally, install a metal plate over the coating 2 m below the surface, and then backfill.

[0015] According to API-1170 (American Petroleum Institute (API). Recommended Practice 1170. Design and Operation of Solution-mined Salt Caverns Used for Natural Gas Storage. First edition, July 2015), there is no industry consensus regarding best practices for CRS abandonment. Most abandonment attempts involve processes analogous to those practiced in the hydrocarbon exploration and production industry.

[0016] However, some steps that must be taken before abandonment are: removal of stored gas (if the CRS that produced rock salt is used for gas storage), mechanical integrity testing must be performed after gas removal; removal of hanging strings; inspection of the production column; sonar survey; and a long-term monitoring program (if the well is not sealed). Monitoring a sealed cavern should include periodic assessment of subsidence as well as visual inspection for unexplained changes in the local topography.

[0017] Segundo as recomendações do Solution Mining Research Institute (SMRI) (PEREIRA, J. C., SMRI. Research Report RR2012-03. Common Practices – Gas Cavern Site Characterization, Design, Construction, Maintenance, and Operation.2012), the basic concepts of abandoning a CRS that must be met when preparing a plan for closing and abandoning a cavern CRS are: offering long-term protection against aquifer contamination and the release of hazardous materials to the surface, in the case of the CRS that produced rock salt being used for gas storage; offering long-term stability of the rocks surrounding the cavern; being maintenance-free; allowing the application of methods and materials as much as possible; being accessible; being accepted by the authorities; having replacement of the stored fluid with brine (preferable) or water; carrying out tests and calculations to estimate the hydraulic, thermal and mechanical characteristics of the rock in situ; waiting until the necessary stabilization of the temperature between the brine and the rock (in special cases it may be necessary to heat the brine to. reduce waiting time); abandon the cavern (well closure activities); and monitor the surface.

[0018] It is also recommended to perform an integrity test on the production string's base before shutting in the well to ensure there are no gaps that could cause percolation of stored material. Furthermore, all equipment inside the well (packer, suspended line, etc.) should be removed before installing the sealing plug. The well should also be properly cleaned.

[0019] Regarding the final position of the sealing plug, three options are recommended: at the base of the production string, provided that the integrity and impermeability of this area are guaranteed; in the unlined area between the production string footing and the cavern ceiling, provided that this area has the appropriate length and cross-section to allow for the installation of the packer. The plug is installed above the packer, in a window milled. However, regardless of the section chosen for the final plug installation, the section above it must be completely cemented.

[0020] Long-term stability must be validated through surface movement monitoring to determine if subsidence is occurring in the region. This period can be on the order of 20 to 30 years for brine production caverns.

[0021] According to the British Geological Survey (BGS) standard, Open Report Or / 07023, An Appraisal of Underground Gas Storage Technologies and Incidents for the Development of Risk Assessment Methodology (2007), prior to abandoning a gas storage facility, state-of-the-art studies should be conducted to define strategies for decommissioning, abandonment, and risk mitigation involved in this stage. It is known that, over time, the pressure inside the cavern will change. Therefore, analysis / modeling should be performed to predict this variation and mitigate the resulting risks. Five possible reasons for a pressure change in the cave are: creep of the salt rock; thermal expansion of the fluid in the cave (in some cases it can be more critical than the creep of the salt); loss of fluid through porous media (interface of the salt with another type of material); leakage along the well; additional dissolution and precipitation of the salt in the cave.

[0022] According to the British Standards Institute (BSI) standard, BS EN 1918-3:2016, Gas infrastructure – Underground gas storage – part 3: Functional recommendations for storage in solution-mined salt caverns. 2016), based on the state of the art, for the abandonment of a CRS at the end of its operating cycle, studies and measurements must be carried out to verify the safety of the site after its abandonment. A specific decommissioning plan must be developed. Well plugs are installed to ensure the mechanical stability of the salt formation and to maintain the seal between the cavern and the surface. Long-term simulations of evaporite rock creep and the resulting pressures at the base of the casing must be conducted to demonstrate the structural stability of the cavern to be abandoned.The decommissioning of the CRS includes: the removal of gas from the cavern, in the case of the CRS that produced rock salt being used for gas storage; flooding the cavern with water or brine, waiting for the temperature to stabilize before closing the well (this process can take a few years); monitoring the cavern; installation of plugs and abandonment of the well; decommissioning of surface facilities; and monitoring.

[0023] Crotogino and Kepplinger (2006) (Crotogino F and Kepplinger J. Cavern well abandonment techniques guidelines manual. SMRI. 2006), summarize several basic R&D projects conducted by the Solution Mining Research Institute (SMRI) on crucial aspects of CRS sealing and abandonment, called Cavern Sealing and Abandonment (CSA), which became the basis for the development of the general manual for planning and implementing this activity.

[0024] In the state of the art, with the abandonment of the CRS, at the end of its operating cycle, it is possible to permanently seal a CRS filled with brine in homogeneous salt structures, such as domes and thick salt beds (Figure 1a), where stability and integrity are ensured almost exclusively by the salt bed. In these cases, if site-specific conditions are met, uncontrolled brine expulsion is not expected to occur in the cap rock, drinking water aquifers, or at the surface.

[0025] As a logical first step toward developing CSA procedures for specific CRSs, this concept must meet the following requirements: Long-term protection against contamination of drinking water aquifers and the escape of brine and / or the escape of flammable and / or environmentally hazardous products (product residues on the surface), in the event that the CRS that produced rock salt is used for hydrocarbon or other product storage; Long-term stability of the rock mass around the cavern; Absence of maintenance requirements; Application of tried-and-tested methods and materials as far as possible; Accessibility; and Acceptance by authorities.

[0026] The following steps are necessary: ​​assessment of the pre-sealing conditions of CRS access wells; replacement of the storage fluid with brine or water, in the case of the CRS that produced rock salt being used for the storage of hydrocarbons or other products; assessment of the minimum waiting time for pressure and temperature stabilization before plugging the CRS; defining and executing the plugging; and monitoring parameters.

[0027] In the first phase of development, the authors analyzed the experience and existing regulations for oil and gas wells, with the aim of integrating this experience whenever possible into the CSA concept for CRS. They then analyzed the existing regulations for CRS (Germany, United States, Netherlands, Poland).

[0028] Specifically, about sealing the CRS, with abandonment plugs with cement to ensure long-term sealing, given the The relatively shallow depths of most CRSs, compared to oil and gas wells, means that continuous cementing of the last CRS access well shoe to the surface offers technical and cost advantages over alternating cement plugs. This procedure should occur after temperature equalization between the brine in the CRS and the surrounding rock. Finally, the CRS access wellhead should be removed, a concrete slab placed, and surface conditions, such as subsidence, identified and monitored.

[0029] According to the National Solid Waste Policy (PNRS), Law No. 12,305, of August 2, 2010, "waste" is the correct term to designate something that has been discarded, no longer has any use, and is classified according to its origin and hazardousness. However, "waste" implies something that becomes useful in another production process, such as raw material in industry, through recycling. The term "reject" was created to designate something that cannot be reused, recycled, or composted. Therefore, "reject" refers to solid waste that, after all treatment and recovery possibilities using available and economically viable technological processes have been exhausted, presents no other possibility than environmentally appropriate final disposal.

[0030] According to ABNT NBR 10.004 / 04, waste classification in Brazil is determined by factors that take into account the potential risks to the environment and public health that the waste may pose. Waste classification involves identifying the process or activity that generated the waste, as well as its constituents and characteristics, and comparing these constituents with a list of wastes and substances whose impact on health and the environment is known. In ABNT NBR 1004 / 04, waste is classified based on the characteristics of hazardous, inert, and non-inert waste: Class I Waste – Hazardous, is waste that presents hazardous characteristics such as flammability, corrosivity, reactivity, toxicity, and pathogenicity; Class II A Waste – Non-inert waste does not fall under the Class I (Hazardous) or Class II B (Inert) waste classifications, and therefore may have properties such as biodegradability, combustibility, or water solubility. Class II B (Inert) waste is any waste that, when sampled representatively and subjected to dynamic and static contact with distilled or deionized water at room temperature, does not have any of its constituents solubilized in concentrations above the potable water standards, except for appearance, color, turbidity, hardness, and taste. It is worth mentioning that ABNT NBR 10004 does not address radioactive waste, as this falls under the exclusive jurisdiction of the National Nuclear Energy Commission.

