An oil-based drilling debris on-site harmless treatment system and method based on smoldering technology

Abstract

The present application relates to a kind of oil-based drilling cuttings harmless treatment system and method based on smoldering technology, smoldering technology is applied to the harmless treatment process of oil-based drilling cuttings generated in the process of oil-based drilling mud not falling, and the heat generated by tail gas treatment system is heated by heat exchanger to mud in the mud not falling treatment collection box, prevent freezing when winter construction, not only effectively ensure the complete oil-based mud not falling, protect the environment around drilling operation, while realizing the harmless treatment of oil-based drilling cuttings on site, avoid the risk of long-distance transportation of oil-based drilling cuttings to dangerous waste treatment plant for terminal processing.This application can carry out oil-based drilling cuttings reduction while drilling on-site, harmless treatment, realize production disposal to avoid the risk of oil-based drilling cuttings leakage in the process of transportation.At the same time, the waste heat of smoldering treatment process is fully utilized, and has the advantages of oil-based drilling cuttings disposal completely.

Description

Technical Field

[0001] This invention relates to the field of oily waste treatment technology, and more specifically, to an on-site harmless treatment system and method for oil-based drilling cuttings based on smoldering technology. Background Technology

[0002] Oil-based drilling cuttings are primarily a mixture of oil-based drilling fluid and cuttings generated during drilling operations using on-site solids control equipment, circulating tank bottoms, and dewatering / reduction equipment. This mixture includes base oil, surfactants, inorganic salts, drill cuttings, wastewater, asphalt-based additives, and lignite-based additives. According to the "National Hazardous Waste List," oil-based drilling cuttings are classified as HW08 hazardous waste. Improper handling and disposal can lead to the spread of pollutants, causing environmental pollution, large-scale soil and groundwater contamination, and air pollution, posing a threat to human health. Therefore, from the perspectives of industry development, environmental protection, and economic benefits, the treatment of oil-based drilling cuttings is particularly urgent and important. It is necessary to promote the centralized and integrated treatment of oil-based drilling cuttings based on the principles of reduction, resource recovery, and harmlessness.

[0003] Around the 1980s, countries worldwide began systematic research on oil-based drilling cuttings treatment, resulting in a series of effective treatment technologies, broadly categorized into two types: conventional treatment technologies, which focus on environmental protection by eliminating the harmful characteristics of oil-based drilling cuttings or isolating them from the ecosystem (a type of end-of-pipe environmental remediation); and resource utilization technologies, which aim for "full value recovery" of oil-based drilling cuttings. Comparatively, conventional oil-based drilling cuttings treatment technologies suffer from poor universality, resource waste, immature technology, and high investment costs, and will gradually be replaced and upgraded. Current resource utilization technologies can recover base oil from oil-based drilling cuttings, improving resource reuse rates, but improvements are still needed. For example, the hot washing centrifugation process has problems such as incomplete treatment and large wastewater generation; the hot desorption process is not yet fully mature and has problems such as coking and equipment deformation. Moreover, when the temperature is higher than 350°C, oil cracking occurs, generating a large amount of waste gas and potentially causing oil deterioration, making it impossible to re-blend base oil into oil-based drilling fluid; the solvent extraction technology has problems such as large equipment investment, high requirements for extractants, and complex processes.

[0004] The current method for handling oil-based drilling cuttings involves on-site, non-landing treatment with oil-based mud to create oil-based drilling cuttings, which are then collected and transported to a mud treatment center for centralized processing. However, the transportation of oil-based drilling cuttings itself consumes a significant amount of energy, which obviously increases transportation costs and incurs high processing fees for the mud treatment center. Furthermore, the transportation of oil-based drilling cuttings also poses environmental and safety hazards such as leakage and spillage. Therefore, there is an urgent need for a process and method that aims at reduction, harmlessness, and resource recovery, enabling effective and thorough on-site treatment of oil-containing drilling cuttings to quickly transform them into environmentally harmless products. Summary of the Invention

[0005] To address the aforementioned issues, this invention proposes an on-site harmless treatment system and method for oil-based drilling cuttings based on smoldering technology. This system enables the on-site harmless treatment of oil-based drilling cuttings, and by treating the cuttings simultaneously with production, it avoids leakage and spillage of oil-based drilling cuttings during transportation. It has the advantages of not generating secondary pollution, having a short treatment cycle, and thoroughly removing pollutants from oil-based drilling cuttings.

