Scholarly article on topic 'Disposal and Reuse of Drilling Solid Waste from a Massive Gas Field'

Disposal and Reuse of Drilling Solid Waste from a Massive Gas Field Academic research paper on "Earth and related environmental sciences"

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Abstract of research paper on Earth and related environmental sciences, author of scientific article — Aiping Zhang, Min Li, Pei Lv, Xiaofeng Zhu, Luping Zhao, et al.

Abstract Drilling solid waste is a typical industrial solid waste, and it is a major pollutant source to ecological environment around gas fields. A gas field in Southwest China is a self-contained marine gas field, presently with a large scale and great abundance. It also belongs to the five large gas fields of China with exploration above 2×1011m3. Spot investigation and experimental study showed that the drilling solid waste was made up of drilling mud and rock cuttings. After solidified disposal, the waste belonged to the second general industrial solid waste, and environmental impacts related to the waste water were characterized as pH, COD and SS. According to traffic distance to the local town, alternative control projects were brick production and cement solidification. Drilling solid waste from the central field was collected and piled up in a massive landfill, then gradually calcined to brick; while drilling solid waste from the ambient field was mainly on-the-spot solidified, later for activity site. The study is significant for waste pollution control and gas field management. However, further studies are in progress to solve the problems such as waste water pollution of the massive landfill and the solidified pools, secondary air pollution of the brick factory.

Academic research paper on topic "Disposal and Reuse of Drilling Solid Waste from a Massive Gas Field"

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Environmental Sciences

Procedia Environmental Sciences 31 (2016) 577 - 581

The Tenth International Conference on Waste Management and Technology (ICWMT)

Disposal and reuse of drilling solid waste from a massive gas field

Aiping Zhang *1,2, Min Li 1, Pei Lv 1, Xiaofeng Zhu 1, Luping Zhao 1, Xue Zhang 1

1. Chemistry and Material Science of Sichuan Normal University, No.5 Jingan Road, Chengdu 610068, China; 2. Chemical Engineering of Sichuan University, No.24 South Section 1, Yihuan Road, Chengdu 610065,China

Abstract

Drilling solid waste is a typical industrial solid waste, and it is a major pollutant source to ecological environment around gas fields. A gas field in Southwest China is a self-contained marine gas field, presently with a large scale and great abundance. It also belongs to the five large gas fields of China with exploration above 2*10um3. Spot investigation and experimental study showed that the drilling solid waste was made up of drilling mud and rock cuttings. After solidified disposal, the waste belonged to the second general industrial solid waste, and environmental impacts related to the waste water were characterized as pH, COD and SS. According to traffic distance to the local town, alternative control projects were brick production and cement solidification. Drilling solid waste from the central field was collected and piled up in a massive landfill, then gradually calcined to brick; while drilling solid waste from the ambient field was mainly on-the-spot solidified, later for activity site. The study is significant for waste pollution control and gas field management. However, further studies are in progress to solve the problems such as waste water pollution of the massive landfill and the solidified pools, secondary air pollution of the brick factory. © 2016PublishedbyElsevier B.V Thisisanopenaccess article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of Tsinghua University/ Basel Convention Regional Centre for Asia and the Pacific Keywords: disposal; reuse; drilling solid waste; gas field

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ELSEVIER

1. Introduction

Drilling solid waste of most gas fields in China is a stabilized suspended substance, and combined with clay, chemical additives, rock cuttings, weighting materials, oil, etc. It is an impact to human health and the environment. As expected from previous studies, drilling solid waste is treated by solidification and landfilling, incineration, or reclamation after biological treated, building materials or paving stones after solidified, calcined brick combined

* Corresponding author. Tel.: +86 13488951126. E-mail: apzhang@sicnu.edu.cn

1878-0296 © 2016 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of Tsinghua University/ Basel Convention Regional Centre for Asia and the Pacific doi:10.1016/j.proenv.2016.02.089

with some clay[1~5]. In consideration of social, environmental and economic benefits, disposal and reuse of drilling solid waste should be in accordance with local conditions.