[0031] According to Resolution No. 307 / 2002 of the National Environmental Council (CONAMA), which establishes guidelines, criteria and procedures for the management of Construction and Demolition Waste (RCC), RCC is classified (Art. 3) as follows: I - Class A, are reusable or recyclable waste as aggregates, such as: a) construction, demolition, renovation and repair of paving and other infrastructure works, including soil from earthworks; b) construction, demolition, renovation and repair of buildings: ceramic components (bricks, blocks, tiles, cladding plates, etc.), mortar and concrete; c) from the manufacturing and / or demolition process of precast concrete parts (blocks, pipes, curbs, etc.) produced on construction sites; II – Class B, are wastes that can be recycled for other purposes, such as: plastics, paper, cardboard, metals, glass, wood and plaster; III – Class C, are wastes for which economically viable technologies or applications have not been developed that allow their recycling or recovery; IV – Class D, are hazardous wastes originating from the construction process, such as paints, solvents, oils and others, or those contaminated or harmful to health originating from demolitions, renovations and repairs of radiological clinics, industrial facilities and others, as well as tiles and other objects and materials that contain asbestos or other products that are harmful to health. STATE OF THE TECHNIQUE

[0032] Some current state-of-the-art documents have already addressed the problem of decommissioning Salt Rock Caves (CRS), as will be presented below:

[0033] The Brazilian Mining Institute's document, "Guide for Mine Closure Planning," Brasília, 2013, presents a vision of post-mining legacy and addresses socioeconomic and environmental issues related to mine closure. It contains a series of general recommendations, providing a more in-depth understanding of the reality of mining in Brazil. It includes practical cases and situations focused on Brazilian characteristics and peculiarities in managing mineral development during the mine closure phase, contributing to long-term sustainable development in regions where mining activities are located.

[0034] However, the aforementioned document reports that "access to the underground excavations was blocked with demolition waste from surface facilities." In other words, this procedure of only blocking the access (entrance) to the mine excavations is equivalent to the state-of-the-art abandonment of a well in a homogeneous salt structure (diapir or thick layer), which is analogous to those practiced in the hydrocarbon exploration and production industry for well abandonment, with the use of a sealing plug only at the well entrance. Therefore, all galleries and mining panels are left without fill material (retaining only air), which can cause compaction in this region and, consequently, subsidence of the surface floor, especially with a well.

[0035] It is worth mentioning that blocking access to underground excavations with demolition waste from surface facilities does not seal off access (it is not a hydro-chemical-mechanical-biological barrier), as it is only a partial mechanical obstruction to the entry of animals and people. Therefore, fluids can pass (from outside to inside) and flood the galleries and panels. If This procedure occurs during the abandonment of a CRS. During its closure, due to creep, the pressure in the fluid inside the cavern increases (pressure buildup), causing this fluid to percolate (from inside to outside the CRS) through the entrance, as it was merely obstructed with demolition waste (without mentioning class, grain size, filling sequence, etc.) and was not sealed. This can compromise the integrity of the CRS, which can cause significant subsidence of the surface floor (formation of a subsidence basin), which can be detrimental to any civil / mechanical construction and even to nature, such as diversion of river courses and roads, and damage to structures. And, over time, the closure of the CRS can collapse the roof of the CRS and even create a sinkhole in the surface.Furthermore, it will previously cause environmental problems due to the leakage of CRS fluid through the access that has only been blocked with demolition waste from surface facilities.

[0036] The article "Decommissioning and Permanent Abandonment of Wells: Contextualization of the National Scenario" (Castro et al., 2021, presented at the IV CONEPETRO – National Congress of Petroleum, Natural Gas, and Biofuels Engineering) presents, in general terms, the general characteristics of permanent well abandonment projects (deactivation of the hydrocarbon production unit), in addition to presenting the main international abandonment standards. It aims to establish a parallel assessment of the situation and future prospects of such practices in Brazil, as well as their temporal and economic context. It then describes the so-called solidary sets of barriers and the main causes of problems arising from inadequate abandonment, which can cause environmental damage. Finally, it provides a quantitative assessment of current abandonment projects in Brazil and possible investments in the coming years.

[0037] O artigo Post-mining Use of Underground Space For Waste Storage (Dinis da Gama C, Paper presented at the 7th ISRM Congress, Aachen, Germany, September 1991. Paper Number: ISRM-7CONGRESS-1991-017) portrays the storage of waste (urban, industrial, toxic and radioactive), and not of residues (material that can be recycled and / or reused), permanently (for a long period) in abandoned underground mines, or in decommissioning, as a means of additional monetization for the mining industry, as well as a means of reliable environmental solution.Furthermore, it also cites the advantages of using underground space, such as: a) the temperature is approximately constant underground, which is advantageous for a series of stored products, b) humidity is easily controlled and the quality of groundwater can be preserved without difficulty; c) security is excellent, whether against fires, floods, hurricanes, heavy rains and snows, etc.; d) the proliferation of insects and bacteria is much better preserved than in conventional warehouses; e) material losses and product deterioration are considerably reduced; f) the soil surface is free of solid, liquid and gaseous pollution, as well as destruction of forests and aggressions to the landscape.

[0038] However, underground mines with geological faults and / or highly permeable sediments and / or roof collapses and / or in seismic areas would require adaptations to prevent the tailings from moving (through fractures and faults or permeable sediments) and contaminating groundwater. Therefore, it would be better (safer and cheaper) to design, construct, and operate an underground repository exclusively for the definitive storage of waste (radioactive and / or toxic) in a favorable and watertight location and geological setting, without the presence of geological faults (fractures) and / or highly permeable sediments and / or roof collapses, as implemented in the Yucca Mountain repository (Nevada / USA) and the Waste Isolation Plant Pilot (New Mexico / USA), which include mine access for repository monitoring and maintenance, in addition to multiple protective barriers against the release of the stored product.

[0039] O artigo Design and Management of Salt Solution Caverns for Toxic Waste Disposal (Davison et al, 1997, Petroleum Society of CIM, paper No 97- 151) describes a safe, practical, and economically viable alternative for managing low-level radioactive waste and toxic industrial waste, through the disposal of such waste in an underground cavern in salt rock (Solution Cavern Disposal - SCD), as it ensures the isolation of the waste over time, thus being a means of permanent environmental safety, in addition to being more economical than other practices, such as sanitary landfill, chemical treatment, incineration, etc. Issues related to the desirable characteristics of an ideal waste repository are also presented, such as: 1. low probability of interacting negatively with the biosphere; 2. the waste disposal technology must be relatively straightforward, economical, and flexible in its ability to handle the waste; 3.Any permanent waste disposal management approach must lead to societal acceptance through a clear understanding of all process aspects; 4. The procedures for transporting, handling, and disposing of the waste must be safe, meeting the requirements of occupational health and safety agencies, as well as the concerns of impacted communities; 5. Repository sites must be permanent, must not impair current and future land use, and must not require ongoing post-maintenance or treatments for any significant period (e.g., >10 years); 6. The price of the disposal method must allow it to operate economically.

