The invention relates to neutralization of drilling wastes and can be used for disposal of drill cutting wastes when drilling deep wells of various purpose.

A method for disposal of well drilling wastes is known from RF Patent for Invention No. 2213121, said method comprising sludge pit reclamation, including evacuating the liquid phase of waste drilling fluid from the pit, eliminating the fluidity of its coagulates, filling the remaining drilling wastes with mineral soil, and land planning. Before the sludge pit is evacuated, contaminant concentrations are determined in waste drilling fluid, and the content of contaminants in the fluid is brought to levels below maximum allowable concentrations. The evacuation is performed by releasing the liquid phase through a sludge pit dike opening.

A method is known for drilling sludge neutralization from RF Patent for Invention No. 2541957, said method comprising reception of drilling sludge from the ditch line of a drilling rig or downstream of the vibrating screens of a central hydrocyclone cleaning system from the screw conveyor of a drilling rig, preparation for drilling sludge neutralization/processing, preparation of chemical solutions for dewatering and neutralization of drilling sludge, drilling sludge mixing with chemicals, and injection (with simultaneous stirring) of a neutralizing and encapsulating compound, coagulant and flocculant into the drilling sludge in reactors connected in series for "maturation" before dewatering. Then the drilling sludge is dewatered on a chamber press filter or belt press filters, and the filtrate is cleaned with subsequent re-use of the neutralized drilling sludge.

A method for disposal of well drilling wastes is also known from RF Patent for Invention No. 2392256. The method includes separation of drilling sludge from the drilling fluid circulating in the drilling process, and storage of drilling sludge in sludge pits. The drilling sludge is processed into a sludge semi-product which is supplemented with humic mineral concentrate as a composite mixture modifier, and the territories of all soil excavations for placement of neutralized drilling products are returned into land circulation. Sludge pits are constructed as several temporary operative parallel pits, each of them receiving sludge from drilling of different rock strata alternately penetrated by a drilling tool. A process station in the form of several parallel basins is provided to obtain an end product, and ameliorant maturation is arranged in each of them on a rotating basis.

A disadvantage of this analog consists in an increase of exposed disturbed lands needed for arrangement of several earth drilling pits, i.e. efforts toward rehabilitation of contaminated territories lead to even greater disturbed areas where earth pits, basins, sumps, etc. are provided for storage and further maturation of drilling sludges, more precisely, their substances. And, despite the fact that it is planned to temporarily occupy these work areas for cleaning and treatment of sludges, the time of such actions may, however, significantly extend for various reasons - climatic, financial, organizational ones (insufficient quantity of additional chemicals because it is necessary to treat the constructed pits themselves as well, rehabilitate them and return them into land circulation).

The closest analog of the claimed invention is the waste drilling sludge disposal method (RF Patent for Invention No. 2486166) which includes the preparation of a process area, collection, excavation and delivery of oil-contaminated soils to the process area, preparation of oil-contaminated soil, application of a humic mineral complex and provision of oil-contaminated soil biostructuring processes. The method for waste drilling sludge neutralization includes liming, chemical coagulation, application of flocculants and a humic mineral complex, step-by-step removal of drilling sludge to a buffer layer with laying of drilling sludge to a maximum layer of 8-10 cm, drying of drilling sludge, and stockpiling for further disposal. The humic mineral complex is obtained in the course of low-temperature mechanochemical extraction of humic acids by disintegration of brown coal in a disperser with mixing of the crushed brown coal with alkali.

A disadvantage of the closest analog consists in the lack of the guaranteed high- quality treatment of the entire drilling sludge volume contained in a sludge pit, without exception, in any part of it— in the corners, on the bottom, etc., both to a sufficient degree of chemical treatment with reagents and a sufficient degree of mechanical mixing, with regard to both duration and intensity, avoiding undermixed areas in any segment of the sludge pit.

