Offshore platform waste water-based drilling fluid while-drilling treatment method and device

Abstract

The invention discloses a while-drilling treatment method and device for waste water-based drilling fluid of an offshore platform, and the method comprises the following steps: screening the waste water-based drilling fluid generated by drilling, outwards transporting screened large-particle materials, adding a gel breaker into a mixture of residual fine particles and wastewater to realize pipeline gel breaking, then adding a flocculating agent for flocculation, and carrying out secondary treatment on the waste water-based drilling fluid; and separating through solid-liquid separation equipment, separating out a solid phase, transporting outwards, feeding the remaining wastewater into a sewage treatment device, and reinjecting the wastewater to an oil layer for resource reutilization after the wastewater is treated to reach the reinjection water index of a production system. According to the invention, the purposes of rapid gel breaking and destabilization of waste slurry, solid-liquid separation and shipping reduction, on-site treatment of sewage, reinjection of the sewage into a production system into an oil layer for resource utilization can be achieved; and the device can also be used for treating land drilling waste mud, and is particularly suitable for occasions with limited installation space.

Description

Technical Field

[0001] The present invention relates to the technical field of waste drilling fluid treatment in oil and gas exploration, and in particular to a method and device for treating waste water-based drilling fluid on an offshore platform while drilling. Background Art

[0002] According to GB4914 "Limits of Pollutant Emission Concentrations for Offshore Petroleum Exploration and Development", waste water-based drilling fluids generated by offshore platforms in the national first-class sea area when drilling in oil layers are prohibited from being discharged into the sea. Literature shows that Bohai Oilfield has developed a small skid-mounted flocculation and filter press machine that can quickly reduce drill cuttings and recycle waste drilling fluids on drilling platforms. The processing capacity of this flocculation and filter press machine is 130-150m 3 / d, covers an area of ​​22.4m 2 , first transport the drill cuttings from the vibrating screen through the cage to the sorting screen for primary solid-liquid separation, and pump the filtrate screened out of the sorting screen to the filter press equipment for final solid-liquid separation. The filtrate is reused, and the drill cuttings are squeezed and recycled in ton bags (2020, Petroleum Machinery, Vol. 48, No. 6, Lv Guang et al., Development and Application of Water-Based Drill Cuttings Flocculation and Filter Press Integrated Machine). At present, most of the drilling fluids produced and discarded in offshore drilling in the Bohai Sea are shipped out to sea to land treatment terminals for centralized treatment. This method has the problems of large shipping volume, high cost, and no reuse of wastewater. According to statistics, the cost of recycling and disposing of drilling waste for a well is several million yuan, accounting for about 25% of the drilling cost of the entire well.

[0003] CN105130145A A waste drilling mud reduction, harmless, resource treatment system and process discloses a waste drilling mud reduction, harmless, resource treatment system and process, including a separation unit, a mud recovery unit, a mud treatment unit and a mud cake storage unit arranged in sequence, wherein the separation unit includes a staggered multi-stage screen, the drill cuttings with a particle size of ≥3mm separated enter the mud cake storage unit, and the mud with a particle size of <3mm separated enters the mud recovery unit; the mud recovery unit includes a primary filtering device and a secondary filtering device arranged in sequence, the liquid phase mud produced by the mud recovery unit is recycled, and the solid phase produced enters the mud treatment unit; the mud treatment unit includes a destabilization device and a solid-liquid separation device arranged in sequence, a destabilization agent is added to the destabilization device, and the solid phase mud cake produced by the solid-liquid separation device is transported to the mud cake storage unit, and reused after the leaching liquid is tested and qualified. 100% harmless treatment of waste water-based mud can be achieved. The filtrate treatment unit includes a multi-stage membrane filtration device and / or an advanced oxidation treatment device.

[0004] CN115028341A discloses a solid-liquid separation and reuse method for waste water-based mud. A one-time filter press process is used to complete the harmless treatment and resource comprehensive utilization of waste water-based drilling mud. While reducing the number of main filter press and stirring equipment, it also indirectly reduces the number of corresponding metering pumps, backwashing facilities and other supporting equipment to a great extent, greatly reduces the platform footprint, and is more suitable for compact drilling platforms. It not only realizes the energy conversion of waste water-based mud, but also allows the waste to be consumed and recycled, meeting the requirements of environmental protection.

