Method for improving water-based drilling cuttings and artificial soil made using water-based drilling cuttings

Abstract

The present application relates to the technical field of shale gas drilling solid waste resource utilization, in particular to a method for improving water-based drilling cuttings by using rotten straw and artificial soil prepared by using the water-based drilling cuttings. The method for improving water-based drilling cuttings comprises the steps of leaching, sieving and mixing water-based drilling cuttings with sieved rotten straw, and can effectively improve the texture performance and physicochemical properties of water-based drilling cuttings, especially the soil cation exchange capacity and permeability, and can be used for treating water-based drilling cuttings generated in oil and gas exploitation. The method for improving water-based drilling cuttings can effectively overcome the problems of high cost, complicated operation, limited source of treatment agent and unsatisfactory improvement of soil texture performance in the prior art.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization technology in shale gas drilling. Specifically, this invention relates to a method for improving water-based drill cuttings and artificial soil made from water-based drill cuttings. Background Technology

[0002] According to estimates and statistics, my country generates approximately tens of millions of cubic meters of water-based drill cuttings annually from oil and gas field extraction. Shale gas has become an important alternative energy resource, and its enormous development potential has made it an indispensable component of the global diversified energy landscape. However, the drilling process for oil and shale gas extraction generates a large amount of water-based drill cuttings solid waste. How to handle water-based drill cuttings has become a major environmental problem.

[0003] In recent years, in particular, with the increased efforts in shale gas development in my country, the amount of water-based drilling cuttings produced has also increased significantly. Taking the Yanchang shale gas field in Shaanxi Province as an example, a total of 42 wells there have produced approximately 42,000 cubic meters of cuttings. 3 Water-based drill cuttings. The large amount of water-based drill cuttings generated and accumulated year by year poses a potential threat to the environment if left unused. However, corresponding to the year-by-year increase in water-based drill cuttings, there has been little progress in their resource utilization, making them a major source of pollution in the oil and gas extraction industry.

[0004] Water-based drill cuttings are not suitable for solidification and landfill disposal because solidification and landfill pose potential environmental risks, such as land occupation and the possibility of leachate from the solidified material seeping out with long-term rainfall and polluting surrounding soil and water bodies. Resource utilization is the best strategy to reduce environmental risks and completely dispose of water-based drill cuttings.

[0005] Currently, the resource utilization of water-based drill cuttings mainly focuses on building material applications and co-processing in cement kilns, while research on the utilization of water-based drill cuttings in soil is relatively limited. The utilization of water-based drill cuttings in building materials has limited dosage, results in large quantities of building materials, and hinders disposal pathways. Co-processing of water-based drill cuttings in cement kilns removes pollutants relatively thoroughly, but this is only feasible if there are large cement plants near shale gas production areas; otherwise, increased transportation distances and higher disposal costs make it less economically feasible. Therefore, the utilization of water-based drill cuttings in soil has become one research direction.

[0006] CN113079732A discloses a method for improving and revegetating saline soil using water-based drill cuttings from shale gas fields. This method employs a composite interlayer consisting of a water-based drill cuttings layer and a straw layer beneath the saline soil, and applies humic acid and desulfurized gypsum. However, this method involves complex operations and is significantly too costly, making large-scale application difficult.

[0007] CN109266353A discloses a water-based drill cuttings cultivation soil conditioner and its improvement method. This method involves collecting, destabilizing, and separating the drill cuttings, and then adding contaminant consolidating agents, conditioners, nutrients, and pH adjusters to improve the water-based drill cuttings into cultivation soil suitable for plant growth. However, this method is still not economical and has limited effectiveness in improving soil texture.

[0008] CN112167004A discloses a method for preparing shale gas water-based drill cuttings soil, which involves adding 20%-40% soil, 20%-50% cow manure fermentation products, and 2%-5% microbial inoculants by weight of the water-based drill cuttings. While this method yields good results, the amount of additives is significantly excessive, reducing the amount of water-based drill cuttings used and offering no cost advantage.