The object of the invention is to ensure improvement in the quality of treated drilling sludge disposal and formation of a product with concentrations lower that maximum allowable values by eliminating "dead areas" (insufficiently processed areas in the bulk of the treated drilling sludge) at each stage of sludge neutralization, as well as by finding optimum conditions with regard to the time of contact between the treated sludge and chemicals and to the quantitative ratios of the chemicals and sludge.

The essence of the claimed invention is that the waste well-drilling sludge disposal method provides for drilling sludge separation from drilling fluid and drilling sludge discharge into a sludge pit, inside which a cell-type separation metal fixture is installed in the form of vertically oriented bottomless cells to ensure capability for further individual batchwise chemical and technological action on drilling sludge in each of the cells, at first, by destabilizing the colloid system by addition of ferric sulfate in the amount of about 1-3 % of the total drilling sludge weight until visible mass liquefaction and uniform structure formation, then by absorbing the obtained mass by addition of expanded vermiculite in the amount of about 1 % of the total drilling sludge weight, and, finally, by adding humic acids in the amount of about 1 % of the total drilling sludge weight; in this regard, the chemical and technological action - destabilization, absorbtion and addition of humic acids - is applied with constant stirring at a rate of about 30-60 revolutions per minute within approximately 30-60 minutes in each of the mentioned operations, and significant parameters are checked until values below maximum allowable concentrations are reached; then the metal fixture is removed from the sludge pit, and soil from the rehabilitated areas is added.

A method is also claimed in which ferric sulfate is used in the form of crystalline hydrate Fe ₂ (S0 ₄ ) ₃ -7H ₂ 0. A method is also claimed in which, along with the features described above, ferric sulfate is used in the form of crystalline hydrate Fe2(S04)3 9H20.

The technical result of the claimed invention is achieved by introducing a new operation that has an influence on the rest of the chemical and technological process of drilling sludge treatment, from the beginning to the very end. Introducing the division of the whole drilling sludge mass to be treated into equal, convenient areas and portions (taking into account the overall dimensions of the operated equipment - mixers, agitators, etc., their work zone sweep diameter and with elimination of "dead areas" during stirring, where agitators have been previously unable to cover all processed material of the sludge pit as a whole, with calculation of minimally required, but sufficient quantity of chemicals) eliminates unreacted areas in the treated sludge mass, while making the treatment process (including chemical action aspects) high-quality, cost-efficient and maximally profitable.

The division of the sludge pit throughout the volume into equal parts in the form of a cellular structure with vertically oriented cells is provided using a prepared strong working metal fixture installed to provide a capability of dismantling after the treatment of the whole processed sludge mass is finished, ensuring easy removal of the cells which are bottomless like molds.

The introduced first (before the beginning of any chemical and even mechanical actions) operation of the formation of the cells dividing the whole treated mass into the parts which thus become more easily and thoroughly treatable in both mechanical and chemical ways until the full completion of each of the operations at all stages, as well as with visual check of each area of the treated mass, allows, if necessary, some correction of time or quantity of interacting materials due to the additional time needed, for example, in case of rock stratum complication in the course of well drilling. The optimally selected and checked mode of action at each of the stages within 30-60 minutes and the chemical ratios presented in the essence of the invention provide guaranteed quality up to the achievement of values below maximum allowable concentrations. However, for uncomplicated rock strata in the course of penetration, we may sometimes limit ourselves to lesser amount of interaction time with obligatory stirring of the appropriate treated sludge portion in each of the pit cells. The visual check of sludge material for color and structural changes from stage to stage suggests the treatment readiness time at each specific stage. The changing color of drilling sludge at the first stage may be a criterion of readiness to the next action stage. The instrumental check with sensors and reference standards of indication is more accurate.

Thus, after the first chemical action (destabilization of the colloid system by ferric sulfate), the gray mossy color of the drilling sludge changes to the rusty red one. This is a kind of a reference mark indicating a degree in which the treated material in a cell is ready for the next stage (absorption with expanded vermiculite). In addition, after the action of ferric sulfate, visible mass liquefaction is observed along with uniform structure formation.