[0040] The aforementioned article defines engineering waste as any waste that has low solubility in saturated brine, which must not contain appreciable amounts of gasoline or ethylene glycol, which may contain up to 10% by volume of the dry residue of more viscous immiscible liquids (chlorinated hydrocarbons, grease, and high molecular weight aromatic hydrocarbons), which must not contain any amount of organic residues, which may contain inert plastics and resin granules. Furthermore, without excluding other suitable wastes, the aforementioned article defines as examples of materials Suitable for disposal in salt caverns (SCD): inert solids rich in toxic metals; low- and intermediate-level radioactive waste; vitrified waste and slag containing toxic or harmful elements or compounds; cement, gypsum, and other building materials containing asbestos fibers; solids and soils contaminated with small amounts of grease and viscous concentrated hydrocarbons; sludge and other process residues containing heavy metals; spent ceramic catalysts and contaminated reaction beds; and other insoluble materials from industrial processes, oil refining, accidental spills, and mineral processing. Such waste may also contain substantial amounts of water because this water becomes a saturated brine when mixed with the granulated salt.The waste may be in the form of large solid particles, such as asbestos cement, in which case it must be ground to meet the specifications required for the mixture and injected through the SCD access tube, with the maximum diameter of the solid particles, one fifth of the internal diameter of the injection tube so as not to create a blockage during the procedure.

[0041] It further clarifies that there are two categories of DCS that can be used for repository purposes: 1. caverns specifically designed to meet the toxicity level of the waste; 2. caverns previously created for use as storage cavities (2a) or for the extraction of saturated brine (2b) for industrial purposes. However, it states that in the latter case, the geometry of the cavern (dimensions and shape) will dictate its use. For example, in case 2a, of DCS used for hydrocarbon storage, which may be in the shape of a "teardrop" or an inverted cone, will have a thick ceiling and floor and will be well spaced from adjacent cavities. If the cavern is intact, it can be used to store the full range of toxic waste. If the cavern has been breached and the overlying strata have been exposed or the cavern ceiling has collapsed, its use should be limited to the disposal of non-toxic to low-toxic waste.

[0042] Regarding the procedure for filling the SCD, the aforementioned article states that it is done through a pipeline (with a reflux check valve), in which brine is withdrawn from the top of the CRS through the annular exterior of the CRS access well to be used in the mixture with the waste (in granular form with a specific gravity higher than that of brine and must not be able to be colloidally suspended in the brine) to be injected into the CRS as a slurry. This allows the waste to quickly settle at the bottom of the CRS, adopting an angle of repose of less than 5 degrees to fill the CRS, even between loose rock blocks within the CRS to eliminate much of the potential for surface subsidence over time.

[0043] Therefore, according to the ABNT NBR 10004 classification, the aforementioned document allows for the storage of hazardous waste (Class I waste) and non-hazardous waste (Class II A waste). And, according to CONAMA (Resolution No. 307 / 2002), the aforementioned document also allows for the storage of Class B, C, and D solid waste (asbestos fibers) in a salt rock cavern. This contradicts Resolution 384 of the National Environmental Council (CONAMA) of 2004, for example, which determines that products containing asbestos as a raw material cannot be disposed of in any location. The recommendation is that asbestos be disposed of along with hazardous waste in specialized landfills. Furthermore, it contradicts global environmental standards.

[0044] Furthermore, the aforementioned document presents conceptual errors, for example, the use of the CRS with a collapsed roof for the repository of low toxicity waste does not guarantee the isolation of the waste in the long term, nor environmental safety, since through the layers of permeable sediments (above the roof of the collapsed cavern) there will be a flow of waste, thus contaminating the groundwater and it may even reach the surface (exudation process) through the geological faults or fractures present in the location or generated by the collapse of the CRS roof.

[0045] And, using integral caverns, which were previously created for industrial purposes, as a repository for the entire range of toxic waste, does not guarantee long-term isolation of the waste nor environmental safety, if the cavern contains layers of inhomogeneous salt (intercalations of clay minerals, layers of sediments with high permeability and other non-evaporitic rocks within the CRS) or if the cavern is close to geological faults and / or fractures (active or not) that are within the radius of influence of the cavern, because through the intercalations or faults (reactivated and open) or fractures, waste flow will occur, thus contaminating the groundwater, and even generating exudation of fluids on the floor.

[0046] Specifically, regarding the abandonment of a CRS with a collapsed roof, it only mentions the procedure of filling the CRS up to 90% of its dissolved volume (geometric volume of the CRS) with granular materials (with a diameter up to 1 / 5 of the diameter of the access well pipe and average porosity of around 42%), with this only 37.8% (0.90 x 0.42 = 0.378) of the CRS volume is filled with granular material, and the remaining 62.2% of the CRS volume remains with brine. After this, the CRS access well is cemented.Thus, due to the creep behavior of the salt rock, the CRS will close over time (for years to decades due to inadequate abandonment), compacting the granulated material and expelling 62.2% of the brine volume through geological faults, fractures and permeable materials, thus generating a subsidence basin on the ground floor above the cavern (around the access well), damaging equipment, structures, etc., as already described in general terms.

[0047] Therefore, in such scenarios and conditions of abandonment of CRS with collapsed roof, the aforementioned document does not maximize disposal capacity, nor does it guarantee long-term waste isolation or even environmental safety.

[0048] The above-mentioned problems are solved by the present invention through the methodology of sequentially filling the CRS with material Granular material (e.g., Class A RCC) with different diameters, from the largest (gravel 3, gravel 2, gravel 1, gravel 0) to the smallest (coarse sand, medium sand, fine sand), is used to form a structural framework, followed by pressurization of the RCC before plugging the access well with cement. This methodology achieves a RCC fill volume greater than 95% (better efficiency), in addition to plugging or sealing faults (without reactivating or opening) or fractures or permeable materials with non-contaminating and non-hazardous RCC, thus significantly minimizing or eliminating the subsidence basin generated and not contaminating surface water or generating seepage (greater effectiveness in solving the problem).It is worth mentioning, for example, that when using Class A RCC, materials that have the characteristic of not decomposing and undergoing any change in their composition over time, do not pollute because they do not alter the soil or water, given that when in contact with both, substances that harm the environment are not released.

[0049] The article "Recycling of Construction and Demolition Solid Waste from the Solid Waste Portal" (https: / / portalresiduossolidos.com) describes how construction and solid waste (CDW) recycling works and the types of recycling plants used for this type of waste. It also reports that the volumes and weights generated by CDW are astronomical, and much of this waste is disposed of inappropriately.

[0050] Specifically, this article refers to the waste defined by Conama Resolution 307 as Class A RCC, in accordance with NR 1701, as defined by the European Waste List. This waste includes waste from construction, demolition, renovation, and repair of paving and other infrastructure works, including soil from earthworks, construction, demolition, renovation, and repair of buildings. The latter three are composed of ceramic elements (bricks, blocks, tiles, cladding panels, etc.) and mortar and concrete from the manufacturing and / or demolition of precast concrete parts. (blocks, pipes, curbs, etc.) produced on construction sites. After selective collection, the RCC undergoes a shredding process. This results in the fractions being mixed, resulting in little added value. Only after granulation—that is, the separation of the fractions—can the new materials (sand, gravel, pebbles, and others) resulting from RCC recycling be properly disposed of and value added. Furthermore, this can alleviate pressure on natural resources and contribute to extending the lifespan of landfills.

[0051] The aforementioned article further describes that RCC recycling plants can be divided into two categories, according to their type: fixed plants and mobile plants. A mobile RCC recycling plant (MRU) is basically composed of three components: a roll-on / roll-off truck, a mobile crusher, and a mobile rotary screen docked to the truck, the latter two powered by diesel or electric power. The MRU's major advantage is that it can move to wherever its service is needed. Being versatile, it can increase profitability, especially by reducing logistics costs. A fixed RCC recycling plant (RRU) has a fixed location, does not own a truck, but has tracks to move the RCC to the crusher and has greater capacity and higher throughput. However, it has higher logistics costs, as it must receive the RCC and, after being processed and granulated, must be transported to the site of use.

