A multi-pathway recycling and gradient treatment process for oil and gas field drilling mud

Abstract

The application discloses a kind of oil and gas field drilling mud multi-way reuse cascade treatment process, drilling mud is oxidized and broken glue, to scatter mud structure, then granulation coagulation is carried out;Subsequently, the following cascade processing is carried out: cascade one, the effluent of granulation coagulation is filtered, filtrate is used as injection water;Cascade two, the filtrate obtained in cascade one is carried out nucleation granulation reaction, effluent is used to prepare drilling fluid, solid phase seed and solid waste treatment are carried out to solid phase mud cake after granulation coagulation;Cascade three, the effluent obtained in cascade two is carried out ozone gas floatation reaction, effluent is used to prepare guanidine gel fracturing fluid.The application realizes the resource recycling of waste drilling mud, reduces the use amount of breaker in traditional "breaker+filter pressing" process, and saves filter pressing plate, improves the processing efficiency in mud reuse processing process, reduces the processing cost of waste water-based drilling mud, and can meet different reuse ways, and specific operation is flexible and changeable.

Description

Technical Field

[0001] This invention belongs to the field of hazardous substance treatment technology, and relates to the harmless treatment of drilling mud in oil and gas fields, and particularly to a tiered treatment process for multi-pathway reuse of drilling mud in oil and gas fields. Background Technology

[0002] Waste drilling mud from oil and gas fields is a complex multiphase system composed of water, rock cuttings, clay, petroleum hydrocarbons, drilling additives, and metal ions. It is characterized by its complex composition, stable properties, high pH, ​​high suspended solids content, diverse organic additives, wide range of pollution sources, and discontinuous discharge, making solid-liquid separation extremely difficult. Currently, the main method for solid-liquid separation of waste drilling mud is the "gel breaking + pressure filtration" process. However, this method has the following main problems:

[0003] 1) Incomplete gel breaking affects separation efficiency: During the gel breaking process, polymers and clay particles in the slurry are not fully decomposed, resulting in the incomplete disintegration of the colloidal system and thus affecting solid-liquid separation efficiency. Incomplete gel breaking leads to a still high slurry viscosity, increasing the burden on the filter press, resulting in poor solid-liquid separation, making it difficult to achieve the expected dewatering target, and ultimately affecting the overall treatment efficiency.

[0004] 2) High energy consumption and severe equipment wear during filter press operation: Filter press operation typically requires high pressure to achieve solid-liquid separation of the slurry. The high concentration of solid particles in the slurry causes wear on the filter press equipment, shortening its lifespan and increasing maintenance and replacement costs. Furthermore, filter press equipment consumes a significant amount of energy under high pressure, especially when the slurry has a high water content, resulting in longer processing times and further increasing operating costs and energy consumption.

[0005] 3) High levels of residual pollutants in the filtrate, making it difficult to meet the relevant standards for different on-site reuse methods: Despite gel breaking and pressure filtration, the filtrate often still contains high concentrations of organic pollutants, heavy metal ions, and suspended solids. These residual pollutants make it difficult for the filtrate to meet relevant reuse standards. Due to the complexity and high cost of subsequent treatment processes, direct discharge of the filtrate will pose a pollution risk to the environment, increasing the difficulty of waste sludge treatment and environmental pressure. Summary of the Invention

[0006] In order to overcome the shortcomings of the prior art, the present invention aims to provide a tiered treatment process for multi-pathway reuse of drilling mud in oil and gas fields. It aims to achieve rapid, efficient and flexible treatment of waste drilling mud to meet the water reuse needs of different reuse paths in the field, and solve the problems of low treatment efficiency, incomplete pollutant removal, high energy consumption and high cost, and unclear resource utilization pathways caused by the large mud production in the prior art.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0008] A tiered treatment process for the multi-pathway reuse of drilling mud in oil and gas fields includes the following steps:

[0009] Step 1: Oxidize and break down the drilling mud to disperse its structure, and then granulate and coagulate it.

[0010] Step 2, to further enrich the reuse pathways, the following tiered processing is performed:

[0011] In the first stage, the effluent from granulation and coagulation is filtered, and the filtrate is used as reinjection water.

[0012] The second stage involves using the filtrate from the first stage to undergo nucleation granulation to remove high-valence metal ions such as aluminum, magnesium, and calcium. The effluent is used to prepare drilling fluid, while the solid seed crystals and the granulated and coagulated solid mud cake are used for solid waste treatment.

[0013] The third stage involves subjecting the effluent from the second stage to ozone flotation to remove organic pollutants. The effluent is then used to prepare guar gum fracturing fluid.

