This document discusses water injection systems and methods for removing solids from water. It introduces concepts like suspended solids removal through gravity settling and flotation units. Gravity settling uses the density difference between solid particles and water to remove solids by allowing them to settle to the bottom of tanks. Other methods like hydrocyclones and centrifuges take advantage of centrifugal forces to separate solids. Proper pretreatment of water is important to remove solids and dissolved gases before injecting water into oil formations to prevent plugging and support microbial growth.

1. Water Injection systems:
Introduction
Solids removal theory
Removal of suspended solids from water
Gravity settling
Flotation units
Filtration

2. WATER INJECTION SYSTEMS
INTRODUCTION
 Oil field waters usually contain impurities, like dissolved minerals,
dissolved gases or suspended solids.
 Suspended solids (SS) can be generated by precipitation,
corrosion, or microbiological activity.
 Changes in temp, pr, pH or mixing of dissolved solids of different
sources of waters may cause scaling.
 The two primary sources of fresh water are surface water and
ground water ( rain or melting snow or ice or river)
 PW usually comes from drilling into a subsurface aquifer, is called
source water;
 The treatment of water to remove calcium & magnesium
dissolved solids (water softening) is important.
 The removal of SS & dissolved gases from water may be desirable
to prepare water for injection into formation

3. WATER INJECTION SYSTEMS
INTRODUCTION (Continued)
 It may be important to remove solids to some extent to avoid
plugging of formation which not only decreases the injection rates
but also increases the pumping rates.
 Oxygen & H2S in dissolved gases in the water may promote
bacteria growth and speed up the scale and corrosion process.
 For injection systems bulk solids should be removed. Oil is
normally separated from produced solids by abrasion in
hydrocyclones or washing with solvents.
 The source of water to be injected to be established for the
compatibility with the reservoir before selection of the water
treating system under surface conditions of pr, temp, and pH.
 Treating water for solids removal and for removal of dissolved
gases are really two separate concepts.

4. WATER INJECTION SYSTEMS : Solids Removal Theory
Removal of Suspended Solids from Water:
 The removal of solids is most commonly done as part of a water
injection system for water flood or EORecovery.
 It may also be necessary to remove SS prior to injecting produced
water in disposal wells.
 Gravity settling uses the density difference between the solid
particle and the water to remove the solids; filtration traps the
solids within a filter medium, allows water to pass
 It is expressed in mg/l or ppm by weight ( mg/l divided by water
sp.gr equals ppm). The size of the suspended particles is expressed
as a diameter in microns ( 10-6mts).
 These values range from 150 µ for gravity separators to less than 0.5
µ for filters.
 SS less than 40 µ in diameter can not be seen with the naked eye.

5. WATER INJECTION SYSTEMS Gravity Settling:
 The force of gr may be used to remove solid particles from water
if the density of these particles is not the same as the density of
water, they fall relative to the water due to the force of gravity.
 PPI, CPI, CFS can be effective at removing SS from water.
 However, the solids tend to cling to the plates and plug the plate
pack, so they are not normally used for the purpose.
 Others hydrocyclones, centrifuges also take advantage of the
density differences, induce centrifugal forces in the water,
causing the heavy solid particles to move away from the axis of
rotation
• Gravity settling in large tanks relies on low fluid velocities and
large particle sizes (>10 µ) to be most effective.