[0009] CN108812184B discloses a method for preparing artificial soil using shale gas water-based drill cuttings and sludge fermentation products. This method can significantly improve soil texture, but it still has problems such as limited sludge sources, potential secondary pollution, and limited applicability of water-based drill cuttings.

[0010] Overall, existing technologies for treating water-based drill cuttings suffer from high costs, complex operations, and limitations in the availability of treatment agents. Moreover, current treatment methods often focus only on improving nutritional properties while neglecting to improve the texture properties of the water-based drill cuttings themselves, particularly their poor soil cation exchange capacity (CEC) and permeability.

[0011] Soil cation exchange capacity (CEC) is the total amount of various cations that soil colloids can adsorb. Soil colloids possess adsorption properties due to their large specific surface area and electrical charge. The CEC value essentially represents the amount of nutrients the soil can retain, i.e., its nutrient retention capacity. CEC is a major source of soil buffering capacity and an important basis for soil improvement and rational fertilization. Water-based drill cuttings often have low CEC values ​​and poor nutrient retention capacity.

[0012] Permeability is another important soil texture characteristic. Water-based drill cuttings often have unsatisfactory permeability due to the presence of many sticky particles. When permeability is poor, water cannot infiltrate due to excessive surface viscosity. On the one hand, poor soil permeability leads to increased soil loss due to surface runoff; on the other hand, poor infiltration also hinders the reduction of soil root zone salt content.

[0013] In summary, the existing technology still needs a more effective, economical, and large-scale promotion method for improving the texture and properties of water-based drill cuttings. Summary of the Invention

[0014] The inventors unexpectedly discovered during their research that treating water-based drill cuttings with decomposed straw can effectively improve the texture and physicochemical properties of the cuttings, promoting their transformation into usable soil. Particularly surprising was that the method of this invention can significantly improve the CEC (Cation Exchange Capacity) and permeability of water-based drill cuttings.

[0015] Based on this discovery, in a first aspect, the present invention provides a method for improving water-based drill cuttings, comprising the following steps:

[0016] S1: Rinse the water-based drill cuttings to reduce their salt content;

[0017] S2: Pass the rinsed water-based drill cuttings through a 2mm sieve;

[0018] S3: Pass the well-rotted straw through a 2mm sieve; and

[0019] S4: Mix the sieved water-based drill cuttings obtained in step S2 with the sieved composted straw obtained in step S3 to obtain a modified mixture of water-based drill cuttings.

[0020] In a preferred aspect, in step S4, the screened water-based drill cuttings and the screened decomposed straw are mixed at a mass ratio of (8-12):(0.5-1). In some specific embodiments, the mass ratio is 8:0.5, 8:1, 9:0.5, 9:1, 10:0.5, 10:1, 11:0.5, 11:1, 12:0.5, or 12:1.

[0021] In the method of this invention, the above-mentioned mass ratios all refer to the mass ratio of the dry weight of the materials. Therefore, the amount of decomposed straw used is calculated based on the straw after decomposition and drying.

[0022] In the method of the present invention, it is preferable to additionally add soil-treated water-based drill cuttings. The soil can be mixed together with sieved water-based drill cuttings and decomposed straw. More preferably, the sieved water-based drill cuttings are first mixed with decomposed straw, and then mixed with the added soil that has been sieved (preferably through a 2 mm sieve).

[0023] Therefore, in a preferred aspect, the method for improving water-based drill cuttings according to the present invention includes a step of further mixing the mixture of the improved water-based drill cuttings with soil after step S4, preferably, the mass ratio of the mixture of the improved water-based drill cuttings to the soil is (8.5-13):(1-4). Wherein the mass ratio refers to the mass ratio of the dry weight of the materials.