[0052] Therefore, the aforementioned documents differ from the present invention by not providing procedures for filling, sealing and abandoning (decommissioning) CRS in inhomogeneous salt structures, that is, CRS in slender salt layers with the presence of intercalations of clay minerals (layers of sediments with high permeability within the CRS) and other non-evaporitic rocks, and by not providing procedures for decommissioning CRS close to geological faults and / or fractures (active or not) that are within the radius of influence of the CRS. Furthermore, the vast majority The state of the art documents also do not deal with CRS that had its roof collapsed.

[0053] Thus, given the difficulties present in the aforementioned prior art, that is, related to the decommissioning of CRS in inhomogeneous salt structures (porous and permeable rocks within the CRS) and / or near geological faults and / or CRS that have had their roof collapsed, the need arose to develop a technique capable of performing the filling, sealing, and abandonment (decommissioning) of the CRS in an environmentally correct, technically safe, effective, and economically viable manner. As reported above, the current prior art does not possess the unique characteristics that will be presented in detail below. SUMMARY OF THE INVENTION

[0054] The present invention relates to a method and system for filling, sealing and abandoning a cavern constructed in saline rock, especially located in a non-homogeneous salt structure (with the presence of layers of porous / permeable rocks within the CRS) and / or close to geological faults (active or not) and / or which has had a cavern ceiling collapse, through the use of Class A recycled demolition waste (RCC) (from the construction of the project itself or not), in filling the CRS, which substantially reduces the cost of abandonment / decommissioning, reduces risks and reduces greenhouse gas (GHG) emissions and, in addition, promotes an environmentally friendly disposal of recycled demolition waste.

[0055] The CRS filling methodology occurs sequentially, that is, first with materials of greater granulometry (gravel 3, gravel 2, gravel 1, gravel 0) and subsequently with materials of smaller granulometry (coarse sand, medium sand, fine sand), in order to: form a structural framework, fill the voids and faults / fractures, pressurize and monitor the CRS before filling the access well with cement, and complete the permanent abandonment of the CRS.

[0056] As described in the state of the art, it is recommended that dissolution mining for the extraction of rock salt occurs in a homogeneous salt layer, as the leaching process will form a cavern in the salt rock, where its sealing and abandonment, at the end of its useful life, may occur through the abandonment of the brine itself in the CRS, with or without plugging, with cement, the access well to the cavern.

[0057] However, in the case of a CRS constructed on an inhomogeneous salt layer (with porous / permeable rock layers within the salt layer), and / or near geological faults, and / or in a condition where rock salt production has dissolved the CRS's protective slab (roof) (the thickness of rock between the top of the CRS and the rock above the salt layer) and caused the CRS roof to collapse, packing the CRS with air or brine, with or without cement packing, is inappropriate. Likewise, filling a CRS with a collapsed roof with non-toxic and low-toxic waste, hazardous waste, or any type of RCC is inappropriate.

[0058] If the state-of-the-art procedure for sealing and abandoning a cavern occurs in a cavern located in an inhomogeneous salt structure (with porous / permeable rock layers within the salt) and / or near geological faults, during the cavern closure, due to creep, the fluid pressure inside the cavern increases (pressure buildup), causing this fluid to percolate through the non-evaporite rock layers present in the cavern due to their high permeability and porosity, and / or through the geological fault. The increased fluid pressure can also fracture the non-evaporite rocks and cause the opening or reactivation of geological faults, contaminating the water table and potentially generating fluid exudation at the surface.As a result, the integrity of the CRS may be compromised, which may cause significant subsidence of the surface floor (formation of a subsidence basin), which is harmful to any civil / mechanical construction and even nature, such as, for example, diversion of river courses and diversion of. roads and damage to structures. Over time, the closure of the CRS can collapse the roof of the CRS and even create a sinkhole.

[0059] In this way, the method and system developed in the present invention make it possible to carry out the filling, sealing and abandonment (decommissioning) of the CRS, through the gradual and sequential filling of the CRS, with recycled solid material, with different granulometries, generated through comminution and recycling of Class A construction demolition waste (RCC), decommissioned from the facilities of the rock salt production or storage enterprise (in loco) or other locations.

[0060] At the end of the CRS filling, it is sealed and abandoned with a cement plug from the last footing in the CRS access well to the floor.

[0061] The procedure illustrated results in greater void filling, and with the closure of the CRS, the compaction of the fill material in the CRS occurs more quickly (almost immediately) and generates negligible floor subsidence. This procedure also buffers geological faults and fluid percolation through the non-evaporitic rock layers present in the CRS against a layer of inhomogeneous saline rock. This prevents CRS stability problems, seismicity, floor subsidence, seepage, and sinkhole formation.

[0062] The method described here aims to replace the use of (i) prefabricated briquettes, which generate greater energy expenditure, incur transportation costs, require a considerable level of compaction (between 15 and 20%) and are not effective in filling voids and faults (Rolfs et al. 1993: Rock Mechanical Studies on the Post-operational Phase of a Disposal Caverns – 3rd Conference on Mechanical Behavior of Salt, Paliseau, France), or the use of (ii) sand extracted and moved from licensed deposits kilometers away from the CRS, which is associated with a high cost (long execution time and a high rate of GHG emissions – greenhouse gases, since 1 truck transports a maximum of 15 m 3 and a CRS may require tens of thousands of trips), in addition to a high risk of exposure to noise generation and traffic congestion due to the circulation of trucks (between the collection of sand from a licensed deposit and / or briquettes to the CRS).

[0063] Furthermore, with the present invention it is possible to avoid the disposal of Class A construction waste (RCC) and demolition waste (rubble) in landfills, as well as avoid the problems associated with moving waste from the CRS project to the landfill, by truck (thousands of trips).

[0064] Therefore, the present method of filling and abandoning CRS makes it possible to: drastically reduce total decommissioning costs, reduce greenhouse gas emissions, reduce execution time, reduce noise emissions, reduce truck traffic, increase efficiency, increase safety and reduce risks (subsidence and traffic accidents), give an environmentally correct and sustainable destination to construction and demolition waste by recycling it, as well as give an environmentally correct destination to CRS brine.

[0065] Therefore, the method and system described and claimed in this document present a condition that surpasses the state of the art by allowing the filling, sealing, and abandonment of the CRS to occur simultaneously and integrated with the decommissioning of the project (civil structure), in an environmentally, technically, and economically sound manner. This enables better results. BRIEF DESCRIPTION OF THE FIGURES

[0066] In order for the invention to be understood more easily, the Figures numbered 1 to 11, which accompany this report and are an integral part of it, are presented by way of illustration, but without the intention of limiting the invention.

[0067] Figures 1a-1e, modified from Crotogino F & Kepplinger J. Cavern well abandonment techniques guidelines manual. SMRI. 2006, illustrate The state-of-the-art method for abandoning a rockfall cavern in a homogeneous salt layer is schematically presented. The figures illustrate: 1a) Definition of a cavern in a homogeneous salt structure (in a diapir or thick layer) and a cavern in an inhomogeneous salt structure (in thin layers or with the presence of intercalations and geological faults), as well as a sketch of the area affected by the cavern; 1b) Sealing and abandonment of a rockfall cavern in a homogeneous salt layer, at atmospheric pressure, with air and with solid particulate matter; 1c) Volume of the rockfall cavern over time as a function of the filling material (air or brine) without (I-II-III) and with (IV) the rockfall cavern sealing; 1d) The most common method for abandoning a rockfall cavern in a homogeneous salt layer, using brine without and with solid particulate matter.As the fluid pressure within the CRS increases due to its closure, brine is released from the CRS; 1e) Sealing and abandonment of the CRS, in a homogeneous salt layer, at atmospheric pressure, with brine, but with a perforation in the casing facing a shallow aquifer. As the fluid pressure within the CRS increases due to its closure, brine is released from the CRS into the aquifer.