The gas field is located in Daba Mountain, with great relief and widespread valley, thus natural environment around is rather sensitive. Since exploited, reduce, reuse and recycle of drilling solid waste is concerned and urgent. Though the work is arduous, it needs to be properly solved in time, for it is related to accomplishment of environment protection object and acceptance by the environmental authorities.

2. Characteristics of drilling solid waste

2.1. Production characteristics of drilling solid waste

Drilling solid waste was produced in construction period of gas well, and included waste mud, rock cuttings, weighting materials, and so on. Waste mud of the drilling field was nearly between 800~1200 m3 per well, rock cuttings were about 1000 m3 per well. In period of drilling, weighting materials may be used when necessary. If emergency probability was 1% and waste yield was 500 m3 per well, weighting materials was 5 m3 per well. Apparently, waste mud and rock cuttings were the main drilling solid waste.

2.2. Physicochemical characteristics of drilling solid waste

Since compound of waste mud and rock cuttings was the main drilling solid waste, the massive landfill received drilling solid waste of the central field was investigated. And the solidified waste was sampled by the common planar method. The solidified waste was loose and of dark grey color. Experimental study showed that density of the solidified waste was1.75 g/cm3, moisture was 24.0%; and its component, heavy metal content, radioactive element content were respectively presented in Table 1~ Table 3.

Table 1. Component of the solidified drilling solid waste from a gas field

Items Cl- SO42" Na Fe Ca Mg Si Al CO32- petroleum other

Content (%) 0.1 5.6 1.0 9.0 12.4 6.8 15.8 22.8 10.2 0.4 15.9

As showed in Table 1, main components of the solidified waste mud and rock cuttings were inorganic and organic matters with element of Al, Si, Ca, Fe, individually reached 22.8%, 15.8%, 12.4%, and 9.0% of the sample weight, totally to 60%.

Table 2. Heavy metal content of the solidified drilling solid waste from a gas field

Items Cd Hg Pb Cr As Zn Ni Cu B

Values(mg/Ag) 0.3 0.27 43 36 3.2 234 70 40 1.2

Limit (pH>6.5) 20 15 1000 1000 75 1000 200 500 150

Limit (pH<6.5) 5 5 300 600 75 500 100 250 150

Table 3. Radioactive element content of the solidified drilling solid waste from a gas field

Items (Ra-226, Th-232, K-40) Internal radiation index IRa External irradiation index Ir

Values 0.19 0.37

Limit 1.0 1.3 (1.0)

Heavy metal content was analyzed by "Standard for pollutants control of agricultural sludge" (GB4284-84) , and radioactive element content was analyzed by "Limit of radionuclides in building materials" (GB6566-2001 ) . Based on data of Table 2 and Table 3, it was found that both heavy metal content and radioactive element content met national standards of non-metal building material or walling material.

2.3. Waste water characteristics of drilling solid waste

In the spot investigation, solidified waste and a mud pool were individually sampled and analyzed, and their waste water characteristics were shown in Table 4.

Table 4. Waste water quality of the solidified drilling solid waste from a gas field

Items Values (mg/L) The massive landfill A mud pool Limit of GB/T5085.3-2007 {mg/L) The first discharge level of GB8978-1996 {mg/L)

pH 11.6 12.3 6~9

Color 45 10 50

COD 69 528 60

SS 225 309 70

Petroleum 2.86 1.34 5

Cr6+ 0.004 0.035 5 0.5

Total Cr 0.026 0.123 15 1.5

Chloride 91.2 22.0 250*

Sulfide 0.010 0.005 1.0

Cu 0.050 0.052 100 0.5

Pb 0.2 0.2 5 1.0

Zn 0.05 0.05 100 2.0

Cd 0.05 0.05 1 0.1

Mn 0.010 0.049 2.0

* Reference of "Environmental quality standards for surface water" (GB3838-2002) .