[0024] In a particularly preferred aspect, the water-based drill cuttings to be treated according to the present invention have the following characteristics: pH 9.3-10.1; electrical conductivity 450-650 μS / cm; total salt content 6-14 g / kg; organic matter content 15-25 g / kg; total nitrogen 0.50-1.15 g / kg; total phosphorus 50-90 g / kg; total potassium 200-500 g / kg; and cation exchange capacity (CEC) 1.0-3.0 cmol / kg. Particularly preferably, the water-based drill cuttings are sourced from Northwest China; in a specific embodiment, the water-based drill cuttings are sourced from Yanchang County, Shaanxi Province.

[0025] In the improved method of this invention, the soil used is preferably yellow loess soil. The yellow loess soil preferably has the following characteristics: pH 7.0-8.0, electrical conductivity 90-120 μS / cm, total salt content 0.5-1.5 g / kg, organic matter content 50-60 g / kg, available nitrogen 70-95 mg / kg, available phosphorus 7-11.5 mg / kg, and cation exchange capacity (CEC) 4.0-5.0 cmol / kg. Through numerous experiments, the inventors have found that using decomposed straw in combination with yellow loess soil to treat water-based drill cuttings with the above characteristics has a particularly good effect, especially in that: 1) the treated artificial soil has a significantly improved cation exchange capacity (CEC); 2) the treated artificial soil has a significantly improved infiltration rate.

[0026] In the improved method of the present invention, preferably, the decomposed straw has the following characteristics: pH 6.8-7.6; electrical conductivity 500-900 μS / cm; total salt content 5-7 g / kg; and organic matter content 55-75 g / kg. In a particularly preferred embodiment, the decomposed straw is decomposed corn straw.

[0027] In the improved method of the present invention, the water-based drill cuttings, decomposed straw, and loess soil to be treated are generally mixed in a mass ratio of (8-12):(0.5-1):(1-4); more preferably, the water-based drill cuttings, decomposed straw, and loess soil to be treated are generally mixed in a mass ratio of 10:(0.5-1):(1-4). In some specific embodiments, the water-based drill cuttings, decomposed straw, and loess soil to be treated are mixed in the following mass ratios: 10:0.5:1, 10:0.5:2, 10:0.5:4, 10:1:1, 10:1:2, or 10:1:4.

[0028] In the improved method of this invention, since the water-based drill cuttings to be processed often have a high salt content, desalination is required first. Therefore, a rinsing step is needed in step S1 to reduce the salt content of the water-based drill cuttings to a predetermined level. The rinsing can be carried out by a suitable method, such as saturating the water-based drill cuttings with fresh water, continuing to add water to about 3 cm above the surface, letting it stand for 24 hours, draining the water to desalinate, and after no more water flows out, sampling and measuring the salt content. If the salt content drops below 2 g / kg, the rinsing and desalination is completed; if the salt content is greater than 2 g / kg, the above rinsing and desalination step is repeated once. Usually, one rinsing is sufficient to meet the standard.

[0029] In another aspect of the invention, an artificial soil is provided, which is composed of water-based drill cuttings that have passed through a 2mm sieve and decomposed straw that has passed through a 2mm sieve at a mass ratio of (8-12):(0.5-1). Preferably, the artificial soil is composed of water-based drill cuttings that have passed through a 2mm sieve and decomposed straw that has passed through a 2mm sieve at a mass ratio of 10:0.5 or 10:1. More preferably, the artificial soil of the present invention is composed of water-based drill cuttings that have passed through a 2mm sieve, decomposed straw that has passed through a 2mm sieve, and loess soil at a mass ratio of (8-12):(0.5-1):(1-4); particularly preferably, the artificial soil of the present invention is composed of water-based drill cuttings that have passed through a 2mm sieve, decomposed straw that has passed through a 2mm sieve, and loess soil at a mass ratio of 10:1:1 or 10:0.5:1.

