Introduction

Oil-field waters usually contain impurities. These impurities are classified as dissolved minerals, dissolved gases, or suspended solids. Suspended solids can be naturally occurring, generated by precipitation of dissolved solids, generated as products of corrosion, or created by microbiological activity. Changes in temperature, pressure, pH, or the mixing of waters from different sources may cause scaling, which is precipitation of dissolved solids. Suspended solids may settle out of the water stream or may be carried as a suspension in flowing water.

The two primary sources of freshwater are surface water and groundwater. A portion of the rain or melting snow and ice at the earth's surface soaks into the ground, while part of it collects in ponds and lakes or runs off into creeks and rivers. This latter portion is termed "surface water."

Water encountered in production operations usually comes from separated produced water or from wells specifically drilling into a subsurface water aquifer. The latter is often called "source water," is often brackish, and may contain a large quantity of dissolved solids.

This chapter provides information about equipment selection and sizing for removing suspended solids and dissolved gases from water. The water's source affects the types and amounts of contaminants in the water. For example, produced water will be contaminated by some hydrocarbons.

The treatment of water to remove calcium and magnesium dissolved solids ("water softening") is important, especially if the water is to be used as boiler feed water for the generation of steam, as in a...