[0014] In one embodiment, step 1, which involves oxidizing and breaking down the drilling mud, is implemented as follows:

[0015] A composite calcium hypochlorite breaker is added to the drilling mud, and the mud structure is broken down by hydraulic stirring to break down the flocculation. The composite calcium hypochlorite breaker is composed of calcium hypochlorite and an activating breaker agent. By weight, the calcium hypochlorite content is 0.8% to 2.5%, and the activating breaker agent content is 0.8% to 1.2%.

[0016] This step utilizes calcium hypochlorite coupled with other breaker additives, which significantly reduces the amount of breaker required for normal destabilization of the mud and effectively reduces the steric hindrance between mud particles, creating favorable conditions for subsequent processing.

[0017] In one embodiment, the activating degelatinizing agent is one or more of sodium hypochlorite, ferrous sulfate, and ferric chloride.

[0018] In one embodiment, step 1, granulation coagulation, is implemented as follows:

[0019] Add flocculant PAC to the oxidized and broken drilling mud and stir rapidly, then add coagulant aid PAM and stir slowly. The rapid stirring speed ranges from 500 r / min to 800 r / min, and the hydraulic residence time is from 1 min to 3 min. The slow stirring speed ranges from 60 r / min to 100 r / min, and the hydraulic residence time is from 7 min to 9 min.

[0020] This step employs a highly efficient solid-liquid separation and granulation coagulation process. By adding flocculants and coagulants and simultaneously using hydraulic control, the particles rapidly flocculate and agglomerate to form dense granules, significantly improving the mud-water separation efficiency and achieving highly efficient solid-liquid separation. This avoids the traditional pressure filtration process, and the effluent can meet reinjection requirements simply by being filtered through a filter cloth.

[0021] In one embodiment, based on the weight of the drilling mud, the amount of flocculant PAC added is 0.6% to 0.8%, and the amount of coagulant aid PAM added is 0.05% to 0.06‰.

[0022] In one embodiment, the first stage uses filter cloth filtration to remove suspended solids from the granulated coagulated water, thereby meeting the requirements for reinjection water.

[0023] In one embodiment, the second stage sends the filtrate into a nucleation reaction device and introduces a special seed crystal for hardening to induce the precipitation and coagulation of metal ions.

[0024] In one embodiment, the seed crystal for hardening is a mixture of Na2CO3 and NaOH, with the Na2CO3 dosage being 2‰ to 4‰ and the NaOH dosage being 0.8‰ to 1‰, based on the weight of the filtrate used.

[0025] In one embodiment, the second stage involves solid-phase seed crystals and granulated coagulated solid-phase sludge cake undergoing solid waste treatment, implemented as follows:

[0026] Solid mud cakes are solidified with a solidifying agent and then landfilled or recycled, while solid seed crystals are directly recycled.

[0027] In one embodiment, the third stage further incorporates coagulant PAC for simultaneous coagulation and ozonation treatment. Based on the weight of the effluent used, the dosage of coagulant PAC is 1.6‰ to 2‰, and the dosage of ozone is 0.12‰ to 0.15‰.

[0028] Compared with existing technologies, the processing of this invention realizes the resource recycling of waste drilling mud, reduces the amount of de-gelling agent used in the traditional "de-gelling + pressure filtration" process for waste drilling mud, eliminates the need for the pressure filtration plate, improves the processing efficiency of mud reuse, reduces the processing cost of waste water-based drilling mud, and introduces deep filtrate treatment for other reuse pathways, thus meeting the needs of different reuse pathways and offering flexible and adaptable operation. Attached Figure Description

[0029] Figure 1 This is a block diagram illustrating the principle of the cascaded processing of this invention.

[0030] Figure 2This is a schematic diagram illustrating the water output effect of an embodiment of the present invention. Detailed Implementation

[0031] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings and examples.

[0032] To achieve efficient treatment of abandoned drilling mud and address the problems of low treatment efficiency, incomplete pollutant removal, high energy consumption, high cost, and unclear resource utilization pathways in existing treatment methods, this invention provides a tiered treatment process for multi-pathway reuse of oil and gas field drilling mud. This process enables rapid, efficient, and flexible treatment of waste drilling mud generated during oil and gas field development, achieving multi-pathway tiered recycling. The process mainly includes oxidative degelatinization, granulation coagulation, and tiered utilization. The tiered utilization is further divided into three stages, achieved through filtration, nucleation granulation, and ozone flotation, respectively.