Following the completion of the second stage of the chemical action with expanded vermiculite and completion of the third stage of chemical action with humic acids, the color of the product in cells also changes - toward the black color gamma.

This is a tentative criterion of the treated material sufficiency for and readiness to preparation to application into the soil of land areas. For more detailed studies, when seeding of the rehabilitated areas is planned, apparatus-based check is used to verify density, acidity and other significant parameters. On this basis, recommendations are made on the optimum use of the rehabilitated soils or their further improvement, provided that it is reasonable to bring them up to the required level of usage for forest plantations, arable lands, pastures, etc.

Thus, the technical result of the claimed drilling sludge disposal method providing capability for the visual check of readiness to the next stage of processing the drilling sludge, which undergoes changes in the course of treatment, makes it possible to eliminate the unnecessary action time and save the resources spent. On the other hand, eliminating the excess of chemicals and changing the action time at each of the stages prevent from drilling sludge treatment quality deterioration due to more thorough, batchwise treatment of each fragment of the whole material mass through division into cells. Due to the modern technological infrastructure, such as the equipment of wells, conventional computer equipment and a conventional controller, along with the measures recommended in the claimed patent, this method corresponds to the high level of the claimed technical solution in this area and is suitable for industrial use with significant saving of costs.

The method is implemented as follows.

Drilling sludge is separated from drilling fluid. Based on the sludge pit design, the necessary quantity of cells is calculated. A cell-type metal fixture in the form of vertically oriented cells, which has been previously delivered to the sludge pit, is installed using a crane into the sludge pit which is empty (or filled with drilling sludge, the structure of which allows doing so). All cells are interconnected by fasteners to provide additional structural stability and strength.

The disposal of drilling sludge is based on sequential addition of various chemicals into it with their thorough stirring using a stirring device. The technological process of drilling sludge disposal is the same in each cell.

After the cell-type separation metal fixture is installed, coagulant (ferric sulfate) is added into the drilling sludge (the cell volume is filled with the sludge by 80 %) in the amount of about 1-3 % of the total drilling sludge weight in order to destabilize the colloid system. The drilling sludge is mixed with the coagulant using a stirring device, for example, an agitator. The calculated amount of ferric sulfate is weighed/dosed and delivered to a cell with an activated agitator; then the calculated amount is filled into the cell. The stirring time is generally about 30-60 minutes. The agitator rotation speed is about 30-60 rpm. At this stage, the end of the process is checked visually by visible mass liquefaction and uniform structure formation, and pH can be measured as well. When pH = 7 is reached, the process is considered to be finished. For the purpose of implementing the claimed method, ferric sulfate is used in the form of crystalline hydrate Fe ₂ (S0 ₄ ) ₃ -7H ₂ 0 or Fe ₂ (S0 ₄ ) ₃ -9H ₂ 0. In the course of interaction between the drilling sludge and coagulant, dissociation of electrolyte Fe ₂ (S0 ₄ ) ₃ in water leads to formation of ions 2(Fe ³⁺ ), 3(S0 ₄ ) ² , which promotes destabilization (breakdown) of the stable drilling sludge gel and its separation into solid and liquid fractions.

Then a coagulation process takes place - solid particles of the drilling sludge stick together during hydrolysis according to the following pattern:

Fe ³⁺ +2HOH (FeOH) ²⁺ +2H ⁺ .

The liberated ion neutralizes the excess of OH groups in the drilling sludge until neutral pH is reached.

If water is in excess in the gel/drilling sludge system, ferric iron ions are hydrolyzed to hydroxide Fe(OH) ₃ which is then, as water evaporates, transforms, respectively, into ferric oxide:

2Fe(OH) ₃ Fe ₂ 0 ₃ +3H ₂ 0.

The formed ferric oxide absorbs organic substances and reduces drilling sludge toxicity.

Then alumosilicate (expanded vermiculite) is added into the obtained drilling sludge mass with ferric sulfate for absorption in the amount of about 1 % of the total drilling sludge weight. The stirring time is about 30-60 minutes. The agitator rotation speed is about 30-60 rpm. The end of stirring is checked visually by formation of the uniform mass structure with inclusions of small blobs.

