EXXON CHEMICAL COMPANY February 24, 1993 Hasmukh C. Shah, Ph.D. - - PDF document

SLIDE 1

EXXON CHEMICAL COMPANY

February 24, 1993

Hasmukh C. Shah,

Ph.D. Chemical Manufacturers Association 2501 M Street,

NW

Washington, DC 20037 Dear Has:

Enclosed are materials

I was able to gather for possible inclusion in the

• ilfield microbiocides education package for the EPA.

I hope some of them may be useful.

Sincerely yours,

Oliver Bourgeois Material Safety Chemis Enclosure

cc:

Gary Bond

8230 Stedman, Houston, Texas 77029-3999 A Division of Exxon Corporation

SLIDE 2

IDENTIFICATION OF MICROORGANISMS FOUND

IN

INDUSTRIAL AND OILFIELD WATERS Many microscopic

• rganisms

exist

in the world in which we live. Bacteria are just

• ne
• f

the groups

• f microorganisms

that surround

us.

Bacteria are found

• n
• ur

skin, in our mouths, stomachs, intestines, and in the water we drink and the air we breathe.

When

the word bacteria is used,

most people think of "germs", disease,

• r

some

• ther unpleasant association.

While

it is

true that many bacteria are harmful

to man,

they are vastly out-numbered by the bacteria that are beneficial

to

man, and required in our daily life processes.

Bacteria are microscopic, unicellular organisms that are capable

• f

carrying out all functions necessary for life and reproduction when they are placed in a favorable environment. Most bacteria measure

less than

8 microns

in length and

1 micron

in width. In order

to place bacteria in

the proper perspective in oil and gas production,

• ne must have an understanding of:

(1)

the classifi- cations

• f microorganisms

(2)

their requirements for sustaining life and reproduction

(3)

how they can be identified

(4)

the problems

associated with bacteria

in the petroleum industry.

CLASSIFICATION

OF MICROORGANISMS The

simplest form of microorganisms can be grouped into three classifi- cations:

1.

Algae

• contains

chlorophyll

• require

sunlight

2.

Fungi

• do not

contain chlorophyll

3.

Bacteria

• have

some properties common

to both algae

and fungi Bacteria

comprise the broad class

• f microorganisms
• f

greatest interest

in the petroleum

industry, and are normally classified

as

belonging

to

• ne
• f

two groups. Group

I aerobic bacteria

• bacteria

which require free oxygen for growth. Growth

II are

anaerobic bacteria

• bacteria

that require the absence

• f

free

• xygen

for growth.

SLIDE 3

• 2-

Slime forming bacteria and iron bacteria are aerobic. They cannot grow or reproduce

in an oxygen

free environment. Sulfate reducing bacteria are anaerobic. They require an oxygen free environment for growth and reproduction. Sulfate reducing bacteria can and

do

exist

in systems that

contain free

• xygen,

but

the

bacteria are located under deposits such

as

scale, mud, corrosion by-products,

• r

some other sheath which shields them from the oxygen bearing water. PHYSICAL REQUIREMENTS OF MICROORGANISMS Bacteria have been found in many different types

• f

environments. They have been found on the ocean floors, in hot sulphur springs, and

in the

arctic

seas. Each of these

environments however met certain requirements which were necessary for

the growth and

reproduction

• f

the bacteria encountered. A particular species

• f

bacteria requires

a particular environment,

and the environment must meet the specific needs

• f

the bacteria. Temperature

is

• ne
• f

the

controlling factors that

is most

important

to

all forms

• f

life. The

limiting temperatures for all forms

• f

life

is

the

temperature

at which enzymes can be

effectively utilized

to

promote the

life processes. Enzymes are protein complexes

which catalyze the chemical reactions necessary for sustaining

life.

Bacteria flourish under an extremely broad temperature range. Depending

• n

the species,

they can g6ow at temperatures

as low as

O°F(-17.8°C) and

as

high

as

180°F (82.2

C).

Each species

• f bacteria will

grow at temperatures within

a

certain range. The temperature which allows

the most rapid growth

is

called

the

• ptimum - growth

temperature

.

The extremes

• f

the growth range temperatures are called the minimum and maximum growth temperatures.

Gaseous constituents are another factor which influences the growth

• f microorganisms.

The two most important gases are oxygen and carbon dioxide. Bacteria

display

a variety of patterns

• f response

to

free oxygen, which results in their being classified into

• ne
• f four groups:

Group

I are

aerobic microorganisms

• they

grow in the presence

• f

free

• xygen.