[0006] A field-based harmless treatment system for oil-based drilling cuttings based on smoldering technology includes: an oil-based mud non-landing treatment unit and a smoldering treatment unit, wherein:

[0007] The oil-based mud non-landing treatment unit includes: drilling cuttings collection box 2, feeding screw conveyor 3, centrifuge 4, first oil-based mud collection box 5, horizontal centrifuge 6, second oil-based mud collection box 7, submersible slurry pump 8, and discharge screw conveyor 11.

[0008] The smoldering treatment unit includes: a burner 12, a smoldering reactor 13, a condensation device 14, a high-temperature oxidation chamber 15, a gas-to-gas heat exchanger 16, a chimney 17, and an oil-water collection tank 18;

[0009] The smoldering reactor 13 consists of a preheated air inlet 131, an air inlet chamber 132, a lower gravel layer 133, a smoldering reaction zone 134, an upper gravel layer 135, a temperature detector 136, and an exhaust gas treatment system inlet 137. The smoldering reactor 13 uses the high-temperature flue gas generated by the burner 12 as the ignition heat source. The air inlet chamber 132 and the lower gravel layer 133 are separated by an air inlet perforation plate. The air inlet perforation plate is made of a high-temperature resistant and anti-clogging air inlet cap to prevent the air inlet from being blocked and to improve the uniformity of heat source input.

[0010] The gas-to-gas heat exchanger 16 is a shell-and-tube heat exchanger. The high-temperature flue gas flowing out of the high-temperature oxidation chamber 15 flows into the gas-to-gas heat exchanger 16. Fresh air from the outside flows through the heat exchange tubes and indirectly exchanges heat with the high-temperature flue gas outside the tubes to achieve waste heat recovery and utilization. After heat exchange, part of the fresh air is led to the smoldering reactor 13 to provide combustion air for the smoldering reaction, and part is led to the drilling cuttings collection box 2, the first oil-based mud collection box 5, and the second oil-based mud collection box 7. Air coils are provided at the bottom of the three boxes. The preheated air is heated by the air coils to prevent the drilling fluid from freezing and affecting the drilling operation.

[0011] Large-diameter drilling cuttings 9 and small-diameter drilling cuttings 10 are discharged via discharge screw conveyor 11 to ensure that the two types of drilling cuttings are uniformly mixed during the discharge process and then form a relatively loose packing layer in the smoldering reaction zone 134 within the smoldering reactor 13, ensuring the porosity to maintain a stable reaction during the smoldering process.

[0012] Furthermore, both the first oil-based mud collection box 5 and the second oil-based mud collection box 7 are equipped with mud stirring devices to prevent mud sedimentation; the bottom of the drilling cuttings collection box 2 is equipped with a spiral conveying device to ensure efficient conveying of cuttings. At the same time, both the first oil-based mud collection box 5 and the second oil-based mud collection box 7 are equipped with temperature monitoring devices to control the heating temperature of the materials inside the box by the preheated air between 20-25°C.

[0013] Furthermore, the condensation device 14 condenses and separates the high-boiling-point organic matter and water vapor in the tail gas from the outlet of the smoldering reactor 13. The condensed high-boiling-point organic matter and water vapor enter the oil-water collection tank 18 and are reinjected into the second oil-based mud collection tank 7, and are finally reused in the preparation process of oil-based drilling mud. The non-condensable gas containing low-boiling-point organic matter flows to the high-temperature oxidation chamber 15 after passing through the flame arrester for complete incineration and degradation, thus avoiding the emission of organic matter into the atmosphere.

[0014] A method for the on-site harmless treatment of oil-based drilling cuttings based on smoldering technology, using the aforementioned system, includes the following steps:

[0015] Step 1: Oil-based drilling cuttings 1 are first collected by drilling cuttings collection box 2. The bottom of drilling cuttings collection box 2 is equipped with a spiral conveyor to transport the oil-based drilling cuttings to the feeding section of the feeding spiral conveyor 3. The feeding spiral conveyor transports the cuttings to the feeding end of the spin dryer 4. After being dispersed by the distribution plate, the cuttings enter the spin dryer 4.