The process of interaction between drilling sludge ecotoxicants and expanded vermiculite is divided into five conditional interaction stages (I - V):

I - interaction between drilling sludge ecotoxicants and vermiculite, physical and chemical processes of drilling sludge ecotoxicant dissolution and dissociation in the liquid phase of expanded vermiculite;

II - physical and chemical processes of overcoming the buffering factors of expanded vermiculite (exchange reactions, reactions of combination, chemical absorption of drilling sludge ecotoxicant ions by the solid colloid-dispersed and sol- gel phases of expanded vermiculite); III - processes of incongruent hydrolysis (destruction) of expanded vermiculite, formation of a multicomponent system of the oxides extracted from expanded vermiculite crystal lattices, formation of primary metastable compounds hydrated to a maximum extent, and formation of the colloid-dispersed and sol-gel phases of the newgrowths;

IV - phase transformations of the primary compounds into more stable secondary, tertiary, etc. ones (processes of bifurcation of the newgrowths), which leads to the condensation and increased stability of the sol-gel phase of the newgrowths;

V - formation (synthesis) of polymineral aluminosilicate newgrowths with binding properties, which is caused by spontaneous optimization of the ratio and composition of products in liquid-phase chemical reactions.

Then the action on the obtained mass is finished by adding humic acids in the amount of about 1% of the initial total drilling sludge weight. The humic acids are purchased by contractors in a ready-to-use powdered form. The stirring time is about 30-60 minutes. The agitator rotation speed is about 30-60 rpm.

The end of stirring is checked visually, or using appropriate equipment as well, by full distribution of black-colored humic acids.

The chemical mechanism behind the neutralization of the obtained mass after addition of humic acids consists in interaction between metals and these acids with formation of water-insoluble humates of heavy metals. The physical and chemical fundamentals of interaction of humic acids with heavy metals and organic compounds include the simultaneous processes of ion exchange, adsorption and absorption, co-coagulation and occlusion that ensure efficient remediation.

A product is formed at the end of this stage. After it is obtained from cells, a composited sample is taken and prepared in compliance with regulatory documents. This sample is analyzed for compliance with the existing requirements. If the sample complies with them, the product remaining in the sludge pit is mixed with the soil produced as a result of sludge pit excavation at the product/soil ratio of 1:1. The result is a soil/sludge mixture. If the sample does not comply with the existing standards, the process of treatment with the humic mineral component is continued until the product with concentrations not higher than maximum allowable values is obtained.

Upon completion of product formation, the special fixture (bottomless cells) is dismantled and removed along with the stirring device from the sludge pit. The side waterproofing layer of the sludge pit is also dismantled and removed from the sludge pit.

The product is mixed with soil using construction machinery, such as bulldozers, excavating machines, etc. A moist soil/sludge mixture is formed as a result of mixing. The end of the technological process is visually checked by the formation of the uniform and evenly colored mixture.

The dry soil/sludge mixture is produced from the moist soil/sludge mixture as a result of natural processes of water evaporation within 10-20 days at ambient temperature within 20-25 °C and normal air humidity.

The obtained dry soil/sludge mixture is used as man-made soil for sludge pit backfilling on site in the field with levelling of the terrain.

The dry soil/sludge mixture is flattened using special machinery, and the top soil removed when the sludge pit was excavated is replaced; it is subsequently sown with herbs, planted with trees and shrubs and returned to the agricultural use.

Example.

The method is implemented in accordance with the technique described above. A stirring device is installed and fastened on a 2 ^c 2 ^c 2.5 m cell in the following order: the cell cover is lifted, an agitator is installed into an opening in the center of the cover, and then it is lowered into drilling sludge while closing the cover.

Stirring is performed, for example, by an agitator with two propeller-type blades located perpendicular to each other and providing the counter-stirring of drilling sludge.

There may be more than one stirring device, depending on the required drilling sludge disposal rate.