Group

II are

anaerobic microorganisms

• they grow

in the

absence

• f

free

• xygen.

SLIDE 4

Group III are facultative microorganisms

• they grow

in either the

presence

• r

absence

• f

free

• xygen.

Group

IV are microaerophilic microorganisms

• they grow

in the

presence

• f minute

quantities

• f free oxygen.

An increase

• f

carbon dioxide content facilitates the growth of some microorganisms, and has no effect

• n others.

pH of

the

environment greatly affects the growth rate

.of micro-

• rganisms

.

The

• ptimum pH range

for most microorganisms

is

6.0- 8.0, but they can grow in an environment with a pH

as

low as 4.0

• r

as

high

as 9.0.

Microbial enzymes are

as

sensitive

to

pH

change

as

they are

to

temperature change .

In addition to affecting the

enzyme action, pH also affects the state

• f colloidal suspension
• f protoplasm and

the

permeability of the cellular membrane. Osmotic pressure

is

the driving force behind the passage

• f fluid

through the cellular membrane ,

as in the process

• f osmosis.

Osmosis tends

to

equalize the concentration of dissolved substances surrounding the cell and the fluid within the cell . Sodium chloride

is

generally

the most common dissolved

substance which affects

• smotic

pressure . Microorganisms receive their nutritional requirements by

the

process

• f osmosis ,

thus if the osmotic pressure

is

altered

in some manner the microorganisms

cannot continue

to

grow and reproduce. Many fresh-water species cannot grow

in an environment with salinities in excess

• f
• ne

percent . However,

• rganisms

from either fresh- water or salt-water environments can adapt

to the

environment

• f

the

• ther.

Thus , microorganisms exist in almost every environment, regardless

• f osmotic

pressure. Radiant energy

( sunlight )

is

required by algae and

a

few species

• f

bacteria . Sunlight

is

required by algae

in order that the metabolic process can be

carried

• ut

for their life functions . The majority

• f bacteria

do

not require radiant energy for their life processes, and in fact , high concentrations

• f X-Rays

and ultraviolet light can be lethal

to

them.

Sublethal doses

• f

radiant energy can cause microorganisms

to

form mutations and give rise

to new species

• f

microcrganisms. Hydrostatic pressure changes can be detrimental

to

some species

• f

microorganisms. Death can occur

to

many species when they are subjected

to

pressures

• f

9,000 pounds per square inch, while many

• ther

species are injured when subjected

to

pressures

• f

5,000 pounds per square inch.

SLIDE 5

• 4-

There

is a

relationship between pressure and temperature . Unduly high temperatures may be thought

• f

as

causing deleterious expansion

• f

the

enzymes within

the

cellular structure

• f

the microorganism. Increased pressure tends

to

lessen the expansion

• f

the enzymes and thus

prevents

• r offsets

the unfavorable effect caused by increased temperatures

.

Some deep sea bacteria and others found in producing oil and gas wells appear

to be

favorably influenced by high pressures . Some bacteria are not injured by pressures up

to

150,000 pounds per square inch, and these are said

to be barophilic

( pressure - loving).

NUTRITIONAL REQUIREMENTS

OF MICROORGANISMS

All living organisms require nutrition

to

sustain

life.

While

the

requirements vary from species

to

species , they are shared by all living organisms. An energy source

is

required by all forms

• f

life.

Green plants utilize radiant energy and are designated as phototrophs. Forms

• f

life which are not capable of using radiant

energy must rely on chemical reactions

to

provide energy and are designated

as

chemotrophs. Chemotrophs are broken down into two other classifications and are said

to be either autotrophs

• r heterotrophs .

Autotrophs utilize inorganic compounds

as

their sole source of energy , while heterotrophs require

• rganic

compounds

as a

source of energy.

A carbon source

is

required by all organisms . Most microorganisms require

• rganic

carbon. Algae and

a

few other bacteria require inorganic carbon in the form of carbon dioxide and carbonates. Some forms require the more complex form such as carbohydrates. Nitrogen

is

required by all living organisms. Algae and a few other

microorganisms use nitrogen

in the

form of inorganic salts. Other forms utilize nitrogen from the atmosphere . Most organisms however require nitrogen

in the organic

form of protein. Metallic

ions such as sodium potassium , calcium, magnesium, iron, copper, and phosphorus are needed by all

• rganisms

.