[0016] Step 2: Under the action of centrifugal force, the liquid phase and solid particles with a diameter of <0.35mm smaller than the gap of the screen basket in the drilling cuttings pass through the screen basket and flow into the liquid outlet ring of the lower cylinder. Then, they are discharged from the machine through the liquid outlet pipes on both sides of the lower cylinder and fall into the first oil-based mud collection box 5 below the centrifuge 4. The other solid phase of the drilling cuttings is kept inside the screen basket. Using the speed difference between the rotor scraper and the screen basket, the rotor scraper scrapes the drilling cuttings off the screen basket and pushes them to the bottom of the screen basket. The dewatered drilling cuttings are discharged into the discharge screw conveyor 11 below the centrifuge 4.

[0017] Step 3: The drilling fluid in the first oil-based mud collection tank 5 is transported to the centrifuge drum by the centrifuge slurry pump and rotates at high speed. The screw conveyor rotates at a speed slightly less than that of the drum under the action of the differential gear. The drum and the screw conveyor form a separation and conveying mechanism with a certain differential speed and high speed rotation in the same direction. Under the action of centrifugal force which is hundreds or even thousands of times greater than gravity, an annular liquid pool is formed in the drum. Due to the density difference between the solid phase and the liquid phase, the heavier solid phase particles have a greater centrifugal force and thus settle to the edge of the liquid pool, thereby forming sludge on the inner wall of the drum. Under the relative movement of the screw blades and the drum, the solid phase sludge is pushed to the small end of the drum and discharged from the sludge discharge hole, falling into the discharge screw conveyor 11 below the horizontal centrifuge 6. The clear liquid phase in the inner ring is discharged to the second oil-based mud collection tank 7 through the overflow hole via the spiral channel, thus realizing the production process of continuous solid-liquid phase separation.

[0018] Step 4: During operation, the low-density drilling fluid in the second oil-based mud collection tank 7 is flushed by the submersible slurry pump 8 to prevent equipment blockage; when a certain amount is accumulated, it is pumped to the solids control system at the drilling site for reuse.

[0019] Step 5: The large-diameter drilling cuttings 9 discharged from the centrifuge 4 and the small-diameter drilling cuttings 10 discharged from the horizontal centrifuge 6 are mixed and stirred by the discharge screw conveyor 11 and then transported to the smoldering reactor 13.

[0020] Step Six: After the smoldering reactor 13 is filled, the burner is started, and the high-temperature flue gas generated by the burner is used as the ignition heat source. After smoldering occurs, the tail gas containing organic gas components first flows into the condensation device 14 for condensation and collection. The condensed high-boiling-point organic matter and water vapor enter the oil-water collection tank 18 and are reinjected into the second oil-based mud collection tank 7, and finally reused in the preparation process of oil-based drilling mud. The uncondensed combustible gas enters the high-temperature oxidation chamber 15 for incineration. The high-temperature flue gas flowing out of the high-temperature oxidation chamber 15 flows into the gas-to-gas heat exchanger 16. Fresh air from the outside flows through the heat exchange tubes and indirectly exchanges heat with the high-temperature flue gas outside the tubes to realize the recovery and utilization of waste heat.

[0021] Step 7: After heat exchange, part of the fresh air is directed to the smoldering reactor to provide combustion air for the smoldering reaction, and part is directed to the drilling cuttings collection box 2, the first oil-based mud collection box 5, and the second oil-based mud collection box 7. Air coils are installed at the bottom of the three boxes. The preheated air is heated by these air coils to prevent the drilling fluid from freezing and affecting the drilling process.

[0022] Furthermore, two smoldering treatment units are set up on site. One unit is used for smoldering treatment, while the other unit is used to collect oil-based drilling cuttings from the discharge screw conveyor 11.

[0023] The beneficial effects of this invention are:

[0024] 1) The oil-based drilling cuttings waste of this invention undergoes multiple processing steps within the system to achieve on-site reduction and harmless treatment, avoiding secondary pollution caused by spillage during transportation, and enabling resource recovery. This provides a novel method for the processing of oil-based drilling cuttings during drilling. After smoldering treatment, the resulting solid phase can be used for well site restoration, road paving, etc.

[0025] 2) The processing system of this invention is fully integrated with the solids control equipment that generates oil-based drilling cuttings, ensuring that oil-based drilling cuttings do not fall to the ground, protecting the environment around the drilling operation, maximizing resource recovery, solving the environmental hazards caused by oil-based drilling cuttings, and also facilitating the scheduling of drilling site equipment.