[0005] CN113105097A discloses a harmless treatment method for waste water-based mud, and provides a harmless treatment method for waste water-based mud. The method comprises the following steps: mixing the waste water-based mud with inorganic salt and PAM, demulsifying and tempering to form tempered slurry; using plate filter press to separate solid and liquid of the tempered slurry to obtain filtrate and filter cake; subjecting the filtrate to electrocatalytic reaction to obtain electrocatalytic liquid; adding calcium and magnesium ion precipitant and flotation agent to the electrocatalytic liquid, and performing oxidation degradation to obtain degradation liquid; filtering the degradation liquid, and then adjusting the pH value of the effluent to 5-7, and adding ion adsorbent for adsorption to obtain treated effluent. The invention treats the waste water-based mud according to the steps of tempering, solid-liquid separation, electrocatalytic reaction, oxidation degradation, pH value adjustment, and ion adsorbent adsorption, and can more fully perform harmless treatment and resource utilization on it, which greatly reduces the cost of oilfield drilling and fracturing operations.

[0006] CN215102808U A skid-mounted waste water-based drilling mud treatment device, a skid-mounted waste water-based drilling mud treatment device, its technical key points are: including 7 skid-mounted sub-devices including drill cuttings cleaning skid, enhanced solid-liquid separation skid, dosing skid, centrifugal separation solidification skid, solid phase storage skid, water storage skid, immersed membrane bioreactor skid and solid phase conveying device belt conveyor; it can continuously treat waste water-based drilling mud while drilling, does not need to occupy additional land for factory construction, saves drilling mud transportation equipment and costs, and avoids the problem of mud generated during transportation falling to the ground and polluting the environment; MBR is used to treat centrifugal clear liquid, and the clean water generated by MBR can be directly used, thereby improving the recycling rate of water and realizing zero wastewater discharge, and the cleaned drill cuttings and solidified products can be obtained, which is convenient for realizing the resource utilization of waste water-based mud. It includes the whole process of cuttings separation and cleaning, solid-liquid separation, wastewater treatment, solid phase transportation, etc. of waste water-based mud from onshore drilling. The centrifugal device used for solid-liquid separation is used in the treatment of waste liquid from onshore drilling.

[0007] However, the above-mentioned prior art has the following problems: since the destabilization and degelling are carried out using equipment such as tempering tanks and agitators, the equipment has many long processes; the plate and frame filter press solid-liquid separation equipment is large and cannot achieve continuous process operation, and the required buffer equipment has a large volume, which is suitable for the treatment of onshore waste water-based drilling fluid. Summary of the invention

[0008] The technical problem to be solved by the present invention is that, in view of the large shipping volume and high cost of shipping all the water-based drilling waste from offshore platforms to the sea for centralized treatment on land, combined with the requirements of limited space and short treatment process on offshore platforms, the present invention provides a method and device for treating waste water-based drilling fluid on offshore platforms while drilling, which can achieve the purpose of rapid gel breaking and destabilization of waste mud, solid-liquid separation and reduction in shipping volume, and on-site treatment of sewage into the production system for reinjection into the oil layer for resource utilization; it can also be used for the treatment of waste mud from onshore drilling, and is particularly suitable for occasions with limited installation space.

[0009] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for treating waste water-based drilling fluid on an offshore platform while drilling, comprising the following steps: first screening the waste water-based drilling fluid generated by drilling, transporting the screened large particles out, adding a degumming agent to the mixture of the remaining fine particles and wastewater to achieve pipeline degumming, then adding a flocculant to flocculate, separating through a solid-liquid separation device, separating the solid phase and transporting it out, and the remaining wastewater entering a sewage treatment device, and the sewage treatment reaches the production system reinjection water index and is reinjected into the oil layer for resource reuse.

