Solids Removal Equipment Description

This section describes several different processes designed to remove suspended solids or dissolved gases from water. As stated, the most common reason for such water treatment is associated with water injection therefore, the subject of water injection will also be discussed throughout this chapter. The principles and equipment involved can also be applied when the water must be treated for other reasons. 

Almost every oil or gas production facility must deal with some produced water at some time during its production life. In many facilities the water may be disposed of once its hydrocarbon content is reduced to acceptable levels. When water is to be injected, it may be necessary to treat the water to attain low levels of oil (on the order of 25-50 mg/1) to prevent impairment of the injection formation or downstream equipment. 

Typically, produced water may require filtration to remove dispersed oil. Filtering will remove all but a very small amount of the dispersed oil. It will be necessary, however, to clean the water to less than approximately 50 mg/1 suspended oil so that oil does not create plugging problems in the filters. The small amount of suspended oil in the water will be removed by the filter and will contaminate the filter backwash. 

Surface water is a common water source for water-flood or other injection projects. If surface water is available, it may be cheaper to obtain than subsurface water. However, surface water may require more treatment than other water sources, and, since it is fresh, it may cause swelling of clays in some formations. 

Chemical injection of biocides is of particular importance for treating surface water. The water contains microscopic marine life, bacteria, plankton, and algae, which cannot be allowed to continue to grow within treating equipment. 

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In addition to scale particles, produced water often contains other suspended solids. These include formation sand and clays, stimulation (fracturing) proppant, or miscellaneous corrosion products. The amount of suspended solids is generally small unless the well is producing from an unconsolidated formation, in which case large volumes of sand can be produced. Produced sand is often oil wet and its disposal is a problem. Sand removal is discussed in a later subsection entitled "Equipment Description" under Section 3.6. 

Evaporation is the removal of a solvent by vaporisation, from solids that are not volatile. It is normally used to produce a concentrated liquid, often prior to crystallisation, but a dry solid product can be obtained with some specialised designs. The general subject of evaporation is covered in Volume 2, Chapter 14. That chapter includes a discussion of heat transfer in evaporators, multiple-effect evaporators, and a description of the principal types of equipment. The selection of the appropriate type of evaporator is discussed by Cole (1984). Evaporation is the subject of a book by Billet (1989). 

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