[0033] Figure 1 A corresponding system for implementing the process of the present invention is shown, mainly including a slurry treatment unit and a filtrate treatment unit, and may further include a solid waste treatment unit. The slurry treatment unit mainly performs oxidation degelatinization, granulation coagulation, and solid-liquid separation, while the filtrate treatment unit mainly performs filtration, nucleation granulation reaction, and ozone flotation reaction to achieve cascaded recovery. The present invention will be further described below in conjunction with the process and units.

[0034] Oxidative depolymerization reaction: A depolymerizing agent is added to the waste drilling mud to be treated, and the mud is depolymerized and flocculated by hydraulic stirring. This breaks down the mud structure, reduces the steric hindrance between suspended colloidal particles in the mud, and creates favorable conditions for subsequent efficient solid-liquid separation of the mud.

[0035] Granulation and coagulation: The drilling mud after oxidation and degelatinization undergoes rapid and slow agitation treatments, with PAC and PAM added in each stage. During the rapid agitation stage, PAC is added with high-intensity hydraulic stirring to break down and homogenize the flocs, resulting in dewatering under hydraulic shear. Then, during the slow agitation stage, PAM is added to homogenize the flocs, leading to flocculation and coagulation of the dewatered flocs, ultimately forming dense granules. The granulated sludge can be efficiently sedimented, yielding solid cake and liquid filtrate in a short time. The filtrate can be further treated for various reuse purposes.

[0036] Deep treatment of filtrate: Through filtration, nucleation granulation reaction and ozone flotation reaction, waste drilling mud is recycled through different pathways. The treatment process is flexible and can be selected according to different recycling requirements on site.

[0037] The preferred embodiment of this invention is as follows: the oxidative degelatinization reaction of the drilling mud involves adding a specific, pre-formulated composite calcium hypochlorite degelatinizing agent to the collected waste drilling mud and hydraulically stirring for approximately 10 minutes. This breaks down the colloidal structure of the mud, significantly reducing its viscosity and improving the separation effect in subsequent processing. Furthermore, the specific, pre-formulated composite calcium hypochlorite degelatinizing agent used in the oxidative degelatinization reaction is achieved by adding other activating degelatinizing adjuvants, including sodium hypochlorite, ferrous sulfate, and ferric chloride, to ordinary calcium hypochlorite agents to enhance the efficiency of the calcium hypochlorite degelatinization reaction. Compared to other common chemical breaker agents, the dosage can be reduced by about 50%, and calcium hypochlorite is cheaper and more readily available. The specific type and dosage vary depending on the type of waste drilling mud and the well depth. The dosage of calcium hypochlorite is 0.8% to 2.5%, and the dosage of activating breaker agent is 0.8% to 1.2%. The type and dosage of the agent should be selected according to the specific characteristics of the waste drilling mud, such as the concentration of suspended solids and organic pollutants. Exceeding the above dosage range will not achieve the best breaker effect and will affect the efficient solid-liquid separation of the mud in the granulation and coagulation process.

[0038] The preferred embodiment of this invention is as follows: In the granulation and coagulation stage, polyaluminum chloride (PAC) and polyacrylamide (PAM) are used to enhance the flocculation and coagulation capabilities between colloidal particles. PAC and PAM are added sequentially to the sludge after oxidative de-gelling to achieve flocculation and coagulation of suspended particles in the sludge. Rapid stirring with a hydraulic retention time of 1-3 minutes and a stirring speed of 500-800 rpm and slow stirring with a hydraulic retention time of 7-9 minutes and a stirring speed of 60-100 rpm are performed respectively. After the reaction, granular sludge with lower moisture content and higher density is formed, which can be directly and efficiently settled. This reduces the settling time and further improves the solid-liquid separation efficiency of the sludge-water mixture, eliminating the need for pressure filtration to achieve solid-liquid separation, thereby reducing the processing time and cost of the process system. Because of the conditions created by the aforementioned oxidative depolymerization, the amount of PAC can be further reduced to 0.6% to 0.8%, the amount of PAM required is between 0.05‰ and 0.06‰, and the total hydraulic retention time required for the rapid and slow stirring can be controlled within 10 minutes.

[0039] The preferred embodiment of this invention is that the effluent from granulation coagulation sedimentation can be treated through three different advanced treatment methods to achieve different reuse pathways, namely the three stages of this invention. Stage one: filtration using filter cloth removes trace amounts of suspended solids from the effluent through simple interception filtration, meeting the requirements for reinjection water and enabling reuse. Stage two: the filtered effluent can be further treated with a nucleation granulation process to remove high-valence metal ions, thus meeting the requirements for preparing drilling fluids for reuse. Stage three: the nucleation effluent undergoes a high-efficiency organic matter removal process involving simultaneous coagulation and ozonation, achieving the effluent quality standards required for preparing guar gum fracturing fluids. By employing these different filtrate treatment methods, the reuse of waste drilling mud can be achieved through various pathways. The treatment process is flexible and adaptable, allowing for the selection of the appropriate process based on specific on-site reuse requirements.