It was indicated that: (1) chemical characteristics of waste water were generally similar except COD, SS, Cr, and Mn; (2) based on "Identification standards for hazardous wastes-Identification for extraction toxicity" (GB/T5085.3-2007) and "Standard for pollution control on the storage and disposal site for general industrial solid wastes" (GB18599-2001) , the solidified drilling solid waste did not belong to hazardous wastes, but belong to the second general industrial solid waste; (3) based on the first discharge level of "Integrated wastewater discharge standard" (GB8978-1996) , only pH, COD and SS of waste water were super-standard.

3. Disposal and reuse of drilling solid waste

3.1. The central field

The gas field was exploited until exhaustion with one exploitation system. For gas wells were distributed irregularly, well spacing was with cluster wells, combined with deviated wells and straight wells. The central field included 16 drilling platforms, 38 gas wells, over 23.2*104 m drilling footage, and took about half and three years. Because the central field was comparatively centralized, drilling solid waste was fit for centralized disposal and reuse. Thus, drilling solid waste of the central field was collected from mud pools, then piled up in the massive landfill, and gradually regenerated in the brick factory.

• Mud pools

Every drilling platform had a mud pool of volume about 3*103 m3. Compound of waste mud and rock cuttings was delivered into the mud pool by a pipe. When accumulated to a certain volume, the drilling solid waste was solidified with complex agent, and then the solidified drilling solid waste was collected and delivered to the massive landfill by special cars. The mud pool was impervious at the bottom and had the canopy on the top, thus could escape spill of waste mud and rock cuttings in rainy period.

• The massive landfill

Storage capacity of the massive landfill was about 3.2*104 m3. One side of the massive landfill was backed hills, and the other three sides were reinforced with rubble concrete. A waste water storage pool was instructed downstream, of volume about 200 m3. Waste water was collected by perforated pipes under the massive landfill and lateral ditches around. Waste water of the drilling solid waste was treated off-site by the chemical method. After delivered to the wastewater treatment station nearby by tank cars, the waste water was treated until reached the standards, and then discharged into rivers nearby.

• The brick factory

Because both heavy metal content and radioactive element content met the standards, the drilling solid waste was safe for brick material. The experiments showed that 1 m3 drilling solid waste and 1 m3 shale clay could be calcined to 1000~1200 bricks. Technological flow sheet of the brick factory was presented in Fig. 1. If the technology was optimized at early stage, such as effective separation of waste mud and rock cuttings, replacement shale clay with mud clay in rock cuttings, operation cost could be further controlled. According to strength of calcined brick, the brick was used for internal instruction of gas filed or domestic building of local residents. Nevertheless, the brick factory had the problems of high operation cost, secondary air pollution during operation, poor sales of brick, and such problems were need to solve step by step.

Fig. 1. Technological flow sheet of the brick factory

3.2. The ambient field

The ambient field included 8 drilling platforms, 15 gas wells, over 10*104 m drilling footage, and nearly lasted two years. Every drilling platform had a mud pool, a wastewater pool, a fire pool and a spurting pool, and all were built in concrete. Firstly, waste mud and rock cuttings were stored in the mud pool. After drilling was completed, drilling solid waste of the ambient field was dewatered and solidified with cement agent. Waste water of the drilling solid waste was stored in the wastewater pool, and then delivered to the wastewater treatment station by tank cars. Until reached the standards, the waste water could discharge into rivers nearby. Until waste water produced from the drilling solid waste was under the first discharge level of GB8978-1996, the mud pool could be closed. Since the drilling solid waste was innocently disposed, its impact on the environment was negligible. After the solidified pool was recovered with earth and plant, it could be regenerated for activity spot of operation.

4. Conclusions

For waste mud and rock cuttings is the main of drilling solid waste, proper disposal and reuse of the drilling solid waste is vital to environment protection. In the case study, drilling solid waste from the central field was collected and stored in the massive landfill, and reused as calcined brick; while drilling solid waste from the ambient field was solidified on the spot and closed in the pool, later recovered with earth and plant or regenerated for activity spot of operation. The above experience put forward an effective method to solve the pollution of drilling solid waste.

Acknowledgements

This study was financially supported by the project of Sichuan education department (15ZB0034), "Youth Creative Project" from Science & Technology Department of Sichuan (2015038, 2015039), the open experimental project of Sichuan Normal University (2015-25).

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