[0026] 3) The processing system of this invention provides unified processing for oil-based drilling cuttings. The system is simple, highly effective, and significantly reduces the transportation and disposal costs of oil-based drilling cuttings produced during drilling operations, while also enabling the resource recovery of oil. Furthermore, the modular system design of this invention allows for the parallel installation of multiple units, enabling the assembly of various devices according to the well site conditions and waste volume. Attached Figure Description

[0027] Figure 1 This is a flowchart of the technical process of the present invention.

[0028] Figure 2 This is a schematic diagram of the smoldering reactor.

[0029] Figure label annotations:

[0030] Oil-based drilling cuttings-1, drilling cuttings collection box-2, feeding screw conveyor-3, centrifuge-4, first oil-based mud collection box-5, horizontal centrifuge-6, second oil-based mud collection box-7, submersible slurry pump-8, large-diameter drilling cuttings-9, small-diameter drilling cuttings-10, discharge screw conveyor-11, burner-12, smoldering reactor-13, condensation equipment-14, high-temperature oxidation chamber-15, gas-to-gas heat exchanger-16, chimney-17 and oil-water collection box-18;

[0031] Preheated air inlet-131, air intake chamber-132, lower gravel layer-133, smoldering reaction zone-134, upper gravel layer-135, temperature detector-136, exhaust gas treatment system inlet-137. Detailed Implementation

[0032] The technical solutions of the present invention will now be clearly and completely described with reference to the accompanying drawings in the embodiments of the present invention.

[0033] Example

[0034] Select a drilling site and install a smoldering reaction system consisting of the following equipment: oil-based drilling cuttings 1, drilling cuttings collection box 2, feeding screw conveyor 3, centrifuge 4, first oil-based mud collection box 5, horizontal centrifuge 6, second oil-based mud collection box 7, submersible slurry pump 8, large-diameter drilling cuttings 9, small-diameter drilling cuttings 10, discharge screw conveyor 11, burner 12, smoldering reactor 13, condensation equipment 14, high-temperature oxidation chamber 15, gas-to-gas heat exchanger 16, chimney 17, and oil-water collection box 18. Connect all interfaces.

[0035] The drilling rig generates approximately 20-25 cubic meters of waste oil-based drilling mud for every 100 meters of drilling. This waste oil-based drilling mud is first preliminarily separated by a vibrating screen. The material remaining on the screen, i.e., oil-based drilling cuttings 1, flows into the drilling cuttings collection box 2. The drilling cuttings collection box 2 in this system has external dimensions of 8000×2300×1800mm and an effective volume of 21m³. 3 It is made of 6mm thick corrugated plate and 100×100mm square steel welded together. The base is made of 3 20# I-beams and 12# I-beams welded together. The top is an open structure with steel grating laid at half the width to prevent large materials from falling into the tank. The side wall of the tank adopts a four-sided conical structure and is connected to the feeding screw conveyor to ensure that the materials can be discharged smoothly.

[0036] The spin dryer 4 has external dimensions of 8500×2200×1600mm and an effective volume of 21.2m³. 3The screen basket has a maximum diameter of 930mm, a gap of 0.35mm, a rotation speed of 0-1200rpm, and a total weight of 4750kg. The main motor is 55kW, and the auxiliary motor is 0.55kW. It is constructed from 6mm thick corrugated steel plates welded together with 100×100mm square steel. The base is made of three 25# and 12# H-beams welded together, topped with an 8mm thick steel plate. Except for the manhole and equipment installation areas, the tank surface is covered with 5mm thick anti-slip patterned plates. The tank bottom slopes 150mm towards the sand-cleaning door. The top of the tank uses 100×100×6mm square steel on both sides, and the dryer end has a lifting structure to ensure lower height during transport. After being processed by the dryer, rock chips larger than 0.35mm fall into the screw conveyor, while materials smaller than 0.35mm and oil-based mud flow into the No. 1 oil-based mud collection tank.