[0010] A double-track vibrating screen is used to separate the waste water-based drilling fluid, and the rock cuttings with a particle size of more than 125μm are screened out for transportation. The water content of the separated rock cuttings is no more than 50%.

[0011] A degumming agent is added to the mixture of the remaining fine particles and wastewater after screening, and the mixture is quickly destabilized and degummed through a pipeline mixer. A flocculant is then added for flocculation, and then the mixture enters the spiral solid-liquid separation device for solid-liquid separation. The moisture content of the separated solid phase is less than 60%, and the separated sewage enters the sewage treatment device.

[0012] The separated sewage enters the sewage treatment device and is further treated through flotation, sedimentation and filtration processes so that the treated sewage meets the platform production system's reinjection water indicators, realizing the resource reuse of sewage by reinjecting it into the oil layer.

[0013] A device for treating waste water-based drilling fluid while drilling on an offshore platform includes a cuttings separation device, a solid-liquid separation device, and a sewage treatment device. The waste water-based drilling fluid generated by a drilling solid control system first enters the cuttings separation device, and large-particle cuttings in the waste water-based drilling fluid are separated and then transported outward. The remaining fine particles and wastewater mixture are input into the solid-liquid separation device to achieve gel breaking and flocculation and solid-liquid separation again, and the solid phase is transported outward. The separated sewage is input into the sewage treatment device, and the treated sewage is reinjected into the oil layer after reaching the sewage reinjection index of the platform production system;

[0014] The cuttings separation device comprises a double-track vibrating screen and a first screw pump which are connected in sequence, the double-track vibrating screen is connected to the platform solid control system, and the first screw pump is connected to the regulating tank of the solid-liquid separation device;

[0015] The solid-liquid separation device comprises a regulating tank, a second screw pump, a pipeline mixer, a screw stack solid-liquid separator, and a first centrifugal pump connected in sequence, and a first automatic dosing device for adding a gel breaker and a flocculant is respectively provided at the front end and the rear end of the pipeline mixer, and the first centrifugal pump is connected to the buffer tank of the sewage treatment device;

[0016] The sewage treatment device comprises a buffer tank, a second centrifugal pump, an air flotation tank, a third centrifugal pump, an inclined plate sedimentation tank, a fourth centrifugal pump, and a filter tank which are connected in sequence. A second automatic dosing device for adding a coagulant and a flocculant is provided in the air flotation tank and the inclined plate sedimentation tank. The second centrifugal pump lifts the liquid phase after solid-liquid separation into the air flotation tank or the front end of the pipeline mixer for adjusting the solid-liquid ratio. The slag phase separated from the air flotation tank is lifted by the third screw pump and enters the inclined plate sedimentation tank. The fine mud precipitated in the inclined plate sedimentation tank is also transported by the fourth screw pump into the regulating tank for solid-liquid separation again. The sewage treated in the inclined plate sedimentation tank enters the filter tank through the fourth centrifugal pump.

[0017] There are at least two filter tanks, which are used in series and / or in parallel.

[0018] The water content of the solid phase separated by the spiral stack solid-liquid separator is no more than 60%.

[0019] The dual-track vibrating screening machine is provided with a screen with an aperture of 80-120 meshes, which can realize the screening and separation of rock cuttings with a particle size of 125 μm or above and the outward transportation of rock cuttings. The mixture of the screened fine particles and wastewater is stored in its own buffer box and transported into the solid-liquid separation device through the first screw pump.

[0020] The cuttings separation device, solid-liquid separation device, and sewage treatment device are assembled in one skid, or are assembled into three skids respectively, or the cuttings separation device is independently composed of a skid for use with a solid control system at a drilling site, and the solid-liquid separation device and sewage separation device are composed of one skid.

