Document Type : Original Article

Authors

Petroleum Research and Development Center (PRDC)-Ministry of oil, Iraq

Abstract

This study dealt with the problem of produced water (PW) at Missan Oil Company (MOC) which results in huge quantities of water annually from different fields of the company and particularly in Alommara oil field .The produced water is discarded to the evaporation ponds outside the field which causes serious problem to the environment. We studied that problem and how to treat the produced water generated from Alammara Degassing Station for reinjection application to increase the secondary oil recovery. A pilot plant (10m3/day) for PW treatment was manufactured based on some bench scale treatment to select the sequence process to treat the targets parameters. Many parameters were selected to be treated based on its effect on water injection specifications .The selected  parameters were  Oil and Grease , Iron ,Turbidity ,TSS, Particle Size , Dissolved Oxygen , PH and Bacteria. Removing oil by using corrugated plate interceptor technique (CPI) is the first stage of treatment. In some circumstances, the presence of iron in the produced water needs a treatment to meet the reinjected specifications of water. A chemical oxidant (Sodium Hypochlorite) was used in the pilot plant to oxidize the iron and removed later. The total suspended solids (TSS) are decreased to the required concentration by using coagulation – Flocculation process and dual sand filter media .The other target parameters to be treated in the pilot plant are bacteria and dissolved oxygen. Chemical agents, Gluteraldehyde and Sodium Sulfite were used to treat bacteria and dissolved oxygen respectively. Caustic Soda solution was used to obtain a suitable PH value. The specifications of treated water by this piot plant were very proper for safely reinjection to increase the recovery of oil. 

Graphical Abstract

Treatment of Produced Water Generated at Alommara Oil Field-Missan Oil Company, IRAQ for Reinjection Application

Keywords

Main Subjects

Produced water (PW) is a huge volume produced from the oil drilling. It is a side product from oil wells [1]. PW is water trapped in underground reservoir rocks and is brought to surface along with crude oil and gas. Besides elevated concentration of heavy metals such as Barium, Uranium, Cadmium, Chromium, Strontium and Lead, PW contains dispersed oil droplets, dissolved organic compounds and significant amount of anions, such as Carbonate, Bromide and Sulfate [2]. The physical and chemical properties of produced water vary considerably depending on the geographic location of the field, the geological formation with which the produced water has been in contact for thousands of years, and the type of hydrocarbon product being produced [3]. The water produced is seven to eight volume larger than the oil produced [4]. Untreated produced water causes number of problems due to the existence of high-concentration toxic substances; the inappropriate disposal of oily sludge can pose serious intimidation to the receiving environment. Oily sludge can disturb the physical and chemical properties of soil, leading to soil morphological transform. The oily sludge contaminated soils may create nutrient dearth, reduce seed germination, and cause limited growth or demises of plants on contact. Due to its high viscosity, oily sludge components can be fixed in soil pores, adsorbed onto the surface of soil mineral constituents, or form a continuous cover on soil surface. These would lead to reduced hygroscopic moisture, hydraulic conductivity, and water retention capacity of soils. In particular, the components with higher molecular weight in sludge and their degradation products could remain near soil surface and form hydrophobic crusts that decrease water availability and limit water/air exchange [5].

 

Characteristics of Produced Water

Natural water or formation water is always found together with petroleum in reservoirs. It is slightly acidic and sits below the hydrocarbons in porous reservoir media [6]. PW is a mixture of injected water, formation water, hydrocarbons and treating chemicals [7].

 

Current Status of Produced Water in Alommara oil field –MOC

The produced water generated at Alommara oil field is driven into the evaporation ponds outside the field which causes serious problem to the environment (Figure 1).