While

the

amounts required are mere trace amounts, life cannot be sustained without them. The metallic elements are present

in most natural environments.

Vitamins and vitamin - like compounds are utilized by all living

• rganisms .

Microorganisms present

a unique

pattern

in this

aspect

• f

nutrition. While many microorganisms will not grow unless vitamins are present

in the

environment, there are others that are capable

• f

SLIDE 6

• 5-

synthesizing their vitamin requirements from other compounds that are present

in the

environment. Water

is

required for the life processes and normal growth.

In the case

• f

lower plants (bacteria, mold, yeast and algae), all nutrients must be in solution before they can enter the

• rganism.

Many microorganisms can survive complete drying (desiccation)

for long periods

• f

time, but they cannot grow under these conditions. They can also enter

a state

• f dormancy when they are

subjected

to an unfavorable

environment, and will become active when conditions

• nce again become

favorable. IDENTIFICATION

OF

BACTERIA

Bacteria

in oilfield waters

can be determined by several different methods. A trained microbiologist can identify species

• f bacteria

by microscopic examination. Serial dilution bottles

• r

an agar

medium can be used by

the engineer in the field to determine the

presence and'general number of bacteria

in the water. The three species

• f bacteria

that create the majority of problems in oilfield waters are sulfate reducing bacteria, slime forming bacteria, and iron bacteria. Sulfate reducing bacteria

are anaerobic. They reduce sulfate (S04=)

to

sulfide

(S=)

which reacts with hydrogen

(H+) in water to

form hydrogen sulfide (H2S). Sulfate reducers can be cultured

in A.P.I.

serum broth bottles

• r

in the

produced water

in the

presence of an agar. Slime forming bacteria are

a

general classification

• f aerobic

bacteria. They are capab le

• f producing dense masses
• f

slime on solid surfaces, and are found

in both fresh and brine waters.

Slime forming bacteria can be cultured

in phenol red serum broth

bottles

• r

in the produced water in the presence

• f an agar.

Iron bacteria are aerobic bacteria. They have the ability

to

• xidize

iron from the ferrous (Fe++)

to the

ferric (Fe''!) state, and pre- cipitate

it as

an oxidized coating. Iron bacteria cannot be cultured in phenol red serum broth bottles. They must be identified by microscopic examination.

SLIDE 7

• 6-

PROBLEMS ASSOCIATED WITH BACTERIA Bacteria in oilfield waters create

a variety of problems.

The reason that bacteria can create

so much trouble is

that they can multiply with incredible speed. Bacteria can double their population every 20 minutes under many conditions, which means that

a single bacterium

can become

a

thriving colony of millions

• f bacteria

in a very few hours.

Corrosion, plugging, line restriction, and increased oil/water interfaces

in production equipment are a

few of the problems created by bacteria . Sulfate reducing bacteria can contaminate

a sweet

formation and cause

it to become sour.

This

is

accomplished by injecting waters containing

the

sulfate reducing bacteria into

the

formation. Bacteria can cause loss

• f heat transfer

in heater - treaters, and in

heat exchangers and condensers

in gas plants , refineries, and petro-

chemical plants.

SLIDE 8

PROBLEMS CAUSED BY BACTERIAL ACTIVITY Problems created by microorganisms

in oilfield waters are

many and varied

in

complexity. Of all species

• f bacteria

encountered

in oil-

field waters, sulfate reducing bacteria probably cause the most serious problems. Sulfate reducing bacteria reduce inorganic sulfate

ions in the water to sulfide ions,

which react with hydrogen

ions to form the

corrosive hydrogen sulfide (H2S)

gas. The H2S causes

corrosion

to

• ccur

in the

system, and the resulting iron sulfide by-product creates additional problems. As

previously stated, sulfate reducing bacteria

are anaerobic. They live in colonies which can be located on pipe and tank walls, in filter media,

beneath deposits

• f sand,

silt, scale,

• r any other

site where they are not in contact with

a moving stream of water.

Pitting type attack occurs wherever the colonies

• f bacteria

are located on the metal surface. Although sulfate reducing bacteria are anaerobic, they can exist and grow

in an oxygenated system,

providing they can find

a

deposit

to

shield them from the

• xygen bearing water.

Sand, silt, clay solids,

corrosion by-products, scale,

• r other

forms

• f bacteria

can provide the sulfate reducers with

a

relatively oxygen free environment. Any deposit which shields

the bacteria also

effectively protects them from microbiocides, which makes

it very difficult to

kill or control

them.