[0021] The beneficial effects of the present invention are as follows: compared with the existing treatment of waste water-based drilling fluid from offshore platforms, the present invention can achieve the solid-liquid separation treatment of waste water-based drilling fluid from offshore platforms while drilling, and the solid phase with a water content of less than 60% after treatment can be shipped out to sea, reducing the shipping volume and treatment costs; the liquid phase can be further treated to meet the platform production system's wastewater injection index and then reinjected into the oil layer for resource utilization; the equipment is integrated and skid-mounted, and can be optimized and assembled according to the site conditions, making installation convenient. Compared with the existing onshore drilling waste water-based drilling fluid treatment equipment, the present invention fully considers the limited installation space of the platform, and can achieve rapid pipeline destabilization, gel breaking and flocculation of waste drilling fluid, with a short process and less equipment; compared with the intermittent operation of the commonly used onshore filter press solid-liquid separation equipment, the present invention can achieve continuous treatment and operation of waste liquid, with high treatment efficiency; compared with the centrifugal solid-liquid separation equipment, it has the advantages of low noise and low energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a process flow chart of the present invention.

[0023] Figure 2 It is a schematic diagram of the structure of the device of the present invention.

[0024] In the figure, 1-rock cuttings separation device, 2-dual-track vibrating screening machine, 3-first screw pump, 4-solid-liquid separation device, 5-adjusting tank, 6-second screw pump, 7-pipeline mixer, 8-first automatic dosing device (including reagent tank, dosing pump, flow meter, liquid level meter and supporting control), 9-stacked screw solid-liquid separator, 10-first centrifugal pump, 11-wastewater treatment device, 12-buffer tank, 13-second centrifugal pump, 14-flotation tank, 15-third screw pump, 16-third centrifugal pump, 17-inclined plate sedimentation tank, 18-fourth screw pump, 19-fourth centrifugal pump, 20-filter tank, 21-second automatic dosing device (including reagent tank, dosing pump, flow meter, liquid level meter and supporting control). DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention; it is obvious that the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments, and all other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making creative work are within the scope of protection of the present invention.

[0026] In the description of the present invention, it should be noted that the terms "upper", "lower", "inner", "outer", "top / bottom" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific position, be constructed and operated in a specific position, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0027] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "provided with", "mounted / connected", "connected", etc. should be understood in a broad sense. For example, "connected" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0028] like Figure 1 As shown, the method for treating waste water-based drilling fluid from an offshore platform while drilling of the present invention comprises the following steps: firstly screening the waste water-based drilling fluid generated by drilling, transporting the screened large particles outward, adding a degumming agent to a mixture of the remaining fine particles and wastewater to achieve pipeline degumming, then adding a flocculant to flocculate, separating the mixture through a solid-liquid separation device, separating the solid phase and transporting it outward, and the remaining wastewater entering a sewage treatment device, and the sewage treatment reaches the production system reinjection water index and is reinjected into the oil layer for resource reuse.

[0029] A double-track vibrating screen is used to separate the waste water-based drilling fluid, and the rock cuttings with a particle size of more than 125μm are screened out for transportation. The water content of the separated rock cuttings is not more than 50%.

[0030] A degumming agent is added to the mixture of the remaining fine particles and wastewater after screening, and the mixture is quickly destabilized and degummed through a pipeline mixer. A flocculant is then added for flocculation, and then the mixture enters the spiral solid-liquid separation device for solid-liquid separation. The moisture content of the separated solid phase is less than 60%, and the separated sewage enters the sewage treatment device.

[0031] The separated sewage enters the sewage treatment device and is further treated through flotation, sedimentation and filtration processes so that the treated sewage meets the platform production system's reinjection water indicators, realizing the resource reuse of sewage by reinjecting it into the oil layer.

[0032] like Figure 2As shown, a device for treating waste water-based drilling fluid while drilling on an offshore platform comprises a cuttings separation device 1, a solid-liquid separation device 4, and a sewage treatment device 11. The waste water-based drilling fluid generated by the drilling solid control system first enters the cuttings separation device 1, and the large-particle cuttings in the waste water-based drilling fluid are separated and then transported outward, and the remaining fine particles and wastewater mixture are input into the solid-liquid separation device 4 to achieve gel breaking and flocculation and solid-liquid separation again, and the solid phase is transported outward, and the separated sewage is input into the sewage treatment device 11. The treated sewage is reinjected into the oil layer after reaching the sewage reinjection index of the platform production system;

