1. Drilling mud system
To understand the composition of drilling wastewater, it is necessary to know the mud system used in the drilling process. Drilling mud systems are formed by adding different mud treatment additives to the mud in order to adapt to the requirements of the drilling process under various circumstances. There are inorganic mud treatment agents, organic mud treatment agents and surfactants. The whole mud system is mainly divided into two categories: water-based mud and oil-based mud.
The main pollutants in the mud that cause pollution to the environment are heavy metals, various organic mud treatment agents and surfactants.
2. Water quality composition of drilling wastewater
Drilling wastewater is in the process of drilling, due to the return of mud during drilling operations, the loss of mud circulating system leakage of mud rinsing equipment oil and cleaning platforms and other aspects of the sewage generated. It consists of solids, liquids and colloidal suspensions, is a multistage dispersion system. Pollutants are mainly:
(1) CODcr, from a variety of organic mud treatment agents and surfactants such as tannin, foaming agents and defoamers.
(2) Oil, from oil-based mud, diesel engine cooling water, rig rinse water, etc..
(3) heavy metals, mainly by adding inorganic treatment additives chromate introduced Cr6+, in addition to iron chromium salt lignosulfonate also introduced chromium ions. Other heavy metal pollutants there are things there are P sub +, Cd2 + and other away.
The current situation of drilling wastewater treatment
1. Treatment method
Most of the major oil fields in China use chemical coagulation treatment for the treatment of drilling wastewater after discharge. As the coagulation method can only remove colloidal or suspended particulate pollutants in the water, and has formed a solution of some mud treatment agents such as iron and chromium salts, sulfonates have little effect. This is the main problem of using chemical coagulation to treat drilling wastewater.
2. Treatment chemicals
Drilling wastewater treatment chemicals are mainly inorganic salt coagulants, organic polymer flocculants, inorganic and organic compound coagulants.
(1) Inorganic salt coagulants
Al2(SO4)3, PAC, PFS is currently used in various oilfields to deal with drilling wastewater inorganic flocculants, inorganic flocculants to the wastewater after its treatment of alumina settling performance, low water content, good results, cheap chemicals, low treatment costs and well team welcome. But Al2 (SO4) 3, PAC and other aluminum salts coagulants are susceptible to Cl- and other interferences to reduce the treatment effect and other iron salts flocculants caused by corrosion phenomenon is the main problem with inorganic flocculants.
(2) Organic polymer flocculant
Organic polymer flocculant with its unique stretching structure and irregular structure of the functional groups such as the structure and electrically charged to determine its dosage, flocculation capacity is high, the effect is good, flocculant coarse, fast settling speed, short treatment time, sludge dewatering is good easier to deal with, low-cost and so on, in the drilling wastewater treatment to play the role of adsorption bridge and charge neutralization, mainly used in the drilling wastewater treatment. Charge neutralization role in drilling wastewater treatment, mainly used as a coagulant. Commonly used coagulants are PAM, but the dosage of organic polymer flocculants should be strictly controlled, otherwise it will be too large and make the alum flower settling effect is poor, or even ineffective, but instead of the CODcr of the wastewater to rise, become a new pollutant.
(3) compounding agents
In order to give full play to the advantages of inorganic and organic flocculants in their respective water treatment, to overcome their shortcomings in water treatment, the more common water treatment agent is the inorganic and organic flocculants are compounded to use, in order to get a better treatment effect. The effect of compounding agent on drilling wastewater treatment depends on the selection of organic and inorganic flocculants, compounding ratio, processing flocculants, such as the process. After the compounding agent treatment of drilling wastewater, petroleum and other pollutant indicators are significantly better than the treatment effect of using inorganic or organic flocculants alone.
3, the treatment device
At present, the drilling wastewater treatment device is mainly used for chemical coagulation process, to the skid direction.
The major domestic oilfields have made some exploratory work, according to information on the Sichuan Bureau of the DZW series of drilling wastewater treatment device for drilling wastewater treatment effect is better, but did not solve the problem of sludge dewatering. Jianghan, Dagang, Yumen and other oilfields in this regard also made a lot of work, and achieved certain results.
In foreign countries, skid-mounted drilling wastewater treatment devices are the United States ROMEC Environmental Research and Development Corporation developed skid-mounted drilling wastewater and waste mud treatment devices; Newpark Waste Treatment Company's oilfield waste purification devices; the former Soviet Union developed the YOB drilling wastewater and YOBC-1M-type drilling wastewater purification devices France International Petroleum Company recently launched a closed-circuit wastewater device, etc.
Several opinions
1. Development of new mud system
Starting from the control of pollution sources, open up new ideas of oilfield chemical additives to meet the needs of the drilling process, but also in order to prevent environmental pollution as the principle, the development of new oilfield chemical reagents to replace the existing pollution control efforts in the mud treatment additives such as difficult to degrade the current diluent sulfonate, defoamers and so on.
The development of oilfield chemical additives and environmental pollution control as a whole.
2. Increase the rate of reuse of well wastewater
Minimize the amount of wastewater discharged from the wells, clean up the sewage diversion, and increase the rate of reuse of drilling wastewater in the wells. The reuse of drilling wastewater should be controlled in sections, with the increase of well depth, the reuse rate of wastewater from high to low timely and reasonable adjustment.
3. Development of drilling wastewater treatment chemicals
The treatment of drilling wastewater, currently inseparable from the chemical coagulation of this link, the successful development of drilling wastewater treatment chemicals, is the key to solving the treatment of drilling wastewater. At present, the main research direction is the development of high polymerization of inorganic treatment agents and multi-functional compounding agents, in order to be able to maximize the characteristics of drilling wastewater, to achieve the best treatment effect. The major mines of Sichuan Bureau have made some useful attempts in this regard, such as the Co-H drilling wastewater treatment agent in the south Sichuan mine.
4. Explore feasible treatment processes
Chemical coagulation is the "traditional" process of drilling wastewater treatment. There has been no new breakthrough in the treatment process of drilling wastewater. Exploring feasible treatment processes is another research direction for drilling wastewater treatment. Biological purification of drilling wastewater has become a promising treatment method with its advantages of low cost and easy management. Sichuan Bureau of Sichuan East Drilling Company cultures aquatic plants in drilling wastewater to purify drilling wastewater, which has good degradation effect on wastewater, oil, phenol and other pollutants.
Recommendations
According to a comprehensive sewage discharge standards, the main pollutants in the drilling wastewater discharge indicators for CODcr<200 mg/L. In the actual pollution control work, with the increase in drilling footage, the use of the mud system accordingly the more complex, this is because in the process of drilling, due to the bottom of the well high temperature and high pressure, the process requires mud system is very stable, and thus requires mud treatment additives This is because during the drilling process, due to the high temperature and pressure at the bottom of the well, the process requires the mud system to be very stable, which in turn requires the mud treatment additives to have a very good stability such as sulfonates, which are discharged back into the drilling wastewater, are not easy to be degraded, which increases the difficulty of the treatment of drilling wastewater, so that the discharge into the receiving body of water in the self-cleaning cycle of the mud treatment agent is very long, and will not bring a large impact on the entire receiving body of water load that caused the pollution accident. Therefore, it is recommended to propose suitable CODcr discharge index for drilling wastewater when the national standard is modified.
Concluding Remarks
Drilling wastewater as a major source of pollution in oil exploration enterprises, its treatment and the development of treatment technology to protect the ecological environment, to ensure the smooth progress of oil exploration and to improve the good neighborly relations with the local community are of great significance.