[0037] When the material in the first oil-based mud collection tank 5 is continuously fed into the feed pipe of the horizontal centrifuge 6, it enters the drum through its discharge port, where the drum rotates at high speed. The screw conveyor, under the action of the differential speed device, rotates at a speed slightly less than that of the drum. The drum and the screw conveyor form a separation-conveyor mechanism with a certain differential speed and high-speed rotation in the same direction. Under the action of centrifugal force hundreds or even thousands of times greater than gravity, an annular liquid pool forms inside the drum. Due to the density difference between the solid and liquid phases, the heavier solid particles settle to the inner wall of the drum, forming sludge. Under the relative motion of the screw blades and the drum, the sludge is pushed to the small end of the drum and discharged through the sludge discharge hole. The clarified liquid phase in the inner ring is discharged through the overflow hole via a spiral channel, thus realizing a continuous solid-liquid phase separation process. The centrifuge parameters used in this system are as follows: drum diameter 360mm, drum length 1217mm, drum speed 0~3200rpm, separation factor 2065, and throughput ≤30m³. 3 / h (mud concentration ≥1.1SG, centrifuge throughput decreases as mud specific gravity increases), total weight 3300kg, main motor power 37kW, auxiliary motor power 11kW, overall protection level IP54, power supply 380V / 50Hz.

[0038] After processing by the horizontal centrifuge 6, small-diameter solid materials (particle size less than 0.35mm) fall into the screw conveyor, while the oil-based mud flows into the second oil-based mud collection tank 7. It can be re-mixed and then reinjected into the drilling platform for recycling via submersible grouting pumps. Two submersible grouting pumps are provided, each with a 4kW motor, a speed of 1450rpm, and a flow rate of 30m³ / h. 3 / h, head is 14m, outlet size is 50mm.

[0039] After treatment by the oil-based drilling mud non-landing treatment system, the drilling platform will generate 7-8 cubic meters of drilling cuttings for every 100m of drilling. Three samples were randomly selected, and the oil content of the cuttings was measured to be 6.23%, 7.89%, and 9.68%, and the water content was 10-15%. These drilling cuttings were uniformly mixed to ensure a certain porosity and then uniformly transported to the smoldering reactor 13.

[0040] Two smoldering treatment systems are installed on site. This allows one system to handle smoldering while the other collects oil-based drilling cuttings from the discharge screw conveyor. Smoldering is a slow, low-temperature, flameless form of combustion. When the fuel reaches its ignition point, heat supply stops, and an energy balance is established between the energy released in the smoldering reaction zone and the heat lost outwards. The smoldering then begins to propagate forward sustainably.

[0041] Smoldering technology has the following advantages: ① Safety: The entire treatment process is controllable and stable. ② Lower cost: Pilot-scale testing by a domestic unit showed that the treatment cost is only one-third of other contaminated soil treatment methods. ③ Fast treatment speed: A certain volume of oil sludge can be treated within a few weeks to a few months. ④ Modular design: The equipment used occupies a small area, increasing the flexibility of oil sludge disposal projects. ⑤ Thorough treatment of organic pollutants: Due to the high-temperature combustion method, pollutants can be completely decomposed during smoldering. ⑥ Controllable secondary pollution: It can be combined with gas phase extraction, condensation, and incineration methods to thoroughly remove pollutants emitted during smoldering.

[0042] The smoldering treatment unit mainly consists of a burner 12, a smoldering reactor 13, and a tail gas extraction and treatment device. The smoldering reaction mainly takes place in the smoldering reactor 13, and the relevant temperature parameters during the reaction are recorded and monitored throughout by a temperature measuring device. The blower provides the air required for smoldering, the burner provides the heat required for the smoldering to begin, and the tail gas extraction and treatment device can effectively reduce the generation of secondary pollution. The system uses natural gas as the fuel for the burner 12, with a gas power of 20kW, a gas source pressure of 3kPa, and a rated voltage of 220V AC. The smoldering reactor 13 is a cylindrical structure with a bottom diameter of 5m and a height of 5m. After the smoldering reactor 13 is filled, the burner 12 is started, using the high-temperature flue gas generated by the burner 12 as the ignition heat source. After smoldering occurs, the tail gas containing organic gas components first flows into the condensation equipment for condensation and collection. The condensed high-boiling-point organic matter and water vapor enter the oil-water collection tank and are reinjected into the second oil-based mud collection tank 7, and finally reused in the preparation process of oil-based drilling mud. Uncondensed combustible gas enters the high-temperature oxidation chamber for incineration. The high-temperature flue gas flowing out of the oxidation chamber flows into the gas-to-gas heat exchanger. Fresh air from the outside flows through the heat exchange tubes, indirectly exchanging heat with the high-temperature flue gas outside the tubes, thus achieving waste heat recovery and utilization. The flue gas after heat exchange is discharged through the chimney in compliance with emission standards.