When sulfate reducing bacteria are found

in a

system, there are always many more securely attached

to

the walls

• f

the pipe and

production equipment. The bacteria found

in the

system are

• nly a

few that have been dislodged from the colony proper. Sulfate reducing bacteria find

it much easier to

colonize

in areas

• f

stagnation and

• n equipment walls

than in

a stream of moving

fluids.

SLIDE 9

• 8-

The

principle contribution

• f sulfate

reducing bacteria

to the

anaerobic corrosion process

is

depolarization of

the

system by removal

• f

the hydrogen film from the cathode

thereby making possible

a continuous loss

• f metallic

ions

from the anodic areas.

In addition ,

sulfate reducing bacteria produce hydrogen sulfide

gas which is well known for its

corrosive properties. The hydrogen sulfide

gas

produced by

the bacteria reacts with soluble iron in the water

to

form insoluble iron sulfide,

a black

precipitate found

in many oilfield waters.

Iron sulfide

is

normally

a preferentially oil-wet substance

that acts as

a plugging agent to

filters and subsurface formations . Iron sulfide will also precipitate

in flowlines

and tubing strings, thus restricting the flow of fluids by reducing the inside diameter of the pipe.

It also

acts

• n flow

meters , dump valves , "L.A.C.T. " Units and other equipment and eventually leads

to equipment malfunctions.

Iron sulfide , being preferentially oil-wet , tends

to accumulate in the

• il/water

interface

in production equipment .

Over a period of time

the accumulation will

increase

to a point where

the

• il section

is

reduced

to nothing and no

longer exists . This prevents complete oil/ water separation in equipment such as separators, gun barrels, and heater-treaters. Iron sulfide

is

an excellent plugging agent. Graded bed rapid filters , cartridge filters , and formation faces can become plugged in

a relatively short period of time .

Flow rates decrease and injection pressures increase

• n disposal wells

and water injection and pressure maintenance wells.

Slime forming bacteria can contribute

to

both corrosion and plugging

in water

systems . These bacteria can produce large masses

• f

slime

• n solid

surfaces such

as

pipe walls, tank bottoms, and formation faces. The mass

• f

slime can contribute

to

corrosion by creating an

• xygen

concentration cell,

• r by providing

an effective shield which sulfate

reducing bacteria can congregate under and carry out their

life functions . High bacterial counts are not an indication that plugging is

• r will
• ccur

in a water handling system.

Additional data must

be

gathered and placed

in

proper perspective. Loss

• f

injectivity, increased injection pressures , evidence

• f

filter plugging, and visual

• bservation of

slime masses recovered from filters and backwash waters can be utilized in determining if the bacteria are present in sufficient numbers

to

cause plugging problems

.

API RP- 38 states that counts

• f

less

than 10,000 organisms per ml are generally of little significance.

SLIDE 10

• 9-

Bacterial counts

in excess

• f

10, 000 organisms per ml should be

thoroughly investigated. Iron bacteria deposit

a sheath of iron hydroxide around

them as they grow, and they contribute to corrosion and plugging in the same manner as slime forming bacteria. The iron

• is. obtained from

soluble iron ions in the water, and not from the corrosion process. Large numbers

• f iron bacteria

can precipitate iron hydroxide in sufficient quantity

to

create severe plugging problems.- The iron hydroxide

is a red to brownish,

gelatinous type material.

SLIDE 11

MICROORGANISM BREEDING SITES Most

• il

field waters fulfill the physical and nutritional requirements for bacterial growth and reproduction. Depending upon the type

• f

system, sulfate reducing bacteria and/or slime forming bacteria may be present in sufficient quantities to create problems. The engineer in the field must have

a knowledge

• f

the likely locations where the

different types

• f bacteria

can be located in the system. Sulfate reducing bacteria must have an oxygen free environment,

• r
• ther

conditions which are favorable for formation

• f

their anaerobic conditions. They can be found in almost all areas

• f
• il and

gas production, and are most likely to be found in stagnant areas

• r

areas

• f

low fluid velocities. The rat hole in producing and water injection wells can provide sulfate

reducing bacteria with

an excellent site for colonization and growth.

They can also exist in the packer fluid between the tubing and casing

if it

is water

• r

a

water base

mud.