[0040] The preferred embodiment of this invention is the nucleation granulation process, which involves introducing a certain amount of hardening-specific seed crystals into the nucleation reactor to induce the precipitation and aggregation of metal ions. Compared to the traditional dual-alkali method, this process offers advantages such as shorter hydraulic retention time and lower reagent consumption. Furthermore, the granules formed by the nucleation granulation process have a higher density than the sludge formed by the dual-alkali method, achieving the same or even better removal effect. It eliminates the need for sludge dewatering and disposal costs, significantly increases effluent volume, and enables resource recycling. The granules after the reaction can be landfilled or recycled after harmless treatment. While offering superior hardening removal performance, nucleation granulation reduces operating costs by approximately 20% compared to the dual-alkali method. The Na2CO3 dosage is 2‰–4‰, and the NaOH dosage is 0.8‰–1‰. The effluent can be used for drilling fluid preparation.

[0041] The preferred embodiment of this invention involves adding a coagulant, PAC, to the three-stage process for simultaneous coagulation and ozonation treatment. This simultaneous coagulation and ozonation process cleverly utilizes PAC as a catalyst for ozone, generating a large number of highly oxidizing hydroxyl radicals, thus improving the efficiency of organic matter oxidation and decomposition. Simultaneously, ozone and free radicals react with the flocs formed by the hydrolysis of the metal salt coagulant, enhancing their adsorption capacity for organic matter. Ultimately, through the synergistic effect of oxidation and coagulation adsorption, highly efficient and low-reagent-consumption removal of organic matter is achieved. Compared to the traditional pre-oxidation-coagulation combined process, this method can increase the removal efficiency of dissolved organic matter by more than two times, while significantly reducing the dosage of ozone and coagulant. The PAC dosage is 1.6‰–2‰, and the ozone dosage is 0.12‰–0.15‰. The effluent can be used for the preparation of guar gum fracturing fluid.

[0042] Preferably, the present invention further includes a harmless treatment stage for solid mud cake and post-reaction solid seed crystals, wherein the harmless treatment stage includes solidifying the solid mud cake with a solidifying agent and then landfilling or resource utilization, and resource recovery of the solid seed crystals.

[0043] In the following embodiment, the multi-path cascade recovery process of the present invention for waste drilling mud is used to treat waste drilling mud generated at different stages during drilling in an oil and gas field without it being dumped onto the ground. The well depths for which the mud is treated are 2560m (intermediate mud) and 5200m (late mud), respectively. The treatment cycle is 10 days, and the daily treatment capacity is 50m³. 3 According to the aforementioned process flow and in conjunction with the relevant process parameters, the following specific treatments are carried out: ① During the oxidative breaking process, the calcium hypochlorite dosage is 1% in the intermediate mud and 2% in the later mud; the sodium hypochlorite dosage is 0.8% in the intermediate mud and 1% in the later mud. ② In the granulation and coagulation stage, the PAC dosage in the intermediate mud is 0.6%, and the PAM (anode type 80) dosage is 0.05‰; in the later mud, the PAC dosage is 0.8%, and the PAM (anode type 80) dosage is 0.06‰. Finally, the reaction is carried out at a stirring speed of 600 r / min for 2 min, and then held at a stirring speed of 100 r / min for 8 min. ③ The effluent from granulation coagulation is first filtered through filter bags. In the intermediate stage, the effluent from granulation coagulation undergoes nucleation granulation to remove hardness at a dosage of 2‰ Na₂CO₃ and 0.8‰ NaOH. In the later stage, the effluent from granulation coagulation undergoes corresponding treatment at a dosage of 4‰ Na₂CO₃ and 1‰ NaOH. ④ The effluent from nucleation granulation undergoes simultaneous ozone flotation coagulation treatment. In the intermediate stage, the ozone dosage is 0.08‰ and the PAC dosage is 1.5‰. In the later stage, the ozone dosage is 0.15‰ and the PAC dosage is 2‰ to reduce the COD of the effluent. The effluent quality diagram is shown in the attached figure. Figure 2 As shown in Table 1, the relevant effluent water quality standards are as follows, and the relevant reclaimed water quality standards are as follows.