[0033] The cuttings separation device 1 comprises a double-track vibrating screen 2 and a first screw pump 3 which are connected in sequence, the double-track vibrating screen 2 is connected to the platform solid control system, and the first screw pump 3 is connected to the regulating tank 5 of the solid-liquid separation device 4;

[0034] The solid-liquid separation device 4 includes a regulating tank 5, a second screw pump 6, a pipeline mixer 7, a stacked screw solid-liquid separator 9, and a first centrifugal pump 10, which are connected in sequence. The front end and the rear end of the pipeline mixer 7 are respectively provided with a first automatic dosing device 8 for adding a gel breaker and a flocculant. The first centrifugal pump 10 is connected to a buffer tank 12 of a sewage treatment device 11.

[0035] The sewage treatment device 11 includes a buffer tank 12, a second centrifugal pump 13, an air flotation tank 14, a third centrifugal pump 16, an inclined plate sedimentation tank 17, a fourth centrifugal pump 19, and a filter tank 20 connected in sequence. A second automatic dosing device 21 for adding a coagulant and a flocculant is provided in the air flotation tank 14 and the inclined plate sedimentation tank 17. The second centrifugal pump 13 lifts the liquid phase after solid-liquid separation into the air flotation tank 14 or the front end of the pipeline mixer 7 for adjusting the solid-liquid ratio. The slag phase separated from the air flotation tank 14 is transported to the regulating tank 5 through the third screw pump 15 for solid-liquid separation again. The effluent treated by the air flotation tank 14 is lifted by the third centrifugal pump 16 and enters the inclined plate sedimentation tank 17. The fine mud precipitated in the inclined plate sedimentation tank 17 is transported by the fourth screw pump 18 and also enters the regulating tank 5 for solid-liquid separation again. The sewage treated by the inclined plate sedimentation tank 17 enters the filter tank 20 through the fourth centrifugal pump 19.

[0036] Preferably, there are at least two filter tanks 20, and the filter tanks are used in series and / or in parallel.

[0037] The water content of the solid phase separated by the spiral solid-liquid separator 9 is not more than 60%.

[0038] The dual-track vibrating screening machine 2 is provided with a screen with an aperture of 80-120 meshes, which can realize the screening and separation of rock cuttings with a particle size of 125 μm or above and the outward transportation of rock cuttings. The mixture of the screened fine particles and wastewater is stored in its own buffer box and transported into the solid-liquid separation device 4 through the first screw pump 3.

[0039] The cuttings separation device 1, the solid-liquid separation device 4, and the sewage treatment device 11 are assembled in one skid, or are assembled into three skids respectively, or the cuttings separation device is independently composed of a skid for use with the solid control system at the drilling site, and the solid-liquid separation device and the sewage separation device are composed of one skid.

[0040] The present invention reduces the shipping and treatment costs of waste water-based drilling fluids from offshore drilling, and realizes the resource utilization of waste water. On the one hand, the waste drilling fluids are separated and reduced by solid-liquid separation during drilling, and the solid phase is shipped out to sea to reduce the shipping volume and cost; on the other hand, the liquid phase is reprocessed to reach the reinjection water index and reinjected into the oil layer to realize resource utilization, thereby solving the problems of large shipping volume, high cost, and failure to realize resource reuse of waste water in existing treatment methods. The present invention is mainly proposed for the limited space of offshore platforms, and can also be used for the treatment of waste water-based muds from onshore drilling, and is particularly suitable for occasions with limited installation space.

[0041] The present invention first screens the waste water-based drilling fluid generated by drilling, separates the large-particle rock cuttings to provide materials with suitable particle sizes for the next solid-liquid separation equipment to adapt to the normal operation of the equipment, and the screened large-particle materials are transported outward, and a quick degumming agent is added to the mixture of the remaining fine particles and wastewater to achieve pipeline degumming, and then an appropriate amount of flocculant is added for flocculation, and the mixture is separated by the solid-liquid separation equipment, and the solid phase is separated and transported outward, and the remaining wastewater enters the sewage treatment device. The sewage treatment reaches the production system reinjection water index and is reinjected into the oil layer for resource reuse.