Heater-treaters

are another excellent site where sulfate reducing

bacteria can be found. The heated water and the reduced flow rate

• f

the water provides them with ideal growth conditions. They can also be found in gun barrels, free water knockouts, precipitators, water storage tanks, and crude

• il

stock tanks. Sulfate reducing bacteria can be found in both sand and gravel rapid bed filters. Channeling

• f

the water through the filter beds can create many areas

• f

low fluid velocity and stagnation. The

• il-water

interface

in any piece

• f production

equipment

is

an excellent

breeding site for sulfate reducers,

as is the bottoms

• f

the vessels where sand, silt, corrosion by-products,

• r
• ther

debris has settled.

SLIDE 12

• 11-

Scale deposits and concentration cells

in flowlines

and tubing strings provide sites under which sulfate reducing bacteria can exist. Cracks in cement or plastic coated lines are also favorable sites. Slime forming bacteria must have free oxygen available in the environment for growth and reproduction, and many oil field waters fulfill this requirement. The free oxygen

is normally not naturally

• ccurring

in the water, but

is

induced into the system through faulty equipment such as hatch gaskets, pump seals, holes

in tank tops,

and through improper gas blanketing of production equipment. Some shallow producing and water supply wells will have the annulus vented to the atmosphere which will allow oxygen

to be

induced into the fluids. The color of the slime masses can indicate

to some extent the type

• f bacteria

present in the system. Red, brown,

• r orange masses

may be produced by iron oxidizing bacteria, while white

• r gray

masses can be produced by many types

• f slime forming bacteria.

Slime forming bacteria can normally be found in most open ponds and open tanks

• f produced water.

They can be found around

the edges ,

and

in some instances floating on the waters surface.

Shallow water supply wells can be found

to contain

large quantities

• f slime forming bacteria .

The masses can be found adhering to the tubing walls and flowlines leading from the wells. They can be found adhering to the sides

• f production equipment,

such as heater - treaters , free-water knockouts , filters, and water storage tanks. The oil-water interface in production equipment

is

also

a

likely site for the masses

to be found. The tubing and formation faces

in water

injection wells provide slime formers

a site

for growth . The masses can contribute greatly

to

plugging

• f

the formation in injection wells. The wells should be back-washed and the water analyzed for the presence

• f bacteria.

SLIDE 13

• 12-

It

is very difficult

to list all the

locations where bacterial activity can occur, and where the engineer should look for their presence. When a system

is

found to'have bacterial activity, the entire system must be checked out in order

to determine the

locations of the microorganisms, and the extent of the problem.

If the sites

• f bacterial growth cannot be accurately pin-pointed,

an effective microbiocide control program cannot be initiated. For a control program to be effective, the microbiocide must be added to the system at some point ahead of the breeding site of the bacteria. Nothing

is

accomplished, and problems are not corrected,

if control measures

are taken down stream of

the

breeding sites.

SLIDE 14

MICROBIOCIDES There are many different chemical compounds used to control micro-

• rganisms

in oil field waters. The compound,

depending

• n

its base,

may function

to

either kill or control the growth rate of the microorganism. Chemicals used for bacterial control can be broadly classed. One classification

is

the manner in which the chemicals function. Bactericides

• Chemicals which kill bacteria.

Bacteriostats

• Chemicals which retard or inhibit

the growth of bacteria. Microbiocides

• Chemicals which kill other

forms

• f life

in addition

to bacteria.

Microbiostats

• Chemicals which retard or inhibit

the

growth of other forms

• f

life in addition to bacteria. Another classification

is

the chemical composition of the compound, either inorganic or organic. Chlorine

is the most widely used inorganic microbiocide applicable to

both industrial and oil field waters . Other inorganic compounds used as either microbiocides

• r microbiostats

are calcium hypochlorite, hydrogen peroxide , and copper sulfate, but these compounds are seldom used in water injection systems. Many organic compounds are used in formulating microbiocides. Amines, phenols, chlorinated phenols, quaternary ammonium compounds, and

• rgan-metallic

compounds are the most widely used microbiocides

in

water injection systems. Caution must be exercised

in the handling and application of

microbiocides due

to their toxicity to all forms

• f life.

Any water which contains

a microbiocide

should not be discharged where

it will drain into ponds, lakes,

• r public waters.

Most microbiocides are cationic compounds, and they tend

to

adsorb

• n clay particles

and

• ther high surface area solids,
• nly -to

be released into the water at

a

later time as the compound undergoes chemical and physical changes.