[0030] In another aspect of the invention, the use of decomposed straw in the preparation of a water-based drill cuttings modifier is provided, wherein the water-based drill cuttings have the following characteristics: pH 9.3-10.1; electrical conductivity 450-650 μS / cm; total salt content 6-14 g / kg; organic matter content 15-25 g / kg; total nitrogen 0.50-1.15 g / kg; total phosphorus 50-90 g / kg; total potassium 200-500 g / kg; available nitrogen 30-65 mg / kg; available phosphorus 12-18 mg / kg; cation exchange capacity (CEC) 1.0-3.0 cmol / kg; and total phosphorus 50-300 g / kg. Preferably, the decomposed straw is decomposed corn straw.

[0031] Detailed description of the invention

[0032] The improved method of this invention can be directly used for the resource utilization of water-based drill cuttings. It can utilize local straw and soil resources in the area where the water-based drill cuttings to be processed.

[0033] The improved method of this invention can effectively reduce the pH of water-based drill cuttings and significantly increase the nutrient content. Surprisingly, it can also significantly improve the texture of water-based drill cuttings and significantly improve the problems of low cation exchange capacity and low infiltration rate. The artificial soil prepared by the improved method is particularly suitable for use in arid and semi-arid regions.

[0034] As is well known in the art, straw refers to the stems and leaves remaining after the ripening and threshing of gramineous crops such as rice, wheat, and corn. In the past two decades in China, due to the widespread availability of coal, electricity, and natural gas, the abundance of various industrial products, and rising labor costs, the demand for straw in rural areas has decreased. The disposal of large quantities of straw has become a serious social problem. Although prohibited by law, farmers in many places still burn straw directly in fields, causing air pollution, fires, and even preventing aircraft from taking off and landing normally. Therefore, how to rationally handle and utilize straw is also a problem. This invention can effectively utilize local straw to treat water-based drill cuttings, achieving a dual benefit tailored to local conditions.

[0035] The present invention uses decomposed straw. Straw must be decomposed before it can be effectively used in the method of the present invention. There are various methods for decomposing straw, including conventional methods. For example, biological decomposition methods such as straw decomposition agents, which often contain compound microbial agents that can decompose fibers, can effectively promote the decomposition of cellulose, hemicellulose, and lignin in the straw; or chemical decomposition methods, such as using chemical decomposition agents like ammonium bicarbonate, alkali lignin, and sodium lignin sulfonate. Alternatively, the straw can be decomposed by keeping it moist in a sealed environment at 25 degrees Celsius for one week.

[0036] In this invention, before mixing the decomposed straw with water-based drill cuttings, it is first passed through a 2mm sieve to make it into particles of similar size.

[0037] To facilitate sieving, the decomposed straw and water-based drill cuttings can optionally be pulverized. The pulverization method is not limited and can be any mechanical processing method.

[0038] Using the method of this invention, and in accordance with the CJ / T 340—2016 standard "Greening Planting Soil", the pH, electrical conductivity, and other physicochemical indicators of the compound substrate were analyzed. The results showed that the pH of the treated compound substrate (i.e., artificial soil) was significantly improved compared to pure water-based drill cuttings. The addition of decomposed straw effectively reduced the pH of water-based drill cuttings, by an average of 19.8% compared to the control. Regarding nutritional properties, the addition of decomposed straw (and soil) significantly increased the nutrient content of water-based drill cuttings in terms of available nitrogen, available potassium, available phosphorus, and organic matter. As for heavy metal content, the heavy metal content in the treated water-based drill cuttings met the Class I standard of CJ / T 340-2016 "Greening Planting Soil", and the ecological risk assessment showed a slight level, therefore it can be used for resource utilization.

[0039] Of particular advantage, the method of the present invention can significantly improve the problems of low cation exchange capacity and low infiltration rate of water-based drill cuttings, wherein the CEC can be increased by more than 15 times and the infiltration rate can be increased by an average of more than 8 times. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific implementation schemes and embodiments. The specific embodiments described are for illustrative purposes only and are not intended to limit the scope of the invention.

[0041] 1. Sample source and properties

[0042] In this invention, water-based drill cuttings collected from the shale gas field in Yanchang County, Yan'an City, Shaanxi Province were leached with an appropriate amount of pure water to reduce the total salt content to below 1.5 g / kg. The properties of the leached samples are shown in Table 1.