[0042] The present invention is designed to include three sub-devices, namely, a cuttings separation device, a solid-liquid separation device, and a sewage treatment device. The cuttings separation device is used to separate large-size cuttings from the waste drilling fluid. The main equipment adopts a double-track vibrating screen. The mesh of the vibrating screen is selected to have an aperture of 80-120 meshes, which can achieve the screening of cuttings with a particle size of 125μm or more. The moisture content of the separated cuttings is not more than 50%; the mixture of fine particles remaining after screening and wastewater is pumped into the solid-liquid separation device. There are two main purposes of setting up this sub-device: one is to separate the cuttings with a particle size greater than 125μm in the waste drilling fluid to provide suitable materials for the next stage of processing; the other is to dehydrate the separated cuttings.

[0043] The solid-liquid separation device includes an automatic dosing device, a pipeline mixer and a spiral solid-liquid separation device. The device first adds a degumming agent to the mixture of the remaining fine particles and wastewater screened out by the cuttings screening device. Since the drilling fluid is a highly stable colloidal substance, especially the drilling fluid used in the offshore platform contains highly stable substances such as xanthan gum and low-viscosity polyanionic cellulose, the waste liquid must first be destabilized and degummed. Considering the limited space on site, a degumming agent with a fast degumming speed is selected, and the pipeline mixer is used for rapid destabilization and degumming, and then a flocculant is added for flocculation, and then the solid-liquid separation device is entered for solid-liquid separation. The separated solid phase has a moisture content of less than 60%, and the separated sewage enters the sewage treatment device. The purpose of setting up this device is to achieve destabilization, degumming and flocculation of the waste drilling fluid with extremely strong stability, and to separate the solid phase with a particle size of less than 125μm, so as to achieve solid-liquid separation and reduction again.

[0044] The sewage treatment device mainly includes an automatic dosing device, an air flotation tank, an inclined plate sedimentation tank and a filter tank. The device further treats the sewage separated by the solid-liquid separation device, so that the treated sewage meets the water re-injection index of the platform production system and realizes the purpose of resource utilization of sewage re-injection into the oil layer.

[0045] Specifically, the waste water-based drilling fluid generated by the drilling solid control system first enters the cuttings separation device 1, and the large-particle cuttings in the waste drilling fluid are separated and then transported out. The remaining fine particles and wastewater mixture are input into the solid-liquid separation device 4 through a pump, and gel breaking and flocculation and solid-liquid separation are achieved in the device, and the solid phase is transported out; the separated sewage is input into the sewage treatment device 11 through a pump, and the treated sewage is reinjected into the oil layer after reaching the sewage reinjection index of the platform production system.

[0046] The rock cutting separation device 1 is mainly used to screen and remove large-size rock cuttings in the waste water-based drilling fluid. The device includes a dual-track vibrating screen 2 and a screw pump 3. The waste liquid generated by the platform solid control system first enters the dual-track vibrating screen 2. The dual-track vibrating screen 2 is equipped with a screen with an aperture of 80-120 meshes, which can realize the screening and separation of rock cuttings with a particle size of 125μm or more. The rock cuttings are transported out, and the mixture of the screened fine particles and wastewater is stored in the buffer box of the device, and transported into the solid-liquid separation device 4 through the screw pump 3.

[0047] The solid-liquid separation device 4 is used to further separate the fine particles and wastewater mixture produced by the cuttings separation device. The device is equipped with a regulating tank 5, a screw pump 6, a pipeline mixer 7, an automatic dosing device 8, a spiral solid-liquid separator 9, and a centrifugal pump 10. The mixture of fine particles and wastewater produced by the cuttings separation device 1 first enters the regulating tank 5, is lifted into the pipeline mixer 7 by the screw pump 6, and a gel breaker is added to the front end of the pipeline mixer 7 through the automatic dosing device 8, and a flocculant is added to the rear end. After gel breaking and flocculation, the waste liquid enters the spiral solid-liquid separator 9 to achieve solid-liquid separation of the waste liquid. The spiral solid-liquid separator mainly relies on the extrusion of the screw to achieve sludge dehydration. The difference in density between mud and water and the oil content will not affect the processing efficiency of the equipment. In addition, the rotation rate of the spiral shaft of the spiral solid-liquid separator is very low, which determines that the spiral separator has the advantages of low energy consumption, low noise and vibration, and low operating cost. The water content of the solid phase separated by the spiral stack solid-liquid separator 9 is not more than 60%. The separated sewage enters the sewage buffer box provided by the spiral stack solid-liquid separator 9 and enters the sewage treatment device 11 through the centrifugal pump 10 .