[0068] Figures 2a-2f schematically illustrate the state of the art for abandoning a CRS, but in a homogeneous salt layer, regarding the operations required to fill a CRS with particulate solid material, with sand extracted from licensed deposits. In this sense, the figures illustrate: 2a) Extraction of sand from licensed deposits; 2b) Loading of sand into a truck (15 m 3- 28 tons); 2c) Transportation of the sand by truck to the location of use; 2d) Unloading of the sand at the site where the cavern to be plugged and abandoned exists; 2e) Loading of the sand on a conveyor belt, mixing of the sand with water and injection of the fluidized sand into the access well to the cavern; and 2f) Filling of the cavern with solid material (sand) with monitoring of pressure, temperature (with piezometer) and the volume filled in the cavern (with sonar).

[0069] Figures 3a-3d schematically illustrate the state of the art for decommissioning facilities at the CRS project location. (civil infrastructure), in relation to the necessary operations from demolition to disposal of debris in a landfill. In this sense, the figures illustrate: 3a) Demolition of installed infrastructure or other buildings; 3b) Loading onto a truck (15 m 3– 28 tons) of construction waste (reject); 3c) Transportation of waste to an appropriate disposal location; 3d) Debris unloaded and truck returning to the location for the next load.

[0070] Figure 4a, modified from Warren, JK2017 (Salt usually seals, but sometimes leaks: Implicatons for mine and cavern stabilities in the short and long term: Earth-Science Reviews, 2017;165:302-341), schematically illustrates the application scenarios of the present invention, when the CRS was constructed in a non-homogeneous salt layer, that is, when the CRS contains the presence of layers of porous / permeable rocks (non-evaporitic rocks), or when the CRS is located close to a geological fault / fracture. Figure 4b, modified from Chen X., et al. 2019 (Study on Sealing Failure of Wellbore in Bedded Salt Cavern Gas Storage. Rock Mechanics and Rock Engineering 2019;52:215–228) schematically illustrates what can occur in a CRS built in the application scenarios of the present invention, if the decommissioning methodology described herein is not carried out.The fluids present in the CRS percolate through the layers of non-evaporitic rocks (present in the CRS) until reaching a geological fault, and with this the fluids can reach the ground, generating an exudation of fluids on the surface (not illustrated), in addition to contaminating aquifers if present in the location (also not illustrated). .

[0071] Figures 5a-5c, modified from Zhang Z, et al. 2019 (Study on the mechanism of roof collapse and leakage of horizontal cavern in thinly bedded salt rocks. Environmental Earth Sciences, 2019;78:292) schematically illustrate another application scenario of the present invention, when the roof of the CRS collapses, which causes the cavern to contain a greater presence of exposed non-saline rocks.

[0072] Figure 6a, modified from Berest et al. 2019 (Review and analysis of historical leaks from storage salt cavern wells. Oil & Gas Science and Technology - Rev. IFP Energies Nouvelles, 2019;74,27), schematically illustrates what the application of the present invention avoids, that is, a subsidence of the floor above the CRS (due to excessive closure of the CRS). Figure 6b shows the formation of a sink hole (sinking of the surface, formation of a crater) due to a collapse of the CRS roof and the formations above the CRS.

[0073] Figures 7a-7g illustrate, schematically, a detail of the first stage of the methodology of the present invention, where a methodology for filling the CRS is presented, in which particulate solids with certain volumes and sizes are inserted sequentially: 7a) insert gravel 3 (14a) (25 < DMC < 50mm) from 30 to 40% of the VGC; 7b) insert gravel 2 (14b) (19 < DMC < 25mm) from 15 to 25% of the VGC; 7c) insert gravel 1 (14c) (9.5 < DMC < 19mm) from 10 to 15% of the VGC; 7d) insert gravel 0 (14d) (4.8 < DMC < 9.5mm) from 5 to 10% of the VGC; 7e) insert coarse sand (15a) (2.0 < DMC < 4.8mm) from 5 to 25% of the VGC; 7f) insert medium sand (15b) (0.42 < DMC < 2.0mm) from 3 to 10% of the VGC; and 7g) insert fine sand (15c) (0.07 < DMC < 0.42mm) from 2 to 5% of the VGC.

[0074] Figures 8a-8c illustrate, schematically, the second stage of the methodology of the present invention, where occurs: 8a) pressurization of the CRS monitoring the pressure, temperature and fluid level in the CRS; 8b) reinjection of fine sand until completing the access well, monitoring the pressure, temperature and fluid level in the CRS; and 8c) injection of cement paste until filling the CRS access well to complete the permanent abandonment of the CRS.

[0075] Figures 9a-9c schematically illustrate the production and use of Class A demolition waste (RCC) as a raw material for filling the CRS. In this sense, the figures illustrate: 9a) demolition of installed infrastructure or other buildings; 9b) insertion of the demolition material by excavator (29), for example, in a mobile recycling plant for construction waste, which is composed of a Roll On / Roll Off truck (28), a mobile crusher (impact or jaw) and a mobile rotary screen docked to the truck. Waste comminution or grinding, which is the fragmentation of the waste by crushing (coarse fragmentation) and grinding (fine fragmentation), followed by granulation (sieve classification), is performed to produce gravel (30 - blue circle) and sand (31 - yellow circle) and / or separated by an electromagnet, which separates the ferromagnetic material; and 9c) loading the gravel and / or sand onto a conveyor belt, mixing the gravel or sand with water, and injecting the gravel and / or fluidized sand into the cavern access shaft.

[0076] Figures 10a-10b illustrate, schematically and respectively, a summary of the distances traveled, in the prior art versus in the present invention, in the decommissioning of a CRS. In this sense, figure 10a illustrates the prior art in which truck transport (up to 15 m 3each) of the sand from the licensed extraction deposit to the CRS location to be abandoned (for up to tens of kilometers with thousands of truck trips), and transportation by truck (up to 15 m 3 each) of demolition waste from the CRS facility to a licensed landfill (up to tens of kilometers with thousands of truck trips). Figure 10b) illustrates the present invention, with the filling of the CRS with solid material recycled in situ from Class A demolition waste (RCC) from the CRS project location and / or from a civil structure affected by the CRS due to the formation of a subsidence basin and condemned for demolition. Thus, the present invention avoids the displacement of thousands of trucks carrying sand and waste over tens of kilometers.

[0077] Figure 11 schematically illustrates ways of disposing of brine, in technically and economically correct ways, replaced in the CRS, due to the filling of the CRS with gravel and sand (as shown in Figures 7a-7g and 8a-8c).

[0078] The present invention aims to provide a method for filling, sealing and abandoning (decommissioning) a salt rock cavern (CRS) located in an inhomogeneous salt structure (with the presence of porous / permeable layers within the CRS) and / or close to geological faults and / or which has had a cavern ceiling collapse. In a preferred embodiment, said method is applied to a salt rock cavern (CRS), especially located in an inhomogeneous salt structure (with the presence of porous / permeable rock layers within the salt layer) and / or close to geological faults or which has had a cavern ceiling (slab) collapse, which can occur simultaneously and integrated with the decommissioning of the facilities at the location of the CRS project or of a civil structure affected by the CRS (due to the formation of a subsidence basin) and condemned to demolition or another area.This modality uses recycled aggregates from Class A construction demolition waste (RCC) from the project's own installation that contains the CRS (in situ) or from other civil construction affected by the CRS or other nearby areas condemned and defined for demolition.