[0044] Table 1: Water Quality Indicators for Reclaimed Water from Sludge Separation

[0045]

[0046]

[0047] Table 2 Water Quality Standards for Relevant Reuse Pathways

[0048]

[0049] As can be seen from Tables 1 and 2, the waste drilling mud treated by the multi-path cascade recycling process technology of the present invention can meet the relevant water quality requirements of three different reuse pathways, thus realizing the resource-based treatment of waste drilling mud.

[0050] Preferred embodiments of the present invention have been described in detail herein. However, upon reading the foregoing, those skilled in the art will readily understand and identify possible modifications and extensions to the embodiments. The applicant intends to include all such possible modifications and extensions within the scope of protection of the claims of this invention.

[0051] The terminology used in this invention is for illustrative purposes only and is not intended to limit the scope of protection of this invention. Unless expressly defined herein, all terms (including technical and scientific terms) should be interpreted according to the common understanding of those skilled in the art. Furthermore, it should be explicitly stated that unless otherwise expressly defined herein, terms commonly found in dictionaries should be interpreted in accordance with their general meaning within this specification and related technical context, and should not be interpreted in an overly idealized or formalistic manner. Well-known functions or structures are not described in detail for the sake of clarity and conciseness.

Claims

1. A tiered treatment process for multi-pathway reuse of drilling mud in oil and gas fields, characterized in that, Includes the following steps: Step 1: Oxidize and break down the drilling mud to disperse its structure, and then granulate and coagulate it. The method for achieving drilling mud oxidation and gel breaking is as follows: A composite calcium hypochlorite breaker is added to the drilling mud, and hydraulic stirring is used to break down the mud structure through flocculation. The composite calcium hypochlorite breaker is composed of calcium hypochlorite and an activating breaker agent, with the calcium hypochlorite content being 0.8%~2.5% and the activating breaker agent content being 0.8%~1.2% by weight. The method for achieving granulation coagulation is as follows: Add flocculant PAC to the oxidized and broken drilling mud and stir quickly, then add coagulant aid PAM and stir slowly. The rapid stirring has a speed range of 500 r / min to 800 r / min and a hydraulic residence time of 1 min to 3 min; the slow stirring has a speed range of 60 r / min to 100 r / min and a hydraulic residence time of 7 min to 9 min. Step 2, perform the following tiered processing: In the first stage, the effluent from granulation and coagulation is filtered, and the filtrate is used as reinjection water. The second stage involves nucleation granulation of the filtrate obtained from the first stage, with the effluent used to prepare drilling fluid and the solid seed crystals and granulated coagulated solid mud cake used for solid waste treatment. The third stage involves subjecting the effluent from the second stage to ozone flotation reaction, with the effluent used to prepare guar gum fracturing fluid.

2. The tiered treatment process for multi-pathway reuse of drilling mud in oil and gas fields according to claim 1, characterized in that, The activating degelatinizing agent is one or more of sodium hypochlorite, ferrous sulfate, and ferric chloride.

3. The tiered treatment process for multi-pathway reuse of drilling mud in oil and gas fields according to claim 1, characterized in that, Based on the weight of the drilling mud, the amount of flocculant PAC added is 0.6%~0.8%, and the amount of coagulant aid PAM added is 0.05~0.06‰.

4. The tiered treatment process for multi-pathway reuse of drilling mud in oil and gas fields according to claim 1, characterized in that, The first stage uses filter cloth filtration to remove suspended solids from the granulated coagulated water, thus meeting the requirements for reinjection water.

5. The tiered treatment process for multi-pathway reuse of drilling mud in oil and gas fields according to claim 1, characterized in that, The second stage sends the filtrate into the nucleation reaction device and introduces special seed crystals for hardening to induce the precipitation and coagulation of metal ions.

6. The tiered treatment process for multi-pathway reuse of drilling mud in oil and gas fields according to claim 5, characterized in that, The seed crystals for hardening are a mixture of Na2CO3 and NaOH. Based on the weight of the filtrate used, the dosage of Na2CO3 is 2‰~4‰ and the dosage of NaOH is 0.8‰~1‰.

7. The cascade treatment process for multi-pathway reuse of drilling mud in oil and gas fields according to claim 1, characterized in that, In the second stage, solid-phase seed crystals and granulated coagulated solid-phase sludge cake are subjected to solid waste treatment, which is achieved as follows: Solid mud cakes are solidified with a solidifying agent and then landfilled or recycled, while solid seed crystals are directly recycled.

8. The tiered treatment process for multi-pathway reuse of drilling mud in oil and gas fields according to claim 1, characterized in that, The third stage also adds coagulant PAC for simultaneous coagulation and ozonation treatment. Based on the weight of the effluent used, the dosage of coagulant PAC is 1.6‰~2‰, and the dosage of ozone is 0.12‰~0.15‰.

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