[0048] The sewage treatment device 11 treats the wastewater generated by the solid-liquid separation device to meet the requirements of the on-site production system re-injection water index. The sewage treatment device 11 includes a buffer tank 12, a centrifugal pump 13, an air flotation tank 14, a screw pump 15, a centrifugal pump 16, an inclined plate sedimentation tank 17, a screw pump 18, a centrifugal pump 19, a filter tank 20, and an automatic dosing device 21. The wastewater generated by the solid-liquid separation device 4 is input into the buffer tank 12 through the centrifugal pump 10, and then input into the air flotation tank 14 through the centrifugal pump 13. The coagulant and flocculant are added respectively through the automatic dosing device 21. Under the action of microbubbles in the air flotation tank 14, the flocculated particles float up, and the scraper is used to scrape out the slag phase buffer box in the air flotation tank 14. The slag phase is transported into the adjustment tank 5 through the screw pump 15 for solid-liquid separation again. The effluent treated in the flotation tank 14 is lifted by a centrifugal pump 16 and enters the inclined plate sedimentation tank 17. A coagulant and flocculant are also added to the inclined plate sedimentation tank 17 to flocculate and remove the residual fine mud. The precipitated fine mud is transported by a screw pump 18 and enters the regulating tank 5 for solid-liquid separation again. The sewage treated in the inclined plate sedimentation tank 17 enters the filter tank 20 through a centrifugal pump 19. In actual production, two or more filter tanks can be set up. The filter tanks can be used in series or in parallel, or in both series and parallel modes. The filtered sewage meets the production system re-injection water index and enters the production sewage injection system. If the solid content of the mixture of fine particles and wastewater produced by the cuttings separation device is high and affects the fluidity, the wastewater generated by the solid-liquid separation device stored in the buffer tank 12 can be used for dilution to facilitate pumping.

[0049] In summary, the content of the present invention is not limited to the above-mentioned embodiments, and people with insight in the same field can easily propose other embodiments within the technical guiding ideology of the present invention, but such embodiments are all included in the scope of the present invention.

Claims

1. A method for treating waste water-based drilling fluid on an offshore platform while drilling, characterized in that: The method comprises the following steps: firstly screening the waste water-based drilling fluid generated by drilling, transporting the screened large particles out, adding a degumming agent to the mixture of the remaining fine particles and wastewater to break the degumming agent in the pipeline, then adding a flocculant to flocculate, separating the mixture through a solid-liquid separation device, separating the solid phase and transporting it out, and the remaining wastewater entering a sewage treatment device. The sewage treatment reaches the production system reinjection water index and is reinjected into the oil layer for resource reuse.

2. The method for treating waste water-based drilling fluid on an offshore platform while drilling according to claim 1, characterized in that: A double-track vibrating screen is used to separate the waste water-based drilling fluid, and the rock cuttings with a particle size of more than 125μm are screened out for transportation. The water content of the separated rock cuttings is no more than 50%.

3. The method for treating waste water-based drilling fluid on an offshore platform while drilling according to claim 2, characterized in that: A degumming agent is added to the mixture of the remaining fine particles and wastewater after screening, and the mixture is quickly destabilized and degummed through a pipeline mixer. A flocculant is then added for flocculation, and then the mixture enters the spiral solid-liquid separation device for solid-liquid separation. The moisture content of the separated solid phase is less than 60%, and the separated sewage enters the sewage treatment device.