[0043] After heat exchange, a portion of the fresh air is directed to the smoldering reactor 13 to provide combustion air for the smoldering reaction, while another portion is directed to the drilling cuttings collection box 2, the first oil-based mud collection box 5, and the second oil-based mud collection box 7. Air coils are installed at the bottom of all three boxes, through which the preheated air heats the oil-based mud. Simultaneously, temperature monitoring equipment is installed inside both the first and second oil-based mud collection boxes 5 and 7 to control the heating temperature of the materials inside the boxes by the preheated air between 20-25°C. This waste heat recovery process effectively prevents the drilling fluid from freezing due to low outside temperatures during winter operations, thus avoiding disruption to the drilling process.

[0044] Using this on-site processing system and method for oil-based drilling cuttings based on smoldering technology, three random samples were collected. The oil content of the processed materials was reduced to 0.11%, 0.14%, and 0.21%, all lower than the highest national requirement (0.3%) for the harmless treatment of oil-based drilling cuttings. Compared to the initial oil content of 5-10% in the oil-based drilling cuttings, this system achieved a significant increase in contaminant removal efficiency, while simultaneously achieving on-site volume reduction and harmless treatment, avoiding secondary pollution problems caused by spillage during transportation. Resource recovery was also implemented, providing a novel method for the on-drilling processing of oil-based drilling cuttings. After smoldering treatment, the resulting solid phase can be used for well site restoration, road paving, etc.

[0045] In addition to the above system operation process, the relevant requirements for the electrical control unit of this system are as follows:

[0046] (1) The power supply system of this project adopts the TN-S form, a three-phase five-wire system. The power supply type for low-voltage power distribution is: AC380V / 220V / 3P+N+PE / 50Hz. The power distribution of this project mainly adopts a radial distribution method. Power is supplied from the main distribution cabinet to the distribution cabinets at each power consumption point through the laying method of unarmored cables with cable trays and conduits, and then to the electrical equipment through each distribution cabinet, or directly to the electrical equipment.

[0047] (2) The lighting used on site is explosion-proof, and the lamp poles are foldable. They can be laid down and fixed on the tanks during relocation and are directly controlled by the main control box. Each mud tank is equipped with a lamp at one of its opposite corners to ensure safety during nighttime operations.

[0048] (3) The horizontal centrifuge is controlled by an independent frequency conversion explosion-proof control switch. The drill cuttings spun dryer electrical control is the main control, which provides power to the centrifuge electrical control. At the same time, the main spun dryer, the conical receiving tank screw conveyor, and the spun dryer feeding screw conveyor are frequency-controlled. In addition, other remaining electrical equipment is magnetically controlled. The explosion-proof control switch is equipped with an overload protector, which automatically cuts off the power to protect the motor when the current is too high.

[0049] (4) The cables are domestically produced brand cables, all of which are used at the maximum power required for the entire system. The cables are installed on the outside of the tank and protected by cable trays.

[0050] (5) The electrical system in the explosion-proof area shall meet the explosion-proof requirements. The explosion-proof rating of the motors, instruments, and control boxes shall not be lower than ExdIIBT4, the protection rating of the motors shall not be lower than IP55, and the protection rating of the instruments shall not be lower than IP65, meeting the requirements for long-term outdoor use. The electrical system in the power distribution and control room shall meet the requirements for use in normal environments, with a protection rating of IP21, for indoor use. All control boxes shall be equipped with emergency stop switches.

[0051] (6) The power distribution system is designed with surge protection devices to protect the electrical system and equipment from damage caused by lightning overvoltage. The electrical control of the receiving tank and the collection tank is connected by aviation plugs, and the main control box is equipped with a connection interface with the MCC.