[0079] It is a second objective of the present invention to provide a system to enable the filling, sealing and abandonment of a salt rock cave (CRS) located in a non-homogeneous salt structure (with the presence of porous / permeable layers within the CRS) and / or close to geological faults and / or which has had a cave ceiling collapse. DETAILED DESCRIPTION OF THE INVENTION

[0080] The present invention relates to a method and a system for filling, sealing and abandoning (decommissioning) a cavern built in salt rock (CRS), especially located in a non-homogeneous salt structure (with the presence of layers of porous / permeable rocks within the salt layer) and / or close to geological faults and / or which has had a collapse of the cavern ceiling (slab), which can occur simultaneously and integrated with the decommissioning of the facilities at the location of the CRS project. and / or a civil structure affected by the CRS (due to the formation of a subsidence basin) and condemned for demolition, or another area. More particularly, in the decommissioning of a rock salt production project, and / or a storage facility in which the salt rock cavern (CRS), built by the dissolution mining process, where there is a need to fill the CRS with solid material.

[0081] The invention can be described by means of the following reference numerals: 01 - Layer of evaporite rock or saline rock 02 - Layer of non-saline rock (porous / permeable rock) between layers of saline rocks; 03 - Cave in saline rock (CRS), 04 - Area of ​​influence of the CRS; 05 - Access well to the CRS; 06 - Geological fault present near the CRS; 07 - Percolation of fluids from the CRS in a layer of non-saline rock present in the CRS; 08 - Percolation of fluids from the CRS through a geological fault close to the CRS; 09 - Layer of non-saline rock (porous / permeable rock) above the CRS; 10 - Collapse of the CRS roof; 11 - Closure of the CRS; 12 - Formation of a subsidence basin of the ground floor above the CRS; 13 – Occurrence of sink hole in the ground floor; 14a – Insertion of gravel 3 in the CRS; 14b – Insertion of gravel 2 in the CRS; 14c – Insertion of gravel 1 in the CRS; 14d – Insertion of gravel 0 in the CRS; 15a – Insertion of coarse sand into the CRS; 15b – Insertion of medium sand into the CRS; 15c – Insertion of fine sand into the CRS; 16 – Lowering of the CRS filling level due to the application of pressure that causes the displacement of the filling materials; 17 – Flow of the smallest particles (15c) filling the empty volumes in the CRS (3); 18 – Percolation followed by plugging of the non-evaporitic rock layers (02) present in the CRS (03); 19 – Percolation followed by plugging of the geological fault (08) present near the CRS (03).20 – Addition of fine sand (15c) to the CRS (1) to complete the displaced volume (16); 21 – Filling the CRS access well (3) with cement paste from the last footing in the access well to the floor; 22 – Completion of the permanent abandonment of the CRS; 23 – Sea; 24 – Saltwater disposal hose into the sea; 25 – Shallow saltwater aquifer near the location of the CRS access well; 26 – Saltwater disposal hose into a saltwater aquifer via a shallow well. 27 – Demolition of civil construction; 28 – Mobile recycling plant for construction waste, for example, which is composed of a Roll On / Roll Off truck, a mobile crusher (impact or jaw) and a mobile rotary screen docked to the truck; 29 – Excavator placing the demolition material in the crusher of the mobile recycling plant; 30 – Gravel thrown by the conveyor belt after demolition material passes through crushing and screening; 31 – Sand thrown by the conveyor belt after demolition material passes through crushing and screening; 32 – Transportation by truck (up to 15 m 3 ) of the sand from the licensed extraction deposit to the CRS location to be abandoned, for tens of kilometers and thousands of trips (state of the art); 33 – Transportation by truck (up to 15 m 3 ) of demolition waste from the CRS installation to a licensed landfill, for tens of kilometers and thousands of trips (state of the art); 34 – Filling the CRS with solid material recycled in situ from the demolition waste, as described in the present invention, that is, without the need to use trucks traveling tens of kilometers and thousands of trips.

[0082] The method of the present invention can be applied when the CRS is built on a non-homogeneous salt layer (Figure 4a), that is, when the CRS contains layers of porous / permeable rocks (non-evaporitic rocks), the CRS is close to a geological fault / fracture or when the roof of the CRS collapses (Figures 5a-5c), which causes the cave to contain a greater presence of exposed non-saline rocks.

[0083] If the decommissioning methodology described in this invention is not implemented, the CRS is subject to the scenarios shown in Figures 4b, 5, and 6. The fluids present in the CRS percolate through the layers of non-evaporitic rocks (present in the CRS) until reaching a geological fault, percolating through it and, as a result, the fluids can reach the floor, generating fluid exudation (not illustrated), in addition to contaminating aquifers if present at the location (not illustrated). Or the CRS roof can collapse and cause floor subsidence followed by the formation of a sinkhole (sinking of the surface floor, crater formation).

[0084] Thus, the method of the present invention also aims to avoid subsidence of the floor above the CRS (due to excessive closure of the CRS), as well as the formation of a sink hole (due to a collapse of the roof of the CRS and the formations above the CRS) (Figures 6a and 6b).

[0085] Below follows a detailed description of a preferred embodiment of the present invention (Example 1), a partial embodiment of the present invention (Example 2) and a comparative embodiment of the present invention with the state of the art (Example 3), which is exemplary and in no way limitative. Nevertheless, it will be clear to a person skilled in the art, from reading this description, possible additional embodiments of the present invention still comprised of the essential and optional features below.

[0086] Example 1 – Preferred embodiment of the present invention

[0087] Figures 7a-7g show a CRS (03) constructed in one of the application scenarios of the present invention, in a non-homogeneous salt layer, that is, the CRS contains the presence of layers of porous / permeable rocks (non-evaporitic rocks) (02) and is located close to a geological fault / fracture (08).

[0088] First, the CRS (03) is filled with crushed stone, machined or industrialized, from Class A RCC, between 60% and 90% of the geometric volume of the cavern (VGC), fluidized with the brine present in the CRS. The filling of the CRS (03) begins with crushed stone 3 (14a), with a maximum characteristic dimension (DMC) between 25 and 50 mm (30 to 40% of the VGC); then, with crushed stone 2 (14b), with DMC between 19 and 25 mm (15 to 25% of the VGC); then, with crushed stone 1 (14c), with DMC between 9.5 and 19 mm (10 to 15% of the VGC); then, with crushed stone 0 (14d) (gravel) with DMC between 4.8 and 9.5 mm (5 to 10% of the VGC).

[0089] In the next stage, the CRS (03) is filled with sand, machined or industrialized (RCC Class A), fluidized with the brine present in the CRS, between 40 and 10% of the VGC. It starts with coarse sand (15a), with DMC between 2.0 and 4.8 mm (from 5 to 25% of the VGC); then, with the sand medium (15b), with DMC between 0.42 and 2.00 mm (3 to 10% of the VGC); and, finally, with fine sand (15c), with DMC between 0.07 and 0.42 mm (2 to 5% of the VGC).

[0090] This procedure forms a framework within the CRS, enabling greater structural capacity, greater filling capacity and better conditions to (i) stop the flow in the layers of porous / permeable rocks (02) present in the CRS or at its collapsed or non-collapsed top, and (ii) stop the flow in faults (08).

[0091] After filling the CRS (03) with gravel and sand, the CRS (03) must be pressurized, between 50% and 90% of the burial gradient or the previously calculated fracture gradient, to help the smallest particles to flow and fill the empty volumes (17), stopping (18, 19) the flow in the pores of the porous / permeable layers (02) and in the faults (08), for a period of 24 to 72h, monitoring the pressure, temperature and fluid level in the CRS (with pressure transducers, temperature sensors and sonar inside the CRS access well).

[0092] After pressurization, fine sand (20) must be added to the CRS to complete the displaced volume (16). At the end of this period, the CRS access well must be filled with cement paste (21), thus concluding the permanent abandonment of the CRS (22).

[0093] The solid particulate material (gravel and sand) used to fill the CRS may be natural gravel and sand (washed or extracted from quarries), but preferably, it must be machined or industrialized from the recycling of Class A construction demolition waste (RCC), whether from the project's own construction site or not (from other areas condemned for demolition), obtained through comminution (grinding and crushing) followed by granulation, by a fixed or mobile recycling plant. Machined or industrialized gravel and sand have the same physical characteristics and granulation as natural gravel and sand (washed or extracted from quarries), the only difference being that they may contain cement particles.