4. The method for treating waste water-based drilling fluid on an offshore platform while drilling according to claim 3, characterized in that: The separated sewage enters the sewage treatment device and is further treated through flotation, sedimentation and filtration processes so that the treated sewage meets the platform production system's reinjection water indicators, realizing the resource reuse of sewage by reinjecting it into the oil layer.

5. A device for processing waste water-based drilling fluid while drilling on an offshore platform, comprising a cuttings separation device (1), a solid-liquid separation device (4), and a sewage treatment device (11), characterized in that: The waste water-based drilling fluid generated by the drilling solid control system first enters the rock cutting separation device (1), the large rock cuttings in the waste water-based drilling fluid are separated and then transported out, and the remaining fine particles and wastewater mixture are input into the solid-liquid separation device (4) to achieve gel breaking and flocculation and solid-liquid separation again, the solid phase is transported out, and the separated wastewater is input into the wastewater treatment device (11). The treated wastewater reaches the wastewater reinjection index of the platform production system and is then reinjected into the oil layer; The rock cuttings separation device (1) comprises a double-track vibrating screen (2) and a first screw pump (3) which are connected in sequence, the double-track vibrating screen (2) is connected to a platform solid control system, and the first screw pump (3) is connected to a regulating tank (5) of a solid-liquid separation device (4); The solid-liquid separation device (4) comprises a regulating tank (5), a second screw pump (6), a pipeline mixer (7), a stacked screw solid-liquid separator (9), and a first centrifugal pump (10) which are connected in sequence. A first automatic dosing device (8) for adding a gel breaker and a flocculant is provided at the front end and the rear end of the pipeline mixer (7), respectively. The first centrifugal pump (10) is connected to a buffer tank (12) of a sewage treatment device (11); The sewage treatment device (11) comprises a buffer tank (12), a second centrifugal pump (13), an air flotation tank (14), a third centrifugal pump (16), an inclined plate sedimentation tank (17), a fourth centrifugal pump (19), and a filter tank (20) which are connected in sequence. A second automatic dosing device (21) for adding a coagulant and a flocculant is provided in the air flotation tank (14) and the inclined plate sedimentation tank (17). The second centrifugal pump (13) lifts the liquid phase after solid-liquid separation into the air flotation tank (14) or the front end of the pipeline mixer (7). In order to adjust the solid-liquid ratio, the slag phase separated from the flotation tank (14) is transported to the regulating tank (5) through the third screw pump (15) for solid-liquid separation again, the effluent treated by the flotation tank (14) is lifted by the third centrifugal pump (16) and enters the inclined plate sedimentation tank (17), the fine mud precipitated in the inclined plate sedimentation tank (17) is transported by the fourth screw pump (18) and also enters the regulating tank (5) for solid-liquid separation again, and the sewage treated by the inclined plate sedimentation tank (17) enters the filter tank (20) through the fourth centrifugal pump (19).

6. The device for processing waste water-based drilling fluid while drilling on an offshore platform according to claim 5 is characterized in that: There are at least two filter tanks (20), which are used in series and / or in parallel.

7. The device for processing waste water-based drilling fluid while drilling on an offshore platform according to claim 5 is characterized in that: The water content of the solid phase separated by the spiral stack solid-liquid separator (9) is no more than 60%.

8. The device for processing waste water-based drilling fluid while drilling on an offshore platform according to claim 5 is characterized in that: The dual-track vibrating screening machine (2) is provided with a screen with an aperture of 80-120, so as to realize the screening and separation of rock cuttings with a particle size of 125 μm or more for outward transportation. The mixture of the screened fine particles and wastewater is stored in a self-contained buffer box and transported into the solid-liquid separation device (4) through the first screw pump (3).

9. The device for processing waste water-based drilling fluid while drilling on an offshore platform according to claim 5, characterized in that: The cuttings separation device (1), the solid-liquid separation device (4), and the sewage treatment device (11) are assembled in one skid, or are separately assembled into three skids, or the cuttings separation device is independently composed of a skid for use with a solid control system at a drilling site, and the solid-liquid separation device and the sewage separation device are composed of one skid.

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