[0052] The aforementioned on-site harmless treatment system and method for oil-based drilling cuttings based on smoldering technology innovatively applies smoldering technology to the on-site harmless treatment of oil-based drilling cuttings generated during the non-landing treatment process of drilling mud. The heat generated by the exhaust gas treatment system is used to heat the mud in the non-landing treatment collection tank of the oil-based mud through a heat exchanger, preventing freezing during winter construction. This not only effectively ensures that the oil-based mud is completely non-landing, protecting the environment surrounding drilling operations, but also simultaneously achieves on-site harmless treatment of oil-based drilling cuttings, avoiding the cost of long-distance transportation of oil-based drilling cuttings to hazardous waste treatment plants for final disposal. This invention can perform on-site reduction and harmless treatment of oil-based drilling cuttings during drilling, achieving simultaneous production and disposal, saving transportation costs, and avoiding the risk of oil-based drilling cuttings leakage during transportation. At the same time, the residual heat from the smoldering treatment process is fully utilized, avoiding energy waste, and offering advantages such as thorough treatment of oil-based drilling cuttings.

[0053] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Various changes that can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A field harmless treatment system for oil-based drilling cuttings based on smoldering technology, comprising: The oil-based mud non-landing treatment unit and smoldering treatment unit are characterized by: The oil-based mud non-landing treatment unit includes: drilling cuttings collection box (2), feeding screw conveyor (3), centrifuge (4), first oil-based mud collection box (5), horizontal centrifuge (6), second oil-based mud collection box (7), submersible slurry pump (8) and discharge screw conveyor (11). The smoldering treatment unit includes: a burner (12), a smoldering reactor (13), a condensation device (14), a high-temperature oxidation chamber (15), a gas-to-gas heat exchanger (16), a chimney (17), and an oil-water collection tank (18). The smoldering reactor (13) consists of a preheated air inlet (131), an air inlet chamber (132), a lower gravel layer (133), a smoldering reaction zone (134), an upper gravel layer (135), a temperature detector (136), and an exhaust gas treatment system inlet (137). The smoldering reactor (13) uses the high-temperature flue gas generated by the burner (12) as the ignition heat source. The air inlet chamber (132) and the lower gravel layer (133) are separated by an air inlet perforation plate. The air inlet perforation plate is made of a high-temperature resistant and anti-clogging air inlet cap to prevent the air inlet from being blocked and to improve the uniformity of heat source input. The gas-to-gas heat exchanger (16) is a shell-and-tube heat exchanger. The high-temperature flue gas flowing out of the high-temperature oxidation chamber (15) flows into the gas-to-gas heat exchanger (16). The fresh air from the outside flows through the heat exchange tube and indirectly exchanges heat with the high-temperature flue gas outside the tube to realize the recovery and utilization of waste heat. After the heat exchange, part of the fresh air is directed to the smoldering reactor (13) to provide combustion air for the smoldering reaction, and part of the air is directed to the drilling cuttings collection box (2), the first oil-based mud collection box (5), and the second oil-based mud collection box (7). Air coils are provided at the bottom of the three boxes. The preheated air is heated by the air coils to prevent the drilling fluid from freezing during winter operations and affecting the drilling process. Large-diameter drilling cuttings (9) and small-diameter drilling cuttings (10) are discharged by a discharge screw conveyor (11) to ensure that the two types of drilling cuttings are uniformly mixed during the discharge process and then form a relatively loose packing in the smoldering reaction zone (134) in the smoldering reactor (13), ensuring the porosity to maintain a stable reaction in the smoldering process. Both the first oil-based mud collection box (5) and the second oil-based mud collection box (7) are equipped with mud stirring devices to prevent mud from settling; the bottom of the drilling cuttings collection box (2) is equipped with a spiral conveying device to ensure efficient conveying of cuttings. At the same time, both the first oil-based mud collection box (5) and the second oil-based mud collection box (7) are equipped with temperature monitoring devices to control the heating temperature of the preheated air on the materials inside the box to be stable between 20-25℃. The condensation device (14) condenses and separates the high-boiling-point organic matter and water vapor in the tail gas from the outlet of the smoldering reactor (13). The condensed high-boiling-point organic matter and water vapor enter the oil-water collection tank (18) and are reinjected into the second oil-based mud collection tank (7), and are finally reused in the preparation process of oil-based drilling mud. The non-condensable gas containing low-boiling-point organic matter flows to the high-temperature oxidation chamber (15) after passing through the flame arrester for complete incineration and degradation, thus avoiding the emission of organic matter into the atmosphere.