[0094] Specifically, when filling the CRS with recycled solid material with different granulometries, generated through the comminution of construction demolition waste (RCC), it must be Class A, according to CONAMA Resolution No. 307 / 02, which establishes guidelines, criteria and procedures for the management of construction waste (amended by Resolutions 348, of August 16, 2004, and No. 431, of May 24, 2011 of the National Environmental Council - CONAMA).

[0095] Class A RCCs can preferably come from the on-site construction facilities of the rock salt production project or from storage at the CRS, if the latter is being decommissioned along with the CRS decommissioning, or from other areas. This substantially reduces decommissioning costs and greenhouse gas (GHG) emissions.

[0096] Class A RCC, according to CONAMA, corresponds to the RCC defined by the European Waste List (ERL), that is: concrete, bricks, tiles, roof tiles and ceramic materials.

[0097] Example 2 - Partial embodiment of the present invention

[0098] In a partial embodiment of the invention, it applies to the demolition (Figure 9a) of the civil construction infrastructure installed in the CRS project (27) or of other nearby buildings, affected by the CRS, and condemned to demolition (27).

[0099] After demolition (Figure 9b), the demolition material is inserted by excavator (29), for example, into a mobile recycling plant for construction waste, which is composed of a Roll On / Roll Off truck (28), a mobile crusher (impact or jaw) and a mobile rotary screen docked on the truck. The comminution or crushing of the waste, which is the fragmentation of the waste by crushing (coarse fragmentation) and grinding (fine fragmentation), followed by granulation (sieve classification), is carried out to produce gravel (30 - blue circle) and produce sand (31 - yellow circle) and or separated by an electromagnet, which separates the ferromagnetic material.

[0100] Alternatively, crushed stone and processed sand can be sourced from a fixed RCC recycling plant (not illustrated) and transported to the CRS decommissioning site.

[0101] Furthermore, gravel and sand can be alternatively processed or industrialized from other civil construction demolition areas (outside rock salt processing facilities) and / or from Class A RCC landfill.

[0102] Next, the crushed stone or processed sand is loaded onto a conveyor belt (Figure 9c), the crushed stone or sand is mixed with water (from the CRS itself, i.e., the brine) in a mixing vessel, and, finally, the crushed stone and / or fluidized sand are injected into the access well to the cavern, individually, at a flow rate lower than the fracture gradient of the shoe at the top of the CRS or permeable porous layers.

[0103] Example 3 - Comparative embodiment between the present invention and the state of the art in relation to truck transport

[0104] A summary of the distances covered by the state of the art (32) and (33) and by the present invention (34), for the decommissioning of the CRS (03) in a non-homogeneous salt layer (02) close to the fault (08) can be seen in Figures 10a-10c.

[0105] In the state of the art, for example, when filling the CRS with sand from a licensed deposit, it is transported by truck (up to 15 m 3 ) of the sand extracted from the licensed deposit to the location of the CRS to be abandoned / decommissioned, in the order of tens of kilometers (32) for thousands of trips. Using as a reference an average CRS, with approximately 300,000 m 3 in volume, 20,000 round trips would be necessary, which would directly lead to an increase in traffic and greenhouse gas (GHG) emissions, in addition to the increase in costs for truck, driver and diesel rental and the risks due to increased exposure.

[0106] Furthermore, still in the state of the art, the disposal of construction demolition waste (RCC) from the infrastructure of the rock salt production or CRS storage facilities (on-site) takes place by means of transportation by truck (up to 15 m 3 ) of demolition waste from the CRS facility to a licensed landfill (33), on the order of tens of kilometers, for thousands of trips. This would also involve thousands of round trips, which would directly lead to an increase in traffic and greenhouse gas (GHG) emissions, in addition to the increased costs of truck, driver and diesel rental and the risks due to increased exposure.

[0107] By the method of the present invention, the filling of the CRS with particulate solid material (Figure 7), first gravel (14a-14d) and then sand (15a-15c), can be done, preferably, by recycling the demolition waste from the civil construction installed on site (27), which operated the CRS (Figures 9a-9c and 10a-10c). This results in an exceptional reduction in decommissioning costs, minimizing greenhouse gas (GHG) emissions, avoiding an increase in vehicle traffic, reducing the risk of traffic accidents, given the shorter distance (34) between obtaining the raw material (27) and the CRS (03), in addition to minimizing the RCC to be discarded (Class non-A).

[0108] Alternatively, depending on the size and quantity of CRS to be decommissioned, the gravel and sand may come from the recycling of construction demolition waste (CDR) from another area, outside the rock salt processing facilities, and even from a construction waste landfill (not illustrated).

[0109] Additionally, oil well drilling waste (within national specifications) can be discarded during the CRS filling process, between the injection of gravel and sand (not illustrated).

[0110] During the filling of the CRS (03) with gravel (14a-14d) or sand (15a-15c), the brine present in the cavern is drained out of the CRS, in which it can be processed (tank, filters) to become drinking water, and the rock salt extracted from the brine can be used (not illustrated), as seen in Figure 11. Furthermore, in the case of the CRS close to the sea (23), the brine from the CRS can be disposed of there via a hose or brine pipeline (24), within the environmental specifications (concentration and temperature). Furthermore, in the case of a shallow saltwater aquifer, close (25) to the location of the CRS access well (03), the brine can be disposed of in a shallow well (26) built for this purpose and then abandoned. Such concepts are not mentioned in the prior art, which only mentions that the brine is released from the CRS.

[0111] Therefore, in the case of a CRS located in an inhomogeneous salt structure, or near geological faults or with a collapsed roof, the present invention buffers fluid percolation through the non-evaporitic rock layers present in the CRS and geological faults. This prevents CRS stability problems, seismicity, floor subsidence, and sinkhole formation.

[0112] Thus, after filling, sealing and abandoning the CRS, subsidence and inclinometry measuring instruments are installed on the ground, around the CRS, to monitor the measurements for 2 years, or as specified by the relevant legislation.

[0113] With the procedure illustrated in Examples 1 to 3, there is a greater filling of the voids and with the closing of the CRS, the compaction of the filling material in the CRS occurs more quickly (almost immediately) and generates negligible subsidence of the floor.

[0114] Furthermore, with the methodology of the present invention, the filling of the CRS is ensured with a larger filled volume (lower void index); with the blockage of flow by the faults and pore / permeable layers, avoiding the opening / propagation of faults; and the subsidence of the ground floor is minimized. This maximizes the discarded volume of RCC; ensures the long-term isolation of the CRS; and guarantees environmental, civil and property safety in the vicinity of the CRS.

[0115] Furthermore, the present invention is environmentally friendly and sustainable; it has lower greenhouse gas (GHG) emissions, that is, a smaller carbon footprint; it causes less environmental impact; and it has a lower overall cost, as it uses Class A RCC, instead of using gravel or washed sand extracted from deposits or riverbeds, and transported tens of kilometers by thousands of truck trips, emitting greenhouse gases and congesting traffic.

[0116] It is worth noting that the method described here perfectly complies with the provisions of article 9 of Law 12,305 / 2010, which states: “In the management of solid waste, the following order of priority must be observed: non-generation, reduction, reuse, recycling, treatment of solid waste and environmentally appropriate final disposal of waste.” (National Solid Waste Policy - PNRS).

[0117] The present invention also provides a system to enable the filling, sealing and abandonment of a salt rock cave (CRS) located in a non-homogeneous salt structure (with the presence of porous / permeable layers within the CRS) and / or close to geological faults and / or which has had a cave roof collapse, which is composed of: (i) equipment for demolishing the installed infrastructure or other buildings; (ii) excavator; (iii) mobile recycling plant for construction waste, composed of a Roll On / Roll Off truck, a mobile crusher and a mobile rotary screen docked to the truck; (iv) conveyor belt for loading gravel or sand; (v) gravel or sand mixer with water; (vi) pressure, flow, temperature and volume meters filled in the cave (sonar); (vii) pumps to pressurize the CRS; and (viii) system to prepare and inject cement paste until filling the CRS access well to complete the permanent abandonment of the CRS.