[0043] The straw was selected from corn stalks. After being ground, the corn stalks were placed in a sterilized plastic box, an appropriate amount of deionized water was added to keep them moist, and the mixture was stirred evenly before being compacted. The box was then sealed and stored at 25°C for 20 days to allow for decomposition. The properties of the decomposed straw are shown in Table 1.

[0044] The soil samples were collected from Yanchang, Shaanxi Province, and belong to loess soil. Its properties are shown in Table 1.

[0045] Table 1. Physicochemical properties of water-based drill cuttings, decomposed straw, and soil.

[0046]

[0047] 1.2 Material Mixing (Different Processing Groups)

[0048] Water-based drill cuttings, soil, and decomposed straw are sieved through a 2mm sieve and mixed in a certain proportion (see Table 2 below). The mixture is placed in a cylindrical soil basin, and water is sprayed on the mixture as it becomes dry and wet. After one month of stabilization, the resulting mixture is the treated water-based drill cuttings, which is the artificial soil of this invention.

[0049] Table 2 Material Proportions

[0050]

[0051] 1.3 Analysis and Evaluation Methods

[0052] The following indicators were all measured using methods known in the art:

[0053] pH was determined using the potentiometric method; electrical conductivity was determined using the electrical conductivity method (soil-water ratio 1:5); total salt content was determined using the gravimetric method; available nitrogen was determined using the alkaline hydrolysis-diffusion method; available phosphorus was determined using the sodium bicarbonate extraction-molybdenum antimony colorimetric method; available potassium was determined using the ammonium acetate extraction-flame photometric method; total nitrogen was determined using elemental analysis; total potassium was determined using the alkaline fusion-flame photometric method; total phosphorus was determined using the alkaline fusion-molybdenum antimony spectrophotometric method; organic matter was determined using the potassium dichromate oxidation-external heating method; cation exchange capacity was determined using the hexaamminecobalt trichloride extraction-spectrophotometric method; heavy metals were determined using inductively coupled plasma mass spectrometry; mechanical composition was determined using a soil hydrometer; and soil infiltration rate was determined using the percolation cartridge method.

[0054] 1.4 Results of Index Measurement

[0055] a. pH value

[0056] The pH values ​​of each group are shown in Table 3 below:

[0057] Table 3 pH values ​​of each treatment group

[0058]

[0059] The results above show that the pH value was significantly reduced after treatment with decomposed straw or a mixture of decomposed straw and yellow cotton soil.

[0060] b. Artificial soil texture

[0061] Water-based drill cuttings alone (CK group) contained a significant amount of clay particles (<0.002 mm, exceeding 50%) and silt (0.002-0.02 mm, exceeding 30%), indicating that their texture characteristics did not yet meet the requirements for suitable soil texture. After treatment with decomposed straw or a mixture of decomposed straw and loess, the texture characteristics of the water-based drill cuttings were improved, shifting from clay to sandy soil and loam.

[0062] Table 4 Soil texture under different treatments

[0063]

[0064] c. Cation Exchange Capacity (CEC)

[0065] The cation exchange capacity (CEC) of water-based drill cuttings alone was significantly low (1.0 cmol / kg). After treatment with decomposed straw or decomposed straw + loess soil, the CEC increased significantly, as shown in Table 5.

[0066] Table 5. Cation exchange capacity of different treatments

[0067]

[0068] As shown in the table above, the cation exchange capacity increased significantly to more than 10 times the original value after treatment with decomposed straw or a mixture of decomposed straw and loess soil. This result is surprising. It indicates that the treated artificial soil possesses good buffering capacity and reliable fertilizer retention performance.

[0069] d. Soil infiltration rate

[0070] The soil infiltration rate of water-based drill cuttings alone was significantly low (5.7 mm / h). As mentioned earlier, the excessively low soil infiltration rate makes the soil more susceptible to loss due to surface runoff and is also not conducive to reducing the salt content of the soil root zone.