2. A method for on-site harmless treatment of oil-based drilling cuttings based on smoldering technology, characterized in that: The system described in claim 1 is used in the following steps: Step 1: Oil-based drilling cuttings (1) are first collected by the drilling cuttings collection box (2). The bottom of the drilling cuttings collection box (2) is equipped with a spiral conveyor to transport the oil-based drilling cuttings to the feeding section of the feeding spiral conveyor (3). The cuttings are then transported to the feeding end of the spin dryer (4) by the feeding spiral conveyor and then dispersed by the distribution plate before entering the spin dryer (4). Step 2: Under the action of centrifugal force, the liquid phase and solid particles with a diameter of <0.35mm smaller than the gap of the screen basket in the drilling cuttings pass through the screen basket and flow into the liquid outlet ring of the lower cylinder. Then, they are discharged out of the machine through the liquid outlet pipes on both sides of the lower cylinder and fall into the first oil-based mud collection box (5) below the dryer (4). The other solid phase of the drilling cuttings is kept inside the screen basket. Using the speed difference between the rotor scraper and the screen basket, the rotor scraper scrapes the drilling cuttings off the screen basket and pushes them to the bottom of the screen basket. The dehydrated drilling cuttings are discharged into the discharge screw conveyor (11) below the dryer (4). Step 3: The drilling fluid in the first oil-based mud collection tank (5) is transported to the centrifuge drum by the centrifuge slurry pump and rotates at high speed; the spiral pusher rotates at a speed slightly smaller than that of the drum under the action of the differential gear. The drum and the spiral pusher form a separation and conveying mechanism with a certain differential speed and high speed rotation in the same direction. Under the action of centrifugal force which is hundreds or even thousands of times greater than gravity, an annular liquid pool is formed in the drum. Due to the density difference between the solid phase and the liquid phase, the heavier solid phase particles have a large centrifugal force and thus settle to the edge of the liquid pool, thereby forming sludge on the inner wall of the drum. Under the relative movement of the spiral blades and the drum, the solid sludge is pushed to the small end of the drum and discharged from the sludge discharge hole, falling into the discharge spiral conveyor (11) below the horizontal centrifuge (6); the clear liquid phase in the inner ring is discharged to the second oil-based mud collection tank (7) through the overflow hole via the spiral channel, thereby realizing the production process of continuous solid-liquid phase separation. Step 4: During operation, the low-density drilling fluid in the second oil-based mud collection tank (7) is flushed by the submersible slurry pump (8) to prevent equipment blockage; when it accumulates to a certain amount, it is pumped to the solids control system at the drilling site for reuse. Step 5: The large-diameter drilling cuttings (9) discharged by the centrifuge (4) and the small-diameter drilling cuttings (10) discharged by the horizontal centrifuge (6) are mixed and stirred by the discharge screw conveyor (11) and then transported to the smoldering reactor (13). Step 6: After the smoldering reactor (13) is filled, start the burner and use the high-temperature flue gas generated by the burner as the ignition heat source. After smoldering occurs, the tail gas containing organic gas components first flows into the condensation equipment (14) for condensation and collection. The high-boiling-point organic matter and water vapor after condensation enter the oil-water collection tank (18) and are reinjected into the second oil-based mud collection tank (7), and finally reused in the preparation process of oil-based drilling mud. The uncondensed combustible gas enters the high-temperature oxidation chamber (15) for incineration. The high-temperature flue gas flowing out of the high-temperature oxidation chamber (15) flows into the gas-gas heat exchanger (16). Fresh air from the outside flows through the heat exchange tube and indirectly exchanges heat with the high-temperature flue gas outside the tube to realize the recovery and utilization of waste heat. Step 7: After heat exchange, part of the fresh air is directed to the smoldering reactor to provide combustion air for the smoldering reaction, and part is directed to the drilling cuttings collection box (2), the first oil-based mud collection box (5), and the second oil-based mud collection box (7). Air coils are installed at the bottom of the three boxes. The preheated air is heated by these air coils to prevent the drilling fluid from freezing and affecting the drilling process.

3. The method for on-site harmless treatment of oil-based drilling cuttings based on smoldering technology according to claim 2, characterized in that: Two smoldering treatment units are set up on site. One unit is used for smoldering treatment, while the other unit is used to collect oil-based drilling cuttings from the discharge screw conveyor (11).

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