[0118] The description made thus far of the present method and system, as well as its examples of embodiment, must be understood as not limiting the invention, which is limited only to the scope of the claims that follow.

Claims

CLAIMS 1- Method of filling, sealing and abandonment (decommissioning) of a cavern characterized by being applied to a cavern built in saline rock (CRS), especially located in a non-homogeneous salt structure, close to geological faults or which has had a cavern ceiling collapse, preferably comprising the following steps: a) demolition of the civil construction infrastructure installed in the CRS project (27) or of other nearby buildings, affected by the CRS and condemned to demolition (27); b) insertion of the demolition material by excavator (29) in a mobile recycling plant for construction waste (RCC) (28), for the comminution of Class A Construction Waste (RCC) to obtain gravel (30) or sand (31), machined or industrialized, with different granulometries;c) loading gravel (30) or sand (31) onto a conveyor belt, mixing with water in a mixing vessel and injecting the gravel or fluidized sand into the cavern access well, individually; d) sequential filling of the cavern with particulate solid material, i.e., first with materials of larger grain size (gravel 3, gravel 2, gravel 1, gravel 0) and subsequently with material of smaller grain size (coarse sand, medium sand, fine sand), to form a structural framework within the CRS; e) pressurization of the cavern and monitoring of variables (temperature, volume, pressure) for a period of 24 to 72 hours; f) completion of the displaced volume in the cavern for the non-saline rocks and for the faults, adding fine sand (20) to the CRS to complete the displaced volume (16); eg) filling the access shaft to the CRS with cement paste (21), thus concluding the permanent abandonment of the CRS (22).; 2- Method, according to claim 1, characterized in that the mobile RCC recycling plant is powered by electricity or a diesel engine; being composed of a Roll On / Roll Off type truck (28), a mobile crusher (impact or jaw), and a mobile rotary screen, both docked to the truck. 3- Method, according to claim 1, characterized by filling the CRS (03): a) starting with gravel 3 (14a), with maximum characteristic dimension (DMC) between 25 to 50mm (30 to 40% of the Geometric Volume of the Cavern - VGC); then with gravel 2 (14b), with DMC between 19 to 25mm (15 to 25% of the VGC); then with gravel 1 (14c), with DMC between 9.5 to 19mm (10 to 15% of the VGC); and with gravel 0 (14d) (gravel) with DMC between 4.8 and 9.5 mm (5 to 10% of the VGC); b) start with coarse sand (15a), with DMC between 2.0 and 4.8 mm (5 to 25% of the VGC); then with medium sand (15b), with DMC between 0.42 and 2.00 mm (3 to 10% of the VGC);and with fine sand (15c) with DMC between 0.07 and 0.42 mm (2 to 5% of the VGC); c) pressurize the CRS (03), between 50% and 90% of the burial gradient or the previously calculated fracture gradient, to help the smallest particles to flow and fill the empty volumes (17), stopping (18, 19) the flow in the pores of the porous / permeable layers (02) and in the faults (08), d) for a period of 24 to 72 hours, monitor the pressure, temperature and fluid level in the CRS (with pressure transducers, temperature sensors and sonar inside the CRS access well); e) replenish the displaced volume in the cavern to the non-saline rocks and to the faults, adding fine sand (20) to the CRS to complete the displaced volume (16). 4- Method, according to claim 1, characterized by the fact that the gravel and sand can be alternatively machined or industrialized, from; from other civil construction demolition areas (outside rock salt processing facilities) and / or Class A RCC landfill. 5- Method according to claim 3, characterized in that the gravel used in filling the CRS (03) is machined or industrialized, from Class A construction demolition waste (RCC), fluidized with the brine present in the CRS, comprising between 60% and 90% of the VGC. 6- Method according to claim 3, characterized in that the sand used in filling the CRS (03) is machined or industrialized, from Class A construction demolition waste (RCC), fluidized with the brine present in the CRS, comprising between 40 and 10% of the VGC.7- Method, according to claim 1 or 3, characterized in that, in step (d), a filling volume of the CRS greater than 95% is obtained, in addition to plugging or sealing the faults, fractures or permeable materials with non-contaminating and non-hazardous RCC, minimizing the subsidence basin generated, avoiding contamination of surface waters and the generation of exudation.8- Method, according to claim 1 or 4 to 6, characterized in that the gravel or sand is produced: - preferably, via comminution or crushing processes (crushing, grinding and granulating) of the construction demolition waste (RCC), on site, of the enterprise in which the CRS is located; and - alternatively, via comminution or crushing processes (crushing, grinding and granulating) from the recycling of construction demolition waste (RCC) from another area, outside the rock salt processing facilities, and even from a construction waste landfill, or even extracted from deposits. 9- Method, according to claim 1 or 3, characterized in that, in addition, oil well drilling waste (within national specifications) can be discarded in the process of filling the CRS, between the injection of gravel and sand. 10- Method, according to claim 1 or 3, characterized in that the brine, which is drained out of the CRS, is processed, in tanks or filters, to become drinking water or is disposed of in a shallow saltwater aquifer or in the sea. 11- Method, according to claim 1, characterized in that the access well to the cavern is sealed and abandoned, definitively (step g), with cement plugs from the last casing shoe to the floor. 12- System for filling, sealing and abandoning (decommissioning) a cavern, characterized in that it is applied to a cavern built in saline rock (CRS), especially located in a non-homogeneous salt structure, close to geological faults or which had a cavern ceiling collapse, comprising: (i) equipment for demolishing the installed infrastructure or other constructions (27); (ii) excavator (29) for inserting the demolition material into the mobile recycling plant for construction waste (28);(iii) mobile recycling plant for construction and demolition waste (28), consisting of at least one Roll On / Roll Off truck, one mobile crusher and one mobile rotary screen docked to the truck; (iv) conveyor belt for loading gravel (30) or sand (31); (v) gravel or sand mixer with water; (vi) pressure, flow, temperature and volume meters filled in the cavern (sonar); (vii) pumps to pressurize the CRS; (viii) system to prepare and inject cement paste until filling the CRS access well to complete the permanent abandonment of the CRS. 13- System, according to claim 12, characterized in that the recycling plant can obtain waste, such as gravel and sand, with the following dimensions:; a) gravel 3 (14a), with maximum characteristic dimension (DMC) between 25 and 50 mm (comprising 30 and 40% of the VGC); b) gravel 2 (14b), with DMC between 19 and 25 mm (comprising 15 and 25% of the VGC); c) gravel 1 (14c), with DMC between 9.5 and 19 mm (comprising 10 and 15% of the VGC); d) gravel 0 (14d) (gravel) with DMC between 4.8 and 9.5 mm (comprising 5 to 10% of the VGC); e) coarse sand (15a), with DMC between 2.0 and 4.8 mm (comprising 5 to 25% of the VGC); f) medium sand (15b), with DMC between 0.42 and 2.00 mm (comprising 3 to 10% of the VGC); and g) fine sand (15c) with DMC between 0.07 and 0.42 mm (comprising 2 to 5% of the VGC). 14- System, according to claim 12 or 13, characterized in that the waste of larger grain size (gravel) is inserted at the bottom of the CRS and that of smaller grain size (sand) is inserted at the end of filling the CRS to fill the voids and flaws.15- System, according to any one of claims 12 to 14, characterized by completing the displaced volume in the cavern, after the pressurization and monitoring period, with the addition of fine sand (20) in the CRS and finally filling the access well to the CRS with cement paste (21), thus concluding the permanent abandonment of the CRS (22).

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