[0071] After treatment with decomposed straw or a mixture of decomposed straw and yellow cotton soil, the soil infiltration rate increased significantly, as shown in Table 6.

[0072] Table 6 Soil infiltration rates under different treatments

[0073]

[0074] As can be seen from the results in the table above, the soil infiltration rate was significantly restored after treatment with decomposed straw or treatment with decomposed straw plus yellow cotton soil.

[0075] Furthermore, regarding other measurement indicators, such as nutrient content (organic matter, alkaline nitrogen, organic phosphorus and available potassium), conductivity, and salt content, the above-described treatment of the present invention can meet the utilization standards, particularly the requirements of standards such as CJ / T 340-2016.

[0076] In addition, regarding the heavy metal content of the artificial soil prepared above, its heavy metal content has reached the Class I standard, and the coefficients of each potential ecological risk are all less than 40, which is considered a "minor" risk. It is suitable for water conservation forests and other green (forest) areas that are subject to natural conservation.

[0077] 1.5 Potential toxicity testing

[0078] Artificial soils A1 to B3 were extracted at a soil (air-dried soil sample):water ratio of 1:2, shaken at 160 rpm for 1 hour, and then filtered to prepare soil sample filtrate. 5 mL of the filtrate was placed in a petri dish lined with filter paper, and 10 cabbage seeds were placed on the filter paper. The mixture was incubated at 25°C in the dark for 48 hours. The germination rate and average root length of the seeds were measured, and the soil germination index was calculated. The germination index of the artificial soils A1 to B3 of this invention was all above 80%, further demonstrating that the artificial soil prepared with water-based drill cuttings of this invention has no potential toxicity.

[0079] 1.6 Plant Cultivation Experiment

[0080] Artificial soils A1 to B3 were used as cultivation soils, and Amorpha fruticosa seeds were sown, while water-based drill cuttings were used as a cultivation control. The results showed that after three months of planting, the germination rate, average plant height, and biomass of Amorpha fruticosa cultivated in the artificial soils A1 to B3 of this invention were significantly higher than those of the control group. This further verifies the feasibility of the water-based drill cuttings improvement method of this invention.

Claims

1. A method for improving water-based drilling cuttings, comprising the following steps: S1: leaching water-based drilling cuttings to be treated to reduce salt content; S2: screening the leached water-based drilling cuttings through a 2 mm screen; S3: screening the rotten straw through a 2 mm screen; and S4: mixing the screened water-based drilling cuttings obtained in the step S2 with the screened rotten straw obtained in the step S3 to obtain a mixture of improved water-based drilling cuttings; and further comprising a step of further mixing the mixture of improved water-based drilling cuttings with loess after the step S4; wherein the water-based drilling cuttings to be treated have the following characteristics: pH 9.3-10.1; conductivity 450-650 μS / cm; total salt content 6-14 g / kg; organic matter content 15-25 g / kg; total nitrogen 0.50-1.15 g / kg; total phosphorus 50-90 g / kg; total potassium 200-500 g / kg; available nitrogen 30-65 mg / kg; available phosphorus 12-18 mg / kg; cation exchange capacity (CEC) 1.0-3.0 cmol / kg; the loess has the following characteristics: pH 7.0-8.0, conductivity 90-120 μS / cm, total salt content 0.5-1.5 g / kg, organic matter content 50-60 g / kg, alkali-hydrolyzable nitrogen 70-95 mg / kg, available phosphorus 7-11.5 mg / kg, cation exchange capacity (CEC) 4.0-5.0 cmol / kg; the rotten straw has the following characteristics: pH 6.8-7.6; conductivity 500-900 μS / cm; total salt content 5-7 g / kg; organic matter content 55-75 g / kg; the water-based drilling cuttings to be treated, the rotten straw and the loess are mixed in the following mass ratio: 10:0.5:1, 10:1:1 or 10:1:

2. 2.The method for improving water-based drilling cuttings according to claim 1, wherein the rotten straw is rotten corn straw.

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